Sound from one explosion skipped over near regions and reached far ones

Evidence

The explosion was heard loudly in Munich, and many places more than 300 km away, but it was not heard at all in dozens of places only 150 km away. The map of where the explosion was heard and where it was not is revealing (figure 28.1). Evidently, the sound left the ground altogether from about 50 km away to about 150 km away from the source, returning to ground level about 200 km from the explosion. From there, it bounced off and again entered the upper atmosphere. The whole phenomenon is a spectacular example of refraction, due to wind speed gradients and temperature gradients, both of which refract ray paths. The temperature profile of the atmosphere grows cooler with altitude until about 10 km up, then it starts to warm again as altitude increases. The sound speed accordingly drops (in summer) from about 340 m/s to 285 m/s at 10 km, rising again to 370 m/s at 40 km. Sound at ground level will be refracted toward the slower sound speeds—that is, up into the atmosphere—until it meets the reverse temperature gradient above 10 km. There, it begins to arc back down, reaching ground level again at about 200 km. — Eric J. Heller, Why You Hear What You Hear- An…, 2605

Categorization

• XREF: Directly parallels the SOFAR channel treatment in chapter 2 box 2.2, which the text itself flags at location 2607 — reflection of sound waves in stratified media.
• SEED: Essay angle: the 1921 Oppau explosion as a natural experiment in acoustic refraction — how temperature inversions created a ‘zone of silence’ ring around a 300 km broadcast. The map of heard/not-heard regions is a vivid visual.
• DEEPTHINKING: The zone-of-silence phenomenon — hearing something far away while being deaf to it nearby — crystallizes how strongly propagation medium structures what we can perceive, a genuinely paradigm-shifting demonstration of ‘why we hear what we hear’.
• QUESTION: How do seasonal and diurnal temperature profiles shift the inner and outer boundaries of the zone of silence? The passage notes summer values only.