Planetary atmosphere observation analysis

Abstract:

Atmospheric Waves Workshop; Noordwijk, Netherlands, 9-10 November 2011 Experts in observations and modeling of atmospheric waves from the Earth and planetary atmospheric science communities came together at a November 2011 workshop held at the European Space Agency's (ESA) European Space Research and Technology Centre (ESTEC) site in the Netherlands to discuss the nature of waves observed in Venus's atmosphere and their comparison to those on Earth and Mars. ESA's Venus Express (VEx) satellite and ground-based observers find atmospheric waves at many scales. Migrating solar tides and other planetary-scale waves are observed in cloud-tracking wind vectors and temperature fields. Mesoscale gravity waves (GWs) can also be seen at a variety of levels from the cloud base up to the thermosphere, evident in imagery and in vertical profiles of temperature, density, and aerosol abundance. This workshop focused particularly on GWs, as their role in the atmospheric circulation is still poorly understood. © 2012 American Geophysical Union. All Rights Reserved.

Abstract:

Thunderstorm activity has been observed on Saturn via radio emissions from lightning discharges and optical detections of the lightning flashes on the planets nightside. Thunderstorms provide extreme environments in which specific atmospheric chemistry can be induced - namely through energy release via lightning discharges, and fast vertical transport resulting in rapid advection of tropospheric species. It is thus theorised that certain atmospheric trace species such as C 2H 2, HCN, and CO can be generated in the troposphere by large bursts of energy in the form of lightning, and transported upward towards the upper troposphere by the extreme dynamics of thunderstorms, where they should be observable by satellite instruments. In this work, high-spectral-resolution Cassini/CIRS observations from October 2005 through April 2009 are used to study whether there is an observable increase in upper tropospheric acetylene in regions of known normal thunderstorm activity. Using both individual measurements in which there is known thunderstorm activity, as well as large coadditions of data to study latitudinal-dependencies over the full disc, no systematic enhancement in upper tropospheric (100 mbar) C 2H 2 was detected around regions in which there are known occurrences of normally sized (2000 km) thunderstorms, or in normally sized thunderstorm-prone regions such as 40°S. It is likely that the magnitude of the enhancement theorised is too generous or that enhancements are not advected into the upper troposphere as vertical mixing rates in models would suggest, since Cassini/CIRS can only detect C 2H 2 above the 200 mbar level - although the massive northern hemisphere thunderstorm of 2010/2011 seems able to decrease stratospheric concentrations of C 2H 2. From this, it can be asserted that lightning from normal thunderstorm activity cannot be the key source for upper tropospheric C 2H 2 on Saturn, since the upper-tropospheric concentrations retrieved agree with the concentrations stemming from the photolysis of CH 4 (23 ppbv) from solar radiation penetrating through the Saturnian atmosphere, with an upper limit for lightning-induced C 2H 2 volume mixing ratio of 10 -9. © 2012 Elsevier Ltd. All rights reserved.

Abstract:

The existence of methane in Titan's atmosphere (∼6% level at the surface) presents a unique enigma, as photochemical models predict that the current inventory will be entirely depleted by photochemistry in a timescale of ∼20Myr. In this paper, we examine the clues available from isotopic ratios (12C/13C and D/H) in Titan's methane as to the past atmosphere history of this species. We first analyze recent infrared spectra of CH4 collected by the Cassini Composite Infrared Spectrometer, measuring simultaneously for the first time the abundances of all three detected minor isotopologues: 13CH4, 12CH3D, and 13CH3D. From these we compute estimates of 12C/13C= 86.5 ± 8.2 and D/H= (1.59 ± 0.33) × 10-4, in agreement with recent results from the Huygens GCMS and Cassini INMS instruments. We also use the transition state theory to estimate the fractionation that occurs in carbon and hydrogen during a critical reaction that plays a key role in the chemical depletion of Titan's methane: CH4+ C2H→ CH3+ C2H2. Using these new measurements and predictions we proceed to model the time evolution of 12C/13C and D/H in Titan's methane under several prototypical replenishment scenarios. In our Model1 (no resupply of CH4), we find that the present-day 12C/13C implies that the CH4 entered the atmosphere 60-1600Myr ago if methane is depleted by chemistry and photolysis alone, but much more recently - most likely less than 10Myr ago - if hydrodynamic escape is also occurring. On the other hand, if methane has been continuously supplied at the replenishment rate then the isotopic ratios provide no constraints, and likewise for the case where atmospheric methane is increasing. We conclude by discussing how these findings may be combined with other evidence to constrain the overall history of the atmospheric methane. © 2012 The American Astronomical Society. All rights reserved.

Abstract:

The European Venus Explorer (EVE) mission described in this paper was proposed in December 2010 to ESA as an 'M-class' mission under the Cosmic Vision programme. It consists of a single balloon platform floating in the middle of the main convective cloud layer of Venus at an altitude of 55 km, where temperatures and pressures are benign (~25°C and ~0. 5 bar). The balloon float lifetime would be at least 10 Earth days, long enough to guarantee at least one full circumnavigation of the planet. This offers an ideal platform for the two main science goals of the mission: study of the current climate through detailed characterization of cloud-level atmosphere, and investigation of the formation and evolution of Venus, through careful measurement of noble gas isotopic abundances. These investigations would provide key data for comparative planetology of terrestrial planets in our solar system and beyond. © 2011 Springer Science+Business Media B.V.