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- Author or Editor: Steven M. Hunter x
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Abstract
Balloon soundings of electric field in Oklahoma mesoscale convective systems (MCS's) were made by the National Severe Storms Laboratory (NSSL) during the spring of 1989. A sounding made in the rearward edge of an MCS stratiform rain area on 7 June 1989 is the centerpiece of this study. We used data from Doppler radars, a lightning ground-strike location system, satellite, and other sources to relate the mesoscale attributes of the MCS to the observed electric-field profile.
The stratiform area did not lag an organized convective line, but was apparently initiated by anvil precipitation downwind of convective cells that were at the west and southwest flanks of the MCS. The mature system produced a bipolar cloud-to-ground lightning pattern, in which most flashes of positive polarity came to ground in the downshear anvil or stratiform region. The bipole was oriented from 220°, parrallel to upper-level geostrophic flow, and its length was 190 km. We visually observed lightning flashes in the stratiform region that had long segments along cloud base.
At least two cells separated from the main convective zone and moved near the region of stratiform cloud penetrated by the balloon. These convective cells may have influenced the intricate charge structure, which was manifested by 11 distinct charge layers from the electric-field sounding. Ten of the 11 charge layers were found between 3 and 8 km MSL (+10° to −24°C), a depth coinciding with rear inflow into the stratiform region. Charge-density magnitudes (up to 3.9 nC m−3) are comparable to those reported for convective cells. The brightband level had negative charge, and just above that was the maximum total electric-field magnitude (120 kV m−1). The horizontal component of the field was 20–40 kV m−1 through much of the flight and attained a peak value of 70 kV m−1, supporting the presence of charge distribution inhomogeneities in the stratiform region. Despite the complexity of the vertical electric-field profile, its coarse structure is similar to others reported for the stratiform region and transition zone. Charged particle advection from the main convective zone may have produced this structure, prior to its complication by convection.
Abstract
Balloon soundings of electric field in Oklahoma mesoscale convective systems (MCS's) were made by the National Severe Storms Laboratory (NSSL) during the spring of 1989. A sounding made in the rearward edge of an MCS stratiform rain area on 7 June 1989 is the centerpiece of this study. We used data from Doppler radars, a lightning ground-strike location system, satellite, and other sources to relate the mesoscale attributes of the MCS to the observed electric-field profile.
The stratiform area did not lag an organized convective line, but was apparently initiated by anvil precipitation downwind of convective cells that were at the west and southwest flanks of the MCS. The mature system produced a bipolar cloud-to-ground lightning pattern, in which most flashes of positive polarity came to ground in the downshear anvil or stratiform region. The bipole was oriented from 220°, parrallel to upper-level geostrophic flow, and its length was 190 km. We visually observed lightning flashes in the stratiform region that had long segments along cloud base.
At least two cells separated from the main convective zone and moved near the region of stratiform cloud penetrated by the balloon. These convective cells may have influenced the intricate charge structure, which was manifested by 11 distinct charge layers from the electric-field sounding. Ten of the 11 charge layers were found between 3 and 8 km MSL (+10° to −24°C), a depth coinciding with rear inflow into the stratiform region. Charge-density magnitudes (up to 3.9 nC m−3) are comparable to those reported for convective cells. The brightband level had negative charge, and just above that was the maximum total electric-field magnitude (120 kV m−1). The horizontal component of the field was 20–40 kV m−1 through much of the flight and attained a peak value of 70 kV m−1, supporting the presence of charge distribution inhomogeneities in the stratiform region. Despite the complexity of the vertical electric-field profile, its coarse structure is similar to others reported for the stratiform region and transition zone. Charged particle advection from the main convective zone may have produced this structure, prior to its complication by convection.
