Long-wave emission from trees in snow-covered Arctic boreal forests: measurement and modelling

Modelling energy balance interactions between forests and sub-canopy snow requires an improved understanding of how trees absorb then emit radiation. The amount of long-wave enhancement at the sub-canopy snow surface, relative to above canopy long-wave emittance from the atmosphere, is strongly affected by the surface temperature of forest elements (trunks, crowns, needles, leaves) exposed to incoming radiation. Here we present in-situ meteorological, tree temperature and forest canopy structure measurements from Arctic European snow-covered boreal forests; March through April in Abisko, Sweden (2011) and Sodankylä, Finland (2012). Meteorological measurements are used to assess spatial and temporal variations in tree temperatures and sub-canopy long-wave enhancement. Simple models, which use hemispherical photography to derive sky-view fractions, are used in conjunction with measured air temperature, tree trunk temperature and Terrestrial Laser Scanning measurements to assess the influence of tree type, forest canopy structure and application of sky-view fraction in modelled estimation of sub-canopy long-wave radiation.