Chapter 7 Part Ib: Weather and Climate: Coriolis Effect, Convection Cells, and

Global Winds

Major Factors Influencing Climate 1. Composition of the Atmosphere and

Greenhouse Effect

2. Incoming Solar Radiation Angle: leads to uneven heating of troposphere from beneath;

3. Air circulation patterns: determined by - Uneven heating of Earth's surface, due to Earth’s tilt; - Seasonal changes due to Earth's tilt on axis & revolution

about the sun; - Location of land and water masses (land heats up and

cools down faster than water) - Coriolis Effect: caused by Earth's rotation on its axis; - Large scale convection cells

4. Ocean currents (Part II) - influenced by factors that influence air circulation plus

differences in water density.

5. Milankovitch Cycles (Part II): long–term variations in incoming solar energy

• What direction does the Earth rotate?

• View a globe rotating in this direction.

• What is the direction of the motion (clockwise vs. counterclockwise) when viewed from the Northern Hemisphere ?

• What is the direction of the motion (clockwise vs. counterclockwise) when viewed from the Southern Hemisphere ?

• Why?

Wind and the Coriolis Effect

Rotational Velocity Due to the different circumferences at different points on the earth, the rotational velocity varies from 1700 km/hr at the equator to ________ at the poles.

Rotational speed decreases by the cosine of your latitude so that Seattle, which has a latitude of 47.6 degrees, cos(47.6) = .674. The speed is .674 x 1670 = _______ km/hr. You can use this formula to find the speed of rotation at any latitude. •http//www.youtube.com/watch?v=9QDKnQm_poI (first 30 sec only)

Coriolis Effect • The _______________ deflection of

a moving object when viewed from a _________ frame of reference.

• as Earth rotates, surface turns __________ beneath air masses near __________ than near poles, resulting in deflection of wind

• Northern Hemisphere: winds are deflected to the _______.

• Southern Hemisphere: winds are deflected to the _______. http://www.classzone.com/books/earth_science/terc/content/v

isualizations/es1904/es1904page01.cfm?chapter_no=19 http://www.youtube.com/watch?v=aeY9tY9vKgs watch to 2 min, 45 sec

Northern Hemisphere Circulation Patterns: http://www.classzone.com/books/earth_science/terc/content/visualiz

ations/es1905/es1905page01.cfm?chapter_no=visualization Winds blow ________________Winds blow __________________ ______from high pressure areas ____ towards low pressure areas

H L

Hurricanes Hurricanes rotate around ______ pressure, so Northern Hemisphere hurricanes rotate counterclockwise

Southern Hemisphere hurricanes (cyclones) rotate clockwise

http://www.youtube.com/watch?v=i2mec3vgeaI

Pressure and Precipitation • High pressure is associated

with ____________ --Rising air pressure means an area of high pressure is moving in = _______ weather

• Low pressure is associated with _________

--Falling air pressure means an area of low pressure is moving in = _______ weather

High Pressure

Low Pressure

H

In summer, the Pacific Northwest is dominated by High Pressure off our coast (the “Pacific High”), which brings cool, dry air down from Canada

L

In winter, the Pacific Northwest is dominated by Low Pressure, which brings in wet, warm air off the Pacific Ocean (the “Pineapple Express”)

https://www.youtube.com/watch?v=V3I6PBwU5fQ

Floating Bridges, Waves, and Weather • Floating bridges dampen waves,

so water on the downwind side will be calm, water on the upwind side will be choppy

• Waves will be bigger on the north side of I-90 when there is high pressure (wind from the north) = _______ weather

• Waves will be bigger on the south side of I-90 when there is low pressure (wind from the south) = ______ weather

N S

S N

Floating Bridges, Waves, and Weather

• If you see sunny skies, but waves on the south side of I-90 or 520, it means bad weather is moving in

N S

Mini-Review: • Winds blow towards _____ pressure, where air ________________ H2O, which ______________ • The higher the gradient, the higher the ____________ • Winds ________ due to the Coriolis Effect

Winds will “follow” isobars due to Coriolis Effect

Climate: Predominate weather patterns

Where are most rainforests and deserts located and why?

The pattern of a fluid rising and then sinking due to heating and cooling is called a _______________.

Convection Currents

Convection cells, combined with the Coriolis Effect, drive major _____ patterns on Earth

Convection Currents and Global Wind Patterns

Fig. 7–5

• Convection cells mix air in the troposphere & transport ______ & ________ from one area to another. • Relative humidity increases as the air ______ (right side) & decreases as it _____ (left side).

Global Air Flow: Convection Cells •Huge convection cells of air movement result in global patterns of low & high pressure: •_____ pressure near 0º latitude (tropics), leads to high ________ as warm, moisture–laden air rises •_____ pressure at 30º N & S latitudes, results in deserts as ____ air descends; Fig. 7–6

This convection cell between the equator and 30° N or S is called a Hadley cell

• Most rainforests are located at the equator or at 60oN (or S). •Since the equator receives the most direct light, it heats up the most. •As air heats up it expands and

rises (______ pressure Zone). •As the air rises, it cools in the upper troposphere and can no longer hold as much ____________. • This excess water vapor rains

down on the tropical region.

Most deserts are located at 30° N or 30° S.

• Air from the equator, moves towards the poles, _______ and descends back towards the Earth at these latitudes.

• This air is ____ because it lost its moisture at the equator

• As it descends, it warms so it has a greater water vapor capacity. _______________ (% of moisture relative to its maximum) decreases.

• This causes very little __________

60oN

At 60oN and 60oS, convection cells create ____________ air, producing a ______climate. The climate is cold due to the high latitudes

What about the Poles? • Air is ________so the relative

humidity will be ______, and the air will be ______ (it is also so cold that it cannot hold much moisture.

• The poles are sometimes called Polar __________

• Most precipitation is at the equator, since the warm temperatures will lead to the most________________

These Hadley Cells are not fixed right at the equator- they are centered at the location that receives the most direct heating, which drives the process. The area between the two Hadley Cells is called the Intertropical Convergence Zone (ITCZ)

Predict in which season(s): The ITCZ is located at the equator. The ITCZ is to the North of the equator. The ITCZ is to the South of the equator

Discuss with your table partner:

http://www.youtube.com/watch?v=T6Us1sPXBfA

The drier seasons at the equator occur when the ITCZ is shifted __________ from it.

Since the Hadley Cells are centered around the equator for the majority of the year, the diagrams will show it as centered at the equator.

Global Wind Patterns The convection cell

patterns and the Coriolis effect interact to create general global wind patterns.

Winds are named based on the direction of their _________, and reflect wind direction at Earth’s ________ (not at high altitudes). Westerlies= From the ______

Discuss with your table partner: Review the Hadley Cell between the equator (O°) and 30° N. At the ground level does wind blow from North to South or South to North? Hint: Where is the low pressure? (Air moves towards low pressure).

Review which direction does the Coriolis Effect deflects wind in the Northern and Southern Hemispheres.

On the next slide, draw these directions as vector lines and combine them to determine the direction of the wind in this zone. Then repeat the process for the 30 S to equator zone and the 30 N to 60 N zones on the following slides.

30° N ______ Pressure

0° (equator) ____ Pressure

Direction of the Coriolis Force in the Northern Hemisphere: ____________ Be sure to draw the right or left arrow from the perspective of the North/South arrow.

Due to sinking air in Hadley cell.

Due to rising air in Hadley cell.

30° S ______ Pressure

0° (equator) _____ Pressure

Direction of the Coriolis Force in the Southern Hemisphere _____________________

Be sure to draw the right or left arrow from the perspective of the North/South arrow.

60° N ________ Pressure

30° N _______ Pressure

Direction of the Coriolis Force in the Northern Hemisphere _____________________

Be sure to draw the right or left arrow from the perspective of the North/South arrow.

Due to sinking air in Hadley cell.

Global Wind Patterns

Doldrums (fairly still air) along the equator)

Tradewinds blow from the east (0-30N and S)

Westerlies: blow from the west (30-60oN and S),

Easterlies: blow from the east 60-90oN and S)

Fig. 7–4

The Coriolis Effect deflects __________ winds to the right in the Northern Hemisphere, and to the left in the S. Hemisphere, causing the prevailing winds. Winds are named based on the direction of their origin:

Trade winds or Easterlies: equator (0 °) to 30° N and S • Air returns across the surface of the earth to the

_____ pressure zone at the equator (Hadley cell) • It is deflected to the _________ in the Northern

hemisphere. • Moving N to S, right deflection= towards the west. • NE trade winds between equator and 30° N (to SW)

• In Southern Hemisphere, the air is deflected to ____. • Moving S to N, left deflection = towards the _______ • SE trade winds between equator and 30° S (to NW)

30° N

0°

Westerlies: 30°- 60° (both N & S), • Air moves from high pressure zone at 30° N

___________ the poles. • Air moving ___________ the poles goes towards

the east (westerly winds)

•http://www.youtube.com/watch?v=ieILUnkdD90

Microclimate Local climate conditions due to factors such as topography or water bodies are known as microclimate.

For example, as air moves over a mountain range it _________ as it rises. The cooler air can not hold as much moisture, resulting in ________ on the ____________ side.

The leeward side (downwind) of the mountain range is ____________ because the air temperature rises as it moves to lower elevations.

The leeward side of a mountain range is called the ______________.

Prevailing winds during wet weather (from SW)

Small Rain Shadow

Rain Shadow

Discuss with your table partner:

Explain why the west coast of Peru is mostly a desert biome. (Hint: what is the latitude of Peru? )

Air flows _________ from the Equator and gets deflected to the ______ (_____). These are ________ winds, known as the ________ winds. The east side of the Andes is _______ and the west

side is _______ between 0° and 30° S.