unit 4 – atmospheric processes. winds… earth’s atmospheric circulation is an important...
TRANSCRIPT
Winds and Air MassesUnit 4 – Atmospheric Processes
Winds…Earth’s atmospheric circulation is an
important transfer mechanism for both energy and mass
The imbalance between equatorial energy surpluses and polar energy deficits is partly resolved
Wind – the horizontal motion of air across Earth’s surfaceDifferences in air pressure (density) between
one location and another produce windNames for the direction from which they
originate
Driving Forces within the Atmosphere
Gravitational forcePressure gradient forceCoriolis forceFrictional force
Earth’s Gravitational ForceEarth’s gravitational force on the atmosphere
is practically uniform, equally compressing the atmosphere near the ground worldwide
Density decreases as altitude increases
Pressure Gradient ForceHigh- and low-pressure areas exist in the
atmosphere because of uneven heating of the Earth’s surface
A pressure gradient is the difference in atmospheric pressure between areas of higher pressure and lower pressureA steep gradient causes faster air movement from a
high-pressure area to a low-pressure area.High and low pressure areas are caused by
differences in surface heating and cooling.Land versus water.Different albedos and energy absorbing abilities of
land, vegetation and human built surfaces
Isobars Isobars are lines of equal atmospheric pressure drawn on
a map.Widely spaced isobars display a gradual pressure gradient.
Gradual pressure gradients imply light winds.Closely spaced isobars display a steep pressure gradient.
Steep pressure gradients imply strong winds.
Coriolis Force
Deflects from a straight path any object that flies or flows across Earth’s surfaceWind, airplane, ocean currents
Deflection to the right in the Northern Hemisphere; to the left in Southern Hemisphere
The strength of the Coriolis force strengthens with an increase in latitude.
Friction ForceDrags on the wind as it moves across surfaces; up
to 500mVaries with surface texture, wind speed, time or day
and year, and atmospheric conditionsSince surface friction decreases wind speed, it
reduces the effect of the Coriolis force Anticyclone
Winds in the Northern Hemisphere spiral out from a high-pressure area clockwise
Cyclone Spiral into a low-pressure area counterclockwise
In the Southern Hemisphere these circulation patterns are reversed
When the “forces” combine…When the gravitational force, pressure gradient force,
Coriolis force and frictional force combine we see the development of ‘predictable’ global wind patterns.
Air MassesAir masses are bodies of air that develop
over large areas of the Earth’s surfaceTwo conditions needed:
1. Air must stay over the source region for a long period of time so that it can take on the characteristics of that region
2. Air must be stableUsually form where air is descending back to
Earth These high-pressure cells line up roughly over
the polar circles and the Tropics
Your taskLook at the defining characteristics of the 6 major air masses.
This will be done by completing the “Characteristics of Air Masses” chart
You will then look at cloud formation along fronts Complete the “cloud development in fronts” diagram and associated
questions on handout
Additional questions:
1. Explain a mid-latitude storm.2. Why are storms more common in the mid-latitudes than
elsewhere?3. Explain the differences between continental and maritime
air masses.4. Explain the role of convections currents and the rotation of
the Earth in the development of a storm.5. Explain how studying jet streams could help long-range
weather forecasting.All info is found in Chapter 16, pages 262-268