Researchers found surprising evidence of sea salt and frozenplankton in high, cold, cirrus clouds, the remnants of Hurricane Nora,over the U.S. plains states. Although the 1997 hurricane was a strongeastern Pacific storm, her high ice-crystal clouds extended many milesinland, carrying ocean phenomena deep into the U.S. heartland.
Kenneth Sassen of the University of Utah, Salt Lake City, andUniversity of Alaska Fairbanks; W. Patrick Arnott of the DesertResearch Institute (DRI) in Reno, Nev.; and David O. Starr of NASA'sGoddard Space Flight Center, Greenbelt, Md., co-authored a paper aboutHurricane Nora's far-reaching effects. The paper was published in theApril 1, 2003, issue of the American Meteorological Society's Journalof Atmospheric Sciences.
Scientists were surprised to find what appeared to be frozenplankton in some cirrus crystals collected by research aircraft overOklahoma, far from the Pacific Ocean. This was the first time examplesof microscopic marine life, like plankton, were seen as "nuclei" of icecrystals in the cirrus clouds of a hurricane.
Nora formed off the Panama coast, strengthened as it traveled up theBaja Peninsula, and the hurricane crossed into California in September1997. Over the western U.S., Nora deposited a stream of high cirrus,ice crystal, clouds that created spectacular optical effects, such asarcs and halos, above a broad region including Utah and Oklahoma. Thatstream of cirrus clouds enabled researchers to analyze growth of icecrystals from different nuclei.
Different nuclei, like sulfate particles, sea salt and desert dust,affect ice-crystal growth and shape. Torn from the sea surface bystrong hurricane winds, sea salt and other particles from evaporatedsea spray are carried to the cold upper troposphere in storm updrafts,where the drops freeze and become ice crystals. Plankton, a microscopicorganism, is also likely present in the sea spray and is similarlylofted to high levels.
"Understanding how ice crystals grow and what determines theirshapes is important in understanding how they interact with sunlightand infrared energy," Starr noted. "These interactions are importantprocesses in the global climate system. They are also critical tosensing cloud properties from space, where NASA uses measurements ofthe reflected solar radiation to infer cloud physical properties, suchas ice-crystal size," he said.
Data were gathered using ground-based remote sensors at the Facilityfor Atmospheric Remote Sensing in Salt Lake City and at the Clouds andRadiation Testbed in northern Oklahoma. A research aircraft collectedparticle samples over Oklahoma. Observations from the GeostationaryOperational Environmental Satellite 9 (West), launched by NASA andoperated by the National Oceanic and Atmospheric Administration, werealso used. DRI analyzed the ice crystals collected from Nora.
Scientists were using data generated through the U.S. Department ofEnergy (DOE) Atmospheric Radiation Measurement (ARM) Program. The ARMProgram's purpose is obtaining field measurements and developingcomputer models of the atmosphere. Researchers hope to betterunderstand the processes that control the transfer of solar and thermalinfrared energy in the atmosphere, especially in clouds, and at theEarth's surface.
The ARM energy measurements also double-check data from the ModerateImaging Spectroradiometer instrument aboard NASA's Terra and Aquasatellites. By ensuring the satellites are recording the same energyreflected and absorbed by clouds from Hurricane Nora as those providedby the ground data in this study, scientists hope to take fewer groundmeasurements in the future, and enable the satellites to provide thedata.
The DOE ARM program, National Science Foundation, and NASA's EarthScience Enterprise funded this research. The Earth Science Enterpriseis dedicated to understanding the Earth as an integrated system andapplying Earth System Science to improve prediction of climate, weatherand natural hazards, such as hurricanes, using the unique vantage pointof space.
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