Abstract
A prediction experiment is performed with a very-fine-mesh (42km at 60°N) primitive equation model for a heavy snowfall event in the Hokuriku District associated with a convergent cloud band over the Japan Sea. Using the result of the experiment, together with observed data including special
soundings, we elucidate the structure of the convergent cloud band with a line of active convection on its southwestern edge.
The atmosphere around the cloud band has the following characteristic features:
- a low-level convergence, middle-level divergence zone accompanied by intense positive vorticity along the line of active convection,
- a warm and weak-wind zone along the line of active convection embedded in cold airmass
- a weak stable layer on the northeastern side of the line of active convection as a boundary between two layers: a lower layer with northerly cold air flow toward the line of active convection and an upper layer with southwesterly warm air flow which has been heated in the line of active convection,
- a west-northwesterly air flow on the southwestern side of the line of active convection with weak vertical wind shear and nearly neutral stratification up to the top of the cold airmass,
- a strong-wind zone at the divergent level (700-6OOmb) 300-500km northeast of the line of active convection.
On the basis of cross-section and trajectory analyses, we can make a clear picture of the atmosphere around the cloud band.
Heat and water vapor budget analysis indicates that over the southern Japan Sea the mesoscale thermal structure around the cloud band is largely maintained by localized release of latent heat in large-scale cold air advection field.
