lecture 5: (In)stability and local winds 3

Question 1

SIGNS OF A STABLE ATMOSPHERE

Answer 1

• When the vertical temperature gradient (ELR) is small then the atmosphere is often absolutely stable.
• If air is forced to rise in an absolutely stable atmosphere it will resist the vertical movement and rather spread out horizontally.
• This is reflected in stratiform (layered) clouds or in horizontally spreading radiation fog.
• Steady winds, poor visibility due to pollution accumulation

Question 2

SIGNS OF AN UNSTABLE ATMOSPHERE

Answer 2

• When the vertical temperature gradient (ELR) is large then the atmosphere is often absolutely or conditionally unstable.
• Clouds grow vertically and plumes rise to great heights
• Cumulus/cumulonimbus type clouds
• Upwards and downwards currents, gusty
turbulent winds
• Good visibility
• Dust whirls

Question 3

INFLUENCE OF ATMOSPHERIC STABILITY

Answer 3

Vertical atmospheric stability is a major factor in the transport of pollutants:
• (a) During the afternoon, when the atmosphere is most unstable, pollutants rise, mix, and disperse downwind.
• (b) At night when a radiation inversion exists, pollutants from the shorter stacks are trapped within the inversion, while pollutants from the taller stack, above the inversion, are able to rise and disperse downwind.

Question 4

INCREASED POLLUTION DURING INVERSION

Answer 4

During weather periods with stable stratification pollutants can accumulate to values well above safe air quality standards (e.g. Los Angeles-type photochemical ozone smog)