Implementation and calibration of a stochastic multicloud convective parameterization in the NCEP Climate Forecast System (CFSv2)

Date

2017

Authors

Goswami, B.B.
Khouider, B.
Phani, R.
Mukhopadhyay, P.
Maijda, A.J.

Journal Title

Journal ISSN

Volume Title

Publisher

Journal of Advances in Modeling Earth Systems

Abstract

A comparative analysis of fourteen 5 year long climate simulations produced by the National Centers for Environmental Predictions (NCEP) Climate Forecast System version 2 (CFSv2), in which a stochastic multicloud (SMCM) cumulus parameterization is implemented, is presented here. These 5 year runs are made with different sets of parameters in order to figure out the best model configuration based on a suite of state‐of‐the‐art metrics. This analysis is also a systematic attempt to understand the model sensitivity to the SMCM parameters. The model is found to be resilient to minor changes in the parameters used implying robustness of the SMCM formulation. The model is found to be most sensitive to the midtropospheric dryness parameter (MTD) and to the stratiform cloud decay timescale (τ30). MTD is more effective in controlling the global mean precipitation and its distribution while τ30 has more effect on the organization of convection as noticed in the simulation of the Madden‐Julian oscillation (MJO). This is consistent with the fact that in the SMCM formulation, midtropospheric humidity controls the deepening of convection and stratiform clouds control the backward tilt of tropospheric heating and the strength of unsaturated downdrafts which cool and dry the boundary layer and trigger the propagation of organized convection. Many other studies have also found midtropospheric humidity to be a key factor in the capacity of a global climate model to simulate organized convection on the synoptic and intraseasonal scales

Description

Keywords

stochastic multicloud model, CFSv2, implementation, calibration

Citation

Goswami, B. B.; Khouider, B.; Phani, R.; Mukhopadhyay, P.; & Majda, A. J. (2017). Implementation and calibration of a stochastic multicloud convective parameterization in the NCEP Climate Forecast System (CFSv2). Journal of Advances in Modeling Earth Systems, 9(3), 1721-1739. doi: 10.1002/2017MS001014