March 11, 2004
Southern California's legendary Santa Ana winds wreak havoc every year, creating hot, dry conditions and fire hazards. Despite their often-destructive nature, a study of the "Devil Winds," conducted using data from NASA's Quick Scatterometer (Quikscat) spacecraft and its SeaWinds instrument shows the winds have some positive benefits.
"These strong winds, which blow from the land out into the ocean, cause cold water to rise from the bottom of the ocean to the top, bringing with it many nutrients that ultimately benefit local fisheries," said Dr. Timothy Liu, a senior research scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif., and Quikscat project scientist. Santa Ana consequences include vortices of cold water and high concentrations of chlorophyll 400 to 1,000 kilometers (248 to 621 miles) offshore.
Liu and Dr. Hua Hu of the California Institute of Technology, Pasadena, in a paper published last year in Geophysical Research Letters, revealed satellite observations of the Santa Ana effects on the ocean during three windy days in February 2003. According to the findings, Quikscat was able to identify the fine features of the coastal Santa Ana wind jets. It identified location, strength and extent, which other weather prediction products lack the resolution to consistently show, and moored ocean buoys lack sufficient coverage to fully represent.
Quikscat's high-resolution images of air-sea interaction were used to measure wind forces on the ocean. Other satellites and instruments, like the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the Advanced Very High Resolution Radiometer, onboard a National Oceanic and Atmospheric Administration polar orbiting weather satellite, were used to measure the temperature and biological production of the ocean surface, which respond to the wind.
The latter instrument showed sea surface temperatures dropped four degrees Celsius (seven degrees Fahrenheit) during the February 2003 Santa Anas. That was a sign that upwelling had occurred, meaning, deep cold water moved up to the ocean surface bringing nutrients. Images from SeaWiFS confirmed the increased biological productivity by measuring chlorophyll concentrations in the surface water. It went from negligible, in the absence of winds, to very active biological activity (more than 1.5 milligrams per cubic meter) in the presence of the winds.
"There really is no other system that can monitor Santa Ana winds over the entire oceanic region," Liu said. "Scatterometers such as Quikscat have a large enough field of view and high enough resolution to easily identify the details of coastal winds, which can affect the transportation, ecology and economy of Southern California." Red and yellow areas in this Sea-viewing Wide Field-of-view Sensor image show high levels of chlorophyll off the California coast during Santa Ana winds.
High pressure develops inland when cold air is trapped over the mountains, driving the dry, hot and dusty Santa Anas (also called Santanas and Devil's Breath) at high speeds toward the coast. The winds, occurring in fall, winter and spring, can reach 113 kilometers (70 miles) per hour. They happen at any time of day and usually reach peak strength in December. Telltale signs on the coast include good visibility inland, unusually low humidity and an approaching dark brown dust cloud.
The Quikscat satellite, launched in June 1999, operates in a Sun- synchronous, 800-kilometer (497-mile) near-polar orbit. It circles Earth every 100 minutes and takes approximately 400,000 daily measurements over 93 percent of the planet's surface. It passes over Southern California about twice a day, skipping a day every three or four days.
Quikscat is part of an integrated Earth observation system managed by NASA's Office of Earth Science. The NASA 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 using the unique vantage point of space.
For information about NASA programs on the Internet, visit:
For information about Quikscat and SeaWinds on the Internet, visit:
JPL is managed for NASA by the California Institute of Technology in Pasadena.
Alan Buis (818) 354-0474
Jet Propulsion Laboratory, Pasadena, Calif.