Atmosphere& Climate Change

Section #1:Climate & Climate Change

Climate

• the long-term prevailing weather conditions at a particular place based upon records taken

• determined by a variety of factors including latitude, atmospheric circulation patterns, oceanic circulation patterns, the local geography, solar activity, & volcanic activity

Most Important Factor = Latitude

• the distance from the equator measured in degrees north or south of the equator

• 0° = the equator• 90° north = North Pole• 90° south = South Pole

Low Latitudes

• those areas closer to the equator receive a greater amount of solar energy throughout the year & the sun’s rays are more direct here which concentrates the sun’s energy

• night & day are about 12 hours long throughout the year

• yearly temps remain consistently high

High Latitudes

• those areas closer to the poles receive less solar energy because the sun is lower in the sky causing the sun’s rays to be spread out over a larger surface area

• hours of daylight can vary throughout the year

• yearly temps vary greatly

Vertical vs. Oblique Solar Rays

Atmospheric Circulation Basics

• cold air sinks because it is denser• air close to Earth’s surface will

warm, expand, & rise• warm air can hold more moisture

(water vapor) that cold air can• as warm air rises, it cools and

condenses into liquid water to form precipitation

Wind

• the movement of air that is created when warm, rising air is replaced at the surface with cooler air

• also affected by Earth’s rotation & the amount of solar energy that warms the surface at each latitude

• global wind patterns are created & show how atmospheric circulation can affect precipitation patterns

Global Winds

Deserts

• air that is warmed at the equator rises & flows northward & southward to 30° north & south latitude where it sinks

• the sinking air compresses causing the temp to rise

• this warmer air can hold a larger quantity of water vapor

• evaporation from the surface below this warm, sinking air is so great that there is little precipitation returning water to Earth, thus creating very dry conditions at the surface

Prevailing Winds

•winds that blow predominantly in one direction throughout the year

•Earth’s rotation cause these winds to be deflected to the right in the Northern Hemisphere & to the left in the Southern Hemisphere

Bands of Prevailing Winds

• Trade Winds = between 0° & 30° north & south latitude

• Westerlies = between 30° & 60° north & south latitude

• Polar Easterlies = between 60° & 90° north & south latitude

• Note: winds are named based on where they come from

Smoke from Fires Showing the Wind Direction

Oceanic Circulation Patterns

•ocean water holds large amounts of heat which can dramatically impact climate patterns

•most surface ocean currents are caused by winds & Earth’s rotation

•these currents redistribute warm & cold masses of water around the planet

El Niño

•short-term (6 to 18 months) periodic change in the location of warm & cold water masses in the Pacific Ocean

•normally weak winds in the west will strengthen & push warm water eastward

•produces increased rainfall in the southern ½ of the U.S., Central America, & upper parts of South America

•causes drought in Indonesia & Australia

La Niña

•the opposite phase to the El Niño cycle

•water in the eastern Pacific Ocean is cooler than usual, resulting in less rainfall

•these two cycles combine to form the Southern Oscillation

Southern Oscillation

Pacific Decadal Oscillation

•a long-term change (20 to 30 years) in the location of warm & cold water masses in the Pacific Ocean

•influences the climate in the northern Pacific Ocean & North America

•affects ocean surface temps, air temps, & precipitation patterns

Topography

•temperatures will drop with elevation at a rate of about 6°C (about 11°F) for every 1000 meter increase in elevation

•mountains & mountain ranges also influence the distribution of precipitation, like creating rain shadows where the mountains block moisture from reaching the opposite side of the mountains

Rain Shadow

A Solar Maximum

•the sun emits an increased amount of ultraviolet radiation

•this produces more ozone•this warms the stratosphere, the lower atmosphere, & the surface of the Earth

Sun’s 11 Year Cycle from Max to Min

Volcanic Eruptions

•during a larger volcanic eruption, large amounts of sulfur dioxide gas can reach the upper atmosphere where it remains for up to 3 years

•here it reacts with smaller amounts of water vapor & dust in the stratosphere forming a layer of haze that reflects enough sunlight to cause global temps to decrease

Seasonal Changes in Climate

•temperatures & precipitation change with the seasons because of the tilt of Earth’s axis

•the angle at which the sun’s rays strike the Earth changes as the Earth moves around the sun

Summers

•during our summer, the Northern Hemisphere tilts towards the sun & receives direct sunlight

•the number of daylight hours is greatest in the summer

•thus the amount of time available for the sun to heat the Earth is greater

•everything is reversed in the Southern Hemisphere

The Earth’s Tilt