Extended Abstract (224K)8B.7
Decadal Trends in Tropical CAPE
Charlotte A. DeMott, Colorado State University, Fort Collins, CO; and D. A. Randall
The diurnal cycle of various meteorological variables provide a useful method of evaluating global circulation model (GCM) performance as well as a framework for investigating physical interactions of various climate components.
As an example of the former, in this paper we conduct an analysis of the simulated diurnal cycle of heating terms in the tropical East Pacific is used to investigate causes for weaker-than-observed subtropical highs in this region. Results suggest that anomalous nighttime convection in this region warms the middle troposphere through latent and long-wave heating sufficiently to reduce the magnitude of compensating sinking motion, thereby reducting the strength of the subtopical highs.
In a closely related exercise, we evaluate the diurnal cycle of surface pressure (the atmospheric tides) in the CSU GCM and compare the results to those of Dai and Wang (1999) based on observational data. While the magnitude of both diurnal (S1) and semidiurnal (S2) cycles are about twice those seen in observations, other characteristics are very similar. Noteably, S1 and S2 are of comparable magnitude over tropical land masses, and both exhibit spatial variability beyond what can be explained by classical tidal theory. While the zonal variability in S1 is related to surface heating over land, zonal variability of S2 may be more closely related to clouds' influence on atmospheric heating. We are in the process of constructing diurnal cycles of reflected and absorbed insolation both from simulations and CERES data to investigate this relationship, as well as to evaluate the models performance in this area.
Of course, clouds may also affect S2 via latent heating, which is closely tied to the diurnal cycle of precipitation. Two model runs, one with a correct diurnal cycle of precipitation and one without, will be compared to asses the impact of the diurnal cycle of latent heating on S2 behavior.
Session 8B, Large-Scale Dynamics and Convection III (Parallel with Sessions 8A, 8C, and 8D)
Wednesday, 1 May 2002, 9:15 AM-10:30 AM
Previous paper