Thermal mesoscale circulations on the Baltic coast: 2. Perturbation of surface parameters

A three‐dimensional numerical study of an observed seabreeze (SB) is presented in a companion paper, part 1. This paper, part 2, addresses the influence of various forcing parameters emanating from the physical surface and perturbing the control run. The control run in part 1 reveals that the SB stage is preceded by a coastal jet (CJ) stage and that even moderate terrain seems to have a strong influence on the coastal mesoscale circulation. The parameter sensitivity analysis attempts to 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, three land surface, and two sea surface temperature perturbations. It is shown that the terrain elevations ( h 0 ≤ 206m) have profound impact on the flow and its time history. The main offshore island has a notable impact but does not change the main flow structure. Surface temperature perturbations modify the CJ pattern dictated by the mesoscale thermal wind; they also influence the SB shape more but the SB front propagation less. The SB at one coast is “locked up in phase” with another SB at an almost perpendicular coast (i.e., the first SB waits until the other SB removes the opposing ambient flow). This is governed by the specific distribution of land and water, and by the direction of the ambient flow against the coastline. Introduced SST gradients have minor to moderate, localized influence on the dynamics for this case.