Lab5
10/09/2013
Pressure Levels
 3 forces that control wind direction?
 PGF or HGF, Coriolis, Friction
 What is geostrophic wind?
 PGF = Coriolis
 Wind blows parallel to isobars and height lines
 Is friction greatest at low or high elevations?
 Low, because of the earth’s surface!
 Friction slows the wind and reduces the effect of the
coriolis force
Friction
 Air in motion near the earth’s surface is slowed by
contact with the ground
 The magnitude of friction is dependent on the
“roughness” of the surface
 Where is friction greater? Over land or over water?
Friction
Pressure and Boiling Water
ScienceBlogs
Pressure and Boiling Water:
Higher Pressure (Lower Elevation)
Boiling Water at high pressure
Water vapor
molecules
Boiling Water
Pressure and Boiling Water:
Lower Pressure (Higher Elevation)
Water vapor
molecules
Boiling Water
Pressure Levels
Pressure Levels and Friction
 Surface Pressure
 What is the height
of the “surface”
pressure?
 Wind crosses
isobars at a rather
large angle
Pressure Levels and Friction
 850mb-heights
 Wind crosses
height lines at a
small angle
Pressure Levels and Friction
 500mb-heights
 Wind blows parallel
to height lines
Buys-Ballot’s Law
 If you stand with the wind at your back on a constant
pressure surface, lower heights (lower pressure) will be
on your left in the Northern Hemisphere
Jet Stream!
 Vertical profile of
winds measured at
Caribou, ME
 Mandatory Pressure
Levels – pressure
levels which
radiosondes always
take measurements
Jet Stream
 The jet stream is caused by differences in temperature
between the tropics and the polar regions
 The greater the temperature difference, the faster the
jet stream
 Remember: Pressure decreases faster in cold air than in
warm air!!!!!!!!
North Pole
9800m 9950m
North Pole
9950m
11000m 11000m
Tropics
Tropics
Winter
Summer
*Jet
Streaks
Do you think it is faster to fly from Seattle to Boston,
or from Boston to Seattle?
Temperature and Altitude
Buoyancy and Vertical Ascent
 Less dense air rises
 More dense air sinks
 Think about a hot air balloon…why does it rise?
Lab 5 Problems:
 6.13
 6.18 a, b, c
 7.1 a, b, c
 7.2 b, c
 7.8 a, b, c
 7.10 a, b
 8.6 a, b