Detection of layering in the upper cloud layer of Venus northern polar atmosphere observed from radio occultation data

Abstract

Observations of radio wave scintillations represent an important tool for measuring of small‐scale irregularities in the atmosphere of Venus. Prominent features of enhanced scintillation located in the 60‐km region were observed in Mariners 5 and 10, Venera 9, and Pioneer Venus occultations. It is possible that the enhanced scintillations are due to the random turbulence in the upper region which is caused by trapped small‐scale gravity waves. However, other interpretations are possible. Thin stable layers, which are commonly observed in the Earth stratosphere under cloud‐free conditions, could also contribute to scattering in the Venus stratosphere. If scintillations observed in different occultations are correlated, then these scintillations may be attributed to the persistent layers. Cross correlations of 32‐cm radio wave amplitude fluctuations have been determined for seven radio occultation measurements of Venus's northern polar atmosphere using Venera 15 and 16. Significant cross correlations were found between 59.0 and 61.5 km in four different radio occultations. Layering is revealed in the upper layer of the Venus clouds at altitudes of 59.0–61.5 km, which is specified by enhanced turbulence of the atmosphere. It is found that the lifetime of the small‐scale layered irregularities is 2 d or more and that their horizontal extension in the meridional direction can exceed 180 km. A possible cause of emergence of the layered structures inside the upper layer of polar clouds of Venus is discussed.