Atmospheric Stability & Cloud Formation

Question 1

What are the 5 initial causes of vertical motion?

Answer 1

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

Question 2

How do you calculate the cloud base altitude?

Answer 2

Lifting condensation level = (Ta - Td) x 400

Question 3

What is the Dry Adiabatic Lapse Rate (DALR)?

Answer 3

3°C per 1000ft

This is for dry air (Ta)

Question 4

What is the Dew Point Lapse Rate (DPLR)?

Answer 4

0.5°C per 1000ft

This is for the Dew Point temperature (Td)

Question 5

Define an Adiabatic Process?

Answer 5

A process that occurs without heat or matter leaving the system

These processes are reversible

Question 6

How does Adiabatic warming and cooling occur?

Answer 6

Air forced to ascend expands and cools

Air forced to descend compresses and warms

Question 7

What is the Saturated Adiabatic Lapse Rate (SALR)?

Answer 7

Normally between 0.5 - 2.9°C per 1000ft

But for equations use ——-
1.8° per 1000ft

Question 8

How does Saturated Adiabatic Lapse Rate differ between Tropical/Polar climates?

Answer 8

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

Question 9

Define the Environmental Lapse Rate (ELR)

Answer 9

The ELR is the actual rate that temperate decreases with altitude

ELR determines whether the air is:
Absolutely Unstable/Stable, or Conditionally Unstable

Question 10

Which of the air stabilities are buoyant?

Answer 10

Absolutely Unstable - Buoyant
Absolutely Stable - NOT buoyant

Conditionally Unstable:
Saturated - Buoyant
Unsaturated - NOT buoyant

Question 11

When does Absolute Stability occur?

Answer 11

When ELR is LESS than SALR

ELR < SALR

Question 12

When does Absolutely Instability occur?

Answer 12

When ELR is GREATER than DALR

ELR > DALR

Question 13

When does Conditionally Instability occur?

Answer 13

When ELR is GREATER than SALR, but LESS than DALR

SALR < ELR < DALR

Question 14

What is an Inversion?

Answer 14

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)

Question 15

What causes an Inversion to form?

Answer 15

Surface cooling —- (radiation)
Katabatic drainage —- (air rolling down a mountain)
Weather fronts
Subsidence —- (going downwards)
Turbulence

Question 16

What are the 4 types of Inversion?

Answer 16

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)

Question 17

What is a Marked Temperature Inversion, and what are the effects?

Answer 17

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

Question 18

How are Inversions cleared?

Answer 18

By heating the air from below
Through strong winds
Or a change in the weather pattern

Question 19

Explain the Foehn Effect with a diagram

Answer 19

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

Question 20

How is the upper air measured?

Answer 20

Using a Radiosonde,

Which features: a helium balloon
Radar reflector/GPS - to measure wind
Temp., humidity and pressure sensor