California's III Wind

Since mid-September, the hot, arid "Santa Ana winds" had whistled westward through the mountain passes half a dozen times, raising Los Angeles temperatures to unseasonable levels, unnerving residents, roasting the hillside shrubs and trees until they were tinder dry. As the winds rose once again last week, the stage was set for disaster.

High atop a mountain, a gust toppled a transmission tower; a crackling power line dropped into the brush and started a fire. Winds up to 50 m.p.h. quickly whipped blazes into conflagrations that ruined 2,100 acres of the Angeles National Forest, killed 14 fire fighters and severely burned twelve others. Even those not directly threatened by the flames felt the wrath of the Santa Ana. Temperatures in downtown Los Angeles rose to a stifling 100DEG; extremely low humidity dried the throats, chapped the lips, and helped bring an unaccustomed irritability to untold millions of Southern Californians.

Santa Anas are not strangers to the Los Angeles area. They visit it on an average of 15 times a year, mostly in the fall and winter. They were described in detail by Richard Henry Dana as early as 1836 in Two Years Before the Mast, and through the years they have been responsible for scores of disastrous fires that have caused millions of dollars' property damage and destroyed hundreds of homes.

Collapsing Dome. Southern California's ill winds have their genesis over the Great Basin, a vast plateau that includes the Mojave Desert and is bounded by the Rocky Mountains on the east and the Sierra Nevada to the west. For reasons still not fully understood by meteorologists, dry winds from the north and northwest are occasionally trapped over the basin and form into a stationary dome of high-pressure air. Two or three days later, when the enormous dome collapses, its great mass of air begins moving toward nearby low-pressure areas. Blocked by the towering walls of the Rockies and the Sierra, the warm, dry air heads southwestward toward the group of lower mountain ranges that stand between it and a low-pressure trough hovering over Southern California.

Most of the desert air is pushed through the mountain passes (one of which, the Santa Ana canyon, gave the wind its name), where it picks up speed before roaring out into the Los Angeles basin at velocities as high as 100 m.p.h. The remainder flows over the mountains and down the western slopes. Descending toward low-lying coastal areas, the air is compressed and heated--five degrees for every 1,000 ft. of descent. As a result, the Santa Anas often bring 100DEG temperatures with them--though temperatures in the Great Basin where they started may have been only in the 70s or 80s at the time. During its precipitate plunge toward the coast, the Santa Ana loses much of its remaining moisture, sometimes bringing Los Angeles humidity readings down to as low as 1%.

Irrational Behavior. Santa Ana-like phenomena are not confined to Southern California. Similar hot, dry wind sweeping down mountain slopes is called "foehn" (pronounced, approximately, fain) in Austria and Germany, "chinook" along the U.S. and Canadian Rockies, "sky sweeper" on Majorca, "khamsin" in Israel, and "the Canterbury northwester" in New Zealand.

Wherever they blow, the winds stir strange human actions. In Munich, as in Los Angeles, most residents are convinced that the foehn causes general lassitude, irrational behavior, suicides and an increase in crime. Israelis swear that headaches, asthma, high blood pressure, mental aberrations and other assorted ills are accentuated during the khamsin. In Sicily and some Arab nations, courts have considered the hot, dry winds as mitigating circumstances for those accused of crimes committed while they blow.

The fearsome winds can also have beneficial results. In Canada, chinooks sometimes produce refreshing, springlike thaws in the midst of long, sub-zero winters. They often melt enough snow to allow deer and cattle to forage for food on the uncovered ground. In Los Angeles last week, as the smog was temporarily displaced by dry, clear air, residents out for an evening walk could look up to see an unfamiliar and refreshing sight: the stars.

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