Wednesday, September 1, 2010

NASA Images Dissect Hurricane Earl

AIRS image of Hurricane Earl
AIRS infrared image of Hurricane Earl on Sept. 1, 2010, shows the temperature of Earl's cloud tops or the surface of Earth in cloud-free regions. The coldest cloud-top temperatures appear in purple, indicating towering cold clouds and heavy precipitation. › Larger image | › See related images
With the peak of the 2010 Atlantic hurricane season still 10 days away, the relative calm of the first half of the season has quickly evaporated. As of Sept. 1, there were three named tropical cyclones in the Atlantic-Hurricane Earl and Tropical Storms Fiona and Gaston.

NASA satellites, instruments and researchers are hard at work, providing the National Oceanic and Atmospheric Administration and other agencies with many kinds of data used to help forecast and track these monster storms.

The NASA imagery presented here depicts Hurricane Earl, currently a Category Four hurricane on the Saffir-Simpson scale with maximum sustained winds of 115 knots (near 135 miles per hour), with higher gusts. As of 5 p.m. EDT on Sept. 1, Earl was located about 1,010 kilometers (630 miles) south-southeast of Cape Hatteras, N.C., moving to the northwest at 28 kilometers per hour (17 mph). Hurricane and tropical storm warnings and watches currently extend up the U.S. East Coast from North Carolina to Massachusetts. Hurricane force winds extend outward up to 150 kilometers (90 miles) from Earl's center, with tropical storm-force winds extending outward up to 325 kilometers (200 miles).

Earl is expected to continue to move northwest, and then make a gradual turn to the north on Thursday, Sept. 2. The core of Earl is expected to approach the North Carolina coast by late Thursday with hurricane-force winds. Tropical-storm-force winds are likely to reach the East Coast from Virginia northward to New Jersey by early Friday, Sept. 3. Earl is expected to fluctuate in intensity through Thursday, then gradually weaken.

Earl's storm surge will raise water levels by 1 to 1.5 meters (3 to 5 feet) above ground level within the hurricane watch level. Elsewhere, the storm surge will raise water levels by as much as 0.3 to 1 meter (1 to 3 feet) above ground level within the tropical storm warning area. The storm surge will be accompanied by large and destructive waves.

Rainfall accumulations of 5 to 10 centimeters (2 to 4 inches), with isolated amounts up to 15 centimeters (6 inches) are expected over parts of eastern North Carolina. Large surf swells will continue to affect the Bahamas and U.S. East Coast through Friday, bringing dangerous surf conditions and rip currents.

NASA imagery of Earl from various satellites and aircraft reveal many kinds of information about this impressive storm. Click here to view all related multimedia.

In Figure 1, the Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite, built and managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., captured this infrared image of Earl on Sept. 1 at 1:53 p.m. EDT. The AIRS data create an accurate 3-D map of atmospheric temperature, water vapor and clouds, data that are useful to hurricane forecasters. The image shows the temperature of Earl's cloud tops or the surface of Earth in cloud-free regions. The coldest cloud-top temperatures appear in purple, indicating towering cold clouds and heavy precipitation. The infrared signal of AIRS does not penetrate through clouds. Where there are no clouds, AIRS reads the infrared signal from the surface of the ocean waters, revealing warmer temperatures in orange and red.

The view of the storm for AIRS' visible-light camera is seen in Figure 2.

Figure 3 is an animation created from data from NASA's CloudSat spacecraft, which flew over Hurricane Earl on Aug. 31, 2010, at 2:20 a.m. EDT, when the storm had maximum wind speeds of 115 kilometers (approximately 135 mph). At that time, there were three named storms in the Atlantic: Danielle, Earl and Fiona.

The animation begins by depicting global cloud motion for the 72 hours prior to CloudSat's observation of Earl, from NOAA's GOES satellites. It then zooms in to reveal the vertical cross-section of Earl from CloudSat. CloudSat intersected Earl's eastern edge as the hurricane was just beginning an eyewall replacement cycle, during which the outer eyewall band strengthened, while the inner eyewall began to shrink. CloudSat captured Earl's intense cumulonimbus clouds and eye, along with cloud-free regions known as "moats" that contain a thick cirrus cloud canopy between the storm's spiral rain bands. The storm's most intense convection and precipitation are depicted in shades of oranges and reds.

Figure 4 is from the Multi-angle Imaging SpectroRadiometer (MISR) instrument on NASA's Terra spacecraft, captured at 11 a.m. EDT on Aug. 30, 2010, when Earl was a Category 3 storm on the Saffir-Simpson scale. The image (left panel) extends approximately 1,110 kilometers (690 miles) in the north-south direction and 380 kilometers (236 miles) in the east-west direction. The hurricane's eye is just visible on the right edge of the MISR image swath.

Winds at various altitudes were obtained by processing the data from five of MISR's nine cameras to produce the display shown on the right. The lengths of the arrows indicate the wind speeds, and their orientation shows wind direction. The altitude of a given wind vector is shown in color. Low clouds, less than 4 kilometers (2.5 miles) in altitude (shown in purple), follow the cyclonic (counter-clockwise) flow of air into the hurricane. This warm, moist air is the power source for the hurricane. Mid- and high-level clouds (green and yellow-orange, respectively) move in an anti-cyclonic (clockwise) direction as they flow out from the top of the storm. The very highest clouds, with altitudes around 17 kilometers (10.6 miles), are flowing directly away from the eye of the hurricane.

Figure 5 and Figure 6 were generated with data from NASA's Jason-1 and Ocean Surface Topography Mission (OSTM)/Jason-2 satellites. They depict Earl's wind speeds (top) and wave heights (bottom), respectively. The images were created by compositing three days of data from the two satellites' radar altimeters from Aug. 29 to Sept. 1.

NASA and JPL scientists are currently engaged in the agency's first major U.S.-based hurricane field campaign in nearly a decade. The Genesis and Rapid Intensification Processes mission, or GRIP, is studying hurricanes in the Atlantic and Gulf of Mexico. Three NASA aircraft carrying 15 instruments are being used, including the JPL-developed High-Altitude Monolithic Microwave Integrated Circuit Sounding Radiometer (HAMSR), which is flying aboard NASA's Global Hawk uninhabited aerial vehicle. The instrument infers the 3-D distribution of temperature, water vapor and cloud liquid water in the atmosphere. A second JPL instrument, the Airborne Precipitation Radar (APR-2), is a dual-frequency weather radar that is taking 3-D images of precipitation aboard NASA's DC-8 aircraft. Three NASA satellites are also playing a key role in supplying data about tropical cyclones during the mission, including the JPL- developed and managed CloudSat spacecraft and the Aqua spacecraft, which includes JPL's Atmospheric Infrared Sounder.

The DC-8, with JPL's APR-2 instrument, has already flown over Earl twice, with additional sorties planned for Sept. 1 and 2. NASA's Global Hawk is currently en route to Earl and is expected to fly over Earl for 10 to 12 hours on Sept. 2. The progress of NASA's GRIP aircraft can be followed in near-real-time when they are flying by visiting: "Click to start RTMM Classic" will download a KML file that displays in Google Earth.

Near-real-time images from HAMSR and APR-2 will be displayed on NASA's TC-IDEAS website, available at The website is a near-real-time tropical cyclone data resource developed by JPL to support the GRIP campaign. In collaboration with other institutions, it integrates data from satellites, models and direct measurements, from many sources, to help researchers quickly locate information about current and recent oceanic and atmospheric conditions. The composite images and data are updated every hour and are displayed using a Google Earth plug-in.

With a few mouse clicks, users can manipulate data and overlay multiple data sets to provide insights on storms that aren't possible by looking at single data sets alone. The data can be animated and downloaded on demand. TC-IDEAS is a component of JPL's Tropical Cyclone Information System (TCIS) website, located at: Researchers can use the TCIS to better understand hurricane processes, improve hurricane models and plan future satellite missions.

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    Semper Fi