Our weather is strongly influenced by what’s happening in the upper atmosphere. For example, high-level equatorial winds, known as the “equatorial jet”, swing between easterlies and westerlies roughly every two years. When they are in their westerly phase, we tend to see stormier and wetter winter weather in northern Europe.
Understanding this pattern helps meteorologists to produce long-term forecasts. But, in 2016, the forecasts went to pot, when the equatorial jet did something unheard of, and flipped from west to east and back to west again, all within the space of six months. Possibly the strong El Niño was to blame but, given that measurements only go back to 1953 and there are no other examples of such a fast switch in the equatorial jet, it is hard to be sure.
Kevin Hamilton, a retired professor from the University of Hawaii, is using the unusual sunsets and lingering twilights associated with large volcanic eruptions to push the record of the equatorial jet back hundreds of years. For example, the coloured skies caused by the ash thrown up by Indonesian volcano Krakatoa in 1883 were first observed close to the volcano, but moved steadily westwards, taking about 16 days for the phenomenon to travel completely around the equator.
By contrast, the glowing sunsets after the devastating eruption of the Caribbean volcano Mont Pelée in 1902 took about twice as long to complete a westward equatorial journey, suggesting that the equatorial jet was in a weaker westerly phase at that time. So far, Hamilton has identified 22 suitable volcanic eruptions, that could reveal equatorial jet behaviour right back to 1812.
