The Role of Diabatic Heating on the Co-Variability of Finite-Amplitude Wave Activity and Zonal Index with Implications in a Changing Climate

Water vapor profoundly shapes our basic climate and its response to climate forcings. In mid-latitude troposphere, the radiative forcing from water vapor is roughly one third of the total solar radiation received at the ground. Idealized atmospheric dry models parameterize the radiation effects by linearly relaxing the temperature profile toward a "radiative equilibrium state" profile (Held and Surarez 1994). However, such a dry model lacks an important interactive diabatic heating that is due to the condensation of water vapor. On synoptic timescale, the diabatic heating in fact strongly interacts with the dry dynamics, shaping up a very different co-variability of atmospheric waves and mean flow compared to that in a dry model. The co-variability's intrinsic timescale is an important indicator for estimating climate sensitivity in light of the Fluctuation-Dissipation Theorem (Leith 1975), but the long-standing puzzle is that the observed decorrelation timescale of Annular Mode is substantially smaller than that in a dry atmosphere, hinting a possible negative feedback may exist in a moist atmosphere. In this presentation, we will introduce a new zonal momentum - finite-amplitude wave activity framework, in which the role of diabatic heating is explicitly incorporated and accurately quantified. We depict the mid-latitude wave-mean flow interaction through this zonal momentum-wave activity cycle. We will demonstrate a robust negative diabatic eddy feedback to the zonal index in a hierarchy of idealized GCMs and reanalysis products. This negative feedback is achieved through the changes in finite-amplitude wave activity and eddy forcing. We will discuss this negative feedback's possible role in the magnitude of the jet shift in a warming climate by extracting the interactive diabatic eddy feedback from a grey-radiation AGCM (Frierson et al. 2006). We will also discuss a further implication for the climate sensitivity that arises from the strong interactions between synoptic atmospheric waves and moisture's diabatic heating.