Science Source

Climatology and Changes of Extratropical Cyclone Activity: Comparison of ERA-40 with NCEP–NCAR Reanalysis for 1958–2001

Uses a cyclone detection/tracking algorithm to identify cyclones from two gridded 6-hourly mean sea level pressure datasets: the 40-yr ECMWF Re-Analysis (ERA-40) and the NCEP–NCAR reanalysis (NNR) for 1958–2001
Intercompares the cyclone activity climatology and changes inferred from the two reanalyses
Finds the most notable historical trends in cyclone activity are associated with strong-cyclone activity
Finds:
- over the boreal extratropics, both ERA-40 and NNR show a significant increasing trend in January–March (JFM)
- strong-cyclone activity over the high-latitude North Atlantic and over the midlatitude North Pacific
- a significant decreasing trend over the midlatitude North Atlantic
- and a small increasing trend over northern Europe
Holds the JFM changes over the North Atlantic are associated with the mean position of the storm track shifting about 181 km northward
States there is no evidence of abrupt changes identified for the boreal extratropics, although previous studies have suggested that the upward trend found in the NNR data could be biased high