Abstract. The parameter-space dependence of the eigenmodes of the coupled tropical ocean-atmosphere system, linearized about a climatological basic state, is further examined in a stripped-down intermediate coupled model using the formulation derived in Part II to permit analytical treatment for a finite ocean basin. Part II examined the limit of weak coupling and showed the rapid transition to the mixed SST/ocean-dynamics modes of Part I, where it was argued that realistically coupled modes are best understood from strong coupling. Here we explore cases with order unity and larger coupling to provide analytical prototypes for the fully-coupled case from a system which explicitly treats spatial structure in a finite basin. The coupled dynamics is explored for several regions of parameter space where simplifications are possible, as well as for the transition from the well-separated case to mixed modes.
Convective parameterizations in general circulation models (GCMs) generally only aim to simulate the mean or first-order moment of convection; higher-moments associated with sub-grid variability are not explicitly considered. In this study, an empirically-based stochastic convective parameterization is developed that uses an assumed mixed lognormal distribution of rainfall, tuned with parameter values derived from observations, to control selected non-mean statistical properties of convection. Testing of this stochastic convective parameterization reveals that large-scale model dynamics interacts heavily with the convective parameterization, in ways such that the resulting output is fundamentally different from the input. This suggests stochastic parameterizations cannot be calibrated outside of a model's dynamical framework. Implications are discussed for the relative merits of the empirical approach versus another approach that introduces the stochastic process within the framework of the convective parameterization. Inclusion of the variance arising from unresolved scales by stochastic parameterization of convection is found to have a substantial impact upon atmospheric variability in the tropics, including intraseasonal and longer time scales.
Citation. Lin, J. W.-B., and J. D. Neelin, 2002: Considerations for stochastic convective parameterization. J. Atmos. Sci., 59 , 959-975.
Acknowledgments.
This research was partially supported by
National Science Foundation grant ATM-0082529 and
National Oceanic and Atmospheric Administration grant NA86GP0314.
During final preparation and revisions of the manuscript,
JWL was supported by a visiting fellowship from the Cooperative Institute
for Research in Environmental Sciences (CIRES) at the University of
Colorado, Boulder.