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.


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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