The correct answer is option 'D': Neutral.

Explanation:
In plume dispersion, the term "upward vertical rise" refers to the movement of the plume in an upward direction. The plume can either rise or fall depending on the buoyancy effects and the surrounding atmospheric conditions.

In the given options, the term "upward vertical rise" prevails in a neutral plume. Let's understand why this is the case:

1. Trapping plume:
- In a trapping plume, the buoyancy effects are such that the plume tends to stay close to the ground, sometimes even hugging the surface.
- The plume is trapped within a layer of stable air, which acts as a barrier preventing the plume from rising vertically.
- As a result, the upward vertical rise is limited or suppressed in a trapping plume.

2. Fanning plume:
- In a fanning plume, the buoyancy effects are such that the plume disperses laterally, spreading out in a fan-like pattern.
- The plume tends to disperse horizontally rather than rise vertically.
- While there may be some vertical rise initially, the predominant behavior in a fanning plume is lateral dispersion rather than upward vertical rise.

3. Looping plume:
- In a looping plume, the buoyancy effects cause the plume to form a loop or a U-shaped trajectory.
- The plume rises initially, then loops back and descends before rising again.
- While there is some vertical rise in a looping plume, it is not a continuous upward vertical rise.

4. Neutral plume:
- In a neutral plume, the buoyancy effects are balanced, and the plume rises vertically without significant horizontal dispersion or trapping.
- The upward vertical rise prevails in a neutral plume as the plume is not affected by strong buoyancy effects that would cause it to disperse laterally or trap close to the ground.

Therefore, the correct answer is option 'D': Neutral, where the upward vertical rise prevails in the plume.