Cloud Formation All types of cloud formation depend on water vapour condensing in the air Condensation occurs when the air cannot hold as much water as it has dissolved in it Most common reason for condensation is temperature Hot- holds lots of water Cold- hold very little water
Continued In order to form clouds we need condensation in the atmosphere. This can happen in a number of ways: Convection clouds Frontal clouds Orthographic clouds Fog
Convection Clouds The sun heats the ground Hot air rises Air cools and condenses Why does air cool? Warm air rises, less pressure up high, less pressure = expansion = cooling
Frontal Clouds Fronts are regions of air with the same general properties Cold: low temperature, high pressure, and low humidity Hot: high temperature, low pressure, and high humidity On a front line two different air masses interact creating clouds. As the two air masses interact the warm front moves over the cold front.
Orthographic Clouds Works the same way as frontal clouds, but instead of a cold front forcing the warm air mass up, a geographic feature does. Ex. Moist air moves over Vancouver to the base of the Rockies. The warm moist air rises and cools at the top of the mountain. The water vapour condenses and falls as rain or snow on the side of the mountain. The warm, dry air continues down the other side of the mountain, often is called a chinook.
Fog Is a cloud that forms near the ground Can be caused multiple ways: Cool ground cools the air and condenses the water vapour into clouds Warm air drifts over snow covered ground and condenses Moist air drifts over a cold current
Classifying Clouds There are two main shapes of clouds Cumulus- billowing, rounded shapes Stratus- flattened, layered shapes There are ten main clouds: Cirrus- thin, wispy clouds made of ice crystals ( below 8000m) Cirrocumulus- thin, patchy clouds that form wavy patterns ( 6000m to 8000m)
Continued Cirrostratus- thin veiled clouds (6000m to 8000m) Cumulonimbus- large, darker clouds (8000m to 15000m) Altostratus- sheets of grey or blue (3000m to 7000m) Altocumulus- grey or white puffy clouds (3000m to 7000m) Stratocumulus- irregular rolling or puffy clouds (2000m) Cumulus- low, rounded clouds (below 2000m) Nimbostratus- rain clouds, dark wet looking (below 2000m) Stratus- low, uniform sheet clouds (below 2000m)
Regional Weather There are five main types of regional weather: thermals, sea breezes, land breezes, lake-effect snow, and Chinook winds Thermals- solar energy heats up the land, the energy is converted to heat and warms the air it comes in contact with Warm air expands and becomes less dense The less dense air rises and is replaced by cooler, denser air, setting up a convection current A local convection current set up during the day is called a thermal of a thermal updraft
Continued Sea breezes- when a thermal forms near a body of water it is called a sea breeze Land warms faster than water The convection current moves the air from the water to the land Land Breezes- land cools down faster than water The air above the water rises and is replaced by cooler air from above the land This causes a land breeze, a convection thermal that flows form land to water
Continued Lake effect snow- moisture laden air rises and moves across a body of water and reaches the far side of the body of water The temperature of the land is cooler so the moisture becomes snow Chinook winds- on the windward side of the mountains, orographic lift causes water vapour to condense and make clouds and snow or rain Condensing water vapour releases energy, warming the air The air that sinks on the leeward side of the mountain is dry but gained some heat The resulting warm dry air is called a chinook
Weather Systems Air masses have the properties of the surface that they originate over Form over water = humid (maritime) Form over land = dry (continental) Form in the south = warm (tropical) Form in the north = cold (polar) Ex. Colorado Lows: maritime tropical Bring in most of the blizzard in Manitoba
Thunderstorms Most often caused by convection clouds, usually paired with a frontal system The one thing it needs is rapidly rising air Ex. Sun heats ground, air continues to rise “pushing” cloud up. Makes a anvil shaped cumulonimbus cloud, top is flattened by jet stream Rising and falling air rub against each other, friction creates large static charge, or in other words, lightning Sheet lightning is the positive and negative charges in the cloud “jumping” to one another Fork lightning is the negative charge of the base of the cloud “jumping” to the positive ground
Hail Rain falls and the wind blows it back up The rain freezes and falls Ice gathers more water and is blown back up The cycle continues until the ice is too heavy Ice falls to earth as hail, the stronger the wind, the larger the hail
Tornados When the updrafts are strong enough tornados develop Anytime there is a severe storm it carries the risk of a tornado If hail forms, it sometimes is a precursor to a tornado When the updrafts are strong enough the air begins to swirl When the swirling winds develops in the clouds it does not “touch down” on its own When conditions are “right” a large sudden down pour causes a rear flanking down draft This down draft causes the fennel down to a “touch down”
ContinuedScale Winds (km/h) Length of path Width Damage (km)0 (very weak) Under 116 Under 1.5 Under 15m Minor roof, tree, chimney, antenna, and sign damage1 (weak) 117-180 1.6-5 50m Barns torn apart, trees snapped2 (Strong) 181-252 5.1-15.9 160m Roofs torn off buildings, trees uprooted3 (severe) 253-332 16-50 61-500m Weaker homes completely disappear4(devastating) 333-419 51-159 0.5-1.4 km Cars thrown, walls of homes blown apart5 (incredible) 420-512 160-507 1.5-16 km Strongly built homes completely blown away
Hurricanes (Cyclogenesis) Northern Hemisphere: hurricane Southern Hemisphere: hyphoon Storm develops in Africa Warm water feeds the storm Hits land and dissipates quickly The circular shape I caused by the coriolis effect Warm air rises and circles in rings, causing very low pressure The eye is the center, it has extremely low pressure
Continued The pressure isn’t enough to pick you up but is low enough to raise there ocean level This along with waves is the “storm surge” and is the most damaging part of the storm The water level rises between 1 and 6m If this happens at a high tide dyke or a levee, they are often breached
ContinuedCategory Max surface Min surface Storm surge Remarks pressure pressure (m) (km/h) (kPa)1 (minimal) 119-153 98.0 or more 1.0-1.7 Damage to trees and signs, flooding in low- lying areas2 (moderate) 154-177 97.9-96.5 1.8-2.6 Trees blown down, evacuation of shore areas3 (extensive) 178-209 96.4-94.5 2.7-3.8 Serious coastal flooding, mobile homes destroyed4 (extreme) 210-249 94.4-92.0 3.9-5.6 Extensive damage to buildings, evacuation from shore required5 (catastrophic) Above 250 Under 92.0 Above 5.6 Buildings destroyed, evacuation up to 20km inland required
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