The Madden–Julian Oscillation (MJO) is characterized by a planetary-scale circulation coupled with convection propagating eastward along the equator. It is the most dominant intraseasonal variability in the tropics, and its different phases influence global weather and climate. However, MJO simulation remains a great challenge as most General Circulation Models (GCMs) do not capture its basic propagation features.New research from an international group of Chinese and American scientists, funded in part by CPO’s Climate Variability & Predictability (CVP) program, aims to understand the cause of MJO bias in the High Resolution Atmospheric Model (HiRAM) driven by observed sea-surface temperature (SST) through a process-oriented diagnosis. Their findings, available as an early online release in Atmospheric and Oceanic Science Letters, show that HiRAM underestimates the spectral amplitude over the MJO band and mainly produces non-propagating rather than eastward-propagating intraseasonal rainfall anomalies. The study further discusses that the model bias can be a result of the unrealistic simulation of MJO vertical circulation anomalies in the upper troposphere, as well as the overestimation of the Rossby wave response.
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