A Numerical Study Of The Impact Of Urbanization Extension Over The Eastern China On Process Of Eastern Asian Summer Monsoon

The effect of urban land-use change over eastern China on the processing of Easter China summer monsoon is investigated using Community Atmosphere Model Version 5.1 (CAM5.1). Results show that:(1)Comparison of the CTRL and NOURB runs shows that urbanization over eastern China may advance the date of South China Sea monsoon onset by one pentad. Possible mechanisms were analyzed and it was found that urbanization will induce strengthened warming and sensible heating from land to air in the middle to high latitudes over eastern China continent and the thermal contrast between ocean and land is reduced, which caused advancing the formation of land low pressure, and leading zonal wind over South China Sea appeared early. It provides abundant vapor conditions for precipitation in the South China Sea. The increase of precipitation caused the increase of the condensation latent heat release, makes CTRL experiment generate condensation latent heating center in advance, the related dynamic diagnosis showed that the vertical change of condensation latent heating has important influence to the vorticity field, it caused abnormal circulation contributed to the north of South Asia high jump and strengthen, prompted the West Pacific subtropical high eastward withdrawal, and low-level generate cyclonic circulation, led to the South China Sea monsoon onset in advance.(2) Comparison of the urbanization extension runs with NOURB run,results show that the character of land and surface energy balance is changed with the expansion of urbanization, the surface net radiation and sensible heat fluxes is enhanced while the latent heat fluxes is reduced.As a result, a significant increase in Eastern China near-surface air temperature is detected. Urbanization effect is contribution to the change of land and sea temperature difference (LSTD), leading to put off the time of LSTD convert from positive to negative, and also the transform from negative to positive. As a result, the onset date and end date of Eastern Asian subtropical monsoon were delayed. With the effect of the expansion of urbanization, the onset date of Changjiang-Japan Meiyu is later and the end date is earlier, on the while the duration is became shorter and the precipitation at that time is also decreased. the general circulation characteristic of the Changjiang-Japan Meiyu is studied, the result show that urbanization leaded to significant difference characters of general atmospheric circulation in the corresponding period between different runs,The precipitation of Changjiang-Japan Meiyu is marked decreasing over the Changjiang-Japan region, which is owing to the south Asian high is weaken, intensity of divergence is decreased in 100 hPa; while both the Okhotsk blocking high in 500 hPa and the western pacific subtropical high in 850 hPa is weaken, leading to fewer water-vapor transfer from ocean to Eastern China, the intensity of convergence over the Changjiang-Japan region is decreased. As a result, the precipitation of Changjiang-Japan Meiyu is marked decreasing. Finally, under the effect of urbanization effect, the EASM north edge position in lower attitude.