NCAR scientists Jordan Powers and Christopher Davis will present imagery from their hurricane simulation on Thursday, August 2, in Fort Lauderdale, Florida, at the Ninth Conference on Mesoscale Processes of the American Meteorological Society (AMS). NCAR's primary sponsor is the National Science Foundation, which funded the research.

The simulation, which used the NCAR/Penn State Mesoscale Model, Version 5 (MM5), marks the first time a cloud-resolving simulation has been able to reproduce the formation of a tropical cyclone, given only information about atmospheric conditions on a scale much larger than that of the cyclone. (Tropical cyclones include tropical storms and hurricanes.)

The breakthrough points toward future forecasting power that will soon be available to the National Weather Service.

NCAR is part of a team now building a model similar to the MM5, but with more advanced capabilities, that will generate daily weather forecasts for the NWS beginning in 2004.

According to Davis, "One of the remaining mysteries about hurricanes is how they form, especially when they're influenced by midlatitude weather systems that move into the subtropics and tropics.

"We hope that by analyzing the mechanisms behind storm formation in these simulations, we can make hypotheses of tropical cyclone formation that can be tested using aircraft, radar and satellite data. We also hope to understand what's needed to predict storm formation in operational weather forecast models."

Operational computer models used for day-to-day weather prediction have become increasingly adept at projecting a hurricane's motion. Yet even the best models have little skill in predicting intensity, especially the rapid strengthening often noted in the most powerful hurricanes.

Part of the problem is that the compact core of a hurricane, including the spiral bands of showers and thunderstorms that gather and focus energy, can't be modeled in sufficient detail on the computers and models used for everyday forecasting.

For instance, the finest horizontal scale resolved in operational computer models is 10-30 miles, but spiral bands can be less than 10 miles wide.

To "see" the eyewall and precipitation bands within a tropical cyclone, Davis and Powers turned to the MM5, one of the world's highest-resolution research models for reproducing storm-scale weather across a large area. The model's horizontal distance is as fine as 0.75 miles between computation points.

For their experiment, Davis and Powers studied Hurricane Diana, which struck North Carolina in 1984. Diana was chosen because of ample surface data and because a well-defined nontropical low preceded its formation.

The MM5 successfully reproduced several stages in Diana's development, from its original state as a nontropical low to its intensification to hurricane status more than a day later.

The Weather Research and Forecasting Model now being developed for future use by the National Weather Service is designed to regularly operate with resolutions from 0.6 to 6.2 miles. Together with more powerful computers, this will put the type of fine-scale detail in the MM5 into the hands of daily weather forecasters.

The National Oceanic and Atmospheric Administration, the University of Oklahoma and the U.S. Air Force are collaborating with NCAR on the project.

NCAR is managed by the University Corporation for Atmospheric Research, a consortium of 66 universities offering Ph.D.s in atmospheric and related sciences. The AMS is the nation's leading professional society for scientists in the atmospheric, oceanic, hydrologic and related sciences.

[Contact: Anatta]

01-Aug-2001