dc.description.abstract | The land surface processes not only involve the interaction among the earth’’s surface and atmosphere but also influence the characteristics of weather and regional climate. Therefore, if the course of the land surface processes in the way can play a correct role, the true land use type distribution and the good parameter is decisive factors. With the economic development of Taiwan, the U. S. Geological Survey (USGS) land use data used nowadays in the Fifth-generation Mesoscale Model (MM5) is out of date and unable to reflect the real land use condition correctly. After the upgraded 3.5 version of MM5, the land use type data also had been renewed, there is quite difference land use distribution compared with the old edition on Taiwan. In addition, The China Technical Consultants Inc. (CTCI) land use data was digitized with the aerial photograph from Taiwan Ministry of the Interior (MOI). The apparent difference in these three kinds of land use data is the range and location of urban area, cropland and forest. And different land use type is corresponding to different soil parameters, for example: moisture, albedo, roughness length, etc. This research extends Cao (2007), to simulate and compare to the case of winter in MM5, and discuss the land use type impact on local circulation and meteorological field simulation.
Under the northeasterly wind, three land uses have not much difference between with each other in the result of simulation in north and middle part of Taiwan. However, the simulations with USGS-NEW and CTCI all imitate higher temperature in the south of Taiwan. There is stronger heating effect in USGS-NEW, so there are more water vapor in the soil can evaporate into the atmosphere. Because of the transfer by onshore wind, air has higher equivalent potential temperature in mountain area. In other way, due to relatively widely distribution with the type of the shrub and irrigated cropland in the land use type of CTCI, the soil has more energy is transported in sensible heat flux have low humidity. Therefore, air parcels heating and upward motions are much obviously. Compared the simulation result with observe data can find, there is clearly underestimate in the simulation of temperature in winter, but the USGS-NEW and CTCI simulation results are relatively near observed value.
In winter case, because of precipitation mainly fell area in the near coast, there is no obvious influence of land use change to rainfall simulation in winter time. On the contrary, the simulation result of the convective precipitation in summer case show that different land use type causes obviously influence on the distributed and intensity of the rainfall simulation. The primary land use type in USGS-OLD and CTCI are irrigated cropland and shrub, which the setting of roughness length is shorter then others. Consequently, the simulation in wind speed is relatively strong, and the convection rainfall system occurred in slight northern area. The primary land use type in USGS-New is urban, which setting in roughness length is longer, so the simulated wind speed is relatively small. Because of that, the rainfall area leaned towards the south. Because of the surface state drier and stronger upward motion obviously, CTCI simulation rainfall began earlier, and ended earlier also; USGS-NEW heat comparatively obvious, more water vapor can evaporate into the air of the surface layer, so the precipitation distribution area is extensively. It is not more obvious that the heating effect in USGS-OLD, so the rainfall phenomenon takes place later, but the soil available moisture of the surface is higher, so the precipitation time sustain longer. | en_US |