UPPER-LEVEL WINDS

1
UPPER-LEVEL WINDS
Atmospheric pressure, temperature and winds at
surface
2
Weather conditions
3
Atmospheric pressure and elevation
4
Winds at upper level (500mb 5600 m of
elevation or 18000 feet)
1 knot 1 nautical mile/h 1 knot 1.15 MPH 1
knot 1.85 km/h
5
Height and pressure at upper level (500mb 5600
m of elevation)
6
Winds at upper level (200mb 11800 m of
elevation)
7
WINDS ALOFT
How does air move at higher elevations? The
gradient force INCREASES with altitude
stronger winds
How does pressure changes with elevation?
8
800mb
warmer
colder
H4
850mb
800mb
H3
900mb
850mb
High Height
H2
900mb
Low Height
950mb
H1
950mb
Sea level
30 latitude
POLE (90)
Pressure decreases with elevation SLOWER in
WARMER air FASTER in COLD air
Height (of pressure) HIGH in WARMER air LOW in
COLDER air
Figure 5.17, Page 139
9
500mb
10
GEOSTROPHIC WIND
When the Coriolis force balances the gradient
force. The speed and direction of wind remain
constant
It takes place at upper levels
geostrophic wind
11
(No Transcript)
12
GLOBAL CIRCULATION AT UPPER LEVELS

• Weak equatorial easterlies (from 25 to poles)
• Tropical high pressure belts (15 -20)
• Upper air westerlies (from 25 to poles, see
  undulations)
• Polar low

(See Fig 5.19)
13
ROSSBY WAVES

• Undulations of upper air westerlies

• Formation
• Waves arise in region of contact between cold
  polar air and warm tropical air (Polar front)

14
ROSSBY WAVES FORMATION
2. Warm air pushes pole ward and a tongue of cold
air is moved to south (undulation development)
3. Waves are strongly developed. Cold air are
troughs of low pressure 4. Waves are pinched
off, forming cyclones of cold air
15
ROSSBY WAVES

• They are important for poleward heat transport
• Reason for variable weather in midlatitudes

16
JET STREAMS

• Regions at high elevation with strong wind
  streams
• According to the World Meteorological
  Organization we can call a jet stream any speed
  exceeding
• 67mph, 58 knots, 108 km/h
• The core of jet streams reaches 102mph
• They take place where atmospheric pressure
  gradients are strong

The greater the contrast in temperature, the
stronger the jet streams blow
17
JET STREAM

• Polar jet stream
• Follows the edge of Rossby waves.
• Found at 10-12 km elevation (33,000-40,000 ft)
• Wind speed 75-125 m/s (170-280 mi/hr)
• 2. Subtropical jet stream
• In the subtropical latitude zone
• Speed 100-110 m/s
• 3. Tropical easterly jet stream
• In summer season, over Asia, India, Africa, only
  in Northern Hemisphere

Figure 5.21
18
JET STREAMS

• Jet streams tend to be weaker in summer than in
  winter
• Jet streams are less intense in the Southern
  Hemisphere due to smaller land masses
• Strongest jet stream have been recorded during
  winter over Southern Japan (speeds up to 310 mph)

19
(No Transcript)
20
(No Transcript)
21
Wind at 200 mb (12 km or 8 miles)
22
Atmospheric pressure and temperature at surface
(summer)
23
Atmospheric pressure and winds at surface
24
Winds at upper level (500mb 5600 m of
elevation)
http//weather.unisys.com
25
(No Transcript)
26
Winds at upper level (200mb 11800 m of
elevation)