Analysis of extratropical cyclones in the northern hemisphere using the NOAA historical reanalysis

Extratropical cyclone (ETC) climatologies in the Northern Hemisphere are analyzed from 1891 to 2005. Sea level pressure fields from the 20th Century Reanalysis (Compo et al, 2010) were used to identify ETCs and assemble tracks. Transformation of the data into an equal area coordinate system and modifications to traditional ETC identification and tracking methods are discussed. Next, frequency and intensity measures confirm some trends previously reported with data back to the 1950s while showing remarkably different trends in the extended record. Climatological maps and time series of the ETC frequencies and intensities, stratified by season and geographic region, are presented demonstrating the relationships between ETC characteristics and temperature anomalies and other climate indices. Preliminary results indicate that ETC intensities in the high latitudes have declined.