Doyle’s team of 10 researchers works on testing and further refining the COAMPS-TC annually. Those refinements can take years to implement operationally; sometimes, they take just one hurricane season. The most-recent COAMPS-TC version to go into operations transitioned in May 2019.
“Each season, we come up with new ideas on how to improve it,” Doyle said. “Then we'll have to test it on many, many storms across multiple seasons to be able to get a statistical signal on whether it improves the system or not.”
How does COAMPS-TC work?
COAMPS-TC uses multiple nested grid meshes to follow tropical storms. Increasingly smaller grid cells on each mesh descend from the outermost mesh to the innermost. The innermost mesh uses a grid of cells, each measuring 4 square kilometers, to create high resolution representations of the hurricane, its inner core, and various aspects of its circulation.
“At each of these cells, 12 predictive equations are solved and information from the neighboring cells is shared frequently as the model runs,” Doyle said. “The outer mesh doesn't cover the whole globe. It covers only part of the globe, and usually it's an entire basin — for example the Western Pacific, along with other basins such as the Atlantic, Eastern and Central Pacific, and Indian Ocean.
“We have several different areas around the world for COAMPS-TC, where it has a basin-scale outer grid mesh. And then within that outer mesh, the two nested grids that follow the storm operate.”
And where does all the data for all those cells come from? Though the researchers are in the habit of referring to COAMPS-TC in the singular, today there are two versions of COAMPS-TC, each a limited area system coupled with a different global model that provides the large-scale conditions for its initial state. The data come from those two global models.
One version of COAMPS-TC begins with data from the Navy Global Environmental Modeling system. The other version of COAMPS-TC makes use of data from the National Oceanic and Atmospheric Administration’s Global Forecast System. Essentially, these global systems drive the limited area systems. The arrangement is called one-way coupling.
NAVGEM and GFS are both sophisticated numeric weather prediction models that employ data assimilation systems taking in observational data from every conceivable source. These include weather balloons, surface stations, aircraft, ships, and satellites that make up most of the observing system. The number of observations per day used in these systems are in the millions.
“The number of satellites is finite, and it's smaller than the number of observations,” Doyle said. “But, of course, you can have one satellite sensor with hundreds of channels – these are hyperspectral satellites.
“The global models provide the initial state that COAMPS-TC is using, and we specify the hurricane vortex itself using the information directly from the forecasters about the intensity, position, and size. We insert the vortex based on that information into the COAMPS-TC initial model fields.”
Generally, the operational versions of COAMPS-TC run on a supercomputer at The Fleet Numerical Meteorology and Oceanography Center in Monterey, while NRL Monterey runs test versions at the Department of Defense Supercomputer Resource Center at Stennis Space Center in Mississippi.