ABSTRACT:The Korea Meteorological Administration has limited understanding of how users interpret probabilistic forecast information and use it in their decision-making processes. Thus, a survey was conducted among users to find out at which probability threshold for adverse weather they would react and take protective action to minimize the losses. According to previous studies, probability threshold depends on the type of users but they are in general higher than a 50% forecasts chance of adverse weather, even though research has shown that the forecast value is maximized when actions are taken for probability of adverse weather lower than 50%. A collective value score model, defined as a weighted sum of user's satisfaction and threshold distribution in a group of users, is introduced as a measure of total satisfaction of a user group. The collective value score model is applied to a set of precipitation probabilistic forecasts of Seoul, South Korea during 2002-2011. The results show that the collective value score can be improved if the range of users' probability thresholds is widened rather than improving the forecast accuracy.

This study assessed drought conditions in northern China and Mongolian areas using the Palmer drought severity index (PDSI). Droughts in this area were intensified throughout all seasons. In particular, this intensifying trend was pronounced in the summer and autumn. In the summer, the PDSI showed an overall increase from the early 1990s to the late 1990s, and then, it rapidly decreased after the late 1990s. Therefore, this study focused on summer droughts and analysed mean differences before the late 1990s (9098) and after the late 1990s (9905). Regarding differences in 850 hPa stream flows between the two periods, anomalous anticyclonic circulations were strengthened in northern China and Mongolia that showed strong negative anomalies in the PDSI. These anomalous anticyclones were formed as a positive North Atlantic Oscillation pattern formed in the European region spread eastward in the form of wave trains. The anomalous anticyclones formed in northern China and Mongolia led to reduced total cloud cover. As a result, this region exhibited high sensible heat net fluxes. Consequently, warm and dry anticyclones may have recently been strengthened in this region, thereby intensifying droughts. As this shows, recently strengthened warm and dry anticyclones in northern China and Mongolia were associated with recently reduced snow depths in this region during the preceding spring. In recent years, the frequency of Asian dust has also increased due to warm and dry air conditions.