Climate and Weather

The lower atmosphere - composition  Historically – H2, CH4, NH3, H20, etc.  Currently –78% N 2, 21% O 2, 1% Ar,.038% CO 2 –varying amounts of H 2 O vapor (1-4%) –Oxygen added by action of organisms (which?)

The Atmosphere – its layers  Troposphere –extends from surface to 17km –75% of total mass of atmosphere –where weather occurs, air currents etc. –highest atmospheric pressure –temperature decreases with altitude  ends at tropopause –Source of natural greenhouse effect

The Atmosphere  Stratosphere –extends from 17km to 48km –contains less matter than troposphere –ozone layer (1000x more than trop.) –very little water vapor (1000x less than trop) –very calm (good for flying), no weather, suspended matter will stay for many years,

Climate and Weather  What is weather?  What is climate?

Climate and Weather Topics  Solar radiation  Convection Currents  Coriolis effect  Rain shadow effect  Jet streams  Frontal weather  Cyclonic storms  Seasonal winds  ENSO  Milankovich cycles

CLIMATE  The two most important aspects of climate are temperature and precipitation. –These two factors determine what type of species (biome) will be found in a given location.  The climate in an area is determined by 1.Latitude 2.Direction from which winds arrive 3.Proximity to large bodies of water and mountains

Solar Radiation  The same amount of sunlight hits the equator and poles.  However, at the poles the light is spread over a wider area resulting in less intense sunlight, and less heating.  So, the equator is warmer than the poles.

Convection Cells  Warm air rises; cold air falls  Warm air holds more moisture than cold air  When air rises, it cools; when air falls, it warms  SO, warm, moist air rises, cools, and loses moisture as rain; cool, dry air falls, warms, and picks up moisture from the ground. Cool, dry warm, dry Warm, moist precipitation

Global Convection Cells  Wet areas (warm, moist air rising) –0 o (equator) - TRF –60 o (Seattle) - TempRF  Dry areas (cold, dry air falling) –30 o - desert –90 o (poles) – tundra

Surface Wind Currents  The air traveling between these points travels primarily north or south over the Earth’s surface to complete the cells.  This gives rise to prevailing winds that are predictable in all areas of the world. They have been used by sailors for centuries.

Coriolis Effect - Cont  As the earth spins, the air currents (which would ordinarily travel mostly north-south) are deflected by the Coriolis effect. –Deflected to right in NH and left in SH  Coriolis video Coriolis video Coriolis video  This causes winds to form huge circular paths – clockwise in the N. Hem and counter-clockwise in the S. Hem.

Effect of Oceans and Mountains  Oceans –Being near a large body of water tends to minimize temperature fluctuations because of water’s high specific heat capacity  Ex. coastal areas in CA are warmer in winter and cooler in summer than inland areas.

Rain-shadow effect  In areas where there is a strong on-shore wind pattern and coastal mountains, there is a pattern of wet coastal sides and dry inland sides of the mountains.  Mountains force warm, moist air upward; –Air cools, decreasing moisture holding capacity –windward side is rainy  Dry, cool air at the top of the mountain descends the to other (leeward) side –the moisture-holding capacity  as air warms –moisture is sucked from the ground, causing desert

Longterm Effects on Climate - Milankovich Cycles  The Earth’s tilt and orbit tend to wobble over time –Orbit stretches and shrinks in a 100,000yr cycle –Axis tilt changes in a 40,000yr cycle –Axis wobbles in a 26,000yr cycle  These variations impact solar radiation and result in climatic fluctuations  These also limit our ability to know what is “natural” variation and what is “human-induced” variation in temperatures

WEATHER: Jet Stream  Giant rivers of air that flow around the earth.  Their location (north and south) determine which areas receive storms  Their speed dictates how fast weather systems move across land masses.

Fronts  A front is a boundary between two air masses of different temps (and pressures). –Warm front – approaching air is warmer than local air –Cold front- approaching air is colder than local air –Both can cause rain; cold fronts are associated with more severe weather

Cyclonic storms  masses of rotating air caused by pressure differentials between the ground and air.  Tornadoes and form over land are more localized –Form with thunderstorms

Typhoon/Cyclones/Hurricanes  Form in many areas in the world near tropics –US hurricanes mostly form off Africa north of equator.  Are fed by warm water  Decrease with –Wind shear –Moving over cold H2O –Moving over land  Spin CC in NH and C in SH

Seasonal Winds  Many parts of the world experience seasonal winds, or wind direction reversals –Ex. monsoons (rain shadow effect) –Sirocco –Santa Anas

El Nino (ENSO)  The winds in the Pacific normally blow across the surface of the water in the Westward direction  This causes –Rain in Indonesia, mild winters in CA, upwelling off the coast of S.Am., cold surface waters on Eastern Pac. La Nina is an increased flow in this direction.

El Nino (ENSO)  In El Nino years, the winds blow across the surface in the Eastern direction  This causes –Drought in Indonesia, wet winter in CA, (due to movement of jet stream) –no upwelling (fish and mammal die-offs), –warm surface water in Eastern Pac.