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# SU GEO 155 - Moisture in the Atmosphere

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Phase ChangesAir Temperature and Amount of Water VaporHumidityHow to Reach SaturationMechanism of UpliftGEO 155 1st Edition Lecture 8Outline of Last Lecture I. General Circulation and Moisture in the AtmosphereOutline of Current Lecture I. Moisture in the Atmospherea. Phase Changesb. Relationship between Air Temperature and Maximum Water Vapori. Saturationii. Dew Pointc. Humidityd. Ways to Reach Saturationi. Mixingii. Cooling1. Diabatic Cooling2. Adiabatic CoolingCurrent Lecture Moisture in the AtmospherePhase Changes1. Latent Cooling used for:a. Ice to melt to liquid waterb. Water to evaporate to water vapor2. Heat released during:a. Water vapor condensing to waterb. Liquid water freezing to iceAir Temperature and Amount of Water Vapor- Warm air can hold more vapor than cold air1. Saturation Curve – tells how much vapor air can hold at a given temperature2. Dew Point – the temperature that air is saturated atThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Humidity1. Actual Humidity – how much vapor is in the air2. Saturation Humidity – how much vapor the air could holdo Depends on the temperature3. Relative Humidity – how full the air iso Calculated by dividing Actual over Relative Humidity and multiplied by 100%o Need 100% for condensation – the closer the percentage is to 100, the more likely condensation will occur- Air needs to be saturated for condensation to occur- Humidity is measured in g/m^3How to Reach Saturation1. Mixing Cooling – mix together two parcels of air – one at a cooler temperature and one at a warmer temperature – when mixed, they are too saturated to reach the curve so they condensea. Jet Contrails b. Cold, dry land has cold, dry air above it; the land surrounds a warm body of water that has warm, moist air above it; a breeze blows the cold dry air over the body of water causing them to mix leading to saturation and condensation2. Cooling – take unsaturated air and cool it until it reaches dew point and 100% relative humiditya. Diabatic Cooling – change in the amount of energyi. Advection Fog - warm surface with warm air above it, wind blows, moves air to a place where the surface underneath it is cold, warm air loses energy to the cold ground underneath it, air cools, if it reaches dew point – condensationii. Radiation Fog – warm surface has warm air above it, sun goes down so it stops emitting shortwaves, surface emits longwave radiation, ground cools, warm air loses energy to the ground, air cools – if it reaches dew point – condensation will occurb. Adiabatic Cooling – lift parcel of air into the atmosphere, pressure decreases- Forms clouds – precipitationi. Air sinks, compressed by more pressure, energized, adiabatic warmingMechanism of UpliftHow to get air to rise1. Orographic Uplift – cause by a topographic barrier (mountains)a. Air expands and cools, condensation, and precipitationb. Downwind of mountain – as air sinks, there is a “rain-shadow” or dry area2. Frontal Uplift – pushed up by other air3. Dynamic Uplift – pulled up by Jet Stream4. Convective Uplift – hot air

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