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Treebeard's Stumper Answer
31 October 2003

Devil Winds

Halloween is fun. Chaparral wildfires driven by Santa Ana winds are scary. We've been spared this time, so far. Our local fires were controlled because the winds didn't happen, though this smoky fire weather is scary enough. Why don't we get these dangerous Santa Ana (or santana?) winds in Santa Barbara? We do have local sundowner winds, so what's the difference? Heat rises, but all these devil winds get hotter and dryer as they blow down the canyons. How does this work? The real stumper is how should we live in a natural landscape that is adapted to burn.

We got an inch of rain on Halloween day. A lot of people had to change their Halloween plans. The big fires are still out of control, and the weather will change again. But I feel much better about our wildfire situation at home.

This beautiful image of Southern California wildfires (red) and smoke plumes was captured on October 26, 2003 by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on the Terra satellite. The NASA Earth Observatory Natural Hazards site has links to more images of the fires this week. The MODIS Image Gallery has impressive hi-res images to download.

I added a few markers. I live in the mountains behind Santa Barbara (#1). Santa Ana winds blow from the high Mojave Desert (#2) on the edge of the Great Basin. That striking wedge on the western edge of the desert is formed by the San Andreas and Garlock earthquake faults. It's like an arrow pointing to the ocean, which is about how Santa Ana winds move. The top fires (#3) are the Piru and Simi Fires. The next arc of fires (#4) are the Grand Prix (west) and Old (east) Fires on both sides of Cajon Pass. It's interesting that there are no fires near San Gorgonio Pass (#5). The Paradise and Cedar Fires (#6) are covering San Diego with thick smoke.

This satellite image really shows the effects of Santa Ana winds blowing offshore from east-to-west across Southern California. You can also see that we missed the worse of it near Santa Barbara, though it was smoky enough. (Click or visit Treebeard's Photos for a larger image.) Our local winds stayed onshore, which brought the smoke around in an eddy.

Why don't we get Santa Ana winds in Santa Barbara? Heat rises, so why do these hot and dry down-slope winds exist at all? For bonus stumpers, where else in the world do these devil winds occur, and what are they called? What cultural links in books and movies and song can you find?

Smoky sunrise, fire weather.
(San Marcos Pass, 28 October 2003)


Santa Ana winds occur when high-pressure desert air blows toward the coast through passes like Cajon Pass and the Santa Clara River. The dry air is heated by compression, gaining up to 5.5 degrees per 1,000 foot drop as momentum carries it along. We are isolated from the desert by local mountains, but we get similar sundowner winds when valley air spills over our mountain passes to the coast. For many years, Goleta held the U.S. high temperature record of 133 degrees from a sundowner event on June 17, 1859. I'm so glad the rains came!

Notes:

It's remarkable how fast the weather can change everything. When I wrote this stumper, it was 95+ degrees and the air was full of smoke even here in the Santa Barbara mountains. Two days later it was cold and raining for Halloween. It's raining again today a week later. The wildfires are history and I'm relieved. (We're not officially out of fire season until we get two inches of rain. We're not quite there yet.)

Santa Ana winds blow from the desert, but that's not why they are so hot and dry. Usually the high-pressure desert air starts cool after a northern storm has passed over. The relatively cool desert air moves downslope through mountain passes and river valleys towards the coast. That's when things happen:

This is a classic example of an adiabatic heat process. It's a temperature shift due to pressure changes rather than any transfer of heat from outside. A bicycle pump is a good example that I used in my Pumping Up for a Ride (14 May 1999) stumper. Pump up your bike tire with a hand pump and feel the bottom of the pump. It will be hot. Now wait a moment and release the pump (and a puff of air) from the tire and quickly feel the valve stem on the tire. It will feel cool. The pump gets hot because you are compressing the air within. The tire valve feels cool because the escaping air is expanding. I have more examples in that stumper answer.

LA's Santa Ana winds happen because of local geography. There are a number of remarkable mountain passes through the mountains that separate the desert from the coast. The Santa Clara River (#3 on the map) has somehow cut a path completely through the coast ranges so that it drains the desert side of the San Gabriel Mountains. (Is this a geological remnant of a much larger river??) This brought wind to the Piru and Simi Fires. Tejon Pass and San Gorgonio Pass (#4 and #5) are narrow gaps many thousands of feet lower than the mountains on the side that brought wind to other fires. I don't know the San Diego backcountry, but I'm sure there are similar passes for the wind.

Santa Barbara county doesn't have this desert connection, so I don't think we get "real" Santa Ana winds. But we have our own local Santa Ana-like winds formed by our unique local geography. The Santa Ynez Valley runs east-west for 70 miles, but it is only about 10 miles from the ocean, separated by the steep 4,000 foot high Santa Ynez Mountains. (See my map.) The Santa Ynez Valley is usually much warmer than the coast in the summer. When conditions are right, the hot valley air rises to the level where it can spill over the mountain passes towards the coast. It then warms by adiabatic compression. This typically happens late in the day, hence the local name sundowner winds. This is strictly a local effect

I live on top of the mountains, where it's usually much warmer than the coast. But during a sundowner, the situation is reversed. The compressing air can heat to 100 degrees and more as it descends the mountain wall. For many years, Goleta (next to Santa Barbara on the coast) held the U.S. temperature record of 133 degrees from a sundowner heat burst event on June 17, 1859.

I found this event hard to believe when I first read about it in the book "California's Wonderful Corner" (1975) by local historian Walker A. Tompkins. He called the wind a simoon, an Arabic word, and the whole story seemed impossible. Then on June 27, 1990, it happened again. Sundowner winds brought the temperature in Goleta to 108 degrees and the arson-caused Painted Cave Fire took off and threatened the city of Santa Barbara itself. We were at the beach and couldn't get home. We spent the night with friends in town watching the fire on the hills and listening to exploding propane tanks. We did get home the next day, and stayed there. The winds returned to normal and turned the fire back into the mountains towards us. The weather and the Hot Shot fire crews and the bombers managed to keep the fire away from most mountain homes, including ours. That fire destroyed 500 homes, and killed a local resident. I think this was the first time I heard the phrase "sundowner wind". The fires this year are much worse.

There's an eerie feeling that comes with the devil winds. Only surfers look forward to the offshore winds. Raymond Chandler talks about it in his story "Red Wind" (another name for the winds):

"It was one of those hot dry Santa Anas that come down through the mountain passes and curl your hair and make your nerves jump and your skin itch... On nights like that, every booze party ends in a fight. Meek little wives feel the edge of the carving knife and study their husbands' necks. Anything can happen."

Is it truth or urban legend that LA crime rates go up during Santa Anas? Did serial killer Richard Rameriz, aka "The Night Stalker", go on a killing spree during hot, dry winds in 1984? Maybe it's "negative ions"? I don't know about murder and assault, but I know arson becomes a great concern. It's scary living in these summer-dry mountains when the devil winds are blowing, listening to the scanner radio and the cars going by on the distant highway, just waiting...

Yep, the real stumper is how should we live in a natural landscape that is adapted to burn like our California chaparral. These mountains should burn every few decades. But we put out the wildfires until the inevitable conflagration becomes disastrous and burns so hot that it kills the native vegitation that should survive, like the stump-sprouting Scrub Oak (Quercus berberidifolia) in the photo on the right after a small wildfire two years ago. Controlled burns are only part of the answer.

We have Smokey the Bear fire policies that postpone wildfires and make them worse, and insurance policies that pay us to rebuild in the same place so it can happen again. I'm sure the answer is that we shouldn't live here, at least not in the mountains like I do. It's an impossible situation in the long-term. Maybe insurance costs will make a real difference. But I don't plan to move. This is my home, and it's where I want to live. Now there's a stumper!

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Copyright © 2003 by Marc Kummel / mkummel@rain.org