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