Planetary atmosphere observation analysis

Abstract:

High spectral resolution observations of Venus were obtained with the TEXES instrument at NASA’s Infrared Telescope Facility. These observations focus on a CO2 absorption feature at 791.4 cm-1 as the shape of this absorption feature can be used to retrieve the vertical temperature profile in Venus’ mesosphere. By scan-mapping the planet, we are able to build up three-dimensional temperature maps of Venus’ atmosphere, covering one Earth-facing hemisphere and an altitude range of 60–83 km. A temperature map from February 12, 2019 clearly shows the three-dimensional structure of a planetary-scale thermal wave. This wave pattern appears strongest in the mid-latitudes of Venus, has a zonal wavenumber of 2–4 and the wave fronts tilt eastward with altitude at an angle of 8–15 degrees per km. This is consistent with a thermal tide propagating upwards from Venus’ upper cloud decks. Ground-based observations provide the opportunity to study Venus’ temperature structure on an ongoing basis.

Abstract:

The temperature structure of Titan's upper atmosphere exhibits large variability resulting from numerous spatially and temporally irregular external energy sources, seasonal changes, and the influence of molecular species produced via photochemistry. In particular, Titan's relatively abundant HCN is thought to provide substantial cooling to the upper atmosphere through rotational emission, balancing UV/EUV heating, and thermal conduction. Here we present the analysis of ALMA observations of Titan from 2012, 2014, 2015, and 2017, corresponding to planetocentric solar longitudes of ∼34°–89°, including vertical HCN and temperature profiles retrieved from the lower mesosphere through the thermosphere (∼350–1200 km; 3 × 10−2–2 × 10−8 mbar). Throughout the atmosphere, temperature profiles differ by 10 to 30 K between observations approximately 1 Earth yr apart, particularly from 600 to 900 km. We find evidence for a large imbalance in Titan's upper atmospheric energy budget between 2014 and 2015, where the mesospheric thermal structure changes significantly and marks the transition between a mesopause located at ∼600 km (2 × 10−4 mbar) and ∼800 km (3 × 10−6 mbar). The retrieved HCN abundances vary dramatically during the 2012–2017 time period as well, showing close to 2 orders of magnitude difference in abundance at 1000 km. However, the change in HCN abundance does not appear to fully account for the variation in mesospheric temperatures over the LS ∼ 34°–89° period. These measurements provide additional insight into the variability of Titan's mesospheric composition and thermal structure following its 2009 vernal equinox and motivate continued investigation of the origins of such rapid changes in Titan's atmosphere throughout its seasonal cycle.

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.