Adjoint sensitivity analyses for three Asian dust events affected the Korean Peninsula

Asian dust is a seasonal meteorological phenomenon. Mostly in spring, dust particles blown into atmosphere in the arid area over North China desert and Manchuria are transported to East Asia by prevailing flows. Recently, it has been reported that the Asian dust occurs even in fall or winter. Such change causes difficulty in forecasting Asian dusts due to the different transport pattern related to seasonal meteorological systems. In this study, three Asian dust events occurred in different seasons were chosen to investigate the forecast sensitivity with respect to the initial condition: March 2007 case (case 1), May 2008 case (case 2), and Dec. 2008 case (case 3). To assess the sensitivities to the initial condition, adjoint sensitivities that calculate gradient of the forecast aspect (i.e., response function) with respect to the initial condition were used. The forecast aspect relevant to the Asian dust events is energy of the forecast error. In case 1, the vertically integrated energy distributions of the sensitivity are located in the south and southwest away from the lower trough in the source region. The sensitive regions south (southwest) of the lower trough are vertically located in the low (mid-) level. Those sensitivities horizontally distinguishable in mid and low levels can affect the forecast error in the Korean peninsula respectively. In contrast, the sensitive regions of case 2 and 3 are located in the lower trough near the source region. The lower trough is located near the Inner Mongolia and Gobi desert, then propagates eastward. Although the horizontal sensitivity structures are different for three cases, the vertically upshear-tilted baroclinic structures appear for all three cases, implying that the perturbations of baroclinic structure at the initial time are closely related with the forecast error at the verification time for three Asian dust events. In the vertical profile of the cases, the initial sensitivities of case 1 are concentrated in the low to mid- level, and the sensitivities of case 2 (case 3) are located at mid (low) level. More comprehensive results for the energy forecast aspects above and additional results for the sensitivity with respect to vorticity will be presented in the meeting.