What primarily drives the dispersion of radiation fog?

The dispersion of radiation fog is primarily driven by the cooling of the earth's surface at night, which leads to condensation of water vapor when the temperature drops. This cooling occurs rapidly after sunset due to the loss of outgoing radiation, especially in clear skies where cloud cover is minimal. As the ground cools, particularly in low-lying areas, the air in contact with the surface also cools, leading to saturation and the formation of fog.

When evaluating the options, an increase in wind speed generally disperses fog rather than causing its formation, as moving air mixes and prevents the necessary conditions for fog to establish. Sun evaporation, while important for lifting fog in the morning, does not drive the initial formation of radiation fog during the night. Cloud cover can insulate the surface, reducing the effectiveness of cooling, and thus is not a driving factor for the dispersion of fog either.

In essence, the primary mechanism influencing the formation of radiation fog is the significant temperature drop at night, making that answer the most appropriate choice.