Indian Monsoon Low‐Pressure Systems Feed Up‐and‐Over Moisture Transport to the Southwestern Tibetan Plateau. Issue 22 (20th November 2017)

• Record Type: Journal Article
• Authors: Dong, Wenhao; Lin, Yanluan; Wright, Jonathon S.; Xie, Yuanyu; Xu, Fanghua; Xu, Wenqing; Wang, Yan
• Is Part Of: Journal of geophysical research. Volume 122:Issue 22(2017)
• Page Start: 12, 140
• Page End: 12, 151
• Publication Date: 2017-11-20
• Subjects: South Asian monsoon -- monsoon low‐pressure systems -- up‐and‐over route -- summer rainfall -- moisture transport -- Southwestern Tibetan Plateau; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1002/2017JD027296
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: As an integral part of the South Asian summer monsoon system, monsoon low‐pressure systems (LPSs) bring large amounts of precipitation to agrarian north and central India during their passage across the subcontinent. In this study, we investigate the role of LPSs in supplying moisture from north and central India to the southwestern Tibetan Plateau (SWTP) and quantify the contribution of these systems to summer rainfall over the SWTP. The results show that more than 60% of total summer rainfall over the SWTP is related to LPS occurrence. LPSs are associated with a 15% rise in average daily rainfall and a 10% rise in rainy days over the SWTP. This relationship is maintained primarily through up‐and‐over transport, in which convectively lifted moisture over the Indian subcontinent is swept over the SWTP by southwesterly winds in the middle troposphere. LPSs play two roles in supplying up‐and‐over moisture transport. First, these systems elevate large amounts of water vapor and condensed water to the midtroposphere. Second, the circulations associated with LPSs interact with the background westerlies to induce southwesterly flow in the midtroposphere, transporting elevated moisture and condensate over the Himalayan Mountains. Our findings indicate that LPSs are influential in extending the northern boundary of the South Asian monsoon system across the Himalayas into the interior of the SWTP. The strength of this connection depends on both LPS characteristics and the configuration of the midtropospheric circulation, particularly the prevailing westerlies upstream of the SWTP. Key Points: Most summer rainfall over the southwestern Tibetan Plateau occurs when low‐pressure systems are active over India Interactions with middle tropospheric westerlies induce up‐and‐over moisture transport from northern India Average daily precipitation and the fraction of rainy days increase over both regions during active phases