Changes in MJO Characteristics and Impacts in the Past Century

Abstract

Abstract The changes of the MJO behavior and its impact on global precipitation, precipitation extremes, and high-frequency variability during the past century (1901–2010) were investigated using the NOAA-20CR dataset. It was found that the MJO amplitude was significantly strengthened, while its eastward phase speed hardly changed. The impacts of the MJO on precipitation in South China (SC), northern Australia (AU), and California (CA) were investigated. The anomalous rainfall in the regions was strengthened from the early to late twentieth century, with the percentage increase ranging from 67% in AU to 14% in CA. A moisture budget analysis indicated that the enhanced precipitation was primarily attributed to the effect of anomalous wind while the effect of the mean moisture change was small. The impact of the local meridional wind anomaly was critical in SC, while in AU and CA the zonal wind component dominated. The precipitation extremes had a significant increase from the early to late twentieth century. The cumulative extreme precipitation amount increased by 140%–150% in SC and AU and by 100% in CA, and the number of the extreme days increased by 110% in SC and AU and 70% in CA. Such increases are consistent with the strengthening of the high-frequency (HF; with a period less than 10 days) variability across the globe. The pattern of percentage increase of the HF variability resembles the pattern of percentage increase of MJO-scale precipitation. This implies that the MJO teleconnection pattern could exert a large-scale control on the HF variability and weather extremes. Significance Statement The Madden–Julian oscillation (MJO), a dominant mode of tropical intraseasonal oscillations, plays an important role in affecting global weather and climate. To understand to what extent the MJO and associated teleconnections change with global warming, this study adopts an alternative approach by analyzing a century-long reanalysis dataset rather than the outputs of climate models that consist of large uncertainties due to poor MJO simulations. We found that MJO-induced tropical and midlatitude precipitation and associated extremes and high-frequency variabilities were strengthened during the past century while the global mean surface temperature increases approximately by 1°C. The results derived from the present study provide a basis for assessing the future MJO behavior and associated climate impacts and for improving the extended-range prediction of severe weather and climate extremes.