The Energy Balance of a Tropical Evergreen Forest

R. T. Pinker Department of Meteorology, University of Maryland, College Park 20742

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O. E. Thompson Department of Meteorology, University of Maryland, College Park 20742

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T. F. Eck Department of Meteorology, University of Maryland, College Park 20742

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Abstract

This study presents the radiation climate of a dry tropical forest. It is based on measurements of incoming and outgoing shortwave and longwave radiation at the top and floor of the forest canopy during five months spanning the monsoon cycle in Southeast Asia. The 24 h daily totals of the downward radiation in the 0.3–60 μm range seem to be independent of season in this monsoonal region (∼1200 ly at forest top and 900 ly at forest floor). The total 24 h daily downward radiation (0.3–60 μm) at forest floor amounts to 75% of the total daily downward radiation at canopy top. The total 24 h daily net radiation at the forest floor amounts only to 5% of the net radiation at the canopy top showing a very small diurnal and seasonal variation. The average daytime total of the shortwave radiation (0.3–3 μm) at the forest floor amount only to ∼8% of the corresponding value at forest top. The daily total (24 h) of the downward longwave (3–60 μm) radiation at the forest floor is ∼8% higher than the corresponding value at the forest top. Sensible heat flux computations are expressed in the framework of the Thornthwaite-Holzman equation. Regression equations are developed between the shortwave (0.3–60 μm) at the canopy top for each season.

Abstract

This study presents the radiation climate of a dry tropical forest. It is based on measurements of incoming and outgoing shortwave and longwave radiation at the top and floor of the forest canopy during five months spanning the monsoon cycle in Southeast Asia. The 24 h daily totals of the downward radiation in the 0.3–60 μm range seem to be independent of season in this monsoonal region (∼1200 ly at forest top and 900 ly at forest floor). The total 24 h daily downward radiation (0.3–60 μm) at forest floor amounts to 75% of the total daily downward radiation at canopy top. The total 24 h daily net radiation at the forest floor amounts only to 5% of the net radiation at the canopy top showing a very small diurnal and seasonal variation. The average daytime total of the shortwave radiation (0.3–3 μm) at the forest floor amount only to ∼8% of the corresponding value at forest top. The daily total (24 h) of the downward longwave (3–60 μm) radiation at the forest floor is ∼8% higher than the corresponding value at the forest top. Sensible heat flux computations are expressed in the framework of the Thornthwaite-Holzman equation. Regression equations are developed between the shortwave (0.3–60 μm) at the canopy top for each season.

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