1135 Km/h Pressure Wave

The enormous explosion from the under sea volcano near Tonga caused not only a tsunami across the Pacific but also a pressure wave in the atmosphere which sped right round the Earth. The speed of the pressure wave was estimated to be about 1135 Km/h by Sandy Macdonald in a post on Twitter. Many weather watchers, amateur and professional, noticed the sudden drop in pressure as the effect passed over their locality - mine included:



a steadily dropping air pressure all day with a sudden change at 7.14 p.m. local time. The same person predicted that a second wave would be detected about 2 a.m. local time resulting from the pressure wave travelling in the opposite direction. (Think about the way ripples travel in a pond when a pebble in dropped in the water.) From this morning's pressure readings here it certainly looks as though he was correct:



There definitely appears to be a sudden drop at 1.49 a.m. local time. It looks a deeper drop but the scales are different on the two graphs.