Seasonal Analysis of Spatial Variability in Radiation Components Over a Deciduous Mid-Latitude Forest

Seasonal trends in spatial variability of radiation components across a forested area of heterogeneous terrain, using a topographic surface radiation budget model are examined. Radiation components provide fundamental inputs to the surface energy budget and photosynthesis. Changes in magnitude over space, both within the footprint of turbulent flux measurements and within the broader ecosystem provides an important constraint on spatial extrapolation of estimates of carbon and energy exchanges. This constraint is also important for sub-grid scale radiation fluxes estimated by numerical models ranging in scale from meso- to global. Analysis is based on simulations of diurnal mean radiation budgets under both clear sky and cloudy conditions for the Morgan-Monroe State Forest in south-central Indiana. Comparisons between modeled values and observations from a 46 m instrumented tower show very close agreement. Spatial variability is assessed under different seasonal and cloud conditions, and estimates of the influence of variability of photosynthetically active radiation on carbon budget estimates are presented. The importance of spatial resolution in modeling of spatial variability of radiation fluxes is also investigated.