ENSO-induced teleconnection: development of process-oriented diagnostics (POD) to assess Rossby wave sources in climate models

Abstract:

Over the past half century, sustained research from observations, theory and numerical modeling has confirmed that sea surface temperature (SST) anomalies associated with El Niño–Southern Oscillation (ENSO) serve as the source of predictability of seasonal to interannual climate variations over many parts of the globe, including those over North America and the insular U.S. affiliated Pacific Islands. During ENSO, the efficacy of climate models’ ENSO-induced global teleconnection can be assessed by their fidelity in representing Rossby wave sources (RWS). Besides biases in ENSO-related precipitation and horizontal and vertical distributions of diabatic heating, the anomalous RWS depends on the models’ basic state characteristics (e.g., upper-level jet stream, meridional gradient in absolute vorticity, stationary wave number etc.,).

A process-based diagnostics (POD) package has been developed that estimates upper-level climatological flow characteristics, and solves the barotropic vorticity budget. The POD is applied to CMIP and AMIP era-models and the results are compared and contrasted with those obtained from reanalysis products. Apart from assessing RWS properties (location, strength etc.,), various metrics are developed to identify models’ systematic errors leading to possible source(s) of errors. A clear application of the POD is in during the stages of climate model development. In this presentation, we will discuss its applicability in identifying the improvement of anomalous RWS and associated teleconnection features during CAM6 developmental stages (from CAM5 to CAM6). It is clear that the net improvement did not manifest monotonically and we will show that individual steps can result in both improvement and/or degradations in the POD.