Julio Bacmeister (PI)
University of Maryland Baltimore County
bacmj@janus.gsfc.nasa.gov

Moist Physics Development for GEOS-5 Using Single Column Models with Parameterized Dynamics

AGCMs exhibit a number of major, long-standing deficiencies which are at partly caused by  inadequacies in their moist physics parameterization schemes.  These deficiencies include an inability to correctly simulate most aspects of the tropical subseasonal oscillation in precipitation - the Madden-Julian Oscillation (MJO), and an inability to correctly simulate the seasonal means of tropical precipitation.  The second problem is usually manifested by the existence of a so-called “double ITCZ” bias, which refers to the presence of an excessively strong Intertropical Convergence Zone (ITCZ) in the southern hemisphere.  This bias exists in most current AGCMs (Meehl and Arblaster, 1998). .  In addition to these clearly manifested errors, AGCMs also exhibit a bewildering variety of sensitivities to parameters and to external forcings.  A critical area of uncertainty is in the response of the climate system to increases in CO2 and other greenhouse gases.  The major part of this uncertainty can be traced to the behavior of simulated clouds in AGCMs.  Even AGCMs with similar net senstitivites to imposed changes in CO2 can arrive at this sensitivity through very different combinations of cloud responses.This project will support on-going moist physics development for the GEOS-5 AGCM.  Ultimately it aims to understand and alleviate biases in GEOS-5 due to problems in moist process parameterization. As part of this of this effort we plan to develop a Single Column Model (SCM) framework with parameterized large-scale dynamics (SCM/PD).

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