2002 Annual

Monday, 14 January 2002: 11:44 AM
Land-atmosphere feedback across eastern Oklahoma following the MCS events of August 1994
Derek S. Arndt, Oklahoma Climatological Survey, University of Oklahoma, Norman, OK; and K. C. Crawford
Poster PDF (189.9 kB)
During a 60-hour period in August 1994, two mesoscale convective systems deposited 50 mm of rainfall in a “footprint” across central and eastern Oklahoma. No significant rainfall occurred across the region during the week before and the week after these events. The region was dominated by a single air mass through the period. Mesonet observations indicated a pronounced diurnal oscillation of moisture over the footprint during each of the six days following the event. Afternoon dew point temperatures were greater, and air temperatures less, than nearby areas that received no rainfall. This oscillation suggests a larger latent heat component in the heat flux over the footprint, relative to those areas that did not receive rainfall.

The Pawnee and Blackwell Mesonet stations are 60 km apart in north-central Oklahoma. Pawnee observed 52 mm rainfall during the events, while Blackwell received none. During the six days following the rainfall events, the average diurnal trends of surface moisture evolved differently at the two sites despite their proximity. At Pawnee, the mixing ratio increased relative to the pre-event period, while at Blackwell, the mixing ratio decreased.

Both the Oklahoma Mesonet and the federal surface observation network captured broad patterns of change in surface moisture from six days before the event to six days after the event. However, the Mesonet captured mesoscale detail during the post-event period that escaped detection by the federal network. The presentation will provide details on how the land and the atmosphere were connected following the rainfall event.

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