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Monday, October 07, 2013

Geography 02:

Weather & Climate

Weather and Climate

►Weather

Day-to-day variations in temperature and precipitation

►Climate

Statistical summary of weather conditions through time

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Solar Energy

►Radiant energy from sun

►Powers circulation of atmosphere and oceans and supports life on Earth

►Varies across Earth’s surface

Insolation

►Amount of energy intercepted by Earth

► 2 factors

Intensity of solar radiation

Angle of incidence

Duration of sunlight

Varies by season

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Intensity of Solar Radiation

Angle of incidence

Varies daily & seasonally

Axial tilt = 23.5 degrees

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Length of Day

►Total heat received by a place is dependent upon the number of hours of sunlight and its intensity

►Equator

►Higher latitudes

Seasonal Variation in Radiation

►Varies because of angle of incidence, day length, distance from sun

►Equator

►High latitudes

►Temperature

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Heat Transfer

►Responsible for movement of energy from place to place on Earth

►Radiation (radiant energy) Energy

Electromagnetic waves

Radiate

Examples

2 wavelengths: Short (sun) and long (Earth)

Greenhouse Effect

►Short vs. long waves

►Greenhouse gases

Critical to heat exchange

Water vapor, carbon dioxide, ozone, methane

►Increased greenhouse gases = increased global warming

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Latent Heat Exchange

►Transfers energy from low to high latitudes

►Causes precipitation

►Two types Sensible

►Detectable by touch

Latent ►“In storage” in water

and water vapor

►Latent heat exchange

Heat Exchange & Atmospheric Circulation

►Convection Upward movement of fluids caused by heating

“Boiling water”

Atmosphere

►Advection Horizontal

movement of air

Monsoons

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Precipitation

►“Normal” precipitation

►Condensation Conversion of water from vapor to liquid state

►ALL air holds water Dependent on temperature

►Saturation vapor pressure Maximum water vapor air can hold at a

particular temperature

Relative Humidity

►Water content of air

► Percent of water air could hold at a given temperature

► Fluctuates hourly as temperature changes

► Saturation point = condensation

►Condensation = clouds

Temperature Relative Humidity

86 degrees F 50% if holds half water vapor possible

71 degrees F 75%

60 degrees F 100%

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Convectional Precipitation

Warm, humid air rises, expanding and cooling

Saturation point is reached

Clouds form

Adiabatic cooling ►Decrease in temperature that results from

expansion of rising air

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Orographic Precipitation

►Wind forces air up and over mountains

►Rain on windward side

►Desert on leeward side: Rain shadow

►Examples

Cascades & Sierras

Rockies

Exception: Appalachians

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Frontal Precipitation

►Air forced up a boundary between cold and warm air masses

►Air mass Region of air with similar characteristics

►Cold front Cold air mass moves towards warm air mass

Typical weather

►Warm front Warm air mass moves towards cooler air mass

Typical weather

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Pressure and Winds

► Air density

Warm air = less dense

► Pressure gradient

Difference in pressure between two places

► Coriolis Effect

Indirect, curving path of wind caused by rotation of the Earth

Strongest in polar regions

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Coriolis Effect

Global Circulation ► 4 zones

Intertropical convergence zone (ITCZ)

► Convectional precipitation

► Trade winds

Subtropical high-pressure zones

► Areas of dry, bright sunshine, little precipitation

Midlatitude low-pressure zones

► Polar front

►Westerlies

Polar high-pressure zones

► Dense air, high pressure

► Little precipitation

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Ocean Circulation Patterns ►Wind creates waves

and currents

►Gyres

Wind-driven circular flows

►El Niño

Occasional shifts in ocean circulation

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Storms

►Cyclones Large low-pressure areas

Winds ►Counterclockwise in Northern Hemisphere

►Clockwise in Southern Hemisphere

►Hurricanes and typhoons Tropical cyclones

Need warm, moist air ►Most powerful over oceans

Storm surge ►Elevated sea level in center of storm

►Midlatitude cyclones

Climate

►Summary of weather conditions over several decades or more

►Influences

►Changes over time

►Humans and climate

►2 primary measures Temperature

Precipitation

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Air Temperature

►Variation

Latitude

Seasonal solar energy input

Elevation

Topography

Precipitation ►Variable between places and through

time

►Worldwide variation = 0-120 inches

►Global circulation patterns

►Amount of precipitation

►Reliability

►Regularity

Soil saturation

Human adjustments

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Classifying Climate

►Allows analysis and planning

►Communication

►Köppen System

Wladimir Köppen, 1918

Distribution of plants

5 basic climate types with subdivisions

Most widely used system

Climate Regions

►Horizontal bands based on latitude

►Climate regions similar to

Bioregions

Temperature and precipitation maps

►Other influences

Continents

Mountains

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Humid Low-Latitude Tropical Climates (A)

►Warm all year

►Humid tropical (Af, Am) +/- 10 degrees N/S of equator

Warm & humid; Little seasonal temp. variation

High temps; Rain

Amazon River Basin, Equatorial Africa, Islands of Southeast Asia

► Seasonally humid tropical climates (Aw) Concentrated rainfall

►Seasonal shifts of ITCZ

Central & South America

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Dry Climates (B)

►Dry climates, BW & BS 35% of Earth’s land area

Border low-latitude humid climates on North and South

North Africa, Central Asia

►Desert climates (BWh, BWk) Warm and dry

Subtropics

New Mexico (BWh), China (BWk)

► Semi-arid climates (BSh, BSk) Transitional areas between deserts and humid areas

Grasslands, steppes

Seasonal temperature contrasts

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Warm Midlatitude Climates (C)

► Seasonal temp variation

► Less precipitation

►Humid subtropical (Cfa, Cw) Latitude: 25-40 degrees on east side of continents

Eastern China, SE US, Brazil, Argentina

►Marine west coast (Cfb, Cfc) Continental west coasts, 35-65 degrees

Mild climates

California to coastal Alaska, Southern Chile

►Mediterranean climates (Cs) Dry summers with seasonal precipitation

Cold Midlatitude Climates (D)

►Humid continental climates (Dfa, Dwa, Dfb, Dwb) Strong contrasts

Remote from oceans = little moisture

Interior & eastern side of Northern Hemisphere Continents (35-60 degrees)

► Subarctic climates (Dfc, Dwc, Dfd, Dwd) Northern edge of humid continental climates

No agriculture

Northern Hemisphere only

Vegetation: Boreal forests

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Polar Climates (E)

►High-latitude climates

►Low temps

►Extreme seasonal variability

►Tundra climate (ET) Permafrost

Tundra

►Ice-cap climates (EF) Near poles & high altitudes at low latitudes

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Climate Change

► 3 hypotheses

►Astronomical

Geometry of Earth’s orbit

Sunspots

►Geologic

Continental drift

Volcanic eruptions

►Human

Atmospheric Changes

Vegetation Changes