March goes out like a lion

NATURAL PERSPECTIVES

March is supposed to come in like a lion and go out like a lamb. It

sure didn’t this year. The winds that blew here on Friday, March 28th

put that old saw to rest.

By the time you read this, the Santa Ana winds of last week will

be but a memory and gentle April will have arrived. At least we hope

it will be gentle. But as we write our column, winds are howling,

dogs are barking and tree limbs are undoubtedly falling somewhere. We

don’t plan to venture outside to check.

With the wind blowing branches onto power lines, we’re likely to

lose electricity. That always makes writing exciting, never knowing

when the computer will go down and we’ll lose our work. But we’re not

complaining. At least we’re not weathering a sandstorm in Iraq while

hunkered down beside an Abrams tank, wondering if someone will shoot

at us.

The howling wind and whipping trees suggested to us that it was a

good time to write about Santa Ana winds. Normally, the breeze that

softly blesses us every afternoon is a cool, relatively moist,

onshore breeze that wafts in from the ocean. It’s part of what gives

us our lovely Mediterranean climate. But occasionally, meteorological

conditions are such that the wind blows in the opposite direction. At

those times, usually between October and March, the wind comes toward

us from the northeast and we experience Santa Ana conditions.

Here’s how it happens. When a high pressure area sits over the

Great Basin on the other side of the Sierra Nevada Mountains, and a

low pressure area exists off the California coast, the wind reverses

direction and flows from the desert to the ocean. That hot, dry wind

comes rattling out of Santa Ana Canyon and blows desert dust all over

us.

The Santa Ana Canyon isn’t the only canyon through which these

winds blow. It’s merely the canyon for which the phenomenon was

named. When the Santa Ana winds blow, they blast through all of

Southern California’s canyons.

As these desert winds move toward us through mountain passes and

canyons, they are confined and constricted by the canyon walls. That

constriction causes the wind to pick up speed, a phenomenon called

the Bernoulli effect. The normal wind speed of a Santa Ana wind is 25

to 35 knots, with gusts up to 50 or 60 knots. A knot is defined as a

speed of 1.15 miles per hour. We don’t know why wind speed is often

given in knots instead of miles per hour. Why not measure them in

furlongs per fortnight?

A major Santa Ana wind on Jan. 6, 2003, was clocked in Fremont

Canyon at 94 mph. That’s a wind speed equivalent to a category 2

hurricane. That was one of our strongest recent windstorms. Here in

Huntington Beach, that January storm blew over trees in Central Park

and Shipley Nature Center. It also blew down a power line that

ignited some trees near the Chevron Bulk Tank Farm at Talbert Avenue

and Gothard Street. Quick work by the Fire Department kept the

gasoline tanks from igniting. We hope this storm doesn’t prove to be

as exciting.

When the Santa Ana wind blows, it sucks the moisture out of trees

and plants. As hot, dry wind passes rapidly over leaves, it increases

evaporation, which is called transpiration in plants. Often, plants

lose water faster than they can take it up through their roots.

Plants wilt and desiccate during Santa Anas. A good watering the next

day will usually revive ornamental landscaping and potted plants.

Native plants have adapted to Santa Ana winds and survive just fine

without additional watering. Native vegetation, however, does dry out

enough to become more susceptible to fire during high windstorms.

Santa Ana winds blow our smog out to Catalina, but they also stir

up enormous quantities of dust and pollen. People with allergies,

sinus problems and asthma really suffer during Santa Anas because of

the increased pollutants in the air. Hard to say which is worse on

our lungs, the smog that forms on a hot breezeless day or the dust

that is stirred up by Santa Anas. Basically, one type of respiratory

assault replaces another.

Satellite images taken during Santa Ana conditions show the dust

clouds quite clearly. Dust and sand travel down canyons and show up

on the satellite images as winding narrow stripes of tan that follow

the canyon curves. Then the dust fans out to sea, forming huge clouds

over the ocean. The mouth of the Santa Ana canyon is fairly broad as

it spreads out over Long Beach, Seal Beach, Huntington Beach and

Newport Beach, so the dust is distributed over a wide area. We

actually may be less impacted by dust here in Huntington Beach than

are people living in the canyons or at the mouths of more narrow

canyons, like Laguna Canyon. Still, those satellite pictures were

quite sobering and graphically illustrated the true extent of the

dust problem.

* VIC LEIPZIG and LOU MURRAY are environmentalists. They can be

reached at [email protected].