Sub-synoptic circulation variability in the Himalayan extreme precipitation event during June 2013
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ORIGINAL PAPER
Sub‑synoptic circulation variability in the Himalayan extreme precipitation event during June 2013 Ramesh K. Vellore1 · Jagat S. Bisht1,2 · Raghavan Krishnan1 · Umakanth Uppara1 · Giorgia Di Capua3,4 · Dim Coumou3,4 Received: 22 May 2019 / Accepted: 11 November 2019 © Springer-Verlag GmbH Austria, part of Springer Nature 2019
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.
1 Introduction
Responsible Editor: A.-P. Dimri. * Ramesh K. Vellore [email protected] 1
Centre for Climate Change Research (CCCR), Indian Institute of Tropical Meteorology (IITM), Pune 411 008, India
2
Research and Development Centre for Global Change, Japan Agency for Marine Earth Science Technology, Yokohama, Japan
3
Potsdam Institute for Climate Impact Research, Potsdam, Germany
4
Institute for Environmental Studies, Vrije Universiteit, Amsterdam, The Netherlands
The western part of the Himalayas (WH) (Fig. 1) has been constantly witnessing extreme rainfall episodes during the Indian summer monsoon (ISM) months (June–September) in recent decades (e.g., Joshi and Kumar 2006; Rasmussen and Houze 2012; Mujumdar et al. 2012; Nandargi and Gaur 2013; Dobhal et al. 2013; Manish et al. 2013; Chaudhuri et al. 2015;
