Adiabatic

• Explanation:
• When you change the temperature of air _________ adding or subtracting ______, you’ve changed the temp adiabatically
• How does this happen?

Adiabatic

• Equation of State: pV = nRT
• Don’t worry about the n and R, they are constants
• p (pressure), V (volume), and T (temp) are related such that a change in one forces a change in one or both of the others

Adiabatic

• We have our ________ of air--our imaginary volume of air around a few hundred cubic meters in size
• A change in p can result in a change in T, and they are ___________ related--if p goes down, T goes ____
• A change in p can also result in a change in V, and they are __________ related--if p goes down, V goes ____

Adiabatic—Fig. 4-18

Adiabatic--See Fig. 4-18

• When the parcel rises, pressure goes down, so the parcel cools and expands
• When the parcel sinks, pressure rises, so the parcel warms and compresses
• As long as no heat was being exchanged between the parcel and the outside air, the parcel was ascending and descending adiabatically

Adiabatic

• When the parcel is moving adiabatically and is not saturated, it cools or warms at the dry adiabatic lapse rate
• The dry adiabatic lapse rate is ~ 10ºC / km (actually 9.8ºC / km)--so for every km the air rises, it cools by about 10ºC
• This dry rate is always 10ºC / km, so remember it!

 Adiabatic

• Eventually, as the air rises it will _____ to the dew point and become _________
• A ______ will now form because as the parcel continues to _____ after reaching saturation, net ____________ must occur
• The altitude at which a parcel reaches saturation and begins ______ formation is called the lifting ___________ level (____)

Adiabatic

• Once the condensation begins, the rising parcel will cool at a new lapse rate
• Why? The condensation is releasing heat to the air in the parcel, which partially offsets the cooling of 10ºC / km as the parcel rises
• So as the parcel continues to rise, it will not cool as fast as it did when it was "dry"
• Now it will cool at the wet adiabatic lapse rate, usually between 5º and 9ºC / km

Adiabatic

• If the water vapor content of the air is ____, when net condensation occurs and the parcel rises wet adiabatically, its rate will be close to the dry rate, around ___ ºC / km
• If water vapor content is _____, the _______ will be slower due to more condensation, so the rate might be closer to ___ ºC / km

Adiabatic—Fig. 4-19

Notes in the following section have no blanks to fill in and will not be covered in lecture, but you should study them and their relevant pages of the book as part of your preparation for Test #2

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Processes That Lift Air

• The tendency is for air to resist upward movement
• What causes air to rise?
• Orographic Lifting (the word “orographic” means “pertaining to mountains”)
• Frontal Wedging
• Convergence
• Localized Convective Lifting

Orographic Lifting

• Orographic Lifting: areas of elevated terrain, like mountains, act as barriers to airflow
• Air is forced up over the mountains
• As it rises, the air cools to condensation and clouds and precip can form on the windward side
• Some of the rainiest places in the world are on windward mountain slopes

Orographic Lifting

• Once the air comes down the leeward side, most of the moisture has already been rained out, and clouds quickly evaporate
• Air compresses and warms on the way down
• Locations on the leeward side are often hot and dry—rain shadow deserts

Orographic Lifting—Figs. 4-20 and 4-C

Frontal Wedging--Fig. 4-21

Frontal Wedging

• Fronts act as boundaries between different air masses, like a warm, moist air mass on one side, and a cool, dry air mass on the other side
• The cooler air mass has denser air which will lift the warmer air up over it

Convergence

• Convergence: air flowing together
• Whenever air flows together at the surface, it has nowhere to go but up
• You can have winds from different directions coming together
• You can also have faster winds behind slower winds—faster moving air catches up and causes a pile-up of air—air is forced to rise

Convergence—Fig. 4-22

Localized Convective Lifting

• What we’ve talked about before: warm air rises
• Unequal heating of Earth’s surface causes some pockets of air to be warmer than their surroundings—these pockets are called thermals
• Thermals may rise high enough to form clouds and precip

Localized Convective Lifting—Fig. 4-23

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Atmospheric Stability

• We can determine stability by comparing the temp of the ______ to the temp of the ___________ (the air outside the _______)
• If the parcel is ________, it won’t rise-->stable
• If the parcel is ________, it will rise-->unstable
• A ________ situation means air will tend to stay in its original position

Atmospheric Stability

• Air that is ________ at the surface and starts rising will continue to rise until its temp is ________ than the environment’s
• So the rate of ________ is important
• If environment temp is not _______ as fast as parcel is _______ as it rises, parcel will eventually become ________ than environment and sink

Stability—Fig. 4-26

Types of Stability

• Three main types of stability
• Absolute __________
• Absolute Instability
• _____________ Instability

Types of Stability

• First, let’s review our lapse rates
• Environmental Lapse Rate (___): how environmental temp is changing with height
• Dry Adiabatic Lapse Rate (___): Rate of cooling of unsaturated parcel as it rises: ~ 10ºC / km
• Wet Adiabatic Lapse Rate (___): Rate of cooling of saturated parcel as it rises: varies between 5º and 9ºC / km

Absolute Stability

• L < L_w
• Since environmental rate of cooling is less than both wet and dry adiabatic rates of cooling, rising parcels will cool _______ than the environment, so they soon will become cooler and _______

Absolute Stability—Fig. 4-27

Absolute Stability

• Under absolutely stable conditions, parcels won't rise on their own—need lifting mechanism (like mountains, fronts, convergence) to force them to rise
• Temperature inversions create absolutely stable conditions since environment temp increases with height in an inversion

Absolute Instability

• L > L_d
• Whether the parcel rises dry adiabatically or wet adiabatically, it will always cool more _______ than the environment and will remain _______, so it will continue to _____ on its own

Absolute Instability—Fig. 4-28

Conditional Instability

• L_d > L > L_w
• More common type of instability than absolute instability
• This means that parcels that are still dry are _______, but when they become saturated, the extra heat released through condensation gives them enough added heat to eventually become _______ than the environment and rise—________

Conditional Instability

• Thus, conditional instability depends on the condition that something (i.e. a _______) will lift the air until it becomes ____________ and can rise on its own

Conditional Instability—Fig. 4-29

Stability and Daily Weather

• Read pgs. 119-123