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The Global Character of the Flux of Downward Longwave RadiationFour different types of estimates of the surface downwelling longwave radiative flux (DLR) are reviewed. One group of estimates synthesizes global cloud, aerosol, and other information in a radiation model that is used to calculate fluxes. Because these synthesis fluxes have been assessed against observations, the global-mean values of these fluxes are deemed to be the most credible of the four different categories reviewed. The global, annual mean DLR lies between approximately 344 and 350 W/sq m with an error of approximately +/-10 W/sq m that arises mostly from the uncertainty in atmospheric state that governs the estimation of the clear-sky emission. The authors conclude that the DLR derived from global climate models are biased low by approximately 10 W/sq m and even larger differences are found with respect to reanalysis climate data. The DLR inferred from a surface energy balance closure is also substantially smaller that the range found from synthesis products suggesting that current depictions of surface energy balance also require revision. The effect of clouds on the DLR, largely facilitated by the new cloud base information from the CloudSat radar, is estimated to lie in the range from 24 to 34 W/sq m for the global cloud radiative effect (all-sky minus clear-sky DLR). This effect is strongly modulated by the underlying water vapor that gives rise to a maximum sensitivity of the DLR to cloud occurring in the colder drier regions of the planet. The bottom of atmosphere (BOA) cloud effect directly contrast the effect of clouds on the top of atmosphere (TOA) fluxes that is maximum in regions of deepest and coldest clouds in the moist tropics.
Document ID
20120009331
Document Type
Reprint (Version printed in journal)
Authors
Stephens, Graeme L. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Wild, Martin (Eidgenoessische Technische Hochschule Zurich, Switzerland)
Stackhouse, Paul W., Jr. (NASA Langley Research Center Hampton, VA, United States)
L'Ecuyer, Tristan (Colorado State Univ. Fort Collins, CO, United States)
Kato, Seiji (NASA Langley Research Center Hampton, VA, United States)
Henderson, David S. (Colorado State Univ. Fort Collins, CO, United States)
Date Acquired
August 25, 2013
Publication Date
April 1, 2012
Publication Information
Publication: Journal of Climate
Volume: 25
Issue: 7
ISSN: 0894-8755
Subject Category
Meteorology and Climatology
Report/Patent Number
NF1676L-14677
Funding Number(s)
WBS: WBS 281945.02.20.01.48
CONTRACT_GRANT: NAS5-99237
CONTRACT_GRANT: NNX09AK02G
CONTRACT_GRANT: NNX07AR11G
Distribution Limits
Public
Copyright
Other