Atmospheric Circulation Trends, 1950–2000: The Relative Roles of Sea Surface Temperature Forcing and Direct Atmospheric Radiative Forcing
- 15 January 2009
- journal article
- Published by American Meteorological Society in Journal of Climate
- Vol. 22 (2), 396-413
- https://doi.org/10.1175/2008jcli2453.1
Abstract
The relative roles of direct atmospheric radiative forcing (due to observed changes in well-mixed greenhouse gases, tropospheric and stratospheric ozone, sulfate and volcanic aerosols, and solar output) and observed sea surface temperature (SST) forcing of global December–February atmospheric circulation trends during the second half of the twentieth century are investigated by means of experiments with an atmospheric general circulation model, Community Atmospheric Model, version 3 (CAM3). The model experiments are conducted by specifying the observed time-varying SSTs and atmospheric radiative quantities individually and in combination. This approach allows the authors to isolate the direct impact of each type of forcing agent as well as to evaluate their combined effect and the degree to which their impacts are additive. CAM3 realistically simulates the global patterns of sea level pressure and 500-hPa geopotential height trends when both forcings are specified. SST forcing and direct atmospheric radiative forcing drive distinctive circulation responses that contribute about equally to the global pattern of circulation trends. These distinctive circulation responses are approximately additive and partially offsetting. Atmospheric radiative changes directly drive the strengthening and poleward shift of the midlatitude westerly winds in the Southern Hemisphere (and to a lesser extent may contribute to those over the Atlantic–Eurasian sector in the Northern Hemisphere), whereas SST trends (specifically those in the tropics) are responsible for the intensification of the Aleutian low and weakening of the tropical Walker circulation. Discrepancies between the atmospheric circulation trends simulated by CAM3 and Community Climate System Model, version 3 (CCSM3), a coupled model driven by the same atmospheric radiative forcing as CAM3, are traced to differences in their tropical SST trends: in particular, a 60% weaker warming of the tropical Indo-Pacific in the CCSM3 ensemble mean than in nature.Keywords
This publication has 65 references indexed in Scilit:
- Trends in Southern Hemisphere Circulation in IPCC AR4 Models over 1950–99: Ozone Depletion versus Greenhouse ForcingJournal of Climate, 2007
- A New Globally Complete Monthly Historical Gridded Mean Sea Level Pressure Dataset (HadSLP2): 1850–2004Journal of Climate, 2006
- Contributions of External Forcings to Southern Annular Mode TrendsJournal of Climate, 2006
- The Community Climate System Model Version 3 (CCSM3)Journal of Climate, 2006
- Origin of regional climate differences: role of boundary conditions and model formulation in two GCMsClimate Dynamics, 2005
- Internal variability, external forcing and climate trends in multi-decadal AGCM ensemblesClimate Dynamics, 2004
- An interpretation of the results from atmospheric general circulation models forced by the time history of the observed sea surface temperature distributionGeophysical Research Letters, 2000
- Long-Term Changes in the Equatorial Pacific Trade WindsJournal of Climate, 1996
- The Influence of Hadley Circulation Intensity Changes on Extratropical Climate in an Idealized ModelJournal of the Atmospheric Sciences, 1995
- Latent and Sensible Heat Flux Anomalies over the Northern Oceans: Driving the Sea Surface TemperatureJournal of Physical Oceanography, 1992