Development of the Korean Turbulence Guidance (KTG) system based on the Unified Model and pilot reports (PIREPs) over East Asia

The Korean Turbulence Guidance (KTG) system is developed using the Unified Model (UM) with 12 km horizontal grid spacing that is the operational numerical weather prediction (NWP) model in the Korea Meteorological Administration (KMA). The KTG system is comprised of ten turbulence diagnostics that represent various turbulence potentials and have the best forecasting skills, which are combined into a single ensemble-averaged index, namely KTG, at upper- (above FL250) and mid-(below FL250) levels. Pilot reports (PIREPs) over East Asia for 1-yr from 1 June 2011 to 31 May 2012 are used for evaluation. 7007 (288) and 415 (17) of null (NIL) and moderate-or-greater (MOG) PIREPs observed within ± 2-hrs around 00, 06, 12, and 18 UTC are available at upper-(mid-) levels. It is found that the overall performance of the KTG at upper- and mid-levels is higher than those produced from the one single best diagnostic at each level. To test the sensitivity of the KTG system to model vertical grid spacing, two different types of the UM outputs are used. One uses isobaric coordinates that have 24 layers between 50 and 1000 hPa, and second one uses a hybrid coordinate that has 70 layers between z = 0 and 80 km. The KTG on isobaric coordinate (coarser vertical resolution) has lower performance than that on hybrid coordinate (finer vertical resolution). When the KTG is comprised of the ten best diagnostics that are normalized by Ri, the overall performance is improved.