Sub-synoptic circulation variability in the Himalayan extreme precipitation event during June 2013

Abstract

This study investigates the sub-synoptic scale circulation aspects associated with the extreme rainfall event occurred over the North Indian state of Uttarakhand located in the western Himalayas (WH) during the 15-18 June 2013 period. A diagnosis based on hourly ERA5 reanalyzed circulation products archived on finer grids reveals that sustenance of heavy rains during the event period is supported by a propensity of cyclonic vorticity sources channeled toward the WH region through a narrow quasi-steady conduit in the lower troposphere from the ISM circulation. The equatorward segregating mesoscale potential vorticity (PV) structures from the quasi-stationary upper level PV anomaly (trough) during the event administered two pathways for vorticity sources. The first pathway is from the base of the trough culminating into longer horizontal conduit path from the western Arabian Sea, lending perpetual cyclonic vorticity support to the ISM environment. The second pathway is from the right flank of the trough, which promotes sustained environment of deeper mesoscale convergence zone, potentially unstable atmosphere and strong ascent over the Uttarakhand region. The convergence zone is potentially viewed as a region for strong monsoon and extratropical circulation interactions to occur on finer horizontal scales of motion, where significant vertical synchronization of positive PV advection is realized during the 16-17 June 2013 period. In addition to orographic precipitation enhancements, deeper advective synchronization noticed at sub-synoptic time periods is accredited to the nearly doubling 24-h rainfall amounts in the foothill region of Uttarakhand during the event period. The ERA5 diagnosed diabatic heating additionally indicates that precipitating systems at higher (foothill) elevations contribute to upper (lower) tropospheric heat sources.

Analysis of Himalayan summer monsoon rainfall characteristics using Indian High‐Resolution Regional Reanalysis

“…The Himalayas are vulnerable to heavy rainfall and flooding during the Indian summer monsoon (ISM), particularly on south‐facing slopes and the Indian Gangetic Plains (Aggarwal et al, 2022; Bhatt & Nakamura, 2005; Dimri, 2013; Singh & Kumar, 1997). The Himalayas are the world's highest mountainous region with diverse topography, with steep southern slopes and bare and mild northern slopes (Kripalani et al, 2003; Krishnan et al, 2019; Kulkarni et al, 2013; Rasmussen & Houze, 2012; Vellore et al, 2020) and heterogeneous precipitation distribution. It is also known as the world's third pole (Krishnan et al, 2019), which supplies water to millions of people (Li et al, 2018) throughout the year in terms of snowfall in winter and snow melt in summer.…”

“…The ISM contributes 75%–80% to the annual precipitation of the western Himalayas (e.g., Singh & Bharti, 2019). The local population is primarily dependent on precipitation feed streams for drinking water, industry, agriculture, fishing and hydropower generation, one of the main sectors of the local economy (Adhikari & Mejia, 2021; Aggarwal et al, 2022; Banerjee et al, 2020; Priya et al, 2017; Rasmussen & Houze, 2012; Shrestha et al, 2012; Vellore et al, 2020).…”

“…As a result, the study of the patterns, trends and mechanisms of ISM precipitation in the Himalayas remains limited and insufficient compared to the core monsoon region. Previous studies reported that data scarcity is the most pressing issue for understanding rainfall variability (Maharana & Dimri, 2014; Singh & Kumar, 1997; Vellore et al, 2020) over the region. Therefore, a precise understanding of precipitation characteristics across the Himalayan range using high‐resolution data is important for enlightening our understanding of the regional monsoon climate (e.g., Bharti et al, 2016; Hunt & Parker, 2016; Rasmussen & Houze, 2012; Shrestha et al, 2012).…”

Hydrological Extremes in Western Himalayas-Trends and Their Physical Factors

“…Several studies, involving observations or climate model simulations, indicate that the frequency of these events would intensify with global warming due to an increment in the atmospheric moisture holding capacity as per Clausius Clapeyron relationship [43][44][45][46]. Additionally, the influence of local thermodynamics and orographic forcing in the WH produces abrupt changes in synoptic circulation, which have the potential to produce EPEs that can last for a few days [12,47].…”

Extreme Storms

“…Rainfall occurrences of unprecedented intensity have also been witnessed in the recent decades during the Indian summer monsoon (ISM; June-September) season. For example, heavy downpour that caused calamitous floods and heavy casualties in Mumbai during July 2005 (Bohra et al 2006), in Leh of the trans-Himalayan region during August 2010 (Thayyen et al 2013;Rasmussen and Houze 2012), in the northern states of Uttarakhand and Jammu and Kashmir during June 2013 and September 2014 (Lotus 2015;Ranalkar et al 2016;Vellore et al 2016Vellore et al , 2019Priya et al 2017), and in the southern state of Kerala during August 2018 (Mishra and Shah 2018) are to name a few. Various synoptic-scale signatures have been recognized in connection with these extreme rain situations, viz localized convective instabilities, large-scale organized monsoon activity and anomalous extratropical circulation, and their interactions with the monsoon circulation across the Himalayas (e.g., Vellore et al 2014Vellore et al , 2016; see also Krishnan et al 2019).…”