A lightning strike in Africa helps take the
pulse of the sun
Tel Aviv University discovers an accurate tool for tracking solar rotation
Sunspots, which rotate around the sun's surface, tell us a great deal about our
own planet. Scientists rely on them, for instance, to measure the sun's rotation
or to prepare long-range forecasts of the Earth's health.
But there are some years, like this one, where it's not possible to see
sunspots clearly. When we're at this "solar minimum," very few, if any, sunspots
are visible 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 Tel Aviv University's Prof. Colin
Price, head of TAU's Department of Geophysics and Planetary Science, and his
graduate student Yuval Reuveni, science now has a more definitive and reliable
tool for measuring the sun's rotation when sunspots aren't visible –– and even
when they are. The research, published in the Journal of Geophysical Research –
Space Physics, could have important implications for understanding the
interactions between the sun and the Earth. 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 resemble clotheslines,
Prof. Price and his team monitored distant lightning strikes from a field
station in Israel's 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 miles from Israel, lightning signals
there bounce off the Earth's ionosphere ― the envelope surrounding the Earth ―
as they move from Africa to Israel," Prof. Price explains. "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."
He describes it as akin to hearing music or voices from across a lake:
depending on the humidity, temperature and wind, sometimes they're crystal clear
and sometimes they're 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. Prof. 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.
Taking the pulse of the sun
The discovery describes a phenomenon not clearly understood by scientists.
Prof. Price, an acclaimed climate change scientist, believes it may help
scientists formulate new questions about the sun's effect on our climate. "This
is such a basic parameter and not much is known about it," says Prof. Price. "We
know that Earth rotates once every 24 hours, and the moon once every 27.3 days.
But we haven't been able to precisely measure 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 says.
Prof. Price cannot yet say how this finding will impact life on Earth. "It's
an interesting field to explore," he says, "because nothing has been done to
investigate the links between changing weather patterns and the rotation of the
sun.
"Short-term changes in solar activity can also impact satellite performance,
navigational accuracy, the health of astronauts, and even electrical power grid
failures here on Earth. Many scientists claim that the sun's variability is
linked to changes in climate and weather patterns, so the small changes we
observed every 27 days could also be related to small variations in weather
patterns.
"Our data may help researchers examine short-term connections between
weather, climate, and sun cycles. With this tool, we now have a good system for
measuring the pulse of the sun."- AFTAU
More information:
 George Hunka
ghunka@aftau.org
American Friends of Tel Aviv University www.aftau.org
|
