摘要
利用NCEP/NCAR再分析数据资料及CMAP降水资料,进一步对东亚副热带季风季节转换特征及其可能机理进行研究。首先根据东亚副热带季风经向风分量的季节性转变特征界定了东亚副热带季风活动代表区;联合"热成风"原理和"热力适应"理论推导得出了"热风雨"关系式,即纬向海陆热力(温度)差异、经向风垂直切变以及与季风雨相联系的垂直运动三者在副热带季风演变过程中的一致相关关系;比较分析了季风区不同时段的区域平均风向垂直变化以及相应的冷暖平流特征。结果表明:冬季风期间,区域平均风向随高度逆转,呈现冷平流特征;夏季风期间,区域平均风向随高度顺转,呈现暖平流特征。同时还分析了区域平均的风向季节转变,讨论了副热带季风经圈环流的演变过程以及相应的地面10 m风场转变过程特征。上述研究表明,无论是纬向海陆温度差异、经向风垂直切变、低层风向角、冷暖平流,还是中高层垂直运动及其相应降水距平都统一于18—22候发生显著季节转变,这说明副热带夏季风应于3月底4月初开始建立。最后给出了东亚副热带季风的季节转换概念框图。
The NCEP/NCAR reanalysis dataset and CMAP rainfall data are used to investigate the large-scale seasonal transition of East Asian subtropical monsoon （EASM） and its possible causes. Based on the feature that the meridional wind change is dominant in the seasonal transition of EASM, the precursory area of the EASM is defined. By combining the ＂thermal-wind＂ formula and the ＂thermal adaptation＂ equation, a new ＂thermal-wind-precipitaion＂ relation is deduced. The area-averaged wind directions and thermal advections in different seasons are analyzed for comparison, with the result showing that in the winter monsoon period, the averaged wind direction above the precursory region varies clockwise with altitude and warm advection in dominance; in the summer monsoon, everything is reversed. The seasonal evolution of the wind direction at different levels and the corresponding meridonal circulation of other elements all indicted that the subtropical summer monsoon is established at the end of March and the beginning of April. At last, a conceptual scheme of mechanism for seasonal transition of EASM is proposed.
出处
《热带气象学报》
CSCD
北大核心
2013年第2期245-254,共10页
Journal of Tropical Meteorology
基金
国家自然科学基金资助项目(41075068
40905044)资助
关键词
东亚副热带季风
“热风雨”关系式
季节转变时间
转变特征
可能机理
subtropical East Asia monsoon
seasonal transition
thermal-wind-precipitation relationship
possible mechanism
