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The Representation of Low Cloud in the Antarctic Mesoscale Prediction System

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2015, Master of Science, Ohio State University, Atmospheric Sciences.
The accuracy of cloud prediction in Antarctica can have a significant impact on aviation operations. Unforecast low cloud can endanger an aircraft attempting to land, and affect a pilot’s ability to distinguish the horizon and surface features while in flight. Over-forecasting of low cloud results in fewer missions completed. A number of cloud forecast products have been developed over the years however forecasters often prefer to use the low level relative humidity (RH) fields to forecast low cloud. This study investigated the use of the Stoelinga-Warner algorithm to generate the current Antarctic Mesoscale Prediction System (AMPS) cloud base height forecast and whether a RH threshold could be used as a proxy for cloud base height. The Stoelinga-Warner algorithm was tested using a case study of a mesoscale low in Prydz Bay near Davis station. The algorithm was insensitive to changes in the phase scheme and light extinction threshold used to predict cloud base. Further investigation revealed inadequate quantities of cloud hydrometeors, indicating a problem with the model’s microphysics scheme. Therefore, AMPS combined with the Stoelinga-Warner algorithm does not accurately predict cloud base height. Cloud base heights derived from radiosonde RH thresholds were compared with synoptic observations for Davis, McMurdo and Halley. Lidar observations were also tested against both synoptic observations and radiosonde-derived cloud base heights at Halley. The optimal RH threshold for predicting cloud base height was ~70% at Davis and McMurdo, and ~90% at Halley. AMPS RH data was used to generate cloud base heights at different thresholds, and these were verified against synoptic observations. Results were mixed due to the comparatively large scatter in the model RH field, with the optimal RH threshold changing according to the verification metric used. However there was broad agreement that Davis and McMurdo required a lower RH threshold than Halley. The thresholds found for Davis and McMurdo are consistent with a study by Inoue et al. (2015) which found optimal RH thresholds between 58% and 66% for Davis, Casey and Mawson stations. The reason for the much higher threshold at Halley is unclear, and further studies are required to determine whether a general RH threshold can be applied across the continent to predict cloud base height.
David Bromwich (Advisor)
Jay Hobgood (Committee Member)
Jialin Lin (Committee Member)
93 p.

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Citations

  • Pon, K. (2015). The Representation of Low Cloud in the Antarctic Mesoscale Prediction System [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440428143

    APA Style (7th edition)

  • Pon, Karen. The Representation of Low Cloud in the Antarctic Mesoscale Prediction System. 2015. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1440428143.

    MLA Style (8th edition)

  • Pon, Karen. "The Representation of Low Cloud in the Antarctic Mesoscale Prediction System." Master's thesis, Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440428143

    Chicago Manual of Style (17th edition)