南海—西太平洋地区ITCZ气候学特征的研究

ON THE CLIMATOLOGICAL ITCZ OVER THE AREA OF SOUTH CHINA SEA AND WEST PACIFIC OCEAN

本文利用1965—1984年6—9月逐日08时850hPa历史天气图上分析的ITCZ,统计出ITCZ频数分布图,研究了南海—西太平洋地区ITCZ的气候特性和季节性进退,揭示了ITCZ具有与副热带高压同步北跳现象和频数突增现象。发现:西太平洋上的ITCZ容易在12°N和20°N附近形成和维持,使ITCZ频数图上出现南、北两个多频带.这一分支现象与热带低层赤道西风和高层热带东风的分支现象密切相关。由于ITCZ存在着活跃与间歇的低频振荡,加上海陆、地形和热带气旋活动的影响,以及ITCE的结构特点,因而月平均多云带和最小OLR轴位置比流场ITCZ显著偏南,而且在南海地区出现偏离季风槽而沿地形槽的走向.对比分析表明,用OLR标准差与平均值之比值X来表征ITCZ的位置可能比直接用最小OLR轴更合理.

Day-to-day ITCZ set analysed from June-September 850 hPa historic data (1965-1984) at 0000 GMT were used to determine ITCZ's distribution of occurrence frequency and investigate its climatology and seasonal advancement over the area of the South China Sea and West Pacific , with the result that ITCZ displaces itself northward simultaneously with the Subtropical High and increases its own frequency of occurrence. It is found that ITCZ in the West Pacific tends to take place and stay roughly along 12°N and 20°N , substantiating two belts of high frequency. The bifurcation is closely associated with those for the low-level westerlies and upper easterlies over the equatorial tropics. It is also suggested that the geographical location of ITCZ may be more properly described with the ratio of OLR standard deviation to its average than directly with the minimum axis of OLR.