Aircraft turbulence is a hazard to in-flight passengers and crews. According to a recent report of National Transportation Safety Board, the turbulence was a major cause of commercial aircraft accidents producing serious injuries from 1993 to 2002. To reduce these damages, the Korea Meteorological Administration developed the Korean Integrated Turbulence Forecasting Algorithm (KITFA) in 2002 which was based on the Integrated Turbulence Forecasting Algorithm of the National Center for Atmospheric Research / Research Applications Program. The KITFA routinely ingests 30 km and 5 km horizontal resolution outputs of the Regional Data Assimilation and Prediction System as its inputs, and then it weights and combines 12 clear air turbulence (hereafter, CAT) diagnostic indices with the Pilot Reports (PIREPs) data. In this study, to improve the CAT forecasts, we primarily analyze the spatial and temporal distribution of turbulences occurred in South Korea using the PIREPs data for 10 years from 1996 to 2007 excluding 2001 and 2002.

Among the total PIREPs data in this period, turbulences were reported approximately 18 percents (2,153/11,773). Seasonally, the monthly frequency of turbulence occurrence is highest in winter season, which is likely associated with the strong Jet streams. When the monthly frequency is classified by intensity of the turbulence, the frequency of moderate or greater intensity is highest in spring season due to the unstable conditions often caused by well-developed low pressure system.

As for the spatial distribution of turbulence occurrence, the turbulences occurred below 25,000 ft are concentrated on the lee side of the Sobaek mountain region especially in winter and spring seasons. This result would be related to the strong northwesterly flow induced by Siberian High expending to the Korean peninsula. The turbulences occurred above 25,000 ft were located near the west and south coastal regions in South Korea for all seasons. Those turbulences could be caused by various weather systems such as Changma front and local convections. Validation of KITFA results compared with the PIREPs data will be presented in the conference.