Figure 6: Tracks of the three synoptic-scale cyclones extracted as typical cases. The location of the initial appearance of a cyclone is denoted by blue rectangles. The locations of explosive cyclones when their rates of development reached the maximum are indicated by red circles. The size of the circles denotes the magnitude of the maximum deepening rate (hPa hr−1). The topography and climatological mean 925 hPa horizontal wind divergence for December are also shown. The shading interval for wind divergence is 3 10−6 s−1.