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Icing A Hurricane
Mon Jan 26, 2004
Listen in RealAudio 
Clouds of microscopic life forms float in from the Pacific, riding high in the remnants of a
hurricane to Oklahoma and beyond. Sounds like the promo for a new horror film; but it's what
researchers have found in high-altitude cirrus clouds. Hi, I'm Bryan Yeaton for The Weather
Notebook.
Over water, hurricane winds rip the tops off ocean waves and fill the air with sea spray. Any
material in that water such as salt or plankton can be caught in the cyclone and pushed by
fierce updrafts high into the troposphere, where the particles freeze and help form ice
crystals.
After Hurricane Nora formed off western Panama in September 1997, it moved north across the
Baja Peninsula and diminished to a tropical storm at the mouth of the Colorado River. Nora's
remnants then crossed southeastern California heading northeast, its large shield of icy
cirrus clouds extending into Utah and Oklahoma.
A NASA-sponsored research team collected ice crystals from Nora's cirrus shield to see exactly
what materials helped the water freeze in the clouds, which is important knowledge for
understanding global climate. Usually, sea salts, sulfate particles, and desert dust act as
freezing nuclei.
But when Kenneth Sassen, Patrick Arnott, and David Starr analyzed those samples, they were
surprised to find frozen plankton acting as nuclei in a fraction of the cirrus crystals. Never
before had microscopic marine plant life like plankton been found seeding ice crystals high in
a hurricane's cloud shield.
Plankton and other microscopic organisms are also present in the sea spray and are thus also
lofted to high levels. Ultimately, ice crystals evaporate, and the plankton settle out of the
air to the surface below.
Thanks to our contributing writer, meteorologist Keith Heidorn. Our show is supported by The
National Science Foundation and Subaru - Driven By What's Inside.
Today's Links
http://www.spaceref.com/news/viewpr.html?pid=11366
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