Abstract
AbstractWe implemented a spectral cumulus parameterization based on a cloud‐resolving model (SC scheme) in the icosahedral nonhydrostatic atmospheric model (ICON‐A). We compared the resulting simulated climatology and tropical variability with results from the standard version of ICON‐A using a variant of the Tiedtke‐Nordeng scheme (TK scheme) using observational and reanalysis data. The climatological errors of the SC scheme were similar to those of the TK scheme, but several biases, such as properties of meridional winds and precipitation pattern in the western Pacific, were much improved. For tropical variability, we found that the SC scheme improved the interannual response of the precipitation in the western Pacific and was able to simulate Madden‐Julian oscillation (MJO) features much better than the TK scheme. We investigated the reason for the better simulation of the MJO using composite analysis and column process analysis for moisture. Our results suggest that the entrainment parameterization of the SC scheme is necessary to reproduce the MJO; however, spectral representation and improved convective closure are also found to contribute for better MJO simulation. These parameterizations improved moisture supply from low‐level clouds and cloud mass flux which were needed to sustain the MJO.
Highlights
Cumulus parameterizations are one of the most important physical parameterizations that influence climates simulated by general circulation models (GCMs)
We found that the SC scheme improved the interannual response of the precipitation in the western Pacific and was able to simulate Madden-Julian oscillation (MJO) features much better than the TK scheme
Our results suggest that the entrainment parameterization of the SC scheme is necessary to reproduce the MJO; spectral representation and improved convective closure are found to contribute for better MJO simulation
Summary
Cumulus parameterizations ( referred to as convection schemes) are one of the most important physical parameterizations that influence climates simulated by general circulation models (GCMs). Coupled equatorial waves (CCEWs) and the Madden-Julian oscillation (MJO, Madden & Julian, 1971; Zhang, 2005) in the tropics are responsible for the atmospheric variability represented by various convective clouds They play important roles in the global atmospheric circulation. The scheme was found to be able to simulate reasonable CCEWs and MJO behaviors in the AMIP experiment This may have been due to the fact that the unresolved clouds were more accurately considered using the spectral representation and improved in-cloud parameterization. Results from further analysis on intraseasonal variability are presented, related to earlier studies, which showed that some bulk convection schemes were able to simulate the tropical variability and MJO (e.g., Hirons et al, 2013; Hung et al, 2013; Kim et al, 2009).
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