A case of a remarkable polar low development over the Japan Sea on 21 January 1997 was simulated by a non-hydrostatic cloud-resolving model ( Meteorological Research Institute Non-Hydrostatic Model: MRI-NHM) with a horizontal resolution of 2km. The evolution of the polar low as well as a number of observed features such as spiral cloud bands and a cloud-free eye including cloud streets associated with the cold air outbreak are well reproduced. The maximum vorticity of more than 3.5x10^-3 s^-1 occurs at the height of 130m above the sea surface. The detailed structure of the simulated polar low will be reported.

The developing mechanism of the simulated polar low has been also examined by a sensitivity study in which effects of surface fluxes and condensational heating are turned on and off for different time periods. The results of the sensitivity study suggest that the development of the polar low itself is mainly caused by the condensational heating. However, the surface fluxes are also important in a sense that they maintain the basic field that supports the development of the low.