4.1 The association of outgoing solar (albedo) and OLR radiation with variations of precipitation

Tuesday, 25 January 2011: 8:30 AM
608 (Washington State Convention Center)
William M. Gray, Colorado State Univ., Fort Collins, CO; and B. E. Schwartz
Manuscript (1.3 MB)

We have analyzed 21 years (1984-2004) of ISCCP (International Satellite Cloud Climatology Project) outgoing solar (albedo) and OLR radiation on various time and space scales. We have investigated how these outgoing radiation measurements changes with variations in local and broadscale precipitation as determined from NOAA Reanalysis data on time scales from a day to multi-years.

We find that the increase of albedo which occurs in precipitation and cloud areas is greater than is the suppression of OLR in these areas. We find that increased tropical and/or global precipitation energy produces radiation energy loss to space which is near equivalent. Enhanced tropical rainfall does not lead to enhanced upper tropospheric warming as the GCMs have indicated. Global surface temperature changes appear to be largely controlled by global rates of surface evaporation (and resulting condensation). When evaporation (and precipitation) are larger than average the globe tends to cool, when evaporation (and precipitation) are less than average the globe tends to warm. Global evaporation and precipitation are enhanced during periods when the global ocean's Meridional Overturning Circulation (MOC) is enhanced. Less global evaporation-precipitation occurs when the MOC is weaker than average.

Our measurements cast doubt on the radiation assumptions implicit in the GCM doubling of CO2 simulations. Doubling CO2 should cause an increased strength of the hydrologic cycle but very little global temperature increase. What small temperature increases that occurs with a doubling of CO2 will bring about (should be dwarfed) by the natural temperature changes resulting from variations in the MOC.

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