Entropy evolution characteristics during an intense tropical cyclone

Abstract

Entropy characteristics are investigated during the tropical cyclone Haiyan (TCH) using the weather research and forecasting (WRF) model in a downscaling experiment with two nests, 18- and 6-km grid spacing. This TC was stronger than most Saffir–Simpson category 5 typhoons. In this research, entropy, air–sea thermodynamic disequilibrium (ASTD) and entropy fluxes (including surface, convective and lateral entropy fluxes) have been analyzed. Scale analysis of these parameters has been done using integrated values over two types of areas including fixed square-ring areas and circular structural-based areas, all surrounding TCH center. The considered parameters (using downscaled data with 6-km grid spacing) integrated over the various areas showed the maximum or minimum value with various lag or lead times, comparing with TCH peak intensity (at 18:00 UTC 07 November, when TCH made landfall in the Philippine Islands). In addition, the multiscale analysis emphasized that entropy transport between different parts of TCH could not be ignored. Most of the considered parameters integrated over the larger areas reached the extremum values before TCH maximum intensity. Integrating over the fixed square areas led to that more parameters got the extremum value before TCH greatest intensity comparing with those integrated over the circular structural-based areas. This indicates that it is unnecessary to focus only on the circular structural-based areas. Conclusively, hierarchy of derived extremum values of entropy and its derivations over the various scales (especially those integrated over the fixed square areas) showed that this parameter could be served as a relevant proxy parameter and its evolution is worthwhile to be considered in TC investigation.