ATMOSPHERIC PRESSURE,

WIND & CLOUDS

Mt. Washington Observatory

ATMOSPHERIC PRESSURE

Weight of the air above a given area

p = F/A

Measured in mb (millibars)

Average Atmospheric Pressure at 0m

(Sea Level) is 1013mb

Your book

PRESSURE

50 miles

(Barometer measures 1013mb)

As you go up in altitude, there’s less weight (less molecules) above

you…

…as a result, pressure decreases with height!

PRESSURE

500mbpressure

1013mb pressure

ATMOSPHERIC PRESSURE

Your book

ATMOSPHERIC

PRESSUREPRESSURE

VARIATIONS

OVER PVDBarometers

Buybarometers.com

CAUSES OF

PRESSURE VARIATIONS

Universal Gas Law

Pressure depends on:

Number of Moles, Volume,

Density, and Temperature of all the air above PVD

PV = nRT

SEA LEVEL PRESSURE

VARIATIONS - RECORDS

Lowest pressure ever recorded in the Atlantic Basin: 882 mbHurricane Wilma, October 2005

Highest pressure ever recorded in the world: 1086 mbMongolia, December 2001

Pressure Differences cause Air to move

PRESSURE GRADIENT FORCE

EARTH’S ROTATION

ROTATION OF THE EARTH

ROTATION OF THE EARTH

ROTATION OF THE EARTH

ROTATION OF THE EARTH

ROTATION OF THE EARTH

CORIOLIS EFFECT

CORIOLIS EFFECT

WIND

WIND

HOW IS THIS APPLIED?

http://ww2010.atmos.uiuc.edu/(Gh)/wx/surface.rxml

MODERATE

SOUTH WINDS

NORTH WINDS

WARM

COLD

VALIDATION

Coolwx.com

L

VALIDATION

H

Coolwx.com

VALIDATION

NCAR UCAR RAP Realtime weather (http://www.rap.ucar.edu/weather/satellite/)

LH

SUMMARY UP TO THIS POINT1) Differences in atmospheric pressure across the globe

lead to winds across the surface of the planet

2) The PRESSURE GRADIENT FORCE pushes air

from high to low pressure (WIND)

3) The BIGGER the difference between high and low pressure

the STRONGER the wind

3) As air moves away from high pressure and towards

low pressure, the CORIOLIS EFFECT deflects it to its right (NH)

4) The above leads to air circulating COUNTER-CLOCKWISE

around LOW PRESSURE

and CLOCKWISE around HIGH PRESSURE (NH)

5) South or North winds will result in higher or lower temps

WHAT ABOUT THE CLOUDS?

Remember that air converges towards low pressure

and air diverges away from high pressure and

FRICTION due to the surface of Earth “enhances” this

WHAT ABOUT THE CLOUDS?

So, as the air moves towards the low pressure

it has nowhere to go but UPWARDS

WHAT ABOUT THE CLOUDS?

So, as the air moves away from high pressure

it must be replaced by air from above that is

moving DOWNWARDS

TEST

A World of Weather (Lee Grenci PSU)

INTERESTING NOTE!