Evaluation of 3D structural changes in general atmospheric and monsoon circulations during Kedarnath disaster (India), 16–17 June 2013

Abstract

Intense rains on 16–17 June 2013 over Mandakini River catchment caused Kedarnath disaster in Uttarakhand State (India). Normal and departure-from-normal 3D global atmospheric thermal structure and general and monsoon circulations during the event have been compared using equatorially/globally- conditioned surface and upper air parameters (1000–100 hPa) (period: 1979–2013). Briefly, normal monsoon structure is: 1000‒850 hPa layer- cross-equatorial flows over Indian Ocean and Eurasian westerlies confluence over Indian domain, the two flows further confluence downstream with Pacific easterlies and then the accumulated airmasses blow northeastward; 700‒500 hPa layer- Eurasian westerlies after sweeping entire Indian subcontinent make exit northeastward; and 400‒100 hPa layer- upper tropospheric anticyclone well-developed over subtropical Asia and outflows are spread all around. On 16–17 June 2013, two upper tropospheric anticyclonic cells occurred, one over Tibet-China and another Mediterranean-Middle East. Troposphere (1000–250 hPa) was significantly warmer-and thicker over Tibet-China followed by Mediterranean-Middle East while cooler-and-thinner over central Asia-India sector. Departures in downward slopes of tropospheric temperature and thickness from Tibet-China outward were significantly steeper. A huge trough evolved over Indo-Pacific region from an interaction between Eurasian westerlies and Indo-Pacific easterlies, and outflows from the trough made forced exit through western Himalaya which modulated north mid-high lati tudes westerlies into a single wave structure. Combined five factors produced disastrous rains over Kedarnath: cool-low and warm-low regime contrast; squeezing of deep warm-moist flows; orographic lifting; and pumping and suction effects. Forced warm-moist outflows from Indo-Pacific region caused warmer-thicker troposphere over eastern Russia-North America. Lesser outflows from Tibet-China anticyclone were directed southward, consequently troposphere was cooler-thinner over southern mid-high latitudes.