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Relative Humidity changes when: 1. Atmosphere gains or loses water vapor - evaporation 2. temperature changes - lower temperature = relative humidity rises - raise temperature = relative humidity decreases
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Maximum water vapour possible can change which will change the percentage even if there is still the same amount of water vapour.
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Specific Humidity:actual quantity of water held by a parcel of air Grams of water vapor per kg of airg/kg Highest in equatorial zonesLowest near poles
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Dew point temperatureTemperature at which air with a given humidity will reach saturation when cooled without changing its pressure Warmer air - greater max water vapour possibleCooler air - lesser maximum water vapour possible
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Adiabatic Principle: the physical principle that a gas cools as it expands and warms as it is compressed Change in temperature:- caused only by a change in pressure NOT caused by heat floing in or out of the gas
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Adiabatic Process - NO heat is transfered to or from, absence of heat transfer. Dry adiabatic rate 10C/ 1000m(for air less than saturated) Moist adiabatic rate 6C/1000m(for saturated air)
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Atmospheric pressure DECREASES with altitude so...As a parcel of air rises, - pressure on the parcel decreases- air expands and cools
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As a parcel of air descends,- pressure on the parcel increases- air is compressed and warms
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Air parcel cools internally as it expands under lower air pressure, as it RISES
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Air parcel heats internally as it is compressed by higher air pressure, as it DESCENDS Cooling by expansion (rising)Heating by compression (descending)
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Unstable air - when air parcel is warmer than the aurrounding air and so continues to rise Stable - when air parcel is at the same temp as surrounding air and does not rise Conditionally unstable conditions - air parcel rises only if it is saturated.At this temp, condensation begins and the latent heat of condensation is released, warming the air parcel and making it unstable as long as this situation persists.
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TEST If ELR is between DAR and MAR - conditional instability. If it cools to the dew point, ex. the mountains of a summers day. Air starts off clear, about noon clouds start forming (once we have moisture forming it becomes unstable - conditional instability
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ELR<MAR = StableELR>DAR = Unstable
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Dry adiabatic lapse rate: rate at which rising air is cooled by expansion when no condensation is occurring:Dry value is 10 degrees C per 1000m Wet adiabatic lapse rate: rate at which air is cooled by expansion when condensation is occurring: Ranges from 4-9. For us, it's 6 degrees per 1000m
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Types of Atmospheric Stability MED(moist, environmental, dry) ELR (12C) > DALR (10/1000m) = STABLEELR (8C) < DALR (10/1000m) UNSTABLEELF = DALR = NEUTRAL MALR (6C/1000m) < ELR (8C/1000m) < DALR (10C/1000m)CONDITIONALLY UNSTABLE
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When you get condensation, that's when you get the release of latent heat inside the bubble of air (no exchange of heat with surroundings - adiabatic) that then offsets the DALR and you get MALR - becomes unstable.
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Clouds - consist of...water dropletsice crystals, or both.
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Condensation nucleus: a tiny bit of solid matter (aerosol) in the atmosphere, on which water vapor condenses to form a tiny water droplet. ALWAYS need a nuclei to form on. Nuclei can be small bits of dust or salt crystals from the ocean. Why you get more precipitation over urban areas bc there's more dust/pollution.
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Different cloud families mean different weather.
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High Clouds (Cirrus) - clouds that are very high. Whispy clouds. Summers day. typically formed from ice crystals. Middle Clouds (Altostratus) - mean weather system is moving in. Warm patch of weather coming in. Spread over large area. Low Clounds (Stratus) - blanket of clouds. Typically not much vertical development. Typically when there's a warm fron comin in. (maybe 12 hours or so)
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Clouds with VERTICAL development. Cumulus clouds (heat clouds) air being forced over a cold front. Cumulus fair weather - scattered Cumulonimbus - thunderstorm clouds
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Anvil head - clouds are rising through the freezing air and you get ice crystals - how you get big thunderstorms. Nimbo - means it's raining.
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Fog is a cloud layer at or close to Earth's surface. Radiation fog - formed when temperature of the air at ground level falls below dew point.
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Advection fog: forms when warm moist air moves over a cold surface. (common over oceans - sea fog)
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To form precipitation, air must move upward and chill by adiabatic processes. Four ways for air to move upward:
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1. Orographic precipitation2. Convectional precipitation3. Cyclonic precipitation4. Convergence
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Orographic precipitation: precipitation induced when moist air is forced over a mountain barrier.
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Rain shadow: a belt of dry climate that extends down and beyond the leeward slope of a mountain range leeward - the side sheltered or away from the wind.
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Convectional precipitation: precipitation induced when warm, moist air is heated at the ground surface, rises, cools, and condenses to form water droplets, raindrops, and rainfall.
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Thunderstorm: intense local storm associated with a tall, dense cumulonimbus cloud in which there are very strong updrafts of air .Conditions:1. Warm moist air2. an ELR in which temp decreases more rapidly with altitude than it does for either the dry or wet adiabatic lapse rates.
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