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鈥檚 busy, stormy surface, causing changes in heat in the earth鈥檚 atmosphere. That can influence atmospheric pressure, which helps control two broader weather patterns 鈥� El Ni帽os and the North Atlantic Multidecadal Oscillation 鈥� which are linked to higher king tides.
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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.
鈥淥ur analysis allows us to help be prepared when the next king tides are going to be problematic or more problematic than they are now,鈥� said UF oceanographer Arnoldo Valle-Levinson, a co-author of 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.
鈥淭hese king tides are not as bad because we鈥檙e not in an interference of these two forces,鈥� 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.
鈥淭he lunar orbits only explain a small portion of the variability, which is around 10 percent only,鈥� 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鈥檛 necessarily answer the king tide question.
鈥淭hen we started looking at other disciplines and in particular dendrochronology 鈥� those are studies of tree rings,鈥� 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 Ni帽os and the North Atlantic oscillation. Lunar orbits also showed up in tree ring patterns, as well as solar activity.
This solar activity 鈥� like the moon 鈥� undergoes a regular cycle, where solar storms fueled by the sun鈥檚 magnetic field builds until it peaks and causes the sun鈥檚 positive and negative poles to flip flop. Once reversed, the storminess begins again. The rotation usually takes about 11 years.
鈥淲hat we found out is that the sunspots can increase heat fluxes to the atmosphere. So it can affect atmospheric pressure,鈥� Valle-Levinson said. 鈥淎nd these pressure systems, the El Ni帽o and the North Atlantic Oscillation, would be altered also.鈥�
In September, that another solar cycle, which can take a few months to detect, had begun yet again.
鈥淚 didn't know anything about this until I started looking at it,鈥� he said. 鈥淚t has a beautiful periodicity of 10 to 11 years that releases sunspots. And I realized that it has tremendous implications on Earth.鈥�
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鈥檚 still some question over how accurate the forecasts can be.
鈥淲e would be able to do a good forecast if we had at least a 300-year record, which unfortunately we don't have yet,鈥� he said. 鈥淩ight 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.鈥�
For now, he鈥檚 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.
鈥淧eople 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 Ni帽o and the North Atlantic oscillation,鈥� he said. 鈥淭o 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?鈥�
And to suggest the changes are being driven by something outside the earth鈥檚 atmosphere is, well, a little out there.
鈥淪ome colleagues are saying that it's only an internal variability of the ocean,鈥� he said. 鈥淪o for the most part, people have been intrigued. That鈥檚 what I would say.鈥�
