Size of tropical cyclones as inferred from ERS-1 and ERS-2 data

The sizes of the tropical cyclones (TCs) occurring over the western North Pacific (WNP) and the North Atlantic between 1991 and 1996 are estimated to establish a database for the study of the climatology of TC size and the physical processes responsible for the size changes of TCs. Wind data from the scatterometer onboard the European Remote-Sensing Satellites 1 and 2 (ERS-1 and ERS-2) form the data source for defining the TC size. The size of a TC is defined as the mean radius at which the relative vorticity decreases to 1 × 10^-5 s^-1. The mean TC size is found to be 3.7° lat for WNP TCs and 3.0° lat for those in the North Atlantic. Such a difference in size between the two basins is statistically significant at the 95% confidence level. The mean TC size in the WNP is also found to vary seasonally, with a value larger in the late season (October and November) than in midsummer (July and August). These results generally agree with those from previous studies using other measures of size. The size changes (increasing or decreasing) of some TCs are also identified. The high-resolution surface wind data from the ERS satellites are shown to be a valuable tool in the study of TC sizes.