Abstract
High-resolution simulations over a large tropical domain (~20°S–20°N, 42°E–180°) using both explicit and parameterized convection are analyzed and compared during a 10-day case study of an active Madden–Julian oscillation (MJO) event. In this paper, Part II of this study, the moisture budgets and moist entropy budgets are analyzed. Vertical subgrid diabatic heating profiles and vertical velocity profiles are also compared; these are related to the horizontal and vertical advective components of the moist entropy budget, which contribute to gross moist stability (GMS) and normalized GMS (NGMS). The 4-km model with explicit convection and good MJO performance has a vertical heating structure that increases with height in the lower troposphere in regions of strong convection (like observations), whereas the 12-km model with parameterized convection and a poor MJO does not show this relationship. The 4-km explicit convection model also has a more top-heavy heating profile for the troposphere as a whole near and to the west of the active MJO-related convection, unlike the 12-km parameterized convection model. The dependence of entropy advection components on moisture convergence is fairly weak in all models, and differences between models are not always related to MJO performance, making comparisons to previous work somewhat inconclusive. However, models with relatively good MJO strength and propagation have a slightly larger increase of the vertical advective component with increasing moisture convergence, and their NGMS vertical terms have more variability in time and longitude, with total NGMS that is comparatively larger to the west and smaller to the east.
Highlights
In the first part of this paper (Holloway et al 2013, hereafter H13), we presented results comparing six largedomain limited-area Met Office Unified Model (MetUM) simulations of a 10-day Madden–Julian oscillation (MJO)Denotes Open Access content
H13 showed that the two explicit convection simulations in the present study, the 4-km 3Dsmag and 12-km 3Dsmag models, had significantly better MJO amplitude and propagation compared with the two parameterized simulations, the 12-km param and 40-km param models
We first compare the moisture budgets of the 4-km 3Dsmag model and 12-km param model, finding that moisture convergence mostly balances total convective heating as expected
Summary
In the first part of this paper (Holloway et al 2013, hereafter H13), we presented results comparing six largedomain limited-area Met Office Unified Model (MetUM) simulations of a 10-day Madden–Julian oscillation (MJO). Benedict et al (2014) find that the two convectional GCMs with altered convection schemes have different relationships between the vertical and horizontal components of moist entropy advection to MC than SPCAM and ERA-Interim (as well as a somewhat different relationship between radiative fluxes and MC), the relationship between total advective increments of moist entropy and MC are similar among all four One interpretation of these findings is that, at least for those two models with altered convection schemes, it might be a cancellation of errors that was leading to an improved MJO. We are limited to a single 10-day case study on a large but limitedarea domain, there is still some benefit to asking these kinds of questions of simulations in our novel framework These results will inspire other studies of the relationship between convective processes and large-scale phenomena, as well as ideas of further potential improvements to convective parameterizations in GCMs. The paper layout is as follows.
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