Ch6 meteorology Air pressure and winds

how does atmospheric pressure affect wind?

Wind is the result of horizontal differences in atmospheric pressure

atmospheric pressure

the force exerted against a surface by continuous collision of gas molecules

Measuring Air Pressure

Air pressure is measured in millibars (mb), where 1 millibar is equal to 100 newtons/m^2

Mercury Barometer

An instrument that measures changes in air pressure, consisting of a glass tube partially filled with mercury.

- Air pressure pushes on a pool of mercury, which forces the mercury up a tube

Pressure Changes with Altitude

Air pressure is defined as the force exerted against a surface by continuous collision of gas molecules

Air pressure decreases with altitude

Air pressure increases with depth

Why does air pressure vary?

Altitude, Temperature, Humidity, Movement of air masses

how does moisture affect air pressure?

- the amount of water vapor reduces the density of air

- cold hair has higher pressure

- warm, dry air has higher pressure compared to moist air

Convergence/Divergence and Air Pressure

-Convergence occurs when a net airflow causes pressure to rise

- Divergence results when there is a net outflow of air from a region and surface pressure drops

Factors affecting wind

1. pressure gradient force

2. coriolis effect

3. friction

Pressure Gradient Force

Drives air from areas of higher barometric pressure to areas of lower barometric pressure, causing winds.

Coriolis Effect and how it effects wind

-Doesn't generate wind, only modify airflow

- In northern hemisphere, deviates to the right

- in southern hemisphere, deviates to the left

Friction in Wind

- Friction significantly influences airflow near Earth's surface, but its effect is negligible at higher altitudes.

- Slows down the air speed causing a reduction in the Coriolis effect, allowing the wind to cross the isobars at an angle-

Geostrophic Flow

occurs when the pressure gradient force and the Coriolis force are balanced.

curved airflow

winds around cells of high pressure or low pressure follow curved paths

cyclone/anticyclone

Cyclone: A low pressure region with an accompanying surface wind Anticyclone: a high pressure system with accompanying winds

cyclone and anticyclone at north and south hemispheres

Northern hemisphere: Counterclockwise

Southern hemisphere: Clockwise