92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Wednesday, 25 January 2012
Hurricane Force Winds in Winter Ocean Storms: A Look At the Evolution
Hall E (New Orleans Convention Center )
Benjamin Albright, Howard Univ., Washington, DC; and J. M. Sienkiewicz and T. W. Yu

Ocean vector winds from the NASA QuikSCAT satellite demonstrated that hurricane force winds occur more frequently in maritime extratropical cyclones than formerly thought. Earlier wind observations were primarily from the sparse network of volunteer observing ships. Based on QuikSCAT data, we know that extreme winds occur in the rapid deepening to mature phase of the life cycle, typically, on the cold side of the bent back portion of the occluded front. Maritime extratropical cyclones can be very large, with radii of gale force winds in excess of 800 n mi or more. The cyclones produce extreme winds and waves and pose a significant threat to shipping, fishing, and oil exploration. Waves generated by these storms impact coastlines far removed from the storm system. Because of the rapid intensification, the development of dangerous conditions, and inability of global numerical models to accurately predict the timing, structure and intensity of these storms, it is necessary to better understand the evolution of these storms and diagnose the causes of extreme winds.

This study follows a particularly strong North Atlantic storm from January 31, 2011 at 1200 UTC to February 2, 2011 at 1200 UTC. The Weather Research and Forecast Environmental Modeling System (WRF EMS) was used to model the evolution of this cyclone. This storm was chosen for examination because of its strength, rapid intensification, and high resolution in situ data acquired by the NOAA WP-3D research aircraft as part of the Ocean Winds Winter Experiment. NOAA WP-3D N43RF flew within the storm from 1605-1851 UTC on February 1 during rapid intensification and sampled hurricane force winds via the Stepped Frequency Microwave Radiometer (SFMR) and GPS dropsondes. The WRF EMS was used to downscale model data from the NCEP Global Forecast System (GFS), which was used to initiate the WRF EMS run. Input was every three hours at one degree resolution and output from the WRF EMS was hourly at 12 km resolution. The output showed a 1007 hPa low at 1200 Z on Janurary 31, 2011 that rapidly deepened to 966 hPa at 1200 Z on February 1, 2011, a 41 hPa drop in 24 hours. The WRF EMS produced hurricane force winds three separate times over the 48 hour period to the south of the low. Cross sections orthogonal to the area of strongest winds and the associated bent back front show a low level jet with winds as high as 100 knots between 800-950 mb.

Future work on this storm will include trajectory analysis on the airflow through the low level jet and bent back front to try and determine the origin and evolution of the flow. Also, dynamic diagnostic tools will be applied to the storm and bent back front region in an effort to understand the forcing and resultant evolution.

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