Forecasting Error of Cold-Air Damming Atmospheric Fields in a Mesoscale Numerical Weather Prediction Model

抄録

In the Kanto region in Japan, cold-air damming (CAD) is known to occur approximately 13 times a year and to be linked to snowfall and heavy rainfall, making its accurate forecasting critically important. This study evaluated the forecast accuracy of CAD in the Japan Meteorological Agency's operational mesoscale model (MSM) over the period 2007-2024. The results revealed that 12-h forecasts showed a warm bias exceeding +0.8 K in the lower atmosphere over southern Kanto and an underestimation of the southwestward cold-air flow. These biases increased with longer forecast lead times and tended to extend southwestward over the ocean south of the Tokai region. Analysis of the position of the isentropic surfaces revealed that the thickness of dammed cold air and its seaward extent tended to be underestimated. Although the warm bias exhibited a gradual decreasing trend (−0.02 K/year), a warm bias persisted even after the MSM was updated to the new non-hydrostatic model.