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1
GUO, Haiqiang. "A dataset of carbon dioxide flux from Chongming Dongtan Wetland of Shanghai during 2004–2010." China Scientific Data 9, no. 1 (March 31, 2024): 1–5. http://dx.doi.org/10.11922/11-6035.csd.2023.0043.zh.
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As one of the standard methods of micrometeorology, eddy covariance technology has become the primary tool for monitoring the exchange of carbon dioxide, water and heat flux between terrestrial ecosystems and the atmosphere. This dataset includes the flux data accumulated by the National Observations and Research Station for Wetland Ecosystems in the Yangtze Estuary, collected in Dongtan Wetland on Chongming Island, Shanghai from September 2004 to December 2010, with a time resolution of half hour, and the data items cover air temperature (T_air), relative humidity (RH), soil temperature (T_soil), photosynthetically active radiation (PAR), solar radiation (Solar), net radiation (Rn), rainfall (Precip), sensible heat flux (Hs), latent heat flux (LE) and net carbon dioxide exchange (NEECO2), etc. The ecosystem observed in this study is typical of subtropical coastal salt marshes, predominantly inhabited by such plants as Phragmites australis and Spartina alterniflora. The observation system setup, equipment maintenance, data processing and quality control follows FLUXNET recommended protocols, ensuring high data reliability. The dataset can provide solid data support for the carbon budget, blue carbon estimation and biological invasion impact assessment of China's coastal salt marshes.
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Diamond-Lowe, Hannah, João M. Mendonça, David Charbonneau, and Lars A. Buchhave. "Ground-based Optical Transmission Spectroscopy of the Nearby Terrestrial Exoplanet LTT 1445Ab." Astronomical Journal 165, no. 4 (March 21, 2023): 169. http://dx.doi.org/10.3847/1538-3881/acbf39.
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Abstract Nearby M-dwarf systems currently offer the most favorable opportunities for spectroscopic investigations of terrestrial exoplanet atmospheres. The LTT 1445 system is a hierarchical triple of M dwarfs with two known planets orbiting the primary star, LTT 1445A. We observe four transits of the terrestrial world LTT 1445Ab (R = 1.3 R ⊕, M = 2.9 M ⊕) at low resolution with Magellan II/LDSS3C. We use the combined flux of the LTT 1445BC pair as a comparison star, marking the first time that an M dwarf is used to remove telluric variability from time-series observations of another M dwarf. We find Hα in emission from both LTT 1445B and C, as well as a flare in one of the data sets from LTT 1445C. These contaminated data are removed from the analysis. We construct a broadband transit light curve of LTT 1445Ab from 620 to 1020 nm. Binned to 3 minute time bins, we achieve an rms of 49 ppm for the combined broadband light curve. We construct a transmission spectrum with 20 spectrophotometric bins each spanning 20 nm and compare it to models of clear, 1× solar composition atmospheres. We rule out this atmospheric case with a surface pressure of 10 bars to 3.2σ confidence, and with a surface pressure of 1 bar to 3.1σ confidence. Upcoming secondary eclipse observations of LTT 1445Ab with the James Webb Space Telescope will further probe the cases of a high-mean-molecular-weight atmosphere, a hazy or cloudy atmosphere, or no atmosphere at all on this terrestrial world.
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Poissant, L. "Les échanges surface-atmosphère du mercure gazeux dans l'écosystème lac Ontario/fleuve Saint-Laurent." Revue des sciences de l'eau 15 (April 12, 2005): 229–39. http://dx.doi.org/10.7202/705494ar.
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La volatilisation du mercure des surfaces vers l'atmosphère et les dépôts atmosphériques du mercure sont des phénomènes importants dans la dynamique globale du mercure. Les échanges surface-atmosphère du mercure gazeux dans l'écosystème lac Ontario/fleuve Saint-Laurent sont variables dans le temps et dans l'espace. Bien que le modèle de la double couche montre que la grande partie des écosystèmes aquatiques sont en sursaturation par rapport à la constante d'Henry, des observations in situ, à l'aide de techniques de chambre à flux, montrent que des dépôts gazeux sont également possibles. Les dépôts gazeux du mercure dans l'écosystème lac Ontario/fleuve Saint-Laurent oscillent entre 0 et 4,66 ng/m2/h alors que les valeurs de volatilisation varient entre 0 et 9,28 ng/m2/h. Globalement, la volatilisation médiane du mercure est de 0,77 ng/m2/h alors que le dépôt gazeux médian est d'environ un ordre de grandeur inférieur (0,075 ng/m2/h). En été, l'ensemble des dépôts atmosphériques du mercure semble être mis à contribution lors de la volatilisation du mercure au-dessus des sols. Il semble que la majeure partie de cette volatilisation serait en fait de la ré-émission du mercure vers l'atmosphère. En hiver, seule la portion gazeuse des dépôts de mercure semble être ré-émise vers l'atmosphère. Plusieurs observations dans un marécage fluvial du lac Saint-Pierre (baie Saint-François) montrent que les flux de volatilisation du mercure sont supérieurs en période sèche qu'en période inondée (0,83 vs. 0,52 ng/m2/h). Ainsi, en période d'inondation le mercure réactif disponible pour la volatilisation serait en compétition avec les mécanismes responsables pour la méthylation du mercure (bio-disponible) et/ou la formation du sulfure de mercure (inerte sous forme de cinabre). Cet article a pour objectifs de présenter et discuter les échanges surface-atmosphère du mercure gazeux dans l'écosystème lac Ontario/fleuve Saint-Laurent.
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Ercolano, Barbara, Christian Rab, Karan Molaverdikhani, Billy Edwards, Thomas Preibisch, Leonardo Testi, Inga Kamp, and Wing-Fai Thi. "Observations of PAHs in the atmospheres of discs and exoplanets." Monthly Notices of the Royal Astronomical Society 512, no. 1 (February 25, 2022): 430–38. http://dx.doi.org/10.1093/mnras/stac505.
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ABSTRACT Polycyclic aromatic hydrocarbons (PAHs) play a key role in the chemical and hydrodynamical evolution of the atmospheres of exoplanets and planet-forming discs. If they can survive the planet formation process, PAHs are likely to be involved in pre-biotic chemical reactions eventually leading to more complex molecules such as amino acids and nucleotides, which form the basis for life as we know it. However, the abundance and specific role of PAHs in these environments is largely unknown due to limitations in sensitivity and range of wavelength of current and previous space-borne facilities. Upcoming infrared space spectroscopy missions, such as Twinkle and Ariel, present a unique opportunity to detect PAHs in the atmospheres of exoplanets and planet-forming discs. In this work, we present synthetic observations based on conservative numerical modelling of typical planet-forming discs and a transiting hot Saturnian planet around solar-type star. Our models show that Twinkle and Ariel might both be able to detect the 3.3 $\mu$m PAH feature within reasonable observing time in discs and transiting planets, assuming that PAHs are present with an abundance of at least one-tenth of the interstellar medium value.
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Mikal-Evans, Thomas. "Detecting the proposed CH4–CO2 biosignature pair with the James Webb Space Telescope: TRAPPIST-1e and the effect of cloud/haze." Monthly Notices of the Royal Astronomical Society 510, no. 1 (November 24, 2021): 980–91. http://dx.doi.org/10.1093/mnras/stab3383.
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ABSTRACT It is widely anticipated that the James Webb Space Telescope (JWST) will be transformative for exoplanet studies. It has even been suggested that JWST could provide the first opportunity to search for biosignatures in an alien atmosphere using transmission spectroscopy. This claim is investigated, specifically for the proposed anoxic biosignature pair CH4–CO2. The most favourable known target is adopted (TRAPPIST-1e), with an assumed atmospheric composition similar to the Archean Earth. Compared to previous studies, a more systematic investigation of the effect that cloud/haze layers have on the detectability of CH4 and CO2 is performed. In addition to a clear atmosphere scenario, cloud/haze layers are considered at eight pressure levels between 600 and 1 mbar. These pressures cover a plausible range for H2O cloud and photochemical haze, based on observations of solar system atmospheres and physical models of tidally locked planets such as TRAPPIST-1e, although no assumptions regarding the cloud/haze-layer composition are made in this study. For the clear atmosphere and cloud/haze-layer pressures of 600–100 mbar, strong (5σ) detections of both CH4 and CO2 are found to be possible with approximately 5–10 co-added transits measured using the Near Infrared Spectrograph (NIRSpec) prism, assuming a dry stratosphere. However, approximately 30 co-added transits would be required to achieve the same result if a cloud/haze layer is present at 10 mbar. A cloud/haze layer at 1 mbar would prevent the detection of either molecule with the NIRSpec prism for observing programmes up to 50 transits (>200 h of JWST time), the maximum considered.
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Efimenko, V., and V. Krivodubskij. "Life and scientific way of Pavlo Rodionovych Romanchuk." Bulletin of Taras Shevchenko National University of Kyiv. Astronomy, no. 61 (2020): 28–33. http://dx.doi.org/10.17721/btsnua.2020.61.28-33.
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One hundred years have passed since the birth of P.R. Romanchuk – Hero of the Soviet Union, Candidate of Physical and Mathematical Sciences, Associate Professor, Director of the Astronomical Observatory (1972–1987). At his initiative, the observatory began to develop new scientific directions: theoretical research of magnetic fields and the beginning of experimental work after the purchase of a magnetograph, study of changes in the solar atmosphere associated with flare activity, solar-terrestrial connections and the impact of solar activity on weather phenomena, development of methods for predicting solar activity. An important result of his work was the strengthening of the observatory’s material base – purchase of a purchase of a magnetograph, modernization of a horizontal solar telescope, joint work with the National Academy of Sciences of Ukraine on the development and manufacture of an axial meridian circle, purchase of equipment for television observations of meteors.
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Singh, Rakesh Kumar, Anna Vader, Christopher J. Mundy, Janne E. Søreide, Katrin Iken, Kenneth H. Dunton, Laura Castro de la Guardia, Mikael K. Sejr, and Simon Bélanger. "Satellite-Derived Photosynthetically Available Radiation at the Coastal Arctic Seafloor." Remote Sensing 14, no. 20 (October 17, 2022): 5180. http://dx.doi.org/10.3390/rs14205180.
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Climate change has affected the Arctic Ocean (AO) and its marginal seas significantly. The reduction of sea ice in the Arctic region has altered the magnitude of photosynthetically available radiation (PAR) entering the water column, impacting primary productivity. Increasing cloudiness in the atmosphere and rising turbidity in the coastal waters of the Arctic region are considered as the major factors that counteract the effect of reduced sea ice on underwater PAR. Additionally, extreme solar zenith angles and sea-ice cover in the AO increase the complexity of retrieving PAR. In this study, a PAR algorithm based on radiative transfer in the atmosphere and satellite observations is implemented to evaluate the effect of these factors on PAR in the coastal AO. To improve the performance of the algorithm, a flag is defined to identify pixels containing open-water, sea-ice or cloud. The use of flag enabled selective application of algorithms to compute the input parameters for the PAR algorithm. The PAR algorithm is validated using in situ measurements from various coastal sites in the Arctic and sub-Arctic seas. The algorithm estimated daily integrated PAR above the sea surface with an uncertainty of 19% in summer. The uncertainty increased to 24% when the algorithm was applied year-round. The PAR values at the seafloor were estimated with an uncertainty of 76%, with 36% of the samples under sea ice and/or cloud cover. The robust performance of the PAR algorithm in the pan-Arctic region throughout the year will help to effectively study the temporal and spatial variability of PAR in the Arctic coastal waters. The calculated PAR data are used to quantify the changing trend in PAR at the seafloor in the coastal AO with depth < 100 m using MODIS-Aqua data from 2003 to 2020. The general trends calculated using the pixels with average PAR > 0.415 mol m−2day−1 at the seafloor during summer indicate that the annual average of PAR entering the water column in the coastal AO between 2003 and 2020 increased by 23%. Concurrently, due to increased turbidity, the attenuation in the water column increased by 22%. The surge in incident PAR in the water column due to retreating sea ice first led to increased PAR observed at the seafloor (∼12% between 2003 and 2014). However, in the last decade, the rapid increase in light attenuation of the water column has restricted the increase in average annual PAR reaching the bottom in the coastal AO.
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Loeb, Norman G., Bruce A. Wielicki, Wenying Su, Konstantin Loukachine, Wenbo Sun, Takmeng Wong, Kory J. Priestley, Grant Matthews, Walter F. Miller, and R. Davies. "Multi-Instrument Comparison of Top-of-Atmosphere Reflected Solar Radiation." Journal of Climate 20, no. 3 (February 1, 2007): 575–91. http://dx.doi.org/10.1175/jcli4018.1.
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Abstract Observations from the Clouds and the Earth’s Radiant Energy System (CERES), Moderate Resolution Imaging Spectroradiometer (MODIS), Multiangle Imaging Spectroradiometer (MISR), and Sea-Viewing Wide-Field-of-View Sensor (SeaWiFS) between 2000 and 2005 are analyzed in order to determine if these data are meeting climate accuracy goals recently established by the climate community. The focus is primarily on top-of-atmosphere (TOA) reflected solar radiances and radiative fluxes. Direct comparisons of nadir radiances from CERES, MODIS, and MISR aboard the Terra satellite reveal that the measurements from these instruments exhibit a year-to-year relative stability of better than 1%, with no systematic change with time. By comparison, the climate requirement for the stability of visible radiometer measurements is 1% decade−1. When tropical ocean monthly anomalies in shortwave (SW) TOA radiative fluxes from CERES on Terra are compared with anomalies in Photosynthetically Active Radiation (PAR) from SeaWiFS—an instrument whose radiance stability is better than 0.07% during its first six years in orbit—the two are strongly anticorrelated. After scaling the SeaWiFS anomalies by a constant factor given by the slope of the regression line fit between CERES and SeaWiFS anomalies, the standard deviation in the difference between monthly anomalies from the two records is only 0.2 W m−2, and the difference in their trend lines is only 0.02 ± 0.3 W m−2 decade−1, approximately within the 0.3 W m−2 decade−1 stability requirement for climate accuracy. For both the Tropics and globe, CERES Terra SW TOA fluxes show no trend between March 2000 and June 2005. Significant differences are found between SW TOA flux trends from CERES Terra and CERES Aqua between August 2002 and March 2005. This discrepancy is due to uncertainties in the adjustment factors used to account for degradation of the CERES Aqua optics during hemispheric scan mode operations. Comparisons of SW TOA flux between CERES Terra and the International Satellite Cloud Climatology Project (ISCCP) radiative flux profile dataset (FD) RadFlux product show good agreement in monthly anomalies between January 2002 and December 2004, and poor agreement prior to this period. Commonly used statistical tools applied to the CERES Terra data reveal that in order to detect a statistically significant trend of magnitude 0.3 W m−2 decade−1 in global SW TOA flux, approximately 10 to 15 yr of data are needed. This assumes that CERES Terra instrument calibration remains highly stable, long-term climate variability remains constant, and the Terra spacecraft has enough fuel to last 15 yr.
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Yadav, Rahul, Maria D. Kazachenko, Andrey N. Afanasyev, Jaime de la Cruz Rodríguez, and Jorrit Leenaarts. "Solar Atmospheric Heating Due to Small-scale Events in an Emerging Flux Region." Astrophysical Journal 958, no. 1 (November 1, 2023): 54. http://dx.doi.org/10.3847/1538-4357/acfd2b.
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Abstract We investigate the thermal, kinematic, and magnetic structure of small-scale heating events in an emerging flux region (EFR). We use high-resolution multiline observations (including Ca ii 8542 Å, Ca ii K, and the Fe i 6301 Å line pair) of an EFR located close to the disk center from the CRISP and CHROMIS instruments at the Swedish 1 m Solar Telescope. We perform non-LTE inversions of multiple spectral lines to infer the temperature, velocity, and magnetic field structure of the heating events. Additionally, we use the data-driven Coronal Global Evolutionary Model to simulate the evolution of the 3D magnetic field configuration above the events and understand their dynamics. Furthermore, we analyze the differential emission measure to gain insights into the heating of the coronal plasma in the EFR. Our analysis reveals the presence of numerous small-scale heating events in the EFR, primarily located at polarity inversion lines of bipolar structures. These events not only heat the lower atmosphere but also significantly heat the corona. The data-driven simulations, along with the observed enhancement of currents and Poynting flux, suggest that magnetic reconnection in the lower atmosphere is likely responsible for the observed heating at these sites.
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Liang, Shiyu, Ziyuan Wang, Zhenghua Huang, Hengyuan Wei, Hui Fu, Ming Xiong, and Lidong Xia. "Electron Densities of Transition Region Loops Derived from IRIS O iv Spectral Data." Astrophysical Journal Letters 966, no. 1 (April 24, 2024): L6. http://dx.doi.org/10.3847/2041-8213/ad3d5e.
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Abstract Loops are fundamental structures in the magnetized atmosphere of the Sun. Their physical properties are crucial for understanding the nature of the solar atmosphere. Transition region loops are relatively dynamic and their physical properties have not yet been fully understood. With spectral data of the line pair of O iv 1399.8 Å and 1401.2 Å ( T max = 1.4 × 10 5 K) of 23 transition region loops obtained by IRIS, we carry out the first systematic analyses to their loop lengths (L), electron densities (n e ), and effective temperatures. We found electron densities, loop lengths, and effective temperatures of these loops are in the ranges of 8.9 × 109–3.5 × 1011 cm−3, 8–30 Mm, and 1.9 × 105–1.3 × 106 K, respectively. At a significant level of 90%, regression analyses show that the relationship between electron densities and loop lengths is n e [cm−3] ∝ (L[Mm])−0.78±0.42, while the dependences of electron densities on effective temperatures and that on the line intensities are not obvious. These observations demonstrate that transition region loops are significantly different than their coronal counterparts. Further studies on the theoretical aspect based on the physical parameters obtained here are of significance for understanding the nature of transition region loops.
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Campbell, R. J., M. Mathioudakis, M. Collados, P. H. Keys, A. Asensio Ramos, C. J. Nelson, D. Kuridze, and A. Reid. "Temporal evolution of small-scale internetwork magnetic fields in the solar photosphere." Astronomy & Astrophysics 647 (March 2021): A182. http://dx.doi.org/10.1051/0004-6361/202040028.
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Context. While the longitudinal field that dominates in photospheric network regions has been studied extensively, small-scale transverse fields have recently been found to be ubiquitous in the quiet internetwork photosphere and this merits further study. Furthermore, few observations have been able to capture how this field evolves. Aims. We aim to statistically characterize the magnetic vector in a quiet Sun internetwork region and observe the temporal evolution of specific small-scale magnetic features. Methods. We present two high spatio-temporal resolution observations that reveal the dynamics of two disk-centre internetwork regions taken by the new GREGOR Infrared Spectrograph Integral Field Unit with the highly magnetically sensitive photospheric Fe I line pair at 15648.52 Å and 15652.87 Å. We record the full Stokes vector and apply inversions with the Stokes inversions based on response functions code to retrieve the parameters characterizing the atmosphere. We consider two inversion schemes: scheme 1 (S1), where a magnetic atmosphere is embedded in a field free medium, and scheme 2 (S2), with two magnetic models and a fixed 30% stray light component. Results. The magnetic properties produced from S1 inversions returned a median magnetic field strength of 200 and 240 G for the two datasets, respectively. We consider the median transverse (horizontal) component, among pixels with Stokes Q or U, and the median unsigned longitudinal (vertical) component, among pixels with Stokes V, above a noise threshold. We determined the former to be 263 G and 267 G, and the latter to be 131 G and 145 G, for the two datasets, respectively. Finally, we present three regions of interest, tracking the dynamics of small-scale magnetic features. We apply S1 and S2 inversions to specific profiles of interest and find that the latter produces better approximations when there is evidence of mixed polarities. We find patches of linear polarization with magnetic flux density of the order of 130−150 G and find that linear polarization appears preferentially at granule-intergranular lane boundaries. The weak magnetic field appears to be organized in terms of complex ‘loop-like’ structures, with transverse fields often flanked by opposite polarity longitudinal fields.
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Albuquerque, L. M. M., K. M. Longo, S. R. Freitas, T. Tarasova, A. Plana Fattori, C. Nobre, and L. V. Gatti. "Sensitivity studies on the photolysis rates calculation in Amazonian atmospheric chemistry – Part I: The impact of the direct radiative effect of biomass burning aerosol particles." Atmospheric Chemistry and Physics Discussions 5, no. 5 (September 28, 2005): 9325–53. http://dx.doi.org/10.5194/acpd-5-9325-2005.
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Abstract. The impact of the direct radiative effect of the aerosol particles on the calculation of the photolysis rates and consequently on the atmospheric chemistry in regional smoke clouds due to biomass burning over the Amazon basin is addressed in this work. It explores a case study for 19 September 2002 at LBA-RACCI-SMOCC (The Large-Scale Biosphere-Atmosphere experiment in Amazonia – Radiation, Cloud, and Climate Interactions – Smoke, Aerosols, Clouds, Rainfall and Climate) pasture site in SW Amazonia. The Tropospheric Ultraviolet Visible radiation model (TUV) version 4.2, (Madronich et al., 1987) is used for the photolysis rates calculation considering the layer aerosol optical depth from the Coupled Aerosol Tracer Transport model to the Brazilian Regional Atmospheric Modeling System (CATT-BRAMS) (Freitas et al., 2005). A dynamical aerosol model (Procópio et al., 2003) is included in the radiative transfer model to take into account the high temporal variability of the aerosol optical thickness. This methodology is tested by comparing modeled and measured clear sky solar irradiances. The results show a good agreement with measured PAR radiation values. The actinic flux attenuation, for AOT (500 nm) values around 1.94, decreases the photolysis rates by about 70% in the presence of near-ground smoke aerosol and above the smoke layer the photolysis process tends to increase by about 40%. A simulation of the ozone production is carried out using a one-dimensional photochemical box model and comparisons with observation are shown.
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Siegelman, Lia. "Le rôle climatique des fronts océaniques de fine échelle en profondeur (prix Prud'homme 2020)." La Météorologie, no. 114 (2021): 038. http://dx.doi.org/10.37053/lameteorologie-2021-0069.
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L'océan est le plus grand réservoir d'énergie de notre planète. La quantité de chaleur qu'il est capable de stocker est modulée par sa circulation complexe, opérant sur des échelles allant du centimètre à la dizaine de milliers de kilomètres. Les découvertes scientifiques des deux dernières décennies ont révélé l'existence de fronts de fine échelle (d'environ 1 à 50 km), analogues aux fronts atmosphériques, dans la couche de mélange océanique de surface. Ces fronts agissent comme des conduits entre l'océan et l'atmosphère, contrôlant les échanges de gaz et de chaleur. Combinant observation et modélisation, nous démontrons pour la première fois le rôle capital de ces fronts jusqu'à 1000 m de profondeur. Ils génèrent d'importants flux de chaleur dirigés de l'intérieur de l'océan vers la surface, pouvant modifier la capacité de stockage de chaleur de l'océan, avec des répercussions potentiellement majeures pour les systèmes biogéochimique et climatique. The ocean is the largest solar energy collector on Earth. The amount of heat it can store is modulated by its complex circulation, which spans a broad range of spatial scales, from centimeters to thousands of kilometers. Scientific discoveries of the past two decades revealed the existence of fine-scale fronts (≈ 10-20 km wide), analogous to atmospheric fronts, in the oceanic surface mixed layer. These fronts control the exchanges between the ocean and the atmosphere just as the capillary vessels of our pulmonary alveoli facilitate the exchange of gas when breathing. Combining observation and modeling, we demonstrate for the first time the crucial role played by these fronts in the ocean interior. These fine-scale fronts drive an anomalous upward heat transport from the ocean interior back to the surface. This can alter the ocean heat storage capacity, with potential major implications for the biogeochemical and climate systems.
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Gupta, Girjesh R., and Sushree S. Nayak. "Spectroscopic and imaging observations of transient hot and cool loops by IRIS and SDO." Monthly Notices of the Royal Astronomical Society 512, no. 3 (March 31, 2022): 3149–62. http://dx.doi.org/10.1093/mnras/stac657.
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ABSTRACT Coronal loops are the basic building blocks of the solar atmosphere and are observed on various length scales. However, their formation mechanism is still unclear. In this paper, we present spectroscopic and imaging observations of small-scale transients and the subsequent formation of transient loops. For this purpose, we have utilized the multiwavelength observations recorded by the Atmospheric Imaging Assembly (AIA) and the Interface Region Imaging Spectrograph (IRIS) slit-jaw imager (SJI), along with spectroscopic measurements provided by IRIS. For the photospheric magnetic field data, we obtained line-of-sight magnetogram data provided by the Helioseismic and Magnetic Imager (HMI). Small-scale transients are simultaneously observed with several EUV and UV passbands of AIA and IRIS/SJI. The HMI magnetogram provides evidence of negative flux cancellations beneath these transients. Differential emission measure (DEM) analysis shows that one of the transients attains temperatures up to 8 MK whereas another one only reaches 0.4 MK. These transients further lead to the formation of small-scale loops with similar temperature distributions, thus termed hot and cool loops respectively. During the course of events, the IRIS slit was rastering the region and thus provided spectroscopic measurements at both transients and associated loops. This enabled us to perform in-depth investigations of the hot and cool loops. Using a density-sensitive O iv line pair, we obtained average electron densities along the hot and cool loops to be 1011.2 and 1010.8 cm−3 respectively. Energy estimates suggest that flux cancellation could easily power the hot transient, while it is insufficient for the cool transient. Lifetime estimates and magnetic field extrapolation suggest the presence of small-scale and fine structures within these loops. The results provide crucial ingredients for the physics of loop formation and the thermodynamics involved.
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Chen, Feng, Matthias Rempel, and Yuhong Fan. "Eruption of a Magnetic Flux Rope in a Comprehensive Radiative Magnetohydrodynamic Simulation of Flare-productive Active Regions." Astrophysical Journal Letters 950, no. 1 (June 1, 2023): L3. http://dx.doi.org/10.3847/2041-8213/acda2e.
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Abstract Radiative magnetohydrodynamic simulation includes sufficiently realistic physics to allow for the synthesis of remote sensing observables that can be quantitatively compared with observations. We analyze the largest flare in a simulation of the emergence of large flare-productive active regions described by Chen et al. The flare releases 4.5 × 1031 erg of magnetic energy and is accompanied by a spectacular coronal mass ejection. Synthetic soft X-ray flux of this flare reaches M2 class. The eruption reproduces many key features of observed solar eruptions. A preexisting magnetic flux rope is formed along the highly sheared polarity inversion line between a sunspot pair and is covered by an overlying multipole magnetic field. During the eruption, the progenitor flux rope actively reconnects with the canopy field and evolves to the large-scale multithermal flux rope that is observed in the corona. Meanwhile, the magnetic energy released via reconnection is channeled down to the lower atmosphere and gives rise to bright soft X-ray post-flare loops and flare ribbons that reproduce the morphology and dynamic evolution of observed flares. The model helps to shed light on questions of where and when the a flux rope may form and how the magnetic structures in an eruption are related to observable emission properties.
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Chen, Yepei, Kaimin Sun, Wenzhuo Li, Xiuqing Hu, Pengfei Li, and Ting Bai. "Vicarious Calibration of FengYun-3D MERSI-II at Railroad Valley Playa Site: A Case for Sensors with Large View Angles." Remote Sensing 13, no. 7 (April 1, 2021): 1347. http://dx.doi.org/10.3390/rs13071347.
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Vicarious calibration, as one on-orbit calibration method, is a supplement to onboard calibration of sensors. The application of vicarious calibration, however, is greatly limited due to the time- and effort-consuming field measurements of atmosphere and surface. Fortunately, the Radiometric Calibration Network (RadCalNet) provides automated in situ data at multiple sites, thus increasing the opportunities to achieve ongoing ground-reference calibration of in-orbit instruments. The MEdium Resolution Spectrum Imager-II (MERSI-II) onboard FengYun-3D (FY) has the temporal, spectral, spatial, and radiometric capacity for image capture at a level on par with other sensors used worldwide, such as the Moderate Resolution Imaging Spectroradiometer (MODIS). Its on-orbit radiometric performance, however, is assessed in a limited manner. In this study, the reflectance-based vicarious calibration method was employed to calibrate the MERSI-II sensor using ground measurements from RadCalNet at the Railroad Valley Playa site. The calibration of the MERSI-II sensor with large view angles presents difficulties due to the uncertainties introduced by surface bidirectional reflectance distribution function (BRDF) effects. Thus, we performed BRDF correction to harmonize the sensor and ground measurements to consistent observation geometries, before the in-situ measurements were taken as inputs for the 6SV radiative transfer model to predict at-sensor radiance. The calibration results were comprehensively validated with ground data and MODIS benchmark datasets. The results show that accounting for BRDF correction could improve the accuracy of vicarious calibration and ensure inter-consistency between different sensors. An analysis of the vicarious calibration of FY-3D MERSI-II yielded uncertainties of <5% for solar reflective bands, which meets the radiometric accuracy requirements typical for land-monitoring space missions. The proposed approach is also applicable to the calibration of other large footprint sensors.
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Hu, Xiuqing, Ling Wang, Junwei Wang, Lingli He, Lin Chen, Na Xu, Bingcheng Tao, Lu Zhang, Peng Zhang, and Naimeng Lu. "Preliminary Selection and Characterization of Pseudo-Invariant Calibration Sites in Northwest China." Remote Sensing 12, no. 16 (August 5, 2020): 2517. http://dx.doi.org/10.3390/rs12162517.
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Pseudo-invariant calibration sites (PICS) have been used for the radiometric calibration and stability monitoring of satellite optical sensors. Several stable PICS, such as those in the Sahara Desert in North Africa, were selected for the vicarious calibration of earth remote sensing satellites. However, the selection procedure of PICSs in the whole of Northwest China has not been fully explored before. This paper presents a novel technique for selecting PICS in Northwest China by combined using the coefficient of variation (CV) and the iteratively reweighted multivariate alteration detection (IR-MAD) technique. IR-MAD, which calculates the differences between two multispectral N-band images from the same scene acquired at different times, is used to identify no-change pixels (NCPs) of the scene through one image pair. The NCPs from IR-MAD using the long-term data of FY-3 visible infrared radiometer (VIRR) and aqua Moderate Resolution Imaging Spectroradiometer (MODIS) were aggregated into the contiguously stable sites. The traditional spatial uniformity and temporal stability from MODIS surface products were used to select the potential PICS. By combining the results of both methods, over thirty PICSs with a wider brightness range of the scene types were selected. To confirm and characterize these PICSs over Northwest China, Landsat operational land imager (OLI) high-spatial-resolution images were used to check the spatial uniformity of the selected site to determine the specific location and the size of these sites. Additionally, the surface spectral reflectance and bidirectional reflectance distribution function (BRDF) were obtained from the field campaign at Chaidamu Basin, 2018. To demonstrate the practical utilization and usability of these PICSs, they were employed in the multi-site top of atmosphere (TOA) reflectance simulation to validate the operational calibration performance of Aqua/MODIS and FY-3D/MERSI-II (Medium Resolution Spectral Imager II). The simulation results showed good consistency compared with the observations from both MODIS and MERSI-II, with a relative bias and root mean square error (RMSE) of <5% and <0.05%, respectively. These sites provide prospects for multi-site vicarious calibrations of solar reflective bands, which may help to evaluate or characterize instrumental nonlinear responses using a wider signal dynamic from the sites in different seasons.
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Singh, Jagdev. "The Sun-Spectroscopic Observations of the Coronal Emission Lines and ADITYA-1 Mission." Journal of Mountain Research 14, no. 1 (June 2019). http://dx.doi.org/10.51220/jmr.v14i1.5.
Full textAbstract:
The sun and the solar atmosphere, known as solar corona have been studied in detail for centuries but still lot need to be understood about the sun. In the late 19th and earlier 20th century, the information gathered about the solar corona was from the brief moments available during the total solar eclipses. In the later part space observations provided a large body of information about the solar corona. We obtained systematic high resolution spectroscopic observations in [Fe x] 637.4 [Fe xi] 789.2, [Fe xiii] 1074.7, and [Fe xiv] 530.3 nm emission lines during the period of 1997-2007 with the 25-cm coronagraph at Norikura, Japan. The variation in line widths with height above the solar limb implies that one pair of lines indicate that top of coronal loops are hotter where as other pair of lines shows that loop top is cooler. To explain these results, we proposed an empirical model as all these results are difficult to explain using the existing models. With this background we planned and designed a visible emission line coronagraph (VELC). This instrument is in advance stage of fabrication and is expected to be launched in 2019-20. The challenges and required technical development for this mission are discussed.
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Singh, Jagdev. "The Sun-Spectroscopic Observations of the Coronal Emission Lines and ADITYA-1 Mission." Journal of Mountain Research 14, no. 1 (June 2019). http://dx.doi.org/10.51220/jmr.v19i1.5.
Full textAbstract:
The sun and the solar atmosphere, known as solar corona have been studied in detail for centuries but still lot need to be understood about the sun. In the late 19th and earlier 20th century, the information gathered about the solar corona was from the brief moments available during the total solar eclipses. In the later part space observations provided a large body of information about the solar corona. We obtained systematic high resolution spectroscopic observations in [Fe x] 637.4 [Fe xi] 789.2, [Fe xiii] 1074.7, and [Fe xiv] 530.3 nm emission lines during the period of 1997-2007 with the 25-cm coronagraph at Norikura, Japan. The variation in line widths with height above the solar limb implies that one pair of lines indicate that top of coronal loops are hotter where as other pair of lines shows that loop top is cooler. To explain these results, we proposed an empirical model as all these results are difficult to explain using the existing models. With this background we planned and designed a visible emission line coronagraph (VELC). This instrument is in advance stage of fabrication and is expected to be launched in 2019-20. The challenges and required technical development for this mission are discussed.
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Mahieu, Emmanuel, Olivier Flock, Justus Notholt, Mathias Palm, Irene Pardo Cantos, Maxime Prignon, Ginette Roland, Christian Servais, and Arpita Verma. "Surveillance à long terme de l’atmosphère terrestreà la station du Jungfraujoch." Bulletin de la Société Royale des Sciences de Liège, 2019, 31–41. http://dx.doi.org/10.25518/0037-9565.9136.
Full textAbstract:
C’est au début des années 1950, bien avant qu’il ne soit question de changement climatique, que l’Université de Liège a réalisé ses premières mesures atmosphériques à la station scientifique internationale du Jungfraujoch, dans les Alpes bernoises. Ces observations pionnières ont alors notamment permis de confirmer la présence de méthane et de monoxyde de carbone dans l’atmosphère non polluée prévalant à ce site. Ravivé au milieu des années 1970 par les premières inquiétudes relatives à la destruction de l’ozone stratosphérique, le programme de surveillance n’a depuis plus cessé de fournir des données essentielles à la caractérisation de notre atmosphère et aux changements qu’elle subit sous l’influence des activités humaines ou de phénomènes naturels d’ampleur. Dans cet article, nous présentons quelques résultats déduits récemment de ce programme de longue haleine, pertinents pour la vérification de traités environnementaux internationaux.
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Limbach, Mary Anne, Andrew Vanderburg, Kevin B. Stevenson, Simon Blouin, Caroline Morley, Jacob Lustig-Yaeger, Melinda Soares-Furtado, and Markus Janson. "A new method for finding nearby white dwarf exoplanets and detecting biosignatures." Monthly Notices of the Royal Astronomical Society, October 3, 2022. http://dx.doi.org/10.1093/mnras/stac2823.
Full textAbstract:
Abstract We demonstrate that the James Webb Space Telescope (JWST) can detect infrared (IR) excess from the blended light spectral energy distribution of spatially unresolved terrestrial exoplanets orbiting nearby white dwarfs. We find that JWST is capable of detecting warm (habitable-zone; Teq = 287 K) Earths or super-Earths and hot (400 − 1000 K) Mercury analogs in the blended light spectrum around the nearest 15 isolated white dwarfs with 10 hrs of integration per target using MIRI’s Medium Resolution Spectrograph (MRS). Further, these observations constrain the presence of a CO2-dominated atmosphere on these planets. The technique is nearly insensitive to system inclination, and thus observation of even a small sample of white dwarfs could place strong limits on the occurrence rates of warm terrestrial exoplanets around white dwarfs in the solar neighborhood. We find that JWST can also detect exceptionally cold (100 − 150 K) Jupiter-sized exoplanets via MIRI broadband imaging at λ = 21 μm for the 34 nearest (<13 pc) solitary white dwarfs with 2 hrs of integration time per target. Using IR excess to detect thermal variations with orbital phase or spectral absorption features within the atmosphere, both of which are possible with long-baseline MRS observations, would confirm candidates as actual exoplanets. Assuming an Earth-like atmospheric composition, we find that the detection of the biosignature pair O3+CH4 is possible for all habitable-zone Earths (within 6.5 pc; six white dwarf systems) or super-Earths (within 10 pc; 17 systems) orbiting white dwarfs with only 5 − 36 hrs of integration using MIRI’s Low Resolution Spectrometer (LRS).
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Frouin, Robert, Jing Tan, Mathieu Compiègne, Didier Ramon, Marshall Sutton, Hiroshi Murakami, David Antoine, Uwe Send, Jeff Sevadjian, and Vincenzo Vellucci. "The NASA EPIC/DSCOVR Ocean PAR Product." Frontiers in Remote Sensing 3 (April 12, 2022). http://dx.doi.org/10.3389/frsen.2022.833340.
Full textAbstract:
The EPIC/DSCOVR observations of the Earth’s surface lit by the Sun made from the first Lagrange point several times during the day in spectral bands centered on 443, 551, and 680 nm are used to estimate daily mean photosynthetically available radiation (PAR) at the ice-free ocean surface. The PAR algorithm uses a budget approach, in which the solar irradiance reaching the surface is obtained by subtracting from the irradiance arriving at the top of the atmosphere (known), the irradiance reflected to space (estimated from the EPIC Level 1b radiance data), taking account of atmospheric transmission and surface albedo (modeled). Clear and cloudy regions within a pixel do not need to be distinguished, which dismisses the need for often-arbitrary assumptions about cloudiness distribution within a pixel and is therefore adapted to the relatively large EPIC pixels. A daily mean PAR is estimated on the source grid for each EPIC instantaneous daytime observation, assuming no cloudiness changes during the day, and the individual estimates are remapped and weight-averaged using the cosine of the Sun zenith angle. In the computations, wind speed, surface pressure, and water vapor amount are extracted from NCEP Reanalysis 2 data, aerosol optical thickness and Angström coefficient from MERRA-2 data, and ozone amount from EPIC Level 2 data. Areas contaminated by Sun glint are excluded using a threshold on Sun glint reflectance calculated using wind data. Ice masking is based on NSIDC near-real-time ice fraction data. The product is evaluated against in situ measurements at various locations and compared with estimates from sensors in polar and geostationary orbits (MODIS, AHI). Unlike with MODIS, the EPIC PAR product does not exhibit gaps at low and middle latitudes. Accuracy is satisfactory for long-term studies of aquatic photosynthesis, especially given the much larger uncertainties on the fraction of PAR absorbed by live algae and the quantum yield of carbon fixation. The EPIC daily mean PAR product is generated operationally on a Plate Carrée (equal-angle) grid with 18.4 km resolution at the equator and on an 18.4 km equal-area grid, i.e., it is fully compatible with the NASA Greenbelt OBPG ocean-color products. Data are available since the beginning of the DSCOVR mission (i.e., June 2015) from the NASA Langley ASDC website.
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RAPONI, M. M., E. WOLFRAM, J. SALVADOR, F. GOUTAIL, J. TOCHO, and E. QUEL. "ESTUDIO DE LA VARIACIÓN ESTACIONAL DE LA COLUMNA VERTICAL DE NO2 y O3 ATMOSFÉRICO EN RÍO GALLEGOS, MEDIANTE UN ESPECTRÓMETRO DE LA RED SAOZ STUDY OF THE ATMOSPHERIC NO2 AND O3 VERTICAL COLUMN SEASONAL VARIABILITY AT RÍO GALLEGOS, BY MEANS OF A SAOZ SPECTROMETER." Anales AFA, 2010, 262–65. http://dx.doi.org/10.31527/analesafa.2010.21.262.
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The stratospheric ozone (O3) is one of the most important gases in our atmosphere due to its capacity to absorb biologically harmful solar radiation (called UV-B) that would otherwise arrive to the terrestrial surface producing dangerous effects on different organisms. On the other hand, the nitrogen dioxide (NO2) is a key trace gas in the ozone photochemical. The systematic sensing of the concentration of NO2 and other minority gases is essential in order to understand the stratospheric ozone destruction and formation processes. In this work we present the study carried out on the seasonal variation of the atmospheric O3 and NO2 vertical column concentration, using a SAOZ spectrometer (System d' Analyse par Observation Zenitale) belonging to the Service d'Aéronomie (Centre National de Recherche Scientifique, France), located in Río Gallegos, Santa Cruz province (51º 36’ S, 69º 19’ W), in the CEILAP-RG remote sensing station. We analyze the correlation between the O3 and NO2 concentration and study the behavior of these gases in ozone hole situation. Likewise, we compare the ground-based measurement with those coming from the OMI/AURA (Ozone Monitoring Instrument, AURA satellite)