Evaluating convective parameterization closures using cloud‐resolving model simulation of tropical deep convection

Abstract

Closure is an important component of a mass flux-based convective parameterization scheme, and it determines the amount of convection with the aid of a large-scale variable (closure variable) that is sensitive to convection. In this study, we have evaluated and quantified the relationship between commonly used closure variables and convection for a range of global climate model (GCM) horizontal resolutions, taking convective precipitation and mass flux at 600 hPa as measures for deep convection. We have used cloud-resolving model simulation data to create domain averages representing GCM horizontal resolutions of 128 km, 64 km, 32 km, 16 km, 8 km, and 4 km. Lead-lag correlation analysis shows that except moisture convergence and turbulent kinetic energy, none of the other closure variables evaluated in this study show any relationship with convection for the six subdomain sizes. It is found that the correlation between moisture convergence and convective precipitation is largest when moisture convergence leads convection. This correlation weakens as the subdomain size decreases to 8 km or smaller. Although convective precipitation and mass flux increase with moisture convergence at a given subdomain size, as the subdomain size increases, the rate at which they increase becomes smaller. This suggests that moisture convergence-based closure should scale down the predicted mass flux for a given moisture convergence as GCM resolution increases.

Convective cloud vertical velocity and mass‐flux characteristics from radar wind profiler observations during GoAmazon2014/5

“…Additional attempts were also considered to segregate the GoAmazon2014/5 data set into ensemble mean profiles according to the upper and lower standard deviation values for CAPE, CIN, and low‐level RH. One alternative was to explore basic correlations between the thermodynamic quantities of interest and velocity or mass flux profile values (as in other conventional GCM efforts) [e.g., Suhas and Zhang , ]. Unfortunately, those breakdowns typically reflected insufficient sample populations or required larger increments of the thermodynamic quantities (e.g., CAPE bins in 1000 J kg −1 increments) to generate representative profiles with confidence (peaked distributions as in Figure ).…”

“…As in that study, we document the vertical structure of convective mass flux, the relative role of convective area fraction and vertical velocity on mass flux, and the sensitivity of vertical velocity and mass flux profiles to changes in thermodynamics conditions. Efforts along these lines may act as a pure observational complement to help anchor other recent GCM convective parameterization environmental forcing and closure studies [e.g., Suhas and Zhang , ].…”

Convective response to large-scale forcing in the Tropical Western Pacific simulated by spCAM5 and CanAM4.3

“…divided by 32). Following the definition in Suhas and Zhang (2015), a CSRM column is categorized as convective if at any level the Geosci. Model Dev.…”

Relating Convection to GCM Grid-Scale Fields Using Cloud-Resolving Model Simulation of a Squall Line Observed during MC3E Field Experiment

“…The examination of the relationship between convective activity and large-scale fields can provide valuable information for evaluating and improving convective parameterization. Suhas and Zhang examined several large-scale variables used in convective parameterization closures using a cloud-resolving model (CRM) simulation of unorganized tropical convection by Zeng et al [19]. They found that moisture convergence has the best relationship with convection among all closure variables they examined.…”

“…On the other hand, an earlier study [20] found that the quasi-equilibrium closure broke down when the domain size was too small to provide an adequate sampling of the cloud field or under rapidly changing large-scale forcing. In addition, Suhas and Zhang [19] was for unorganized convection. Do their conclusions apply to organized convection such as mesoscale convective systems?…”