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Thomas J. Galarneau Jr., Thomas M. Hamill, Randall M. Dole, and Judith Perlwitz

Abstract

This manuscript presents a detailed multiscale analysis—using observations, model analyses, and ensemble forecasts—of the extreme heat wave over Russia and historic floods over Pakistan during late July 2010, with an emphasis on the floods over northern Pakistan. The results show that recirculation of air and dynamically driven subsidence occurring with the intensification of the blocking anticyclone in late July 2010 were key factors for producing the exceptionally warm temperatures over western Russia. Downstream energy dispersion from the blocking region led to trough deepening northwest of Pakistan and ridge building over the Tibetan Plateau, thereby providing the linkage between the Russian heat wave and Pakistan flood events on the large scale, in agreement with previous studies.

The extratropical downstream energy dispersion and enhanced convective outflow on the large scale associated with the active phase of the Madden–Julian oscillation facilitated the formation of an intense upper-level jet northwest of Pakistan. During this same period an intense southeasterly, low-level, barrier jet–like feature formed over northern Pakistan in conjunction with a westward-moving monsoon depression. This low-level jet and deep easterly flow on the equatorward flank of an anomalous anticyclone over the Tibetan Plateau further enhanced the transport of deep tropical moisture into Pakistan and produced a sustained upslope flow and an extended period of active convection, thereby providing an important contribution leading to the exceptional rainfall amounts. The deep easterly flow and intense low-level jet were features that were absent during previous convective episodes over northern Pakistan in 2010, and hence, were likely key factors in the increased severity of the late July event.

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