Supersonic generation of atmospheric waves

Abstract

Chimonas and Hines1 have pointed out that the Moon's shadow on the Earth's atmosphere during a solar eclipse constitutes a cooling region travelling at supersonic speeds, and may generate atmospheric gravity waves with periods from a couple of minutes up to twelve hours. Atmospheric wave generation by solar eclipses has been observed2-4, though within the source region (the region of total or partial eclipse) the gravity waves have substantially shorter period than outside it. Here I draw an analogy between the supersonic motion of the Moon's shadow and the supersonic motion of the Earth's terminator. The terminator is supersonic between ± 45° latitudes at all altitudes below 100 km and may therefore generate gravity waves in this region. © 1973 Nature Publishing Group.