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Quasi-geostrophic (QG) theory describes the dynamics of synoptic scale flowsin the trophosphere that are balanced with respect to both acoustic andinternal gravity waves. Within this framework, effects of (turbulent) frictionnear the ground are usually represented by Ekman Layer theory. The tropospherecovers roughly the lowest ten kilometers of the atmosphere while Ekman layerheights are typically just a few hundred meters. However, this two-layerasymptotic theory does not explicitly account for substantial changes of thepotential temperature stratification due to diabatic heating associated withcloud formation or with radiative and turbulent heat fluxes, which, in themiddle latitudes, can be particularly important in about the lowest threekilometers. To address this deficiency, this paper extends the classicalQG-Ekman layer model by introducing an intermediate, dynamically andthermodynamically active layer, called the "diabatic layer" (DL) from here on.The flow in this layer is also in acoustic, hydrostatic, and geostrophicbalance but, in contrast to QG flow, variations of potential temperature arenot restricted to small deviations from a stable and time independentbackground stratification. Instead, within the diabatic layer, diabaticprocesses are allowed to affect the leading-order stratification. As aconsequence, the diabatic layer modifies the pressure field at the top of theEkman layer, and with it the intensity of Ekman pumping seen by thequasi-geostrophic bulk flow. The result is the proposed extendedquasi-geostrophic three-layer QG-DL-Ekman model for mid-latitude (dry andmoist) dynamics.

QG-DL: Dynamics of a diabatic layer in the quasi-geostrophic framework