18 July 2016

Simplified Metrics for the Identification of the Madden-Julian Oscillation in Models

Timescale and coherence of MJO propagation from lead-lag correlation of principal components of OLR

Science

The simplified Madden Julian Oscillation (MJO) metrics, the maximum positive correlation and time lag at which it occurs, provide consistent information relative to more complex diagnostics developed by the Madden-Julian Oscillation Working Group (CLIVAR MJOWG, 2009; Kim et al., 2009).

Impact

Our simplified approach to analyzing the fidelity of the MJO will promote the evaluation of intrasesonal variability in large ensembles of models, and during the model development phase in which the sensitivity to parameterized physics is being evaluated.

Summary

This investigation promotes the adoption of simple metrics, the maximum positive correlation and the time lag at which it occurs, to perform a preliminary evaluation of boreal winter MJO in models. These metrics are based on projecting model bandpass filtered daily OLR onto observed MJO spatial patterns, and evaluating the lag correlation structure of the resulting PC’s. It is demonstrated that there is a statistically significant relationship between the maximum positive correlation and the East/West power ratio obtained from frequency-wavenumber decomposition of near-equatorial precipitation. Additionally, the simple metrics are consistent with MJO fidelity as determined from the composite life-cycle of MJO convection derived from the Wheeler and Hendon (2004) multivariate EOF approach. As such, these simple metrics may be useful as a first-look indication of MJO fidelity by modeling groups and as candidate variability metrics of the MJO for use by the WGNE/WGCM Climate Model Metrics Panel.

Contact
Kenneth R. Sperber
Lawrence Livermore National Laboratory (LLNL)
Publications
Sperber, KR, and D Kim.  2012.  "Simplified Metrics for the Identification of the Madden-Julian Oscillation in Models."  Atmospheric Science Letters 13: 187-193, doi:10.1002/asl.378.