High Rayleigh number compressible convection in Venus' atmosphere: Penetration, entrainment, and turbulence

Abstract

Numerical simulations of two‐dimensional, nonlinear fully compressible convection at the subsolar point in the clouds of Venus are presented. One moderate Rayleigh number case (Raq= 6.8 × 106) and two high Rayleigh number (Raq= 1.1 × 109) cases are considered. Cloud‐level convection is characterized by cold, narrow downwellings that deeply penetrate the underlying stable layer and that entrain warmer air from the overlying stable layer. The convection layer depth, as determined from the horizontally averaged static stability, spans 9 km (47–56 km altitude) and 14 km (46–60 km altitude) for the moderate Rayleigh number and high Rayleigh number simulations, respectively. In the high Rayleigh number cases, convective penetration extends over a scale height from the bottom of the convection layer down to 38 km altitude. Strong convective entrainment completely erodes the overlying stable layer in the highRaqcases and incorporates it into the convection layer. The timescale for entrainment of the overlying stable layer is roughly 1 day and may explain why cellular features are predominantly found near and downwind of the subsolar point. The high Rayleigh number simulations are convectively turbulent and exhibit a spectral energy cascade ofk−3, wherekis the horizontal wavenumber. Our results suggest that cellular features in the subsolar region are observed at the cloud tops because convection may extend to much higher altitudes there. Downward penetrative convection may also be responsible for turbulence observed in Venus' atmosphere at 45 km altitude.