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Three of the hundreds of sketches carried out by William Ascroft in the winter of 1883/4 – used as the frontispiece of The Eruption of Krakatoa, and Subsequent Phenomena: Report of the Krakatoa committee of the Royal Society (1888), ed. by G.J. Simmons.

Recent research by climate modelers Kevin Hamilton and Takatoshi Sakazaki at the University of Hawaiʻi at Mānoa International Pacific Research Center (IPRC) investigated the possibility of using historical observations after large equatorial volcanic eruptions to learn about the properties of the winds in the stratosphere, the layer of the atmosphere 10–30 miles above Earth’s surface.

Detailed tracking of stratospheric winds in the tropics has only been possible since regular weather balloon soundings began at some near-equatorial stations in the early 1950s. One particularly predictable pattern that has emerged is in the winds along the equator, which show regular swings in the prevailing wind direction from easterlies to westerlies and back, roughly every couple of years (28 months on average).

This pattern, called the quasi-biennial oscillation (QBO), had a surprising hiccup in 2016, breaking a routine that had lasted for at least 27 cycles. The disruption in the predictability of the QBO pattern prompted many to consider how to understand the QBO better in order to predict when the reliable pattern may change again and affect the European winter weather patterns that follow it.

Explosive volcanic eruptions force particles into the stratosphere that move with the prevailing winds and affect how light passes through the atmosphere. By examining the progressive onset and character around the world of colorful sunsets generated by volcanic eruptions, scientists can calculate factors like direction, speed and jet center position of the upper atmosphere winds at the time.

Hamilton and Sakazaki compiled historical accounts of the effects noted around the world after the eruptions of Krakatoa (1883), Saint Vincent and Mount Pelee (1902), and Mount Pinatubo (1991). The most notable effects, commonly, were brilliant sunsets or sun haloes due to the volcanic aerosols lofted high into the atmosphere.

“Any actual pre-1953 wind observations are very valuable as contributors to reconstructing the QBO record,” said Hamilton. “We want to show that observations of the effects of volcanic aerosols can provide credible estimates of the equatorial stratospheric wind at the time (of the eruption).”

For more info, see the IPRC website.

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