华南冬季异常冷月预测概念模型Ⅱ──大气环流、极冰、积雪等物理因子特征

SCHEMATIC PREDICTIVE MODEL FOR EXTREMELY SEVERE COLD MONTHS IN SOUTH CHINA MINTER ──Physical factors of general circulation, polar sea ice and perpetual snow

统计分析了华南冬季异常冷月及其前期大气环流及外部强迫因子的变化特征。结果表明,异常冷月当月至其前期3月西太平洋副热带高压持续偏弱或位置偏东偏南。前一年东亚夏季风弱,当年冬季风强。前期7、8、9月和当年冬季亚洲极涡扩展。1月前期11月和12月青藏高原积雪日数偏少。2月前期11个月,特别是3～8月北极Ⅳ区极冰偏多,12月前期1～11月Ⅱ区极冰偏多,3～8月Ⅲ区极冰偏少。综合上述各因子以及500 hPa高度场和海温场前期特征,给出了华南冬季异常冷月预测概念模型。

The work statistically studies the variations of the general circulation and external forcing factors in and before the extremely severe cold months. The result shows that the subtropical high in the west Pacific keeps weak or on an eastward or southward position in the current and previous 3 months. A weak summer monsoon in the previous year is accompanied by strong winter monsoon in the current year. The Asian polar vortex expands in the previous July, August and September and the current winter. There is less perpetual snow in the Tibetan Plateau in November and December prior to the current January. There is more sea ice in Region Ⅳ of the Arctic Ocean in the previous 11 months, especially March through August, prior to the current February. There is more polar ice in Region Ⅱ in January through November and less polar ice in Region Ⅲ in March through August prior to the current December. Integrating the preceding factors and previous characteristics of 500 hPa geopotenial fields and SST fields, a schematic predictive model is presented for extremely severe cold months in South China winter.