7A.3 MIPS Observations of a Heat Burst Event

Tuesday, 5 October 2004: 5:00 PM
Kevin R. Knupp, University of Alabama, Huntsville, AL; and K. R. Knupp and J. Walters

On 23 June 2003 the Mobile Integrated Profiling System (MIPS) acquired detailed observations on the entire evolution of a nocturnal heat burst event just north of Omaha, Nebraska. The MIPS was deployed at this location as part of 2003 Bow Echo and MCV Experiment. A widespread, thick anvil from several massive supercell storms that formed ~100 km towards the upshear direction, covered the MIPS for an 11-h time period. This site was ideally located about 30 km northeast of the Omaha WSR-88D and rawinsonde location. MIPS observations include 915 MHz profiler, 12-channel microwave profiling radiometer (MPR), lidar ceilometer, Doppler sodar, electric field mill and surface measurements.

During the evening hours, strong winds were associated with microburst-like phenomena that formed within a dry, unstable layer beneath the anvil cloud base. The collisions of strong downdrafts on the composite stable layer associated with the residual convective boundary layer and developing nocturnal boundary layer, produced gravity waves and associated strong winds over a period of 6-8 h. The maximum measured wind gusts (3.7 m AGL) attained 31 m s-1. Gravity wave activity was detected by surface pressure oscillations of 1-2 mb magnitude, and 915 MHz profiler vertical motion and backscatter measurements. Although warming and drying at the surface did occur, it was not extreme. However, measurements by the MIPS 12-channel microwave profiling radiometer detected a very impressive warming and drying in the 600-900 mb layer. This event produced an appreciable loss in integrated water vapor, as measured by GPS receivers in this region. The implication is that significant mesoscale downdrafts formed below the anvil cloud base and produced widespread divergence and drying over the lower 3-4 km of a large region, on the order of ~105 km2. This analysis will assess the interactions between downdrafts of both scales.

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