Observations of a squall line using high-frequency rawinsonde launches during VORTEX2
George H. Bryan, NCAR, Boulder, CO; and M. D. Parker
Rawinsonde data were collected before and during passage of a squall line in Oklahoma on 15 May 2009 during VORTEX2. Nine soundings were released within 3 hours, allowing for unprecedented analysis of the squall line's internal structure and nearby environment. Four soundings were released in the pre-storm environment and they document changes in environmental properties such as CAPE, precipitable water, and vertical wind shear as the squall line approached. There was also evidence of ascent extending at least 75 km ahead of the squall line. One sounding was released after the gust front passed but before precipitation began; this sounding showed the cold pool to be 4 km deep, with a cold pool intensity C ≈ 35 m/s, even though this sounding was located only 8 km behind the surface gust front. The final three soundings were released in the trailing stratiform region of the squall line, and they showed typical features such as: "onion" shaped soundings; nearly uniform equivalent potential temperature over a deep layer; and an elevated rear inflow jet. The cold pool was 4.7 km deep in the trailing stratiform region, and extended about 1 km above the melting level, suggesting that sublimation was a contributor to cold pool development. A mesoscale analysis of the sounding data shows an upshear tilt to the squall line, which is consistent with the cold pool intensity (C) being much larger than a measure of environmental vertical wind shear (ΔU). This dataset should be useful for evaluating cloud-scale numerical model simulations and analytic theory, but we argue that additional observations of this type should be collected in future field projects.
Session 2, Mesoscale Convective Systems: Initiation and Structure
Monday, 11 October 2010, 10:45 AM-12:00 PM, Grand Mesa Ballroom F
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