testing the super-greenhouse thermostat with eos observations dan feldman yly sunday meeting...
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Testing the Super-Greenhouse Thermostat with EOS
observationsDan Feldman
YLY Sunday meeting
10/30/05
The Super Greenhouse Effect
• First proposed by Collins and Ramanathan, 1991
• Feedback relationship between warm SSTs and production of anvil cirrus leads to thermostat
• Used ERBE data for 1987 El Nino year
– 0.2-50 um band– 0.2-5 um band– 5-50 um band
• Proposed an upper limit to SSTs as governed by this mechanism.
From Collins and Ramanathan, 1991
Super Greenhouse Knowns• Tropical SSTs are stable• H2O greenhouse effect
increases rapidly for SST>300 K
• Warm SSTs associated with increased convection
• Anvil cirrus efficiently reflect SW radiation, and detrained evaporation humidifies upper troposphere
From Collins and Ramanathan, 1991
Super Greenhouse Unknowns
• Can tropical dynamics explain SST stability?• Are other mechanisms of poleward heat transport able to
explain SST observations• Is the radiative impact of anvil cirrus a strong and local
function of SSTs >300 K leading to a stable negative feedback?
From Wallace, 1991
Observations of Cirrus Character
• From ISCCP data
From Fu et al, 1992
Modeling Efforts
• Hartmann et al propose Fixed Anvil Temperature from:– Clausius-Clapeyron
definition of saturation vapor pressure dependence on temperature.
– Dependence of emissivity of rotational lines of water vapor on vapor pressure.
EOS observations• MLS sensitive to UT H2O and Cloud IWC• Observations of MLS tend to support Super Greenhouse
Hypothesis.• AQUA can detect the following at 45 km spatial
resolution:– UT H2O (from AIRS standard product)– Cloud cover & cloud top temperature (from AIRS standard
product)– SST (from AIRS standard product)– Night-time cirrus for OD>0.1 (from AIRS, Kahn et al, 2003)– Shortwave Albedo (from CERES)
• With these products, detailed radiative forcing calculations may be able to address the causal or correlative relationship between anvil cirrus and warm SSTs.