Characteristics of the Madden-Julian Oscillation reproduced in a NICAM-AMIP type simulation
Abstract
Madden-Julian Oscillation (MJO) has been recognized to be a phenomenon especially difficult to reproduce in state-of-the-art atmospheric models. While preceding studies have shown that cloud resolving models that eliminate convective parameterization are useful for reproducing the MJO as an initial value problem, its ability to reproduce the characteristics of MJO events reproduced as internal variabilities of the simulated atmosphere in long-term integrations has not been investigated thoroughly. To address this problem, this study analyzed the characteristics of the MJO events simulated in a 30-year simulation on a global cloud resolving model, nonhydrostatic icosahedral atmospheric model (NICAM), following closely the atmospheric model intercomparison project protocol (AMIP).
It was found that simulation reproduced the observed tendency of the MJO to slow down when they are embedded within stronger Walker circulation cells, which are intensified by background SST states with larger zonal SST gradients between the warmer western Pacific and the cooler Indian ocean and eastern Pacific. However, the mean speed of the simulated MJO events was slower than the observation. Furthermore, MJO events in the simulation occurred disproportionately during El Niño events and were missing during La Niña events. These biases were associated with overestimation of the western Walker circulation cell strength, which was partially counteracted during El Niño events. The results of this study indicate the importance of examining the biases in the mean circulation states of the simulated atmosphere for assessment of reproducibility of MJO characteristics in atmospheric models.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.A45S2127S