H-P. Huang, M. Newman, R. Seager, Y. Kushnir, and Participating CMIP2+ Modeling Groups, 2004:
Relationship between Tropical Pacific SST and global atmospheric angualar momentum in coupled models,LDEO Report, Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York USA, 43 pp.
Abstract
The sensitivity parameter S1 = Delta (AAM)/Delta (SST), where Delta (AAM) and Delta
(SST) represent the anomalies of global atmospheric angular momentum
(AAM) and tropical Pacific sea surface temperature (SST) in the NINO3.4
region, is compared for the CMIP2+ coupled models. The parameter
quantifies the strength of atmospheric zonal mean zonal wind response
to SST anomaly in the equatorial Pacific, an important process for the
climate system. Although the simulated Delta (AAM) and Delta
(SST) are found to exhibit great disparity, their ratios agree better
among the coupled models (and with observation) with no significant
outliers. This indicates that the processes that connect the AAM
anomaly to tropical SST anomaly are not sensitivie to the base SST and
the detail of convective heating and are relatively easy to reproduce
by the coupled models. Through this robust Delta
(SST) - Delta (AAM)
relationship, the model bias in tropical Pacific SST manifests itself
in the bias in atmospheric angular momentum. The value of S1 for
an atmospheric model forced by observed SST is close to that for a
coupled model with a similar atmospheric component, suggesting that the
Delta
(SST) - Delta (AAM) relationship is dominated by a one-way influence of the former forcing the latter. The physical basis for the Delta
(SST) - Delta (AAM) relationship is expored using a statistical equilibrium argument that links Delta
(SST) to the anomaly of tropical tropospheric temperature. The
resulting meridional gradient of tropospheric temperature is then
linked to the change in zonal wind in the subtropical jets, the main
contributor to Delta (AAM), by thermal wind balance.
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