Not all king tides are created equal and in a new study, University of Florida researchers say they may know why: sun spots.
Sun spots regularly occur on the sun’s busy, stormy surface, causing changes in heat in the earth’s atmosphere. That can influence atmospheric pressure, which helps control two broader weather patterns — El Niños and the North Atlantic Multidecadal Oscillation — which are linked to higher king tides.
If the theory holds true, it could provide a powerful new tool in forecasting the kind of flooding that routinely slams South Florida because sun spots are part of regular, predictable cycles.
“Our analysis allows us to help be prepared when the next king tides are going to be problematic or more problematic than they are now,” said UF oceanographer Arnoldo Valle-Levinson, a co-author of the study that appeared last month in the journal, Geophysical Research Letters.
As sea levels have risen, regular king tides that occur when the moon swings closest to the earth have been blamed for increased flooding across South Florida. Last week, just after heavy rain from Eta drenched parts of the state, a king tide also arrived.
While much of coastal South Florida flooded, the king tide was not unusually high, Valle-Levinson said. Had it been among the higher tides linked to sun spots, flooding could have been far worse.
“These king tides are not as bad because we’re not in an interference of these two forces,” he said.
Differences in king tides in the St. Lucie estuary first drew the attention of Valle-Levinson and his co-author, Jonathan Martin, a UF geologist. They wondered why some were worse, so they looked at the obvious culprit: lunar cycles.
“The lunar orbits only explain a small portion of the variability, which is around 10 percent only,” he said.
So they started looking at other drivers.
A slowing Gulf Stream and changes in global wind patterns have been blamed for varying levels of sea rise along the coast. But that didn’t necessarily answer the king tide question.
“Then we started looking at other disciplines and in particular dendrochronology — those are studies of tree rings,” Valle-Levinson said.
Trees grow differently in wet and dry years and data on tree rings is among the largest set of geological data. The rings showed a relationship between climate patterns like El Niños and the North Atlantic oscillation. Lunar orbits also showed up in tree ring patterns, as well as solar activity.
This solar activity — like the moon — undergoes a regular cycle, where solar storms fueled by the sun’s magnetic field builds until it peaks and causes the sun’s positive and negative poles to flip flop. Once reversed, the storminess begins again. The rotation usually takes about 11 years.
“What we found out is that the sunspots can increase heat fluxes to the atmosphere. So it can affect atmospheric pressure,” Valle-Levinson said. “And these pressure systems, the El Niño and the North Atlantic Oscillation, would be altered also.”
In September, NASA announced that another solar cycle, which can take a few months to detect, had begun yet again.
“I didn't know anything about this until I started looking at it,” he said. “It has a beautiful periodicity of 10 to 11 years that releases sunspots. And I realized that it has tremendous implications on Earth.”
So far, Valle-Levinson have detected the pattern in records in the Southeastern U.S. and the Adriatic Sea. Because their data set is relatively short, Valle-Levinson said there’s still some question over how accurate the forecasts can be.
“We would be able to do a good forecast if we had at least a 300-year record, which unfortunately we don't have yet,” he said. “Right now, the portion of the data we're playing with is not long enough to allow us to repeat the forecast. So we don't we don't really know how good it is.”
For now, he’s calling for higher king tides around the southeastern U.S. between 2028 and 2029, and in 2052, 2064, 2072 and 2098.
Reaction to the new theory has been a mix of intrigue, Valle-Levinson said.
“People have tried to explain [the variability] to different mechanisms, right? The slowing of the Gulf Stream, the increase in winds, the changing of barometric pressure, the Atlantic meridional circulation, climate indices like El Niño and the North Atlantic oscillation,” he said. “To come up with an explanation that is related to the forcing from the moon and the solar activity, then that's sort of simple right?”
And to suggest the changes are being driven by something outside the earth’s atmosphere is, well, a little out there.
“Some colleagues are saying that it's only an internal variability of the ocean,” he said. “So for the most part, people have been intrigued. That’s what I would say.”
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