Simulations of Winter Mesoscale Circulations associated with an Isolated Heat and Moisture Source

A fundamental outstanding issue in boundary layer and mesoscale research is how the atmosphere responds to, and interacts with, surface heat and moisture variations. Using an array of thirty idealized mesoscale model simulations, we have examined the atmospheric response and subsequent mesoscale circulation resulting from cold flow over an isolated body of water at mid-latitudes. Parameters such as wind speed, water-air temperature difference, ambient atmospheric stability, and dimensions of the body of water were varied across observed ranges. Our findings suggest that the mesoscale structures that develop under varied ambient conditions are located within several regimes (e.g., vortices, bands) and are dependent on the Rossby number (Ro=V/f·L). Model simulations with low Rossby numbers (i.e., Ro < 0.18) resulted in a mesoscale vortex circulation. Simulations having Rossby numbers between 0.18 and 1.0 generated singular banded structures (e.g., land-breeze convergence zone) and a broad convergent region was produced at large Rossby numbers (Ro > 1.0). Additionally, our results demonstrate that the intensity of the mesoscale response (e.g., maximum vertical motions) can be predicted using a dimensionless function comprised of fundamental variables (e.g., wind speed, water-air temperature difference, ambient stability). This dimensionless function will be described and a physical interpretation will be presented.