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Bramson, A. M., S. Byrne, and J. Bapst. "Preservation of Midlatitude Ice Sheets on Mars." AMER GEOPHYSICAL UNION, 2017. http://hdl.handle.net/10150/626448.
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Excess ice with a minimum age of tens of millions of years is widespread in Arcadia Planitia on Mars, and a similar deposit has been found in Utopia Planitia. The conditions that led to the formation and preservation of these midlatitude ice sheets hold clues to past climate and subsurface structure on Mars. We simulate the thermal stability and retreat of buried excess ice sheets over 21Myr of Martian orbital solutions and find that the ice sheets can be orders of magnitude older than the obliquity cycles that are typically thought to drive midlatitude ice deposition and sublimation. Retreat of this ice in the last 4Myr could have contributed similar to 6% of the volume of the north polar layered deposits (NPLD) and more than 10% if the NPLD are older than 4Myr. Matching the measured dielectric constants of the Arcadia and Utopia Planitia deposits requires ice porosities of similar to 25-35%. We model geothermally driven vapor migration through porous ice under Martian temperatures and find that Martian firn may be able to maintain porosity for timescales longer than we predict for retreat of the ice.
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Skeet, David Richard. "Equatorial and midlatitude circulation of Jupiter's atmosphere." Thesis, University of Oxford, 1999. https://ora.ox.ac.uk/objects/uuid:a308d9e4-b4f4-4dbe-9cf8-d0f47eff1ba9.
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This thesis describes the development of and results from a new numerical model of Jupiter's atmosphere. The model is an adaptation of a general circulation model (GCM) of the Earth's atmosphere. It is a high resolution, limited-area model of the upper troposphere and lower stratosphere of Jupiter, with realistic stratification and simple parametrizations of appropriate physical processes. We have used the model to study two areas of jovian atmospheric dynamics: firstly, mid-latitude vortices (exemplified by the Great Red Spot) and their interaction with baroclinic and barotropic jetstreams, and secondly, the properties of equatorial waves and their effect in driving a superrotating equatorial jet. Before describing the main GCM, we present a time-independent model of a balanced axisymmetric vortex. The model performs a potential vorticity inversion, predicting the vertical variation of winds and temperatures required for balance, given a specified PV anomaly. We show that both shallow eddies (confined above about 20 bars) and deep ones (extending barotropically below 100 bars) could theoretically exist. The two types would be almost indistinguishable if observed only above the cloud-tops, i.e. at pressures p ⤠300 mb. We then describe the primitive-equation GCM, concentrating on the modifications necessary to represent Jupiter. In order to run the GCM, basic-state temperature and zonal wind profiles must be chosen, for these are not adequately constrained by observations. Numerical solution of the vertical structure equation allows the calculation of the eigenmodes of any atmosphere, thus predicting the approximate vertical structure of Rossby waves. This simplified 1D analysis gives an insight into suitable initial profiles and the results of the full model. The first GCM experiments examine midlatitude vortices in the absence of a background flow. Anticyclonic vortices migrate equatorward, while shrinking and intensifying by a process akin to frontogenesis. After intensifying, some eddies become unstable and disintegrate, generating daughter eddies. All eddies seem to adjust their vertical structure toward the first baroclinic normal mode. When eddies are placed in an enviroment of latitudinally alternating zonal jetstreams, meridional migration is blocked by the jets. However, most eddies intensify until they overcome the barrier presented by the jet. Mixed baroclinic/barotropic instability in the jets can generate eddies of either shallow or deep structure, echoing the results of the PV inversion model. Moving on to equatorial dynamics, we analyse the properties of equatorial waves on Jupiter, and their interaction with the zonal mean flow. We find that mean-flow acceleration by dissipation of upward propagating Kelvin waves can (in principle) quantitatively account for the observed superrotating equatorial jet. By considering the effect of a range of possible wave sources below the clouds, we find that the troposphere filters waves primarily by their phase speed, suggesting that the speed and shape of the jet may be less sensitive to the source than to the basic atmospheric stratification. We propose a mechanism of Kelvin-wave forcing, plus weak zonally symmetric solar heating to account for the observed velocity and meridional structure of the equatorial jet. The vertical structure is less realistic, with an underlying easterly jet, but this may be because our sources are insufficiently deep in the atmosphere.
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Coutinho, Mariane M. "Optimal midlatitude growth : impact of physical processes." Thesis, University of Reading, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414569.
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Mullendore, Gretchen Louise. "Cross-tropopause tracer transport in midlatitude convection /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/10061.
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Fytterer, Tilo, Christina Arras, and Christoph Jacobi. "Terdiurnal signatures in midlatitude sporadic E layers occurrence rates." Universität Leipzig, 2013. https://ul.qucosa.de/id/qucosa%3A16409.
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Global Positioning System radio occultation measurements by the FORMOsa SATellite mission-3/Constellation Observing System for Meteorology, Ionosphere and Climate satellites were used to analyse the behaviour of the signature of the terdiurnal tide in sporadic E (ES) layers at midlatitudes (43°N – 63°N). According to theory, the occurrence of ES is expected when the vertical zonal wind shear, which is mainly owing to solar tides, is negative. 4-year means, based on 3-monthly running mean zonal means from December 2006 - November 2010, were constructed for the terdiurnal oscillation in the occurrence frequency of ES. Comparison of the results with VHF meteor radar observations of the terdiurnal tide and the 8-hr oscillation in the vertical zonal wind shear at Collm, Germany (51.3°N, 13°E) shows a clear correspondence between the 8-hr Es and wind shear signature.Radiookultationsmessungen auf der Basis von GPS-Messungen der FORMOsa SATellite mission-3/Constellation Observing System for Meteorology, Ionosphere and Climate-Satelliten wurden verwendet, um die Signatur der 8-stündigen Gezeiten in den Auftrittsraten von sporadischen E (Es)-Schichten zu analysieren. Nach der allgemein anerkannten Windscherungstheorie treten Es-Schichten im Bereich negativer vertikaler Windscherung auf, welche in der unteren Thermosphäre hauptsächlich durch solare Gezeiten hervorgerufen werden. Speziell werden hier 4-jährige Mittelwerte saisonal gemittelter Auftrittsraten untersucht um die 8-stündige Signatur zu finden. Ein Vergleich mit Radarmessungen des Windes über Collm zeigt, dass die saisonale und tägliche Variabilität der 8-stündigen Komponente der Es-Raten sehr gut mit derjenigen der gemessenen Windscherung übereinstimmt.
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Holmes, Caroline Ruth. "The impact of Arctic sea ice change on midlatitude climate." Thesis, University of Reading, 2016. http://centaur.reading.ac.uk/65946/.
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Arctic sea ice loss is a robust feature of observations and of climate model projections. Amplified winter lower tropospheric warming in the Arctic relative to the global mean is associated with this ice loss. Many recent studies have addressed the possible effects of these changes on the midlatitude atmospheric circulation, particularly in the North Atlantic. These studies suggest responses including an equatorward jet shift, a negative annular mode response and changes in Rossby wave behaviour. However, there is disagreement on the magnitude, significance and even sign of these responses. Previous studies have shown the advantages of model hierarchies for understanding the atmosphere. In this thesis, experiments are conducted in HadGAM1 with simplified lower boundary conditions. Two sets of experiments are conducted, one in a zonally symmetric aquaplanet and the other in a configuration with representative northern hemisphere land masses. A wide range of sea ice profiles are imposed. The dominant response to ice removal in an aquaplanet is an equatorward jet shift, consistent with previous work. This response is moderate in magnitude for ice which does not exceed 65◦ latitude, but strongly nonlinear for greater ice extents. The zonal mean response is qualitatively similar in the asymmetric configuration, but the nature of the asymmetric response shows sensitivity to the exact ice edge location. These results have implications for understanding the impact of sea ice anomalies in past as well as present climates. Changes in surface temperature gradients, including from Arctic amplification, could affect midlatitude climate even if circulation changes are small. In particular, changes in thermal advection could alter midlatitude temperature variability and extremes. In this thesis a multiple regression model is used to investigate projected monthly temperature variance changes in a recent single model ensemble. Many robust changes, including reduced winter temperature variance in Europe, are consistent with the effect of changes in the seasonal mean temperature gradient alone.
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O'Reilly, Christopher Horkesley. "The interaction of oceanic jets with the midlatitude storm tracks." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/19231.
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Two mechanisms through which oceanic jets and the atmospheric storm tracks interact in midlatitudes are considered. Firstly, the response of a two-layer ocean model to large- scale stochastic forcing, a simplified model of forcing by the North Atlantic Oscillation, is investigated. Long Rossby waves are excited at the eastern boundary of the square model basin and the waves are baroclinically unstable. A novel aspect is that the instability leads to the generation of zonal jets throughout the domain. Unlike other theories of jet generation, the jets are actually wave-like in nature, and result directly from the instability. The “jets” appear when averaging the zonal velocity field over fixed periods of time. The longer the averaging period, the weaker the jets as the latter are actually time-varying. The jets occur for a wide range of stochastic forcing strength and the presence or not of a time mean circulation. The mechanism described here thereby provides an explanation for the recent observations of alternating zonal jets. The response of the Pacific storm track to the variability of the Kuroshio Extension jet is then studied. An index of the Kuroshio Extension front strength is produced using sea surface temperature and sea surface height observations. The index reflects the strengthening and weakening of the SST gradient associated with the bimodal states of the Kuroshio, and composites of the atmospheric state are presented during its positive and negative phases. The anomalous response of the transient eddy heat transport resembles a zonal dipole structure. With a weaker (stronger) SST front, the eddy heat transport is increased in the eastern (western) Pacific region, consistent with reduced (enhanced) low- level baroclinicity. The response of the large-scale atmospheric circulation is a barotropic blocking-type pattern in the east Pacific, which is interpreted in terms of the barotropic “eddy-straining” mechanism and eddy-mean flow interaction.
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Winchell, Taylor S., David M. Barnard, Russell K. Monson, Sean P. Burns, and Noah P. Molotch. "Earlier snowmelt reduces atmospheric carbon uptake in midlatitude subalpine forests." AMER GEOPHYSICAL UNION, 2016. http://hdl.handle.net/10150/621684.
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Previous work demonstrates conflicting evidence regarding the influence of snowmelt timing on forest net ecosystem exchange (NEE). Based on 15years of eddy covariance measurements in Colorado, years with earlier snowmelt exhibited less net carbon uptake during the snow ablation period, which is a period of high potential for productivity. Earlier snowmelt aligned with colder periods of the seasonal air temperature cycle relative to later snowmelt. We found that the colder ablation-period air temperatures during these early snowmelt years lead to reduced rates of daily NEE. Hence, earlier snowmelt associated with climate warming, counterintuitively, leads to colder atmospheric temperatures during the snow ablation period and concomitantly reduced rates of net carbon uptake. Using a multilinear-regression (R-2=0.79, P<0.001) relating snow ablation period mean air temperature and peak snow water equivalent (SWE) to ablation-period NEE, we predict that earlier snowmelt and decreased SWE may cause a 45% reduction in midcentury ablation-period net carbon uptake.
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Orford, Nicola Diane. "Behaviour of quiet time ionospheric disturbances at African equatorial and midlatitude regions." Thesis, Rhodes University, 2018. http://hdl.handle.net/10962/62672.
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Extreme ionospheric and geomagnetic disturbances affect technology adversely. Prestorm enhancements, considered a potential predictor of geomagnetic storms, occur during quiet conditions prior to geomagnetic disturbances. The ionosphere experiences general disturbances during quiet geomagnetic conditions and these Q- disturbances remain unexplored over Africa. This study used TEC data to characterize the morphology of Q-disturbances over Africa, exploring variations with solar cycle, season, time of occurrence and latitude. Observations from 10 African GPS stations in the equatorial and midlatitude regions show that Q-disturbances in the equatorial region are predominantly driven by E x B variations, while multiple mechanisms affect the midlatitude region. Q- disturbances occur more frequently during nighttime than during daytime and no seasonal trend is observed. Midlatitude Q-disturbance mechanisms are explored in depth, considering substorm activity, the plasmaspheric contribution to GPS TEC and plasma transfer between conjugate points. Substorm activity is not a dominant mechanism, although Q-disturbances occurring under elevated substorm conditions tend to have longer duration and larger amplitude than general Q-disturbances. Many observed Q-disturbances become non-significant once the plasmaspheric contribution to the TEC measurements is removed, indicating that these disturbances occur within the plasmasphere, and not the ionosphere. Transfer of plasma between conjugate points does not seem to be a mechanism driving Q-disturbances, as the corresponding nighttime behaviour expected between depletions in the summer hemisphere and enhancements in the winter hemisphere is not observed. Pre-storm enhancements occur infrequently, rendering them a poor predictor of geomagnetic disturbances. Pre-storm enhancement morphology does not differ significantly from general quiet time enhancement morphology, suggesting pre-storms are not a special case of Q-disturbances.
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Duncan, Bryan N. "The effects of urban ozone control strategies on northern hemispheric, midlatitude tropospheric ozone." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/25875.
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Frissell, Nathaniel A. "Ionospheric Disturbances: Midlatitude Pi2 Magnetospheric ULF Pulsations and Medium Scale Traveling Ionospheric Disturbances." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/74976.
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The ionosphere is an electrically charged atmospheric region which is coupled to the sun, the magnetosphere, and the neutral atmosphere. The ionospheric state can significantly impact technological systems, especially those which utilize radio frequency energy. By studying ionospheric disturbances, it is possible to gain a deeper understanding of not only the ionosphere itself, but also the natural and technological systems it is coupled to. This dissertation research utilizes high frequency (HF) radio remote sensing techniques to study three distinct types of ionospheric disturbances. First, ground magnetometers and a new mid latitude SuperDARN HF radar at Blackstone, Virginia are used to observe magnetospheric Pi2 ultra low frequency (ULF) pulsations in the vicinity of the plasmapause. Prior to these pulsations, two Earthward moving fast plasma flows were detected by spacecraft in the magnetotail. Signatures of inner magnetospheric compression observed by the Blackstone radar provide conclusive evidence that the plasma flow bursts directly generated the ground Pi2 signature via a compressional wave. This mechanism had previously been hypothesized, but never confirmed. Next, ten SuperDARN radars in the North American Sector are used to investigate the sources and characteristics of atmospheric gravity waves (AGW) associated medium scale traveling ionospheric disturbances (MSTIDs) at both midlatitudes and high latitudes. Consistent with prior studies, the climatological MSTID population in both latitudinal regions was found to peak in the fall and winter and have a dominant equatorward propagation direction. Prior studies suggested these MSTIDs were caused by mechanisms associated with auroral and space weather activity; however, it is shown here that the AE and Sym-H indices are poorly correlated with MSTID observations. A new, multi-week timescale of MSTID activity is reported. This leads to the finding that MSTID occurrence is highly correlated with an index representative of polar vortex activity, possibly controlled by a filtering mechanism that is a function of stratospheric neutral wind direction. Finally, a case study of a radio blackout of transionospheric HF communications caused by an X2.9 class solar flare is presented. This study demonstrates the potential of a novel technique employing signals of opportunity and automated receiving networks voluntarily created by an international community of amateur radio operators.Ph. D.
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Bélair, Stéphane. "A numerical study of midlatitude squall lines with the Canadian regional finite-element model." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28676.
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A research version of the Canadian regional finite-element (RFE) model is used to evaluate the capability of the operational model in reproducing the meso-$ beta$-scale structure and evolution of three different types of midlatitude squall-line systems, and to advance our understanding on the development of these features.In this thesis, we use the well-documented 10-11 June 1985 squall line as a test bed to examine the appropriate incorporation of various physical representations and their coupling with RFE's model components. It is demonstrated through a series of sensitivity studies that the operational prediction of squall lines can be improved if more realistic model physics, reasonable initial conditions, and high resolution are used. It is shown that subgrid-scale moist convection and grid-scale moist physics must be adequately treated in order to reproduce the internal structures of the squall line.
Then, the improved version of the RFE model is used to study the role of gravity waves in the development of a prefrontal squall line associated with the 14 July 1987 Montreal flood. It is found that the gravity waves and convection propagate in a "phase-locked" manner and that the wave-CISK mechanism accounts for the maintenance and intensification of the system. It is also found that frontogenetical processes and release of conditional symmetric instability are responsible for the development of a trailing stratiform rainband associated with the July 1987 Montreal flood. Numerous sensitivity experiments are conducted, and they show that the meso-$ beta$-scale structures and the wave-convection system are very sensitive to the interaction of the parameterized convection with grid-scale physical processes.
In the last part of the thesis, the along-line variability 26-27 June 1985 squall line during PRE-STORM is examined. It is found that the three-dimensional structures of the squall's circulations are determined by both a large-scale trough and convectively generated disturbances. In particular, it is shown that rear inflows in the stratiform region tend to be more intense to the south of the mesolow and neat the base of the large-scale trough.
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Jacobi, Christoph, and Dierk Kürschner. "A possible connection of midlatitude mesosphere/lower thermosphere zonal winds and the Southern oscillation." Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-216880.
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Collm (52°N, 15°E) midlatitude mesosphere/lower thermosphere (MLT) zonal winds are investigated with respect to a possible influence of the Southern Oscillation (SO). It is found that in winter the prevailing wind is positively correlated with the Southern Oscillation index (SOI), which qualitatively fits to the response of the low-latitude stratosphere on the SO. In summer, however, there is a negative correlation between MLT zonal winds and SOI. A possible mechanism, which includes slightly enhanced planetary wave propagation to the MLT in summers of low SOI is discussedWindmessungen aus Collm (52°N, 15°E) wurden hinsichtlich eines möglichen Einflusses der Southern Oscillation (SO) in ihnen untersucht. Es zeigt sich, dass im Winter der mittlere Zonalwind positiv mit dem \"Southern Oscillation Index\" SOI korreliert ist, was qualitativ mit der Reaktion der Stratosphäre auf ENSO übereinstimmt. Im Sommer findet sich jedoch ein negativer Zusammenhang zwischen hochatmosphärischem Zonalwind und SOI. Ein möglicher Mechanismus, der die Ausbreitung planetarer Wellen beinhaltet, wird diskutiert
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Jacobi, Christoph, and Dierk Kürschner. "A possible connection of midlatitude mesosphere/lower thermosphere zonal winds and the Southern oscillation." Wissenschaftliche Mitteilungen des Leipziger Instituts für Meteorologie ; 22 = Meteorologische Arbeiten aus Leipzig ; 6 (2001), S. 98-110, 2001. https://ul.qucosa.de/id/qucosa%3A15211.
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Collm (52°N, 15°E) midlatitude mesosphere/lower thermosphere (MLT) zonal winds are investigated with respect to a possible influence of the Southern Oscillation (SO). It is found that in winter the prevailing wind is positively correlated with the Southern Oscillation index (SOI), which qualitatively fits to the response of the low-latitude stratosphere on the SO. In summer, however, there is a negative correlation between MLT zonal winds and SOI. A possible mechanism, which includes slightly enhanced planetary wave propagation to the MLT in summers of low SOI is discussed.Windmessungen aus Collm (52°N, 15°E) wurden hinsichtlich eines möglichen Einflusses der Southern Oscillation (SO) in ihnen untersucht. Es zeigt sich, dass im Winter der mittlere Zonalwind positiv mit dem \"Southern Oscillation Index\" SOI korreliert ist, was qualitativ mit der Reaktion der Stratosphäre auf ENSO übereinstimmt. Im Sommer findet sich jedoch ein negativer Zusammenhang zwischen hochatmosphärischem Zonalwind und SOI. Ein möglicher Mechanismus, der die Ausbreitung planetarer Wellen beinhaltet, wird diskutiert.
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Yokoyama, Tatsuhiro. "A study of midlatitude ionospheric E-region irregularities with rocket/radar experiment and numerical simulation." 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147581.
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Ott, Lesley Elaine. "An analysis of convective transport, lightning NOx̲ production, and chemistry in midlatitude and subtropical thunderstorms." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/4085.
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Thesis (Ph. D.)--University of Maryland, College Park, 2006.Thesis research directed by: Atmospheric and Oceanic Sciences. Title from t.p. of PDF. On t.p. "x̲" is subscript. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Malevich, S. B., and C. A. Woodhouse. "Pacific sea surface temperatures, midlatitude atmospheric circulation, and widespread interannual anomalies in western U.S. streamflow." AMER GEOPHYSICAL UNION, 2017. http://hdl.handle.net/10150/625050.
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Widespread droughts can have considerable impact on western United States (U.S.) streamflow but causes related to moisture delivery processes are not yet fully understood. Here we examine western U.S. streamflow records to identify robust leading modes of interannual variability and their links to patterns of ocean and atmospheric circulation. The leading mode of streamflow variability, a pattern of west-wide streamflow anomalies, accounts for approximately 50% of variability and is associated with persistent high-pressure anomalies related to ridges off the Pacific North American coast. The second mode of variability accounts for approximately 25% of variability and is associated with ocean and atmospheric conditions in the tropical Pacific. Our results suggest that the leading mode of streamflow variability in the western U.S. is more strongly associated with internally driven midlatitude atmospheric variability than equatorial Pacific sea surface temperatures.
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McCormack, John Patrick. "A three-dimensional mechanistic ozone transport model: Applications to midlatitude trends and 11-year variability." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/290698.
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Thirteen years of satellite-based total ozone measurements, extending from January 1979 through December 1991, are analyzed with a multiple regression statistical model to isolate the components of interannual variability associated with (1) linear trends and (2) the 11-year variation in solar ultraviolet irradiance. Lower stratospheric temperature and geopotential height data obtained from satellite- and ground-based sources are analyzed in similarly, providing a comprehensive assessment of the interannual variability in the lower stratosphere over the 1979-1991 period. The results of the statistical analyses indicate coherent variations in ozone, temperature, and geopotential height at extratropical latitudes in NH winter which are related to both the trend and solar-cycle components; the amplitudes of these variations exhibit pronounced spatial dependences. A three-dimensional mechanistic ozone transport model is used to describe the spatial distribution of total ozone in NH winter using observed lower stratospheric temperature and geopotential height fields. Application of this model on a year-to-year basis demonstrates that a large percentage of the observed interannual variability in the spatial distribution of total ozone is directly associated with changes in the dynamical structure of the lower stratosphere. The influence of dynamical variability on zonal mean total ozone is also investigated using an empirical approach. From the results of the observational and modeling studies, it is concluded that changes in the dynamics of the lower stratosphere over the 1979-1991 period have contributed significantly to the observed total ozone trends in the Northern Hemisphere. In contrast, the observed variability in total ozone associated with the 11-year solar cycle could not be explained in terms of a systematic variation in the dynamical forcing of the lower stratosphere in-phase with the 11-year cycle.
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Norris, Joel R. "Interannual variability in cloudiness, sea surface temperature, and atmospheric circulation over the midlatitude North Pacific during summer." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/10050.
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Jacobi, Christoph. "Solar cycle dependence of winds and planetary waves as seen from midlatitude mesopause region wind measurements at Collm." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-213432.
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Windmessungen im Mesopausenbereich über Mitteleuropa (Collm, 52°N, I5°E) werden im Hinblick auf Langzeittrends und eine eventuelle Abhängigkeit vom 11-jährigen Sonnenfleckenzyklus hin untersucht. Der Einfluß der solaren Variabilität ist jahreszeitenabhängig; nur in Frühjahr und Sommer wird eine signifikante Korrelation gefunden. Im Sommer ist diese Abhängigkeit mit stärkeren vertikalen Gradienten des mittleren zonalen Grundwindes im solaren Maximum verbunden. Dies weist auf einen Ursprung dieser Abhängigkeit in der Stratosphäre/Mesosphäre sowie auf Koppelungsmechanismen zwischen Stratosphäre, Mesosphäre und unteren Thermosphäre hin. Da die 2-Tage-Welle vom Gradienten abhängt, führt dies zu einer positiven Korrelation zwischen der Amplitude der 2-Tage-Welle und der SonnenfleckenrelativzahlMesopause winds over Central Europe (Collm, 52°N, I5°E) are analysed with respect to longterm trends and 11-year solar cycle dependencies. The response of the prevailing wind to the solar cycle differs throughout the year. While in winter no significant correlation between the zonal prevailing wind and the solar activity is found, in spring and summer a negative correlation between solar activity and zonal prevailing wind can be seen from the measurements. This is connected with strenger vertical gradients of the zonal prevailing wind during solar maximum than during solar minimum. This hints to a forcing of the mesopause region dynamical reaction on solar activity from the stratosphere/mesosphere and to coupling processes in the stratosphere-mesosphere-lower thermosphere system. Since the amplitude of the quasi twoday wave is dependent on the zonal mean wind gradient, this is connected with a positive correlation between solar activity and quasi two-day wave activity
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Urbanek, Benedikt [Verfasser], and Bernhard [Akademischer Betreuer] Mayer. "Characterization of midlatitude cirrus clouds clouds with airborne lidar - Investigating an indirect aviation effect / Benedikt Urbanek ; Betreuer: Bernhard Mayer." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/1202011969/34.
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Jacobi, Christoph. "The quasi 16-day wave in the summer midlatitude mesopause region and its dependence on the equatorial quasi-biennial oscillation." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-213442.
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Aus täglichen Analysen des sommerlichen zonalen Grundwindes im Mesopausenbereich, der am Observatorium Collm der Universität Leipzig gemessen wurde, werden niederfrequente Variationen im Zeitbereich planetarer Wellen (10 - 20 Tage) bestimmt. Obwohl die direkte Ausbreitung derartiger Wellen durch die stratosphärischen und mesosphärischen Ostwinde verhindert wird, werden in manchen Jahren trotzdem Oszillationen gemessen, die mit planetaren Wellen im Zusammenhang stehen können. Dies unterstützt die Theorie, daß sich planetare Wellen von der Winterhalbkugel entlang der Zonen schwachen Windes bis in die Mesopausenregion mittlerer und polarer Breiten ausbreiten. Betrachtet man die interanuelle Variabilität dieser Wellen, fällt eine Abhängigkeit von der äquatorialen quasi 2-jährigen Schwingung (QBO) auf, wobei während der Ostphase der QBO die Wellenaktivität gering ist, während sie in der Westphase der QBO stärker sein kann. Der Einfluß der QBO auf die sommerliche Wellenaktivität wird vom 11-jährigen Sonnenfleckenzyklus moduliert, wobei während des solaren Maximums stärkere Aktivität zu verzeichnen istFrom daily estimates of the summer mesopause region zonal prevailing wind measured at the Collm Observatory of the University of Leipzig long-term variations in the period range of planetary waves (10-20 days) are detected. Although the direct propagation of these waves from lower layers into the mesosphere is not possible because of the wave filtering in the summer stratospheric and mesospheric easterlies, in some years oscillations are found that can be connected with planetary waves, supporting the theory of the propagation of these waves from the equatorial region to the midlatitude and polar upper mesosphere along the zero wind line. The interannual variability of these waves shows a dependence on the equatorial quasi-biennial oscillation (QBO), so that in general during the east phase of the QBO the planetary wave activity is small, while during the QBO west phase it can be larger. The influence of the QBO on the planetary wave activity is modulated by the I I-year solar cycle, so that the strongest signal is found during solar maximum
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Jacobi, Christoph. "The quasi 16-day wave in the summer midlatitude mesopause region and its dependence on the equatorial quasi-biennial oscillation." Wissenschaftliche Mitteilungen des Leipziger Instituts für Meteorologie ; 9 = Meteorologische Arbeiten aus Leipzig ; 3 (1998), S. 117-129, 1998. https://ul.qucosa.de/id/qucosa%3A15084.
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Aus täglichen Analysen des sommerlichen zonalen Grundwindes im Mesopausenbereich, der am Observatorium Collm der Universität Leipzig gemessen wurde, werden niederfrequente Variationen im Zeitbereich planetarer Wellen (10 - 20 Tage) bestimmt. Obwohl die direkte Ausbreitung derartiger Wellen durch die stratosphärischen und mesosphärischen Ostwinde verhindert wird, werden in manchen Jahren trotzdem Oszillationen gemessen, die mit planetaren Wellen im Zusammenhang stehen können. Dies unterstützt die Theorie, daß sich planetare Wellen von der Winterhalbkugel entlang der Zonen schwachen Windes bis in die Mesopausenregion mittlerer und polarer Breiten ausbreiten. Betrachtet man die interanuelle Variabilität dieser Wellen, fällt eine Abhängigkeit von der äquatorialen quasi 2-jährigen Schwingung (QBO) auf, wobei während der Ostphase der QBO die Wellenaktivität gering ist, während sie in der Westphase der QBO stärker sein kann. Der Einfluß der QBO auf die sommerliche Wellenaktivität wird vom 11-jährigen Sonnenfleckenzyklus moduliert, wobei während des solaren Maximums stärkere Aktivität zu verzeichnen ist.From daily estimates of the summer mesopause region zonal prevailing wind measured at the Collm Observatory of the University of Leipzig long-term variations in the period range of planetary waves (10-20 days) are detected. Although the direct propagation of these waves from lower layers into the mesosphere is not possible because of the wave filtering in the summer stratospheric and mesospheric easterlies, in some years oscillations are found that can be connected with planetary waves, supporting the theory of the propagation of these waves from the equatorial region to the midlatitude and polar upper mesosphere along the zero wind line. The interannual variability of these waves shows a dependence on the equatorial quasi-biennial oscillation (QBO), so that in general during the east phase of the QBO the planetary wave activity is small, while during the QBO west phase it can be larger. The influence of the QBO on the planetary wave activity is modulated by the I I-year solar cycle, so that the strongest signal is found during solar maximum.
24
Albern, Nicole Brigitte Silvia [Verfasser], and J. [Akademischer Betreuer] Pinto. "The radiative impact of clouds on the response of the midlatitude circulation to global warming / Nicole Brigitte Silvia Albern ; Betreuer: J. Pinto." Karlsruhe : KIT-Bibliothek, 2021. http://d-nb.info/1228439303/34.
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Jacobi, Christoph. "Solar cycle dependence of winds and planetary waves as seen from midlatitude mesopause region wind measurements at Collm: evidence for forcing from below." Wissenschaftliche Mitteilungen des Leipziger Instituts für Meteorologie ; 9 = Meteorologische Arbeiten aus Leipzig ; 3 (1998), S. 106-116, 1998. https://ul.qucosa.de/id/qucosa%3A15083.
Full textAbstract:
Windmessungen im Mesopausenbereich über Mitteleuropa (Collm, 52°N, I5°E) werden im Hinblick auf Langzeittrends und eine eventuelle Abhängigkeit vom 11-jährigen Sonnenfleckenzyklus hin untersucht. Der Einfluß der solaren Variabilität ist jahreszeitenabhängig; nur in Frühjahr und Sommer wird eine signifikante Korrelation gefunden. Im Sommer ist diese Abhängigkeit mit stärkeren vertikalen Gradienten des mittleren zonalen Grundwindes im solaren Maximum verbunden. Dies weist auf einen Ursprung dieser Abhängigkeit in der Stratosphäre/Mesosphäre sowie auf Koppelungsmechanismen zwischen Stratosphäre, Mesosphäre und unteren Thermosphäre hin. Da die 2-Tage-Welle vom Gradienten abhängt, führt dies zu einer positiven Korrelation zwischen der Amplitude der 2-Tage-Welle und der Sonnenfleckenrelativzahl.Mesopause winds over Central Europe (Collm, 52°N, I5°E) are analysed with respect to longterm trends and 11-year solar cycle dependencies. The response of the prevailing wind to the solar cycle differs throughout the year. While in winter no significant correlation between the zonal prevailing wind and the solar activity is found, in spring and summer a negative correlation between solar activity and zonal prevailing wind can be seen from the measurements. This is connected with strenger vertical gradients of the zonal prevailing wind during solar maximum than during solar minimum. This hints to a forcing of the mesopause region dynamical reaction on solar activity from the stratosphere/mesosphere and to coupling processes in the stratosphere-mesosphere-lower thermosphere system. Since the amplitude of the quasi twoday wave is dependent on the zonal mean wind gradient, this is connected with a positive correlation between solar activity and quasi two-day wave activity.
26
Robert, Loïc. "Dynamique de variabilité des courants-jets des moyennes latitudes." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066220/document.
Full textAbstract:
Cette étude a pour objectif d'analyser le rôle des ondes de Rossby dans la variabilité des courants-jets troposphériques des moyennes latitudes à l'aide d'un modèle numérique idéalisé. Elle s'intéresse aux mécanismes dynamiques responsables de la persistance des principaux modes de variabilité : celui de déplacement méridien et celui de pulsation d'amplitude. Le premier est souvent le principal mode de variabilité du fait de sa grande persistance causée par une rétroaction positive des ondes de Rossby.Deux nouveaux types de rétroactions négatives ont été mis en évidence à une échelle de temps plus courte que cette rétroaction classique et dont le mécanisme dépend de la nature des ondes impliquées. Ces différents mécanismes sont aussi retrouvés et ainsi validés dans le contexte plus réaliste des données de réanalyse.Une réflexion sur les conséquences du changement climatique est aussi proposée via l'étude de sensibilité menée sur trois paramètres clés du modèle : le gradient méridien de température, conduisant à un mode de déplacement plus persistant dans le futur, la position moyenne du jet, conduisant à un mode moins persistant pour des jets plus proches du pôle, et enfin la friction dans les basses couches de l'atmosphère, aussi étudiée car étant un paramètre plutôt difficile à évaluer et présentant une forte disparité entre les modèles.Cette thèse a donc permis de mettre en évidence deux nouveaux mécanismes de rétroaction des ondes sur les courants-jets et de développer des diagnostics théoriques qui pourront être plus amplement testés et appliqués dans d'autres contextes, particulièrement des réanalyses et des simulations de climat réalistesThis study investigate the impact of Rossby waves on the tropospheric midlatitude eddy-driven jets using an idealized numerical model. It focuses on the dynamical mechanisms driving the persistence of the main modes of variability: a shifting mode and a pulsing mode. The shifting mode is often found to be the leading mode of variability due to an enhanced persistence caused by a positive feedback of Rossby waves. Two new kinds of negative feedbacks have been found for a shorter time-scale than the more classical feedback which mechanism depends on wave properties. These new mechanisms have also been found in the more realistic set up of reanalysis. The impact of climate change is also investigated using the sensitivity analysis of the model to three key parameters : the meridional gradient of temperature, which leads to longer lasting phases of the shifting mode in the future, the jet mean position, which leads to less persistent shifting mode for poleward shifted jets, and frictional damping, because it is a parameter difficult to tune and which varies between numerical models. In conclusion, two new feedback mechanisms acting on eddy-driven jets variability have been found and theoretical diagnostics have been developed and could be used to probe more realistic data such as future climate simulations and reanalysis
27
Quinting, Julian Francesco Daniel [Verfasser], and S. C. [Akademischer Betreuer] Jones. "The impact of tropical convection on the dynamics and predictability of midlatitude Rossby waves : a climatological study [[Elektronische Ressource]] / Julian Francesco Daniel Quinting. Betreuer: S. C. Jones." Karlsruhe : KIT-Bibliothek, 2015. http://d-nb.info/1068263342/34.
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Sivasligil, Mustafa. "A Fast Model For Computing Infrared Atmospheric Background Effects." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/2/12606989/index.pdf.
Full textAbstract:
The infrared atmospheric background modeling can be considered as one of the important key factor to develop a successful target detection technique. During the infrared atmospheric background modeling, defining the input parameters of the atmospheric profile are very important for the calculations of the absorption, emission and scattering effects of the atmosphere. The main objective of this thesis is to find the answer for the question &ldquois it possible to determine the &ldquo
effective&rdquo
height range for the sea level midlatitude clear weather conditions in the three special wavelength bands, 1-3 &
#61549
m, 3-5 &
#61549
m, 8-12 &
#61549
m ?&rdquo
. The answer is important for three cases. These are to overcome the difficulties of finding all the parameters of the new atmospheric profile, to determine the dominant height range for the midlatitude region, and to shorten the time of the calculations of infrared background processes. In this study, it has been shown that it should be possible to determine the effective height range for sea level midlatitude clear weather conditions in the three special wavelength bands. As a result of this study it is shown that a new atmosphere model can be constructed more easily by overcoming the difficulties of finding all the parameters of the new atmospheric profile for the sea level clear weather midlatitude regions in a short time respectively. In this study the infrared radiation flux below 5 % difference between the whole, 100 km, and the effective height ranges is accepted.
29
Robert, Loïc. "Dynamique de variabilité des courants-jets des moyennes latitudes." Electronic Thesis or Diss., Paris 6, 2017. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2017PA066220.pdf.
Full textAbstract:
Cette étude a pour objectif d'analyser le rôle des ondes de Rossby dans la variabilité des courants-jets troposphériques des moyennes latitudes à l'aide d'un modèle numérique idéalisé. Elle s'intéresse aux mécanismes dynamiques responsables de la persistance des principaux modes de variabilité : celui de déplacement méridien et celui de pulsation d'amplitude. Le premier est souvent le principal mode de variabilité du fait de sa grande persistance causée par une rétroaction positive des ondes de Rossby.Deux nouveaux types de rétroactions négatives ont été mis en évidence à une échelle de temps plus courte que cette rétroaction classique et dont le mécanisme dépend de la nature des ondes impliquées. Ces différents mécanismes sont aussi retrouvés et ainsi validés dans le contexte plus réaliste des données de réanalyse.Une réflexion sur les conséquences du changement climatique est aussi proposée via l'étude de sensibilité menée sur trois paramètres clés du modèle : le gradient méridien de température, conduisant à un mode de déplacement plus persistant dans le futur, la position moyenne du jet, conduisant à un mode moins persistant pour des jets plus proches du pôle, et enfin la friction dans les basses couches de l'atmosphère, aussi étudiée car étant un paramètre plutôt difficile à évaluer et présentant une forte disparité entre les modèles.Cette thèse a donc permis de mettre en évidence deux nouveaux mécanismes de rétroaction des ondes sur les courants-jets et de développer des diagnostics théoriques qui pourront être plus amplement testés et appliqués dans d'autres contextes, particulièrement des réanalyses et des simulations de climat réalistesThis study investigate the impact of Rossby waves on the tropospheric midlatitude eddy-driven jets using an idealized numerical model. It focuses on the dynamical mechanisms driving the persistence of the main modes of variability: a shifting mode and a pulsing mode. The shifting mode is often found to be the leading mode of variability due to an enhanced persistence caused by a positive feedback of Rossby waves. Two new kinds of negative feedbacks have been found for a shorter time-scale than the more classical feedback which mechanism depends on wave properties. These new mechanisms have also been found in the more realistic set up of reanalysis. The impact of climate change is also investigated using the sensitivity analysis of the model to three key parameters : the meridional gradient of temperature, which leads to longer lasting phases of the shifting mode in the future, the jet mean position, which leads to less persistent shifting mode for poleward shifted jets, and frictional damping, because it is a parameter difficult to tune and which varies between numerical models. In conclusion, two new feedback mechanisms acting on eddy-driven jets variability have been found and theoretical diagnostics have been developed and could be used to probe more realistic data such as future climate simulations and reanalysis
30
Rivest, Chantal 1961. "Upper-level waves of synoptic scale at midlatitudes." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/58422.
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Ajtic, Jelena. "Dilution of the Antarctic ozone hole into Southern midlatitudes." Thesis, University of Canterbury. Physics and Astronomy, 2003. http://hdl.handle.net/10092/5710.
Full textAbstract:
Reduction in ozone levels in southern midlatitudes, caused by the transport of ozone-depleted air from the Antarctic polar vortex, is examined. The problem is approached from two different, but complementary, directions. First, a case study examining an atypical vertical profile of ozone in December 1998, caused by the presence of vortex air is presented. Second, the overall dilution effect in spring- and summer time in the years 1998, 1999, and 2000 is quantified.
In the first approach, an ozonesonde profile over the Network for Detection of Stratospheric Change (NDSC) site at Lauder (45.0° S, 169.7° E), New Zealand, for 24 December 1998 showing atypically low ozone centred around 24 km altitude (600 K potential temperature), is analyzed. The origin of the anomaly is explained using reverse domain filling (RDF) calculations combined with a PV/O3 fitting technique applied to ozone measurements from the Polar Ozone and Aerosol Measurement (POAM) III instrument.
The RDF calculations for two isentropic surfaces, 550 K and 600 K, show that ozone-poor air from the Antarctic polar vortex reached New Zealand on 24-26 December 1998. The vortex air on the 550 K isentrope originated in the ozone hole region, unlike the air on 600 K, where low ozone values were the result of dynamical effects.
High-resolution ozone maps are generated, and their examination shows that the vortex remnant situated above New Zealand was the cause of the altered ozone profile on 24 December. The maps also illustrate mixing of the vortex filaments into southern midlatitudes, whereby the overall midlatitude ozone levels are decreased.
In the second approach, to quantify the full impact of the dilution of the Antarctic ozone hole into southern midlatitudes in spring and summer of the years 1998, 1999 and 2000, diabatic RDF calculations are performed for parcels between 30° S and 60° S, initialized on a 1° longitude by 1° latitude grid, on seven potential temperature surfaces, between 400 K and 700 K. In each year, the trajectories are run back to 10 October, at which time the ozone depletion processes in the Antarctic vortex have largely ceased. Two distinct regions in the vortex, the core and the edge region, are taken into account.
The reduction in ozone due to the presence of vortex parcels in southern midlatitudes is calculated in the layer between 375 K and 725 K, thus encompassing the stratospheric region where most of ozone depletion occurs and where ozone is most abundant. The calculations are performed under the assumption that the volume mixing ratio of depleted ozone (the difference between undepleted ozone and observed ozone) does not change along the trajectories. To mitigate non-conservation of mass arising from the employment of Lagrangian model, a scaling method is introduced.
The results for the years 1998-2000 show that on average, between 15 October and 15 January of the following year, 17-19% of the midlatitude air parcels originate inside the Antarctic vortex. The corresponding reduction in ozone is 15-18 DU. The reduction caused by the presence of the air parcels originating in the vortex edge region is significant, especially in the early part of the period under examination. The results for four subregions in midlatitudes (spanning longitude regions of 90º, starting from 0º) are also presented, and they indicate that, on average, in the region encompassing New Zealand and Australia ozone reduction is less than in other subregions in the months of October and November, but from mid-December to mid-January the reduction is effectively the same in all subregions.
Furthermore, tests to examine the sensitivity of the results to uncertainties in the wind fields, and to the choice of the initial day, are performed for the year 1998. The results indicate that the method is more sensitive to the initial conditions, including the size of the vortex and the amount of filamentation, than to introduced perturbations in the winds. The corresponding uncertainties in the midlatitude ozone reduction are 38% and 5%, respectively. The uncertainties are generally larger for subregions, and range from 37-65%, and 4-14%, respectively.
The calculated ozone reduction is compared to the Total Ozone Mapping Spectrometer (TOMS) measurements of ozone column to derive relative changes in the total ozone. The results show that without the dilution effect, ozone levels in southern midlatitudes would be 4-6% higher during spring- and summertime. Moreover, a comparison of the calculated ozone reduction with ozone levels in 1979 demonstrates that on average, approximately 50-60% of the change can be attributed to the dilution effect. These results present a lower limit of the impact, as dilution in the lowermost stratosphere and troposphere is not captured in the calculations presented here.
32
Norris, Jesse Michael. "Dynamics and organisation of precipitation bands in the midlatitudes." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/dynamics-and-organisation-of-precipitation-bands-in-the-midlatitudes(b9d8f4e8-ec91-43f2-b3e1-936e2a1995b5).html.
Full textAbstract:
The thesis is presented in alternative format, meaning that the results of the thesis take the form of three journal articles, each telling a distinct story within the subject matter, but collectively highlighting the sensitivity of bands to frictional and diabatic processes. Paper 1 is an idealised-modelling study with the Weather Research and Forecasting (WRF) model, in which moist baroclinic waves are simulated from an initial zonally uniform mid-latitude jet on an f-plane at 20-km grid spacing, and the sensitivity of the resulting precipitation bands is explored. Paper 2 employs further WRF idealised-baroclinic-wave simulations and takes a simulation from Paper 1, after the cold front has formed, as the initial condition. A nested domain at 4-km grid spacing is inserted when this simulation is re-initialised to invesigate the sensitivity of finer-scale precipitation cores along the surface cold front. In both Papers 1 and 2, friction and latent-heat release enhance multiple banding at the two distinct horizontal scales, while surface fluxes hinder multiple banding. Paper 3 studies post-frontal snowbands over the English Channel and Irish Sea during extreme cold-air outbreaks in the winters of 2009-10 and 2010-11, via a climatology of precipitation-radar, sounding, and SST data, and real-data WRF sensitivity simulations of one such band over the English Channel. The observational and modelling results show that strong winds and large differential heat fluxes between land and sea were necessary to generate banded precipitation. Coastal orography and the land-sea frictional contrast aided the morphology of bands, but banded precipitation did still form in the absence of these influences in the sensitivity simulations. These three studies and the thesis as a whole highlight the role of frictional and diabatic processes in modifying various types of precipitation bands within baroclinic waves, and in generating bands that would otherwise not exist.
33
Hegyi, Bradley Michael. "Dynamical and thermodynamical influences of the tropics and midlatitudes on arctic hydroclimate variability." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53869.
Full textAbstract:
The Arctic is an important component of the Earth’s climate system, and it is a region dynamically coupled to climate phenomena at lower latitudes, through both atmospheric and oceanic paths. The coupling has significant effects on the hydroclimate variability in the Arctic, including effects on sea ice and Arctic precipitation. In this dissertation, we explore the coupling of the lower latitudes and the Arctic hydroclimate through atmospheric mechanisms with dynamical and thermodynamical components, with a focus on the following examples of variability: i) the decadal variability of boreal winter Arctic precipitation, ii) the variability of the strength of the stratospheric polar vortex in boreal winter, and iii) the initial melt of Arctic sea ice in late boreal spring. The goal of the research is to understand what drives the Arctic hydroclimate variability in each of these examples through improved knowledge of the mechanisms linking them to the tropics and Northern Hemisphere midlatitudes.
In the first part of the analysis, we explore the mechanisms responsible for the decadal variability of boreal winter Arctic precipitation. We find that the decadal variability of cool-season Arctic precipitation is at least partly connected to decadal modulation of tropical central Pacific sea surface temperatures related to the El Niño-Southern Oscillation (ENSO). The modulation can be described as the oscillation between periods favoring central and eastern Pacific warming events [CPW and EPW, respectively], which are two common types of ENSO variability. By analyzing a collection of CPW and EPW events in reanalysis data, we establish the following connecting mechanism. First, the increase of central Pacific SSTs drive a Rossby wave train that destructively interferes with the zonal wavenumber 1 component of the background extratropical planetary wave in the subpolar region. Next, as a result of this interference, the magnitude of the vertical Rossby wave propagation from the troposphere to the stratosphere decreases and the stratospheric polar vortex strengthens. Finally, the strengthening of the vortex translates into a tendency towards a positive Arctic Oscillation (AO) in the troposphere and a poleward shift of the Northern Hemisphere midlatitude storm tracks, increasing moisture transport from lower latitudes and increasing total Arctic precipitation.
In a further investigation of a crucial component of the above mechanism, the initial response of the stratospheric polar vortex to the influence of CPW and EPW is investigated. A 20-member ensemble run of an idealized model experiment in the NCAR Whole Atmosphere Community Climate Model (WACCM) is conducted with prescribed CPW and EPW pattern SST anomalies. Both CPW and EPW events weaken the polar vortex in the ensemble mean. The weakening is mainly tied to changes in the eddy-driven mean meridional circulation, with some contribution from eddy momentum flux convergence. There is a significant spread between ensemble members with identical CPW and EPW forcing, where a few of the ensemble members exhibit a weak strengthening response. The initial conditions of the extratropical atmosphere and subsequent internal variability after the introduction of the CPW and EPW forcing help drive the spread in response between individual members.
In the last part of the analysis, using MERRA reanalysis data, the means by which atmospheric eddies affect the trend and variability of the initial melt of Arctic sea ice are explored. We focus specifically on the effects of lower troposphere (i.e. 1000-500 mb average) meridional heat transport by atmospheric eddies, a dynamical component of the atmospheric eddy mechanism, and eddy-generated surface downwelling shortwave and longwave radiation anomalies, a thermodynamical component. Although in a climatological sense, atmospheric eddies in all major frequency bands transport heat poleward into the Arctic, we find that the lower-troposphere eddy meridional heat transport does not contribute to the trend of an earlier initial melt date. However, eddy heat transport still plays an important role in the initialization of individual episodes of initial melt with large areal coverage. In the investigation of two specific episodes, the meridional heat transport term that represents the interaction between the eddy wind and mean temperature fields (i.e. the product of the meridional eddy wind and the mean temperature fields) is most associated with the initial melt in both episodes. Additionally, melt in one of the episodes is also associated with surface downwelling longwave and shortwave radiation anomalies, a result of eddy-generated cloud cover anomalies. Therefore, in individual melt events, the combination of direct eddy meridional heat transport and surface longwave and eddy-driven shortwave radiation anomalies may significantly contribute to the initial melt of Arctic sea ice. This combination may be especially important in episodes where significant initial melt occurs over a large area and over a period of a few days.
34
Hood, L. L., and B. E. Soukharev. "Interannual Variations of Total Ozone at Northern Midlatitudes Correlated with Stratospheric EP Flux and Potential Vorticity." AMER METEOROLOGICAL SOC, 2005. http://hdl.handle.net/10150/623351.
Full textAbstract:
At northern midlatitudes over the 1979–2002 time period, column ozone trends are observed to have maximum negative amplitudes in February and March. Here, the portion of the observed ozone interannual variability and trends during these months that can be attributed to two specific dynamical transport processes is estimated using correlative and regression methods. In approximate agreement with a recent independent study, 18%–25% of the observed maximum negative trend is estimated to be due to long-term changes in the diabatic (Brewer–Dobson) circulation driven by global-scale changes in planetary wave [Eliassen–Palm (EP) flux] forcing. In addition, 27%–31% of the observed maximum midlatitude trend during these months is estimated to be due to long-term changes in local nonlinear synoptic wave forcing as deduced from correlated interannual variations of zonal mean ozone and Ertel’s potential vorticity. Like long-term decreases in the Brewer–Dobson circulation, this trend component reflects an overall net increase in the polar vortex strength, which is associated with increased numbers of anticyclonic, poleward-breaking Rossby waves at northern midlatitudes. Together, these components can explain approximately 50% of the observed maximum negative column ozone trend and interannual variance at northern midlatitudes in February and March. The combined empirical model also approximately simulates a leveling off or slight increase in column ozone anomalies that has been observed for some months and latitudes since the mid-1990s.
35
Hood, L., S. Rossi, and M. Beulen. "Trends in lower stratospheric zonal winds, Rossby wave breaking behavior, and column ozone at northern midlatitudes." AMER GEOPHYSICAL UNION, 1999. http://hdl.handle.net/10150/624007.
Full textAbstract:
Statistical trend analyses of National Centers for Environmental Prediction (NCEP) gradient zonal winds for the months of February and March demonstrate that the zonal mean meridional wind shear for these months in the midlatitude lower stratosphere has tended to become more anticyclonic with time over the period from 1979 to 1998. Such a tendency favors the increased occurrence at these latitudes of anticyclonic, poleward, Rossby wave breaking events that transport low potential vorticity (PV), ozone-poor air from the subtropical upper troposphere to the midlatitude lower stratosphere while favoring the decreased occurrence of equatorward breaking, cyclonic events. Composite mean differencing and statistical trend analyses of NCEP-derived PV on the 330 K isentropic surface show that zonal mean PV values at midlatitudes in February and March have decreased with time, consistent with the expected trends in Rossby wave breaking behavior. Similar analyses of Total Ozone Mapping Spectrometer (TOMS) total ozone for the same 2 months show that total ozone trends correlate geographically with PV trends. Regression relationships between 330 K PV and total ozone deviations derived from monthly mean measurements on the Northern Hemisphere are applied to estimate that as much as 40% of the zonal mean total ozone decline at midlatitudes in February during the analysis period may be attributed to long-term trends in Rossby wave breaking behavior. As much as 25% of the midlatitude ozone trend in March may be attributed to such trends in wave-breaking behavior. At specific longitudes the contribution to ozone trends from this source (as well as long-term changes in quasi-stationary wave amplitudes and phases) can be well over 50%.
36
Macron, Clémence. "Les Talwegs Tropicaux Tempérés en Afrique australe : mécanismes et évolution face au changement climatique (2010-2099)." Thesis, Dijon, 2014. http://www.theses.fr/2014DIJOS057/document.
Full textAbstract:
Au sein de l’hémisphère sud, l’Afrique australe et le sud-ouest de l’océan Indien forment l’une des trois zones préférentielles de développement des interactions entre les tropiques et les moyennes latitudes. Il s’agit de la Zone de Convergence Sud-Indienne (ZCSI) où se forment, principalement en été austral, des systèmes synoptiques (entre 3 et 5 jours) caractérisés par des bandes nuageuses orientées nord-ouest/sud-est : les Talwegs Tropicaux-Tempérés (TTT). Cette recherche doctorale vise à améliorer les connaissances liées aux TTT, avec une étude sur la dynamique associée à ces systèmes et une analyse de leur évolution possible au cours du XXIème siècle. La première partie de l’étude s’attache à identifier les conditions favorables à la formation et au développement des TTT. Une classification en régimes de temps est utilisée pour identifier les TTT d’une part, et les perturbations des moyennes latitudes d’autre part, permettant de mieux documenter la variabilité spatio-temporelle des TTT et les conditions de leur développement. Ces événements sont responsables d’environ 20% des précipitations saisonnières sud-africaines. Cette contribution augmente selon un gradient ouest-est. La comparaison entre les deux classifications confirme que les perturbations des moyennes latitudes sont une condition nécessaire pour le développement de TTT, mais non suffisante. Dans les tropiques, des advections d’humidité depuis l’océan Atlantique tropical associées à un excès d'énergie statique humide sur le canal du Mozambique forment les conditions supplémentaires favorables à la convection atmosphérique profonde à proximité du continent. La seconde partie étudie comment les TTT, les précipitations et de manière plus générale le climat d’Afrique australe, pourraient évoluer au cours du XXIème siècle sous l’effet du forçage radiatif associé aux émissions de gaz à effet de serre (GES). Cette approche est multi-modèle (huit modèles climatiques sont retenus de l’exercice 5 du GIEC) et multi-trajectoire (RCP 8.5 et 2.6). Les huit modèles restituent convenablement les caractéristiques actuelles du climat d’Afrique australe ainsi que les bandes nuageuses associées aux TTT, tant en termes de variabilité spatiale que de fréquence d’occurrences. Sur le XXIème siècle, ils divergent sur l’évolution des précipitations saisonnières (NDJF). En revanche, ils convergent sur l’augmentation des quantités précipitées par jour de pluie sur le sud-est de l’Afrique australe. Ces changements ne sont pas à relier à une évolution spatio-temporelle des TTT, leur structure spatiale, leur fréquence d’occurrence et leur contribution aux précipitations restent stationnaires tout au long du siècle, mais à des événements pluviogènes extrêmes plus fréquents et plus intensesIn the Southern Hemisphere, Southern Africa and the south-west Indian Ocean are one of the three preferred regions where interactions between the tropics and midlatitudes develop. This is the South Indian Convergence Zone (SICZ), where northwest-southeast oriented cloud bands form at the synoptic scale (between 3 and 5 days). These bands are mainly found during the austral summer and are commonly referred to as tropical temperate troughs (TTTs). This research aims at improving our knowledge related to TTTs, with a study on the dynamics associated with these systems, and an analysis of their possible evolution during the 21st century.The first part of this thesis aims at identifying favorable conditions for the formation and the development of TTTs. Weather regimes analysis is used to identify TTTs on the one hand and mid-latitude perturbations on the other hand, allowing us to better document the spatial and temporal variability of TTTs together with background climate conditions. The events identified account for 20% of seasonal rainfall on average. Their contribution increases according to a west to east gradient. The comparison between these two classifications, partitioned using a k-means clustering, first confirms that midlatitude perturbations are a necessary condition for TTT development, but they are not sufficient. An excess of moist static energy over the Mozambique Channel partly supplied by advections from remote regions (mostly the southern Atlantic basin and the south-west Indian Ocean) form additional conditions favoring deep atmospheric convection over and near the Southern Africa. The second part investigates possible changes in precipitation, TTTs and more generally climate over Southern Africa during the 21st century in response to radiative forcing associated with greenhouse gas emissions (GHG). A multi-model (height climate models taken on the IPCC Fifth Assessment Report) and multi-scenario (RCP 8.5 and 2.6) approach is chosen. All models are skillful to reproduce Southern Africa current climate characteristics and cloud bands associated with TTTs, both in terms of spatial variability and frequency of occurrences. During the 21th century, there is no consensus between the models on the future evolution of seasonal rainfall (NDJF). However, all simulate an increase in the amounts precipitated by rainy day over the south-east part of southern Africa. These changes are not related to an evolution of TTTs: their spatial patterns, frequency of occurrences and contribution to rainfall remain stationary throughout the 21st century, but they associated with extreme rainfall events that become more frequent and more intense
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Ansmann, Albert, Heike Kalesse, M. Fromm, Andreas Foth, Thorsten Kanitz, Ronny Engelmann, Holger Baars, Martin Radenz, Patric Seifert, and B. Barja. "Vertical aerosol distribution in the Southern hemispheric Midlatitudes as observed with lidar at Punta Arenas, Chile (53.2 ◦S and 70.9 ◦W) during ALPACA." Universität Leipzig, 2019. https://ul.qucosa.de/id/qucosa%3A74179.
Full textAbstract:
This publication gives a brief overview about the main findings of Foth et al. (2019). Within this work, lidar observations of the vertical aerosol distribution above Punta
Arenas, Chile (53:S and 70:9W) which have been performed with the Raman lidar PollyXT from December 2009 to April 2010 are presented. Pristine marine aerosol conditions related to the prevailing westerly circulation dominated the measurements. Lofted aerosol layers could only be observed eight times during the whole measurement period. One case study is presented showing long-range transport of smoke from biomass burning in Australia and regionally transported
dust from the Patagonian Desert. The aerosol sources are identified by trajectory analyses with HYSPLIT and FLEXPART. However, seven of the eight analysed cases with lofted layers show an aerosol optical thickness (AOT) of less than 0.05. The ground-based lidar observations are supplemented by the AERONET Sun photometers and the space-borne lidar CALIOP on board of CALIPSO. The averaged AOT determined by CALIOP was 0:02 0:01 at Punta Arenas from 2009 to 2010.Diese Publikation gibt einen kurzen Überblick über ein paar Ergebnisse aus Foth et al. (2019). In dieser Arbeit werden Lidarbeobachtungen der vertikalen aerosolverteilung über Punta Arenas, Chile (53:2S and 70:9W) präsentiert, welche mit dem Ramanlidar PollyXT zwischen Dezember 2009 und April 2010 durchgeführt wurden. Die Messungen sind durch reine marine Aerosolbedingungen in Verbindung mit vorherrschenden Westwinden gekennzeichnet. Abgehobene Aerosolschichten können nur acht mal während der gesamten Messperiode beobachtet werden. Einer der hier präsentierten Fälle zeigt weitreichenden Aerosoltransport von Rauch aus Biomasseverbrennung in Australien und regional transportierten Mineralstuab aus der patagonischen Wüste. Die Aerosolquellen wurden durch Trajektorienanalysen mit HYSPLIT und FLEXPART identifiziert. Allerdings zeigen sieben dieser acht Fälle mit abgehobenen Schichten ein optische Dicke des Aerosols (AOT) von weniger als 0,05. Die bodengebundenen Lidabeobachtungen werden durch AERONET Sonnenphotometer und das satellitengetragenge Lidar CALIOP an Bord von CALIPSO ergänzt. Die mittlere AOT, die mittels CALIOP zwischen 2009 und 2010 in Punta Arenas bestimmt wurde, beträgt 0:02 0:01.
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Buntoung, Sumaman. "Comparative investigation of erythemal ultraviolet radiation in the tropics and mid-latitudes." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/comparative-investigation-of-erythemal-ultraviolet-radiation-in-the-tropics-and-midlatitudes(127d2859-5aab-4c86-8c50-95ba621811c4).html.
Full textAbstract:
Ultraviolet (UV) radiation has several effects on human health as well as other biological and chemical systems. The radiation can be weighted with the erythemal action spectrum and then converted to the dimensionless UV Index, which is designed to indicate the detrimental 'sunburning power' of the radiation for public heath purposes. A global view of the erythemally weighted irradiance from the Ozone Monitoring Instrument (OMI) on board the Aura spacecraft has been available since July, 2004. However, ground-based validation and correction of the satellite data are still required. In this thesis, the erythemal dose rates at local solar noon taken from the satellite were compared to ground-based data measured by spectroradiometers or broadband radiometers in two different climate areas: the Tropics and midlatitudes. This seeks to redress the lack of data and satellite validation for the Tropics, and also allows comparison with previous work in midlatitudes. The validation results show that the satellite data overestimates the ground-based data by 9%-32% at the cleanest site, with a much higher discrepancy at polluted sites. Using a radiative transfer model confirmed that the positive bias in the satellite data was mainly caused by aerosol absorption that is not taken into account in the satellite retrieval algorithm. Therefore, two empirical methods were introduced in order to correct the OMI UV data for absorbing aerosols under clear sky conditions. These methods required aerosol optical depth and aerosol single scattering, or aerosol absorption optical depth, as input parameters. The methods improved the OMI UV data by up to 30% depending on site and input data source. For cloudy conditions aerosol data is usually not available either from ground-based or satellite-based measurements; however, the effect of cloud is usually far greater than that of aerosol, and some of the aerosol effect (scattering) is intrinsically included in the cloud correction. A further empirical model for cloudy conditions was derived to reduce bias of the OMI UV data with respect to ground-based data. The method only requires the OMI UV data as an input. The cloudy model reduced the bias by about 13%-30% depending on site, and gave similar results even when used with clear sky data. Since ground-based data is sparse, the final goal of the work was to produce a corrected map of UV index for the whole of Thailand, based only on data available from satellite, which gives full regional coverage. Issues with availability and quality of satellite data meant that the best results were achieved by using only the cloudy sky correction, for all conditions. The resulting daily noontime UV Index maps of Thailand were assessed against ground-based data for independent years. The corrected UV Index was within ±2 compared with ground-based data for all sites, compared to discrepancies of up to 4 UV Index for uncorrected data.
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Foussard, Alexis. "Influence des tourbillons océaniques sur le rail des dépressions atmosphériques." Electronic Thesis or Diss., Sorbonne université, 2018. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2018SORUS492.pdf.
Full textAbstract:
Cette thèse est consacrée à l'étude de la variabilité des rails des dépressions des moyennes latitudes induite par les anomalies de température de surface (SST) associées aux tourbillons océaniques. Les effets locaux et de grande échelle de ces tourbillons sur la couche limite et la troposphère libre sont analysés à partir de simulations atmosphériques à haute résolution. Un canal barocline périodique représente de manière idéalisée le rail des dépressions sur une aquaplanète, avec un forçage par des SST décrivant un front océanique et ses tourbillons. La première partie de la thèse traite de la réponse des basses couches de l'atmosphère, en lien avec les mécanismes d'ajustement de pression et de mélange vertical turbulent. L'ajustement de pression domine dans les conditions de vent faible, en accord avec la théorie. En présence d'un front de grande échelle, la direction du vent module également la stabilité des basses couches : pour des vents forts venant du côté chaud du front, la réponse atmosphérique est aussi dominée par une réponse en ajustement de pression, à l'inverse des vents de direction opposée. Cela montre que les mécanismes de réponse sont déterminés par la variabilité rapide de l'atmosphère. La divergence de tension de surface est, comme dans les observations, linéairement reliée au gradient de SST. Pour certaines conditions, la divergence du vent horizontal peut cependant présenter une réponse proportionnelle au laplacien de température de la couche limite. Ceci concerne une gamme d'échelles allant de 100 à 500 km. La seconde partie de la thèse compare la réponse atmosphérique à un champ de tourbillons à une expérience témoin caractérisée par un front de SST zonalement symétrique. Des déplacements vers le pôle du rail des dépressions et du courant-jet apparaissent, tous deux faibles mais statistiquement robustes. Les forçages à la surface conduisent à une réponse locale dans la troposphère libre, qui est dominée par la variabilité synoptique. L'asymétrie de réponses aux tourbillons chauds et froids engendre aussi une augmentation des flux de surface moyens, qui permet d'interpréter une grande partie de la réponse de grande échelle. Les déplacements vers le pôle sont expliqués à partir des bilans de chaleur et d'énergie mécanique du rail des dépressions. Le dégagement additionnel de chaleur latente, qui se produit dans les tempêtes, joue un rôle primordial dans ces deux bilansThis thesis aims to understand how sea surface temperature (SST) anomalies associated with mesoscale oceanic eddies may contribute to mid-latitude storm tracks variability. Based on idealized high resolution atmospheric simulations, local and large scale remote influences of the eddies onto the boundary layer and the free troposphere are investigated. Basic configuration is a generic baroclinic channel above an eddying SST front. The first part of the manuscript deals with the response of the atmosphere in the boundary layer, based on the well-known mechanisms of pressure adjustment and vertical mixing of momentum. As expected from theoretical scaling arguments, the former is important for weak wind conditions. Due to the large scale SST front, direction of strong background wind also controls stability : a transition, from a forcing by mixing of momentum to a forcing by SST-driven pressure forces, occurs for equatorward winds as cold air is advected above warmer SST. It shows how sub-weekly atmospheric variability modulates the low level response. Wind stress divergence matches the linear relationship observed with downwind SST gradient. In specific conditions, horizontal divergence is however proportional to the laplacian of boundary layer temperature, within a large range of horizontal scales (500-100~km). In a second part, the experiment with oceanic eddies is compared to its zonally symmetric counterpart. It reveals weak but robust modifications of atmospheric large-scale circulation and synoptic variability : the Eulerian storm track and the jet stream are shifted poleward. Surface forcing is associated with a local response in the mid-troposphere, which is intermittent and dominated by the day-to-day variability. Because of an asymmetry in the response to cold and warm eddies, the oceanic eddies are also responsible for a net increase of both latent and sensible surface heat fluxes. It accounts for a large part of the differences obtained between eddying and zonally symmetric configurations. Based on heat and mechanical energy budgets, an interpretation of the poleward displacements of the storm track and the jet is given. The contribution of latent heat release to both budgets, occurring mainly within synoptic storms, plays a major role in the atmospheric response
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Wu, Yutian. "Midlatitude Storm Track Response to Increased Greenhouse Warming." Thesis, 2012. https://doi.org/10.7916/D80Z7993.
Full textAbstract:
Storm tracks play a major role in regulating the precipitation and hydrological cycle in midlatitudes. The changes in the location and amplitude of the storm tracks in response to global warming will have significant impacts on the poleward transport of heat, momentum and moisture and on the hydrological cycle. Recent studies have indicated a poleward shift of the storm tracks and midlatitude precipitation zone in the warming world that will contribute to subtropical drying and higher latitude moistening. This dissertation is to investigate the storm track response to increased greenhouse warming and the dynamical mechanisms driving the changes in the storm tracks. First, by analyzing the eddy statistics simulated in the Geophysical Fluid Dynamics Laboratory (GFDL) CM2.1 model simulations (IPCC AR4 model), we confirm the poleward and upward shift and intensification of the storm tracks in the late 21st century. It has been found that this key feature is generally consistent with the change in Eady growth rate. Diagnosis of the latitude-by-latitude energy budget for the current and future climate demonstrates how the coupling between radiative and surface heat fluxes and eddy heat and moisture transport influences the midlatitude storm track response to global warming. Through radiative forcing by increased atmospheric carbon dioxide and water vapor, more energy is gained within the tropics and subtropics, while in the middle and high latitudes energy is reduced through increased outgoing terrestrial radiation in the Northern Hemisphere and increased ocean heat uptake in the Southern Hemisphere. This enhanced energy imbalance in the future climate requires larger poleward atmospheric energy transports in the midlatitudes which are partially accomplished by the intensified storm tracks. This strong connection between intensified storm track energy transports and intensified energy imbalance in the atmosphere is also confirmed in other IPCC AR4 models. We further explore the dynamical mechanisms inducing the changes in the general circulation of the atmosphere due to increased carbon dioxide (CO2) by looking into the transient step-by-step adjustment of the circulation. This allows an assessment of the causality sequence in the circulation and thermal structure response prior to establishment of a quasi-equilibrium state. The transient atmospheric adjustment is examined using the National Center for Atmospheric Research Community Atmospheric Model Version 3 coupled to a slab ocean model and the CO2 concentration in the atmosphere is uniformly and instantaneously doubled. The thermal structure and circulation response is well established after one year of integration with the magnitudes gradually increasing afterwards towards quasi-equilibrium. Tropical upper tropospheric warming occurs in the first month. The expansion of the warming in the middle and upper troposphere to the subtropics occurs later and is found to be primarily dynamically-driven due to the intensification of transient eddy momentum flux convergence and resulting anomalous descending motion in this region. This linkage between the eddy-driven vertical motion anomaly and the subtropical warming expansion in the middle and upper troposphere is also confirmed in the late 21st century in the IPCC AR4 simulations. The poleward displacement of the midlatitude tropospheric jet streams occurs together with the change in eddy momentum flux convergence but only after the intensification of the subpolar westerlies in the stratosphere. The results demonstrate the importance of the tropospheric eddies in setting up the extratropical tropospheric response to global warming. Our modeling results also show the sequence of the zonal wind anomaly in the vertical column of the atmosphere during the period of transient adjustment, indicating that the poleward displacement of the tropospheric jets follows the subpolar westerly anomaly in the stratosphere. It suggests the importance of the stratosphere and the coupling between the stratosphere and the troposphere in regulating the extratropical tropospheric circulation response to increasing CO2. Three phases are defined during this period of transient adjustment including a fast radiatively-induced thermal response in the stratosphere, a westerly acceleration in the stratosphere driven by stationary eddy anomaly, and a 'downward propagation' of westerly acceleration from the stratosphere to the troposphere followed by a poleward displacement of the tropospheric midlatitude jets. Diagnoses using wave spectra and linear index of refraction are used to understand the dynamics underlying the adjustment process.
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Han, Feng. "Midlatitude D Region Variations Measured from Broadband Radio Atmospherics." Diss., 2011. http://hdl.handle.net/10161/3856.
Full textAbstract:
The high power, broadband very low frequency (VLF, 3--30 kHz) and extremely low frequency (ELF, 3--3000 Hz) electromagnetic waves generated by lightning discharges and propagating in the Earth-ionosphere waveguide can be used to measure the average electron density profile of the lower ionosphere (
In order to understand the time scales, magnitudes and sources for the midlatitude nighttime
Based on sferic data similar to those for nighttime, we also measured the daytime
By applying the nighttime and daytime measurement techniques, we also derived the
Dissertation
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Mitovski, Toni. "Interactions between convection and the background atmosphere during high rain events: observations and comparisons with models." 2014. http://hdl.handle.net/10222/50416.
Full textAbstract:
The thesis consists of three projects. Each of these projects is a diagnostic study of the interaction between strong convective events and the background atmosphere. In all projects, we use a satellite rainfall dataset to identify strong rain events. We then use radiosonde soundings to generate composite anomaly patterns of meteorological variables about the strong rain events.
In Project 1, we examine temperature, relative humidity, and divergence anomalies about strong convective events in the Western Tropical Pacific. A low-level convergence coupled to a midlevel divergence develops prior to peak rainfall. A midlevel convergence coupled to a low-level divergence develops after peak rainfall. Strong surface cold pools develop in response to high rainfall. Observations were compared to models and reanalyses. In general, models and reanalyses do not fully represent the timing, strength, and altitude of the mid-level convergence and divergence features. The surface cold anomaly is also underestimated in models. These discrepancies suggest that the mesoscale downward transport of mid-level air into the boundary layer in models may be too weak.
In Project 2, we investigate the impact of convection on the background distribution of a chemical tracer (ozone). Negative ozone anomalies and higher frequency of midlevel cloud tops occur in a layer between 3 and 8 km prior to peak rainfall. Negative ozone anomalies in the upper troposphere develop in response to high rainfall. Chemistry transport model simulations also exhibit negative ozone anomalies at upper and midlevels. However, the ozone anomalies in the model are symmetric about peak rainfall and are more persistent than observations.
In Project 3, we identify regional variations in the interaction between convection and the background atmosphere. In all four regions, deep convection imposes cooling in the lower and warming in the upper troposphere. In mid-latitudes, convection is associated with stronger anomalies in surface pressure, geopotential height, and CAPE. Over land, a low-level warm anomaly develops prior to peak rainfall and the surface cold pool that develops during peak rainfall is more persistent. The PV generated prior to peak rainfall, is advected towards the surface after peak rainfall and may play a role in hurricane genesis.
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Fraser, Annemarie. "Arctic and Midlatitude Stratospheric Trace Gas Measurements Using Ground-based UV-visible Spectroscopy." Thesis, 2008. http://hdl.handle.net/1807/17301.
Full textAbstract:
A ground-based, zenith-sky, UV-visible triple grating spectrometer was installed at the Polar Environment Atmospheric Research Laboratory (PEARL) in the Canadian High Arctic during polar springtime from 2004 to 2007 as part of the Canadian Arctic ACE (Atmospheric Chemistry Experiment) Validation Campaigns. From the solar spectra,
ozone, NO2, and BrO vertical column densities (VCDs) have been retrieved using the DOAS (Differential Optical Absorption Spectroscopy) technique. This spectrometer, the UT-GBS (University of Toronto Ground-Based Spectrometer), was also deployed as part of the fourth Middle Atmosphere Nitrogen TRend Assessment (MANTRA) campaign in Vanscoy, Saskatchewan in August and September 2004.
A near-identical spectrometer, the PEARL-GBS, was permanently installed at PEARL
in August 2006 as part of the refurbishment of the laboratory by CANDAC (Canadian
Network for the Detection of Atmospheric Change). Since then, the instrument has been
making continuous measurements, with the exception of during polar night. Vertical
columns of ozone and NO2 can be retrieved year-round. During the 2007 sunrise campaign,
differential slant column densities (DSCDs) of OClO and VCDs of BrO were also
retrieved.
Ozone and NO2 DSCDs and VCDs from the UT-GBS were compared to the DSCDs and VCDs from three other UV-visible, ground-based, grating spectrometers that also participated in the MANTRA and Eureka campaigns. Two methods developed by the UV-visible Working Group of the NDACC (Network for the Detection of Atmospheric Composition Change) were followed. During MANTRA, the instruments were found to partially meet the NDACC standards. The comparisons from Eureka were an improvement on the MANTRA comparisons, and also partially met the NDACC standards. In 2007, the columns from the UT-GBS and PEARL-GBS were compared, and were found to agree within the NDACC standards for both species.
Ozone and NO2 VCDs from the ground-based instruments were also compared to
integrated partial columns from the ACE-FTS (ACE-Fourier Transform Spectrometer)
and ACE-MAESTRO (ACE-Measurements of Aerosol Extinction in the Stratosphere
and Troposphere Retrieved by Occultation) on board the ACE satellite. ACE-FTS partial
columns were found to agree with the ground-based total columns, while the ACE-MAESTRO
partial columns were found to be smaller than expected for ozone and larger than expected for NO2.
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Bhatt, Uma S. "Role of atmosphere-ocean interaction in the midlatitude North Atlantic on interannual climate variability." 1996. http://catalog.hathitrust.org/api/volumes/oclc/35032198.html.
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Thesis (Ph. D.)--University of Wisconsin--Madison, 1996.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 151-159).
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Hubbard, Shane A. "The explanation for cloud top temperatures using three midlatitude cases from a 3-D model simulation." 2005. http://catalog.hathitrust.org/api/volumes/oclc/61106589.html.
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Thesis (M.S.)--University of Wisconsin--Madison, 2005.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 117-118)
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Hsieh, Ying-Hsun, and 謝瑩薰. "Using potential vorticity of two layer model to explore the characteristics of winter midlatitude synoptic-scale system." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/3uz7k9.
Full textAbstract:
碩士國立中央大學
大氣物理研究所
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The potential vorticity (PV) on each isentropic surface and potential temperature at the lower boundary play important roles in dynamic process of midlatitude synoptic-scale systems. But single isobaric surface or isentropic surface can not represent both PV and potential temperature at the same time. We need understand the dynamic process by combining variant isobaric or isentropic surfaces when exploring the synoptic-scale system. In this paper, we use 310K isentropic surface as the interface to simplify the atmosphere into a two layer system. The main purpose is to explore whether the layered potential vorticity (LPV) can represent the characteristic and dynamic process of midlatitude synoptic-scale system more clearly and concisely than isentropic potential vorticity (IPV). This study is divided into two parts. The first part is, by comparing LPV of lower troposphere with satellite image, 1000 hPa geopotential height, and TRMM rainfall data, during January 2001, to examine whether LPV can show appropriately the characteristics of intensity, position, growth, movement and precipitation of midlatitude synoptic-scale system. The results clearly shows lower troposphere is consistent with satellite image, 1000 hPa geopotential height, and precipitation. The maximum of PV is well-matched with the extratropical cyclone center, low pressure trough, front and rain belt. Similarly, low PV has salient relation with high pressure ridge. The second part is by computing local meridional PV gradients of upper and lower troposphere to get stability, then comparing the pressure of weather systems in stable and unstable status to explore the connection between the local baroclinic instability and the growth of synoptic-scale system. From Monte Carlo test, local baroclinic instability has highly relationship with the intensity of synoptic-scale system. In other words, the system intensity in unstable status is stronger then stable status. In summary, this study indeed shows LPV can represent the characteristics and dynamic process of midlatitude synoptic-scale system more clearly and concisely than IPV. Besides, we also discover that LPV consistent with perturbation in tropical area pretty well. Thus, LPV is a very good tool in studying the dynamic process of system.
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Decker, Steven G. "The local energetics perspective on the life cycles of midlatitude synoptic-scale disturbances case studies and real-time diagnostics /." 2003. http://catalog.hathitrust.org/api/volumes/oclc/52473621.html.
Full textAbstract:
Thesis (M.S.)--University of Wisconsin--Madison, 2003.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 143-145).
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Keng-Gaik, Lum. "The influence of Large-scale 200 mb tropical divergence events on the midlatitude zonal flow over the Asia-Pacific region during the 1983-84 winter." Thesis, 1985. http://hdl.handle.net/10945/21380.
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Jacobi, Christoph. "Long-term trends and decadal variability of upper mesosphere/lower thermosphere gravity waves at midlatitudes." 2012. https://ul.qucosa.de/id/qucosa%3A16426.
Full textAbstract:
Mesosphere/lower thermosphere (MLT) winds over Germany as measured with a lowfrequency spaced receiver system at Collm 1984-2007 have been analysed with respect to variations at the time scales of gravity waves. Background winds are also registered to analyse gravity-mean flow interactions at decadal and interdecadal time scales. In both winter and summer an increasing mesospheric zonal wind jet with time is registered, which is connected with increasing gravity wave variances. At greater altitudes in summer, the mean wind jet trend reverses, and negative trends of gravity wave variances are found. This connection between gravity waves and mean wind is also observed on a quasi-decadal scale: during solar maximum stronger mesospheric zonal wind jets as well as larger gravity wave amplitudes are observed. This results in a solar cycle modulation of gravity waves with larger amplitudes during solar maximum. The connection between gravity waves and mean zonal wind may be explained by wave filtering within linear wave theory, such that stronger mesospheric zonal winds are connected with larger gravity wave amplitudes.