Dynamical effects of solar heating below the cloud layer in a Venus‐like atmosphere

Abstract

[1] The dynamics of Venus' lower-atmospheric superrotation remain an open issue. In the present study, we investigate the sensitivity of the superrotation to diabatic heating rate below the cloud layer using a simplified GCM. A fully developed superrotation fails to develop in the lower atmosphere under the condition with a fairly low diabatic heating below the cloud layer, as is thought to be realistic. Additional radiative forcing in the lower atmosphere and/or eddy momentum source should be considered to produce lower-atmospheric superrotation. The diabatic heating rate below the cloud layer controls the formation of the multiple superrotation states (slow, fast, and extremely fast superrotations). Small changes in the weak lower-atmospheric heating lead to drastic changes of the middle-and lower-atmospheric superrotation.Citation: Yamamoto, M., and M. Takahashi (2009), Dynamical effects of solar heating below the cloud layer in a Venus-like atmosphere,

Decadal variations in a Venus general circulation model

“…More recent GCMs incorporating a simplified Newtonian cooling type radiation scheme (Yamamoto and Takahashi, 2003a,b, 2004, 2006Lee et al, 2005Lee et al, , 2007Herrnstein and Dowling, 2007;Hollingsworth et al, 2007) produce superrotating winds with magnitudes closer to those measured. However, unrealistically large solar heating rates in the lower atmosphere of Venus compared with the measured heating (Tomasko et al, 1980) had to be used to produce zonal wind magnitudes similar to those observed (Hollingsworth et al, 2007;Yamamoto and Takahashi, 2009). Calculations by Lebonnois et al (2010) with realistic radiative transfer produce superrotation above around 40 km altitude, with wind magnitudes around 60-70% of those observed in cloud tracking data (Del Genio and ) and comparable to those found in probe measurements (Schubert et al, 1980;Schubert, 1983).…”

Planetary Atmospheres

“…Attempts to model superrotation on Venus have been made with varying degrees of success, and models that work have generally assumed background superrotation below the cloud base (e.g., Del Genio and Zhou, 1996;Hollingsworth et al, 2007;Lebonnois et al, 2010;Yamamoto and Takahashi, 2009). The waves near the superrotating level on Venus may be atmospheric tides (Newman and Leovy, 1992).…”

Wind‐induced equatorial bulge in Venus and Titan general circulation models: Implication for the simulation of superrotation

“…rial bulge can be compensated otherwise, e.g., by excessive diabatic forcing as shown by some Venus GCMs [Hollingsworth et al, 2007;Yamamoto and Takahashi, 2009;Lebonnois et al, 2010]. However, since quasihydrostatic or nonhydrostatic GCMs could reproduce realistic superrotation with weaker radiative forcing than would be required for hydrostatic GCMs, the meridional circulation may be weaker than predicted by hydrostatic GCMs, which reproduce realistic superrotation possibly at the cost of exaggerated heating/cooling.…”

“…Most Venus and Titan GCMs utilize dynamical cores that are based on the hydrostatic primitive equations, the notable exceptions being the nonhydrostatic GCM of Mingalev et al [2006Mingalev et al [ , 2012. Hydrostatic Venus GCMs underestimate the magnitude of the superrotation if the models are run with realistic diabatic forcing, but the superrotation becomes more realistic if an excessive diabatic forcing is assumed below the cloud level [Hollingsworth et al, 2007;Yamamoto and Takahashi, 2009;Lebonnois et al, 2010], although there is also significant model dependency. The magnitude of the stratospheric zonal wind predicted by Titan GCMs is strongly model dependent and highly sensitive to model parameters, ranging from weak subrotation to strong superrotation [Hourdin et al, 1995;Tokano et al, 1999;Friedson et al, 2009;Newman et al, 2011;Lebonnois et al, 2012a].…”