Sunspots, which rotate around the sun’s surface, tell us a greatdeal about our own planet. Scientists rely on them, for instance, tomeasure the sun’s rotation or to prepare long-range forecasts of theEarth’s health.
But there are some years, like this one, where it’s not possible tosee sunspots clearly. When we’re at this “solar minimum,” very few, ifany, sunspots are visible from Earth. That poses a problem forscientists in a new scientific field called “Space Weather,” whichstudies the interaction between the sun and the Earth’s environment.
Thanks to a serendipitous discovery by Tel Aviv University’s Prof. Colin Price,head of TAU’s Department of Geophysics and Planetary Science, and hisgraduate student Yuval Reuveni, science now has a more definitive andreliable tool for measuring the sun’s rotation when sunspots aren’tvisible — and even when they are. The research, published in theJournal of Geophysical Research – Space Physics, could have importantimplications for understanding the interactions between the sun and theEarth. Best of all, it’s based on observations of common,garden-variety lightning strikes here on Earth.
Waxing and waning, every 27 days
Using Very Low Frequency (VLF) wire antennas that resembleclotheslines, Prof. Price and his team monitored distant lightningstrikes from a field station in Israel’s Negev Desert. Observinglightning signals from Africa, they noticed a strange phenomenon in thelightning strike data — a phenomenon that slowly appeared anddisappeared every 27 days, the length of a single full rotation of thesun.
“Even though Africa is thousands of miles from Israel, lightningsignals there bounce off the Earth’s ionosphere — the envelopesurrounding the Earth — as they move from Africa to Israel,” Prof.Price explains. “We noticed that this bouncing was modulated by thesun, changing throughout its 27-day cycle. The variability of thelightning activity occurring in sync with the sun’s rotation suggestedthat the sun somehow regulates the lightning pattern.”
He describes it as akin to hearing music or voices from across alake: depending on the humidity, temperature and wind, sometimesthey’re crystal clear and sometimes they’re inaudible. He discovered asimilar anomaly in the lightning data due to the changes in the Earth’sionosphere — signals waxed and waned on a 27-day cycle. Prof. Price wasable to show that this variability in the data was not due to changesin the lightning activity itself, but to changes in the Earth’sionosphere, suspiciously in tandem with the sun’s rotation.
Taking the pulse of the sun
The discovery describes a phenomenon not clearly understood byscientists. Prof. Price, an acclaimed climate change scientist,believes it may help scientists formulate new questions about the sun’seffect on our climate. “This is such a basic parameter and not much isknown about it,” says Prof. Price. “We know that Earth rotates onceevery 24 hours, and the moon once every 27.3 days. But we haven’t beenable to precisely measure the rotation rate of the sun, which is a ballof gas rather than a solid object; 27 days is only an approximation.Our findings provide a more accurate way of knowing the real rotationrate, and how it changes over time,” he says.
Prof. Price cannot yet say how this finding will impact life onEarth. “It’s an interesting field to explore,” he says, “becausenothing has been done to investigate the links between changing weatherpatterns and the rotation of the sun.
“Short-term changes in solar activity can also impact satelliteperformance, navigational accuracy, the health of astronauts, and evenelectrical power grid failures here on Earth. Many scientists claimthat the sun’s variability is linked to changes in climate and weatherpatterns, so the small changes we observed every 27 days could also berelated to small variations in weather patterns.
“Our data may help researchers examine short-term connectionsbetween weather, climate, and sun cycles. With this tool, we now have agood system for measuring the pulse of the sun.”