Influence of Storm Relative Flow (SRF) on Intensity Change of Tropical Cyclones

In this study, the influence of storm relative flow (SRF) on intensity change of tropical cyclones (TCs) has been examined based on the JTWC best track data of tropical cyclones over the western North Pacific and the ERA-Interim reanalysis data. The results are also compared with the traditionally defined environmental vertical wind shear (VWS). Composite analysis centered on each of the individual TCs reveals that the correlations between the intensity change and VWS vary with season and are the lowest in August and the highest in October. In sharp contrast, the correlations between the intensity change and and SRFs at different levels are much less dependent on seasons. SRFs at 200 to 400 hPa averaged within a radius of 5° in the TC-filtered fields have the highest correlation with the following 24-h intensity change. This implies that the upper-level SRF may be a better indication of TC intensity change than the traditionally used vector wind difference between 200 and 850 hPa. Results from idealized numerical experiments using the multiply nested nonhydrostatic TC model TCM4 generally confirm the results from the statistical analyses and also provide a basis for understanding the physical mechanisms behind the statistics. Details will be presented at the conference.