A warm layer in Venus' cryosphere and high-altitude measurements of HF, HCl, H2O and HDO

Abstract

Venus has thick clouds of H2SO4 aerosol particles extending from altitudes of 40 to 60 km. The 60-100 km region (the mesosphere) is a transition region between the 4 day retrograde superrotation at the top of the thick clouds and the solar-antisolar circulation in the thermosphere (above 100 km), which has upwelling over the subsolar point and transport to the nightside. The mesosphere has a light haze of variable optical thickness, with CO, SO2, HCl, HF, H2O and HDO as the most important minor gaseous constituents, but the vertical distribution of the haze and molecules is poorly known because previous descent probes began their measurements at or below 60 km. Here we report the detection of an extensive layer of warm air at altitudes 90-120 km on the night side that we interpret as the result of adiabatic heating during air subsidence. Such a strong temperature inversion was not expected, because the night side of Venus was otherwise so cold that it was named the 'cryosphere' above 100 km. We also measured the mesospheric distributions of HF, HCl, H2O and HDO. HCl is less abundant than reported 40 years ago. HDO/H2O is enhanced by a factor of approximately 2.5 with respect to the lower atmosphere, and there is a general depletion of H2O around 80-90 km for which we have no explanation.

Photolysis of sulphuric acid as the source of sulphur oxides in the mesosphere of Venus

“…The unexpected warm layer on the night side at about 90 km was detected by SPICAV and is believed to be the result of adiabatic heating by downwelling motion on the night side 11 . The aerosol particles would evaporate when transported by winds to the night side.…”

“…In this study, we adopt the temperature profile measured in orbit 104 at latitude 4° S and local time 23:20 h (black curve in the Fig. 1 of Bertaux et al 11 ). This temperature profile has a peak value about 234K around 97km which is larger than the other measurements [22][23][24][25] by 40-50 K. We applied a scaling factor to the saturation ratio on the night time H 2 SO 4 SVP profile above 90 km for the sensitivity study.…”

Venus Atmospheric Thermal Structure and Radiative Balance

“…SPICAV worked in three different geometries, nadir, solar and stellar occultation. In the stellar occultation mode, the ultraviolet channel was particularly well suited to measure the vertical profiles of CO 2 local density, temperature, SO 2 , SO, clouds and aerosols of Venus upper atmosphere from 90 to 140 km (Bertaux et al 2007b;Montmessin et al 2011).…”

“…Kasprzak et al (1997) have previously discussed the neutral composition, thermal structure, dynamics and effects of the solar activity and Marcq et al (2018) present an update on the composition and chemistry of the neutral atmosphere. Since then, the SOIR infrared Nevejans et al 2006) and SPICAV-UV (Bertaux et al 2007a(Bertaux et al , 2007b spectrometers, the aerobraking experiment VEXADE (Müller-Wodarg et al 2006) and the torque experiment (Persson 2015;Rosenblatt et al 2012) of the Venus Express mission focused on studying the composition, mass density and temperature structure of the thermosphere. Ground based campaigns also collected observations during the spacecraft observation periods such as the ones from the THIS heterodyne spectrometer (Sonnabend et al 2012).…”

Optical and radiometric models of the NOMAD instrument part II: the infrared channels - SO and LNO

“…The design of the SO channel has been inspired by the existing spectrometer, SOIR [2], which was part of the SPICAV/SOIR spectrometers' suite [3] on board Venus-Express [4]. The SO channel has been optimized for solar occultation observations, i.e.…”