Figure 10-4 shows the path of the sound energy along the rays of sound during a hot summer day. Balloonists often find they hear conversations from the ground but cannot make themselves heard by people on the ground during a hot summer day. But, after the inversion sets in and they descend to get in it the reverse is true. They can be heard quite well by people on the ground but they cannot hear what the people on the ground are saying until they are really close. The moral is on a hot sunny day, don't worry about sound getting to the ground from above pattern altitude but on late afternoon and night time flights obey sound restrictions as much as possible.
Light is different from sound.
Light and radar waves are electromagnetic waves which move faster through less dense air than they do in more dense air. But the process is much the same. Years ago I was introduced to a prism, a triangular piece of glass which separates light into colors. I noticed that the blue light was bent more than the red light. Later, when I learned that red light had a longer wavelength than blue, I guessed that the wavelength might have something to do with it.