19.2 Pressure Centers & Winds

Highs & Lows

0Cyclones – centers of LP

0In cyclones, the pressure DECREASES from the outer isobars toward the centers.

0In anitcyclones, the isobars INCREASE from the outside toward the center

Cyclonic & Anticyclonic Winds

0When Pressure Gradient & Coriolis Effect are applied to pressure centers in the NH, winds blow inward & counterclock wise around a low. Around a high they blow outward & clockwise

02 Most Significant factors that affect wind are0 Pressure Gradient0 Coriolis Effect

Weather & Air Pressure

0Rising air = clouds & precipitation

0Sinking air = clear skies

Global Winds

0The atmosphere balances these differences by acting as a giant heat transfer system.

0This system moves warm air toward higher latitudes & cool air toward the equator (BALANCE)

0Trade Winds0Westerlies0Polar Easterlies 0Polar Front

NON ROTATING MODEL

ROTATING MODEL

Influence of Continents

0ONLY true continuous pressure belt is the subpolar low in the SH (bc its uninterrupted)

0Monsoons – seasonal reversal of wind direction associated with large continents, esp. Asia0 Winter = winds blow from land to sea0 Summer = winds blow from sea to land

Review Questions

0How do winds blow around pressure centers in the NH?

0Compare and contrast cyclone & anticyclone0Describe how the atmosphere balances the unequal

heating of Earth’s surface.0What is the only TRUE continuous pressure belt?

19.3 Regional Wind Systems

Local Winds

0Caused by either topographic effects or by variations in surface composition in the immediate area

0Coastal land is heated more than the water during the day causing air above the land to be warmer and rising = lower pressure areas

0On mountains, the air along the slope is heated more than the same elevation over the valley

How Wind is Measured?

02 Basic Measurements: direction & speed0North winds blow from the N to the S0East winds blow from the E to the W0Instrument used to determine wind direction

= vane0In US westerlies are always moving weather

from W to E across the continent0Instrument used to measure speed:

anemometer

El Nino & La Nina

0Southern Oscillations – irregular intervals of 3 – 7 yrs., warm countercurrents become unusually strong & replace normally cold offshore waters with warm water from equator -> El Nino

0La Nina – opposite – researchers have come to recognize that when surface temps. In the eastern Pacific are colder than avg. La Nina is triggered

Review Questions

0What are locals winds and what are they caused from?0Describe the general movements of weather in the US0How is La Nina recognized?