edu.ucar.opensky::technotes:160 UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact 2025-12-26T16:48:59.051644 ISO 19115-2 Geographic Information - Metadata - Part 2: Extensions for Imagery and Gridded Data ISO 19115-2:2009(E) https://n2t.org/ark:/85065/d7rj4hvd Diagnosis and Sensitivity of the 200 hPa Circulation in NCAR Community Climate Models 1993-01-01T00:00:00Z publication https://n2t.org/ark:/85065/d7rj4hvd https://doi.org/10.5065/D6MG7MF8 Hoerling, M. author DeHaan, L. author Hurrell, J. author UCAR/NCAR - Library publisher The purpose of this report is to determine the nature of systematic errors in several different seasonal cycle versions of the National Center for Atmospheric Research (NCAR) Community Climate Models (CCMs) and to assess the dynamical impact of such errors on climate perturbation studies. Our diagnosis focuses on the seasonal mean December- January-February (DJF) 200 hPa circulation and evaluates the sensitivity of that flow to anomalous tropical forcing. Other features of the CCM climatologies for January and July, including the mass fields and hydrologic cycle, are evaluated in Hurrell et al. (1993). A linear barotropic stationary wave model is used to examine the sensitivity of observed and CCM climatological flows to idealized tropical forcing. The forcing consists of a mass source/sink dipole over the equatorial Pacific that mimics the horizontal structure of anomalous rainfall during El Ni&#241o. The climatological flows on which the forcing is imposed differ among the various CCMs, and these in turn differ from observations. Differences between the responses to tropical forcing imposed on each base state relative to observations then indicate the dynamical significance of the CCM climate errors. The northern wintertime teleconnections during El Ni&#241o are particularly strong with the Northern Hemisphere (NH) flow, and our assessment of the significance of the CCM climate biases focuses on how such errors impact the NH stationary wave response. Of course, the full CCM behavior during El Ni&#241o is considerably more complicated than just the steady barotropic response to tropical forcing. As such, the approach taken herein should be viewed as only one component of a more thorough model evaluation that ultimately requires diagnosis of CCM integrations with interannual sea surface temperature (SST) anomalies. Relationships between climate errors in CCM divergent and rotational flow components are examined in the context of the linear model. These experiments are designed to determine the link between various features of the CCM 200 hPa circulation biases, and to provide guidance for, model development. Our principal results common to all the CCM versions studied herein are: * The zonally averaged zonal wind at 200 hPa has a westerly bias in the tropics. The error is not zonally uniform but is strong locally with a 20 m s-1 maximum over the equatorial central Pacific. This is associated with an erroneous westward shift of the CCMs' subtropical Pacific stationary wave troughs in both hemispheres. UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact PDF Text theme Resource Type 2016-01-01T00:00:00Z publication Upper level winds Atmospheric general circulation models Wind dynamics theme U.S. National Aeronautics and Space Administration Global Change Master Directory GCMD 2021-09-17 revision 11.2 NASA Global Change Master Directory originator Valids List: Science and Services Keywords Copyright Author(s). This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License. None eng geoscientificInformation