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AOSC Seminar by Dr. Richard Clark, 10/14/2021

AOSC Seminar

Dr. Richard Clark


Millersville University

Title: Nocturnal Destabilization Associated with the Summertime Great Plains Low-Level Jet


The Great Plains low-level jet (LLJ) has long been associated with summertime nocturnal convection over the central Great Plains of the United States. Destabilization effects of the LLJ are examined using composite fields assembled from the North American Mesoscale Forecast System for June and July 2008–12. Of critical importance are the large isobaric temperature gradients that become established throughout the lowest 3 km of the atmosphere in response to the seasonal heating of the sloping Great Plains. Such temperature gradients provide thermal wind forcing throughout the lower atmosphere, resulting in the establishment of a background horizontal pressure gradient force at the level of the LLJ. The attendant background geostrophic wind is an essential ingredient for the development of a pronounced summertime LLJ. Inertial turning of the ageostrophic wind associated with LLJ provides a westerly wind component directed normal to the terrain-induced orientation of the isotherms. Hence, significant nocturnal low-level warm-air advection occurs, which promotes differential temperature advection within a vertical column of atmosphere between the level just above the LLJ and 500 hPa. Such differential temperature advection destabilizes the nighttime troposphere above the radiatively cooled near-surface layer on a recurring basis during warm weather months over much of the Great Plains and adjacent states to the east. This destabilization process reduces the convective inhibition of air parcels near the level of the LLJ and may be of significance in the development of elevated nocturnal convection. The 5 July 2015 case from the Plains Elevated Convection at Night field program is used to demonstrate this destabilization process.



Richard D. Clark is the Chair of the Department of Earth Sciences and Professor of Meteorology at Millersville University. Rich is 2021 AMS President-Elect and Fellow and served as a member of AMS Council (2008-11) and currently serves on several AMS Committees. He served two terms as an at-large member of the UCAR Board of Trustees (2009-2015) and served on UCAR governance committees. His research interests span boundary layers, low-level jets, and air chemistry with a special emphasis on field observations and instrumentation using airborne and balloon-borne platforms. He recently completed a collaborative effort with NCAR and COMET to produce a 10-lesson interactive online course on atmospheric instrumentation and measurement. Rich is the program coordinator of two graduate programs: the M.S. in Integrated Scientific Applications, which is focused on creating business-ready scientists, and a Graduate Certificate Program in Space Weather and Environment: Science, Policy, and Communication. He is the recipient of the 2006 Unidata DeSouza Award and the 2008 AMS Teaching Excellence Award. Rich has a Ph.D. in atmospheric science from the University of Wyoming (’87).


Contact: Jonathan Poterjoy


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AOSC Seminar

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Seminar: 3:30-4:30pm, Zoom
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