GEOMAGNETIC STORM WATCH: NOAA forecasters say G2-class geomagnetic storms are possible on May 17th when a CME is expected to deliver a glancing blow to Earth’s magnetic field. High-latitude sky watchers should be alert for auroras, especially in the southern hemisphere where deepening autumn darkness favors visibility. Free: Aurora Alerts
POTENT CORONAL HOLE: Another coronal hole (CH) is turning toward Earth, and it is a potent one. NASA’s Solar Dynamics Observatory photographed the structure on May 16th:
Image credit: NASA Solar Dynamics Observatory/LMSAL/Spaceweather.com
Coronal holes are places where the sun’s magnetic field peels back and allows the solar wind to escape. Gaseous material flowing from this hole is moving very fast, more than 700 km/s. Moreover, the wind is threaded with “negative polarity” magnetic fields–and that’s what makes it potent. Such fields do a good job connecting to Earth’s magnetosphere and energizing geomagnetic storms.
The solar wind stream should reach Earth later this week, adding its effect to that of the CME due on May 17th. Stay tuned. Free: Aurora Alerts
POLLEN CORONA: It begins with a sneeze. Pollen floating through the air tickles your nose, and your body responds by expelling the allergen. Gesundheit! When the paroxysm subsides, look up at the sky. The same pollen that makes you sneeze can also make beautiful coronas around the sun, like this one photographed on May 15th by John Stetson of Sebago Lake, Maine:
“When white pine pollen is in the air, we often see diffraction rings around our sun here in Maine,” says Stetson. “My wife, Katy, kindly blocked the sun for this picture of the surrounding halo.”
Atmospheric optics expert Les Cowley explains the phenomenon: “Coronas are produced when light waves scatter from the outsides of small particles. Tiny droplets of water in clouds make most coronas, but opaque pollen grains do even better. They make small but very colorful multi-ringed coronas.”
As northern spring turns into summer, pollen coronas become increasingly common. Look for them the next time your nose feels a tickle.