2012 Volume 90 Issue 6 Pages 905-921
On 11 November 2007, record heavy rainfall was observed over Aomori Prefecture in northern Japan. Numerical simulations were performed using a non-hydrostatic model with a horizontal resolution of 5 km (5km-NHM) to clarify the formation mechanisms of this heavy rainfall. The results revealed that a meso-β scale vortical disturbance (MβV) originated over the offshore area with strong horizontal wind shear southeast of Aomori Prefecture at 0600 UTC 11 November. The MβV traveled north-northwestward over the sea and landed in Aomori Prefecture at 1200 UTC. The heavy rainfall was caused by convective systems associated with the MβV.
A kinetic energy budget analysis was conducted using the results of 5km-NHM to account for the development of the MβV. Eddy kinetic energy (EKE) increased with time, while mean kinetic energy decreased. This relation implies that the MβV developed in association with kinetic energy conversion from the mean part to the eddy part. Horizontal shear below a height of 1 km played a key role in EKE production, and vertical advection by mean and perturbation flows transported EKE produced in the lower layers to the upper layers. The vertical shear and buoyancy did not significantly contribute to the EKE increase. The pressure gradient force normal to the shear line also contributed to EKE production by accelerating horizontal wind speed. A sensitivity experiment without diabatic heating indicates that convective activities affected the development and maintenance of horizontal shear, which significantly contributed to the MβV development.
