NASA - National Aeronautics and Space Administration

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.

Image to right: This is a GOES infrared image of Hurricane Erin at 1932 UTC. The numbers and plus (+) signs indicate where a NASA ER-2 aircraft dropped instruments (dropsondes) into the hurricane to measure temperature, pressure, winds, and more. The numbers and asterisks (*) indicate where NASA's DC-8 aircraft released the dropsondes. Click on image to enlarge. Credit: NASA

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.

Image to left: This 3D rendition of hurricane Erin shows elements of the hurricane engine inside the clouds (white): Rainfall (green), as revealed by TRMM, and warmth of the upper level eye (red), as revealed by the dropsondes released from the NASA ER-2 aircraft. Click on image to enlarge. Credit: NASA

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.

Image to right: Dropping a Sensor into Hurricane Erin: Dropsondes Away! - Described by a researcher as "Pringles cans with microprocessors and parachutes," scientists dropped sensors called 'dropsondes' into 2001's Hurricane Erin to gain temperature, pressure, moisture and wind readings throughout different locations in the hurricane. An ER-2 allows for up to 16 dropsondes deliveries, while the fully staffed DC-8 plane drops as many as 30 dropsondes within the hurricane. Click on image to view animation (no audio - 3MB). Credit: NASA Scientific Visualization Studio

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.

Image to left: Erin Heads North: On September 11, Hurricane Erin was making her way northward in the Atlantic Ocean. In this MODIS image, the storm stretches from the latitudes of Virginia in the south, past Massachusetts's boot-shaped Cape Cod, and on up to Maine. Coastal areas along the eastern seaboard have been affected by large swells produced by the storm. Click on image to enlarge. Credit: NASA/MODIS Rapid Response Team

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.

Related Links:

+ CAMEX-4

Camille Haley
Goddard Space Flight Center