TAU scientists use lightning to 'take the sun's pulse'

The Jerusalem Post (Link) - Judy Siegel-Itzkovich (November 8, 2009)

Tel Aviv University geophysicists have unintentionally struck pay dirt by discovering that ordinary lightning hitting Earth can be assessed to use sunspots for measuring the sun's rotation and preparing long-range predictions of the planet's future.

Sunspots are temporary dark blotches that seem to float over the sun's surface and tell scientists much about the Earth. They are caused by intense magnetic activity, which inhibits convection, forming areas of reduced temperatures on the sun's surface.

Sunspots expand and contract as they move across the surface of the sun and can be as large as 80,000 kilometers in diameter, making the larger ones visible from Earth without the aid of a telescope (though the ordinary eye can never look at them directly).

Scientists rely on them, among other things, to measure the sun's rotation. But some years, like this one, sunspots cannot be viewed clearly from Earth. That poses a problem for scientists in a new scientific field called "space weather," which studies the interaction between the sun and the Earth's environment.

Thanks to a serendipitous discovery by TAU Prof. Colin Price, a leading climate change expert and head of the department of geophysics and planetary science, and his graduate student Yuval Reuveni, a more definitive and reliable tool for measuring the sun's rotation when sunspots aren't visible is available.

They just publishing their findings in the Journal of Geophysical Research - Space Physics and believe it will have important implications for understanding the interactions between the sun and the Earth.

Using very low frequency (VLF) wire antennas that look like clotheslines, Price and his team monitored distant lightning strikes from a field station in the Negev desert. Observing lightning signals from Africa, they noticed a strange phenomenon in the lightning strike data - a phenomenon that slowly appeared and disappeared every 27 days, the length of a single full rotation of the sun.

"Even though Africa is thousands of kilometers from Israel, lightning signals there bounce off the Earth's ionosphere - the envelope surrounding the Earth - as they move from Africa to Israel," Price explained.

"We noticed that this bouncing was modulated by the sun, changing throughout its 27-day cycle. The variability of the lightning activity occurring in sync with the sun's rotation suggested that the sun somehow regulates the lightning pattern."

Price compares it to hearing music or voices from across a lake; depending on the wind, humidity and temperature, the tones may sometimes be crystal clear and sometimes inaudible. He discovered a similar anomaly in the lightning data due to the changes in the Earth's ionosphere; signals waxed and waned on a 27-day cycle.

Price was able to show that this variability in the data was not due to changes in the lightning activity itself, but to changes in the Earth's ionosphere, suspiciously in tandem with the sun's rotation.

The discovery describes a phenomenon not clearly understood by scientists, and the TAU team believe what they discovered may help to formulate new questions about the sun's effect on our climate.

"This is such a basic parameter and not much is known about it," said Price. "We know that Earth rotates once every 24 hours and the moon once in 27.3 days. But we haven't been able to measure precisely the rotation rate of the Sun, which is a ball of gas rather than a solid object; 27 days is only an approximation.

"Our findings provide a more accurate way of knowing the real rotation rate, and how it changes over time," he added.

Price cannot yet say how this finding will impact life on Earth.

"It's an interesting field to explore," he suggested, "because nothing has been done to investigate the links between changing weather patterns and the rotation of the sun."