The Coupling of Mixed Rossby-Gravity Waves with Diabatic Heating

Convection plays a key role in the excitation and maintenance of the equatorial atmospheric waves, which are the fundamental building blocks of tropical weather and climate. Current numerical models still cannot simulate many aspects of these waves accurately. The challenge lies in the lack of understanding and proper formulation of how parameterized diabatic heating is coupled with wave dynamics.

We present an analysis of the diabatic heating and its coupling with mixed Rossby-gravity waves (MRG) dynamics by using data from the the TRMM-KWAJEX field campaign. A significant departure of the convectively coupled MRG waves from the dry waves is the existence of a wave phase in which the maximum low-level wind convergence is accompanied by mid-tropospheric divergence and upper-tropospheric convergence. This phase is shown to correspond to shallow and mid-level convections, resulting in moistening and heating of the lower and middle troposphere. This phase is followed by deep convection with the maximum heating centered in the upper troposphere. The upper tropospheric heating evolves to stratiform-like heating with low-tropospheric cooling that precedes the quick demise of convection. Near-surface moisture then gradually builds up from turbulence to pre-condition the next wave cycle. A schematic structure is constructed to describe the waves in four phases. Results shed lights on the physical processes of how tropical waves are maintained and point to directions where numerical models should be improved to correctly simulate these waves. >