Land-Sea Breezes
Figure 6.19
Land-Sea Breezes
Mountain-Valley breezes
Figure 6.20
Chinook, Foehn, & Santa Ana Winds
Winds that flow down the lee
side of mountain ranges
Hierarchy of Wind Systems• Global
– ITCZ, Westerlies, and Rossby Waves– Last decades to centuries
• Synoptic– Cyclones and Anticyclones, Troughs and Ridges,
Pressure cells– Last days to weeks
• Mesoscale– Local winds– Last hours
• Microscale– Dust devils– Last minutes
Kinematics
September 5, 2007
Kinematics
• Means “to move” in Greek
• Describes the motion of objects without considering the masses or forces that bring about that motion
• Studies how the positions of things change over time, measured in coordinates
Atmospheric Pressure and Motion
• Differences in heating cause differences in air density, which cause atmospheric motion
• In the midlatitudes, the surface air temperature is due more to air movement more than radiation received
• Motion is a result of atmospheric pressure differences
Geostrophic Wind• Winds in the upper atmosphere that flow
parallel to isobars
• In the Northern Hemisphere, geostrophic wind flows with low pressure to its left and high pressure to its right
Geostrophic Wind
Gradient Wind
• A wind that blows at a constant speed parallel to curved isobars above the level of frictional influence is a gradient wind
• An object accelerates when there is a change in its speed or direction or both
• Therefore the gradient wind blowing around low-pressure is constantly accelerating because its constantly changing direction – centripetal acceleration
Gradient Wind
Gradient Wind
Eddies
• When the wind encounters a solid object, a whirl of air – or eddy – forms on the object’s downwind side
• The size and shape of the eddy depends on the size and shape of the obstacle
• On a windy night, these produce tiny swirls of air that act as pulses of compressed air that reach you eardrum and produce a howling sound
Turbulence• Eddies that form close to mountains and
beneath wave crests produce rotors• Rotors have violent vertical motion that produce
extreme turbulence
Turbulence
• Sudden changes in wind speed or direction (or both) abruptly produce wind shear
• Any irregular or disturbed flow in the atmosphere that produces gusts and eddies - Turbulence
• Turbulent eddies are common near the jet stream, where large wind speed shears exist
Microburst
• A localized column of sinking air
• Once it hits the ground, it spreads quickly in all directions
• Produces divergent winds at the surface
• Damage similar to that of tornadoes
• Tornadoes spiral inwards, microbursts spiral outwards
• Particularly troublesome for landing aircraft
Clouds: The Basics
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