Numerical Study Of The Impact Of Sea-land Underlying Surface On Thunderstorm In Ningbo Area

The thunderstorm process is simulated by WRF model with1km resolution. In order to simulate a thunderstorm process more accurately, the sensitivities of the thunderstorm process to land surface parameterization schemes (Noah and RUC) are tested. The results showed that,with respect to the temperature field and wind field before the thunderstorm happen, the simulation results with Noah are more close to the observations. However, RUC did not reflect the diversity of underlying surface coverage and impacts of city underlying surface. The difference between rural and urban areas is not obvious in RUC. The start and development processes simulated by Noah are more reasonable. While the RUC scheme described the key stages in the process of thunderstorm’s evolution well, such as three merging processes. Due to the factors and physical process considered are different, the strength and center of accumulation precipitation simulated by Noah scheme are more consistent with the observations than that simulated using the RUC scheme. The duration of thunderstorm is strongly sensitive to land surface process parameterization, and both of duration simulated by the two schemes is longer than the actual duration of the thunderstorm to different degrees.Whatever the land cover category in Ningbo area, the sensible heat flux (latent heat) simulated by Noah scheme is great than (less than) that simulated by RUC scheme during the day. Experiments indicate that using land surface parameterization schemes appropriately is necessary to enhance the modeling capability. So when a thunderstorm is simulated in ningbo area using WRF model, using Noah land surface scheme is better to enhance the modeling capability.Base on these studies, the impcat of difference between sea and land underlying surface on thunderstorm is studied through the sensitivity tests of replacing land cover types.Research shows that the uneven distribution of the land and sea can produce important impact on thunderstorms. Before the thunderstorm takes place, since thermal contrast between the sea surface and land surface, characteristics of sea breeze circulation is very significant. And wind field near ground formed strong convergence along the coast. Strong convergence zone corresponds to greater value of the subsequent thunderstorms accumulated precipitation. The sea breeze meet with background winds when it move inland,then the sea breeze front forms, and air rise significantly on its front.Then the thunderstorm is triggered by strong convergence on the ground and lifting movement.Unlike water, land underlying surface has unique dynamics properties. When water is replaced with land, uplifting movement become stronger in the east part of the study area for the increased land surface roughness. Several powerful convection cells formed in the east part of the uplifting area, which expand the rain area and increase the accumulated rain and extend the maintain time thunderstorm. When we replace land with water, surface fluxes decrease in the daytime and turbulent motion becomes weak. So boundary layer becomes low, the atmospheric stratification turns to stable and the thunderstorm is not easy to develop.