A Heated 3-D Look Into Erin’s Eye

Hurricane Erin raced across the North Atlantic and along the eastern seaboard in September 2001. She was used as an experiment for a study to improve hurricane tracking and intensity predictions, allowing meteorologists to provide more accurate and timely warnings to the public. Studies show that temperatures measured at an extremely high altitude collected from a hurricane’s center or eye can provide improved understanding of how hurricanes change intensity.

Hurricane Erin was analyzed during the fourth Convection And Moisture EXperiment (CAMEX-4), which took place from August 16 through September 24, 2001. The mission originated from the Naval Air Station in Jacksonville, Fla. The mission united researchers from 10 universities, five NASA centers and the National Oceanic and Atmospheric Administration. CAMEX-4 is a series of field research investigations to study tropical cyclones — storms commonly known as hurricanes.

Twenty instrumented packages, called dropsondes, were dropped into Erin’s eye by two NASA research aircraft (the ER-2 and DC-8). The special packages included instruments that mapped temperature patterns.

For the first time, researchers were able to reconstruct the structure of the eye in three dimensions from as high as 70,000 feet, down to the ocean surface, in great detail. The dropsondes showed Erin’s warm core decreasing while it was rapidly weakening, making the storm more vulnerable to wind shear, a change in horizontal winds, which led to the storm falling apart.

Hurricane Erin’s rainfall pattern adjusted quickly to surprisingly small changes in wind speed patterns in the surrounding atmosphere. Weak horizontal winds rearrange rain and wind structure, which create uneven weather conditions around the hurricane’s core.

Observations from the study show the relationship between warm air from the eye of the storm is linked to reduction in sea surface pressure, which is the basic process that drives the hurricane’s destructive winds.

Although little is known about the birth of a hurricane and what causes it to strengthen or weaken, scientists have made substantial steps toward improving predictions of where a hurricane will move or make landfall. The ability to forecast intensity change, however, has always been a challenge for meteorologists.

The research done on Hurricane Erin was important because it could help forecasters understand factors that control rain intensity and distribution for hurricanes landing along the Eastern Seaboard.

Freshwater flooding is the number one killer from hurricanes in the Western Hemisphere and the study of a hurricane’s rainfall pattern could better prepare us for the next big storm.

This research paper, titled “Warm Core Structure of Hurricane Erin Diagnosed from High Altitude Dropsondes During CAMEX-4” by J. Halverson et al., is going to be published in an upcoming issue of the American Meteorological Society’s Journal of Atmospheric Science, CAMEX Special Issue, at the end of 2005.