THERMAL MESOSCALE CIRCULATIONS ON THE BALTIC COAST .2. PERTURBATION OF SURFACE PARAMETERS

A three-dimensional numerical study of an observed seabreeze (SE) is p resented in a companion paper, part 1. This paper, part 2, addresses t he influence of various forcing parameters emanating from the physical surface and perturbing the control run. The control run in part 1 rev eals that the SE stage is preceded by a coastal jet (CJ) stage and tha t even moderate terrain seems to have a strong influence on the coasta l mesoscale circulation. The parameter sensitivity analysis attempts t o identify the hierarchy of surface effects on the previously observed and modeled dynamics, while the background airflow parameters remain unchanged. Seven perturbation runs are presented: two topographic, thr ee land surface, and two sea surface temperature perturbations. It is shown that the terrain elevations (h(0) less than or equal to 206m) ha ve profound impact on the flow and its time history. The main offshore island has a notable impact but does not change the main flow structu re. Surface temperature perturbations modify the CJ pattern dictated b y the mesoscale thermal wind; they also influence the SE shape more bu t the SE front propagation less. The SE at one coast is ''locked up in phase'' with another SE at an almost perpendicular coast (i.e., the f irst SE waits until the other SE removes the opposing ambient flow). T his is governed by the specific distribution of land and water, and by the direction of the ambient flow against the coastline. Introduced S ST gradients have minor to moderate, localized influence on the dynami cs for this case.