A Mechanism Causing Mesoscale Organizations of Precipitation in Midlatitude Cyclones

Results from a linear analysis and numerical integrations of a two-dimensional model of moist frontogenesis show that mesoscale organizations of precipitation in midlatitude cyclones may be caused by a positive feedback process between potential-vorticity anomalies and latent heat release in condensation. The instability analysis indicates that the instability is a mesoscale process due to the small magnitude of the temperature perturbations associated with potential-vorticity anomalies at the small end of the mesoscale and the small vertical velocity induced by beating at the synoptic scale. Numerical model results show considerable mesoscale organizations in the condensation field can be created by this instability process.