One sunspot mystery solved, researchers say
Earth seems to warm up too much during sunspot activity. Now scientists say they've found where the extra energy is coming from.
For some time, scientists have observed that sunspots seem to have an inordinate impact on earth's weather.Skip to next paragraph
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Sunspots are areas of intensified magnetic activity on the sun's surface. They occur roughly on an 11-year cycle. Right now, we're at the minimum of the cycle, and poised, most likely, to enter a phase of increased activity.
Here's the mystery when it comes to sunspots:
The small increase in energy emitted by the sun during solar maximums (the peak of sunspot activity) doesn't seem to match the higher temperatures observed on earth. During sunspot years, the sun's total energy output rises by just one-tenth of one percent. During those years, average sea surface temperatures increase by about 0.1 degrees C. But scientists calculate that, to get those higher temperatures, the amount of solar energy reaching earth would have to increase by about 0.5 Watts per square meter. And that's where observed reality refuses to align with scientists' number-crunching. During the peak of the sunspot cycle, the energy reaching Earth only increases by about 0.2 Watts per square meter – less than half what scientists think is necessary.
In short, Earth seems to warm up too much during solar maximums. Where is that extra energy coming from?
A new study appearing today in the journal Science offers an answer to this longstanding mystery. Two climate processes, one top-down and the other bottom-up, amplify the effects of increased solar activity, say the authors, raising temperatures beyond what you might expect. How do they know? With ever more powerful computers, scientists can run increasingly complex climate models. In this case, scientists at the National Center of Atmospheric Research took two existing models, neither of which was able to reproduce observed changes alone, and combined them. This "super" model includes more atmospheric layers than in the past, like the stratosphere, and allows for changes in atmospheric chemistry induced by solar radiation, both of which proved crucial to getting a result that approximated reality.
The scientists focused on the Pacific Ocean, which shows a strong response to periods of increased solar activity. And here's what they came up with:
First, more incoming solar radiation warms the stratosphere over the tropics. Warmer conditions, in turn, lead to the production of more ozone. More ozone causes more of the sun's incoming energy to be "caught" in the stratosphere. This feedback changes circulation patterns in the stratosphere.
The stratosphere is separated from the troposphere (the lower atmospheric layer where most weather happens) by the tropopause. So if the two layers are distinct, how does what happens up high affect what we experience down low?