Santa Ana Winds
January 22, 2003
On January 6, strong Santa Ana winds blew dust from the Great Basin, across southern California and all the way to the Pacific Ocean. This true-color image from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on the Aqua satellite shows streamers of dust blowing southwestward over the Los Angeles metropolitan area, roughly centered in the top half of the image. Santa Ana winds result when a high pressure system forms over the Great Basin region (between the Sierra Nevada Mountains and the Rocky Mountains). Clockwise winds around the "high" blow from east to west toward the Pacific Ocean. Having originated over arid basins, the air is of course very dry, and as it pours through mountain passes and canyons, it becomes warmer and even drier. To qualify as a Santa Ana wind event, winds must exceed 25 knots (28 miles per hour). The winds on January 6, exceeded 50 knots (56 miles per hour)! These Santa Ana winds occur most frequently in autumn and winter and pose significant fire hazards.