Chapter 9 - Southern Teleconnection Between the Indian Summer Monsoon Onset and Meiyu in China

Abstract

Based on the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis and precipitation data, the relationship between the Indian summer monsoon (ISM) onset and Meiyu in China has been examined in this chapter. It is noted that the date of ISM onset over Kerala on the southwestern coast of the Indian Peninsula is about 2 weeks earlier than the beginning of Meiyu in China. After the outbreak of ISM, the teleconnection mode sets up from the western coast of India via the Bay of Bengal (BOB) to the Yangtze River basin and southern Japan, which is called the southern teleconnection in the Asian monsoon region. During the formation process of southern teleconnection, Asian monsoon circulations experience a series of important changes: the ISM onset, northward movement of the south-Asian high (SAH), the onset of vortex occurrence, eastward extension of the stronger tropical westerly belt, and northeastward jump of the western Pacific subtropical high (WPSH), among others. Consequently, after ISM sets up over Kerala, the whole Asian continent is covered by the upper SAH within 2 weeks, while in the middle and lower troposphere, a strong westerly belt forms from the Arabian Sea via southern India, BOB, and the South China Sea, then along the western margin of the WPSH and to the Yangtze River basin and southern Japan. With the northward movement of the subtropical jet streams, the upper-westerly jet stream and the low-level jet are coupled vertically over East Asia, while the Yangtze River basin happens to locate in the ascending motion area between the upper-jet stream and the low-level jet, that is, to the right of the entrance of the upper-jet stream and to the left of the low-level jet. This structure of the vertical movement can trigger the Meiyu onset over the Yangtze River basin.