The Santa Ana Winds
Ryan Kittell
AS 240A
2004
Well Known
Fire wind oh desert wind
She was born in a desert breeze
And wind her way
Through canyon way
From the desert to the silvery sea
- The Beach Boys
What Are They
•
•
•
•
North to Easterly Wind
Warm and Dry Wind on Leeside of Local Mtns
Originates from the Great Basin
Impacts:
–
–
–
–
Wind damage below passes and canyons
Favorable wildfire environment
Aircraft hazards
Beach busy-ness
Wildfires
Where Did the Name Come
From?
• Named
after
Mexican
presidentTerry
and E. Stephenson
Reporter
and
casual historian
general
Antonio
Anna
researched
the Lopez
originde
of Santa
the name
in 1943. He
concluded
that
settlers
• First
to occur
onearly
SaintSpanish
Anne’s Day
- Julyliving near
th Santa Ana Canyon named the wind after the
the
26
canyon.from the Spanish word Satana
• Derived
• Derived from the Native American word
Santana – “Big Bad Wind”
• Named by early Orange County settlers
Climatology
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
-0.4
-0.6
-0.8
Santa Ana winds impact the long term
climatology.
Nov
Dec
Climatology
Strong events impact more than
just the local environment.
Climatology
• Have occurred between September – June
– Most occur between October – February
•
•
•
•
Last 1 ½ days on average
Average winds 35kts, Gust 50kts canyon winds
~20 events per year
Gusts over 100kts possible
– Mt Wilson, early 1900’s, Cat 2 Hurricane Strength
Climatology
Climatology work by
Raphael, 2003
Peak in November and
December
Take a Ride…
Typical MSLP
pattern 
• High pressure in
eastern deserts
and Great Basin
– From passing
upper-level
troughs.
H
L
L
Take a Ride…
H
L
Flow tries to maintain geostrophic/cyclostrophic balance
… but complex terrain causes air to flow across isobars
Take a Ride…
4 major entry points into coastal plain
Why So Hot and Dry?
• Great Basin: elevation 4000- 6000 feet
– Tonopah: 5426 ft.
• Air compresses along the way.
– Warming ~ 5.4oF per 1000ft
– ~30oF warming potential
– Beaches often warmest
• Relative Humidity ~ inverse temperature
Why So Windy?
• Strongest winds often seen below passes and
canyons.
– Conservation of Mass & The Bernoulli Effect
– Area decreases  velocity increases
Why So Windy?
• During strong Santa Ana events, intense winds
felt throughout the leeside of the Southern
California mountains
– Strong event  large airmass
– Flow spills over mountains
– Downslope wind amplification
• Often surface winds are stronger than aloft
• Energy source needed to accelerate wind
Three Theories
1. Hydraulic Jump Theory
- Long, 1954; Durran, 1986
2. Gravity Wave Reflection
- Klemp and Lilly, 1975
3. Breaking Wave Trapping
- Clark and Peltier, 1977; Durran and Klemp, 1987
Hydraulic Jump
Fr = U / (gH)1/2
Supercritical
Fr > 1
Subcritical
Fr < 1
Hydraulic Jump
Fluid Transition
What Panu said…
Gravity Wave Reflection
Vertically propagating GWs
formed by downslope flow
…regions of strong stability
(Scorer Number) gradients
reflect them back toward the
surface
…mountain wave amplification
by superposition.
Breaking Waves
Vertically propagating GWs
formed by downslope flow
…critical layers formed by
intense GWs that break
…critical layer regions trap and
reflect them back toward the
surface
Forecasting
• All 3 models rely on
the presence of an
inversion layer or
strong static stability.
• Strong events that
lead to downsloping
winds usually has
strong winds aloft.
…often called “upper level support”
Warnings…
Constantly improving observational network
…in strategic locations.
Merry Christmas