Winds Atmospheric Circulation Ch22.3

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Wind is horizontal air movement

Three causes of motion

1. Convection2. Pressure

Differences

3. Coriolis Effect

Convection Currents

Warm air rises and cool air sinks because of densityThis 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 differencesin the atmosphere that are a result of temperature differences

WIND ALWAYS FLOWS FROM HIGH TO LOW PRESSURE

3. Coriolis Effect

The deflection of objects to the right in the northern hemisphere—called the Coriolis Effect Due to rotation of

the earth

effect greatest at poles, decrease to zero at equator

Coriolis Effect

Global Circulation PatternsGlobal 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

ITCZ—Intercontinental convergence zone

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

Trade Winds Winds flowing south

from the horse latitudes is deflected to the west in the northern hemisphere

These aided trading by ship

Jet Stream Jet streams are fast flowing, relatively

narrow air currents found in the atmosphere at around 11 kilometers (36,000 ft) above the surface of the Earth, just under the tropopause.

They form at the boundaries of adjacent air masses with significant differences in temperature, such as of the polar region and the warmer air to the south.

Current jet stream data

Highs and Lows? Winds circle

Clockwise and out around a high

Highs generally mean cold dry air that is sinking

High pressure usually = fair weather

Low Pressure Systems Winds circle

counterclockwise

and into a low Warmer air rises and

cools and forms clouds and precipitation

Low pressure usually = rainy weather

Explore Draw an H in the middle of your paper Draw a

1 inch circle lightly around the H. Place all five fingers inside the circle using

your left-hand if right handed and your right if left-handed.

Standing up if necessary, turn your hand slowly clockwise and gradually spread your fingers and thumb our as your hand turns. Don’t move the map. You hand will end up flat on the paper.

Bring your fingers back inside the circle. Number the starting position of each finger and

thumb with your thumb as number 1, index finger 2, and so on.

Slowly rotate your hand clockwise and gradually spread out your fingers and thumb, stopping after about one inch of motion. Number the position of each finger again.

Continue spreading and numbering every inch or so, until your hand is completely flat on the paper.

Connect each number in a smooth arch, Place arrows at the end of each arch. The result should be a spiral pattern, typical of a high pressure system.

Explore Low Draw an L in the middle of your paper Draw a

1 inch circle lightly around the L. Place your non-writing hand, palm down on

the circle. Rotate your hand counterclockwise, bring your thumb and fingers up into the circle. Practice this twisting motion without moving the paper.

Place your palm down again, and number the position of each finger and thumb, with the thumb as one.

Slowly rotate counterclockwise and gradually bring in your fingers and thumb, numbering the position of the position of each finger after about one inch of motion

Connect each number in a smooth arch, ending with an arrow pointed toward the L. This pattern is typical of a low pressure system.

Wind always blows from high to low

Local Wind PatternsMonsoonsLand breeze/Sea breezeChinook

MonsoonIn winter, air flow is

from cooler (H pressure) to warmer (L pressure) ocean

Air from the land is dry Dry season

In summer, air flow is reversed

Air flows from the cooler ocean to the hotter (L pressure) land

Wet season

Sea Breeze

During the day land heats faster than the water. The hot less dense air rises and cooler air from the sea rushes in to take its place.

Land breeze

Since the air over land cools more rapidly than the air over water, a temperature difference is established, with cooler air present over land and relatively warmer air located over water.

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

Snow may melt or evaporate through sublimation

Loss of moisture due to significant drops in humidity

Beaufort scale Used to estimate

wind speeds Originally used by

sailors

Beaufort Scale on Water

Beaufort Scale on Land

Wind Energy

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)1. The contour intervals

vary

2. Isobars often have an interval of 4

3. 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.

As a result of this every contour line must eventually close on itself to form an irregular circle

Contour lines on the edge of a map do not appear to close on themselves because they run into the edge of the map, but if you got the adjacent map you would find that, eventually, the contour will close on itself.

1) Every point on a contour line represents the exact same temperature or pressure

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