Why are daytime AM stations not permitted to operate at night?

Daytime AM stations are primarily assigned to operate during daylight hours to prevent interference with other AM stations due to changes in atmospheric conditions that occur as the sun sets. At night, the ionosphere's reflective properties change, allowing AM signals to travel much farther than they do during the day. This can result in overlapping coverage areas for multiple stations, leading to significant interference.

The output power and frequency arrangements for daytime stations are calibrated to ensure clear reception during the day, and the absence of nighttime operational constraints increases the likelihood of stronger signals from nearby stations overpowering those from other licensed stations. Therefore, the regulations stipulating night operation limitations for these stations are in place to protect the quality of broadcasting for all stakeholders. Thus, the correct answer reflects the technical and regulatory reasons behind the prohibition of nighttime operations for daytime AM stations.