Quantitative Precipitation Forecast Sensitivity to Microphysics Parameterization and Sea Surface Temperature Source over North Carolina during Two Cold Season Events

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Title: Quantitative Precipitation Forecast Sensitivity to Microphysics Parameterization and Sea Surface Temperature Source over North Carolina during Two Cold Season Events
Author: Haglund, Nicole Lynne
Advisors: Brad S. Ferrier, Committee Member
Sandra E. Yuter, Committee Member
Gary M. Lackmann, Committee Chair
Abstract: In the southeastern United States, some of the most dramatic model quantitative precipitation forecast (QPF) failures in recent years have been associated with winter precipitation events. For example, the Eta model predicted nearly three inches of total liquid equivalent precipitation over most of central and eastern North Carolina for 2-3 December 2000, while less than 0.10 in. (2.54 mm) of liquid equivalent precipitation actually fell over the majority of central North Carolina. While the over-prediction of precipitation for the 21-22 January 2003 event was not as significant, the predicted precipitation nevertheless might have led to a higher impact case, if it had verified. Despite a forecasted liquid cloud with cloud top temperatures warmer than -15°C, the Eta model produced excessive QPF for both cold season events. The purposes of this study are (i) to determine whether sea surface temperature data source (1° by 1° weekly Reynolds SST vs. 1.27-km CoastWatch daily SST) could have significantly impacted the 2-3 December 2000 QPF; (ii) to test sensitivities associated with the Ferrier microphysics scheme by studying the effects of various ice nucleation and total glaciation temperatures on QPF; and (iii) to investigate sensitivity of QPF to sea surface temperature data and to choice of microphysics scheme to determine which change yields a more significant contribution to QPF differences. In an effort to understand why the Eta model over-predicted precipitation in the 2-3 December 2000 and 21-22 January 2003 winter events, sensitivity tests were conducted using the Weather Research and Forecasting model (WRF). These sensitivity studies included testing the QPF differences due to choice of microphysics parameterization scheme and to choice of sea surface temperature (SST) data source for the 2-3 December 2000 case, while only the sensitivity of QPF to choice of microphysics parameterization scheme was tested for the 21-22 January 2003 case. It was hypothesized that by cooling the ice nucleation and total glaciation temperatures, better QPF (less precipitation with a cooler ice nucleation temperature, more precipitation with a cooler total glaciation temperature) would result in both cases. Since the cloud top temperature in the 21-22 January 2003 case was below the original total glaciation temperature (-10°C), cooling the total glaciation temperature was not expected to change the QPF. Additionally, for the 2-3 December 2000 case, it was hypothesized that changes in SST data source would have a greater impact than the choice of microphysics parameterization scheme on QPF. Major findings in this study include: (i) Surface low tracks and total precipitation patterns were not significantly different between the runs using Reynolds SST and CoastWatch SST data; (ii) By cooling the ice nucleation temperature in both case studies, better (closer to analyzed) QPF resulted in the 21-22 January 2003 case. With a cooler total glaciation or ice nucleation temperature in the 2-3 December 2000 case, no clear QPF difference pattern emerged; (iii) While a qualitative analysis of total liquid-equivalent precipitation differences between SST data source and microphysics parameterization scheme runs indicated that SST data source had a greater impact on QPF than choice of microphysics scheme, area-averaged total liquid-equivalent precipitation in three regions showed that choice of SST data source led to QPF biases on the same order of magnitude as the QPF biases due to choice of microphysics scheme; and (iv) Since there are more similarities between simulations run with a particular version of WRF (V2.1.2 vs. a subsequent version) than there are between the two versions using any microphysics scheme, choice of microphysics scheme has less of an impact on QPF than convective parameterization (CP) scheme activity for the winter storm cases studied here.
Date: 2007-05-16
Degree: MS
Discipline: Marine, Earth and Atmospheric Sciences
URI: http://www.lib.ncsu.edu/resolver/1840.16/1042


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