Ch. 7 and Supplement 7 Weather and Climate Ch. 7 and Supplement 7 Weather and Climate Adapted from Ms. Sealy’s ppt

Weather –The short-term day-to- day changes in temperature, air pressure, humidity, precipitation, sunshine, cloud cover and wind direction and speed. –Most weather is predicted using: weather balloons, aircraft, radar, and satellites

Climate –is the long term average precipitation and temperature of an area –is determined by air pressure, albedo, angle of sunlight, clouds, distance to oceans, fronts, heat (convection), land changes, latitude, location, humidity, mountain ranges, pollution, rotation, wind patterns and human –Climate is what you expect, weather is what you get!

Climate the average weather patterns for an area over a long period of time (30 - 1,000,000 years). is It is determined by Average Precipitation Average Temperatureand which are influenced by latitudealtitudeocean currents and affects where people livehow people live what they grow and eat Fig. 6.3, p. 123

Shows the precipitation and temperature on one graph. Easy to compare biomes Climatograms

KEY PROPERTIES OF AIRKEY PROPERTIES OF AIR –Cold air is more dense than warm air –Cold air sinks and warms –Warm air rises and cools –Warm air can hold more water vapor than cold air –As air cools, it cannot hold as much water vapor, so it may precipitate ATMOSPHERIC CIRCULATION PATTERNS

Weather Changes Air Mass: a large body of air that has similar temperature and moisture level throughout. Air Masses that affect the US are cA, cP, mP, mT and cT

When air masses meet, the boundary between them is called a front and it causes changes in weather Cold front: when a cold air mass collides with a stationary warm air mass. The result is: thunderstorms, short bursts of heavy rain

Warm Front: when a warm air mass collides with a stationary cold air mass. The result is: warm steady rain

Air Pressure Atmospheric pressure is highest near Earth’s surface due to weight of air above. Plotting areas of same pressure (isobars, usually measured in mm Hg) shows high and low pressure areas.

High and Low Pressure High pressure = cold, dense air, descends toward surface; usually means fair weather. Low pressure = warm, less dense air; rises, expands then cools; often cloudy, stormy. If there’s enough water and condensation nuclei present, rain results.

Weather is also affected by changes in atmospheric pressure High pressure has descending air that moves outward from the center of the high-pressure system. Descending air is warm and dry. The result is: nice dry weather

Low pressure has ascending air that flows towards the center of the low- pressure area. Ascending air- cools and condenses as it rises. The result is: clouds, rain

Energy Transfer by Convection in the Atmosphere Convection Cell

Global Air currents affect regional climates Uneven heating of the Earth’s surface causes the equator to receive more sunlight making it hotter The poles receive less light making them cooler. This causes areas of high and low pressure and global circulation of winds as air moves from high to low pressure

Climate type Cold Cool Temperate Warm Temperate Tropical (equator) Tropical Warm Temperate Cool Temperate Cold Fig. 6.6a, p. 125

Fig. 6.6b, p. 125 Initial pattern of air circulation Deflections in the paths of air flow near the earth’s surface 30°S Easterlies Westerlies Southeast tradewinds (Doldrums) Northeast tradewinds Westerlies (from the west) Easterlies (from the east) 60°S equator 30°N 60°N

Seasons Seasonal changes in temp and precipitation affect climate because the earth is tilted on its axis. It is colder in the winter and warmer in the summer because: The earth is tilted 23.5° on its axis

Fall (sun aims directly at equator) Summer (northern hemisphere tilts toward sun) Spring (sun aims directly at equator) 23.5 ° Winter (northern hemisphere tilts away from sun) Solar radiation Fig. 6.5, p. 124

Coriolis Effect Rotation of the Earth on its axis prevents air currents from moving directly north or south causing the winds to curve

earth_science/terc/content/visuali zations/es1904/es1904page01.cf mhttp:// earth_science/terc/content/visuali zations/es1904/es1904page01.cf m house.org/nesdis/upwelling/bac kground.html

Albedo Is the reflectivity of a surface to solar radiation. Snow= high albedo (0.8) Water= low (0.07) Forest = Average albedo of the earth is 0.37

Altitude For every 1000 feet, there is a 3°F drop in temperature. Every 300 feet in elevation is equivalent to a shift of 62 miles north in latitude and biome similarity.

CLOUDS

Ocean currents Surface currentsSurface currents –Driven by wind (10%) Deep water currentsDeep water currents –Driven by density and gravity

Influenced by Solar heating- Winds Gravity Coriolis oaa/lesson08.htmlhttp:// oaa/lesson08.html oaa/lesson08/l8la1.htm view at homehttp:// oaa/lesson08/l8la1.htm

Polar (ice) Subarctic (snow) Cool temperate Warm temperate Dry Tropical Highland Major upwelling zones Warm ocean current Cold ocean current River Fig. 6.4, p. 124

–Ocean Currents Affect climate Differences in water temp, winds and the rotation of the earth create currents. Currents redistribute heat. For example the Gulf Stream brings heat to Europe and moderates the climateCurrents redistribute heat. For example the Gulf Stream brings heat to Europe and moderates the climate

Water holds a lot of heat – has a high heat capacity.Water holds a lot of heat – has a high heat capacity. This means water takes a long time to heat up and a long time to cool offThis means water takes a long time to heat up and a long time to cool off Oceans moderate climatesOceans moderate climates –Coastal areas have warmer winters and cooler summers OCEAN CIRCULATION PATTERNS

Cool air descends Land warmer than sea; breeze flows onshore Warm air ascends Fig. 6.15a, p. 130 Water also changes climate by causing land breezes and sea breezes

Warm air ascends Land cooler than sea; breeze flows offshore Cool air descends Fig. 6.15b, p. 130

Upwelling Upwelling is created when the trade winds blow offshore pushing surface water away from land. The outgoing surface water is replaced by nutrient bottom waterUpwelling is created when the trade winds blow offshore pushing surface water away from land. The outgoing surface water is replaced by nutrient bottom water

Wind Movement of surface water Diving birds Nutrients Upwelling Fish Zooplankton Phytoplankton Fig. 6.9, p. 126

The El Nino Southern Oscillation occurs every few years in the Pacific Ocean –In an ENSO, prevailing westerly winds weaken or stop –Surface waters along the coast of North America and South America (west) become warmer –Normal upwelling stops –This reduces the population of some fish species –Also causes severe weather, storms in the US especially CA, and drought in southeast Asia

Normal Conditions Cold water Warm water Thermocline SOUTH AMERICA Warm waters pushed westward AUSTRALIA EQUATOR Surface winds blow westward Fig. 6.10a, p. 127

El Niño Conditions Cold water Thermocline Warm water Warm water deepens off South America SOUTH AMERICA Warm water flow stopped or reversed AUSTRALIA EQUATOR Drought in Australia and Southeast Asia Winds weaken, causing updrafts and storms Fig. 6.10b, p. 127

El Niño Unusually warm periods Unusually high rainfall Drought Fig. 6.11, p. 127

La Nina La Ninas follow an El Nino and are characterized by cooling trends. La Nina brings more Atlantic hurricanes, colder winters in the north and warmer winters in the south. Can lead to wetter winters in the Pacific NW, torrential rains in SE Asia, lower wheat yields in Argentina and more wildfires in Fla.

The chemical makeup of the atmosphere affects the weather. Small amounts of water vapor, carbon dioxide, ozone, methane, nitrous oxide and chlorofluorocarbons trap heat in the atmosphere warming the planet. These gases are called: greenhouse gases The greenhouse effect is when greenhouse gases allow light, infrared radiation and UV radiation through to the surface of the earth where it is reflected back into space. The greenhouse gases trap some reflected infrared radiation

Rays of sunlight penetrate the lower atmosphere and warm the earth's surface. The earth's surface absorbs much of the incoming solar radiation and degrades it to longer-wavelength infrared radiation (heat), which rises into the lower atmosphere. Some of this heat escapes into space and some is absorbed by molecules of greenhouse gases and emitted as infrared radiation, which warms the lower atmosphere. As concentrations of greenhouse gases rise, their molecules absorb and emit more infrared radiation, which adds more heat to the lower atmosphere. (a)(b)(c) Fig. 6.13, p. 128

Topography of the earth also creates microclimates A microclimate is small area that has a different climate than the general climate of an area. –Vegetation in an area influences climate: forests stay warmer in the winter and cooler in the summer because of the trees – Cities create heat islands that trap heat and decrease wind speeds

Mountains Affect Precipitation Air rises, cool and rains Air descends, warms and draws up moisture This creates a rain shadow effect where one side of the mountain receives most of the rain and the other side is very dry LOCAL GEOGRAPHY

a Winds carry moisture inland from Pacific Ocean b Clouds, rain on windward side of mountain range c Rain shadow on leeward side of mountain range Moist habitats 15/25 1,000/85 1,800/125 3,000/85 4,000/75 1,000/25 2,000/25 Fig. 6.14, p. 129 The rain shadow effect changes climate Mojave Desert is in the rain shadow of the Sierra Nevada Mts.

Weather Extremes –Hurricanes: most severe of all What is it? Tropical storm with winds greater than 75 mph The bad: loss of life and property The good: flushes out coastline

Hurricane Katrina- August 2005 The most destructive hurricane (economically ) ever. Landed in Louisiana as a category 3 $75 billion and 1,830 deaths 1900 Galveston Hurricane 6,000-12,000 died

Tornadoes: Form when cold dry air collides with warm moist air, which causes the warm air to rise quickly making a funnel cloud

Winds up to 300 mph Classified as F1-F6 (Fujita) Most common in US Usually occur between April-July and often in the center of the country (Tornado Alley)

Risk of Tornadoes Highest High Medium Low Hurricane Frequency High Moderately high Gulf of Alaska Prince Williams Sound CANADA UNITED STATES Grand Banks Atlantic Ocean MEXICO Fig. 6.2, p. 122

Deforestation Urbanization Release of pollutants Burning of fossil fuels HOW DO HUMANS AFFECT CLIMATE?