Characterizing icing and non-icing events in cold and alpine environments using instrumentation and NASA Langley cloud products

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Rathbun, Brett W.
One of the goals of the NASA EPSCoR (Experimental Program to Stimulate Competitive Research) Icing Assessments in Cold and Alpine Environments Project is to study the environmental factors that lead to icing in mountainous terrain. One part of this research effort involved using instrumentation at mountainous locations in New England during the 2011-2012 winter season to provide icing information for validation of icing forecast models. This part of the project focused on analyzing the instrument data to characterize differences between icing and non-icing conditions. There were two prongs to this research. The first one examined the differences in the synoptic and surface environments between icing and non-icing events. Icing events were defined as periods where icing was reported at the summit of Mount Washington for at least 24 consecutive hours. With this definition, 34 icing events were found with a peak event lasting 93 hours. Synoptic and surface analyses were examined for these 34 events as well as 10 non-icing events (no icing reported in a 24 hour period) using raw METAR observations at Mount Washington and archived frontal analysis charts from the Hydrometeorological Prediction Center. The second prong of this research project dealt with analyzing data retrieved from specialized instrumentation placed in the study area during this past winter. These instruments included radiometers, ceilometers, and ice detectors. Ice detector databases from 1 November 2011 to 30 April 2012 were created comparing liquid water content and daily ice accumulations at three mountain summits in New England. Cloud products developed through GOES satellite imagery (icing potential, cloud-base height, and cloud-top height) were retrieved from the NASA Langley Research Center to determine its accuracy in locating icing and non-icing environments and were compared to ground based instrumentation. During the 2011-2012 winter season, the 34 icing events were divided into the following categories: Post Cold Front (PCF), Warm Front to South (WFS), Multiple Fronts and Cyclones (MFC), Cold Front to West (CFW), Nor'easter (NE), and Miscellaneous (MSC). The 10 non-icing events were divided into the following categories: East Coast Highs (ECH), Northeast/Quebec Highs (NQH), and Nova Scotia Lows (NSL). The ice detector databases showed that the heaviest icing occurred at Mount Washington with many occurrences of daily ice accumulations greater than 100 cm. The highest daily ice accumulation at Mount Mansfield was ~33 cm. However, higher liquid water content values were seen at Mount Mansfield than Mount Washington. These databases will be used for future numerical model verification. Of the three NASA Langley cloud products, icing potential performed the best but, further research should be done to test its performance. Cloud-base height and cloud-top height did a poor job in determining cloud heights as it had a < 50% success rate in determining cloud heights within ± 1.0 km.