The impact of equilibrating hemispheric albedos on tropical performance in the HadGEM2‐ES coupled climate model

The Earth's hemispheric reflectances are equivalent to within ± 0.2 Wm−2, even though the Northern Hemisphere contains a greater proportion of higher reflectance land areas, because of greater cloud cover in the Southern Hemisphere. This equivalence is unlikely to be by chance, but the reasons...

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Bibliographic Details
Published in:Geophysical research letters 2016-01, Vol.43 (1), p.395-403
Main Authors: Haywood, Jim M., Jones, Andy, Dunstone, Nick, Milton, Sean, Vellinga, Michael, Bodas‐Salcedo, Alejandro, Hawcroft, Matt, Kravitz, Ben, Cole, Jason, Watanabe, Shingo, Stephens, Graeme
Format: Article
Language:English
Subjects:
African monsoon
Albedo
albedo symmetry
Atmospheric moisture
Atmospheric precipitations
Atmospherics
Balancing
Climate
Climate models
Cloud cover
couple climate models
Earth
Energy
Energy transfer
Energy transport
ENVIRONMENTAL SCIENCES
Equatorial regions
Equivalence
HadGEM2‐ES
hemispheric albedo
hurricane frequency
Hurricanes
Indicators
inter-hemispheric
Land
Land area
Meteorology
Moisture
Monsoon precipitation
Monsoon rainfall
Monsoons
Northern Hemisphere
Penetration
Precipitation
Rain
Rainfall
Reflectance
Southern Hemisphere
Transport
Tropical climate
tropical precipitation
Wind
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Summary:The Earth's hemispheric reflectances are equivalent to within ± 0.2 Wm−2, even though the Northern Hemisphere contains a greater proportion of higher reflectance land areas, because of greater cloud cover in the Southern Hemisphere. This equivalence is unlikely to be by chance, but the reasons are open to debate. Here we show that equilibrating hemispheric albedos in the Hadley Centre Global Environment Model version 2‐Earth System coupled climate model significantly improves what have been considered longstanding and apparently intractable model biases. Monsoon precipitation biases over all continental land areas, the penetration of monsoon rainfall across the Sahel, the West African monsoon “jump”, and indicators of hurricane frequency are all significantly improved. Mechanistically, equilibrating hemispheric albedos improves the atmospheric cross‐equatorial energy transport and increases the supply of tropical atmospheric moisture to the Hadley cell. We conclude that an accurate representation of the cross‐equatorial energy transport appears to be critical if tropical performance is to be improved. Key Points Tropical precipitation, monsoon jump, and hurricane frequency are all improved in HadGEM2‐ES Equilibrating hemispheric albedos corrects the atmospheric cross‐equatorial energy transport At a minimum, this suggests that models should tune against hemispheric albedo equivalence
ISSN:0094-8276
1944-8007
DOI:10.1002/2015GL066903