Researchers found surprising evidence of sea salt and
frozen plankton in high, cold, cirrus clouds, the remnants
of Hurricane Nora, over the U.S. plains states. Although the
1997 hurricane was a strong eastern Pacific storm, her high
ice-crystal clouds extended many miles inland, carrying
ocean phenomena deep into the U.S. heartland.

Kenneth Sassen of the University of Utah, Salt Lake City,
and University of Alaska Fairbanks; W. Patrick Arnott of the
Desert Research Institute (DRI) in Reno, Nev.; and David O.
Starr of NASA’s Goddard Space Flight Center, Greenbelt, Md.,
co-authored a paper about Hurricane Nora’s far-reaching
effects. The paper was published in the April 1, 2003, issue
of the American Meteorological Society’s Journal of
Atmospheric Sciences.

Scientists were surprised to find what appeared to be frozen
plankton in some cirrus crystals collected by research
aircraft over Oklahoma, far from the Pacific Ocean. This was
the first time examples of microscopic marine life, like
plankton, were seen as “nuclei” of ice crystals in the
cirrus clouds of a hurricane.

Nora formed off the Panama coast, strengthened as it
traveled up the Baja Peninsula, and the hurricane crossed
into California in September 1997. Over the western U.S.,
Nora deposited a stream of high cirrus, ice crystal, clouds
that created spectacular optical effects, such as arcs and
halos, above a broad region including Utah and Oklahoma.
That stream of cirrus clouds enabled researchers to analyze
growth of ice crystals from different nuclei.

Different nuclei, like sulfate particles, sea salt and
desert dust, affect ice-crystal growth and shape. Torn from
the sea surface by strong hurricane winds, sea salt and
other particles from evaporated sea spray are carried to the
cold upper troposphere in storm updrafts,
where the drops freeze and become ice crystals. Plankton, a
microscopic organism, is also likely present in the sea
spray and is similarly lofted to high levels.

“Understanding how ice crystals grow and what determines
their shapes is important in understanding how they interact
with sunlight and infrared energy,” Starr noted. “These
interactions are important processes in the global climate
system. They are also critical to sensing cloud properties
from space, where NASA uses measurements of the reflected
solar radiation to infer cloud physical properties, such as
ice-crystal size,” he said.

Data were gathered using ground-based remote sensors at the
Facility for Atmospheric Remote Sensing in Salt Lake City
and at the Clouds and Radiation Testbed in northern
Oklahoma. A research aircraft collected particle samples
over Oklahoma. Observations from the Geostationary
Operational Environmental Satellite 9 (West), launched by
NASA and operated by the National Oceanic and Atmospheric
Administration, were also used. DRI analyzed the ice
crystals collected from Nora.

Scientists were using data generated through the U.S.
Department of Energy (DOE) Atmospheric Radiation Measurement
(ARM) Program. The ARM Program’s purpose is obtaining field
measurements and developing computer models of the
atmosphere. Researchers hope to better understand the
processes that control the transfer of solar and thermal
infrared energy in the atmosphere, especially in clouds, and
at the Earth’s surface.

The ARM energy measurements also double-check data from the
Moderate Imaging Spectroradiometer instrument aboard NASA’s
Terra and Aqua satellites. By ensuring the satellites are
recording the same energy reflected and absorbed by clouds
from Hurricane Nora as those provided by the ground data in
this study, scientists hope to take fewer ground
measurements in the future, and enable the satellites to
provide the data.

The DOE ARM program, National Science Foundation, and NASA’s
Earth Science Enterprise funded this research. The Earth
Science Enterprise is dedicated to understanding the Earth
as an integrated system and applying Earth System Science to
improve prediction of climate, weather and natural hazards,
such as hurricanes, using the unique vantage point of space.

For more information and images on the Internet, visit:
http://www.gsfc.nasa.gov/topstory/2003/0408plankton.html

For information about the various agencies and programs
mentioned above on the Internet, visit:

U.S. Department of Energy: Atmospheric Radiation Measurement
Program
http://www.arm.gov/

National Hurricane Center: Hurricane Nora Report
http://www.nhc.noaa.gov/1997nora.html

NASA’s GOES Satellite Data:
http://rsd.gsfc.nasa.gov/goes/