Why can you not hear distant 160-metre and AM broadcast stations during daytime hours?

AM broadcast stations and the 160-metre amateur band operate at relatively low frequencies (medium wave and lower HF). During daytime hours, the sun's radiation creates the lowest layer of the ionosphere, known as the D region. Because of the high atmospheric density at the D region's low altitude, radio waves passing through it cause free electrons to collide with gas molecules, dissipating the radio wave's energy as heat. This absorption effect is strongest at lower frequencies. As a result, low-frequency signals are completely absorbed by the D region before they can reach the higher F layers to be refracted back to Earth. At night, the D region disappears, allowing these signals to reach the F region and propagate over long distances.