A latent heating peak in the PBL was detected in a simulation by a global GCM that failed to reproduce Madden Julian Oscillation （MJO）. The latent heating peak in the PBL was generated by very shallow convection, wh...A latent heating peak in the PBL was detected in a simulation by a global GCM that failed to reproduce Madden Julian Oscillation （MJO）. The latent heating peak in the PBL was generated by very shallow convection, which prevented moisture from being transported to the free troposphere. Large amount of moisture was therefore confined to the PBL, leading to a dry bias in the free atmosphere. Suffering from this dry bias, deep convection became lethargic, and MJO signals failed to occur. When the latent heating peak in the PBL was removed in another simulation, reasonable MJO signals, including the eastward propagation and the structure of its large-scale circulation, appeared. We therefore propose that the excessive latent heating peak in the PBL due to hyperactive shallow convection may be a reason for a lack of MJO signals in some simulations by other GCMs as well.展开更多
Long-term integrations are conducted using the Spectral Atmospheric Model （referred to as SAMIL）, which was developed in the Laboratory for Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics ...Long-term integrations are conducted using the Spectral Atmospheric Model （referred to as SAMIL）, which was developed in the Laboratory for Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics （LASG） in the Institute of Atmospheric Physics （IAP）, with different resolutions to inves-tigate sensitivity of the Madden-Julian Oscillation （MJO） simulations to the model＇s resolution （horizontal and vertical）. Three resolutions of the model, R15L9, R42L9 and R42L26, with identical physical processes, all produced the basic observed features of the MJO, including the spatiotemporal space-time spectra and eastward propagation. No fundamental differences among these simulations were found. This indicates that the model resolution is not a determining factor for simulating the MJO. Detailed differences among these modeling results suggest, however, that model resolution can substantially affect the simulated MJO in certain aspects. For instance, at a lower horizontal resolution, high frequency disturbances were weaker and the structures of the simulated MJO were better defined to a certain extent. A higher vertical resolution led to a more realistic spatiotemporal spectrum and spatial distribution of MJO precipitation. Meanwhile, increasing the model＇s resolution improved simulation of the climatology. However, increasing the resolution should be based on improving the cumulus parameterization scheme.展开更多
基金supported by National Science Foundation of U.S.A.(Grant No. ATM0739402)the National Natural Science Foundation of China (Grant Nos. U0833602 and 40905035)
文摘A latent heating peak in the PBL was detected in a simulation by a global GCM that failed to reproduce Madden Julian Oscillation （MJO）. The latent heating peak in the PBL was generated by very shallow convection, which prevented moisture from being transported to the free troposphere. Large amount of moisture was therefore confined to the PBL, leading to a dry bias in the free atmosphere. Suffering from this dry bias, deep convection became lethargic, and MJO signals failed to occur. When the latent heating peak in the PBL was removed in another simulation, reasonable MJO signals, including the eastward propagation and the structure of its large-scale circulation, appeared. We therefore propose that the excessive latent heating peak in the PBL due to hyperactive shallow convection may be a reason for a lack of MJO signals in some simulations by other GCMs as well.
文摘Long-term integrations are conducted using the Spectral Atmospheric Model （referred to as SAMIL）, which was developed in the Laboratory for Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics （LASG） in the Institute of Atmospheric Physics （IAP）, with different resolutions to inves-tigate sensitivity of the Madden-Julian Oscillation （MJO） simulations to the model＇s resolution （horizontal and vertical）. Three resolutions of the model, R15L9, R42L9 and R42L26, with identical physical processes, all produced the basic observed features of the MJO, including the spatiotemporal space-time spectra and eastward propagation. No fundamental differences among these simulations were found. This indicates that the model resolution is not a determining factor for simulating the MJO. Detailed differences among these modeling results suggest, however, that model resolution can substantially affect the simulated MJO in certain aspects. For instance, at a lower horizontal resolution, high frequency disturbances were weaker and the structures of the simulated MJO were better defined to a certain extent. A higher vertical resolution led to a more realistic spatiotemporal spectrum and spatial distribution of MJO precipitation. Meanwhile, increasing the model＇s resolution improved simulation of the climatology. However, increasing the resolution should be based on improving the cumulus parameterization scheme.
