High-Resolution Image

Ability of a model to capture realistic seasonal hurricane-statistics is an indication of the model’s readiness for research on genesis, intensification, and demise of hurricanes. We investigated this ability of the GEOS-4 GCM (Atmospheric General Circulation Model) using finite volume hydrodynamics and our cloud physics package called McRAS (microphysics of clouds employing the Relaxed Arakawa-Schubert convection Scheme) to generate its hurricane-statistics. Model was integrated from August 1 through October 31 with observed sea-surface temperatures (SSTs) for 2005 - a year of most active hurricanes on record. The model simulated 14-intense convective systems that traversed through the Tropical Atlantic. The path of one such system is highlighted as a series of snapshots at roughly 3-day intervals. Following the passage of an easterly wave, an intense convective system with precipitation (shown as black contours) developed. Thereafter, it propagated westward and slowly intensified into a hurricane, with characteristic eye-wall structure, low pressure (isobars shown as green contours) and strong winds (surface wind magnitude is shaded). The system continued to gain strength up until the East Coast of the United States, and thereafter it weakened into an extratropical system. The upper right corner of the figure shows a snapshot of another mature hurricane-like tropical system arriving in the Gulf of Mexico prior to landfall. From the above, we infer that our GCM has the wherewithal to generate hurricanes on its own in response to SST-forcing.

(submitted by Eric Wilcox, Yogesh Sud and G. K. Walker. For details contact G. Walker)