III. Winds & Fronts

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Air movements on the earth. Winds Pressure Gradient. What makes the wind blow? All winds result from uneven heating and pressure of the atmosphere. Land heats faster than water. Warm air over land expands and becomes less dense (lower air pressure). Colder air rushes to fill in the lesser pressure. Winds always blow from high pressure to lower. The larger the difference between the warm air (low air pressure) and the colder air (higher pressure) the stronger the winds. This pressure difference is the pressure gradient

A. How wind develops: -Caused by a difference in air pressure due to unequal heating of the atmosphere. 1. Two types of winds: a. local b. global

B. Winds are created by…. 1. Heating the air, decreases pressure (warm air rises creating low pressure) 2. Cool air rushes into replace the warm air (cooler dense air, produces high pressure) 3. As air goes from high to low pressure, winds form. Based on your knowledge about the pressure gradient ( the difference between two pressure systems)which states would be susceptible to the greatest wind speeds?

C. Local Winds 1. Sea breeze- warm air expands & rises over land, & cool sea/lake air moves toward the land.

2. Land breeze- warm air over water rises, cool land air moves toward the water. How would a Mountain Valley wind occur?

Winds occur on a larger scale. Read pages Red text

Air rises in warm regions where pressure is low (convection) ex the tropics Air descends in cold areas where pressure is high (subsidence) ex the poles Remember! Air rises over warm areas and sinks over cold areas

D. Global Winds 1. Don’t travel North and South because of the Earth rotating on its axis. a. 4 Types of Global Winds – Doldrums: calm, warm winds at equator – Trade Winds: 30 ° N&S of equator, gentle/sinking air – Prevailing Westerlies: ° Strong (big temp. diff.), impacts U.S. weather – Polar Easterlies: ° cold, weak winds from poles

D. Global Winds Polar Easterlies Cool air descend Trade winds Prevailing Westerlies Polar Easterlies Warm air rises Doldrums d. c. e. f. d. b. a. c.

Coriolis Effect Coriolis effect Here is how it works. Caused by earths rotation. Felt by all objects, even air and ocean currents, moving toward or away from the equator. Suppose a rocket is fired from the North Pole aimed directly at central Kansas. Also that it will take the rocket an hour to fly the distance. During that hour the earth will rote 15 degrees. So the rocket will land 15 degrees farther to the west. Aprox 1295 km away from the intended target. Global winds have curved paths due to earth’s rotation. This deflection is called the CORIOLIS EFFECT.

Wind and Coriolis The Coriolis effect deflects the earth's winds. Air flows from high to low; the C.e. turns the wind to the right. The turning continues until the C.e. exactly balances the pressure gradient. In the northern hemisphere the air flowing out from a high turns to the right into a low area which is receiving winds blowing to the left or counterclockwise.

Factors that affect wind direction. 1. Pressure Gradient Difference between the High and low pressure systems.. On a map the highest winds will occur were the isobars are closest 2. The Coriolis effect The tendency of an object moving freely to curve away from its path of travel. 3. Friction. Friction between the air and the ground slows surface winds. Because the Cor. Effect is weaker on slower moving objects winds are deflected less.

Jet Stream- Happens 10 km up. Are bands of high- speed steady winds. Hundreds of Km wide but very thin. Blow generally from west to east mph. Complete the topic questions from pg 558 Red text. 1-3 on a separate sheet of paper Honors only: Blue Text pg. 433 Crit. Thinking 13,15,16 and Interpreting Maps 17-23

F. North American Air Masses Two factors influence Global air masses… Temp and Humidity. Temperature 1. Air masses from N 50º latitude POLAR (P) 2. Air masses from the tropics TROPICAL (T) General global air masses

North American Air Masses Humidity 1. Air masses from over oceans MARITIME (m)very humid. 2. Air masses from over land CONTINENTAL (c) more dry.

Local Air Masses mP mT mP cP cT mT

Fronts.

G. Front 1. The Boundary between two different air masses. a. Water vapor drives storm systems

D. Types of Fronts Name: Cold Front What’s happening: cold air replacing warm air Result: Lot’s of rain, cool temps, thunderstorms, vertical cloud formation.

Name: Warm front What’s happening: warm air replaces cold air Result: little rain/clouds, warmer temps.

Name: Stationary front What’s happening: neither masses move the other Result: clouds & precipitation

Name: Occluded front What’s happening: warm air mass caught between cold air masses Result: warm air cut off, cloudy & rain

pg. 585 #’s 1-2 (red book) Sketch & color diagram 29.8 pg. 548 (black book) Pg. 555 do the critical thinking Map. Front questions Blk Text pg. 549 #’s 6 and 7. Create, Draw & color a weather Super Hero or Villain. ◦Include your hero/villains powers and weaknesses ◦Give your hero/villain a catchy name & costume