Rethinking convective quasi-equilibrium observational constraints for stochastic convective schemes in climate models

J. David Neelin, Ole Peters, Johnny W.-B. Lin, Katrina Hales, and Christopher E. Holloway
Phil. Trans. Roy. Soc. Lond. A, 366, 2581-2604. doi:10.1098/rsta.2008.0056.

Available free to the public through EXiS Open Choice. Paper (PDF 460KB).
© Copyright 2008 by the Royal Meteorological Society.

Abstract. Convective quasi-equilibrium (QE) has for several decades stood as a key postulate for parameterization of the impacts of moist convection at small scales upon the large-scale flow. Departures from QE have motivated stochastic convective parame- terization, which in its early stages may be viewed as a sensitivity study. Introducing plausible stochastic terms to modify existing convective parameterizations can have substantial impact, but as for so many aspects of convective parameterization, the results are sensitive to details of the assumed processes. We present observational results aimed at helping to constrain convection schemes, with implications for each of conventional, stochastic or superparameterization schemes. The original vision of QE due to Arakawa fares well as a leading approximation, but with a number of updates. Some, like the imperfect connection between the boundary layer and the free troposphere and the importance of free tropospheric moisture to buoyancy, are quantitatively important but lie within the framework of ensemble average convec- tion slaved to the large scale. Observations of critical phenomena associated with a continuous phase transition for precipitation as a function of water vapor and tem- perature suggest a more substantial revision. While the systems attraction to the critical point is predicted by QE, several fundamental properties of the transition, including high precipitation variance in the critical region, need to be added to the theory. Long-range correlations imply that this variance does not reduce quickly under spatial averaging; scaling associated with this spatial averaging has poten- tial implications for superparameterization. Long tails of the distribution of water vapor create relatively frequent excursions above criticality with associated strong precipitation events.

Citation. J. D. Neelin, O. Peters, J. W.-B. Lin, K. Hales, and C. Holloway, 2008: Rethinking convective quasi-equilibrium observational constraints fo stochastic convective schemes in climate models. Phil. Trans. Roy. Soc. Lond. A, 366, 2581-2604. doi:10.1098/rsta.2008.0056.

Acknowledgments. This work was supported under National Science Foundation Grants ATM-0082529 and OPP-0129800 (JWL) and National Oceanic and Atmospheric Administration Grants NA05- OAR4311134 and NA05-OAR4310007. We thank A. Arakawa for discussions.