Warm-Up What is the device used for mearsuring air pressure called? What is the ultimate energy source for most winds? What is a Jet Stream?

Pressure Centers and Winds Chapter 19, Section 2

Highs and Lows Cyclones – centers of low pressure Anticyclones – centers of high pressure In cyclones, pressure decreases from the outer isobars toward the center In anticyclones, the values of the isobars increase from the outside toward the center

When the pressure gradient and the Coriolis effect are applied to pressure centers in the Northern Hemisphere, wind blows counterclockwise around a low and clockwise around a high In either hemisphere, friction causes a net flow of air inward around a cyclone and a net flow outward around an anticyclone The usual “villain” in weather reports is the low-pressure center

Cyclonic and Anticyclonic winds

Airflow Associated with Cyclones and Anticyclones

Global Winds on a Non-Rotating Earth The underlying cause of wind is the unequal heating of Earth’s surface The atmosphere balances these differences by acting as a giant heat-transfer system The system (atmosphere) moves warm air toward high latitudes and cool air toward the equator On a non-rotating planet, the heated air at the equator would rise until it reached the tropopause The tropopause would act as a lid and deflect the air toward the poles This upper-level airflow would reach the poles, sink, spread out in all directions at the surface, and move back toward the equator

Global Winds on a Non-Rotating Earth

Global Winds on a Rotating Earth When the effect of rotation is added into the system, the two-cell convection model breaks down into smaller cells Near the equator, rising air produces a pressure zone known as the equatorial low (has much precipitation) At 30 degrees north and south latitude, this air comes down, producing hot, arid conditions; this is the subtropical high (many of the world’s deserts are situated around this latitude)

Trade Winds – two belts of winds that blow almost constantly from easterly directions and are located on the north and south sides of subtropical highs Westerlies – dominant west-to-east motion of the atmosphere that characterizes the regions on the poleward side of the subtropical highs Polar Easterlies – winds that blow from the polar high toward the subpolar low Polar Front – stormy frontal zone separating cold air masses of polar origin from warm air masses of tropical origin

Global Winds on a Rotating Earth

Global Winds – Influence of Continents Where landmasses break up the ocean surface, large seasonal temperature differences disrupt the global pattern of pressure zones in the atmosphere Large landmasses can become cold in the winter when a seasonal high-pressure system develops, and the surface airflow will be directed off the land Monsoons – seasonal reversals of wind direction associated with large continents, especially Asia; in the winter, the wind blows from land to sea, and in the summer, the wind blows from sea to land

Global Winds – Influence of Continents

Global Winds – Influence of Continents

Assignment Read Chapter 19, Section 2 (pg. 537-542) Do Section 19.2 Assessment #1-7 (pg. 542)