Vol19 No.11: 3076-3087
【Title】Radiation and energy balance on a hillslope forest: horizontal versus slope-parallel installation of radiometer
【Author】WANG Xing-chang 1,2; LIU Fan 1,3; WANG Chuan-kuan1,2*
【Addresses】1 Center for Ecological Research, Northeast Forestry University, Harbin 150040, China; 2 Key Laboratory of Sustainable Forest Ecosystem Management – Ministry of Education, Northeast Forestry University, Harbin 150040, China; 3 Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China
【Corresponding author】WANG Chuan-kuan
【Citation】Wang XC, Liu F, WangCK(2022) Radiation and energy balance on a hillslope forest: horizontal versus slope-parallel installation of radiometer. Journal of Mountain Science 19(11). https://doi.org/10.1007/s11629-022-7481-8
【Abstract】Radiation is a major driver to the carbon, water, and energy exchanges of an ecosystem. For local radiation balance measurements, one essential question is whether the measurement systems should be installed horizontally or parallel to inclined slope surface. With a case study over a temperate deciduous forest on a moderate inclined (9°) northwest-facing slope, we quantified the slope effect on net radiation (Rn) and its components and the energy balance closure measured by an eddy covariance (EC) system. Compared with the slope-parallel radiometer, the horizontal sensor overestimated the incident solar radiation(SR) by 7%, the incoming photosynthetically active radiation(PAR)by 1.5%, and the incoming near-infrared radiation(NIR)by 10%; while underestimated the reflected shortwave radiation (SR) by 4% and NIR by 5%. The influence of radiometer-orientation on incoming longwave radiation (LR) was about 3%, while that on outgoing LR was negligible.Summing all these components,horizontal sensor overestimated the Rn by 9%. Converting the horizontally-measured incident radiation to slope-surface reduced a half of the biases onincomingSR and Rn. Measuring the Rn with slope-parallel radiometerand correcting the slope-effect on horizontally-measured incident SR improved the energy balance ratio (EBR) by 8% and 5%, respectively. A mini-review indicated that, the horizontal sensorunderestimated (overestimated) the EBR on north-facing (south-facing) slopes in temperate zone in the Northern Hemisphere, with an inclination angular sensitivity of EBR as high as 1.17%per degree of inclination angle. We recommend measuring radiations on inclined terrains with slope-parallel radiometers, or correcting at least for the incident SR in energy balance studies.
【Keywords】Radiation; Sloping terrain; Energy balance closure; Eddy covariance