Enhanced PAR Irradiance Under Broken Cloud Fields and its Significance for Tropical Forest Photosynthesis
Abstract
Field measurements of total and diffuse photosynthetically active radiation (PAR, 400-700 nm) were combined with modeling to investigate the effects of atmospheric scattering by clouds on the surface PAR regime, forest canopy PAR absorption, and simulated photosynthetic rates for a moist tropical site at Putussibau, West Kalimantan Province, Indonesia (0.84N, 112.93E). Time-series PAR data collected in 2007 are characterized by large diffuse PAR fractions and frequent occurrence of enhanced global PAR irradiance (often exceeding the extraterrestrial flux) associated with reflectance and scattering by broken cloud fields. Simulations of canopy-absorbed PAR and gross photosynthesis with the Forest Light Environmental Simulator (FLiES) demonstrate the role of clouds in controlling forest canopy light-use efficiency and rates of photosynthesis and vegetation-atmosphere carbon exchange in this moist tropical environment. Application of a high dynamic range sky imaging system (HDR-SIS) to analysis of the sky radiance distribution of PAR under various atmospheric conditions is described.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.B51A0358D
- Keywords:
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- 0321 Cloud/radiation interaction;
- 0360 Radiation: transmission and scattering;
- 0426 Biosphere/atmosphere interactions (0315);
- 0428 Carbon cycling (4806);
- 0476 Plant ecology (1851)