The Study Of Characteristics Of Near-surface Micrometeorology And Water-heat Exchange Over Snow In The Yellow River Source Region

Using observation data of the Chinese Academy of the Yellow River source region climate and environment comprehensive observation research station in Maqu,analyze the characteristics of local snow field,near formation,radiation and energy budget from December 2011 to March 2012.Finally,using the single point mode of Noah_LSM,to study the influence of snow cover,vegetation and wind speed on the micro meteorological factors,radiation,sensible and latent heat fluxes by using the method of numerical sensitivity experiments.The main conclusions are as follows:1)During December 2011 to March 2012,the monthly average solar net radiation are 345,386,412,544W/m2 in Maqu station,the solar radiation intensity and soil freezing and thawing state during three snow processes are different.The temperature gradient is greater than the nighttime,during the daytime,the average temperature is-0.3?/m below 7.17 m,above average is-0.1?/m.At night,the average value is 0.6?/m below 7.17 m,the average is 0.2?/m above 7.17 m.When the surface is covered with snow,the temperature decreasing with the height of one hour behind the snow free cover,and the evening temperature appears 1 hours ahead with the height increase.In the daytime with snow,the temperature distribution range is smaller than that without snow,the second snow cover process has the largest range of air temperature due to the large wind speed.In addition,the temperature gradient of 4.2-7.17 m is larger than the absolute value of 2.35-4.2m on sunny day,there is a significant increase in snow cover,which may be caused by the observation field inside and outside the surface vegetation cover and different temperature flat flow caused by 4.2m induced by warm.2)Before and after the three snowfall,the upward and downward long wave radiation changes with time,while the downward long wave radiation is smaller than the upward long wave radiation.Three snow after a snowfall before the average net shortwave radiation were reduced by 146?11?8 W/m2,the absolute value of the net longwave radiation were reduced by 66?27? 17 W/m2,net radiation were reduced by 81?38?5 W/m2.In the whole observation period,when the surface is covered with snow,The latent heat flux is not obvious due to lower temperature during the first two snow periods,The latent heat flux of the third process is larger than the previous two of the peak of 120w/m,but the sum of sensible heat flux is less than second times,This may be because the soil began to melt during this process.The surface warming was slower,the ground temperature difference decreased and the sensible heat was smaller.During the three snow cover,the average Bowen ratio is least,this is because the soil began to melt,the proportion of latent heat exchange is relatively large during the third snow cover process.3)The numerical experiment of using Noah_LSM model in the high and cold region of Qinghai-Tibet plateau shows that the model can well simulate the variation characteristics of physical quantity in the near stratum.The model can also simulate the soil temperature,but the shallow 10 cm soil temperature is slightly lower.4)The sensitivity test shows that wen snow cover is not considered in the model,the net radiation value is slightly larger than the control test,and the sensible heat flux,temperature and soil temperature are larger than the control test.With the deepening of soil layer,the extent of soil temperature decreases gradually,and the effect of snow cover on deep soil temperature decreases.In the absense of snow cover,the simulation results of the 10 cm soil temperature are higher than in the snow cover during the day,on the contrary,it shows that the snow cover plays an important role in the soil during the night.5)The result of the sensitivity and latent heat flux are higher than that of bare land under the condition of vegetation cover,which is because the surface albedo is lower and the energy absorbed is higher than that of bare soil,and the surface temperature is smaller than that of bare ground,so the temperature is smaller than that of bare ground,which may mean that the uneven distribution of vegetation is leading to this one.6)Observations show that the larger wind speed of February 18 is a reason for the larger latent heat flux and negative heat flux.The sensitivity test of wind field shows that the wind field of 6m is reduced from 13m/s to 3m/s.The simulated latent heat flux will reduce about 140W/2,the negative sensible heat flux will increase about 80W/m2.This indicates that large wind speed is one of the reasons leading to large heat flux and negative sensible heat flux during snow process in February 18 th.