Examining the Madden-Julian Oscillation in Climate Models

The variability of the Madden-Julian Oscillation (MJO) has been a topic of study in the meteorological community for many years. The MJO can have far-reaching impacts on global weather and climate, and one area of interest is its future impact on atmospheric variability and sea ice levels around Antarctica. For example, tropical forcing from the MJO could affect long-duration ice melt events in West Antarctica. The specific details of the MJO-Antarctic relationship in climate models have not been examined in detail, and to do so, an MJO metric is needed.

Various metrics have been created that classify the intensity and location of the MJO active convective envelope. One such metric, the Real-time Multivariate MJO (RMM) index, is based on empirical orthogonal function (EOF) analyses of zonal winds at 850 hPa and 200 hPa, and OLR. In this study, daily OLR, u850, and u200 data fields from NCEP/NCAR and NOAA Physical Science Division reanalyses were subsetted across all longitudes, and from latitudes 15°S to 15°N. These data fields were further subsetted across a date range 01 January 1975 to 31 December 2018. Anomalies of each variable were calculated using a 30-year mean and examined to remove the seasonal cycle. Finally, the anomalies of each data field were filtered using a bandpass function. Through the use of EOF analyses, long-range climate model data will be used to calculate an RMM-like index of the MJO at a daily level. Specifically, this index will be based on OLR and 850 hPa, and 200 hPa zonal winds from Coupled Model Intercomparison Project Phase 6 (CMIP-6) output in future climatological scenarios through the year 2050. Characteristics of the modeled MJO events will be compared and contrasted with MJO events over the present period.