Download Diurnal Mountain Winds Introduction

Diurnal
Mountain
Winds
Cerro Fitz Roy
C. David Whiteman
University of Utah
Salt Lake City, Utah USA
[email protected]
Diurnal Mountain Winds
Introduction
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Mountain Meteorology
Atmos 6250
Mountain-Plain Wind System
Slope Wind System
Valley Wind System
Cross-Valley Winds
The Diurnal Cycle of Mountain Winds
Evening Transition
Morning Transition
Plateau Meteorology
Basin Meteorology
Glacier Winds
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© CD Whiteman
The Mountain Wind System
Introduction
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Four interacting wind systems are found over mountain terrain:
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Slope wind system (upslope and downslope winds)
Along-valley wind system (up-valley and down-valley winds)
Cross-valley wind system (from the cold to warm slope)
Mountain-plain wind system (plain-mtn and mtn-plain winds)
Because diurnal mountain winds are driven by horizontal
temperature differences, the regular evolution of the winds in a
given valley is closely tied to the thermal structure of the
atmospheric boundary layer within the valley, which is
characterized by a diurnal cycle of buildup and breakdown of a
temperature inversion.
Dolomite Mtns, Italy © CD Whiteman
Diurnal Mountain Winds
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Develop over complex terrain of all scales
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Produced by horizontal temperature differences (and
resulting horizontal pressure differences)
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Circulations are closed by return or compensatory
circulations aloft.
Characterized by a reversal of wind direction twice per day
Strongest with clear skies when winds aloft are weak
As a rule, upslope, up-valley and from plain to mtns during
daytime and in the opposite direction during nighttime.
Diurnal Mountain Winds
Diurnal Wind Systems
Diurnal Mountain Winds
Campfire smoke
Cayuse Valley, ID
You can observe an awful lot just
by watchin’.
- Lawrence (Yogi) Berra’.
Valley winds
Terminology
♦ valley wind = up-valley wind (day)
♦ mountain wind = down-valley wind (night)
♦ anabatic flow = up-slope wind (day)
Slope winds
♦ katabatic flow = down-slope wind (night)
♦ drainage flows = down-slope & down-valley
♦ cross-valley flow = toward heated hillside
♦ mountain-plain circulation
♦ anti-winds
Improper terminology is widespread in mountain meteorology literature
© C. Clements
The continuum concept
Forecasting and Applications
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general forecasting
fog forecasting
minimum temperatures
fire weather
air pollution
mountain aviation
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agriculture (vineyards, orchards,
crops)
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urban planning
Mountain-Plain
Wind System
wind energy
propagation of light, sound, RF
ecosystems
© Adam Naisbitt
The Southwest or Mexican Monsoon
Mean 850 mb pressure and wind patterns
adapted from Reiter & Tang (1984)
adapted from Stensrud et al. (1995)
Mean 850 mb pressure and wind patterns
Clouds are
indicators of
upslope flow
convergence at
ridgetops (and
mountain-plain
circulations)
adapted from Reiter & Tang (1984)
Bernhard Muehr photos, Karlsruher Wolkenatlas © 2000
Day
Diurnal mountain-plain wind system
from 915 MHz radar wind profiler data
Composite for days with
global rad ≥ 20 MJ d -1
6
2 m s-1
2 m s-1
5
Night
MB
MC
FB
A
LT
WC
A'
AZ
Elevation (km MSL)
4
PV
3
2
PV
• Circulation to 100 km N of Alps
• Q?: Is circulation closed?
1
WS
MC
FB
LT
00 UTC/18 CST
Daytime
Winds at 500 m AGL
00 UTC/18 CST
0
A
WC
E-W section along 40*N
A'
Whiteman & Bian (1998)
Lugauer & Winkler (2005)
Diurnal mountain-plain wind system
from 915 MHz radar wind profiler data, cont’d
6
2 m s-1
2 m s-1
5
A
A'
Elevation (km MSL)
4
3
1-4 m/s
2
PV
1
MC
FB
0
Nighttime
LT
WC
12 UTC/06 CST
A
A'
Whiteman & Bian (1998)
Late morning through
afternoon
Winkler et al. (2006)
Weissmann et al. (2006)
Contributors to mountain-plain
wind system research
Peter Winkler
Martin Weissmann
Matthias Lugauer
Slope Wind System
Stefan Henne
Roundtop Pk from Carson Pass, Sierra Nevada © Craig Clements
Upslope flows
Slope flows
During daytime, upslope flows occur on
mountainsides. The climber might notice them
only when they suddenly stop or weaken as a
cloud drifts in front of the sun.
Slope winds are gravity or buoyancy circulations following the dip of the underlying slope
and caused by differences in temperature between air heated or cooled over the
mountain slopes and air at the same altitude over the valley center. Quick response.
Affected by along-valley wind system, weather (SEB and radiation budget, ambient
flows), changing topography/surface cover, obstacles. --- Difficult to find in a pure form.
In winter, an upslope flow can occur over a
forest, even when the ground is snow-covered.
Downslope flows
Upslope flows
During nighttime, weak
downslope flows are
often most noticeable
when they start on
shaded slopes in the
late afternoon or early
evening. They can also
be visualized by smoke
drift (left).
Brush Creek Valley tracer plume.
Photos by Thorp and Orgill
Schumann (1990)
Downslope flows
Gruenloch Basin sidewall
2051 UTC 2 June 2002
Early in the evening when the atmosphere is near-neutral, downslope flows
are strong and they converge on the valley floor. As the ambient stability
(valley inversion) builds later in the evening, the downslope flows cannot
penetrate readily to the valley floor and converge at higher altitudes.
From R. Steinacker
Cold air outflows can
travel some distance
out over an adjacent
plain. Here tributary
flows run out into the
Rhine Valley. The
Rhine River flows
northward.
Salt Lake Valley, UT
Downslope
flow example
VTMX, 8 Oct 2000
• Jet profile max velocity
~ 15m AGL increases with
downslope distance,
reaching 7 m/s
• Temperature deficit
increases with downslope
distance, reaching 7 K
• Downslope flow layer
extends to ~150 m AGL
• Volume (mass) flux
increase with downslope
distance
Heldt and Höschele, 1989
Höschele, 1980
Whiteman & Zhong (2008)
40°N
Radiation Budget, Heat Budget &
Turbulence
Sun path
summer & winter
Northern
Hemisphere
Ahrens (1994)
Oke (1978)
Whiteman (2000); Whiteman and Allwine (1986)
METCRAX (Meteor Crater Exp) Instrumentation
Propagation of shadows and insolation patterns
Whiteman et al. (2008)
© John S. Shelton
Meteor Crater, Arizona
Whiteman & Kahler (2006)
see Ramona Hull thesis
Sensible heat flux, 21 Oct
Radiative transfer modeling within topography
SW diffuse
SW direct
1200 MST 21 Oct 2006
Hoch et al. (2008)
Shortwave diffuse (left) and direct (right) radiation as simulated with
MYSTIC 3D Monte Carlo model, 1200 MST 21 October 2006.
Hoch, S. W., C. D. Whiteman, and B. Mayer, 2011: A systematic study of longwave radiative heating and cooling
within valleys and basins using a three-dimensional radiative transfer model. J. Appl. Meteor. Climatol., 50,
2473-2489.
Mayer, B., S. W. Hoch, and C. D. Whiteman, 2010: Validating the MYSTIC three-dimensional radiative transfer
model with observations from the complex topography of Arizona's Meteor Crater. Atmos. Chem. Phys., 10,
8685-8696. doi:10.5194/acp-10-8685-2010.
Hoch, S. W., and C. D. Whiteman, 2010: Topographic effects on the surface radiation balance in and around
Arizona's Meteor Crater. J. Appl. Meteor. Climatol., 49, 1114-1128.
Sebastian Hoch
Open questions - slope flows
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Models developed and run with little comparison
to scarce data
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Numerical models often overemphasize speeds
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Valley Wind
System
Work needed:
- Interactions of thermal circulations
- Effects of ambient stability (“simple slopes”)
- No radiative flux divergence models
- Intermittency
Representativeness of observations on slopes
COMAP
Boulder, CO
Brush Creek Valley © CD Whiteman
Valley wind system
What causes the temperature range difference?
Valley winds are closed
circulations that attempt to
equalize horizontal pressure
gradients that are built up
hydrostatically between the
valley and plain caused by
the greater temperature
range of a column of air
within the valley compared to
a similar column of air over
the plain at the same
elevation.
1. Horizontal area over valley receives same insolation as
that over the plain. Insolation heats ground surface and
a portion is redistributed to the air above by radiation,
conduction, and convection. An equal amount of
energy is applied to a smaller mass of air within valley,
producing a larger temperature response in the smaller
volume (FLT). Similarly, at night loss of heat by
radiation is applied to the smaller volume (topographic
amplification factor, TAF; area-height relationship).
2. There is an efficient distribution of heat in the valley, where slopes are good heat
exchange surfaces. During day, heat is transferred efficiently to cross section by
sinking motions that compensate for upslope flows on sidewalls. During night,
downslope flows continually cause new air to contact the cold radiating slopes and fill
valley with cold air, whereas over plain only a shallow layer is cooled near the surface.
3. Valley air is somewhat protected from gradient winds by surrounding topography.
Heated air by day and cooled air by night is stored up within the valley.
adapted from Hawkes (1947)
TAF depends on valley
geometry. Heating in a Vshaped valley produces an
amplification of 2 relative to a
plane (or vertical sidewall
valley). TAF is less for a Ushaped valley and more for a
convex-sidewall valley.
Valley wind system
Avon, CO is in the Eagle Valley
below the Vail/Beaver Creek ski
area. The observations come
from an automatic weather
station operated in the early
1980s before the ski resort
was built.
Whiteman
Typical T and wind profiles near sunrise
Diurnal Wind Frequencies
Gudiksen (1989)
Gudiksen and Walton (1981)
down-valley flows near sunrise
from Ekhart (1944)
average of all ascents during upvalley and down-valley periods.
Eagle Valley
700 m deep
Yampa Valley
450 m deep
S. Fk. White R.
750 m deep
Brush Creek Valley, CO
Anderson Creek Valley, CA
Valley wind regimes
∂θ
ρ c p ∇ ⋅ (V θ ) dv
∫∫∫ ρ c p ∂t dv = 
∫∫∫−



B
A = B +C + D
A
+
)θ ,
ρ c p ∇ ⋅ (V/θ /) dv
∫∫∫ −+*T .- ∇ ⋅R dv + 
∫∫∫−
€



D
C
Trappers
A
B
−
=1
C +D C +D
Drainers
1
Coolers
€
€
0.8
Sinbad Basin
0.6
Aizu Basin
Brush Creek Valley
A/(C+D)
0.4
Whiteman et al. (1996)
0.2
Steady
Staters
0
0
0.2
0.4
0.6
-B/(C+D)
0.8
1
Reiter et al. (1983)
The valley exit jet
Riviera Valley, Switz.
adapted from
Pamperin &
Stilke (1985)
from M. Rotach
Rotach et al. (2008)
Switzerland’s Riviera
Valley
Exit jet at Weber Cyn, UT
© M. Farley-Chrust
Odd Wind Systems - Maloja Wind
Channeling
LAGO DI GARDA
S
Laghi Valley
Forced Channeling
Terlago
Adige Valley
TRENTO
Roncafort
Pressure Driven Channeling
Lavis
E
Italy, Looking S from Alps
San Michele
L’Ora del Garda:
ricerche su un vento locale
molto particolare
N
Dino Zardi
Contributors to valley flow and turbulence
Tina Chow
Mathias Rotach
Andreas Weigel
Cross-Valley
Wind System
Bob Banta
Lisa Darby
Magdalena Rucker
Bugaboo Spire © Adam Naisbitt
Generally, there is a difference in insolation
on the two sidewalls of a valley that varies
during the course of a day, and is a function
of season, the valley’s orientation, the
sidewall inclination angle, etc.
Here, we assume the sidewalls have equal
inclination angles, and we look at the
difference in theoretical insolation on the
sidewalls of two valleys, one running northsouth and one east-west, for the dates of the
summer and winter solstices and the
equinoxes.
This insolation difference is the basic driving
force for cross-valley circulations. Crossvalley wind strength, however, would depend
on the distance between sidewalls and the
transfer of heat to the air above the sidewalls.
adapted from Bader & Whiteman (1989)
See Manuela Lehner’s dissertation
The diurnal cycle
Convective BL
The Diurnal Cycle
of Mountain Winds
Stephan de Wekker
Kathrin Baumann
Whiteman, adapted from Fiedler (1987)
www.pramhus.com
Wind turning: Left bank - CCW; Right bank - CW
1. The vertical motion necessary for the development of the horizontally
moving valley wind is taken care of by the slope winds, and
2. the circulation of the slope winds makes possible the relatively large
diurnal temperature range in the valley. Vertical motions over the valley
center that compensate for the mass carried up or down the slopes by
the slope wind system transfer heat throughout the valley cross section
3. “An unweakened valley wind can take place only if the air mass as a
whole can flow horizontally. The necessary work done in lifting or
sinking is compensated by heat transfer along the slopes. It is only at
the time of transition between the up- and down-valley wind that the air
mass of the valley moves parallel to the valley floor. Under these
conditions the system is soon destroyed and the opposing system
develops.” Hawkes (1947)
adapted from Hawkes (1947)
Evening
Transition
Example: Rush Valley winds
Fletch=1 m/s
Great
Salt
Lake
Jebb Stewart
Salt
Lake
Valley
Tooele Valley
Rush Valley
adapted from Stewart et al. (2002)
Colorado Rocky Mtns © CD Whiteman
The evening transition winds as the
inversion builds up
Thermal belt
Whiteman (1986)
Geiger et al. (1995)
Morning Transition
Morning
Transition
Eagle Valley
13 Oct 1977
Yampa Valley
13 Feb 1978
Eastern Alps © Georg Pistotnik
Whiteman (1980)
Three patterns of inversion
destruction were identified in
Colorado valleys (left).
Recent laboratory tank
simulations (right) by Fernando
at Arizona State University have
identified a fourth pattern that is
supported by observations in
large Alpine valleys and
elsewhere.
Temperature and wind structure layers at
a time midway through the transition
Whiteman (1980)
Whiteman (1980)
Subsidence!
Atmospheric structure evolution in valley terrain
Morning breakup of stratus, Redwood Valley, CA
Hindman (1973)
Plateaus
Plateau Meteorology
off web
Grand Mesa, Colorado
© Daniel Miller
Tibetan Plateau
© Daniel Miller
Tibetan Plateau
Mountains: 20% of land area
Plateaux: 80% of land area
Barry (1992)
Southern Bolivia Altiplano © Jochen Reuder
Advection of plateau mixed layer
Wind break-in (evening)
Jim Bossert
Ray Arritt
Jim Wilczak
George Young
Bill Cotton
Bossert and Cotton (1984)
Elevated plateau
Contributors to plateau
meteorology research
A baroclinic zone develops
on the periphery during
daytime and winds suddenly
break into the basin/plateau
in the early evening.
Chris Doran
Jerome Fast
Joe Egger
Basin Meteorology
Basin
Meteorology
Salt Lake City, UT
Ron Smith
Vail, CO
“One of the most difficult
unsolved problems in mountain
meteorology is the prediction of
cold air trapping in valleys and
larger basins. With human
populations clustered in valleys,
advances in this area would
assist a high percentage of our
citizens living in mountainous
regions.”" -Smith et al. (1997)
USWRP
PDT-4
NASA photo, Mars
METCRAX Overview, IUGG ’07
Cold air pools in valleys
Basin Meteorology
Whiteman (1990)
Extreme minimum temperatures usually occur in mountain
basins, rather than in valleys:
Peter Sink, UT -69.3°F (-56.3°C) Feb 1, 1985
West Yellowstone, MT -66°F (-54°C) Feb 1933
Taylor Park, CO -60°F (-51°C) Feb 1951
Fraser, CO -53°F (-47°C) Jan 1962
Stanley, ID -54°F (-48°C) Dec 1983
Gruenloch Basin, Austria -63°F (-52.6°C) between 19 Feb and 4 Mar 1932
Temperature time series - Gruenloch
Classification of cold pool events
10
Dec 1
5
Dec 4
GL00D
NW01
0
NW02
NW03
-5
NW04
NW05
NW06D
-10
NW08
NW10U
-15
NW12
NW14
-20
NW16
-25
-30
334
335
336
337
338
339
Day of 2001
Dorninger et al. (2011)
Whiteman
The Meteor Crater Experiment
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METCRAX (October 2006)
SLC winter cold-air pool
Near-circular$impact$
crater$basin$(49$ky$old)
• Surrounded$by$a$
uniform$plain$sloping$
upwards$to$the$SW$with$
2%$slope
• Uniform$rim$height$-$no$
major$saddles$or$passes
1.2$km
50$m$
Whiteman
170$m$
Whiteman, C. D., et al., 2008: METCRAX 2006 – Meteorological experiments in
Arizona's Meteor Crater. Bull. Amer. Meteor. Soc., 89, 1665-1680.
© John S. Shelton
tle
Lit
Temperature evolution
do
ra
lo
Co
Meteor Crater, 22-23 Oct 2006
r
ve
Ri
te
ra
rC
eo
et
M
r
Savage et al. (2008)
• Strong 30-m deep
M
on
oll
og
inversion on crater
floor
• Isothermal
atmosphere in
remaining 75% of
crater depth
• Temperature jump
develops at rim level
• Crater cools while
remaining isothermal
• Horizontally
homogeneous
m
Ri
What physical process(es) produce the isothermalcy?
Cold air intrusions
Temperature inversions in Bingham Canyon Mine
Mining extends to elevations
of 2500 m ASL
Mine bottom
1373 m ASL
Depth > 1100 m
Diameter ~ 3000 m
Lowest gap
1973 m ASL
Depth 600 m
A southwesterly drainage flow comes down the Colorado Plateau. A cold air mass builds
up on the front side of the crater, the flow splits around the crater, and some of the cold air
spills over the rim. The cold air flows down the upwind inner sidewall, detraining cold air
into the basin atmosphere. This horizontal mixing into the crater atmosphere, which
decreases with distance down the sidewall and the compensatory rising motion,
destabilizes the basin atmosphere driving it towards isothermalcy.
Whiteman, C. D., S. W. Hoch, M. Lehner, and T. Haiden, 2010: Nocturnal cold air intrusions into Arizona's
Meteor Crater: Observational evidence and conceptual model. J. Appl. Meteor. Climatol., 49, 1894-1905.
Haiden, T., C. D. Whiteman, S. W. Hoch, and M. Lehner, 2011: A mass-flux model of nocturnal cold air
intrusions into a closed basin. J. Appl. Meteor. Climatol., 50, 933-943.
Photo provided by Rio Tinto / Kennecott Utah Copper
Glacier wind
Glacier Wind
Pigeon Spire, Bugaboo Mtns © Adam Naisbitt
The End
Torres del Paine © Sigrid & Ron Smith