Evaluation of new radio occultation observations among small satellites at Venus by data assimilation

TL;DR

This study uses data assimilation experiments to evaluate the effectiveness of radio occultation observations from small satellites for studying Venus's polar atmosphere, demonstrating improved cold collar reproduction.

Contribution

It introduces a method to assess observation strategies for Venus missions using OSSEs, highlighting the advantages of radio occultation over infrared imaging.

Findings

Radio occultation observations effectively reproduce Venus's cold collar.

High-latitude temperature observations twice daily improve atmospheric structure modeling.

Infrared camera observations were less effective and appeared unrealistic.

Abstract

We conducted observing system simulation experiments (OSSEs) for radio occultation measurements (RO) among small satellites, which are expected to be useful for future Venus missions. The effectiveness of the observations based on realistic orbit calculations was evaluated by reproduction of the "cold collar", a unique thermal structure in the polar atmosphere of Venus. Pseudo-temperature observations for the OSSEs were provided from the Venus atmospheric GCM in which the cold collar was reproduced by the thermal forcing. The vertical temperature distributions between 40 and 90 km altitudes at observation points were assimilated. The result showed that the cold collar was most clearly reproduced in the case where the temperature field in high-latitudes was observed twice a day, suggesting that the proposed observation is quite effective to improve the polar atmospheric structure at least. Although the cold collar was also reproduced in the OSSEs for Longwave Infrared Camera (LIR) observations, the result seemed unrealistic and inefficient compared to that obtained in the RO OSSEs. The present study shows that the OSSEs can be used to evaluate observation plans and instruments in terms of reproducibility of specific atmospheric phenomena, and applied to future missions targeting planetary atmospheres.