Convectively Coupled Kelvin Waves in an Idealized Moist General Circulation Model

Abstract

The dynamics of convectively coupled Kelvin waves and their dependence on convection scheme parameters are studied within a simplified moist general circulation model. The model consists of the primitive equations on the sphere over zonally symmetric aquaplanet, slab mixed layer ocean boundary conditions, and idealized physical parameterizations including gray radiative transfer and a simplified Betts-Miller convection scheme. This framework allows the authors to study the dependence of Kelvin waves on quantities such as the gross moist stability in a clean manner.A control simulation with the model produces convectively coupled Kelvin waves that are remarkably persistent and dominate the variability within the Tropics. These waves propagate with an equivalent depth of Ϸ40 m. Linear regression analysis with respect to a Kelvin-filtered time series shows that the waves are driven by evaporation-wind feedback and have structures broadly consistent with theoretical predictions for Kelvin waves.Next, the determination of the speed and structure of the Kelvin waves is studied by examining the response of the waves to changes in convection scheme parameters. When the convective relaxation time is lengthened, the waves are damped and eventually are completely eliminated. The propagation speed additionally increases with longer relaxation time. Then changes to a convection scheme parameter that essentially controls the fraction of convective versus large-scale precipitation are examined. When some large-scale precipitation occurs, the waves increase in strength, propagate more slowly, and move to larger scales. However, when mostly large-scale precipitation occurs, the Kelvin wave disappears, and the Tropics are dominated by tropical storm-like variability. The decrease in speed is related here to the gross moist stability of the atmosphere, which is reduced with increased large-scale precipitation.

Idealized Simulations of the Intertropical Convergence Zone and Its Multilevel Flows

“…For example, NZC07 found that convection was strongly organized by a single, robust convectively coupled Kelvin wave (CCKW). That convection is organized into a dominant, domain-length CCKW was also found for a global aquaplanet simulation by Frierson (2007). In our case, it will be shown that this wave is not so dominant when the free-slip wall at the equator is removed and that an equatorial wave feature similar to the mixed Rossbygravity wave will appear.…”

“…For HYP2.5-8N and IEP, the eddy fluxes are mostly associated with the TCs; for HYP2.5, the eddy fluxes are maximized only a few degrees on either side of the equator and are associated with the meridional circulations generated by the CCKWs. Although pure Kelvin waves have zero meridional flow, CCKWs in the atmosphere (Wheeler et al 2000), in idealized simulations (NZC07; Frierson 2007), and in the theory of Dias and Pauluis (2009) are found to have significant meridional flow into and out of their convecting regions.…”

Stochastic Convection Parameterization with Markov Chains in an Intermediate-Complexity GCM

“…Dor15 is only able to improve on this issue by strongly reducing rw c . By increasing the relaxation time scale of the relaxation closure in CTRL, similar changes are to be expected (Frierson 2007). For Dor15, it seems that changing the mean M b has a larger impact on the representation of the equatorial waves than changing the magnitude of stochastic fluctuations of M b on a time step level.…”

Column-Integrated Moist Static Energy Budget Analysis on Various Time Scales during TOGA COARE

“…Equation (3) can be separated into horizontal and vertical components as Previous research has used G y in various ways such as a diagnostic quantity in general circulation models (e.g., Frierson 2007;Hannah andMaloney 2011, 2014;Benedict et al 2014), in observational data (e.g., Yu et al 1998;Sobel et al 2014), 2 as an output quantity of a MJO toy model (e.g., Raymond and Fuchs 2009), and as an input parameter of a MJO toy model (e.g., Sugiyama 2009;Maloney 2012, 2013). As Hannah and Maloney (2011) and Masunaga and L'Ecuyer (2014) pointed out, values of G y generally fluctuate in convective life cycles primarily as a result of variations of vertical velocity profiles (as seen in Fig.…”