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G107 Physical Geography

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Section II Power Point Slides

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Winds and Global Circulation Wind is air in motion Results from difference in pressure between two

areas Pressure is force acting on an area Standard Pressure… Standard barometric pressure

(SBP) is pressure at mean sea level Pressure Scales (numbers at mean sea level)

Inches of mercury (29.92 in) Centimeters (76 cm) Millibars 91013 mb)

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Winds Pressure Gradient Force… mass movement of air High temp results in low pressure & low temp

results in high pressure Pressure gradient, Friction, Gravity and Coriolis

effect affect wind speed and direction Coriolis effect is due to earth’s rotation & it is the

deflection of wind to the right in the northern hemisphere or to the left in the southern hemisphere (imagine yourself going in the same direction as the wind)

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Circular Moving Air Cyclone is the circular moving air mass

around a low pressure center Anticyclone is a circular moving air around

a high pressure center Note the pattern of cyclone/anticyclone in

both the northern and southern hemispheres

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Circular Moving Air Note the pattern of cyclone/anticyclone in

both the northern and southern hemispheres

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Circular Moving Air

Note the convergent and divergent winds

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Circular moving air in Ft. Wayne Photos my Burnet

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Tornado Pictures from Ft. Wayne

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Global Air Pattern Low and High pressure areas of the world (linked

to solar radiation/temperature) Pressure zones include low equatorial zone and

midlatitude high pressure zone The NE Trades and SE Trades – air moves toward

the equator from the north and south respectively Where the two trade winds collide, the area is

called Intertropical Convergence Zone (ITCZ) and when they do not collide violently, the are is called Doldrum

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Global Air Pattern Contd. Global wind pattern

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Local Winds Land & Sea breezes

Heating of the land and sea Mountain and Valley Winds Drainage winds (e.g. Chinook, Bora, Taku,

Foehn, Mistral, & Santa Ana)

Winds Aloft- winds at high altitude Geostrophic winds (Jet stream & Rosby waves)-

winds flow parallel to isobars

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Ocean Currents Currents- form when wind moves over water

surface in a given direction... frictional force Ocean current could be warm or cold Some ocean currents are

Alaska, Agulhas, Antartic circumpacific current, Benguela, Brazi, California, Canaries, Falkland, Guinea, Gulf Stream, Kuroshio (Japan), Labrador, North Atlantic drift, N. Equatorial, Oyashio (China), Pacific, Peru, S. Equatorial, and West Wind Drift.

Circular moving ocean currents are called GYRES

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Atmospheric Moisture and precipitation Humidity – amount of water vapor in the air Humidity can be measured three different ways

Absolute Humidity…mass of water vapor in a given volume of air

Specific humidity… the mass of water vapor in a given mass of air

Relative humidity… ratio of water vapor present in the air compared to the amount of water vapor that will be present when the air is saturated at the given temperature

Concept of saturation point

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When air becomes Saturated Air can become saturated either with

addition of water or cooling of the air. When air cools such that it becomes

saturated, the temperature at which it becomes saturated is called the DEW POINT.

Cloud is the first physical evidence that the air is saturated

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Clouds Several cloud types… but they all begin as cirrus

(high altitude clouds that are feather like), stratus (form layers), or cumulus (cotton bulb-like or cauliflower like)

Clouds are classified based on elevations High > 7.6 km e.g. Cirrus, cirrostratus, cirro cumulus Intermediate (middle) 2-7.6 km (stratus, stratocumulus Low 0.2 km. Cumulus, cumulonimbusNimbus or Nimbo are prefix or suffix in cloud

terminology that indicate precipitation

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Clouds

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Classification of Clouds

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Precipitation forms Drizzle Rain Snow Hail Sleet

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Classification of Precipitation Orographic- rain shadow effect

Best found near the west coast… effective side is east of the west coast mountains

Convectional Precipitation Cyclonic/Frontal Systems Convergent

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Weather systems Air mass- covers large area with similar

temperature, pressure and moisture Air Mass properties depend on

a) source region and b) region over which the wind passes

The area over which an air mass forms is called the Source Region

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Types of Air Masses Classified is based on latitudinal position

and underlying surface (water or land) Artic (A) mA (maritime) & cA

(continental) Antarctic (AA) mAA & cAA Polar (P) mP & cP Tropical (T) mT & cP Equatorial (E) mE & cE

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Fronts When air masses move, the leading edge is called

a FRONT There are four types of fronts

Warm

Cold

Stationary

Occluded

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Traveling Cyclones Wave cyclone (midlatitude and Artic

regions) Tropical (Hurricanes & Typhoons) Tornado (small storm related to sever

convectional activity)

Why do most storms occur in Spring and Summer?

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Weather and Climate Weather involves the every day weather related

activities Elements of weather include temperature, cloud

types, cloud cover, wind, wind direction, fog, precipitation, sunshine, etc.

Climate is the average weather condition of a given location Takes into account the extreme weather conditions

also.

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Physical components of climate Radiation Sensible heat Barometric pressure Winds Relative and Specific Humidity Dew Point Cloud cover and type Fog Precipitation type and intensity Evaporation and Transpiration Cyclones

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Climate Controls Latitude Distribution of land & water Ocean current Mountain

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Climate classification Criteria Thermal regimes Precipitation Air masses and Frontal zones Koppen-Geiger climate system

Five major climate groups A B C D E

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Key words Air mass, relative, specific, absolute

humidity, dew point, rain shadow, pressure, cloud types, climatic controls, winds, cyclones, anticyclone, coriolis effect, winds aloft, Geostrophic wind, front types, precipitation types, climates, climographs, nimbos, nimbus, cumulonimbus, convergent, divergent