QuikScat Finds Tempests Brewing in ‘Ordinary’ Storms

Feature June 25, 2009

QuikScat Finds Tempests Brewing in 'Ordinary' Storms

Satellite, Now Entering Its Second Decade, Has Revolutionized Marine Weather
Forecasts

"June is busting out all over," as the song says, and with it, U.S. residents along the Atlantic
and Gulf coasts begin to gaze warily toward the ocean, aware that the hurricane season is
revving up. In the decade since NASA's QuikScat satellite and its SeaWinds scatterometer
launched in June 1999, the satellite has measured the wind speed and wind direction of
these powerful storms, providing data that are increasingly used by the National Oceanic
and Atmospheric Administration's (NOAA) National Hurricane Center and other world
forecasting agencies. The data help scientists detect these storms, understand their wind
fields, estimate their intensity and track their movement.

But tropical cyclones aren't the only storms that generate hurricane-force winds. Among
others that do is a type of storm that dominates the weather in parts of the United States
and other non-tropical regions every fall, winter and into spring: extratropical cyclones.

Extratropical Cyclones: Meteorological 'Bombs'

Scientists have long known that extratropical cyclones (also known as mid-latitude or
baroclinic storms) sometimes produce hurricane-force winds. But before QuikScat,
hurricane-force extratropical cyclones were thought to be relatively rare. Thanks to
QuikScat, we now know that such storms occur much more frequently than previously
believed, and the satellite has given forecasters an effective tool for routinely and
consistently detecting and forecasting them.

These storms, which occur near busy trans-oceanic shipping lanes, pose a significant threat
to life and property for those on the high seas, generating high winds and waves up to 30
meters (100 feet) high. When they make landfall, in areas like Alaska, the Pacific Northwest,
New England and the U.S. mid-Atlantic coast, they produce strong winds, high surf, coastal
flooding, heavy rains, river flooding and even blizzard conditions.

Take the "Hanukkah Eve" extratropical cyclone of Dec. 14-15, 2006, for example. That
storm viciously raked the U.S. Pacific Northwest and British Columbia with torrential rainfall
and hurricane-force winds exceeding 87 knots (100 miles per hour) in spots. Dozens of
people were injured and 18 people lost their lives, while thousands of trees were downed,
power was knocked out for more than 1.5 million residents and structural damage topped
$350 million.

NOAA defines an extratropical cyclone as "a storm system that primarily gets its energy
from the horizontal temperature contrasts that exist in the atmosphere." These low pressure
systems have associated cold fronts, warm fronts and occluded fronts. Tropical cyclones, in
contrast, don't usually vary much in temperature at Earth's surface, and their winds are
generated by the energy released as clouds and rain form in warm, moist, tropical air. While
a tropical cyclone's strongest winds are near Earth's surface, the strongest winds in
extratropical cyclones are about 12 kilometers (8 miles) up, in the tropopause. Tropical
cyclones can become extratropical, and vice versa.

Extratropical cyclones occur in both the North Atlantic and North Pacific year-round. Those
with hurricane-force winds have been observed from September through May. Their
frequency typically begins to increase in October, peaks in December and January, and
tapers off sharply after March. They can range from less than 100 kilometers (62 miles) in
diameter to more than 4,000 kilometers (nearly 2,500 miles) across. They typically last
about five days, but their hurricane-force winds are usually short-lived--just 24 hours or less.
Because they can intensify rapidly, they're often referred to as meteorological "bombs."
Wind speeds in extratropical cyclones can vary from just 10 or 20 knots (12 to 23 miles per
hour) to hurricane-force (greater than 63 knots, or 74 miles per hour). During their
development, they can trek along at more than 30 knots (35 miles per hour), but they slow
down as they mature. At their seasonal peak, up to eight such storms of varying intensity
have been observed at once in both the North Atlantic and North Pacific.

Early work by scientists at NASA, NOAA and other organizations demonstrated the
effectiveness of using scatterometers for detecting these powerful and destructive winds.
Scatterometers work by sending radar signals to the ocean surface and measuring the
strength of the radar signals that bounce back. The higher the wind speed, the more the
ocean surface is disturbed, and the stronger the reflection that is bounced back to the
satellite.

Among those who pioneered these efforts at NASA was Senior Research Scientist Timothy
Liu of NASA's Jet Propulsion Laboratory, Pasadena, Calif., who used data from the NASA
Scatterometer, the predecessor to QuikScat, to study the transition of tropical cyclones into
extratropical storms in 1997. In addition, Robert Atlas of NASA's Goddard Space Flight
Center, Greenbelt, Md., demonstrated that scatterometer data were able to improve
predictions of extratropical storm strength and location.

Raising Forecaster Awareness

Joe Sienkiewicz, chief of the Ocean Applications Branch at NOAA's Ocean Prediction
Center, Camp Springs, Md., says QuikScat data have raised the awareness of forecasters
to the occurrence of hurricane-force intensity conditions in extratropical cyclones and have
significantly advanced their short-term wind warning and forecast processes.

"QuikScat winds have given forecasters at NOAA's Ocean Prediction Center a high level of
situational awareness over the data-sparse waters of the North Atlantic and North Pacific
Oceans," he said. "Ocean Prediction Center forecasters daily examine every QuikScat pass
and patch of wind and frequently base wind warning and forecast decisions solely on
QuikScat winds. Through confidence gained from QuikScat, the National Weather Service
began issuing warnings for dangerous hurricane-force winds in extratropical cyclones in
December 2000.

"From 10 years of QuikScat, we have learned that hurricane force winds in extratropical
cyclones occur more frequently than thought, are most frequent in winter months, and the
conditions are most often observed south of the cyclone center," he added.

Over the years, the number of storms observed with hurricane-force winds has steadily
increased due to forecasters gaining confidence using the data, and improvements to the
QuikScat data. From the fall of 2006 through 2008, NOAA's Ocean Prediction Center
identified and issued warnings for 115 separate extratropical cyclones (64 in the Atlantic
and 51 in the Pacific) that reached hurricane force.

As confirmed in a 2008 study, QuikScat substantially extends the ability of forecasters to
detect hurricane-force wind events in extratropical storms. For the studied case, QuikScat
was able to identify more than three-and-a-half times as many hurricane-force events as
combined data from the European ASCAT sensor on the METOP-A satellite, directly-
measured buoy and ship information, and model predictions.

Another study in 2002 found that incorporating QuikScat data increased the number of wind
warnings the Ocean Prediction Center issued for extratropical cyclones by 30 percent in the
North Atlantic and by 22 percent in the North Pacific. Between 2003 and 2006, the Ocean
Prediction Center's forecasters successfully predicted hurricane-force winds two days in
advance 58 percent of the time in the Atlantic and 44 percent in the Pacific. Considering that
a successful forecast of hurricane-force winds requires accurate prediction of the timing and
intensity of an explosive deepening cyclone, these numbers are impressive.

QuikScat data have been instrumental in the ability to forecast hurricane-force extratropical
cyclones several days in advance, while they are still well out over the ocean. Forecasters
can use the data to determine which numerical weather prediction models are handling a
storm the best, thereby improving the accuracy of forecasts and increasing warning lead
times. QuikScat data are available to forecasters within three hours of acquisition.

The availability of a consistent observing capability for extratropical cyclones from QuikScat
has allowed NOAA to add a third "hurricane-force" warning category for extratropical
cyclone winds, in addition to gale and storm, providing better warnings of a coming storm's
severity. The U.S. Coast Guard broadcasts these warnings by radiofax, and they are posted
online at: http://www.opc.ncep.noaa.gov .

A Boon to Shipping

These extratropical cyclone warnings have a great economic impact on the $200 billion
global marine shipping industry. A recent study estimates improvements to warning and
forecast services due to QuikScat save the container and bulk shipping industry $135
million a year by reducing their exposure to hurricane-force wind conditions in non-tropical
storms over the North Pacific and North Atlantic. Without QuikScat, the severity of many
extratropical cyclones would not be determined. The data are also vital to the fishing
industry, offshore energy industries, search and rescue organizations, and agencies that
track and manage marine hazards like oil spills.

Paul Chang, ocean winds science team lead at NOAA's National Environmental Satellite,
Data and Information Service/Center for Satellite Applications and Research, Camp
Springs, Md., said ocean vector wind measurements from QuikScat have become a basic
part of NOAA's day-to-day forecasting and warning processes.

"The 10 years of observations from the QuikScat mission have provided critical information
for the monitoring, modeling, forecasting and research of the atmosphere, oceans and
climate," he said.

For more information about QuickScat, visit http://winds.jpl.nasa.gov/.

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