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.