PULSATING AURORAS: During the geomagnetic storm of Feb. 4th, Fredrik Broms of Kvaløya, Norway, witnessed an episode of elusive pulsating auroras. “The sky was filled with patches of green that oscillated in brightness,” he explains. A snapshot with his Nikon D3 caught the phenomenon in mid-pulse: “The patches didn’t move much, but their intensity changed. When one patch got brighter another became more diffuse and so on,” Broms describes. Reports of pulsating auroras go back more than a century, but until recently no one knew what made the aurora borealis behave like a strobe light. Researchers from UCLA solved the puzzle in 2009-10. Using data from NASA’s THEMIS spacecraft, they discovered that auroras pulse in sync to ‘chorus waves’ in Earth’s magnetosphere. This is a type of plasma wave that seems to be able to modulate the flow of solar wind particles down to Earth during geomagnetic storms. Clearly, the chorus was singing on Feb. 4th. –Space Weather

We detected this unusual oscillating pattern in our report of a magnetospheric anomaly associated with the planetary tremor event on February 4th. See - Anomalistic 21:00 hour tremor