Atmospheric Stability & Cloud Formation Flashcards
What are the 5 initial causes of vertical motion?
Convection - the movement of warm/cold air
Turbulence - stable air disturbed by surface friction
Orographic Uplift - air flowing over high ground
Convergent Uplift - converging air forced to rise
Frontal Uplift - warm air rising over cold air
How do you calculate the cloud base altitude?
Lifting condensation level = (Ta - Td) x 400
What is the Dry Adiabatic Lapse Rate (DALR)?
3°C per 1000ft
This is for dry air (Ta)
What is the Dew Point Lapse Rate (DPLR)?
0.5°C per 1000ft
This is for the Dew Point temperature (Td)
Define an Adiabatic Process?
A process that occurs without heat or matter leaving the system
These processes are reversible
How does Adiabatic warming and cooling occur?
Air forced to ascend expands and cools
Air forced to descend compresses and warms
What is the Saturated Adiabatic Lapse Rate (SALR)?
Normally between 0.5 - 2.9°C per 1000ft
But for equations use ——-
1.8° per 1000ft
How does Saturated Adiabatic Lapse Rate differ between Tropical/Polar climates?
Tropical climates have a much lower SALR, compared to Polar climates
(1°C per 1000ft) (2.9°C per 1000ft)
Polar climate SALR = Upper Troposphere SALR
Define the Environmental Lapse Rate (ELR)
The ELR is the actual rate that temperate decreases with altitude
ELR determines whether the air is:
Absolutely Unstable/Stable, or Conditionally Unstable
Which of the air stabilities are buoyant?
Absolutely Unstable - Buoyant
Absolutely Stable - NOT buoyant
Conditionally Unstable:
Saturated - Buoyant
Unsaturated - NOT buoyant
When does Absolute Stability occur?
When ELR is LESS than SALR
ELR < SALR
When does Absolutely Instability occur?
When ELR is GREATER than DALR
ELR > DALR
When does Conditionally Instability occur?
When ELR is GREATER than SALR, but LESS than DALR
SALR < ELR < DALR
What is an Inversion?
A level of air that temperature increases with altitude.
They are very stable conditions
They can occur from the surface (Surface Inversion) or above it (Inversion Aloft)
What causes an Inversion to form?
Surface cooling —- (radiation) Katabatic drainage —- (air rolling down a mountain) Weather fronts Subsidence —- (going downwards) Turbulence
What are the 4 types of Inversion?
Radiation —- (Earths surface cooling the air in contact)
Frontal —- (warm air rising above cold air)
Subsidence —- (wide layer of air descends, becoming more compressed due to atmospheric pressure, and warming up - normally 2000-6000ft above surface)
Turbulence —- (mixing air cools the top of the layer to be colder than the air above it)
What is a Marked Temperature Inversion, and what are the effects?
Where there is a temperature difference of 10°C or more between the surface and 1000ft above the airfield
This can cause a decrease in A/C handling and performance
As well as possibly creating (marked) windshear
How are Inversions cleared?
By heating the air from below
Through strong winds
Or a change in the weather pattern
Explain the Foehn Effect with a diagram
Things to remember:
Cold, wet air blows into the side of a mountain and rises
As it rises, Ta = Td (due to lapse rates) - creating clouds
Ta and Td, then decrease at SALR
As the air comes over the mountain top, it warms at DALR
Resulting with warm, dry air on the Leeside of the mountain
How is the upper air measured?
Using a Radiosonde,
Which features: a helium balloon
Radar reflector/GPS - to measure wind
Temp., humidity and pressure sensor
