Inverse insolation dependence of Venus’ cloud-level convection

• The dependence of the vigor of cloud-level convection on solar flux is studied.
• 2-D convection model is used to examine physical processes.
• The vigor of convection should be enhanced in high latitudes and on the nightside.
• Long radiative timescale of the lower atmosphere is essential to this relationship.

It is generally accepted that convection in planetary atmospheres is enhanced in low latitudes and in the daytime where incoming solar radiation is intense. Here we demonstrate, using a local convection model, that this tendency is reversed for Venus’ cloud-level convection, which is driven by heating of the cloud base by upwelling infrared radiation. The dense lower atmosphere of Venus serves as a heat reservoir, whose temperature is horizontally well homogenized by large-scale dynamics, and thus upwelling infrared flux heats the cloud base almost equally over the entire planet. Since solar radiation preferentially heats the upper part of the cloud and has a stabilizing influence on the atmosphere, convection is relatively suppressed in low latitudes and in the daytime. The inverse insolation dependence seen in the numerical model explains observations of the latitudinal dependence of the convective layer depth and the gravity wave activity. The mechanism suggested in this study should be taken into account in climate modeling of Venus and cloudy exoplanets. How the combination of the opposite effects of the infrared heating and the solar heating determines the global distribution of the convective activity is an issue of universal importance. A long-lifetime Venus balloon floating at cloud heights would be useful for understanding these dynamical processes and the associated material transport.

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