Teleconnection of Hydrometeorologic Extremes: Russia Heat Wave and Pakistan Flood
Image of the Week - January 16, 2011
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The two record setting hydrometeorologic extreme events during the summer of 2010, i.e., the Russian heat wave/wildfires and the Pakistan flood occurred almost contemporaneously. A recent study (Lau and Kim 2011) shows that these two seemingly unrelated events were indeed physically related.
The intense heat wave and wildfires in Russia were caused by a strong and prolonged atmospheric blocking in the extratropics over northern Europe and western Russia. The blocking initiated a surface-to-mid-troposphere high pressure system and a mid-to-upper level Rossby wavetrain propagating eastward and southeastward. Vorticity perturbations in the leading edge of the trough ahead of the anticylone was instrumental in leading to the development of subtropical mid-tropospheric cyclones triggering of torrential rain over northern Pakistan and vicinity,
Approximately 24-48 hours before the onset of heavy rain events over northern Pakistan (July 19, July 27, August 3), an upper-level V-shaped positive (cyclonic) vorticity filament formed at the southeastern edge of the 500 hPa anticyclone, entering the target region from the north. The upper level vorticity perturbations triggered upward motion ahead (to the east), leading to the development of subtropical mid-tropospheric cyclones (MTC), with cold air below and warm core structure above 600 hPa. The vertical motion associated with the MTC pumped moisture from the Bay of Bengal, and the northern Arabian Sea, feeding the extreme rainfall events over northern Pakistan.
Lau, K-M., and K-M Kim, 2011: The 2010 Pakistan flood and the Russia heat wave: Teleconnection of Hydrometeorologic Extremes. Submitted to J. of Hydrometeorology.