Structure and evolution of numerically simulated misocyclones along a snowband over the Shonai region on 25 January 2008

On 25 January 2008, strong wind gusts (about 30 m s^-1) occurred locally in the Syonai region, coastal area of the Sea of Japan, during the passage of a snowband. Doppler radar system detected a number of low-level misocyclones in the snowband, indicating that the near-surface wind gusts were associated with the misocyclones. However, detailed features of the misocyclones were not captured by the observation.

In order to clarify the structure and evolution of the misocyclones, we performed numerical simulations in which fully compressible nonhydrostatic models (JMANHM; Saito et al., 2006) having horizontal grid spacings of 5km, 1km, 250 m and 50 m, respectively are nested into the operational regional analysis of the Japan Meteorological Agency (JMA).

The simulation well reproduced the developed snowband accompanied by the low-level wind shear. Wavelike disturbances (3~4 km wavelength) developed along the shear line in the snowband around the Syonai region. The distribution of eddy-component horizontal winds showed that the kinematic energy was converted from the mean flow to the eddies. As the wavelike pattern was amplified, several vortical disturbances became prominent along the low-level shear line and exhibited characteristics of a misocyclone. One misocyclone had a strong cyclonic circulation of about 1 km diameter and large vertical vorticity exceeding 0.01 s^-1 at a height of 500 m. The vortical disturbance was generated below 300 m height and developed into the subsequent misocyclone.