The Impact of the Prevailing Synoptic Situation on the Lake-Aggregate Effect

Abstract

The effects of a group (aggregate) of relatively warm circular meso-?-scale lakes on different flow regimes were investigated by conducting a series of idealized numerical experiments. This investigation was motivated by the observed behavior of synoptic-scale cyclones moving through the Great Lakes region during winter. Three with-lake (WL) and three corresponding no-lake (NL) simulations were initialized with 1) zonal flow, 2) a solitary trough, and 3) continuous sinusoidal waves, respectively. The WL experiments were intercompared to examine the importance of a preexisting disturbance and preconditioning. The NL simulations were compared to the corresponding WL simulations to study the contributions of the lake aggregate. The simulation results suggest that the lake aggregate induced or enhanced warm fronts when there were preexisting disturbances. They also suggest that a perturbation mesoscale aggregate vortex was generated in each of the three different flow scenarios even though the lake aggregate alone could only generate a weak meso-α-scale trough. To identify the physical processes that were altered by the lake aggregate to enhance cyclone development, surface pressure tendency diagnosis using the extended Zwack?Okossi (ZO) equation was applied to the simulation results. The results of the ZO surface pressure (PSFC) tendency diagnosis indicated that the preconditioning from the preceding ridge contributed to the further development of the lake-aggregate?enhanced cyclones. The results also indicated that the lake aggregate not only reduced the PSFC locally through surface sensible heating but also and, more importantly, contributed to large-scale surface pressure deepening by enhancing the surface warm front.