Stationary waves and slowly moving features in the night upper clouds of Venus

At the cloud top level of Venus (65-70 km altitude) the atmosphere rotates 60 times faster than the underlying surface, a phenomenon known as superrotation. Whereas on Venus's dayside the cloud top motions are well determined and Venus general circulation models predict a mean zonal flow at the upper clouds similar on both day and nightside, the nightside circulation remains poorly studied except for the polar region. Here we report global measurements of the nightside circulation at the upper cloud level. We tracked individual features in thermal emission images at 3.8 and 5.0 $\mathrm{\mu m}$ obtained between 2006 and 2008 by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS-M) onboard Venus Express and in 2015 by ground-based measurements with the Medium-Resolution 0.8-5.5 Micron Spectrograph and Imager (SpeX) at the National Aeronautics and Space Administration Infrared Telescope Facility (NASA/IRTF). The zonal motions range from -110 to -60 m s$^{-1}$, consistent with those found for the dayside but with larger dispersion. Slow motions (-50 to -20 m s$^{-1}$) were also found and remain unexplained. In addition, abundant stationary wave patterns with zonal speeds from -10 to +10 m s$^{-1}$ dominate the night upper clouds and concentrate over the regions of higher surface elevation.Comment: 15 pages, 4 figures, 6 supplementary figure

Venus Atmospheric Thermal Structure and Radiative Balance

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The Martian daytime convective boundary layer: Results from radio occultation measurements and a mesoscale model

We investigate the behavior of the Martian daytime convective boundary layer (CBL) through a combination of data analysis and modeling. This study relies on two subsets of Mars Express radio occultation (RO) measurements that sounded the atmosphere in north- ern spring of successive Mars years. Only the first year of observations has been examined previously (Hinson et al., 2008); the second year provides complementary spatial coverage and greatly increases the total number of observations. Analysis of the RO profiles yields basic characteristics of the CBL, such as its depth D and the average potential temperature of the mixed layer θm. We also combine RO retrievals of surface pressure with surface tem- peratures from infrared sounding to characterize the surface forcing, expressing the result as a potential temperature θs. These observations are at local times in early afternoon for θs and late afternoon for θm and D, when each parameter is near its diurnal maximum. We use measurements at mid-to-low latitudes, which sample a wide range of θs (227–294 K), to determine the response of the lower atmosphere to spatial variations in surface forcing. The depth of the CBL ranges from less than 3 km in the midlatitude topographic basins to more than 9 km above elevated terrain in the tropics. The dependence of θm on θs is linear, with a characteristic slope of about 0.7 in both years. We gain further insight by performing a simulation with the Oregon State University Mars Mesoscale Model in a region centered on Isidis Planitia, which includes two potential landing sites for the Mars 2020 Rover. As expected from previous modeling of much smaller craters, the arc of steep to- pography along the western and southern margins of Isidis produces a distinctive, diurnally varying, mesoscale circulation. The simulation captures key features of the observations, such as the wide variations in θm and D — by 34 K and 9 km, respectively — that occur within this region. The model also accounts for peculiar features of RO profiles on the rim of Isidis, where the wind field strongly influences the depth and diurnal evolution of the CBL. Detailed comparisons with the observations validate the general performance of the model and confirm several aspects of the simulated wind field

A combined transmission spectrum of the Earth-sized exoplanets TRAPPIST-1 b and c

Three Earth-sized exoplanets were recently discovered close to the habitable zone of the nearby ultracool dwarf star TRAPPIST-1. The nature of these planets has yet to be determined, since their masses remain unmeasured and no observational constraint is available for the planetary population surrounding ultracool dwarfs, of which the TRAPPIST-1 planets are the first transiting example. Theoretical predictions span the entire atmospheric range from depleted to extended hydrogen-dominated atmospheres. Here, we report a space-based measurement of the combined transmission spectrum of the two inner planets made possible by a favorable alignment resulting in their simultaneous transits on 04 May 2016. The lack of features in the combined spectrum rules out cloud-free hydrogen-dominated atmospheres for each planet at 10-$\sigma$ levels; TRAPPIST-1 b and c are hence unlikely to harbor an extended gas envelope as they lie in a region of parameter space where high-altitude cloud/haze formation is not expected to be significant for hydrogen-dominated atmospheres. Many denser atmospheres remain consistent with the featureless transmission spectrum---from a cloud-free water vapour atmosphere to a Venus-like atmosphere.Comment: Early release to inform further the upcoming review of HST's Cycle 24 proposal

Sunlight refraction in the mesosphere of Venus during the transit on June 8th, 2004

Many observers in the past gave detailed descriptions of the telescopic aspect of Venus during its extremely rare transits across the Solar disk. In particular, at the ingress and egress, the portion of the planet's disk outside the Solar photosphere has been repeatedly perceived as outlined by a thin, bright arc ("aureole"). Those historical visual observations allowed inferring the existence of Venus' atmosphere, the bright arc being correctly ascribed to the refraction of light by the outer layers of a dense atmosphere. On June 8th, 2004, fast photometry based on electronic imaging devices allowed the first quantitative analysis of the phenomenon. Several observers used a variety of acquisition systems to image the event -- ranging from amateur-sized to professional telescopes and cameras -- thus collecting for the first time a large amount of quantitative information on this atmospheric phenomenon. In this paper, after reviewing some elements brought by the historical records, we give a detailed report of the ground based observations of the 2004 transit. Besides confirming the historical descriptions, we perform the first photometric analysis of the aureole using various acquisition systems. The spatially resolved data provide measurements of the aureole flux as a function of the planetocentric latitude along the limb. A new differential refraction model of solar disk through the upper atmosphere allows us to relate the variable photometry to the latitudinal dependency of scale-height with temperature in the South polar region, as well as the latitudinal variation of the cloud-top layer altitude. We compare our measurements to recent analysis of the Venus Express VIRTIS-M, VMC and SPICAV/SOIR thermal field and aerosol distribution. Our results can be used a starting point for new, more optimized experiments during the 2012 transit event.Comment: Icarus, in pres

Modeled O 2 nightglow distributions in the Venusian atmosphere

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/96410/1/jgre3128.pd

Transcriptomic profile of host response in Japanese encephalitis virus infection

<p>Abstract</p> <p>Background</p> <p>Japanese encephalitis (JE) is one of the leading causes of acute encephalopathy with the highest mortality rate of 30-50%. The purpose of this study was to understand complex biological processes of host response during the progression of the disease. Virus was subcutaneously administered in mice and brain was used for whole genome expression profiling by cDNA microarray.</p> <p>Results</p> <p>The comparison between viral replication efficiency and disease progression confirms the active role of host response in immunopathology and disease severity. The histopathological analysis confirms the severe damage in the brain in a time dependent manner. Interestingly, the transcription profile reveals significant and differential expression of various pattern recognition receptors, chemotactic genes and the activation of inflammasome. The increased leukocyte infiltration and aggravated CNS inflammation may be the cause of disease severity.</p> <p>Conclusion</p> <p>This is the first report that provides a detailed picture of the host transcriptional response in a natural route of exposure and opens up new avenues for potential therapeutic and prophylactic strategies against Japanese encephalitis virus.</p