The deepest radiation inversion would be observed:

At the equator any day of the year
In polar regions in winter
At the top of a high mountain in winter
On a desert in winter E. In a deep valley during the summer

The correct answer is: B. In polar regions in winter.

A radiation inversion is a layer of the atmosphere where the temperature increases with height. This can happen when the sun is low in the sky and the ground is not able to absorb as much heat. The cold air at the surface sinks and traps the warm air above it, creating an inversion.

Polar regions are more likely to experience radiation inversions in winter because the sun is lower in the sky and the days are shorter. This means that the ground is not able to absorb as much heat, and the cold air at the surface sinks and traps the warm air above it.

The other options are incorrect because:

  • The equator receives more direct sunlight than any other part of the Earth, so it is not likely to experience a radiation inversion.
  • Mountains are typically colder than the surrounding areas, so they are not likely to experience a radiation inversion.
  • Deserts are typically hot and dry, so they are not likely to experience a radiation inversion.
  • Valleys are typically warmer than the surrounding areas, so they are not likely to experience a radiation inversion.