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ECU - AS 1300 - Class Notes - Week 5

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ECU - AS 1300 - Class Notes - Week 5

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background image Week 5     9/18-9/21 Relative Humidity(RH) – ratio of water vapor in the air to water vapor in 
air at saturation
Actual Vapor Pressure          Saturation Vapor Pressure Dew point: located on bottom left corner on a weather map o If ground cools to dew point temperature, dew forms (change of  water vapor to liquid: condensation o If the surface dew point temperature is below 0C, frost forms  (change of water vapor to solid: deposition) Humidity – the water in the air doesn’t evaporate so it sticks to surfaces 
(i.e. your skin)
Relative humidity is related to 2 things: o How much water vapor is in the air?
o How much water vapor can be in the air? (change of liquid to 
water vapor: evaporation) Temperature – average kinetic energy of molecules 
(determines how much water vapor is in the air)
Higher temperature=more water vapor/more 
humidity
Higher temperature = more water molecules can “escape” 
(evaporate) from liquid to air
Saturation- when air is full of water vapor o Ex: leave a lid on a jar of water it traps the  water vapor which creates saturation Evaporation rate=condensation rate  Fog- when air is saturated and condensation occurs 
(gas to liquid) only if there are condensation nuclei 
for water molecules to stick on to 
o Condensation is more likely when air is cool         Sea salt, dust, smoke: is needed to help  water       vapor turn to liquid Saturation vapor pressure – amount of water vapor that can be in the air As temp rises, saturation vapor pressure increases At higher temps there can be more water vapor in the air o How can we make the air unsaturated? o Increase the temp...more liquid water molecules can  enter the air 1%– 4% water vapor in the air air pressure – related to the amount of air above your head/weight of 
the air (the sum of the pressures of each gas in the air)
pressure – the force exerted by the air per unit area from the  weight of the column of air above o troposphere = more air pressure Actual Vapor Pressure- the “weight” of water vapor Q: How do you lower the Relative Humidity (RH)? RH = 
100% x
background image Week 5     9/18-9/21 Remove water vapor from the air (at constant temp) - lowers actual 
vapor pressure
Raise temp – increases saturation vapor pressure (heat the air to 
make it less humid)
Clouds and Stability Recap: Cool the air to the dew point temperature = clouds Air near the surface cools at night to the dew point temperature = fog
o
       Both require condensation nuclei Stability – how we know whether air will cool to form clouds Concept of stability- will air rise or sink?
o Make observations:
Lapse rate of the environment: a measurement of the 
temperature with height (change of temperature as you 
move up in the atmosphere)
Environmental lapse rate – actual temperature profile “Sounding”     measured with a radiosonde (on a weather  balloon) Temperature Pressure Relative humidity Wind speed Wind direction *REMEMBER: Dew point less than the temperature = low humidity Stable equilibrium – will return to its original state o Ex: push a ball up a hill it comes back Unstable equilibrium – will not return to original state o Ex: push a ball up a hill it rolls down away from you Will air rise (cool) and form a cloud or will it return back to where it started? *REMEMBER: air rises – expands and cools; air sinks – compresses and 
warms
If rising air is: Dry air-no condensation
Adiabatic – no heat exchange with surroundings
dry     adiabatic lapse rate - as air rises temperature 
decreases:
-10C per 1000m moist air- condensation in a cloud
o latent heat added to air in the cloud
moist
    adiabatic lapse rate- as air rises temperature  decreases:  -6C per 1000m

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School: East Carolina University
Department: Atmosphere Sciences
Course: Weather and Climate
Professor: Thomas Rickenbach
Term: Fall 2015
Tags: relative, humidity, Unstable, and stable
Name: ATMO/GEOG 1300: Weather & Climate - week 5
Description: This week we learned about relative humidity and how to calculate if a cloud is stable or unstable.
Uploaded: 09/21/2017
3 Pages 10 Views 8 Unlocks
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