Observation Study On The Characteristics Of The Land-air Interaction That Plastic Films Cover The Cropland

Plastic film and greenhouses of large area is used to improve agricultural production and efficiency,further change the surface mulching and the way of land use,and have important influence on the regional environment,climate and even the global atmospheric circulation and climate change.Surface albedo and other land-air interaction characteristics are significantly changed after the plastic film covers the surface.Based on the data of micro meteorological observation experiment in Inner Mongolia on May 15,2015-November 4,2015?membrane and parallel contrast?and micro meteorological observation experiment in ShouGuang,ShanDong on November 16,2016-April 11,2017?greenhouses?,this paper studies the observation consistency of surface energy flux,discusses the influence of observation inconsistency on energy closure rate,and analyzes the characteristics of land-air process that the plastic film and greenhouse cover the surface of the farmland,which provide reference for the land characteristic parameters of the plastic film covering the cropland.The main results as following:?1?The parallel comparison results of the observed instruments in tests are shown:The inconsistency of the main energy component of observation instruments in the energy balance analysis is that:the mean variance of surface soilheat flux,sensible heat flux and latent heat flux respectively is 14.3W·m^-2,8.9W·m^-2 and8.0W·m^-2.The uncertainty of the energy closure rate formed by the above energy component is 6⁸%.?2?The soil temperature,water content and heat flux of bare soil,plastic film and cropland covered with corn were obviously different,those 5 cm soil temperature are19.4,19.9,and 18.7?respectively,the water content are 0.32,0.36 and 0.37 m³/m³respectively,and the heat flux are 4.9,-0.6 and 3.8 W·m^-2 respectively;The radiative energy distribution characteristics of the underlying surface are significantly changed by the plastic film.Comparing and analyzing the radiating components of bare soil,plastic film and farmland covered with corn,the results show that the surface albedo of three kinds of underlying surfaces are:0.22,0.23 and 0.18 respectively;that the surface reflected radiation components are:52.1,56.4 and 47.7 W·m^-2;The surface long wave radiation components are 416.2,428.7 and 412.2 W·m^-2 respectively.The surface reflected radiation and the surface albedo increases after the plastic film covering the surface.The impermeability of plastic prevents evaporation of soil water,which the soil moisture content is obviously higher than that of bare soil and shallow soil heat flux is the smallest.?3?The differences of conventional meteorological elements between greenhouse and outside sheds are obvious.The wind speed scale is 10^-1m/s in the shed and is10¹m/s in the outside;the air temperature are 8.8 and 3.5?respectively,which the highest temperature in the shed is 1.6 times that of the outside;the air humidity are81.4%and 77.7%respectively;the 5 cm soil temperature are 10.3 and 4.8?respectively;the water content are 0.41 and 0.35 m³/m³ respectively;and the heat flux are 0.33 and-5.4W·m^-2 respectively.The differences of energy distribution between greenhouse and outside sheds are also obvious.The total radiation components are89.1 and 122.8 W·m^-2 respectively in the shed and out the shed;the atmospheric long-wave radiation components are 326.0 and 276.1 W·m^-2 respectively;the net radiation are 36.1 and 37.3 W·m^-2 respectively;the surface albedo are 0.19 and 0.23respectively.Greenhouse has obvious warming and moisturizing effect,which the air temperature and humidity in the shed are obviously higher than that of the outside.Plastic film of greenhouse reduces total radiation and increase surface and atmospheric long-wave radiation,which the shallow soil temperature,water content and heat flux of greenhouse are higher than those outside the shed.?4?The sensible heat flux of cropland covered by the plastic film in arid region is10.2 W·m^-2,and the latent heat flux is 98.0W·m^-2,which the latent heat is much greater than the sensible heat flux;The scale of the latent and sensible heat flux of the small environment that the greenhouse in the semi-humid area covers the farm greenhouse are both 10⁰.The mean value of sensible heat and latent heat flux outside the shed are 10.6 and 13.2 W·m^-2 respectively,which the latent heat is slightly higher than the sensible heat flux.