Meteorology of Windstorms
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Meteorology of Windstorms - Wind Engineering - Lecture Slides, Slides of Environmental Law and Policy
Some concept of Wind Engineering are Aeroelastic Effects, Along-Wind Dynamic Response, Antennas and Open-Frame Structures, Atmospheric Boundary Layers and Turbulence, Atmospheric Boundary, Basic Bluff-Body Aerodynamics. Main points of this lecture are: Meteorology of Windstorms, Producing Extreme Winds, Tropical Depressions, Tropical Cyclones, Thunderstorms, Downslope Winds, Topographic Situations, Small Radius, Surface -Significant, Boundary Layer
Typology: Slides
2012/2013
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- Types of storms producing extreme winds :
- extra-tropical depressions (gales)
- synoptic scale 40-60° latitude
- extra-tropical depressions (gales)
- tropical cyclones (hurricanes, typhoons)
- synoptic scale 5°-30° latitude oceans and coast
- thunderstorms (downbursts, tornados)
- meso scale 0°-50° latitude local convection
- downslope winds (chinook, Santa Ana)
- meso scale certain topographic situations thermally driven
- Pressure gradient force :
x
p
a
Pressure gradient force per unit mass =
p y z z^ (p+ x) y z x
p
x
y
Net force =
Net force per unit volume = x
p
x y z x
p
- Coriolis force :
- an apparent force due to the rotation of the earth
AA = U (t)
2
a = 2 U
= (½)a (t)
2
(S. Pole)
- Geostrophic wind :
- Balance between pressure gradient and Coriolis forces
- Approximates wind speed in upper atmosphere
- Ugeostrophic = x
p
ρ f
1
a
- Geostrophic wind :
- Flow parallel to isobars
- Anti-clockwise rotation around low pressure centre in N. Hemisphere
- Gradient wind :
Includes centrifugal force : (U
2
/r) per unit mass
r = radius of curvature of isobars
- Equation of motion :
anti-cyclone
Quadratic equations for gradient wind speed, U
cyclone
2
r
p fU r
U
a
2
r
p f U r
U
a
- Gradient wind :
- Solutions :
anti-cyclone
U is limited to for an anti-cyclone, but unlimited for a cyclone
cyclone
r
f r f r r p U a
2 2
r
f r f r r p U a
2 2
f r
- Characteristics of hurricanes :
- Can exist between 5 and 40 latitude
full strength between 10 and 30 latitudes
- Require ocean temperature greater than 26 Celsius (79°F)
taken to higher latitudes by warm ocean currents
- 3-dimensional vortex structure with ‘eye’ of calm winds
- Known as ‘typhoons’ in S. China sea and elsewhere as ‘tropical cyclones’
- Characteristics of hurricanes :
- 3-dimensional vortex structure with ‘eye’ of calm winds
(S. Hemisphere)
- Wind field of hurricanes :
- Wind field of hurricanes :
- Profiles of pressure and gradient windspeed :
pressure
gradient wind speed
pressure gradient
p = pn-p 0 where p 0 is central pressure
B n o
o r
A
p p
p p exp
Holland (1980)
B B r
A
r
AB
p r
p 1 exp
) r
A exp( r
AB
ρ
Δp
4
f r
2
fr U (^) B B a
2 2
- Profiles of pressure and gradient wind :
pressure
profile
gradient wind
speed profile
940
950
960
970
980
990
1000
1010
0 10 20 30 40 50 Radial distance from centre (km)
Pressure atsea level (mb)
0
10
20
30
40
50
60
0 10 20 30 40 50 Radial distance from centre (km)
Gradient wind speed
(^) (m/s) Cyclone ‘Tracy’
1974