| Beijing Tianjin Hebei region is the political and cultural center of China as well as an important core area of northern China's economy.The underlying surface of the region is complex,developing rapidly,and the annual precipitation and temperature change rate is large,which is prone to extreme weather events.Through the numerical simulation method,the influence of the underlying surface change on the extreme weather process in Beijing Tianjin Hebei region is studied in detail,which can provide accurate weather forecast for the region Provide theoretical reference.In this paper,two typical high impact weather cases,the extreme precipitation process in Beijing Tianjin Hebei region from July 19 to 21,2016 and the abnormal warming process at night in Hebei Winter Olympic Games area from February8 to 9,2020,are selected to set up sensitivity contrast experiments,and high-resolution numerical simulation is carried out by using mesoscale weather numerical model to analyze the impact of underlying surface on Rainstorm and abnormal warming at night.From July 19 to 21,2016,an extreme precipitation process occurred in Beijing Tianjin Hebei region,with long duration,large amount,wide range and strong locality.The heavy rain center of this rainstorm is located in the south of Beijing,with 24-hour accumulated precipitation of more than 250 mm,causing serious economic losses in the urban area of Beijing.In this paper,the high-resolution underlying surface data is introduced.By changing the underlying surface land use type,terrain height data and the single-layer urban canopy model modified by coupling parameters,the sensitivity experiment is set up to focus on the impact of urban canopy on the numerical simulation of the rainstorm process.The results show that:(1)the urban canopy has a significant impact on heavy rainfall in Beijing.The urban canopy can enhance the convergence of water vapor flux in the urban area to a certain extent,but its impact on the precipitation area is mainly related to the internal structure and related processes of the urban canopy.In addition,the simulated hourly precipitation of UCM experiment coupled with urban canopy has a good fitting effect with the measured precipitation,which indicates that considering the geometric characteristics of urban canopy non-uniform distribution and its related processes is conducive to improving the accuracy of precipitation simulation.(2)The CTL experiment of uncoupled urban canopy model does not consider the urban non-uniform distribution and anthropogenic heat.Compared with the UCM experiment of coupled urban canopy model,the CTL experiment weakens the thermal effect of the city to a certain extent.The barrier effect of urban buildings is stronger,the rain belt is blocked by the urban canopy in its periphery,and the precipitation in the urban area is weaker than the UCM experiment.(3)The results show that the urban canopy has an impact on the cloud microphysical transformation process of rainstorm.The content of liquid phase particles in the lower layer of CTL and nourban experiments is lower than that of UCM experiment,the efficiency of raindrop transformation into graupel is higher than that of UCM experiment,and the heating rate and rain evaporation cooling rate of cloud droplet condensation process are lower than that of UCM experiment,which is not conducive to the development of precipitation.From the night of February 8 to the early morning of February 9,2020,an obvious abnormal warming process occurred in Hebei Winter Olympic Games area.The terrain of the area is high and the underlying surface is complex.Whether the terrain has an impact on the Nighttime Warming needs to be studied in depth by numerical simulation.Based on this,this paper introduces high-resolution terrain data,and uses the mesoscale regional numerical model WRF4.1.5 to refine the nocturnal warming process,and sets up sensitivity experiments to explore the meteorological characteristics and the causes of the process And the influence mechanism of topography on the warming process.The results show that:(1)the nocturnal warming process of Hebei Winter Olympic Games area is affected by the high-altitude cold vortex.The cold advection in the middle and upper atmosphere is significant.The westerly and southwest winds in the lower atmosphere bring some warm air.The strong cold advection in the middle and upper atmosphere is conducive to strong subsidence,and the wind shear and temperature advection difference in the high and lower atmosphere easily cause vertical mixing,which makes the ground temperature rise abnormally.(2)The update experiment with high-precision terrain data of 30 m resolution is introduced to simulate the near surface meteorological elements,which can better reflect the influence of terrain.The wind shear,warm advection and turbulent motion in the boundary layer simulated by the update experiment are stronger than those simulated by the default experiment,and the phenomenon that the warm advection in the lower layer weakens before the temperature increases is simulated,which makes the daily minimum temperature closer to the measured value.However,the surface wind field simulated by the default experiment suddenly increases,which brings warm air and causes the temperature to fail to drop to the lowest value,which indicates that the terrain is mainly caused by topography The results show that the wind field changes in the lower level,which has an impact on the process of temperature change in mountainous areas.According to the numerical simulation and analysis of the case of rainstorm and nocturnal warming in Beijing,Tianjin and Hebei,the research results show that the introduction of high-precision underlying surface data is conducive to improving the accuracy of numerical simulation results,and the sensitivity experiment is set to quantitatively analyze the possible influence mechanism of underlying surface in different weather processes,which can provide reference for accurate weather forecast in this region. |
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