2:15 PM - 2:30 PM
[U07-12] Issues on numerical weather prediction detected by formation mechanisms of Hiroshima heavy rainfall on 20 August 2014
Keywords:heavy rainfall, band-shaped precipitation system, numerical weather prediction model
The Japan Meteorological Agency operates Local Model (LM) with a horizontal resolution of 2 km every hour for nine hour forecasts. The forecasts with initial conditions at 18 JST (= UTC + 9hours) 19 August 2014 successfully reproduced the band-shaped precipitation system; those with initial conditions after then, however, produced different features in rainfall amounts and the location of the precipitation system. Even when low-level inflow has the same equivalent potential temperature, rainfall amounts depend on water vapor flux amounts that are changed by wind speed and the 1~2 degree change of wind direction alters the location of the precipitation system by a few tens kilometers. These indicate that the accuracy of wind speed and direction is necessary for the improvement of heavy rainfall predictions, as pointed out by Kato and Aranami (2005), in addition to the accuracy information of low-level water vapor upstream of the occurrence location of heavy rainfall. In Hiroshima heavy rainfall case, water vapor was accumulated in the lower atmosphere over Bungo Strait, which suggests that boundary layer processes in numerical models should be validated to be improved. Since observations over the sea are necessary to be obtained, the cooperation with different fields of research institutes is important as well as that of meteorology.
Kato, T., and K. Aranami, 2005: Formation factors of 2004 Niigata-Fukushima and Fukui heavy rainfalls and problems in the predictions using a cloud-resolving model, SOLA, 1, 1-4.