Similarities And Differences In Surface Heat Fluxes And Evapotranspiration Over The Northern And Southern Slopes Of The Himalayas

The observation data of six stations on the northern slope of Himalaya(Naqu Station,Qomolangma Station,Muztag Station)and the southern slope(Kirtipur Station,Simara Station,Tarahara Station)are selected for the comparative analysis of the surface heat fluxes and evapotranspiration of the northern and southern slopes.The observation stations data of the northern and southern slopes in 2016(March-November2016 on the southern slope)were used in this study,including conventional meteorological data,sensible heat flux,latent heat flux,soil heat flux,and surface radiation flux.The change characteristics of meteorological elements,sensible heat flux and latent heat flux of each observation station,the components of the surface radiation balance and the evapotranspiration(ET)changes,the degree of energy closure,the relationship between heat sources and meteorological factors are also analyzed between the northern and southern slopes of Himalayas.The results are shown as follows:(1)The distribution of precipitation at each station is basically the same.There is little precipitation in spring and winter,and more precipitation in summer and autumn.The maximum precipitation occurs from May to September.The soil moisture content in the southern slope area is much higher than that in the northern slope area.The soil moisture content of the Kirtipur station in the southern slope area is 2 to 4 times that of the stations in the northern slope area in summer.On the northern slope,Naqu Station,Qomolangma Station,and Muztag Station have high altitudes,lower temperatures and colder,and less rain than on the southern slope;Kirtipur Station,Simara Station,and Tarahara Station on the southern slope have low altitudes.The temperature is relatively high and it is relatively warm all year round.The rainfall is much higher than that of the northern slope and the value is about 6 to 7 times that of the stations in the northern slope.(2)Bowen ratio in the northern slope area is much larger than the stations in the southern slope area.The monthly average daily changes of sensible heat flux and latent heat flux at each station are in a single-peak structure.The northern slope area shows a large sensible heat and a small latent heat.The heat flux exchange characteristics of large latent heat and small sensible heat indicate that the heating method of the underlying surface is mainly sensible heat exchange on the northern slope,and latent heat exchange is dominant on the southern slope.(3)The diurnal variation of each component of the surface radiation balance is obviously single-peak structure,and there are obvious monthly changes.The downward shortwave radiation and upward shortwave radiation on the northern slope are higher than those on the south slope,and the temperature on the south slope is much higher than that of the northern slope.As a result,The downward long-wave radiation and upward long-wave radiation are significantly higher than the northern slope.The net radiation flux is higher on the southern slope in spring and winter,and the difference between summer and the northern slope is slightly smaller.(4)The surface albedo is a typical "U"-shaped diurnal variation,morning and evening are higher,and noon small.The average albedo of each station from May to October is 0.21 to 0.23 in the northern slope area and 0.14 to 0.16 in the southern slope area.The vegetation in the area is in good condition and absorbs a lot of solar radiation,resulting in its albedo lower than the northern slope.(5)The energy balance closure rates of Naqu Station,Qomolangma Station,Muztag Station,Kirtipur Station,Simara Station,and Tarahara Station obtained by using TDEC method to correct the soil heat flux are respectively85.1%,51.2%,and 53.5%,64.3%,65.6%,and 68.2%.The energy closure of the southern slope area is better than that of the northern slope area due to the influence of surface vegetation coverage.(6)The evapotranspiration of each observation station has significant seasonal variation characteristics,the strongest in summer,followed by autumn and spring,and the smallest in winter.The monthly cumulative evapotranspiration of all stations except Naqu Station in the northern slope area is lower than that in the southern slope.(7)The correlation between surface heat sources and net radiation flux,ground temperature,soil moisture content and air temperature is analyzed.The correlations between ground heat sources and net radiation flux,ground temperature and air temperature are all significant,and basically all have passed the 95% significance test.The correlation with soil water content is poor.