Interannual and synoptic-scale features of two types of cold-air outbreaks over the East China Sea during 1988-2006

For the 1988-2006 cold seasons, we investigated the characteristic structures of two types of cold-air outbreaks over the East China Sea: Type N, for which a thick layer of northerly meridional wind was formed during the cold-air outbreak; and Type S, for which an initially thin layer of northerly meridional wind was gradually thickened as the cold-air outbreak developed. The emergence frequencies of Type N and Type S outbreaks are sensitive to winter monsoon intensity at the 500-hectopascal (hPa) level. Type S outbreaks are dominant during strong El Niño events, leading to enhanced southerly meridional flow at 500 hPa over the East China Sea. The development of the 500-hPa Pacific High strongly influences the synoptic-scale structures of the two different types of outbreaks over the East China Sea.