Abstract This study investigates the formation of the monsoon gyre (MG) in August 1991. The results suggest the mid-latitudinal processes play an important role in the formation of the MG. The repeating upper-tropospheric Rossby wave breaking events took place in the exit region of mid-latitude jet during the period of interest. The wave energy dispersed southeastward and downward from the jet exit region, exciting a low-level subtropical low. Furthermore, the Rossby wave breaking induced salient ageostrophic forcing by disturbing the upper-level PV fields. The Q-vector analysis shows that the ageostrophic motion forced by the upper PV streamer favors the early development of the subtropical low. Thereafter, this system moved southwestward, and interacted with the tropical monsoon flows to induce a strong convective band to the southern and southeastern periphery. The enhanced convective heating further strengthened the cyclonic low through the Gill-type response. Furthermore, the asymmetric water vapor transport induced asymmetric convective structure. This pattern suppressed the scale contraction and maintained a large size, leading to the formation of a large-scale monsoon gyre eventually.

中文翻译：

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中纬度对1991年8月季风环流形成的影响

摘要 本研究调查了1991 年8 月季风环流(MG) 的形成。结果表明，中纬度过程在MG 的形成中起重要作用。在感兴趣的时期内，中纬度急流的出口区域发生了重复的对流层上层罗斯贝波断裂事件。波浪能从急流出口区向东南向下扩散，激发了一个低层副热带低压。此外，罗斯比波破碎通过扰动上层光伏场引起显着的地转强迫。Q矢量分析表明，上层PV拖缆强迫的地转运动有利于副热带低压的早期发展。此后，这个系统向西南移动，并与热带季风流相互作用，在南部和东南部外围产生强对流带。增强的对流加热通过吉尔型响应进一步加强了气旋低压。此外，不对称的水蒸气传输引起了不对称的对流结构。这种格局抑制了尺度收缩并保持了较大的尺度，最终导致了大规模季风环流的形成。