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Mesoscale Structure of an Oklahoma Squall Line

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  • 1 National Severe Storms Laboratory, Norman OK 73069
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Abstract

A squall line, which passed through the National Severe Storms Laboratory measonetwork in Oklahoma on 26 April 1969, is analyzed to determine the mesoscale structure. The analyses are based on data from 23 rawinsonde ascents, 29 automatically recording surface stations, and radar PPI coverage.

A composite analysis revealed the existence of a mesoscale descent-ascent doublet in the vertical-motion pattern. The descent was centered about 10 km ahead of, and the ascent about 5 km behind the leading edge of the radar echoes. The downdraft appears to be driven by evaporative cooling from the tops of cumulus clouds and cooling due to the dissipation of a middle cloud layer; the updraft seems to be driven mainly by condensational heating. On the basis of this and other cases, it is tentatively concluded that this doublet of mesoscale vertical motions may be distinguishing feature of large convective storm systems in their mature stages of development, whether they be of frontal or of squall-line character.

Abstract

A squall line, which passed through the National Severe Storms Laboratory measonetwork in Oklahoma on 26 April 1969, is analyzed to determine the mesoscale structure. The analyses are based on data from 23 rawinsonde ascents, 29 automatically recording surface stations, and radar PPI coverage.

A composite analysis revealed the existence of a mesoscale descent-ascent doublet in the vertical-motion pattern. The descent was centered about 10 km ahead of, and the ascent about 5 km behind the leading edge of the radar echoes. The downdraft appears to be driven by evaporative cooling from the tops of cumulus clouds and cooling due to the dissipation of a middle cloud layer; the updraft seems to be driven mainly by condensational heating. On the basis of this and other cases, it is tentatively concluded that this doublet of mesoscale vertical motions may be distinguishing feature of large convective storm systems in their mature stages of development, whether they be of frontal or of squall-line character.

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