Evaluation and Improvement of a SVD-Based Empirical Atmospheric Model

An empirical atmospheric model (EAM) based on the singular value decomposition (SVD) method is evaluated using the composite El Nino/Southern Oscillation (ENSO) patterns of sea surface temperature (SST) and wind anomalies as the target scenario. Two versions of the SVD-based EAM were presented for comparisons. The first version estimates the wind anomalies in response to SST variations based on modes that were calculated from a pair of global wind and SST fields (i.e., conventional EAM or CEAM). The second version utilizes the same model design but is based on modes that were calculated in a region-wise manner by separating the tropical domain from the remaining extratropical regions (i.e., region-wise EAM or REAM). Our study shows that, while CEAM has shown successful model performance over some tropical areas, such as the equatorial eastern Pacific (EEP), the western North Pacific (WNP), and the tropical Indian Ocean (TIO), its performance over the North Pacific (NP) seems poor. When REAM is used to estimate the wind anomalies instead of CEAM, a marked improvement over NP readily emerges. Analyses of coupled modes indicate that such an improvement can be attributed to a much stronger coupled variability captured by the first region-wise SVD mode at higher latitudes compared with that captured by the conventional one. The newly proposed way of constructing the EAM (i.e., REAM) can be very useful in the coupled studies because it gives the model a wider application beyond the commonly accepted tropical domain.