Tropical cyclones in ERA-40: A detection and tracking method

Abstract

A tracking method for tropical cyclones (TCs) ispresented and their characteristics for data sets with alower horizontal resolution, e.g., the ERA-40 Reanalysisdata set from 1958 to 2001 are explored. The trackingmethod uses sea level pressure, relative vorticity and windspeed at 850 hPa, and vertical wind shear. The method,assessed in the Atlantic basin, identifies a realistic number ofTCs. However, the ERA-40 TCs compared with best trackdata from the U.S. National Hurricane Center are too weak toreach hurricane character, i.e., the tracked TCs do not showhurricanes of category three to five. Another caveat is that thelife cycle of central pressure values is often not realisticallyreproduced by ERA-40 TCs. To correct the life cycle of thecentral pressure, a two-step statistical downscaling approachis applied to the ERA-40 TCs which strongly improves thefinding of major hurricanes.