AOS 270 Seminars


Wednesday, May 9 (Rescheduled)


Akio Arakawa, AOS-UCLA




Math Science 7124

TOPIC: "Multiscale Modeling of the Moist-Convective Atmosphere"


The importance of multiscale modeling of the moist-convective atmosphere was well recognized in the 1960s when cumulus parameterization was introduced in tropical cyclone and general circulation models. Since then, the cumulus parameterization problem has always been a central issue in numerical modeling of the atmosphere, but its progress has been unacceptably slow comparing to the speed of gaining popularity of General Circulation Models (GCMs). As far as representation of deep moist convection is concerned, we use only two kinds of model physics at present: highly parameterized as in the low-resolution GCMs and explicitly simulated as in the high-resolution cloud-resolving models (CRMs), leaving a wide range of “Gray Zone” in-between. Ideally, the physics of these two families of models should be unified so that a continuous transition of model physics from one kind to the other takes place as the resolution changes. In this way, horizontal resolutions of the dynamics core can be freely chosen with essentially the same formulation of model physics. There can be two routes for such unification. ROUTE I, which we call “Unified Parameterization”, is an intellectually challenging approach of breaking through the Gray Zone through generalizing the conventional parameterization. Route II, on the other hand, which we call “Quasi-3D Multiscale Modeling Framework (Q3D MMF)”, is a technically challenging approach of bypassing the Gray Zone through replacing the conventional parameterization with the CRM physics throughout. This seminar discusses what we have done following these approaches, ROUTE I in particular, including detailed statistical analyses of CRM-simulated data to test various parameterization hypotheses.