Chapter #6 Flashcards
(21 cards)
Define stable and unstable in the atmosphere
Stable - The air parcel will return to its place of origin if forced to rise (temperature of the parcel is colder than outside air)
Unstable - Air parcel will rise on its own (temperature of the parcel is warmer than outside air)
What is an adiabatic process?
No exchange of hear with the surrounding air outside the parcel
Lapse rates and use (3)
Dry Lapse rate: 10 degrees C /km
Dew Point Lapsre Rate: 2 degrees C/km
Moist Lapse Rate: 6 degrees C/km (Temperature/Dew-point lapse rate are the same when saturated)
Lapse rate for the vertical temperature profile of the atmospere
Environmental Lapse rate (not a constant number, to calculate, use temperature data collected)
What are the conditions needed to determine the various lapse rates for a parcel of air
Dry Lapse Rate - When the parcel of air is unsaturated (under 100% RH)
Dew-point Lapse Rate - For dew point when unsaturated (under 100% RH)
Moist Lapse Rate - When parcel reaches saturation (for both temperature and dew-point temperature
Why do we use 10 degrees C/km for the dry lapse rate and only 6 degrees C/km for the moist lapse rate?
Once saturation occurs (with moist lapse rate), it will slow the rate of cooling within the parcel.
Difference between dry lapse rate and the environmental lapse rate?
Dry lapse rate - cooling/warming of a parcel
Environmental - cooling/warming of an environment
What is an absolutely stable atmosphere?
When a parcel of air remains colder than the surrounding air while being lifted (when environmental lapse rate is colder than moist adiabatic (6 degrees C/km))
What conditions cause a stable atmosphere?
When the temperature difference at the surface and aloft are small; need warm air aloft or cold air at the surface.
What can make an atmosphere more stable?
1) Warm air advection above the surface
2) Downward movement of air above (subsidence) that will cause the air temperatures above to warm due to compression
3) Cold air advection on and/or near the surface
4) Overnight radiational cooling on the surface
5) Air moving over a colder surface which will cause the surface air temperature to decrease
Clouds associated with a stable temperature
- Cirrostratus
- Altostratus
- Stratus
- Nimbostratus
What is an unstable atmosphere?
When a parcel of air remains warmer than the surrounding air while being lifted
(environmental lapse rate is greater than the dry lapse rate = absolutely unstable)
What conditions cause an unstable atmosphere?
Difference in temperatures between the ground and the temperatures aloft. Need cold air aloft and warm air at the surface.
What mechanisms causes the air to become more unstable?
1) Cooling aloft
- Cold air advection above the surface
- Radiational cooling off of top of clouds
2) Warming at the surface
- Daytime solar heating
- Warm air advection on the surface
- Cool air moving over a warmer surface
On a typical summer day, how does atmospheric stability change from the daytime to nighttime?
During the daytime:
- Earth’s surface/lowest region of troposphere warms = unstable
During the Night:
- Radiational cooing on ground and lower troposphere = stable
What kind of stability is needed for the development of a thunderstorm. In other words, what kind of atmospheric stability will allow the thunderstorm to grow in the vertical?
-T/S temperature must be warmer than outside air, unstable air causes it to rise
Define “Conditionally Unstable”
- if unsaturated air could be lifted to a level where it becomes saturated, instability would result
Name the four mechanisms that are responsible for the development of the majority of the clouds we observe
1) Surface heating and free convection
2) Topography (orographic lift) forced ascent
3) Widespread ascent (convergence of surface air) Example: Low pressure system
4) Uplift along weather fronts, air masses of different density interacting with one another
What type of cloud formations are typically associated a warm front and cold front?
Warm front
- Stratus clouds
Cold front
- Cumulus category
Formula for base of cloud layer
Cloud Base = (T-Td)/2.5 Deg. C X 1000 ft
Why rain shadows form on the leeward side of mountains.
Precipitation falls on the windward side of the mountain
