索马里急流和南亚高压对印度夏季风爆发的协同作用

Synergistic Effects of the Somali Jet Stream and the South Asia High on Onset of Indian Summer Monsoon

【目的】探讨索马里急流和南亚高压对印度夏季风(Indian Summer Monsoon,ISM)爆发产生的协同作用。【方法】基于ECMWF欧洲中期天气预报中心第五代再分析资料(ERA5)提供的逐日数据,结合印度气象局对ISM爆发日期(即印度次大陆最南端的喀拉拉邦降水骤升的日期)的统计数据采用功率谱分析、偏相关分析和滑动相关等统计学方法,分析索马里急流和南亚高压对ISM爆发的协同作用。【结果】ISM爆发前1候至当候,印度地区对流层高层南亚高压的范围和强度不断扩大,同时对流层低层索马里急流的强度和范围不断增强,使阿拉伯海地区的西南气流不断增强,将阿拉伯海地区大量水汽输送至印度大陆,在这样有利的条件下,印度南部降水量剧增,ISM爆发;当5月下旬的南亚高压、索马里急流以及阿拉伯海地区水汽通量和气旋性环流均显著偏强时,ISM会提前爆发,降水也会异常偏多。【结论】ISM爆发日期受到索马里急流和南亚高压两者协同作用的影响,而并非单独受到某个系统的影响。

【Objective】The study is to explore the synergistic effects of the Somali jet stream and the SAH(South Asia High)on the onset of the Indian Summer Monsoon(ISM).【Method】The study is based on the daily data provided by the ERA5 of the ECMWF(European Centre for Medium Range Weather Forecasts)which is combined with the statistics of the ISM onset date(the date of a sharp increase in precipitation in the southernmost Indian subcontinent of Kerala)from the Meteorological Administration of India.Statistical methods such as power spectrum analysis,partial correlation analysis and sliding correlation were used to analyze the synergistic effect of the Somali jet and the South Asian High on the ISM onset.【Result】The scope and intensity of SAH in the upper troposphere over India were continuously expanded during the first week before the ISM onset,and the intensity and scope of Somali jet in the lower troposphere were continuously enhanced,which made the southwest airflow over the Arabian Sea continuously strengthened,and a large amount of water vapor from the Arabian Sea transported to the Indian mainland.Under these favorable conditions,there was a surge in precipitation in southern India and an onset of ISM.When the South Asia High,Somali jet stream and the cyclonic circulation over the Arabian Sea in late May are all significantly stronger,ISM will break out in advance and bring abnormally more precipitation.【Conclusion】The ISM onset date was influenced by the synergistic effect of the Somali jet stream and the SAH,rather than by a single system.