Spatial Distribution and Seasonal Variation of Explosive Cyclones over the North Atlantic Spatial Distribution and Seasonal Variation of Explosive Cyclones over the North Atlantic

Spatial distribution and seasonal variation of explosive cyclones(ECs) over the North Atlantic from October 2000 to September 2016 are investigated using the reanalysis data of Final Analysis(FNL),Mean Sea Level Pressure(MSLP) and Optimum Interpolation(OI) Sea Surface Temperature(SST) provided by the National Centers for Environmental Prediction(NCEP),the European Centre for Medium-Range Weather Forecasts(ECMWF) and the National Oceanic and Atmospheric Administration(NOAA),respectively.Considering the meridional distribution of ECs and 10-m height wind field associated with the ECs,the definition of EC given by Yoshida and Asuma(2004) is modified.It is found that the ECs occurred mainly in four regions during winter season,namely,North America continent(NAC),the Northwest Atlantic(NWA),the North-central Atlantic(NCA),and the Northeast Atlantic(NEA),depending on the spatial distribution of EC's maximum deepening rate of central sea level pressure(SLP).According to the magnitude of maximum deepening rate,the trend of EC numbers basically decrease with the increase of EC's maximum deepening rate over the North Atlantic during the whole time period.Over the North Atlantic basin,for monthly statistics,the NEA,NCA,and NWA cyclones occur mainly in December,from December to March,and from January to February,respectively.NWA,NCA and NEA cyclones in winter are associated with low-level baroclinicity,both low-level baroclinicity and upper-level forcing and upper-level forcing,respectively.According to monthly variation,the averaged maximum deepening rate of central SLP firstly increases and then decreases from July to June.Overall,the distribution of ECs' tracks is basically in the southwest-northeast direction.During winter circulation stage(from October to May),the averaged maximum deepening rate of central SLP and the averaged minimum central SLP of ECs decrease,and the averaged explosive-deepening duration of ECs shortens from west to east over the North Atlantic basin.During summer circulation stage(from June to September),the number of ECs is far less than that of winter circulation.NCA cyclones are the lowest in the average minimum central SLP of ECs,and the longest in the average explosive-deepening duration of ECs.NEA cyclones are the strongest in the average maximum deepening rate of central SLP