Impact of circulation on tropical cloud feedbacks in cloud resolving models
<div> <p>Uncertainty in the response of clouds to warming remains&#160;a significant&#160;barrier to reducing the range in projected&#160;climate sensitivity.&#160;A&#160;key&#160;question is to what extent cloud&#160;feedbacks&#160;can be attributed to changes in circulation, such as&#160;the strengthening or weakening of&#160;ascent&#160;or changes in the areas of&#160;convecting&#160;vs&#160;subsiding air.&#160;Previous research has shown that, in general circulation models (GCMs), the &#8216;dynamic&#8217; component of the cloud feedback &#8211; that which is due to changes in circulation rather than changes in the thermodynamic properties of clouds (Bony et al., 2006)&#160;&#8211;&#160;is&#160;generally small (Byrne and Schneider, 2018).&#160;An open question, however,&#160;is&#160;whether this&#160;extends to&#160;models at cloud resolving resolutions&#160;that explicitly simulate deep convection.&#160;&#160;</p> </div><div> <p>Here, we utilize simulations&#160;from&#160;the Radiative-Convective Equilibrium Model Intercomparison Project (RCEMIP, Wing et al., 2018, 2020)&#160;to quantify the&#160;impact of circulation on tropical cloud&#160;feedbacks.&#160;RCE&#160;is&#160;a&#160;simple&#160;idealisation&#160;of the tropical atmosphere&#160;and&#160;we&#160;focus on&#160;simulations&#160;in a long channel configuration&#160;with&#160;uniform sea surface temperatures&#160;of&#160;295, 300 and 305K.&#160;The dynamic component of the&#160;total cloud feedback is&#160;substantial&#160;for&#160;this&#160;suite of cloud resolving models (CRMs),&#160;and is driven by circulation changes&#160;and nonlinearity in the&#160;climatological&#160;relationship between clouds and circulation. The&#160;large spread&#160;in dynamic&#160;component&#160;across models&#160;is linked to&#160;the extent to which convection&#160;strengthens&#160;and narrows&#160;with&#160;warming.&#160;This strengthening/narrowing of convective regions&#160;is&#160;further&#160;linked to&#160;changes in&#160;clear-sky radiative cooling&#160;and mid-tropospheric static stability&#160;in subsiding regions.&#160;</p> </div><div> <p>&#160;</p> </div>