Define Vertical Stability

Question 1

Define vertical stability and instability of the atmosphere:

Answer 1

Vertical stability:

vertical motion is not favoured

-force must be applied to move air vertically
-air returns to original height if force ceases

vertical instability:

Vertical motion is favoured

Once set in motion the air rises or falls freely

Question 2

State what happens to vertically moving parcels of air and why with reference to the parcel and environment temperatures:

Answer 2

Parcel of warm air surrounded by a cooler air mass will rise through the cooler air

Parcel of cold air surrounded by a warmer air mass will sink through the warm air

Wants to return to equilibrium

Will go where it’s moved

Question 3

List (5) weather elements influenced by stability:

Answer 3

Surface wind

Clouds

Precipitation

Visibility

Question 4

How does stability affect surface wind?

Answer 4

Unstable:
Tends to be stronger and gustier
Stronger winds aloft vertically mix with weaker wind’s below = increase in speed and gustiness

Stable:
Tend to be lighter and weaker
Steady
Vertical motion inhibited and slowed more efficiently by surface friction

Question 5

How does stability affect clouds?

Answer 5

Unstable:
Supports clouds of vertical development
Convective or cumuliform

CU, TCU, CB, ACC

Stable:
Tend to be flat, widespread and layer type cloud
Air has to be forced upward in order for cloud to form
Stratiform

FG, SC, ST, AC, AS, NS

Question 6

How does stability affect precipitation?

Answer 6

Unstable:
Convective clouds large enough to produce showers in liquid or solid form
Ex. Rain showers, snow showers, hail

Stable
Stratiform clouds thick enough will produce continuous or intermittent precipitation
Ex: rain, snow, drizzle

Question 7

How does stability affect visibility?

Answer 7

Unstable:
Low-level pollutants or moisture are dispersed upward and away from the surface, allowing for good visibilities
- may produce cumuliform cloud which may cause showers to lower visibility

Stable:
Block vertical motion tending to trap fog , smoke, or pollution near the surface
Poor /limited visibility is associated with Stable air, though if no reductions to visibility, it can be good.