Post by Brindley on Jun 3, 2016 12:44:47 GMT 2
I've put together a step-by-step explanation of stability and instability and lapse rates.
It's quite simplified, but broken down into small parts so that it should be very easy to understand.
Please feel free to use. (and to offer suggestions/corrections). Text inline, and attachment added too.
AS_STABLILITY.docx (16.59 KB)
It's quite simplified, but broken down into small parts so that it should be very easy to understand.
Please feel free to use. (and to offer suggestions/corrections). Text inline, and attachment added too.
STABLILITY, INSTABILITY AND LAPSE RATES.
• REMEMBER that every process or system relating to atmosphere starts with *THE SUN*.
Stability or Instability are conditions of the atmosphere under different circumstances.
Stability will result in clear skies and good weather, while instability will result in clouds and rain.
1. As the surface of the earth is heated by insolation, the surface will begin to warm the air above it.
a. This warming is done through the process of convectional heating.
2. As the air above the surface warms up, it becomes less dense than the air around it.
a. Because of this, it will rise.
3. As the air parcel rises in height the surrounding air pressure becomes less.
a. This is because there is less atmospheric pressure the higher up in the atmosphere.
4. As the air pressure becomes less, the air expands.
5. As the air expands it cools
a. This is because gasses cool as they expand, and warm as they are compressed.
6. The rate at which the cooling of this unsaturated rising parcel of air is known as the DALR.
7. The rate at which the cooling of a saturated (at dew point temp) rising parcel of air is known as the SALR.
8. The rate of cooling of these rising parcels of air is what determines atmospheric stability or instability.
9. If the parcel of air cools quicker with height than the surrounding environment does (ie: when the ELR is lower than the SALR) , it is unlikely to continue rising indefinitely.
a. This is known as “atmospheric stability”
b. This is because it will reach a point where it is the same temperature or cooler than its surrounds.
c. If this is the case, this stability will happen before the parcel reaches dew point temperature.
i. As a result, no condensation takes place and no clouds form, other than light status clouds
10. If the parcel of air cools slower than the surrounding environment (ie: when the ELR is greater than DALR), it will continue to rise.
a. This is known as “atmospheric instability”
11. As it rises it cools.
12. As it cools its ability to retain moisture decreases.
a. This is because warmer air can hold more water vapour than cooler air.
13. As it continues to cool, and the ability to retain moisture decreases, it will reach 100% relative humidity – dew point temperature.
a. This is the point at which the amount of water it is able to hold is equal to or less than the amount of water it is holding.
b. When this occurs, condensation will take place.
14. As condensation takes place, latent heat is released.
a. This is due to the heat energy being released as the molecules form tighter bonds
15. Because of this latent heat released, the parcel of air will cool even slower
a. Now cooling at the SALR.
16. Because the parcel of air is cooling even slower than the environment, it will continue to rise.
17. As it continues to rise, it will lose more water vapour to condensation
a. More clouds will form (cumulus)
b. More latent heat will be given off.
c. The cycle will continue
18. This process may lead to rain clouds or even the anvil shaped cumulo-nimbus clouds.
a. This is commonly seen in the equatorial rainforests
i. This is because of the heating experienced at the equator by the sun.
• REMEMBER that every process or system relating to atmosphere starts with *THE SUN*.
Stability or Instability are conditions of the atmosphere under different circumstances.
Stability will result in clear skies and good weather, while instability will result in clouds and rain.
1. As the surface of the earth is heated by insolation, the surface will begin to warm the air above it.
a. This warming is done through the process of convectional heating.
2. As the air above the surface warms up, it becomes less dense than the air around it.
a. Because of this, it will rise.
3. As the air parcel rises in height the surrounding air pressure becomes less.
a. This is because there is less atmospheric pressure the higher up in the atmosphere.
4. As the air pressure becomes less, the air expands.
5. As the air expands it cools
a. This is because gasses cool as they expand, and warm as they are compressed.
6. The rate at which the cooling of this unsaturated rising parcel of air is known as the DALR.
7. The rate at which the cooling of a saturated (at dew point temp) rising parcel of air is known as the SALR.
8. The rate of cooling of these rising parcels of air is what determines atmospheric stability or instability.
9. If the parcel of air cools quicker with height than the surrounding environment does (ie: when the ELR is lower than the SALR) , it is unlikely to continue rising indefinitely.
a. This is known as “atmospheric stability”
b. This is because it will reach a point where it is the same temperature or cooler than its surrounds.
c. If this is the case, this stability will happen before the parcel reaches dew point temperature.
i. As a result, no condensation takes place and no clouds form, other than light status clouds
10. If the parcel of air cools slower than the surrounding environment (ie: when the ELR is greater than DALR), it will continue to rise.
a. This is known as “atmospheric instability”
11. As it rises it cools.
12. As it cools its ability to retain moisture decreases.
a. This is because warmer air can hold more water vapour than cooler air.
13. As it continues to cool, and the ability to retain moisture decreases, it will reach 100% relative humidity – dew point temperature.
a. This is the point at which the amount of water it is able to hold is equal to or less than the amount of water it is holding.
b. When this occurs, condensation will take place.
14. As condensation takes place, latent heat is released.
a. This is due to the heat energy being released as the molecules form tighter bonds
15. Because of this latent heat released, the parcel of air will cool even slower
a. Now cooling at the SALR.
16. Because the parcel of air is cooling even slower than the environment, it will continue to rise.
17. As it continues to rise, it will lose more water vapour to condensation
a. More clouds will form (cumulus)
b. More latent heat will be given off.
c. The cycle will continue
18. This process may lead to rain clouds or even the anvil shaped cumulo-nimbus clouds.
a. This is commonly seen in the equatorial rainforests
i. This is because of the heating experienced at the equator by the sun.
AS_STABLILITY.docx (16.59 KB)
