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Canopy structure and air temperature inversions impact simulation of sub-canopy longwave radiation in snow-covered boreal forests

Rutter, Nick; Essery, Richard; Baxter, Robert; Hancock, Steven; Horton, Maya; Huntley, Brian; Reid, Tim; Woodward, John

Canopy structure and air temperature inversions impact simulation of sub-canopy longwave radiation in snow-covered boreal forests Thumbnail


Authors

Nick Rutter

Richard Essery

Steven Hancock

Maya Horton

Tim Reid

John Woodward



Abstract

Longwave radiation is often the dominant source of energy for snowmelt in forests. Measurements at forest sites of varying density in Sweden and Finland show that downwelling longwave radiation is enhanced under forest canopies, even for sparse canopies and particularly for clear skies. Canopy density must be estimated accurately to predict this enhancement. Linear regression with above-canopy longwave radiation and air temperature as predictors of sub-canopy radiation gives good predictions of sub-canopy longwave radiation with weightings for transmission through canopy gaps that are close to measured sky view fractions. Air temperature serves here as a proxy for effective canopy radiative temperature. Adding above-canopy shortwave radiation as a predictor gives little improvement in the predictions, suggesting that daytime heating of trunks above the air temperature (“hot trees”) has limited influence on longwave radiation under these continuous canopies. The influence of canopy temperatures falling below the above-canopy air temperature (“cold trees”) on calm, clear nights, however, is apparent. Decoupling of canopy and above-canopy air temperatures in an energy balance model of the type used in large-scale land surface modelling allows this cooling.

Journal Article Type Article
Acceptance Date Jul 6, 2023
Online Publication Date Jul 18, 2023
Publication Date Jul 27, 2023
Deposit Date Jul 7, 2023
Publicly Available Date Jul 31, 2023
Journal Journal of Geophysical Research: Atmospheres
Print ISSN 2169-897X
Electronic ISSN 2169-8996
Publisher American Geophysical Union
Peer Reviewed Peer Reviewed
Volume 128
Issue 14
Article Number e2022JD037980
DOI https://doi.org/10.1029/2022JD037980
Public URL https://durham-repository.worktribe.com/output/1168699
Publisher URL https://agupubs.onlinelibrary.wiley.com/journal/21698996

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