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Hot Airventure 1
Weather 101 and beyondWeather 101 and beyond
Edward J. HopkinsEdward J. HopkinsDept. of Atmospheric &Dept. of Atmospheric &
Oceanic Sciences Oceanic Sciences
Univ. of Wisconsin-MadisonUniv. of Wisconsin-Madison
Midwest Hot Air Balloon Safety SeminarMidwest Hot Air Balloon Safety Seminar““Hot Aireventure”Hot Aireventure”
Oshkosh 3 March 2001Oshkosh 3 March 2001
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Concerns of BalloonistsConcerns of Balloonists
The Weather
The Terrain (or Surface)
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QuizQuiz
Ballooning (Fair) Weather is associated with High or Low Pressure?
Which way do winds blow around:
High pressure?– Low pressure?
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WINDWIND
What is Wind?Why the wind?Review of basic concepts
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ASOS Wind InstrumentsWind Vane (left) & Cup Anemometer (right)
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Aerovane Measures wind speed & direction
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BEAUFORT WIND FORCE SCALE[Modern version, Source: Federal Meteorological Handbook I]
Scale Description Land & Sea Observations Knots
0 Calm Smoke rises vertically.Sea surface is like mirror.
< 1
1 Light air Smoke, but not wind vane, shows direction ofwind.Slight ripples on sea.
1-3
2 Light breeze Wind felt on face, leaves rustle, wind vanesmove.Small, short wavelets.
4-6
3 Gentle breeze Leaves and small twigs moving constantly,small flags extended.Large wavelets, scattered whitecaps.
7-10
4 Moderatebreeze
Dust and loose paper raised, small branchesmoved.Small waves, frequent whitecaps.
11-16
5 Fresh breeze Small leafy trees swayed.Moderate waves.
17-21
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BEAUFORT WIND FORCE SCALE (con’t.)Scale Description Land & Sea Observations Knots
6 Strongbreeze
Large branches in motion, whistling heard inutility wires. Large waves, some spray.
22-27
7 Near gale Whole trees in motion.White foam from breaking waves.
28-33
8 Gale Twigs break off trees.Moderately high waves of great length.
34-40
9 Strong gale Slight structural damage occurs. Crests ofwaves begin to roll over. Spray may impedevisibility.
41-47
10 Storm Trees uprooted, considerable structuraldamage.Sea white with foam, heavy tumbling of sea.
48-55
11 Violentstorm
Very rare; widespread damage.Unusually high waves.
56-63
12 Hurricane Very rare; much foam and spray greatly reducevisibility.
>63
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The wind responds to a Difference The wind responds to a Difference in air pressure in air pressure
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BASIC CONCEPTS Air Pressure BASIC CONCEPTS Air Pressure (con’t.)(con’t.)
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Explaining Differences inExplaining Differences in Air Pressure Air Pressure
Low Pressure High Pressure
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Display of Pressure Differences on Display of Pressure Differences on a Weather Map - Isobarsa Weather Map - Isobars
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Isobars -Isobars -- - lines of equal barometric pressurelines of equal barometric pressure- use sea level corrected pressure- use sea level corrected pressure
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US STANDARD ATMOSPHERE, 1976
0
10
20
30
40
50
0 200 400 600 800 1000
AIR PRESSURE [millibars]
ALT
ITU
DE
[km
]
AIR PRESSURE in the Vertical (con’t.)
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As a Sidebar… Altimetry
Since pressure decreases at a “reasonably” known rate of 1 mb decrease per 10 meter rise
or 0.01 inch of Hg per 10 feet, then… pressure altimeters are
barometers made to read in altitude.But...
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Pressure Change with height depends Pressure Change with height depends upon Temperature of columnupon Temperature of column
- (It is really the density!)
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WHY THE WIND? WHY THE WIND? (con’t.)(con’t.)
Reasons for Atmospheric Motions:Reasons for Atmospheric Motions:– Buoyancy Effects Buoyancy Effects oror Dynamic Effects Dynamic Effects
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-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
6:00 12:00 18:00 23:00 5:00
Time
No
rmal
ized
Hea
t F
lux
Daily HeatingDaily Heating
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10
12
14
16
18
20
22
24
26
0 3 6 9 12 15 18 21 24
HOURS CST
TE
MP
ER
AT
UR
E (
deg
F)
January Temperatures - January Temperatures - Madison, WI (1981-90)Madison, WI (1981-90)
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January Wind Speeds - January Wind Speeds - Madison, WI (1981-90)Madison, WI (1981-90)
0
2
4
6
8
10
12
14
3 6 9 12 15 18 21 24
HOURS CST
AV
ER
AG
E W
IND
SP
EE
D [
mp
h]
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July Temperatures - July Temperatures - Madison, WI Madison, WI (1981-90)(1981-90)
55
60
65
70
75
80
85
0 3 6 9 12 15 18 21 24
HOURS CST
TE
MP
ER
AT
UR
E (
deg
F)
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July Wind Speeds - July Wind Speeds - Madison, WI (1981-90)Madison, WI (1981-90)
0
2
4
6
8
10
12
3 6 9 12 15 18 21 24
HOURS CST
AV
ER
AG
E W
IND
SP
EE
D [
mp
h]
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ENERGY TRANSPORT: ENERGY TRANSPORT: CONVECTIONCONVECTION
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LAPSE CONDITIONSTemperature decreases with height
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0. 5. 10. 15. 20.
Temperature [deg C]
Alt
itu
de
[km
]
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ISOTHERMAL CONDITIONS Temperature remains constant with height
0.00.51.01.52.02.53.03.5
0. 5. 10. 15.
Temperature [deg C]
Alt
itu
de
[km
]
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INVERSION CONDITIONS Temperature increases with height
0.00.51.01.52.02.53.03.5
0. 5. 10. 15.
Temperature [deg C]
Alt
itu
de
[km
]
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U.S. STANDARD ATMOSPHERE See Fig. 1.9 Moran & Morgan (1997)
0.
20.
40.
60.
80.
100.
120.
140.
-100. -50. 0. 50. 100.
Temperature [deg C]
Alt
itu
de
[km
]
Troposphere
Stratosphere
Mesosphere
Thermosphere
Tropopause
Stratopause
Mesopause
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WHY THE WIND? WHY THE WIND? (con’t.)(con’t.)
Reasons for Atmospheric Motions:Reasons for Atmospheric Motions:– Buoyancy Effects Buoyancy Effects oror Dynamic Effects Dynamic Effects
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Air Converging AloftAir Converging Aloft
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Air Diverging AloftAir Diverging Aloft
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The SurfaceThe Surface
The “Obvious”– Obstacles to take-off and landing
(e.g., trees, power lines, animals)The Surface and the Winds
– Affects the Boundary Layer wind flow
– Can produce local wind regimes
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Boundary LayerBoundary LayerWhere we liveExtends from surface to approximately
3000 ft. (1000 m)Consists of
– Surface Boundary Layer (30 to 60 ft. & includes Anemometer Level)
– Ekman or Spiral Layer (above 60 ft. to Free Atmosphere)
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Relative Surface RoughnessRelative Surface RoughnessSource: Stull, 1995
Classification LandscapeSmooth Snow-covered fieldsOpen Prairies, grass farm fields, airportsRoughly open Low crops w/ occasional obstaclesVery rough Mixed fields, small woods, orchardsClosed Mature forests, suburbs, villagesChaotic Large towns, irregular forests
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B. EXPLANATIONS of ATMOSPHERIC MOTION
Practical ProblemsHistorical ConceptsForces of Motion & Newton's Laws
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An example of an equation of motionNASA
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PRESSURE GRADIENT FORCEPRESSURE GRADIENT FORCE
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PRESSURE GRADIENT FORCE (con’t.)
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ASSUMPTIONS
For convenience, assume that:For convenience, assume that: Winds are nearly horizontal;Winds are nearly horizontal; Atmosphere is in nearlyAtmosphere is in nearly
“hydrostatic balance” “hydrostatic balance” i.e., air parcels do not accelerate i.e., air parcels do not accelerate upward or downward; upward or downward;
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HYDROSTATIC BALANCE CONCEPT
See Fig. 9.11 Moran & Morgan (1997)
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HORIZONTAL PRESSURE GRADIENT FORCE (con’t.)
Direction is from High to Low pressure!
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HORIZONTAL PRESSURE GRADIENT FORCE (con’t.)
See Fig. 9.1 Moran & Morgan (1997) Magnitude depends on isobar spacing!
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LOCAL WINDSFLOW RESPONDING TO PRESSURE
GRADIENT FORCE - LOCAL WINDS
Assumptions:– Only Pressure gradient force operates;– Results from temperature differences– Acts for short time & short distances.
Examples:– Sea-Land Breeze Circulation– Mountain-Valley Breeze Circulation– City-Country Circulation
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Sea (Lake) Breeze(Graphics from UIUC WW2010)
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VERTICAL PRESSURE GRADIENTS - Dependency on density (temperature)
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Sea (Lake) Breeze (con’t.)
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Sea (Lake) Breeze (con’t.)
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Sea (Lake) Breeze (con’t.)
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Sea (Lake) Breeze (con’t.)
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Sea (Lake) Breeze (con’t.)
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Sea (Lake) Breeze (con’t.)
(Lake)
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Sea (Lake) Breeze (con’t.)
See Fig. 12.2 A Moran & Morgan (1997)
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Land Breeze
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Land Breeze (con’t.)
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Land Breeze (con’t.)
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Land Breeze (con’t.)
See Fig. 12.2 B Moran & Morgan (1997)
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Mountain BreezeMountain Breeze
See Fig. 12.14 Moran & Morgan (1997)
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Valley BreezeValley Breeze
See Fig. 12.14 Moran & Morgan (1997)
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Larger Scale FlowLarger Scale FlowObservation:
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Right with HeightRight with Height
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PRESSURE GRADIENT FORCEPRESSURE GRADIENT FORCE
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Reason for the ProblemReason for the Problem Because the earth turns:
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CORIOLIS EFFECT CORIOLIS EFFECT oror FORCE FORCE (con’t.)
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Geostrophic AdjustmentGeostrophic Adjustment
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Geostrophic Wind See Fig. 9.12 Moran & Morgan (1997)
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Flow in Friction LayerFlow in Friction Layer
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Variation of Friction Effects with Variation of Friction Effects with HeightHeight
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Right with HeightRight with Height
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Varying effects of Surface RoughnessVarying effects of Surface Roughness
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Curved Flow
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Features in a Surface Low Features in a Surface Low (Convergence & Ascent)(Convergence & Ascent)
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Features in a Surface HighFeatures in a Surface High (Sinking & Divergence)(Sinking & Divergence)
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Numerical Weather Prediction
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Numerical Weather Prediction
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Numerical Weather Prediction
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My office: Dept. of Atmospheric & My office: Dept. of Atmospheric & Oceanic Sciences Oceanic Sciences
hopkins@meteor.wisc.eduhopkins@meteor.wisc.edu
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NORMALIZED DENSITY PROFILEUS STANDARD ATMOSPHERE 1976
0
20
40
60
80
0.0% 20.0% 40.0% 60.0% 80.0% 100.0%
PERCENT OF SEA LEVEL DENSITY
ALTI
TUD
E [k
m]
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UNSTABLE CONDITIONS Compare Environment with DALRWarmer parcel continues upward
-500
0
500
1000
1500
2000
2500
0 5 10 15 20 25 30