Thermal structure of the Venusian atmosphere from the sub-cloud region to the mesosphere as observed by radio occultation

Hideo Sagawa,Bernd Häusler,Raj Kumar Choudhary,Yoshihisa Matsuda,Martin Pätzold,Sanjay Limaye,Norihiko Sugimoto,Masahiro Takagi,Hiroki Ando,Maria Antonita,Takeshi Imamura,Silvia Tellmann

doi:10.1038/s41598-020-59278-8

Abstract

We present distributions of the zonal-mean temperature and static stability in the Venusian atmosphere obtained from Venus Express and Akatsuki radio occultation profiles penetrating down to an altitude of 40 km. At latitudes equatorward of 75°, static stability derived from the observed temperature profiles is consistent with previous in-situ measurements in that there is a low-stability layer at altitudes of 50–58 km and highly and moderately stratified layers above 58 km and below 50 km, respectively. Meanwhile, at latitudes poleward of 75°, a low-stability layer extends down to 42 km, which has been unreported in analyses of previous measurements. The deep low-stability layer in the polar region cannot be explained by vertical convection in the middle/lower cloud layer, and the present result thus introduces new constraints on the dynamics of the sub-cloud atmosphere. The Venusian atmosphere is in striking contrast to the Earth’s troposphere, which generally has a deeper low-stability layer at low latitudes than at mid- and high latitudes.

Highlights

We present distributions of the zonal-mean temperature and static stability in the Venusian atmosphere obtained from Venus Express and Akatsuki radio occultation profiles penetrating down to an altitude of 40 km
The thermal structure of the Venusian atmosphere across this cloud layer is important in terms of understanding aspects of the general circulation, such as the mean meridional circulation and baroclinic instability waves, which contribute to meridional heat transport and atmospheric super-rotation
The static stability is high above ~60 km, especially around the upper half of the cold collar and the lower half of the warm polar regions, which is consistent with the radio occultation measurements of Venus Express[4,12]

Summary

Introduction

We present distributions of the zonal-mean temperature and static stability in the Venusian atmosphere obtained from Venus Express and Akatsuki radio occultation profiles penetrating down to an altitude of 40 km. One of the most useful methods of obtaining vertical temperature profiles, were made as part of the National Aeronautics and Space Administration’s (NASA’s) Pioneer Venus mission and the European Space Agency’s (ESA’s) Venus Express mission[2,3,4] to obtain latitude–height distributions of temperature These observations revealed that a cold latitudinal band called a “cold collar”, which is thought to be formed by dynamics[5] and/or the latitudinal cloud structure[6], is located at roughly 65° latitude near the cloud top (at nearly 65 km altitude) and surrounds a warm polar region and that temperature increases with latitude above 65 km and decreases with latitude below 60 km. The present study investigated the thermal structure of the Venusian atmosphere using temperature profiles obtained by ESA’s Venus Express and Japan Aerospace eXploration Agency’s (JAXA’s) Akatsuki radio occultation measurements to highlight the latitude–height distributions of the temperature and static stability in the cloud regions. Dependencies on local time were not considered, temperature and static stability distributions were averaged zonally and temporally for the investigation of latitude–height structures

Methods

Results

Conclusion