Assessing the fidelity of AOGCM-simulated relationships between large-scale modes of climate variability and wind speeds

Abstract

The ability of atmosphere-ocean general circulation models (AOGCMs) to reproduce associations between surface/near-surface variables over the United States (US) and large-scale modes of climate variability has implications for evaluating possible biases in future climate projections and is an important model diagnostic. Indices of three such modes (El Niño–Southern Oscillation (ENSO), the Arctic Oscillation (AO), and the Pacific-North American (PNA) pattern) and their relationships to wind speeds over the contiguous US are derived using historical reanalysis products and then used to evaluate the fidelity of AOGCM simulations of both the climate modes and the teleconnections. In the reanalysis data, the response of middle and upper troposphere wind speeds to ENSO phase is found to be essentially symmetric with anomalies of opposite sign occurring during the warm and cold phases. The AO and PNA phases are both associated with higher wind speeds relative to “neutral” conditions. AOGCMs from Phase 5 of the Coupled Model Intercomparison Project (CMIP5) produce AO- and PNA-like spatial patterns which exhibit good accord with those from NCEP-NCAR Reanalysis. The AOGCM-derived climate indices also exhibit general agreement with reanalysis-derived indices in terms of the frequencies associated with highest variance, although the agreement is better for AO and PNA than it is for ENSO. The AOGCMs are in good agreement with the NNR in terms of representation of the influence of the AO and PNA on winds over the contiguous US. However, for ENSO, AOGCMs fail to consistently capture the observed relationship between La Niña and near-surface to middle troposphere winds.