WEATHER & CLIMATE Atmosphere Composition: - 78% Nitrogen - 21% Oxygen - Also contains: water vapor carbon dioxide ozone

Atmosphere Structure * Air pressure and temperature decrease with height. Temperature Layers 1) Thermosphere- hottest layer (top) 2) Mesosphere- coldest layer 3) Stratosphere- contains ozone 4) Troposphere- weather occurs (bottom)

Atmospheric Layers

Weather Air Mass - area of atmosphere with a consistent temp. and humidity Front - boundary between different air masses example Warm Front- warm air rises above cold air mass - causes clouds & rain Cold Front- cold air replaces a warm air mass - causes larger thunderstorms

Cool air mass Warm air mass Anvil top Warm air mass Cool air mass

Pressure Systems Highs - descending air that pushes outwards - causes fair weather - rotates clockwise in the north hemisphere Lows - rising air that moves outwards - causes rain & storms - rotates counterclockwise in the north hem.

Climate Coriolis Effect - determined by average temp. & precipitation - caused by: 1) Uneven heating (equator vs. poles) 2) Earth’s tilt (seasonal changes) 3) Earth’s rotation (deflects winds circulating air) Coriolis Effect

Uneven Heating

(sun aims directly at equator) 23.5º Spring (sun aims directly at equator) Winter (northern hemisphere tilts away from sun) Solar radiation Summer (northern hemisphere tilts toward sun) Fall (sun aims directly at equator)

Climate is also affected by: 4) Ocean Currents - movements of the ocean bring warm/cold water towards continents - ocean temperature influences overall climate Example -Gulf Stream- brings up warm water -Upwelling- warm water moves out, cold water rises up taking its place -El Nino- calming of winds that cause upwelling

Polar (ice) Warm temperate Highland Warm ocean current Cold ocean current Subarctic (snow) Dry Major upwelling zones Cool temperate Tropical River

5) Greenhouse gases - gases that reflect Earth’s rising surface heat - natural process that keeps the Earth warm - key gases: water vapor, carbon dioxide, methane, nitrous oxide, CFC’s - creates the Greenhouse Effect - also aided by ozone in the stratosphere - blocks UV radiation - creates a thermal protection from hot gases high in the atmosphere

6) Topography (Earth’s surface) Land Breeze - at night, land cools moving air away from land. Sea Breeze - during day, land heats moving air to the land.

- creation of rain on windward side of a mountain, Rain shadow effect - creation of rain on windward side of a mountain, drying the air on the leeward side.

Rainshadow Effect in the Western U.S.

Microclimates Local climatic conditions that may be different from the general climate of the region Influenced by Topography Wind direction Cities Large bodies of water