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