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The collapse of circulation and the acceleration of upper air superrotation with shortwave optical depth

Fig6-overview.png

When the atmosphere is more opaque to longwaves than to shortwaves (panel a), the ground temperature is higher than the nearby atmosphere in radiative equilibrium. This jump in temperature causes strong meridional circulation near the surface, especially when the rotation effect is weak (e.g. the tropical regions). This circulation fills the entire troposphere with airs that are almost at rest with the surface, and only above the tropopause, when the stratification is strong enough, the zonal wind U can deviate from 0 following the thermal wind balance.

When the atmosphere is more opaque in shortwaves (panel b), the ground temperature becomes lower than the nearby atmosphere in radiative equilibrium, and therefore meridional circulation becomes suppressed. Zonal wind is only close to zero in the boundary layer, and in the free atmosphere, the zonal wind can vary following the thermal wind balance.

Assuming a semi-gray atmosphere, we analytically solve for the radiative equilibrium temperature profile, based on which we attempt to predict the meridional circulation strength following the “Held-2000 scaling” [1], and the equatorial superrotation.

If you are interested, please see our paper for more details.

Kang, W. and R. Wordsworth 2019, Collapse of the general circulation in shortwave-absorbing atmospheres: an idealized model study, Astrophysical Journal Letter, 885:18, doi: 10.3847/2041-8213/ab4c43

 

[1] Held, I. M. (2000), The general circulation of the atmosphere, paper presented at 2000 Woods Hole Oceanographic Institute Geophysical Fluid Dynamics Program, Woods Hole Oceanogr. Inst., Woods Hole, Mass. 

 

 

 

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