Connections Between a Late Summer Snowstorm Over the Southwestern Tibetan Plateau and a Concurrent Indian Monsoon Low‐Pressure System

Abstract

Snowstorms cause more damage to the livelihoods and livestock of more than 2 million herders (~80% of the total population) on the Tibetan Plateau than any other natural disaster. In this study, we investigate an extreme snowstorm over the southwestern Tibetan Plateau (SWTP) that occurred on 18–21 September 2008. We explore sources and transport pathways of moisture to this storm using multiple data sets and a series of regional model simulations. The results show that this snowstorm results from dynamical coupling between an upper‐level trough and a concurrent low‐pressure system over northern India. This tropical‐extratropical interaction provides the dynamical mechanism for the snowstorm to occur: the upper level trough favors southward cold advection upstream of the SWTP while the low‐pressure system over northern India provides an abundant supply of moisture. Model‐based sensitivity tests indicate that large amounts of moisture are transported over the SWTP via both the up‐and‐over and upslope transport pathways. Our findings corroborate that low‐pressure systems over northern India can deliver abundant moisture into the SWTP. The coupling of this abundant supply of moisture with an upper‐level trough further leads to the occurrence of an early snow disaster in this case, aggravating already harsh conditions and causing severe damage. Improved understanding of the interactions between these two types of synoptic systems and the climatic conditions that influence their occurrence would aid the development of effective strategies for climate change adaptation and sustainable husbandry, as well as the mitigation and relief of future snow disasters in this region.

Diagnostic analysis of a regional heavy snowfall event over the Tibetan Plateau using NCEP reanalysis data and WRF

“…Hereafter, the diagnostic results from reanalysis data were concluded and discussed. Different from dynamical coupling between an upper trough and a Indian monsoon low-pressure system triggering a late summer snowstorm (Dong et al 2018), the favorable synoptic system in our current study was characterized by the north vortex and Southern Branch Trough pattern. The cold vortex above Lake Balkhash, the Southern Branch Trough, the meridional shear line and favorable upper and lower jet configurations were the important trigger mechanisms of the formation and evolution of the large-scale snow belt.…”

“…Typically, moisture transport is closely related to synoptic-scale circulations in mid-latitudes when the moisture source is located in the north or the west (Zhang et al 2004;You et al 2011), and to the tropical low-pressure systems near India when the moisture is from the south (Dong et al 2017(Dong et al , 2018. It has been investigated that abundant moisture can be delivered by Indian low-pressure systems via both upslope flow along the Himalayan southern slope and up-and-over transport pathways to the southwestern Tibetan Plateau (Dong et al 2017(Dong et al , 2018. Statistics show that the local specific humidity before heavy snowfalls in the Tibetan Plateau increases significantly, generally above 3 g kg −1 (Zou and Cao 1991).…”

“…Apart from the favorable synoptic systems, an abundant supply of water vapor is also important for the occurrence and maintenance of snowfall (Dong et al 2018). In order to analyze the water vapor condition of the whole layer, a vertical cross section of specific humidity along the narrow snow belt is displayed in Fig.…”

“…In order to explore the initialization and evolution mechanisms of local heavy snowfall over the Tibetan Plateau, a lot of research has been focused on water vapor and the thermodynamic and dynamic conditions (Zhang et al 2004;Dong et al 2018); cold and warm airflow convergence, low-level strong cyclonic vorticity, high-level divergence concurrent with low-level convergence, water vapor transportation and upward motion each play significant roles (Zou and Cao 1991;Shaman and Tziperman 2005;Dong et al 2018;Wang et al 2018). Additional to these atmospheric considerations, local topography strongly influences topographic snowfall (Zou and Cao 1991), and further study has been suggested on the energy and water vapor exchanges caused by complex terrain uplift (Fu et al 2020).…”

Mesoscale precipitation systems and their role in the rapid development of a monsoon depression over the Bay of Bengal

“…Extreme precipitation and catastrophic floods in South Asia are often associated with LPSs (Houze et al ., ; Webster et al ., ; Joseph et al ., ; Bohlinger et al ., ). In addition, LPSs play a role in the transport of water vapour toward high mountain areas such as the Himalayas and the Tibetan Plateau, affecting precipitation processes in these regions (Lang and Barros, ; Ueno et al ., ; Dong et al ., ; ; ). Thus, LPSs play an important role in forming the hydroclimate around their tracks and surrounding areas.…”