Analysis The Sensible And Latent Heat Fluxes Upon A Rice-Wheat Rotation Field

Sensible and latent heat fluxes are important component of the surface energy balance. The quantitative observation of the sensible heat flux is not only the basis to understand the atmospheric dynamic thermal process, but also the core of the research on the agricultural ecology. Rice-wheat rotation field is prevailed in the middle and lower reaches of Yangtze River, the measurement upon this kind of land surface can help understand the characteristic of atmospheric boundary layer in the middle and lower reaches of Yangtze River. Therefore, based on the measurement upon rice-wheat rotation field in Jiangsu, Yancheng Dongtai during July 9, 2015 to May 18, 2016,the variation characteristics of surface fluxes in this field are analyzed. Under different growth period, the characteristics of the average energy fluxes, diurnal variation,energy distribution were discussed. The influence of land surface temperature,humidity and wind speed on energy distribution were also discussed. The sensible heat fluxes measured by large aperture scintillometer and eddy correlation observation system were compared to assess the reliability of the instrument. The main conclusions are as follows:(1) the averaged fluxes showed that: during the day, the largest average sensible(latent) heat flux was observed during the returning green stage of wheat (jointing stage of rice). The sum of sensible and latent heat fluxes overcome the received energy during the period of nudation and the wheat seedling stage. During the observation period, the average (H + LE)/Rn is not more than 80%, and the H/Rn is less than 18%.(2) diurnal variation analysis showed that the similarity variation for sensible heat flux during a day upon the rice, bare land and wheat fields with the average peak of 46.08 Wm-2. The average diurnal variation of the energy distribution showed that(H+LE)/Rn and LE/Rn have the similar diurnal variation upon rice paddy. The H/Rn was first increased then decreased in the rice growth period. In the wheat growing period, (H LE)/Rn and LE/Rn were was different under different stage. The value of H/Rn is mainly divided into first increased then decreased type(seedling stage, over wintering stage and mature stage) and steady wave (regreening and jointing stage). The diurnal variation of (H + LE)/Rn , LE/Rn and H/Rn were similar under bare land.(3) The factors analysis shows that the energy distribution is affected by soil temperature and wind speed independently upon rice paddies. With the increase of soil moisture, the H/Rn slightly increase and LE/Rn reduce. The LE/Rn increase with increasing wind speed. During the wheat growth period, the combined impact of soil temperature and humidity changed the surface energy distribution. As the soil temperature increase, the corresponding soil moisture decreased and the H/Rn decreased.(4) Analysis on averaged footprint resulted that the mulberry seedling field always had a higher contribution to LAS than to EC, which could be the reason that HLAS always larger than HEC. During the days when the contributions of mulberry seedling field to the two systems were close to each other,the sensible heat flux measurements of the two instruments were similar. The case analysis on typical sunny days showed that there would be larger sensible heat fluxes over the mulberry seedling field than in the rice paddy field especially under larger net radiation conditions.