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LIN Ailan, LI Tim, WANG Lu, et al. 2021. The Relationship between Intraseasonal Variation of the South Asian High and Tropical Intraseasonal Oscillation [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 45(3): 633−650. doi: 10.3878/j.issn.1006-9895.2007.20144
Citation: LIN Ailan, LI Tim, WANG Lu, et al. 2021. The Relationship between Intraseasonal Variation of the South Asian High and Tropical Intraseasonal Oscillation [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 45(3): 633−650. doi: 10.3878/j.issn.1006-9895.2007.20144

The Relationship between Intraseasonal Variation of the South Asian High and Tropical Intraseasonal Oscillation

  • The relationship between the tropical ISO (intraseasonal oscillation) and the intraseasonal variation of the SAH (South Asian high) in boreal summer and the associated physical mechanisms are investigated by using both the observational data analysis and numerical model experiments. The results indicate that the intraseasonal variation of SAH is closely related to the tropical ISO activity. The eastern edge of SAH shifts westward when the active phase of the tropical ISO appears in Indian Ocean (including Phase 1, 2, and 3), and shifts eastward when the ISO appears in Pacific (including Phase 5, 6 and 7). The most sensitive region in response to the tropical ISO forcing is over the eastern part of SAH, which is the region connecting East Asia and western Pacific (15°–25°N, 110°–140°E). The vertical profile of tropospheric atmosphere in the region exhibits a baroclinic structure. An eastward extension (westward retreat) of the eastern edge of SAH corresponds well to an eastward retreat (westward extension) of the western edge of the WPSH (western Pacific subtropical high) in the middle and lower troposphere. The intraseasonal variability of SAH is primarily affected by the tropical ISO. About 40% of the variability in the key region is attributed to the tropical ISO, whereas the influence of the SAH on the tropical ISO is weak. The physical processes by which the tropical ISO affects SAH are summarized as follows: As the tropical ISO moves from the Indian Ocean to the western Pacific, part of the convection branches out and propagates northward under the favorable background state of the summer monsoon, which further strengthens the convection. To the northwest of the ISO heat source, cyclonic circulations and negative height anomalies (anticyclonic circulation and positive height anomalies) appear in the lower (upper) troposphere, which leads to the eastward extension of SAH. However, when the tropical ISO appears in the Indian Ocean, the atmospheric circulation responses are in general opposite to the above, leading to the westward retreat of SAH.
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