Extended Abstract (32K)8B.6
Pursuing realistic intra-seasonal wave modes using a novel approach to convective parameterization
Richard B. Neale, NOAA-CIRES/CDC, Boulder, CO; and B. E. Mapes
GCMs have traditionally experienced some difficulty in reproducing the correct characteristics of large-scale tropical intra-seasonal wave activity (e.g. Slingo et al, 1996). Of the models that actually have any kind of coherent eastward propagating signal, most tend to exhibit weak power at too high a frequency when compared to observations.
Speculation as to the reasons for this under-performance in models is wide ranging, but the role of convection is central to many theories. Convectively generated free-troposphere moisture variability has been suggested as a deficiency which may may lead to poor MJO-type variability (Grabowski, 2003), and may be a consequence of the weak entrainment formulation of mass-flux convection schemes.
Using an alternative novel approach to the mass-flux convective formulation results from a 4-layer tropical model are analyzed to investigate intra-seasonal wave behavior. The formulation of the scheme involves the concept of successive, highly entraining convective plumes, whereby a particular plume is able to exploit the moisture signal of a previous plume. Such a framework more closely resembles observed convective cloud anatomy and exhibits a higher degree of sensitivity to tropospheric moisture than traditional weakly entraining plume schemes. Results of the general model behavior are presented and the potential for realistic intra-seasonal wave activity explored.
Session 8B, Intraseasonal variability II
Tuesday, 4 May 2004, 3:45 PM-5:15 PM, Napoleon I Room
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