A 31‐year climatology of tropical cyclone size from the NCEP Climate Forecast System Reanalysis

ABSTRACT A 31‐year tropical cyclone (TC) size climatology (1980–2010) is established using the NCEP Climate Forecast System Reanalysis for the western North Pacific (WNP) and the North Atlantic (NA). The size of a TC, defined as the azimuthally averaged radius of 17 m s−1 wind near the sea surface, is estimated using the strong relationship between TC size and azimuthally averaged winds in the outer‐core region of the TC. The estimation method is verified by comparing the TC size climatology established using the QuikSCAT satellite data. The monthly and annual variations in both climatologies agree with each other. Based on this 31‐year data set, the mean TC sizes over the WNP and NA are 2.01° and 1.61° latitude, respectively. TC size in both basins exhibits temporal intra‐seasonal and annual as well as spatial variations. Inter‐annual TC size variations in the WNP are highly correlated (r = 0.816) with El Niño‐Southern Oscillation events. In WNP, the highest percentage of large TCs occurs near 25°N, which agrees with previous modelling and observational studies. The azimuthally averaged wind in the outer‐core region of the tropical cyclone (TC) in CFSR is found to be highly correlated to TC size. The TC size is estimated by using this strong relationship and establishes a 31‐year TC size climatology. The climatology could be used for study the TC size intra‐seasonal, annual and inter‐decadal as well as spatial variations.