Satellite derived upper ocean thermal structure and its application to tropical cyclone intensity forecasting in the Indian Ocean

Abstract

Upper ocean heat content is a factor critical to the intensity change of tropical cyclones (TCs). Because of the inhomogeneity of in situ observations in the North Indian Ocean, gridded temperature/salinity (T/S) profiles were derived from satellite data for 1993–2012 using a linear regression method. The satellite derived T/S dataset covered the region of 10°S–32°N, 25°–100°E with daily temporal resolution, 0.25°×0.25° spatial resolution, and 26 vertical layers from the sea surface to a depth of 1 000 m at standard layers. Independent Global Temperature Salinity Profile Project data were used to validate the satellite derived T/S fields. The analysis confirmed that the satellite derived temperature field represented the characteristics and vertical structure of the temperature field well. The results demonstrated that the vertically averaged root mean square error of the temperature was 0.83 in the upper 1 000 m and the corresponding correlation coefficient was 0.87, which accounted for 76% of the observed variance. After verification of the satellite derived T/S dataset, the TC heat potential (TCHP) was verified. The results show that the satellite derived values were coherent with observed TCHP data with a correlation coefficient of 0.86 and statistical significance at the 99% confidence level. The intensity change of TC Gonu during a period of rapid intensification was studied using satellite derived TCHP data. A delayed effect of the TCHP was found in relation to the intensity change of Gonu, suggesting a lag feature in the response of the inner core of the TC to the ocean.