Recipe for a Hurricane
9.09.03
Between June 1st and November 30th and peaking between late August and mid-September, the
Atlantic Ocean becomes a meteorological mixing bowl, with all of the ingredients necessary to create
the recipe for hurricanes. And when it does, NASA has a cadre of
satellites ready to serve up a feast of information to the forecasters
who seek to monitor and better understand these awesome storms.
Right Image: Sea-viewing Wide-Field-of-view Sensor (SeaWiFS)
instrument on the Orbview-2 satellite captured this picture of Fabian
Sept. 4, 2003, near Bermuda but not too far from the United States'
East Coast. Click image to zoom into Hurricane Fabian Credit:
NASA/Orbimage.
NASA satellites are critical in helping forecasters determine if all of the ingredients are coming together
to make a hurricane, and if so, how strong the hurricane may be, and who in coastal communities and at
sea will be at risk. NASA satellites improve hurricane forecasts using space-based observations, data
assimilation, and computer climate modeling. NASA-sponsored measurements and modeling of global
sea surface temperature, precipitation, winds and sea surface height have also improved our
understanding of El Nino and La Nina events, which tend to enhance and suppress Atlantic and Gulf
hurricane development, respectively.
Thirty years ago, meteorologists were unable to see the factors in hurricane formation and could only
spot a hurricane with still pictures from the TIROS-N satellite. Over the past 10 years, visible and infrared
satellite sensors were still the workhorses for monitoring hurricanes. Now, multiple NASA satellites
exploit everything from radar pulses to microwaves to enhance forecasts, providing data to researchers
several times a day.
Take Warm Water, Stir
Sea surface temperatures must be 82 degrees Fahrenheit (F) or warmer for tropical cyclone formation
and sustenance. The Aqua satellite's Advanced Microwave Scanning Radiometer (AMSR-E) and the
Tropical Rainfall Measuring Mission (TRMM) Microwave Imager can detect sea surface temperatures
(SST) through clouds, which is valuable information in determining the direction a tropical cyclone is
moving and whether it may strengthen or weaken. Traditional satellite measurements of SST use
infrared instruments and are limited to cloud-free regions. The Jason-1 satellite altimeter provides data
on sea surface height, a key measurement of ocean energy available to encourage and sustain
hurricanes.
http://www.nasa.gov/vision/earth/environment/HURRICANE_RECIPE.html
Images to left: Orange and red indicate the necessary 82-degree and warmer sea surface temperatures
(SSTs) needed. The data for this image was collected by the Advanced Microwave Scanning RadiometerEOS (AMSR/E) aboard the Aqua satellite from May 2002. Click images to see animation
Next, add a disturbance, seen in right image, generally easterly waves off of Africa, formed from winds
resulting from the clash between the hot Sahara Desert and the cooler Gulf of Guinea. These waves
provide the initial energy and spin required for a hurricane to develop, as imaged by the Geostationary
Operational Environmental Satellite (GOES, operated by NOAA) on Sept. 1-15, 2001.
Mix Thoroughly, Bake
Another necessary ingredient is rotating winds over the ocean's surface. These winds are a precursor to
tropical cyclone development and the SeaWinds instruments aboard Japan's Midori 2 and NASA's
QuikSCAT satellites can detect these winds before other instruments, providing even earlier notice of
developing storms to forecasters and scientists.
Image to left: Wind speed/direction, from Seawinds instrument on QuikScat
satellite. Click image to see animation of winds mixing with sea surface
temperatures to form a hurricane. Credit: NASA
With the right mix of winds and SSTs, an ordinary cluster of tropical
thunderstorms can explode into a tropical storm. Winds converge, forming the familiar circular pattern
of clouds. Warm, rising air in the storms draws water vapor up from the ocean. The vapor condenses in
clouds and releases heat, warming the eye, evaporating more surface water and feeding the hurricane's
heat engine, continuing the cycle.
Hurricane Heat Engine
Air temperature and humidity are also important factors. The Atmospheric Infrared Sounder (AIRS)
experiment suite aboard the Aqua satellite obtains measurements of global temperature and humidity
throughout the atmosphere. Improved representation of atmospheric temperature and humidity may
lead to improved weather forecasts and improved determination of cyclone intensity, location and
tracks and the severe weather associated with storms, such as damaging winds.
http://www.nasa.gov/vision/earth/environment/HURRICANE_RECIPE.html
Hurricanes essentially act as engines, drawing energy up from warm tropical ocean waters to power the
intense winds, powerful thunderstorms, and immense ocean surges. Water vapor from the warm ocean
surface evaporates, forming towering convective clouds that surround the eyewall and rainband regions
of the storm. As the water vapor cools and condenses from a gas back to a liquid state it releases latent
heat. The released heat warms the surrounding air, making it lighter and promoting more clouds.
Because the hurricane-speed winds surrounding the clear eye are often absent from the center of a
hurricane, the heaviest rain clouds are pushed out to form a ring around the center, leaving a relatively
fair-weather eye.
Model Hurricane
Rainfall intensity is the final ingredient, and the TRMM Precipitation Radar provides "cat-scan"-like views
of rainfall in the massive thunderstorms of hurricanes. TRMM instruments probe young tropical systems
for rainfall intensity. These initial disturbances of thunderstorms could hint at tropical storm
development based on rainfall intensity. TRMM also sees "hot towers" or vertical columns of rapidly
rising air that indicate very strong thunderstorms. These towers are like powerful pistons that convert
energy from water vapor into a powerful wind and rain producing engine.
By synthesizing data from multiple instruments and satellites, scientists get a full picture of the many
ingredients of a hurricane. Once a storm develops, TRMM provides an inside view of how organized and
tightly spiraled rain-bands are, key indicators of storm intensity.
TRMM covers the global tropics and doesn't rely on a tropical disturbance being close to land to
determine its intensity from hurricane hunter flights through it. TRMM provides tropical cyclone
intensity information from the safe distance of space. For this reason the Hurricane Center and the
Department of Defense's Joint Typhoon Warning Center often rely on TRMM, QuikSCAT and other NASA
satellites for early assessment of young storms in the open ocean.
The hurricane monitoring capabilities enabled by these satellites are funded by NASA's Earth Science
Enterprise (ESE), whose mission is to protect and understand our home planet by enabling improved
prediction capability for climate, weather, and natural hazards
FUTURE OF FORECASTING
The Atmospheric Infrared Sounder (AIRS) aboard NASA's Aqua satellite furnishes three-dimensional
views of temperature, humidity and clouds in the atmosphere. AIRS observes the temperatures of cloud
tops via infrared energy, and, with the help of a pair of companion microwave-energy sensors, maps
temperature and humidity inside and below clouds. This shows scientists a storm's inner structure,
including its most intense regions. A high-resolution visible wavelength sensor adds information about
the clouds' fine structure. With AIRS, these observations come simultaneously from a single satellite,
while previously scientists coordinated observations taken hours apart from several satellites
http://www.nasa.gov/vision/earth/environment/HURRICANE_RECIPE.html