Responses of the atmospheric boundary layer to a low-latitude mesoscale SST front

The responses of the atmospheric boundary layer at low latitudes (20°N) to forcing by an ocean-mesoscale sea surface temperature (SST) front are investigated under the conditions that the background wind intersects with the SST front (i.e., there are cross-frontal and along-frontal wind components) through ideal numerical experiments. The simulation results show that the responses of the atmospheric boundary layer are sensitive to the background wind speed and its direction relative to the SST front. The type of convergence and divergence of Ekman transport and that of the background wind can be constructive or destructive, depending on the relative orientation of the background wind and the SST front. When the two kinds of convergence and divergence are constructive, they can cause strong convergence and divergence in the boundary layer near the SST front; further, the unbalanced state forced over the SST front will excite inertial gravity waves propagating into the free atmosphere. The vertical velocity excited in this case is much greater than that when there is only a cross-frontal background wind component with an equivalent magnitude. On the contrary, when the two kinds of convergence and divergence are destructive, the resultants of convergence and divergence are reduced significantly, and the interaction between the boundary layer and the aloft atmosphere decays rapidly with height. The significance of the results obtained for the analysis of coastal precipitation are discussed.