Energy balance and its closure over a young larch forest in eastern Siberia

To elucidate the energy balance over a forest, seasonal changes in the water and energy exchanges over a young larch forest (E-YL) in eastern Siberia were investigated and compared with the reported characteristics of a mature larch forest (W-ML) in the same region. Observations of the energy fluxes were conducted during the growing season from 15 April through 14 September 2000. The sum of the turbulent heat fluxes H and λE, ground heat flux G and heat storage change rate ΔS was generally in good agreement with the net radiation flux RNET, except when the friction velocity u* was <0.2 m s−1. Atmospheric instability also reduced the energy balance ratio EBR in the daytime. The EBR was defined as the ratio of the turbulent heat flux H + λE toward the available energy input RNET − G − ΔS for the reference horizontal plane, whereas the energy closure fraction CF was defined as the ratio of the net ecosystem heat exchange H + λE + ΔSatmosphere to the available energy input RNET − G − ΔSbiomass for the biomass surface. EBR and CF had different features in their relationship to u* at night. The threshold to reject nighttime data at low u* values was estimated to be 0.2 m s−1 by the EBR, but >0.3 m s−1 by the CF. The averaged features of the CF relationships with u* and atmospheric stability ζ were similar to those reported for Canadian boreal forests. In contrast, hourly CF and hourly EBR were widely scattered. The probability functions of EBR for different wind velocities were consistent with previous results from large eddy simulation. To determine the seasonal course of daily flux values, the Bowen ratio energy budget method was used to estimate the turbulent heat fluxes. The daily latent heat flux maintained a value of approximately 50 W m−2 during the summer, whereas the daily sensible heat flux varied with changes in the available energy. The Bowen ratio had a clear “U” shape over the course of the growing season. The minimum values of approximately 1.0 occurred in the summer from June to August. The general features of seasonal changes at E-YL in 2000 were similar to those at W-ML in 1998, except for the lower Bowen ratio in August at E-YL.