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Last modified
7/28/2009 2:35:13 PM
Creation date
4/15/2008 2:38:48 PM
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Weather Modification
Title
Weather Modification Programme - Catalogue of Data Sets for the International Cloud Modelling Workshop/Conference
Date
6/1/1984
Weather Modification - Doc Type
Report
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<br />3 . 1. 1 . 1 . 4 Ha il <br />A. CCOPE - August 2, 1981 <br /> <br />Excellent aircraft and mesonet observations of a hailstorm were obtained in this <br />case. Comprehensive data for the initialization and verification of model <br />predictions is available for the life cycle of this storm. Therefore it was <br />selected as a hail case study. <br /> <br />A si gnifi cant feature on August 2 was the WE!stward advection of cool, moi st ai r <br />into the region beneath a 700 mb inversion. This inversion allowed potential <br />instability to increase to unusually high levels during the afternoon. The <br />storm developed over higher terrain to the \'Iest of Mi les City and moved rapidly <br />east-southeastward through the heart of the radar and surface networks. Wind <br />and hail damage as well as surface mesolow clccompanied the storm. <br /> <br />The T-28 research aircraft penetrated a weak echo region (WER) associated with <br />the intense thunderstorm. The west-to-east penetration occurred about 2 hours <br />after the storm developed, at a time when the maximum reflectivity factor <br />exceeded 65 dBZ. The WER extended above thE! 10 km level at the time of penetra- <br />tion. Peak updrafts in the WER exceeded 40 m s-l, and a continuous region of <br />updraft extending over a horizontal distance of 11 km was observed. Downdrafts <br />were observed on both sides of the updraft region with minimum values near -20 m <br />s-l. The updraft core appeared to be undiluted but the edges of the updraft <br />were clearly mixed with environmental air. <br /> <br />Virtually no ice particles were observed within the weak echo region, but maxi- <br />mum cloud liquid water concentrations exceeded 6 g m-3. Hail was observed on <br />both sides of the updraft, with the largest particles encountered on the west <br />side. Maximum hail sizes were up to 5 cm. <br /> <br />Hail growth appears to have intiated within feeder cells along the west and <br />south sides of the storm. The embryos were then advected into the vicinity of <br />the main updraft region where they could develop into large hail growing in the <br />high amounts of cloud liquid. <br /> <br />Analysis of Doppler radar measurements reveals that the August 2, 1981 storm had <br />an internal kinematic structure reminiscent of super-cells. Features included <br />low level relative inflow speeds as large as 30-40 m s-l, cyclonic rotation <br />within an intense updraft (maximum speed of 45 m s-l), a bounded weak echo <br />region or reflectivity vault that was coincident with the updraft and strong <br />upper level outflow in excess of 40 m s-l. A modest downdraft and anticyclonic <br />rotation were detected within the high reflectivity region of the low level hook <br />echo behind the gust front. Examination of the reflectivity structure suggests <br />that these features persisted in a nearly steady configuration for more than 90 <br />mi nutes. Synthesi zed wi nds at 1810 MDT show that ai r withi n the updraft stream <br />rose along anticyclonic paths and exhausted into the anvil toward the east and <br />northeast. Simplified precipitation trajectory calculations indicate that some <br />ice particles falling from above 10 km MSL followed cyclonic paths around the <br />south and east flanks of the updraft and fell out on its north side. These par- <br />ticles constituted the radar echo around the southeast periphery of the vault. <br /> <br />15. <br /> <br />__I <br />
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