Fanning type of plume behaviour takes place when
- ASuperadiabatic lapse rate prevails with light to moderate wind speed
- BThere exists a strong superadiabatic lapse rate above a surface of inversion
- CExtreme inversion conditions exist in the presence of light windCorrect
- DPlume is caught between two inversion layers ________________
Solution
Concept
Fanning Plume Behavior
Formula
N/A
Step-by-step solution
1. Read the given question asking for the conditions under which fanning plume behavior occurs. 2. Recall that a fanning plume forms when there is an extreme temperature inversion and weak/light wind speeds, preventing vertical mixing. 3. Match these conditions with the given options and select Option (c) as the correct choice.
Explanation
A fanning plume occurs during strong atmospheric inversion conditions when wind speeds are light. Because the air is extremely stable, vertical air movement is suppressed, causing the smoke to spread out horizontally in a thin, flat layer rather than mixing up or down.
Shortcut
To easily remember Fanning Plume behavior, use the mnemonic "FAN = Flat & Inverted": - Fanning: Smoke spreads horizontally like a flat Fan because vertical air movement is blocked. - Inversion & Light Wind: Occurs under extreme Inversion conditions with Light/Weak winds.
Common mistake
A common mistake is selecting Option A by confusing fanning with looping plume behavior, which occurs under a superadiabatic lapse rate. Students also frequently confuse fanning with fumigation (Option B) or trapping (Option D), failing to remember that fanning specifically occurs during extreme temperature inversion conditions with light winds.
Correct answer: C) Extreme inversion conditions exist in the presence of light wind