An analysis of parameterization interactions and sensitivity of single‐column model simulations to convection schemes in CAM4 and CAM5

Abstract

[1] This paper uses different deep convection triggering functions and closure assumptions in two versions of the Community Atmospheric Model (CAM4 and CAM5) to investigate the interactions of parameterization components and the sensitivity of single-column model simulations of tropical convection. The schemes include those used in the standard CAM4 and CAM5 as well as two variants used in other global models. Large-scale forcing and verification data are from the Global Atmospheric Research Program's Atlantic Tropical Experiment and Kwajalein Experiment field campaigns during which many deep and shallow convective events were observed. Results show that in both CAM4 and CAM5, when the intensity of deep convection decreases as a result of parameterization change, the intensity of shallow convection increases, leading to little change in the total simulated precipitation but very different changes in precipitation types. The different precipitation types manifest themselves in other measures of model performances including temperature and humidity. The standard CAM4 and CAM5 both simulated warm bias in the middle troposphere and dry bias in the lower troposphere. In experiments where deep convection is reduced, these biases are also reduced, but the associated changes in shallow convection create new patterns of model biases. Results imply the need to use multiple independent observations simultaneously to constrain models so that the degrees of model freedom are reduced and to treat model physical parameterizations as an integrated system rather than individual components.Citation: Wang, X., and M. Zhang (2013), An analysis of parameterization interactions and sensitivity of single-column model simulations to convection schemes in CAM4 and CAM5,

Evaluating hydrological processes in the Community Atmosphere Model Version 5 (CAM5) using stable isotope ratios of water

“…Ultimately, given that these changes improved the isotopic simulation without noticeably degrading the rest of the climate (not shown), it indicates that the current CAPE trigger limit is too low, and that deep convection, at least in certain regions in certain seasons, triggers too frequently. A similar result has been found in previous studies [e.g., Xie et al ., ; Wang and Zhang , ; Suhas and Zhang , ], indicating that this result is supported by more than just changes to the water isotope ratios, and that water isotopes can help reveal model parameter choices that improve the model's physical realism. It also has strong implications for examining polar climates using isotope ratios in water, particularly in terms of proxy records of past climates [e.g., Sime et al ., ; Dee et al ., ], as it shows that changes in tropical or midlatitude convective processes, even without a major global temperature change, could produce substantial shifts in the average isotopic ratio of precipitation over the poles and high‐latitudes, including Greenland and Antarctica.…”

“…This finding of a convective trigger threshold that is too weak matches up well with previous studies [e.g. Xie et al ., ; Wang and Zhang , ; Suhas and Zhang , ], indicating that the improvements in the simulated water isotope ratios relate to actual improvements in the model's physical realism. Thus the “4xcape” experiment will be examined more closely to expose the influences of deep convection on the water isotopologue distribution in the model, and to determine to what degree imperfect representation of convective thunderstorms alone can fully explain the isotopic biases seen in iCAM5.…”

Impacts of the triggering function of cumulus parameterization on warm-season diurnal rainfall cycles at the Atmospheric Radiation Measurement Southern Great Plains site

“…Another noteworthy bias of the ZM scheme shown in Figure is that the convection is substantially more frequent than that in the SAS scheme and the ARM observations. This bias was also observed in several other studies in which the ZM scheme was used [ Xie et al , ; Wang and Zhang , ]. Frequent convection over land might lead to more rapid consumption of atmospheric instability and thus suppress nighttime rainfall events.…”

Global energy and water balance: Characteristics from Finite‐volume Atmospheric Model of the IAP/LASG (FAMIL1)

“…The following physical parameterizations of FAMIL1 are the same as those in SAMIL2: the cumulus convective parameterization is based on the bulk mass‐flux framework developed by Tiedtke [], in which three types of convections—penetrative convection in connection with large‐scale convergent flow, shallow convections in suppressed conditions such as trade wind cumuli, and middle convection such as extratropical organized convection—are uniformly treated. In addition to the default trigging function and closure assumption in deep convection, two other variants have also been added, including those based on convective available potential energy (CAPE) [ Nordeng , ], and the dynamic CAPE in which large‐scale dynamics is accounted for [ Xie and Zhang , ; Zhang , ; Wang and Zhang , ]. However, the dynamic CAPE so far on is only for single‐column experiments, through which the sensitivity of triggering and closure assumptions can be easily studied.…”