Planetary atmosphere observation analysis

Abstract:

The loss of water from Mars to space is thought to result from the transport of water to the upper atmosphere, where it is dissociated to hydrogen and escapes the planet. Recent observations have suggested large, rapid seasonal intrusions of water into the upper atmosphere, boosting the hydrogen abundance. We use the Atmospheric Chemistry Suite on the ExoMars Trace Gas Orbiter to characterize the water distribution by altitude. Water profiles during the 2018–2019 southern spring and summer stormy seasons show that high-altitude water is preferentially supplied close to perihelion, and supersaturation occurs even when clouds are present. This implies that the potential for water to escape from Mars is higher than previously thought.

Abstract:

We present, for the first time, retrievals of the vertical distribution of water vapour from Mars Climate Sounder (MCS) aboard Mars Reconnaissance Orbiter (MRO), an original goal of the mission compromised by channel filter performance issues. To work around this problem a two-stage retrieval has been developed and was applied to MCS observations for MY28 NH summer (L_s=111–173°, 26 September 2006 to 27 January 2007). Retrievals were consistent with observations by other instruments for both column abundances (e.g., peak NH summer column abundance of 70 pr. μm compared with 50 pr. μm in the literature) and vertical profiles. Other key results are nightside vertical profiles of water vapour (retrieved for the first time) and interaction of atmospheric water vapour with the aphelion cloud belt. Seasonal changes in the hygropause (a proxy for condensation level) are reflected in changes in the cloud belt. During late northern summer, when the hygropause level is high at the equator and tropics, the cloudbase is higher (increasing by ≈ 10 km from 25 to 35 km) and the belt is weaker.

Abstract:

Dark spots on Neptune observed by Voyager and the Hubble Space Telescope are thought to be anticyclones with lifetimes of a few years, in contrast with very long-lived anticyclones in Jupiter and Saturn. The full life cycle of any Neptune dark spot has not been captured due to limited temporal coverage, but our Hubble observations of a recent feature, NDS-2018, provide the most complete long-term observational history of any dark vortex on Neptune. Past observations suggest some dark spots meet their demise by fading and dissipating without migrating meridionally. On the other hand, simulations predict a second pathway with equatorward migration and disruption. Our HST observations suggest NDS-2018 is following the second pathway. Some of the HST observations reveal transient dark features with widths of about 4000 to 9000 km, at latitudes between NDS-2018 and the equator. The secondary dark features appeared before changes in the meridional migration of NDS-2018 were seen. These features have somewhat smaller size and much smaller contrast compared to the main dark spot. Discrete secondary dark features of this scale have never been seen near previous dark spots, but global-scale dark bands are associated with several previous dark spots in addition to NDS-2018. The absolute photometric contrast of NDS-2018 (as large as 19%) is greater than previous dark spots, including the Great Dark Spot seen by Voyager. New simulations suggest that vortex internal circulation is weak relative to the background vorticity, presenting a clearly different case from stronger anticyclones observed on Jupiter and Saturn.