Winds
Three causes of motion



Convection
Pressure Differences
Coriolis Effect
1. Convection Currents
Warm air rises and cool air sinks because of density
 This is called a convection current
Winds are caused by the uneven heating of Earth’s
surface.
 Land heats up and cools off quicker than water
 So the large amount of water on Earth moderates our
temperatures
2. Pressure Differences
pressure differences
in the atmosphere that are a result of temperature differences
WIND ALWAYS
FLOWS
FROM HIGH TO LOW
PRESSURE
3. Coriolis Effect
 Wind is deflected to the right (Northern hemisphere)
due to earth’s rotation
 effect greatest at poles, decrease to zero at equator
Highs and Lows?
 Winds circle Clockwise around a high
 Highs generally mean cold dry air that is sinking
 High pressure usually = fair weather
Low Pressure Systems
 Winds circle counterclockwise around a low
 Warmer air rises and cools and forms clouds and precipitation
 Low pressure usually = rainy weather
Global Circulation Patterns
 Global winds are the result of several cell-like circulation patterns brought
about by
 uneven heating of Earth’s surface
 and compounded by effects of the Earth’s rotation.
Doldrums or ITCZ
 At the equator hot air
rises and forms an
area known as the
doldrums
 At the boundary
between the
troposphere and
stratosphere it
spreads out to the N
or S
Horse latitudes
 As it reaches about
30 N and S of the
equator it cools and descends
 Sinking air causes an area of dry weather
 The sinking air also causes an area with weak winds
 This caused problems for ships and they sometimes threw their horses
overboard
Trade Winds
 Winds flowing south from the horse latitudes is deflected to the west in the
northern hemisphere
 These aided trading by ship
Local Wind Patterns
 Monsoons
 Land breeze/Sea breeze
 Chinook
Monsoon
Dry season In winter, air flow is from cooler
(H pressure) to warmer (L pressure)
ocean
 Air from the land is dry
Wet season In summer, air flow is reversed
 Air flows from the cooler ocean to the
hotter (L pressure) land
Sea Breeze
Land breeze
reversed
Chinook
 A wind on the eastern side of the Rockies formed when air descends and is
compressed and warms
Effects:
 Rapid. Large Temperature Changes Can Occur
Beaufort scale
 Used to estimate wind speeds
 Originally used by sailors
Beaufort Scale on Water And on Land
Wind and Pressure Relationship Lab
Remember Topographic Maps?
Contours are imaginary lines that join points of equal elevation on the surface of
the land
Now we will use these with equal temperature and pressure
Same Concept—Different Use
 Isotherm=equal temperature
 Isobar=equal barometric pressure
contour interval (CI)
 The contour intervals vary
 Isobars often have an interval of 4
 Read the directions or look at examples to see the contour level
Tips for understanding contour lines.
 There are a few rules that topographic contours must obey, however, and
once you understand these rules the map becomes an extremely useful and
easy to use tool.
2) Contour lines can never cross one another.
 Each line represents a separate temperature or pressure and you can’t have
two different temps or pressures at the same point.
3) Points shown are reporting stations
 There may be areas that do not report or have no station
4) The closer contour lines are to one another, the higher the wind speed.
Where is the wind speed high? Where is it low?
5) Inside a series of closed contours (the contours make a circle) is a High or
Low pressure