Canopy structure and air temperature inversions impact simulation of sub‐canopy longwave radiation in snow‐covered boreal forests

Longwave radiation is often the dominant source of energy for snowmelt in forests. Measurements at forest sites varying density Sweden and Finland show that downwelling longwave enhanced under canopies, even sparse canopies particularly clear skies. Canopy must be estimated accurately to predict this enhancement. Linear regression with above-canopy air temperature as predictors sub-canopy gives good predictions weightings transmission through canopy gaps are close measured sky view fractions. Air serves here a proxy effective radiative temperature. Adding shortwave predictor little improvement predictions, suggesting daytime heating trunks above (“hot trees”) has limited influence on these continuous canopies. The temperatures falling below (“cold calm, nights, however, apparent. Decoupling an balance model type used large-scale land surface modelling allows cooling.