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MAUSAM ◽  
2021 ◽  
Vol 51 (2) ◽  
pp. 119-126
Author(s):  
S. M. BAWISKAR ◽  
M. D. CHIPADE ◽  
S. S. SINGH

Lower tropospheric energetics and energy processes of zonal waves for three consecutive northern summer monsoon seasons of 1994, 1995 and 1996 are presented. Fourier technique is used. The features of the tropical and extra-tropical regions are very well reflected by the data set used for this study. The results do not show marked year to year variations in the pattern of energy processes. The character of energy processes differs significantly from one latitudinal region to other. Wave to zonal mean flow interactions and wave to wave interactions are almost opposite in character over R1 (10° S -10° N) and R2 (10° N -30° N). L (n) interaction indicates that R1 acts as source of kinetic energy to the waves over R2. Particularly, standing waves I and 2 over RI are the major source of kinetic energy to the waves over R2. Extra-tropical region R3 (30° N -50° N) is dominated by transient waves while tropical regions R1 and R2 are dominated by standing waves. Medium and short waves have significant contributions over extra-tropical region whereas tropical regions are dominated by long waves. The pattern of energy processes over R3 is somewhat similar to the energy processes over R1. This is because both the regions have anti-cyclonic lateral shear.


MAUSAM ◽  
2021 ◽  
Vol 49 (2) ◽  
pp. 159-166
Author(s):  
KSHUDIRAM SARA ◽  
SURANJANA SARA

During northern summer, a monsoon stationary wave which maintains as part of its baroclinic structure three well-defined troughs, one each in the region of the Arabian sea, the Bay of Bengal and South China sea, frequently interacts with the mid-latitude baroclinic waves which amplify during their eastward passage with profound influence on the development of the monsoon troughs. The paper discusses the mechanism of this wave-wave interaction as suggested by the temporal evolution of the themla1 and wind fields associated with the waves and reports the findings of a detailed study of a case of tropical-mid latitude interaction in which the development of a monsoon trough led to the birth of a westward-propagating monsoon depression over South China.


Eos ◽  
2021 ◽  
Vol 102 ◽  
Author(s):  
Elise Cutts

InSight data hint that shifting carbon dioxide ice loads, illumination changes, or solar tides could drive an uptick in marsquakes during northern summer—a “marsquake season.”


2021 ◽  
Author(s):  
Athena Coustenis ◽  
Donald Jennings ◽  
Richard Achterberg ◽  
Panayotis Lavvas ◽  
Conor Nixon ◽  
...  

<p>Titan’s atmosphere and surface (a complex system) evolve with season, as Titan follows Saturn in its orbit around the Sun for 30 years with an inclination of about 27°. We performed an analysis of spectra acquired by Cassini/CIRS at high resolution covering the range from 600 to 1500 cm-1 since the beginning and until the last flyby of Titan in 2017 and describe the temperature and chemical composition variations ([1-3]. By applying our radiative transfer code (ARTT) to the high-resolution CIRS spectra we study the stratospheric evolution over almost two Titan seasons [1,2], corresponding to the Cassini mission duration. CIRS nadir and limb spectral together show variations in temperature and chemical composition in the stratosphere during the Cassini mission, before and after the Northern Spring Equinox (NSE) and also during one Titan year.</p> <p>Since the 2010 equinox we have thus reported on monitoring of Titan’s stratosphere near the poles and in particular on the observed strong temperature decrease and compositional enhancement above Titan’s southern polar latitudes since 2012 and until 2014 of several trace species, such as complex hydrocarbons and nitriles, which were previously observed only at high northern latitudes. This effect followed the transition of Titan’s seasons from northern winter in 2002 to northern summer in 2017, while at that latter time the southern hemisphere was entering winter.</p> <p>Our data show a continued decrease of the abundances which we first reported to have started in 2015. The 2017 data we have acquired and analyzed here are important because they are the only ones recorded since 2014 close to the south pole in the far-infrared nadir mode at high resolution. A large temperature increase in the southern polar stratosphere (by 10-50 K in the 0.5 mbar-0.05 mbar pressure range) is found and a change in the temperature profile’s shape. The 2017 observations also show a related significant decrease in most of the abundances which must have started sometime between 2014 and 2017 [3]. In our work, we show that the equatorial latitudes remain rather constant throughout the Cassini mission.</p> <p>We have thus shown that the south pole of Titan is now losing its strong enhancement, while the north pole also slowly continues its decrease in gaseous opacities. It would have been interesting to see when this might happen, but the Cassini mission ended in September 2017. Perhaps future ground-based measurements and the Dragonfly mission can pursue this investigation and monitor Titan’s atmosphere to characterize the seasonal events. Our results set constraints on GCM and photochemical models.</p> <p> </p> <p><strong>References:</strong></p> <p> [1] Coustenis et al., 2016, Icarus 270, 409-420</p> <p>[2] Coustenis et al., 2018, Astroph. J., Lett., 854, no2</p> <p>[3] Coustenis et al., 2020. Titan’s neutral atmosphere seasonal variations up to the end of the Cassini mission. Icarus 344, 113413. https://doi.org/10.1016/j.icarus.2019.113413.<button class="clickandreadBtn" title="La ressource a été trouvée dans Unpaywall" name="CLICKANDREADLink"><img src="data:image/svg+xml;base64,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" width="27" /></button></p>


Author(s):  
Vickie Hearnshaw

This article draws on 20 postcards from a private collection which have only recently come to light, written by New Zealand-born photographer Brian Brake to his father Jack Brake in the 1950s, and therefore during the years when he was establishing himself as a photo-journalist. Although the collection is not large in number, the messages written on the backs of these postcards provide a wonderful opportunity to locate Brian Brake’s whereabouts during these years and retrace the significant events in his life at this time in his own words. Importantly, the postcards cover the critical period immediately prior to Brake undertaking the filming of his remarkable visual documentary, Monsoon, in India during the northern summer months of 1960. It would be this assignment that would establish his name as a world-class photo-journalist.


2020 ◽  
Author(s):  
Athena Coustenis ◽  
Donald Jennings ◽  
Richard Achterberg ◽  
Panayotis Lavvas ◽  
Georgios Bampasidis ◽  
...  

<p>In our recent publication [1] we reported new results concerning the seasonal atmospheric evolution near Titan’s poles and equator in terms of temperature and composition using nadir spectra acquired by the Cassini Composite Infrared Spectrometer (CIRS) at high spectral resolution during the last year of the Cassini mission in 2017 complementing previous investigations covering almost two Titan seasons. In previous papers [2,3], we reported on monitoring of Titan’s stratosphere near the poles after the mid-2009 northern spring equinox. In particular we have reported on the observed strong temperature decrease and compositional enhancement above Titan’s southern polar latitudes since 2012 and until 2014 of several trace species, such as complex hydrocarbons and nitriles, which were previously observed only at high northern latitudes. This effect accompanied the transition of Titan’s seasons from northern winter in 2002 to northern summer in 2017, while at that latter time, the southern hemisphere was entering winter. Our new data, acquired in 2017 and analyzed here, are important because they are the only ones recorded since 2014 close to the south pole in the mid-infrared nadir mode at high resolution. A large temperature increase in the southern polar stratosphere (by 10-50 K in the 0.1 to 0.01 mbar pressure range) is found associated with a change in the temperature profile’s shape. The 2017 observations also show a related significant decrease in most of the southern abundances which must have started sometime between 2014 and 2017 [1]. For the north, the spectra indicate a continuation of the decrease of the abundances which we first reported to have started in 2015 and small temperature variations [1]. We discuss comparisons with other results and with current photochemical and dynamical models which could be updated and improved by the new constraints set by the findings presented here.</p> <p>[1] Coustenis et al., 2019, Icarus 344, 1 July 2020, 113413 ; [2] Coustenis et al., 2016, Icarus 270, 409-420; [3] Coustenis et al., 2018, Astroph. J. Lett. 854, no2.</p>


2020 ◽  
Author(s):  
Alain Khayat ◽  
Michael Smith ◽  
Michael Wolff ◽  
Frank Daerden ◽  
Manish Patel ◽  
...  

<p>The Nadir and Occultation for MArs Discovery (NOMAD) is a spectrometer suite onboard the ExoMars Trace Gas Orbiter (TGO), providing observations in the nadir, limb, and solar occultation modes since April 2018. UVIS, a single spectrometer unit within NOMAD spans the ultraviolet-visible range between 200 nm and 650 nm. It obtained ~ 4000 vertically resolved (< 1 km) solar occultation observations of the martian atmosphere for over a full Mars year (MY, 687 days) starting at MY 34 during late northern summer at L<sub>s</sub> = 163°. Ozone (O<sub>3</sub>), a principal component of the martian atmosphere, is highly responsive to the incoming UV flux, and is a sensitive tracer of the odd hydrogen chemistry. Transmittance spectra returned by UVIS sampled the O<sub>3 </sub>Hartley band around 250 nm and provided unique insights into understanding the vertical, latitudinal and temporal behavior of O<sub>3</sub>. UVIS detected a high-altitude peak of O<sub>3 </sub>between 40 and 60 km that is mostly persistent between L<sub>s</sub> = 340° and ~ 200° at polar latitudes, and is found to be highly dependent on latitude and season. We will present high-resolution results tracking the vertical, latitudinal, diurnal and seasonal evolution of the secondary peak of ozone for a full Mars year. In comparison, we will also provide O<sub>3</sub> simulations from the GEM-Mars General Circulation Model (GCM) with the purpose of shedding light into understanding the photochemical processes that lead to the presence and disappearance of the high-altitude peak of atmospheric ozone. </p>


2020 ◽  
Vol 231 ◽  
pp. 117533
Author(s):  
Georgia Methymaki ◽  
Elissavet Bossioli ◽  
John Kalogiros ◽  
Giorgos Kouvarakis ◽  
Nikolaos Mihalopoulos ◽  
...  

2020 ◽  
Author(s):  
Lei Cai ◽  
Anita Kullen ◽  
Yongliang Zhang ◽  
Tomas Karlsson ◽  
Andris Vaivads

<p>High-latitude dayside aurora (HiLDA) are large-scale discrete arcs or spot-like aurora poleward of the cusp, observed previously in the northern hemisphere by the Viking UV imager [Murphree et al., 1990] and by the IMAGE FUV [Frey et al., 2003]. The particular interest on HiLDA is to understand its formation related to the dayside reconnection and the resulted field-aligned currents (FACs) configuration in the polar cap (open field line region). In addition, the occurrence of HiLDA in the southern hemisphere is not well known.</p><p>In this study, we investigate the properties of HiLDA using DMSP/SSUSI images from the satellites F16, F17, F18, and F19. The combined data with auroral images from DMSP/SSUSI, ion drift velocity from SSIES, magnetic field perturbations from SSM, and energetic particle spectrum from SSJ make it possible to study the electrodynamics in the vicinity of the HiLDA and its connection the dayside cusp. HiLDA is formed due to monoenergetic electron precipitation (inverted-V structures) with the absence of ion precipitation. The field-aligned potential drop can be up to tens of keV. Applying the current-voltage relation, we suggest accelerated polar rain as the source of HiLDA, indirectly controlled by the solar wind/magnetosheath plasma population. The upward field-aligned current associated with the potential drop is a part of the cusp current system, produced by the dayside reconnection. Both lobe reconnection and reconnection on the duskside flanks play a role in the formation of HiLDA.</p><p>The occurrence of HiLDA is highly associated with the sunlit hemisphere and IMF By dominated conditions. Our results agree with previous observations, which show that HiLDA occurs during positive By dominated conditions in the northern summer hemisphere. We also confirmed that HiLDA occurs during negative By dominated conditions in the southern hemisphere. In addition, the fine structures of HiLDA are studied.</p><p>References</p><p><span>Murphree, J. S.</span>, <span>Elphinstone, R. D.</span>, <span>Hearn, D.</span>, and <span>Cogger, L. L.</span> ( <span>1990</span>), <span>Large‐scale high‐latitude dayside auroral emissions</span>, <em>J. Geophys. Res.</em>, <span>95</span>( <span>A3</span>), <span>2345</span>– <span>2354</span>, doi:.</p><p><span>Frey, H. U.</span>, <span>Immel, T. J.</span>, <span>Lu, G.</span>, <span>Bonnell, J.</span>, <span>Fuselier, S. A.</span>, <span>Mende, S. B.</span>, <span>Hubert, B.</span>, <span>Østgaard, N.</span>, and <span>Le, G.</span> ( <span>2003</span>), <span>Properties of localized, high latitude, dayside aurora</span>, <em>J. Geophys. Res.</em>, <span>108</span>, 8008, doi:, <span>A4</span>.</p>


2020 ◽  
Author(s):  
Marcin Pilinski ◽  
Laila Andersson ◽  
Ed Thiemann

<p>The MAVEN satellite has now made two Martian-years of ionosphere-thermosphere (I-T) observations enabling limited studies of seasonal changes in the upper atmosphere. Before examining the ionospheric dynamics associated with space weather, we wish to understand the climatological conditions of the system.  For example, previous studies have revealed the morning electron temperature overshoot as well as a close dependence between electron temperatures and neutral densities in the equatorial regions. In this presentation, we will examine differences in the northern and southern dayside ionosphere during the summer season of each hemisphere. The differences between these two cases will be contrasted with the seasonal dependence at the equator. Differences between the equatorial and polar regions are expected due to (A) differences in neutral scale heights, (B) differences in the solar zenith angle, and (C) the equilibration of I-T coupling due to differences in solar illumination.</p><p>In this work, we present a statistical analysis of MAVEN measurements comparing the north and south summer I-T. We find that when controlling for neutral pressure and latitude, the north and south plasma densities and temperatures are nearly identical below the demagnetization altitude (higher neutral pressures). Above the demagnetization altitude (lower neutral pressures), the southern hemisphere electron densities are higher than those in the northern hemisphere by ~100%. A significantly lower electron temperature is also observed in the south at these lower pressures. Given that the difference in solar EUV (and corresponding neutral heating) is ~20% between the two summer seasons, we postulate that the significantly lower plasma densities (above the demagnetization altitude) in the northern summer are due in part to an increase in ionospheric loss. This loss may be associated with the acceleration of ionospheric particles by the draped magnetic fields at an altitude where ions are not demagnetized. Furthermore, the loss may be diminished in the southern hemisphere where crustal magnetic fields increase the standoff distance to the solar wind magnetic field.</p>


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