ATMO 201 - EXAM 2 STUDY GUIDE
-Expands and cools
-Compresses and warms - Answer -What do rising and sinking air do in adiabatic
processes?
Adiabatic process - Answer --No heat gained/lost
-Unsaturated conditions
-Reversible process bc the air parcel has same temp at beginning and end
Stable - Answer --If an object, when forced to move, tends to move back to its original
position
Unstable - Answer --If an object, when forced to move, tends to continue to move away
from its original position
-Warm air (cool air more dense) - Answer -At the same height, is warm or cool air less
dense?
Dry-adiabatic lapse rate - Answer --An unsaturated (dry) parcel will always rise and
sink at 9.8C per kilometer
-For simplicity sake for this class, we'll use 10C
Moist-adiabatic lapse rate - Answer --When parcels rise and cool, they'll eventually
become saturated
-As they continue to rise, water vapor will condense into liquid water (a cloud)
Remember: during condensation, latent heat released inside parcel
-Instead of cooling at 10C per km, it cools slower appx 6C per km
Environmental lapse rate - Answer --Parcels always rise/sink at either dry or moist
adiabatic lapse rate
-The air surrounding parcel can have a variety of temps
-Measured w radiosondes
-Since adiabatic lapse rates are known, we can compare them to environmental lapse
rate to determine whether parcel will be stable/unstable
-If a parcel is forced to rise, and it's warmer than its environment, it will continue to rise
and be unstable
-If it is forced to rise and is cooler than its environment, it will sink back down to the
original position and be stable
Absolutely stable - Answer --When environmental lapse rate is less than adiabatic rate
(6C per km)
-Air parcels will be colder than their environment and sink back to their original position
-Temp inversion (temp increase w height) acts as a lid
-Often occurs at night due to radiational cooling
, Absolutely unstable - Answer --When environmental lapse rate is greater than dry-
adiabatic lapse rate (10C per km)
-Air parcels will be warmer than their environment and continue to rise
-This condition usually only occurs near the surface, and not for very long since the
rising parcels will bring the warm air up and cool air will mix down around them
Conditionally unstable - Answer --When environmental lapse rate is between the dry
and moist adiabatic lapse rates (6C and 10C per km)
-Unsaturated parcels will sink back to their original position, saturated parcels will
continue to rise
-There is instability, on the condition that the parcel is saturated
-On avg, the atmosphere in this state (avg environmental lapse rate is 6.5C per km)
-This helps to explain why cumulus clouds can grow v tall into cumulonimbus bc ONLY
saturated parcels continue to rise
-Free convection level (LFC)
Naturally stable - Answer --When environmental lapse rate equals the dry adiabatic
lapse rate
-Unsaturated parcels will not tend to rise or sink in this condition, instead they stay
where they are
-If environmental lapse rate equals the moist adiabatic lapse rate, then the atmosphere
is ___ for saturated parcels
-Warming at low levels or cooling aloft
-Mixing
-Lifting or subsidence in layers - Answer -What factors can cause changes in stability?
Warming at low levels or cooling aloft - Answer --Increases lapse rate
-Makes atmosphere less stable
-"Warm air advection" at low levels will destabilize the atmospehre
Mixing - Answer --Makes atmosphere more stable if absolutely unstable
-Makes atmosphere unstable if stable
Lifting or subsidence in layers - Answer --If a whole layer sinks, it compresses in the
denser air near the ground, top warms more than bottom and becomes more stable
-If a whole layer rises, it stretches in the less dense air aloft, it tends to become more
unstable, esp when the bottom is saturated and the top is dry
Convective instability - Answer --If a whole layer rises, it stretches in the less dense air
aloft, it tends to become more unstable, esp when the bottom is saturated and the top is
dry
Lifting Condensation Level (LCL - Answer --Level at which condensation occurs,
represents the cloud base
-Expands and cools
-Compresses and warms - Answer -What do rising and sinking air do in adiabatic
processes?
Adiabatic process - Answer --No heat gained/lost
-Unsaturated conditions
-Reversible process bc the air parcel has same temp at beginning and end
Stable - Answer --If an object, when forced to move, tends to move back to its original
position
Unstable - Answer --If an object, when forced to move, tends to continue to move away
from its original position
-Warm air (cool air more dense) - Answer -At the same height, is warm or cool air less
dense?
Dry-adiabatic lapse rate - Answer --An unsaturated (dry) parcel will always rise and
sink at 9.8C per kilometer
-For simplicity sake for this class, we'll use 10C
Moist-adiabatic lapse rate - Answer --When parcels rise and cool, they'll eventually
become saturated
-As they continue to rise, water vapor will condense into liquid water (a cloud)
Remember: during condensation, latent heat released inside parcel
-Instead of cooling at 10C per km, it cools slower appx 6C per km
Environmental lapse rate - Answer --Parcels always rise/sink at either dry or moist
adiabatic lapse rate
-The air surrounding parcel can have a variety of temps
-Measured w radiosondes
-Since adiabatic lapse rates are known, we can compare them to environmental lapse
rate to determine whether parcel will be stable/unstable
-If a parcel is forced to rise, and it's warmer than its environment, it will continue to rise
and be unstable
-If it is forced to rise and is cooler than its environment, it will sink back down to the
original position and be stable
Absolutely stable - Answer --When environmental lapse rate is less than adiabatic rate
(6C per km)
-Air parcels will be colder than their environment and sink back to their original position
-Temp inversion (temp increase w height) acts as a lid
-Often occurs at night due to radiational cooling
, Absolutely unstable - Answer --When environmental lapse rate is greater than dry-
adiabatic lapse rate (10C per km)
-Air parcels will be warmer than their environment and continue to rise
-This condition usually only occurs near the surface, and not for very long since the
rising parcels will bring the warm air up and cool air will mix down around them
Conditionally unstable - Answer --When environmental lapse rate is between the dry
and moist adiabatic lapse rates (6C and 10C per km)
-Unsaturated parcels will sink back to their original position, saturated parcels will
continue to rise
-There is instability, on the condition that the parcel is saturated
-On avg, the atmosphere in this state (avg environmental lapse rate is 6.5C per km)
-This helps to explain why cumulus clouds can grow v tall into cumulonimbus bc ONLY
saturated parcels continue to rise
-Free convection level (LFC)
Naturally stable - Answer --When environmental lapse rate equals the dry adiabatic
lapse rate
-Unsaturated parcels will not tend to rise or sink in this condition, instead they stay
where they are
-If environmental lapse rate equals the moist adiabatic lapse rate, then the atmosphere
is ___ for saturated parcels
-Warming at low levels or cooling aloft
-Mixing
-Lifting or subsidence in layers - Answer -What factors can cause changes in stability?
Warming at low levels or cooling aloft - Answer --Increases lapse rate
-Makes atmosphere less stable
-"Warm air advection" at low levels will destabilize the atmospehre
Mixing - Answer --Makes atmosphere more stable if absolutely unstable
-Makes atmosphere unstable if stable
Lifting or subsidence in layers - Answer --If a whole layer sinks, it compresses in the
denser air near the ground, top warms more than bottom and becomes more stable
-If a whole layer rises, it stretches in the less dense air aloft, it tends to become more
unstable, esp when the bottom is saturated and the top is dry
Convective instability - Answer --If a whole layer rises, it stretches in the less dense air
aloft, it tends to become more unstable, esp when the bottom is saturated and the top is
dry
Lifting Condensation Level (LCL - Answer --Level at which condensation occurs,
represents the cloud base
