This study discusses the global variation of sonic boom overpressure due to seasonal changes of atmosphere with temperature and pressure gradients, focusing on the variation of overpressure according to the season and geographic position. The seasonal atmospheric gradients were estimated by upper-air radiosonde observations, and the near-field signature for the Sears-Haack body obtained by CFD calculation was used. Sonic boom was extrapolated through all seasonal atmospheric gradients without wind and humidity throughout the world by use of the Waveform Parameter Method. The results demonstrated that sonic boom overpressure varies widely with season and geographic position. The results also showed three general tendencies of the global variation in boom overpressure. The boom overpressure decreases in winter but increases in summer in the northern hemisphere. Low latitudes have slightly increased overpressure throughout the year, as compared to other geographical regions. High-altitude regions were shown to favor a decrease in boom overpressure.