THE COLD-CORE TEMPERATURE STRUCTURE IN A TROPICAL EASTERLY WAVE

The purpose of this study is to identify what effects are responsible for the observed temperature field, in particular the lower-level cold core, in the trough region of a convectively active tropical easterly wave disturbance. GATE Phase III A/B- and B-scale data were used in t he analysis, and the divergence equation, a first-order balance condit ion proposed by Cho and Jenkins applicable to slowly evolving or near- steady-state large-scale convectively active tropical circulation syst ems, and the standard nonlinear and linear balance equations were chos en as the framework in which to assimilate the observational data in o rder to understand the spatial anticorrelation between temperature cha nges and latent heating. It is shown that all three balance conditions reproduced the thermal structure of the easterly waves that passed ov er GATE during Phase III. Despite the differences in formulation and f orm, the simpler standard balance equations were as accurate as the fi rst-order divergence equation in diagnosing the temperature field. The central result of the analysis is that the lower cold-core temperatur e anomaly observed in the near-trough region of easterly wave disturba nces is not a direct consequence of the distribution of latent hear re leased by cumulus clouds, but reflects instead a balance of forces tha t dominate the momentum field and that the agreement between the obser ved and diagnosed temperature fields is dominated by the rotational co mponent of the flow. This has possible implications for a first-order model of the interaction between cumulus-scale and large-scale equator ial wave motions, and for the distinction between developing and nonde veloping easterly waves in terms of the ambient vorticity field, which may aid future numerical investigations of tropical cyclogenesis.