Air Motions

Geology 390WSUV

Dr. Robert M MacKay

1st Law (Law of Inertia)

Every object continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.

acceleration = 0.0 unless the objected is acted on by an unbalanced force

Which path does the ball follow after the string breaks?

Which path does the ball follow after the string breaks? Path C

Forces that influence the wind

1. Pressure Gradient Force

2. Coriolis Force

3. Friction

On average Gravity nearly balances the vertical Pressure gradient(hydrostatic balance)

Fig. 8-16, p. 203Pressure gradient force (PGF) pushes from high to low pressure

Pressure Gradient=∆P/dist

Isobars are lines of constant pressureWhen distance between isobar is large the pressure gradient is small and when the distance is small the pressure gradient is large.

Pressure Gradient

Where is the pressure gradient largest A, B, C, or D ?

Pressure Gradient

Where is the pressure gradient largest A, B, C, or D ?

ANSWER A

Centrifugal force an (Apparent Force)

Centrifugal force an (Apparent Force)

Coriolis Force (apparent force due to Earth’s rotation)

Coriolis Force

Deflects air to right in NH& Left in SH

Is always zero at the equator

Increases with latitude

Increases with wind speed

Increases as planet rotation speed increase

Coriolis Force

Coriolis Force

Geostrophic WindsWind flows parallel to straight line isobars

Geostrophic wind the PGF is balanced by the Coriolis force.Low pressure is always to the Left of the wind direction in NHRight in SH

Geostrophic Winds

When isobars are close wind speeds are high.

In the Northern hemisphere cyclonic flow is counter clock-wise

As air moves toward the center of rotation is spins faster so cyclonic flow is typical relatively fast.

Central low pressure is associated with rising air and hence clouds / rain

In the Northern hemisphere Anti-cyclonic flow is clock-wise

As air moves away from the center of rotation is spins slower so anti-cyclonic flow is typical relatively slow.

Central high pressure is associated with sinking air and clear skies.

Which hemisphere?

Which hemisphere?

NH

Which hemisphere?

Which hemisphere?SH

In the upper atmosphere wind flows parallel to isobars and is fast where isobars are close together.Low pressure is always to the Left of the wind direction in NHRight in SH

Friction near the surface slows wind speeds, weakens the coriolis force and tend to steer winds towards the low pressure.Low pressure is always to the Left of the wind direction in NHRight in SH

Is the above wind pattern associated with a central High pressureOr Low pressure?

Is the above wind pattern associated with a central High pressure (the air flow is away from center)Or Low pressure?

Is the above wind pattern associated the Northern Hemisphere orSouthern Hemisphere

Is the above wind pattern associated the Northern Hemisphere orSouthern Hemisphere (Counter Clockwise around High)