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Tamigneaux, Éric, and Ladd Erik Johnson. "Les macroalgues du Saint-Laurent : une composante essentielle d’un écosystème marin unique et une ressource naturelle précieuse dans un contexte de changement global." Le Naturaliste canadien 140, no. 2 (June 2, 2016): 62–73. http://dx.doi.org/10.7202/1036505ar.
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Aux latitudes moyennes, les grandes algues sont une composante essentielle des écosystèmes côtiers comme source de nourriture et d’habitat pour les communautés benthiques. Les assemblages de macroalgues dans l’écosystème marin du Saint-Laurent (ÉMSL) sont largement dominés par les fucales (Fucus, Ascophyllum) dans l’étage médiolittoral et par les laminaires (Alaria, Saccharina, Agarum) et les algues calcaires dans l’étage infralittoral. Peu d’efforts ont été consacrés à l’étude de leur écologie alors même que les activités de récolte sont en croissance. En dépit des similitudes entre l’ÉMSL et les écosystèmes comparables de l’est du Canada et d’Europe, il y a des différences fonctionnelles frappantes associées à 2 sources de perturbations : le broutage intense des algues par les oursins dans l’étage infralittoral et l’abrasion des communautés de l’étage médiolittoral par les glaces. Dans plusieurs régions de l’ÉMSL, ces perturbations réduisent l’extension des assemblages d’algues, ce qui génère des incertitudes sur le potentiel d’exploitation de cette ressource. Il en ressort qu’il faut approfondir les connaissances sur la répartition et l’abondance des espèces mais aussi développer l’algoculture, cela autant pour conserver les ressources naturelles et leurs services écologiques que pour assurer un approvisionnement stable des marchés émergents avec des ressources de qualité. À terme, ces informations seront indispensables pour anticiper les changements causés par le réchauffement climatique et par l’augmentation des invasions biologiques.
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THIMONIER, J., and A. SEMPERE. "La reproduction chez les cervidés." INRAE Productions Animales 2, no. 1 (February 10, 1989): 5–21. http://dx.doi.org/10.20870/productions-animales.1989.2.1.4395.
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Les principales caractéristiques de la fonction de reproduction des cervidés ainsi que son contrôle par différents facteurs de l’environnement sont présentés dans cette étude bibliographique. Sous les latitudes moyennes et élevées, les cervidés originaires de ces latitudes ont un cycle saisonnier très marqué de la reproduction et il y a synchronisme entre l’activité sexuelle des mâles et celle des femelles. Les naissances ont toujours lieu à la fin du printemps ou au début de l’été. Compte-tenu des durées de gestation des différentes espèces présentées (200 à 290 jours), les périodes d’accouplement sont très variables d’une espèce à l’autre (été, automne, début de l’hiver), mais fixes pour une espèce donnée. La photopériode serait l’entraîneur de l’activité sexuelle comme cela a été démontré plus particulièrement chez les cerfs rouges. Il est possible d’avancer le début de la période de reproduction de 1 à 2 mois (cerfs rouges, daims) par différentes méthodes : effet mâle, traitements progestagène, traitement à la mélatonine. Ces méthodes ne sont toutefois efficaces que dans les 2 mois qui précèdent le début normal de la saison sexuelle. Sous les latitudes plus faibles et pour les cervidés originaires de ces latitudes, la répartition des mise bas au cours de l’année est beaucoup plus uniforme. Cette caractéristique semble subsister même lorsqu’ils sont transportés sous des latitudes plus élevées.
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OUIN, S. "Influence de la reproduction désaisonnée des caprins sur les résultats techniques et économiques des élevages." INRAE Productions Animales 10, no. 4 (October 8, 1997): 317–26. http://dx.doi.org/10.20870/productions-animales.1997.10.4.4005.
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La reproduction des caprins est marquée, sous nos latitudes, par une forte saisonnalité. Afin de satisfaire aux besoins des transformateurs de lait, les éleveurs cherchent à anticiper la période de mise bas des chèvres. Ils utilisent principalement pour cela les traitements de synchronisation hormonale de l’oestrus. L’article analyse les conséquences techniques et économiques du désaisonnement des caprins sur une longue période (1989 à 1992).
La production laitière annuelle moyenne par chèvre n’est pas modifiée par le désaisonnement, alors que s’accroissent le taux protéique moyen (de + 0,7 à 1 g/l) et la proportion de lait produit en hiver (jusqu’à + 20 % pour les troupeaux mettant bas en novembre). Les élevages pratiquant régulièrement le désaisonnement n’obtiennent pas de meilleures performances que ceux ayant maintenu des mise bas tardives, en raison des perturbations provoquées par le programme de désaisonnement. Leur progression sur quatre ans s’avère même inférieure.
Le désaisonnement limite le groupage des mise bas : l’étalement moyen des parturitions s’est accru de 40 jours (+ 41 %) entre 1989 et 1992, atteignant en moyenne 4,5 mois. En conséquence, les renouvellements des troupeaux sont hétérogènes, entraînant des difficultés dans la conduite d’élevage et la mise en reproduction des chevrettes.
En revanche, les élevages qui maîtrisent correctement le désaisonnement et l’élevage des chevrettes de renouvellement sont les plus performants (en 1992 : + 120 l de lait (+ 17 %) et + 326 F de marge brute par chèvre (+ 28 %). L’observation des chevrettes d’élevage est donc un bon critère d’appréciation de la technicité de l’élevage.
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Buka, Irena, and Katherine M. Shea. "Les changements climatiques mondiaux et la santé des enfants canadiens." Paediatrics & Child Health 24, no. 8 (December 2019): 558. http://dx.doi.org/10.1093/pch/pxz158.
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Abstract Les changements climatiques sont une réalité. De nombreuses autorités insistent sur la nécessité de déployer et d’adapter les efforts environnementaux en vue de protéger la santé des êtres humains. Les changements climatiques s’accélèrent, et les pays situés à des latitudes élevées, comme le Canada, les subissent de manière plus directe. De plus, certains paramètres sont plus spectaculaires que dans les pays situés à des latitudes moyennes ou faibles. Les enfants sont vulnérables aux effets des changements climatiques sur la santé, et les médecins et autres dispensateurs de soins doivent être prêts à en détecter, en gérer et en prévenir les dangers. Le présent point de pratique fait ressortir certaines menaces précises des changements climatiques sur la santé des enfants et des adolescents et fournit des ressources pour les professionnels de la santé. Les défis climatiques et leurs effets sur la santé des enfants sont décrits en tenant compte de rapports canadiens importants et d’information prouvée scientifiquement. S’ils connaissent mieux les effets immédiats et à long terme des changements climatiques sur la santé des enfants, les médecins et les autres dispensateurs de soins pourront conseiller les familles et mener leur pratique avec plus d’efficacité.
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Gough, D. O., and M. J. Thompson. "On the implications of the symmetric component of the frequency splitting reported by Duvall, Harvey and Pomerantz." Symposium - International Astronomical Union 123 (1988): 175–80. http://dx.doi.org/10.1017/s0074180900158012.
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The component of the frequency splitting of solar five-minute oscillations observed by Duvall, Harvey and Pomerantz that is even in azimuthal degree measures latitudinal and depth variations in the structure of the sun. We indicate how the data hint that there is a shallow perturbation, possibly associated with a magnetic field, that is concentrated at low latitudes.
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Besancenot, Jean-Pierre. "Climats tempérés et santé : quelques caractères originaux des risques climatiques majeurs aux latitudes moyennes (Temperate climates and health : some specific features of the major climatic risks in mid-latitudes)." Bulletin de l'Association de géographes français 63, no. 5 (1986): 375–80. http://dx.doi.org/10.3406/bagf.1986.1363.
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Brochu, Michel. "Importance de la bioturbation naturelle dans les zones climato-botaniques des hautes et moyennes latitudes (The importance of natural bioturbation in climato-botanic zones of higher and mid-latitudes)." Bulletin de l'Association de géographes français 71, no. 4 (1994): 445–51. http://dx.doi.org/10.3406/bagf.1994.1772.
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Jensen, J. W., and B. G. Fejer. "Longitudinal dependence of middle and low latitude zonal plasma drifts measured by DE-2." Annales Geophysicae 25, no. 12 (January 2, 2007): 2551–59. http://dx.doi.org/10.5194/angeo-25-2551-2007.
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Abstract. We used ion drift observations from the DE-2 satellite to study for the first time the longitudinal variations of middle and low latitude F region zonal plasma drifts during quiet and disturbed conditions. The quiet-time middle latitude drifts are predominantly westward; the low latitude drifts are westward during the day and eastward at night. The daytime quiet-time drifts do not change much with longitude; the nighttime drifts have strong season dependent longitudinal variations. In the dusk-premidnight period, the equinoctial middle latitude westward drifts are smallest in the European sector and the low latitude eastward drifts are largest in the American-Pacific sector. The longitudinal variations of the late night-early morning drifts during June and December solstice are anti-correlated. During geomagnetically active times, there are large westward perturbation drifts in the late afternoon-early night sector at upper middle latitudes, and in the midnight sector at low latitudes. The largest westward disturbed drifts during equinox occur in European sector, and the smallest in the Pacific region. These results suggest that during equinox SAPS events occur most often at European longitudes. The low latitude perturbation drifts do not show significant longitudinal
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Unnikrishnan, K., A. Saito, Y. Otsuka, M. Yamamoto, and S. Fukao. "Transition region of TEC enhancement phenomena during geomagnetically disturbed periods at mid-latitudes." Annales Geophysicae 23, no. 11 (December 21, 2005): 3439–50. http://dx.doi.org/10.5194/angeo-23-3439-2005.
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Abstract. Large-scale TEC perturbations/enhancements observed during the day sectors of major storm periods, 12-13 February 2000, 23 September 1999, 29 October 2003, and 21 November 2003, were studied using a high resolution GPS network over Japan. TEC enhancements described in the present study have large magnitudes (≥25×1016 electrons/m2) compared to the quiet-time values and long periods (≥120 min). The sequential manner of development and the propagation of these perturbations show that they are initiated at the northern region and propagate towards the southern region of Japan, with velocities >350 m/s. On 12 February 2000, remarkably high values of TEC and background content are observed at the southern region, compared to the north, because of the poleward expansion of the equatorial anomaly crest, which is characterized by strong latitudinal gradients near 35° N (26° N geomagnetically). When the TEC enhancements, initiating at the north, propagate through the region 39-34° N (30-25° N geomagnetically), they undergo transitions characterized by a severe decrease in amplitude of TEC enhancements. This may be due to their interaction with the higher background content of the expanded anomaly crest. However, at the low-latitude region, below 34° N, an increase in TEC is manifested as an enhanced ionization pattern (EIP). This could be due to the prompt penetration of the eastward electric field, which is evident from high values of the southward Interplanetary Magnetic Field component (IMF Bz) and AE index. The TEC perturbations observed on the other storm days also exhibit similar transitions, characterized by a decreasing magnitude of the perturbation component, at the region around 39-34° N. In addition to this, on the other storm days, at the low-latitude region, below 34° N, an increase in TEC (EIP feature) also indicates the repeatability of the above scenario. It is found that, the latitude and time at which the decrease in magnitude of the perturbation component/amplitude of the TEC enhancement are matching with the latitude and time of the appearance of the high background content. In the present study, on 12 February 2000, the F-layer height increases at Wakkanai and Kokubunji, by exhibiting a typical dispersion feature of LSTID, or passage of an equatorward surge, which is matching with the time of occurrence of the propagating TEC perturbation component. Similarly, on 29 October 2003, the increase in F-layer heights by more than 150km at Wakkanai and 90 km at Kokubunji around 18:00 JST, indicates the role of the equatorward neutral wind. On that day, TEC perturbation observed at the northern region, after 18:30 JST, which propagates towards south, could be caused mainly by the equatorward neutral wind, leading to an F-layer height increase. These observations imply the role of the equatorward neutral wind, which increases the F-layer height, by lifting the ionization to the regions of lower loss during daytime, when production is still taking place, which, in turn, increases the TEC values. Large-scale traveling ionospheric disturbances (LSTIDs) are considered as ionospheric manifestations of the passage of Atmospheric Gravity Waves (AGWs) that are generated at the high latitude by energy input from the magnetosphere to the low-latitude ionosphere. This study shows that large-scale TEC perturbations observed here are produced at the northern region due to the combined effects of the equatorward neutral wind, the subsequent F-layer height increase, and LSTIDs. When these perturbation components propagate through the region, 39-34° N, they undergo transitions characterised by a decrease in magnitude. Also, at the low-latitude region, below 34° N, an increase in the TEC exhibits EIP feature, due to the prompt penetration of the eastward electric field.
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Daget, Ph, and S. Reyes. "Sur la variabilite des precipitations dans la basse californie du nord (Mexique)." Geofísica Internacional 28, no. 4 (October 1, 1989): 693–720. http://dx.doi.org/10.22201/igeof.00167169p.1989.28.4.1318.
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Les données de 36 stations climatologiques, pour la période 1957 - 1983, ont été utilisées pour caractériser l’influence tropicale sur les précipitations observées en Basse Californie du Nord. Les résultats obtenus mettent en évidence que les variabilités spatiale et temporelle sont associées á la tropicalité. Pendant l’hiver, les précipitations sont surtout originaires des latitudes moyennes (c’est-á-dire du Pacifique Nord). Pendant l’été, les précipitations ont une origine tropicale, c’est-á-dire, du Pacifique et de l’Atlantique équatoriaux ; cependant, le volume des précipitations est étroitement dépendant d’un phénomène á échelle planétaire. L’analyse met en effet en évidence une très forte influence tropicale pendant les périodes de « NO-ENSO » (ou El Niño/Oscillation australe). L’indice de tropicale (défini comme le quotient de la somme des médianes mensuelles des précipitations estivales par la somme des médianes mensuelles des précipitations estivales par la comme des médianes mensuelles sur l’ensemble de l’année ) est maximal en 1963, 1967, 1971 et 1976 avec des valeurs de 42%, 48%, 59% et 57% respectivement. Tous les quatre coïncident avec des anomalies positives du Southern Oscillation Index
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Kidston, Joseph, G. K. Vallis, S. M. Dean, and J. A. Renwick. "Can the Increase in the Eddy Length Scale under Global Warming Cause the Poleward Shift of the Jet Streams?" Journal of Climate 24, no. 14 (July 15, 2011): 3764–80. http://dx.doi.org/10.1175/2010jcli3738.1.
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Abstract The question of whether an increase in the atmospheric eddy length scale may cause a poleward shift of the midlatitude jet streams is addressed. An increase in the length scale of the eddy reduces its zonal phase speed and so causes eddies to dissipate farther from the jet core. If the eddy dissipation region on the poleward flank of the jet overlaps with the eddy source latitudes, shifting this dissipation to higher latitudes will alter which latitudes are a net source of baroclinic eddies, and hence the eddy-driven jet stream may shift poleward. This behavior does not affect the equatorward flank of the jet in the same way because the dissipation region on the equatorward flank is well separated from the source latitudes. An experiment with a barotropic model is presented in which an increase in the length scale of a midlatitude perturbation results in a poleward shift in the acceleration of the zonal flow. Initial investigations indicate that this behavior is also important in both observational data and the output of comprehensive general circulation models (GCMs). A simplified GCM is used to show that the latitude of the eddy-driven jet is well correlated with the eddy length scale. It is argued that the increase in the eddy length scale causes the poleward shift of the jet in these experiments, rather than vice versa.
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Dimdore-Miles, Oscar B., Paul I. Palmer, and Lori P. Bruhwiler. "Detecting changes in Arctic methane emissions: limitations of the inter-polar difference of atmospheric mole fractions." Atmospheric Chemistry and Physics 18, no. 24 (December 17, 2018): 17895–907. http://dx.doi.org/10.5194/acp-18-17895-2018.
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Abstract. We consider the utility of the annual inter-polar difference (IPD) as a metric for changes in Arctic emissions of methane (CH4). The IPD has been previously defined as the difference between weighted annual means of CH4 mole fraction data collected at stations from the two polar regions (defined as latitudes poleward of 53∘ N and 53∘ S, respectively). This subtraction approach (IPD) implicitly assumes that extra-polar CH4 emissions arrive within the same calendar year at both poles. We show using a continuous version of the IPD that the metric includes not only changes in Arctic emissions but also terms that represent atmospheric transport of air masses from lower latitudes to the polar regions. We show the importance of these atmospheric transport terms in understanding the IPD using idealized numerical experiments with the TM5 global 3-D atmospheric chemistry transport model that is run from 1980 to 2010. A northern mid-latitude pulse in January 1990, which increases prior emission distributions, arrives at the Arctic with a higher mole fraction and ≃12 months earlier than at the Antarctic. The perturbation at the poles subsequently decays with an e-folding lifetime of ≃4 years. A similarly timed pulse emitted from the tropics arrives with a higher value at the Antarctic ≃11 months earlier than at the Arctic. This perturbation decays with an e-folding lifetime of ≃7 years. These simulations demonstrate that the assumption of symmetric transport of extra-polar emissions to the poles is not realistic, resulting in considerable IPD variations due to variations in emissions and atmospheric transport. We assess how well the annual IPD can detect a constant annual growth rate of Arctic emissions for three scenarios, 0.5 %, 1 %, and 2 %, superimposed on signals from lower latitudes, including random noise. We find that it can take up to 16 years to detect the smallest prescribed trend in Arctic emissions at the 95 % confidence level. Scenarios with higher, but likely unrealistic, growth in Arctic emissions are detected in less than a decade. We argue that a more reliable measurement-driven approach would require data collected from all latitudes, emphasizing the importance of maintaining a global monitoring network to observe decadal changes in atmospheric greenhouse gases.
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Gizon, L. "Comments on the Influence of Solar Activity on P-Mode Oscillation Spectra." Symposium - International Astronomical Union 185 (1998): 173–74. http://dx.doi.org/10.1017/s0074180900238540.
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The systematic p-mode frequency changes which are observed through the solar cycle are believed to be associated with near-surface perturbations confined to the magnetically active latitudes. In this paper, we study the perturbation arising from the presence of a large “active region”, corresponding to a localized structural change in a thin region close to the photosphere. We shall ignore the difficult question of the magnitude of the effect, and simply consider some geometric and observational implications for low-degree modes.
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Surkov, V. V., O. A. Pokhotelov, M. Parrot, E. N. Fedorov, and M. Hayakawa. "Excitation of the ionospheric resonance cavity by neutral winds at middle latitudes." Annales Geophysicae 22, no. 8 (September 7, 2004): 2877–89. http://dx.doi.org/10.5194/angeo-22-2877-2004.
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Abstract. A new mechanism for the ionospheric Alfvén resonator (IAR) excitation at middle latitudes is considered. It is shown that the ionosphere wind system in this region is capable of sustaining the generation of geomagnetic perturbations that can be detected by ground magnetometers. The general IAR dispersion relation describing the linear coupling of the shear Alfvén and fast magnetosonic/compressional modes is obtained. The dependence of the IAR eigenfrequencies and damping rates on the perpendicular wave number and on the ground conductivity during the day- and nighttime conditions is analyzed both analytically and numerically. In order to demonstrate the IAR excitation by neutral winds the power spectra of the geomagnetic perturbation on the ground surface are calculated. Furthermore, it is found that Kolmogorov spectra of the ionospheric turbulent neutral winds and the IAR eigenfrequencies lie in the same frequency range that make it possible to enhance the IAR excitation. The relevance of the developed theoretical model to the ground-based observations is stressed.
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Liu, Chun, Yuefeng Li, and Wei Song. "Variation in Dipole Blocking Associated with Arctic Warming in Winter: Potential Contributions to Cold and Extremely Cold Events over Eurasia." Atmosphere 10, no. 5 (May 6, 2019): 249. http://dx.doi.org/10.3390/atmos10050249.
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In this study, the barotropic mode of thermal forcing responsible for the difference in temperature between the Arctic and midlatitude regions was simplified by the nonlinear Schrӧdinger equation with disturbance terms using multiscale perturbation methods. The impact of Arctic warming on dipole blocking, which results in temperature anomalies over the midlatitudes of Eurasia, was studied using the direct perturbation theory for solitons. The results showed: (1) if only nonlinear effects exist between waves and zonal flows, a dipole blocking structure can present in the westerly air flows; (2) the temperature gradient between midlatitude warming and Arctic cooling inhibits the development of dipole blocking structures; and (3) Arctic warming is theoretically more conducive to intensifying the strength of dipole blocking and meridional activities over Eurasia and is more likely to cause the southward invasion of cold air from the Arctic, thereby inducing regionally cold and even extremely cold events in the mid- and low latitudes of Eurasia, including eastern China.
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Jesch, David, Alexander S. Medvedev, Francesco Castellini, Erdal Yiğit, and Paul Hartogh. "Density Fluctuations in the Lower Thermosphere of Mars Retrieved From the ExoMars Trace Gas Orbiter (TGO) Aerobraking." Atmosphere 10, no. 10 (October 15, 2019): 620. http://dx.doi.org/10.3390/atmos10100620.
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The upper atmosphere of Mars is constantly perturbed by small-scale gravity waves propagating from below. As gravity waves strongly affect the large-scale dynamics and thermal state, constraining their statistical characteristics is of great importance for modeling the atmospheric circulation. We present a new data set of density perturbation amplitudes derived from accelerometer measurements during aerobraking of the European Space Agency’s Trace Gas Orbiter. The obtained data set presents features found by three previous orbiters: the lower thermosphere polar warming in the winter hemisphere, and the lack of links between gravity wave activity and topography. In addition, the orbits allowed for demonstrating a very weak diurnal variability in wave activity at high latitudes of the southern winter hemisphere for the first time. The estimated vertical damping rates of gravity waves agree well with theoretical predictions. No clear anticorrelation between perturbation amplitudes and the background temperature has been found. This indicates differences in dissipation mechanisms of gravity waves in the lower and upper thermosphere.
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Otsuka, Y., K. Suzuki, S. Nakagawa, M. Nishioka, K. Shiokawa, and T. Tsugawa. "GPS observations of medium-scale traveling ionospheric disturbances over Europe." Annales Geophysicae 31, no. 2 (February 5, 2013): 163–72. http://dx.doi.org/10.5194/angeo-31-163-2013.
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Abstract. Two-dimensional structures of medium-scale traveling ionospheric disturbances (MSTIDs) over Europe have been revealed, for the first time, by using maps of the total electron content (TEC) obtained from more than 800 GPS receivers of the European GPS receiver networks. From statistical analysis of the TEC maps obtained 2008, we have found that the observed MSTIDs can be categorized into two groups: daytime MSTID and nighttime MSTID. The daytime MSTID frequently occurs in winter. Its maximum occurrence rate in monthly and hourly bin exceeds 70% at lower latitudes over Europe, whereas it is approximately 45% at higher latitudes. Since most of the daytime MSTIDs propagate southward, we speculate that they could be caused by atmospheric gravity waves in the thermosphere. The nighttime MSTIDs also frequently occur in winter but most of them propagate southwestward, in a direction consistent with the theory that polarization electric fields play an important role in generating the nighttime MSTIDs. The nighttime MSTID occurrence rate shows distinct latitudinal difference: The maximum of the occurrence rate in monthly and hourly bin is approximately 50% at lower latitudes in Europe, whereas the nighttime MSTID was rarely observed at higher latitudes. We have performed model calculations of the plasma density perturbations caused by a gravity wave and an oscillating electric field to reproduce the daytime and nighttime MSTIDs, respectively. We find that TEC perturbations caused by gravity waves do not show dip angle dependencies, while those caused by the oscillating electric field have a larger amplitude at lower latitudes. These dip angle dependencies of the TEC perturbation amplitude could contribute to the latitudinal variation of the MSTID occurrence rate. Comparing with previous studies, we discuss the longitudinal difference of the nighttime MSTID occurrence rate, along with the E- and F-region coupling processes. The seasonal variation, of the nighttime MSTID occurrence rate in Europe, is not consistent with the theory that the longitudinal and seasonal variations of the nighttime MSTID occurrence could be attributed to those of the Es layer occurrence.
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Pinedo, Jose Luis, Fernando Mireles-Garcia, Carlos Rios, Victor Manuel Garcia-Saldivar, J. Ignacio Davila-Rangel, and Jose Roberto Espinosa. "Assessment of the Latitudinal Behavior of Total Column Ozone at Nine Discrete 1º-Wide Latitude Bands, from TOMS and OMI Data." Open Atmospheric Science Journal 7, no. 1 (November 1, 2013): 92–109. http://dx.doi.org/10.2174/1874282301307010092.
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Total Ozone Mapping Spectrometer (TOMS) and Ozone Monitoring Instrument OMI Version 8 data, from November 1978 to February 2013, have been used to retrieve the shape and amplitude of the daily mean of the total column ozone (TCO) and their associated dispersion over eleven selected 1°-wide latitude bands. Their inter-annual variation at 44.5° S, 23.5° S, 23.5° N, 44.5° N and 59.5° N shows a quasi-regular periodic behavior. However, Polar Regions exhibit abrupt changes, whereas at the Equator a complex perturbation of periodicity is highlighted, which could be associated to the effect of the quasi-biennial oscillation (QBO). The discrete 1°-wide latitude bands show a stabilization of TCO levels from the late nineties, but they do not display a generalized recovery. Indeed, at the Equator, between 1997 and 2013, a 1.4% per decade decrease in the total column ozone is exhibited, which may be significant given that during the 1987-1994 period the decrease was only of 0.5%. Additionally, the discrete bands reveal the appearance of a perturbation of the inter-annual ozone variations at 59.5° S, in contrast to regular behavior in the Northern Hemisphere and at other latitudes. The perturbation apparently begins in the 1980-1984 time series and is clear and systematic after 1998.
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Jakowski, N., A. Jungstand, K. Schlegel, H. Kohl, and K. Rinnert. "The ionospheric response to perturbation electric fields during the onset phase of geomagnetic storms." Canadian Journal of Physics 70, no. 7 (July 1, 1992): 575–81. http://dx.doi.org/10.1139/p92-093.
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The generation and propagation of ionospheric storms are studied by analyzing EISCAT radar, and vertical-sounding and total-electron-content data obtained under different geophysical conditions. Both, case studies as well as the average storm pattern of percentage deviations of different ionospheric parameters from their corresponding reference values such as total electron content, F2-layer critical frequency foF2, F2-layer height hmF2, and slab thickness τ indicate the action of a perturbation electric field during the first few hours during the onset phase of geomagnetic storms. Considering the onset phase of the storm on July 28–29, 1987 evidence has been found that high-latitude electric fields may penetrate to lower latitudes before the ring current has developed. In most cases this process is accompanied by a positive phase in the upper ionosphere and F2-layer ionization. Different mechanisms are assumed to be responsible for the daytime and nighttime behaviour, respectively. The negative phase propagates equatorward with velocities in the order of 70–350 m s−1 following a strong heating of the thermosphere and ionosphere due to the auroral electrojet.
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Wunsch, Scott. "Harmonic generation by nonlinear self-interaction of a single internal wave mode." Journal of Fluid Mechanics 828 (September 5, 2017): 630–47. http://dx.doi.org/10.1017/jfm.2017.532.
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Weakly nonlinear theory is used to explore the dynamics of a single-mode internal tide in variable stratification with rotation. Nonlinear self-interaction in variable stratification generates a perturbation which is forced with double the original frequency and wavenumber. The dynamics of the perturbation is analogous to a forced harmonic oscillator, with the steady-state solution corresponding to a bound harmonic matching the forcing frequency and wavenumber. When the forcing frequency is near a natural frequency of the system, even a small-amplitude (nearly linear) internal tide may induce a significant harmonic response. Idealized stratification profiles are utilized to explore the relevance of this effect for oceanic $M_{2}$ baroclinic internal tides, and the results indicate that a rapidly growing harmonic may occur in some environments near the Equator, but is unlikely at higher latitudes. The results are relevant to recent observations of $M_{4}$ (harmonic) internal tides in the South China Sea and elsewhere. More generally, nonlinear self-interaction may contribute to the transfer of energy to smaller scales and the dissipation of baroclinic internal tides, especially in equatorial waters.
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Bozbiyik, A., M. Steinacher, F. Joos, T. F. Stocker, and L. Menviel. "Fingerprints of changes in the terrestrial carbon cycle in response to large reorganizations in ocean circulation." Climate of the Past 7, no. 1 (March 28, 2011): 319–38. http://dx.doi.org/10.5194/cp-7-319-2011.
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Abstract. CO2 and carbon cycle changes in the land, ocean and atmosphere are investigated using the comprehensive carbon cycle-climate model NCAR CSM1.4-carbon. Ensemble simulations are forced with freshwater perturbations applied at the North Atlantic and Southern Ocean deep water formation sites under pre-industrial climate conditions. As a result, the Atlantic Meridional Overturning Circulation reduces in each experiment to varying degrees. The physical climate fields show changes qualitatively in agreement with results documented in the literature, but there is a clear distinction between northern and southern perturbations. Changes in the physical variables, in turn, affect the land and ocean biogeochemical cycles and cause a reduction, or an increase, in the atmospheric CO2 concentration by up to 20 ppmv, depending on the location of the perturbation. In the case of a North Atlantic perturbation, the land biosphere reacts with a strong reduction in carbon stocks in some tropical locations and in high northern latitudes. In contrast, land carbon stocks tend to increase in response to a southern perturbation. The ocean is generally a sink of carbon although large reorganizations occur throughout various basins. The response of the land biosphere is strongest in the tropical regions due to a shift of the Intertropical Convergence Zone. The carbon fingerprints of this shift, either to the south or to the north depending on where the freshwater is applied, can be found most clearly in South America. For this reason, a compilation of various paleoclimate proxy records of Younger Dryas precipitation changes are compared with our model results. The proxy records, in general, show good agreement with the model's response to a North Atlantic freshwater perturbation.
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Cook, Joseph A., Kurt E. Galbreath, Kayce C. Bell, Mariel L. Campbell, Suzanne Carrière, Jocelyn P. Colella, Natalie G. Dawson, et al. "The Beringian Coevolution Project: holistic collections of mammals and associated parasites reveal novel perspectives on evolutionary and environmental change in the North." Arctic Science 3, no. 3 (September 1, 2017): 585–617. http://dx.doi.org/10.1139/as-2016-0042.
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The Beringian Coevolution Project (BCP), a field program underway in the high northern latitudes since 1999, has focused on building key scientific infrastructure for integrated specimen-based studies on mammals and their associated parasites. BCP has contributed new insights across temporal and spatial scales into how ancient climate and environmental change have shaped faunas, emphasizing processes of assembly, persistence, and diversification across the vast Beringian region. BCP collections also represent baseline records of biotic diversity from across the northern high latitudes at a time of accelerated environmental change. These specimens and associated data form an unmatched resource for identifying hidden diversity, interpreting past responses to climate oscillations, documenting contemporary conditions, and anticipating outcomes for complex biological systems in a regime of ecological perturbation. Because of its dual focus on hosts and parasites, the BCP record also provides a foundation for comparative analyses that can document the effects of dynamic change on the geographic distribution, transmission dynamics, and emergence of pathogens. By using specific examples from carnivores, eulipotyphlans, lagomorphs, rodents, ungulates, and their associated parasites, we demonstrate how broad, integrated field collections provide permanent infrastructure that informs policy decisions regarding human impact and the effect of climate change on natural populations.
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Bernardello, Raffaele, Irina Marinov, Jaime B. Palter, Jorge L. Sarmiento, Eric D. Galbraith, and Richard D. Slater. "Response of the Ocean Natural Carbon Storage to Projected Twenty-First-Century Climate Change." Journal of Climate 27, no. 5 (February 24, 2014): 2033–53. http://dx.doi.org/10.1175/jcli-d-13-00343.1.
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Abstract The separate impacts of wind stress, buoyancy fluxes, and CO2 solubility on the oceanic storage of natural carbon are assessed in an ensemble of twentieth- to twenty-first-century simulations, using a coupled atmosphere–ocean–carbon cycle model. Time-varying perturbations for surface wind stress, temperature, and salinity are calculated from the difference between climate change and preindustrial control simulations, and are imposed on the ocean in separate simulations. The response of the natural carbon storage to each perturbation is assessed with novel prognostic biogeochemical tracers, which can explicitly decompose dissolved inorganic carbon into biological, preformed, equilibrium, and disequilibrium components. Strong responses of these components to changes in buoyancy and winds are seen at high latitudes, reflecting the critical role of intermediate and deep waters. Overall, circulation-driven changes in carbon storage are mainly due to changes in buoyancy fluxes, with wind-driven changes playing an opposite but smaller role. Results suggest that climate-driven perturbations to the ocean natural carbon cycle will contribute 20 Pg C to the reduction of the ocean accumulated total carbon uptake over the period 1860–2100. This reflects a strong compensation between a buildup of remineralized organic matter associated with reduced deep-water formation (+96 Pg C) and a decrease of preformed carbon (−116 Pg C). The latter is due to a warming-induced decrease in CO2 solubility (−52 Pg C) and a circulation-induced decrease in disequilibrium carbon storage (−64 Pg C). Climate change gives rise to a large spatial redistribution of ocean carbon, with increasing concentrations at high latitudes and stronger vertical gradients at low latitudes.
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Dummann, W., C. Schröder-Adams, P. Hofmann, J. Rethemeyer, and J. O. Herrle. "Carbon isotope and sequence stratigraphy of the upper Isachsen Formation on Axel Heiberg Island (Nunavut, Canada): High Arctic expression of oceanic anoxic event 1a in a deltaic environment." Geosphere 17, no. 2 (February 11, 2021): 501–19. http://dx.doi.org/10.1130/ges02335.1.
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Abstract The Early Cretaceous oceanic anoxic event (OAE) 1a documents a major perturbation of the global carbon cycle with severe consequences for the ocean-climate-biosphere system. While numerous studies over the past decades have provided a relatively detailed picture of the environmental repercussions of OAE 1a at low and mid-latitudes, studies from high latitudes, in particular the High Arctic, are limited. In this study, we present a high-resolution carbon isotopic and sequence stratigraphic framework for the lower to lower upper Aptian interval of the Isachsen Formation of the High Arctic Sverdrup Basin (Canada). These data enable us to precisely locate the stratigraphic position of OAE 1a in a deltaic sedimentary environment. The carbon isotope record allows, for the first time, identification of the different carbon isotope segments (CISs) of OAE 1a in the Sverdrup Basin and thereby correlation of the High Arctic record with sections from lower latitudes. Based on this improved chemostratigraphy, we revise the age of upper Paterson Island, Rondon, and Walker Island Members, important regional lithostratigraphic marker units. Whole-rock geochemical data record two episodes of marine incursion into the Sverdrup Basin during OAE 1a (CISs Ap3 and Ap6), which are interpreted as regional maximum flooding surfaces. This information is used in conjunction with detailed sedimentological logs and geochemical grain-size proxies to refine the sequence stratigraphic framework for the upper Isachsen Formation. We propose that transgressive-regressive cycles in the Sverdrup Basin were controlled mainly by the combined effects of eustatic sea-level changes and regional tectonic uplift, potentially related to the emplacement of Alpha Ridge, which culminated at ca. 122 Ma during CIS Ap9.
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Wang, Yuwei, and Yi Huang. "Understanding the Atmospheric Temperature Adjustment to CO2 Perturbation at the Process Level." Journal of Climate 33, no. 3 (February 1, 2020): 787–803. http://dx.doi.org/10.1175/jcli-d-19-0032.1.
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AbstractClimate model comparisons show that there is considerable uncertainty in the atmospheric temperature response to CO2 perturbation. The uncertainty results from both the rapid adjustment that occurs before SST changes and the slow feedbacks that occur after SST changes. The analysis in this paper focuses on the rapid adjustment. We use a novel method to decompose the temperature change in AMIP-type climate simulation in order to understand the adjustment at the process level. We isolate the effects of different processes, including radiation, convection, and large-scale circulation in the temperature adjustment, through a set of numerical experiments using a hierarchy of climate models. We find that radiative adjustment triggers and largely controls the zonal mean atmospheric temperature response pattern. This pattern is characterized by stratospheric cooling, lower-tropospheric warming, and a warming center near the tropical tropopause. In contrast to conventional views, the warming center near the tropopause is found to be critically dependent on the shortwave absorption of CO2. The dynamical processes largely counteract the effect of the radiative process that increases the vertical temperature gradient in the free troposphere. The effect of local convection is to move atmospheric energy vertically, which cools the lower troposphere and warms the upper troposphere. The adjustment due to large-scale circulation further redistributes energy along the isentropic surfaces across the latitudes, which cools the low-latitude lower troposphere and warms the midlatitude upper troposphere and stratosphere. Our results highlight the importance of the radiative adjustment in the overall adjustment and provide a potential method to understand the spread in the models.
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Bozbiyik, A., M. Steinacher, F. Joos, and T. F. Stocker. "Fingerprints of changes in the terrestrial carbon cycle in response to large reorganizations in ocean circulation." Climate of the Past Discussions 6, no. 5 (September 23, 2010): 1811–52. http://dx.doi.org/10.5194/cpd-6-1811-2010.
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Abstract. CO2 and carbon cycle changes in the land, ocean and atmosphere are investigated using the comprehensive carbon cycle-climate model NCAR CSM1.4-carbon. Ensemble simulations are forced with freshwater perturbations applied at the North Atlantic and Southern Ocean deep water formation sites under pre-industrial climate conditions. As a result, the Atlantic Meridional Overturning Circulation reduces in each experiment to varying degrees. The physical climate fields show changes that are well documented in the literature but there is a clear distinction between northern and southern perturbations. Changes in the physical variables affect, in return, the land and ocean biogeochemical cycles and cause a reduction, or an increase, in the atmospheric CO2 by up to 20 ppmv, depending on the location of the perturbation. In the case of a North Atlantic perturbation, the land biosphere reacts with a strong reduction in carbon stocks in some tropical locations and in high northern latitudes. In contrast, land carbon stocks tend to increase in response to a southern perturbation. The ocean is generally a sink of carbon although large re-organizations occur throughout various basins. The response of the land biosphere is strongest in the tropical regions due to a shift of the Intertropical Convergence Zone. The carbon fingerprints of this shift, either to the south or to the north depending on where the freshwater is applied, can be found most clearly in South America. For this reason, a compilation of various paleoclimate proxy records of Younger Dryas precipitation changes are compared with our model results.
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Yeager, Stephen, and Gokhan Danabasoglu. "The Origins of Late-Twentieth-Century Variations in the Large-Scale North Atlantic Circulation." Journal of Climate 27, no. 9 (April 23, 2014): 3222–47. http://dx.doi.org/10.1175/jcli-d-13-00125.1.
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Abstract Surface forcing perturbation experiments are examined to identify the key forcing elements associated with late-twentieth-century interannual-to-decadal Atlantic circulation variability as simulated in an ocean–sea ice hindcast configuration of the Community Earth System Model, version 1 (CESM1). Buoyancy forcing accounts for most of the decadal variability in both the Atlantic meridional overturning circulation (AMOC) and the subpolar gyre circulation, and the key drivers of these basin-scale circulation changes are found to be the turbulent buoyancy fluxes: evaporation as well as the latent and sensible heat fluxes. These three fluxes account for almost all of the decadal AMOC variability in the North Atlantic, even when applied only over the Labrador Sea region. Year-to-year changes in surface momentum forcing explain most of the interannual AMOC variability at all latitudes as well as most of the decadal variability south of the equator. The observed strengthening of Southern Ocean westerly winds accounts for much of the simulated AMOC variability between 30°S and the equator but very little of the recent AMOC change in the North Atlantic. Ultimately, the strengthening of the North Atlantic overturning circulation between the 1970s and 1990s, which contributed to a pronounced SST increase at subpolar latitudes, is explained almost entirely by trends in the atmospheric surface state over the Labrador Sea.
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Rugenstein, Maria A. A., Michael Winton, Ronald J. Stouffer, Stephen M. Griffies, and Robert Hallberg. "Northern High-Latitude Heat Budget Decomposition and Transient Warming." Journal of Climate 26, no. 2 (January 15, 2013): 609–21. http://dx.doi.org/10.1175/jcli-d-11-00695.1.
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Abstract Climate models simulate a wide range of climate changes at high northern latitudes in response to increased CO2. They also have substantial disagreement on projected changes of the Atlantic meridional overturning circulation (AMOC). Here, two pairs of closely related climate models are used, with each containing members with large and small AMOC declines to explore the influence of AMOC decline on the high-latitude response to increased CO2. The models with larger AMOC decline have less high-latitude warming and sea ice decline than their small AMOC decline counterpart. By examining differences in the perturbation heat budget of the 40°–90°N region, it is shown that AMOC decline diminishes the warming by weakening poleward ocean heat transport and increasing the ocean heat uptake. The cooling impact of this AMOC-forced surface heat flux perturbation difference is enhanced by shortwave feedback and diminished by longwave feedback and atmospheric heat transport differences. The magnitude of the AMOC decline within model pairs is positively related to the magnitudes of control climate AMOC and Labrador and Nordic Seas convection. Because the 40°–90°N region accounts for up to 40% of the simulated global ocean heat uptake over 100 yr, the process described here influences the global heat uptake efficiency.
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Vukcevic, Miroslava, and Luka Č. Popović. "Nonlinear vortex solution for perturbations in the Earth's ionosphere." Nonlinear Processes in Geophysics 27, no. 2 (May 25, 2020): 295–306. http://dx.doi.org/10.5194/npg-27-295-2020.
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Abstract. There is much observational evidence of different fine structures in the ionosphere and magnetosphere of the Earth. Such structures are created and evolve as a perturbation of the ionosphere's parameters. Instead of dealing with a number of linear waves, we propose to investigate and follow up the perturbations in the ionosphere by dynamics of soliton structure. Apart from the fact that this is a more accurate solution, the advantage of soliton solution is its localization in space and time as a consequence of the balance between nonlinearity and dispersion. The existence of such a structure is driven by the properties of the medium. We derive the necessary condition for having a nonlinear soliton wave, taking the vortex shape as a description of the ionosphere parameter perturbation. We employ a magnetohydrodynamical description for the ionosphere in plane geometry, including rotational effects, magnetic field effects via ponderomotive force, and pressure and gravitational potential effects, treating the problem self-consistently and nonlinearly. In addition, we consider compressible perturbation. As a result, we have found that Coriolis force and magnetic force on the one hand and pressure and gravity on the other hand determine dispersive properties. Dispersion at higher latitudes is mainly driven by rotation, while near the Equator, within the E and F layers of the ionosphere, the magnetic field modifies the soliton solution. Also, a very general description of the ionosphere results in the conclusion that the unperturbed thickness of the ionosphere layer cannot be taken as an ad hoc assumption: it is rather a consequence of equilibrium property, which is shown in this calculation.
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Yang, Chengyun, Tao Li, Anne K. Smith, and Xiankang Dou. "The Response of the Southern Hemisphere Middle Atmosphere to the Madden–Julian Oscillation during Austral Winter Using the Specified-Dynamics Whole Atmosphere Community Climate Model." Journal of Climate 30, no. 20 (September 15, 2017): 8317–33. http://dx.doi.org/10.1175/jcli-d-17-0063.1.
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Abstract Using the specified-dynamics (SD) Whole Atmosphere Community Climate Model (SD-WACCM), the effects of the Madden–Julian oscillation (MJO) on the midwinter stratosphere and mesosphere in the Southern Hemisphere (SH) are investigated. The most significant responses of the SH polar cap temperature to the MJO are found about 30 days after MJO phase 1 (P1) and about 10 days after MJO phase 5 (P5) in both the ERA-Interim data and the SD-WACCM simulation. The 200- and 500-hPa geopotential height anomalies in the SH reveal that wave trains emanate from the Indian and Pacific Oceans when the MJO convection is enhanced in the eastern Indian Ocean and the western Pacific. As a result, the upward propagation and dissipation of planetary waves (PWs) in the middle and high latitudes of the SH stratosphere is significantly enhanced, the Brewer–Dobson (BD) circulation in the SH stratosphere strengthens, and temperatures in the SH polar stratosphere increase. Wavenumber 1 in the stratosphere is the dominant component of the PW perturbation induced by the MJO convection. In the SH mesosphere, the MJO leads to enhancement of the dissipation and breaking of gravity waves (GWs) propagating as a result of wind-filtering change in the SH extratropics and causes anomalous downwelling in the middle and high latitudes of the mesosphere. The circulation thus changes significantly, resulting in anomalous cooling in the mesosphere in response to MJO P1 and P5 at lags of 10 and 30 days, respectively.
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Li, Xianghui, Jingyu Wang, Troy Rasbury, Min Zhou, Zhen Wei, and Chaokai Zhang. "Early Jurassic climate and atmospheric CO<sub>2</sub> concentration in the Sichuan paleobasin, southwestern China." Climate of the Past 16, no. 6 (November 4, 2020): 2055–74. http://dx.doi.org/10.5194/cp-16-2055-2020.
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Abstract. Climatic oscillations have been developed through the (Early) Jurassic from marine sedimentary archives but remain unclear from terrestrial records. This work presents investigation of climate-sensitive sediments and carbon and oxygen isotope analyses of lacustrine and pedogenic carbonates for the Early Jurassic Ziliujing Formation taken from the Basin in southwestern China. Sedimentary and stable isotope proxies manifest that an overall secular (semi)arid climate dominated the Sichuan Basin during the Early Jurassic, except for the Hettangian. This climate pattern is similar to the arid climate in the Colorado Plateau region in western North America but is distinct from the relatively warm and humid climate in northern China and at high latitudes in the Southern Hemisphere. The estimated atmospheric CO2 concentration (pCO2) from carbon isotopes of pedogenic carbonates shows a range of 980–2610 ppmv (∼3.5–10 times the pre-industrial value) with a mean of 1660 ppmv. Three phases of pCO2 (the Sinemurian 1500–2000 ppmv, the Pliensbachian 1000–1500 ppmv, and the early Toarcian 1094–2610 ppmv) and two events of pCO2 rapidly falling by ∼1000–1300 ppmv are observed, illustrating the pCO2 perturbation in the Early Jurassic. The perturbation of pCO2 is compatible with seawater temperature and carbon cycle from the coeval marine sediments, suggesting a positive feedback of climate to pCO2 through the Early Jurassic.
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Msadek, Rym, Gilles Garric, Sara Fleury, Florent Garnier, Lauriane Batté, and Mitchell Bushuk. "Prévoir les variations saisonnières de la glace de mer arctique et leurs impacts sur le climat." La Météorologie, no. 111 (2020): 024. http://dx.doi.org/10.37053/lameteorologie-2020-0089.
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L'Arctique est la région du globe qui s'est réchauffée le plus vite au cours des trente dernières années, avec une augmentation de la température de surface environ deux fois plus rapide que pour la moyenne globale. Le déclin de la banquise arctique observé depuis le début de l'ère satellitaire et attribué principalement à l'augmentation de la concentration des gaz à effet de serre aurait joué un rôle important dans cette amplification des températures au pôle. Cette fonte importante des glaces arctiques, qui devrait s'accélérer dans les décennies à venir, pourrait modifier les vents en haute altitude et potentiellement avoir un impact sur le climat des moyennes latitudes. L'étendue de la banquise arctique varie considérablement d'une saison à l'autre, d'une année à l'autre, d'une décennie à l'autre. Améliorer notre capacité à prévoir ces variations nécessite de comprendre, observer et modéliser les interactions entre la banquise et les autres composantes du système Terre, telles que l'océan, l'atmosphère ou la biosphère, à différentes échelles de temps. La réalisation de prévisions saisonnières de la banquise arctique est très récente comparée aux prévisions du temps ou aux prévisions saisonnières de paramètres météorologiques (température, précipitation). Les résultats ayant émergé au cours des dix dernières années mettent en évidence l'importance des observations de l'épaisseur de la glace de mer pour prévoir l'évolution de la banquise estivale plusieurs mois à l'avance. Surface temperatures over the Arctic region have been increasing twice as fast as global mean temperatures, a phenomenon known as arctic amplification. One main contributor to this polar warming is the large decline of Arctic sea ice observed since the beginning of satellite observations, which has been attributed to the increase of greenhouse gases. The acceleration of Arctic sea ice loss that is projected for the coming decades could modify the upper level atmospheric circulation yielding climate impacts up to the mid-latitudes. There is considerable variability in the spatial extent of ice cover on seasonal, interannual and decadal time scales. Better understanding, observing and modelling the interactions between sea ice and the other components of the climate system is key for improved predictions of Arctic sea ice in the future. Running operational-like seasonal predictions of Arctic sea ice is a quite recent effort compared to weather predictions or seasonal predictions of atmospheric fields like temperature or precipitation. Recent results stress the importance of sea ice thickness observations to improve seasonal predictions of Arctic sea ice conditions during summer.
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Kloss, Corinna, Gwenaël Berthet, Pasquale Sellitto, Felix Ploeger, Ghassan Taha, Mariam Tidiga, Maxim Eremenko, et al. "Stratospheric aerosol layer perturbation caused by the 2019 Raikoke and Ulawun eruptions and their radiative forcing." Atmospheric Chemistry and Physics 21, no. 1 (January 15, 2021): 535–60. http://dx.doi.org/10.5194/acp-21-535-2021.
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Abstract. In June 2019 a stratospheric eruption occurred at Raikoke (48∘ N, 153∘ E). Satellite observations show the injection of ash and SO2 into the lower stratosphere and an early entrainment of the plume into a cyclone. Following the Raikoke eruption, stratospheric aerosol optical depth (sAOD) values increased in the whole Northern Hemisphere and tropics and remained enhanced for more than 1 year, with peak values at 0.040 (short-wavelength, high northern latitudes) to 0.025 (short-wavelength, Northern Hemisphere average). Discrepancies between observations and global model simulations indicate that ash may have influenced the extent and evolution of the sAOD. Top of the atmosphere radiative forcings are estimated at values between −0.3 and -0.4Wm-2 (clear-sky) and of −0.1 to -0.2Wm-2 (all-sky), comparable to what was estimated for the Sarychev eruption in 2009. Almost simultaneously two significantly smaller stratospheric eruptions occurred at Ulawun (5∘ S, 151∘ E) in June and August. Aerosol enhancements from the Ulawun eruptions mainly had an impact on the tropics and Southern Hemisphere. The Ulawun plume circled the Earth within 1 month in the tropics. Peak shorter-wavelength sAOD values at 0.01 are found in the tropics following the Ulawun eruptions and a radiative forcing not exceeding −0.15 (clear-sky) and −0.05 (all-sky). Compared to the Canadian fires (2017), Ambae eruption (2018), Ulawun (2019) and the Australian fires (2019/2020), the highest sAOD and radiative forcing values are found for the Raikoke eruption.
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Moore, J. Keith, Keith Lindsay, Scott C. Doney, Matthew C. Long, and Kazuhiro Misumi. "Marine Ecosystem Dynamics and Biogeochemical Cycling in the Community Earth System Model [CESM1(BGC)]: Comparison of the 1990s with the 2090s under the RCP4.5 and RCP8.5 Scenarios." Journal of Climate 26, no. 23 (December 2013): 9291–312. http://dx.doi.org/10.1175/jcli-d-12-00566.1.
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The authors compare Community Earth System Model results to marine observations for the 1990s and examine climate change impacts on biogeochemistry at the end of the twenty-first century under two future scenarios (Representative Concentration Pathways RCP4.5 and RCP8.5). Late-twentieth-century seasonally varying mixed layer depths are generally within 10 m of observations, with a Southern Ocean shallow bias. Surface nutrient and chlorophyll concentrations exhibit positive biases at low latitudes and negative biases at high latitudes. The volume of the oxygen minimum zones is overestimated. The impacts of climate change on biogeochemistry have similar spatial patterns under RCP4.5 and RCP8.5, but perturbation magnitudes are larger under RCP8.5. Increasing stratification leads to weaker nutrient entrainment and decreased primary and export production (>30% over large areas). The global-scale decreases in primary and export production scale linearly with the increases in mean sea surface temperature. There are production increases in the high nitrate, low chlorophyll (HNLC) regions, driven by lateral iron inputs from adjacent areas. The increased HNLC export partially compensates for the reductions in non-HNLC waters (~25% offset). Stabilizing greenhouse gas emissions and climate by the end of this century (as in RCP4.5) will minimize the changes to nutrient cycling and primary production in the oceans. In contrast, continued increasing emission of CO2 (as in RCP8.5) will lead to reduced productivity and significant modifications to ocean circulation and biogeochemistry by the end of this century, with more drastic changes beyond the year 2100 as the climate continues to rapidly warm.
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Berger, A., M. F. Loutre, and J. L. Mélice. "Equatorial insolation: from precession harmonics to eccentricity frequencies." Climate of the Past Discussions 2, no. 4 (July 24, 2006): 519–33. http://dx.doi.org/10.5194/cpd-2-519-2006.
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Abstract. Since the paper by Hays et al. (1976), spectral analyses of climate proxy records provide substantial evidence that a fraction of the climatic variance is driven by insolation changes in the frequency ranges of obliquity and precession variations. However, it is the variance components centered near 100 kyr which dominate most Upper Pleistocene climatic records, although the amount of insolation perturbation at the eccentricity driven 100-kyr period is much too small to cause directly a climate change of ice-age amplitude. Many attempts to find an explanation to this 100-kyr cycle in climatic records have been made over the last decades. Here we show that the double maximum which characterizes the daily irradiation received in tropical latitudes over the course of the year is at the origin in equatorial insolation of not only a strong 100-kyr, but also of a 11-kyr and a 5.5-kyr periods related respectively to eccentricity and to precession.
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Chiodo, Gabriel, and Lorenzo M. Polvani. "The Response of the Ozone Layer to Quadrupled CO2 Concentrations: Implications for Climate." Journal of Climate 32, no. 22 (October 11, 2019): 7629–42. http://dx.doi.org/10.1175/jcli-d-19-0086.1.
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Abstract The quantification of the climate impacts exerted by stratospheric ozone changes in abrupt 4 × CO2 forcing experiments is an important step in assessing the role of the ozone layer in the climate system. Here, we build on our previous work on the change of the ozone layer under 4 × CO2 and examine the effects of ozone changes on the climate response to 4 × CO2, using the Whole Atmosphere Community Climate Model. We show that the global-mean radiative perturbation induced by the ozone changes under 4 × CO2 is small, due to nearly total cancellation between high and low latitudes, and between longwave and shortwave fluxes. Consistent with the small global-mean radiative perturbation, the effect of ozone changes on the global-mean surface temperature response to 4 × CO2 is negligible. However, changes in the ozone layer due to 4 × CO2 have a considerable impact on the tropospheric circulation. During boreal winter, we find significant ozone-induced tropospheric circulation responses in both hemispheres. In particular, ozone changes cause an equatorward shift of the North Atlantic jet, cooling over Eurasia, and drying over northern Europe. The ozone signals generally oppose the direct effects of increased CO2 levels and are robust across the range of ozone changes imposed in this study. Our results demonstrate that stratospheric ozone changes play a considerable role in shaping the atmospheric circulation response to CO2 forcing in both hemispheres and should be accounted for in climate sensitivity studies.
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Blackport, Russell, and Paul J. Kushner. "The Transient and Equilibrium Climate Response to Rapid Summertime Sea Ice Loss in CCSM4." Journal of Climate 29, no. 2 (January 7, 2016): 401–17. http://dx.doi.org/10.1175/jcli-d-15-0284.1.
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Abstract The impact that disappearing Arctic sea ice will have on the atmospheric circulation and weather variability remains uncertain. In this study, results are presented from a sea ice perturbation experiment using the coupled Community Climate System Model, version 4 (CCSM4). By decreasing the albedo of the sea ice, the impact of an ice-free summertime Arctic on the coupled ocean–atmosphere system is isolated in an idealized but energetically self-consistent way. The multicentury equilibrium response is examined, as well as the transient response in an initial condition ensemble. The perturbation drives pronounced year-round sea ice thinning, Arctic warming, Arctic amplification, and moderate global warming. Even in the almost complete absence of summertime sea ice, the atmospheric general circulation response is very weak and the transient response is small compared to the internal variability. Surface temperature variability is reduced on all time scales over most of the middle and high latitudes with a 50% reduction in the standard deviation of temperature over the Arctic Ocean. The reduction is attributed to decreased temperature gradients and increased maritime influence once the sea ice melts. This reduced variability extends weakly into the variability of the midlatitude and free tropospheric geopotential height (less than 10% reduction in the standard deviation). Consistently, eddy geopotential height variability is found to decrease while geopotential isopleth meandering, which reflects Arctic amplified warming, increases moderately. The sign of these changes is consistent with recent observations, but the size of these changes is relatively small.
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Yang, Yang, Hailong Wang, Steven J. Smith, Richard Easter, Po-Lun Ma, Yun Qian, Hongbin Yu, Can Li, and Philip J. Rasch. "Global source attribution of sulfate concentration and direct and indirect radiative forcing." Atmospheric Chemistry and Physics 17, no. 14 (July 25, 2017): 8903–22. http://dx.doi.org/10.5194/acp-17-8903-2017.
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Abstract. The global source–receptor relationships of sulfate concentrations, and direct and indirect radiative forcing (DRF and IRF) from 16 regions/sectors for years 2010–2014 are examined in this study through utilizing a sulfur source-tagging capability implemented in the Community Earth System Model (CESM) with winds nudged to reanalysis data. Sulfate concentrations are mostly contributed by local emissions in regions with high emissions, while over regions with relatively low SO2 emissions, the near-surface sulfate concentrations are primarily attributed to non-local sources from long-range transport. Regional source efficiencies of sulfate concentrations are higher over regions with dry atmospheric conditions and less export, suggesting that lifetime of aerosols, together with regional export, is important in determining regional air quality. The simulated global total sulfate DRF is −0.42 W m−2, with −0.31 W m−2 contributed by anthropogenic sulfate and −0.11 W m−2 contributed by natural sulfate, relative to a state with no sulfur emissions. In the Southern Hemisphere tropics, dimethyl sulfide (DMS) contributes 17–84 % to the total DRF. East Asia has the largest contribution of 20–30 % over the Northern Hemisphere mid- and high latitudes. A 20 % perturbation of sulfate and its precursor emissions gives a sulfate incremental IRF of −0.44 W m−2. DMS has the largest contribution, explaining −0.23 W m−2 of the global sulfate incremental IRF. Incremental IRF over regions in the Southern Hemisphere with low background aerosols is more sensitive to emission perturbation than that over the polluted Northern Hemisphere.
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Wolfe, Christopher L., and Paola Cessi. "Multiple Regimes and Low-Frequency Variability in the Quasi-Adiabatic Overturning Circulation." Journal of Physical Oceanography 45, no. 6 (June 2015): 1690–708. http://dx.doi.org/10.1175/jpo-d-14-0095.1.
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AbstractWhen interior mixing is weak, the ocean can support an interhemispheric overturning circulation on isopycnals that outcrop in both the Northern Hemisphere and a high-latitude southern circumpolar channel. This overturning cell participates in a salt–advection feedback that counteracts the precipitation-induced surface freshening of the northern high latitudes. The net result is an increase in the range of isopycnals shared between the two hemispheres, which strengthens the overturning circulation. However, if precipitation in the Northern Hemisphere sufficiently exceeds that in the Southern Hemisphere, the overturning cell collapses and is replaced by a cell circulating in the opposite direction, whose southern end point is equatorward of the channel. This reversed cell is shallower and weaker than its forward counterpart and is maintained diffusively. For a limited range of parameters, freshwater hysteresis occurs and multiple overturning regimes are found for the same forcing. These multiple regimes are, by definition, unstable with regard to finite-amplitude disturbances, since a sufficiently large perturbation can affect a transition from one regime to the other. Both overturning regimes show pronounced, nearly periodic thermohaline variability on multidecadal and multicentennial time scales. The multidecadal oscillation is expressed in the North Hemisphere gyre and driven by a surface thermohaline instability. The multicentennial oscillation has the character of an interhemispheric loop oscillation. These oscillations mediate transitions between overturning regimes by providing an internal source of finite-amplitude disturbances. As the diffusivity is reduced, the reverse cell becomes weaker and thus less stable to a given perturbation amplitude. This causes the width of the hysteresis to decrease with decreasing diffusivity.
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Gregory, Jonathan M., Nathaelle Bouttes, Stephen M. Griffies, Helmuth Haak, William J. Hurlin, Johann Jungclaus, Maxwell Kelley, et al. "The Flux-Anomaly-Forced Model Intercomparison Project (FAFMIP) contribution to CMIP6: investigation of sea-level and ocean climate change in response to CO<sub>2</sub> forcing." Geoscientific Model Development 9, no. 11 (November 9, 2016): 3993–4017. http://dx.doi.org/10.5194/gmd-9-3993-2016.
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Abstract. The Flux-Anomaly-Forced Model Intercomparison Project (FAFMIP) aims to investigate the spread in simulations of sea-level and ocean climate change in response to CO2 forcing by atmosphere–ocean general circulation models (AOGCMs). It is particularly motivated by the uncertainties in projections of ocean heat uptake, global-mean sea-level rise due to thermal expansion and the geographical patterns of sea-level change due to ocean density and circulation change. FAFMIP has three tier-1 experiments, in which prescribed surface flux perturbations of momentum, heat and freshwater respectively are applied to the ocean in separate AOGCM simulations. All other conditions are as in the pre-industrial control. The prescribed fields are typical of pattern and magnitude of changes in these fluxes projected by AOGCMs for doubled CO2 concentration. Five groups have tested the experimental design with existing AOGCMs. Their results show diversity in the pattern and magnitude of changes, with some common qualitative features. Heat and water flux perturbation cause the dipole in sea-level change in the North Atlantic, while momentum and heat flux perturbation cause the gradient across the Antarctic Circumpolar Current. The Atlantic meridional overturning circulation (AMOC) declines in response to the heat flux perturbation, and there is a strong positive feedback on this effect due to the consequent cooling of sea-surface temperature in the North Atlantic, which enhances the local heat input to the ocean. The momentum and water flux perturbations do not substantially affect the AMOC. Heat is taken up largely as a passive tracer in the Southern Ocean, which is the region of greatest heat input, while the weakening of the AMOC causes redistribution of heat towards lower latitudes. Future analysis of these and other phenomena with the wider range of CMIP6 FAFMIP AOGCMs will benefit from new diagnostics of temperature and salinity tendencies, which will enable investigation of the model spread in behaviour in terms of physical processes as formulated in the models.
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Liu, Jing, Dong-He Zhang, Anthea J. Coster, Shun-Rong Zhang, Guan-Yi Ma, Yong-Qiang Hao, and Zuo Xiao. "A case study of the large-scale traveling ionospheric disturbances in the eastern Asian sector during the 2015 St. Patrick's Day geomagnetic storm." Annales Geophysicae 37, no. 4 (August 5, 2019): 673–87. http://dx.doi.org/10.5194/angeo-37-673-2019.
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Abstract. This study presents a comprehensive observation of the large-scale traveling ionospheric disturbances (LSTIDs) in the eastern Asian sector during the 2015 St. Patrick's Day (17 March 2015) geomagnetic storm. For the first time, three dense networks of GPS receivers in China and Japan are combined together to obtain the two-dimensional (2-D) vertical total electron content (VTEC) perturbation maps in a wider longitudinal range than previous studies in this region. Results show that an LSTID spanning at least 60∘ in longitude (80–140∘ E) occurs as a result of possible atmospheric gravity waves (AGWs) propagating from high to lower latitudes at around 09:40–11:40 UT (universal time), and the crest of this LSTID shows a tendency of dissipation starting from the eastern side. The manifestation of the 2-D VTEC perturbation maps is in good agreement with the recordings from two high-frequency Doppler sounders and the iso-frequency lines from eight ionosondes. Then, the propagation parameters of the LSTIDs are estimated by applying least-square fitting methods to the distinct structures in the 2-D VTEC perturbation plots. In general, the propagation parameters are observably longitudinally dependent. For example, the propagation direction is almost due southward between 105 and 115∘ E, while it is slightly southwest and southeast in the western and eastern sides of this region. This feature is probably related to the regional geomagnetic declination. The mean values of the period, trough velocity (Vt), crest velocity (Vc), and wavelength of the LSTIDs in the studied longitudinal bands are 74.8±1.4 min, 578±16 m s−1, 617±23 m s−1, and 2691±80 km, respectively. Finally, using the VTEC map data from the Madrigal database of the MIT Haystack Observatory, the characteristics of the ionospheric disturbances over the European sector (30–70∘ N, 10–20∘ E) are also studied. The results are very different from those in the eastern Asian sector in parameters like the occurrence time, oscillation period, and propagation velocities.
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Berger, A., M. F. Loutre, and J. L. Mélice. "Equatorial insolation: from precession harmonics to eccentricity frequencies." Climate of the Past 2, no. 2 (October 12, 2006): 131–36. http://dx.doi.org/10.5194/cp-2-131-2006.
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Abstract. Since the paper by Hays et al. (1976), spectral analyses of climate proxy records provide substantial evidence that a fraction of the climatic variance is driven by insolation changes in the frequency ranges of obliquity and precession variations. However, it is the variance components centered near 100 kyr which dominate most Upper Pleistocene climatic records, although the amount of insolation perturbation at the eccentricity driven periods close to 100-kyr (mainly the 95 kyr- and 123 kyr-periods) is much too small to cause directly a climate change of ice-age amplitude. Many attempts to find an explanation to this 100-kyr cycle in climatic records have been made over the last decades. Here we show that the double maximum which characterizes the daily irradiation received in tropical latitudes over the course of the year is at the origin in equatorial insolation of not only strong 95 kyr and 123 kyr periods related to eccentricity, but also of a 11-kyr and a 5.5-kyr periods related to precession.
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Sridharan, S., and S. Sathishkumar. "Seasonal and interannual variations of gravity wave activity in the low-latitude mesosphere and lower thermosphere over Tirunelveli (8.7° N, 77.8° E)." Annales Geophysicae 26, no. 11 (October 21, 2008): 3215–23. http://dx.doi.org/10.5194/angeo-26-3215-2008.
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Abstract. The Mesosphere and Lower Thermosphere (MLT) winds acquired by medium frequency (MF) radar at Tirunelveli (8.7° N, 77.8° E) for the years 1993–2007 are used to study seasonal and interannual variabilities of gravity wave (GW) variances in the altitude region 84–94 km. The GW variances in zonal and meridional winds show semiannual oscillation with maximum variance during March–April and August–September and minimum during June–July and November–December months. The wind variances, in general, are observed to be enhanced during and after the year 1998 and they undergo large interannual variability, in particular, during spring equinox months. An enhancement of GW variances is observed during spring equinox months of the years 2000, 2004 and 2006. These larger GW enhancements, most of the times, coincide with eastward phase of zonally averaged stratospheric QBO at 30 hPa over equator and sudden stratospheric warming occurred at high latitudes. From the zonal and meridional variances, the perturbation ellipses are calculated and they show that the predominant direction of propagation of gravity waves is in SE-NW plane.
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Valks, P. J. M., and G. J. M. Velders. "The present-day and future impact of NO<sub>x</sub> emissions from subsonic aircraft on the atmosphere in relation to the impact of NO<sub>x</sub> surface sources." Annales Geophysicae 17, no. 8 (August 31, 1999): 1064–79. http://dx.doi.org/10.1007/s00585-999-1064-7.
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Abstract. The effect of present-day and future NOx emissions from aircraft on the NOx and ozone concentrations in the atmosphere and the corresponding radiative forcing were studied using a three-dimensional chemistry transport model (CTM) and a radiative model. The effects of the aircraft emissions were compared with the effects of the three most important anthropogenic NOx surface sources: road traffic, electricity generation and industrial combustion. From the model results, NOx emissions from aircraft are seen to cause an increase in the NOx and ozone concentrations in the upper troposphere and lower stratosphere, and a positive radiative forcing. For the reference year 1990, the aircraft emissions result in an increase in the NOx concentration at 250 hPa of about 20 ppt in January and 50 ppt in July over the eastern USA, the North Atlantic Flight Corridor and Western Europe, corresponding to a relative increase of about 50%. The maximum increase in the ozone concentrations due to the aircraft emissions is about 3-4 ppb in July over the northern mid-latitudes, corresponding to a relative increase of about 3-4%. The aircraft-induced ozone changes cause a global average radiative forcing of 0.025 W/m2 in July. According to the ANCAT projection for the year 2015, the aircraft NOx emissions in that year will be 90% higher than in the year 1990. As a consequence of this, the calculated NOx perturbation by aircraft emissions increases by about 90% between 1990 and 2015, and the ozone perturbation by about 50-70%. The global average radiative forcing due to the aircraft-induced ozone changes increases by about 50% between 1990 and 2015. In the year 2015, the effects of the aircraft emissions on the ozone burden and radiative forcing are clearly larger than the individual effects of the NOx surface sources. Taking chemical conversion in the aircraft plume into account in the CTM explicitly, by means of modified aircraft NOx emissions, a significant reduction of the aircraft-induced NOx and ozone perturbations is realised. The NOx perturbation decreases by about 40% and the ozone perturbation by about 30% in July over Western Europe, the eastern USA and the North Atlantic Flight Corridor.Keywords. Atmospheric composition and structure (troposphere · composition and chemistry) · Meteorology and atmospheric dynamics (radiative processes)
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Foster, J. C., J. M. Holt, and L. J. Lanzerotti. "Mid-latitude ionospheric perturbation associated with the Spacelab-2 plasma depletion experiment at Millstone Hill." Annales Geophysicae 18, no. 1 (January 31, 2000): 111–19. http://dx.doi.org/10.1007/s00585-000-0111-1.
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Abstract. Elevation scans across geomagnetic mid latitudes by the incoherent scatter radar at Millstone Hill captured the ionospheric response to the firing of the Space Shuttle Challenger OMS thrusters near the peak of the F layer on July 30, 1985. Details of the excitation of airglow and the formation of an ionospheric hole during this event have been reported in an earlier paper by Mendillo et al.. The depletion (factor ~2) near the 320 km Shuttle orbital altitude persisted for ~35 min and then recovered to near normal levels, while at 265 km the density was reduced by a factor of ~6; this significant reduction in the bottomside F-region density persisted for more than 3 hours. Total electron content in the vicinity of the hole was reduced by more than a factor of 2, and an oscillation of the F-region densities with 40-min period ensued and persisted for several hours. Plasma vertical Doppler velocity varied quasi-periodically with a ~80-min period, while magnetic field variations observed on the field line through the Shuttle-burn position exhibited a similar ~80-min periodicity. An interval of magnetic field variations at hydromagnetic frequencies (~95 s period) accompanied the ionospheric perturbations on this field line. Radar observations revealed a downward phase progression of the 40-min period density enhancements of -1.12° km-1, corresponding to a 320-km vertical wavelength. An auroral-latitude geomagnetic disturbance began near the time of the Spacelab-2 experiment and was associated with the imposition of a strong southward IMF Bz across the magnetosphere. This created an additional complication in the interpretation of the active ionospheric experiment. It cannot be determined uniquely whether the ionospheric oscillations, which followed the Spacelab-2 experiment, were related to the active experiment or were the result of a propagating ionospheric disturbance (TID) launched by the enhanced auroral activity. The most reasonable conclusion is that the ionospheric oscillations were a result of the coincident geomagnetic disturbance. The pronounced depletion of the bottomside ionosphere, however, accentuated the oscillatory behavior during the interval following the Shuttle OMS burn..Key words. Ionosphere (active experiments; ionospheric disturbances) · Magnetospheric physics (storms and substorms)
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Přech, L., Z. Nĕmeček, J. Šafránková, and A. Omar. "Actively produced high-energy electron bursts within the magnetosphere: the APEX project." Annales Geophysicae 20, no. 10 (October 31, 2002): 1529–38. http://dx.doi.org/10.5194/angeo-20-1529-2002.
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Abstract. The APEX project (Active Plasma Experiment) has been launched into a polar orbit in December 1991 and consists of two satellites (IK-25 and MAGION-3), with a distance between them from 200 km to 10 000 km. The mission used intensive electron beam emission, complemented by a low-energy Xenon plasma generator during the electron beam injection, for the study of dynamic processes in the magnetosphere and upper ionosphere. The paper deals with short, intensive bursts of field-aligned electrons observed during the APEX mission on board the MAGION-3 satellite. These events are located pre-dominantly at the middle geomagnetic latitudes in the day-side magnetosphere. The time-energy structure of these electron bursts is similar to the inverted-V one, but the pitch-angle width is less than 10°. Electrons with an energy up to 700 keV are often observed during the events. We analyze the observed events, discuss the possible mechanisms of the particle spreading, and the role of the main satellite’s activity as a possible source of these events.Key words. Ionosphere (particle acceleration; particle precipitation) – Space plasma physics (active perturbation experiments)
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Graham, Jennifer A., David P. Stevens, and Karen J. Heywood. "Nonlinear Climate Responses to Changes in Antarctic Intermediate Water." Journal of Climate 26, no. 22 (October 29, 2013): 9175–93. http://dx.doi.org/10.1175/jcli-d-12-00767.1.
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Abstract The global impact of changes in Antarctic Intermediate Water (AAIW) properties is demonstrated using idealized perturbation experiments in a coupled climate model. Properties of AAIW were altered between 10° and 20°S in the Atlantic, Pacific, and Indian Oceans separately. Potential temperature was changed by ±1°C, along with density-compensating changes in salinity. For each of the experiments, sea surface temperature responds to changes in AAIW when anomalies surface at higher latitudes (>30°). Anomalous sea-to-air heat fluxes leave density anomalies in the ocean, resulting in nonlinear responses to opposite-sign perturbations. In the Southern Ocean, these affect the meridional density gradient, leading to changes in Antarctic Circumpolar Current transport. The response to cooler, fresher AAIW is both greater in magnitude and significant over a larger area than that for warmer, saltier AAIW. The North Atlantic is particularly sensitive to cool, fresh perturbations, with density anomalies causing reductions in the meridional overturning circulation of up to 1 Sv (1 Sv ≡ 106 m3 s−1). Resultant changes in meridional ocean heat transport, along with surfacing anomalies, cause basinwide changes in the surface ocean and overlying atmosphere on multidecadal time scales.
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Korotova, G. I., D. G. Sibeck, and V. I. Petrov. "Interball-1 observations of flux transfer events." Annales Geophysicae 30, no. 10 (October 4, 2012): 1451–62. http://dx.doi.org/10.5194/angeo-30-1451-2012.
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Abstract. We present the results of a survey of 807 FTEs observed by Interball-1 on the mid- and high-latitude dayside and flank magnetopause. Dayside magnetosheath events show a strong tendency to occur for southward magnetosheath magnetic fields suggesting origin via component (or perhaps antiparallel) reconnection near the equatorial plane. Flank FTEs occur for both magnetosheath magnetic field orientations with only a slight preference for southward magnetosheath magnetic fields. These events are consistent with generation along an extended subsolar component reconnection line for all IMF orientations or a combination of reconnection along a subsolar component reconnection line for southward IMF and antiparallel reconnection at higher latitudes for northward IMF. The distribution of direct and reverse magnetosheath FTEs and the tilt angle of the reconnection line for dawnward and duskward IMF are in a good agreement with the theoretical predictions of the component merging model. The clear anticorrelation between the magnitude of the east/west (Bm) perturbation observed within magnetosphere FTEs versus Bm in the magnetosheath also demands an explanation of the FTEs in terms of reconnection along a tilted subsolar merging line, e.g. in terms of component merging.
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Shi, Xiaoxu, Gerrit Lohmann, Dmitry Sidorenko, and Hu Yang. "Early-Holocene simulations using different forcings and resolutions in AWI-ESM." Holocene 30, no. 7 (March 10, 2020): 996–1015. http://dx.doi.org/10.1177/0959683620908634.
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The earliest part of the Holocene, from 11.5k to 7k (k = 1000 years before present), is a critical transition period between the relatively cold last deglaciation and the warm middle Holocene. It is marked by more pronounced seasonality and reduced greenhouse gases (GHGs) than the present state, as well as by the presence of the Laurentide Ice Sheet (LIS) and glacial meltwater perturbation. This paper performs experiments under pre-industrial and different early-Holocene regimes with AWI-ESM (Alfred Wegener Institute–Earth System Model), a state-of-the-art climate model with unstructured mesh and varying resolutions, to examine the sensitivity of the simulated Atlantic meridional overturning circulation (AMOC) to early-Holocene insolation, GHGs, topography (including properties of the ice sheet), and glacial meltwater perturbation. In the experiments with early-Holocene Earth orbital parameters and GHGs applied, the AWI-ESM simulation shows a JJA (June–July–August) warming and DJF (December–January–February) cooling over the mid and high latitudes compared with pre-industrial conditions, with amplification over the continents. The presence of the LIS leads to an additional regional cooling over the North America. We also simulate the meltwater event around 8.2k. Big discrepancies are found in the oceanic responses to different locations and magnitudes of freshwater discharge. Our experiments, which compare the effects of freshwater release evenly across the Labrador Sea to a more precise injection along the western boundary of the North Atlantic (the coastal region of LIS), show significant differences in the ocean circulation response, as the former produces a major decline of the AMOC and the latter yields no obvious effect on the strength of the thermohaline circulation. Furthermore, proglacial drainage of Lakes Agassiz and Ojibway leads to a fast spin-down of the AMOC, followed, however, by a gradual recovery. Most hosing experiments lead to a warming over the Nordic Sea and Barents Sea of varying magnitudes, because of an enhanced inflow from lower latitudes and a northward displacement of the North Atlantic deep convection. These processes exist in both of our high- and low-resolution experiments, but with some local discrepancies such as (1) the hosing-induced subpolar warming is much less pronounced in the high-resolution simulations; (2) LIS coastal melting in the high-resolution model leads to a slight decrease in the AMOC; and (3) the convection formation site in the low- and high-resolution experiments differs, in the former mainly over northeastern North Atlantic Ocean, but in the latter over a very shallow subpolar region along the northern edge of the North Atlantic Ocean. In conclusion, we find that our simulations capture spatially heterogeneous responses of the early-Holocene climate.
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Douville, H. "Impact of Regional SST Anomalies on the Indian Monsoon Response to Global Warming in the CNRM Climate Model." Journal of Climate 19, no. 10 (May 15, 2006): 2008–24. http://dx.doi.org/10.1175/jcli3727.1.
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Abstract While transient climate change experiments with coupled atmosphere–ocean general circulation models undoubtedly represent the most comprehensive tool for studying the climate response to increasing concentrations of greenhouse gases (GHGs), less computationally expensive time-slice experiments with atmospheric GCMs are still useful to test the robustness of the projected climate change. In the present study, three sets of time-slice experiments with prescribed sea surface temperature (SST) are compared to a reference climate scenario obtained with the Centre National de Recherches Météorologiques Coupled Climate Model (CCM). The main objective is to assess the sensitivity of the monsoon response to the magnitude or pattern of SST anomalies in two regions where such anomalies are highly model dependent, namely, the circumpolar Southern Ocean and the tropical Pacific Ocean. On the one hand, it is shown that the regional climate anomalies predicted by the CCM can be reproduced at least qualitatively by a pair of time-slice experiments in which the present-day SST biases of the CCM are removed. On the other hand, the results indicate that the Indian monsoon response to increasing amounts of GHG is sensitive to regional uncertainties in the prescribed SST warming. Increasing the sea surface warming in the southern high latitudes to compensate for the weak sea ice feedback simulated by the CCM around the Antarctic has a significant influence on the regional climate change simulated over India, through a perturbation of the regional Hadley circulation. Prescribing zonal mean rather than El Niño–like SST anomalies in the tropical Pacific has an even stronger impact on the monsoon response, through a modification of the Walker circulation. These results suggest that both deficiencies in simulating present-day climate (even at high latitudes) and uncertainties in the SST patterns caused by enhanced GHG concentrations (especially in the tropical Pacific) are major obstacles for predicting climate change at the regional scale.