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Moderate Geomagnetic Storm Watch Issued


The National Oceanic and Atmospheric Administration’s Space Weather Prediction Center (SWPC) has issued a moderate (G2) geomagnetic storm watch for September 13. A coronal hole high-speed stream, originating from a recurrent, positive polarity coronal hole on the Sun’s surface, prompted the prediction. Minor (G1) geomagnetic storming is possible on September 14.

It’s been a turbulent time on the HF bands over the past several days. On Sunday, September 10, a strong (R3) radio blackout occurred at 1606 UTC. The source, Region 2673, has rotated just around the visible disk. Severe (G4) geomagnetic storm levels were observed at 2350 UTC on September 7, and again at 0151 UTC and 1304 UTC on September 8, due to the effects of a coronal mass ejection (CME).

“This R3 event produced a rapid increase in relativistic proton levels which are currently above the Strong (S3) threshold,” the SWPC said, offering a technical explanation. “There was also an associated CME from this event. While a fast event, the CME was off the Sun-Earth line and is not expected to produce notable geoeffective impacts.”

As the SWPC explains in less-technical terms, CMEs are “huge explosions of magnetic field and plasma from the Sun’s corona. When CMEs impact the Earth’s magnetosphere, they are responsible for geomagnetic storms and enhanced aurora. CMEs originate from highly twisted magnetic field structures, or ‘flux ropes,’ on the Sun, often visualized by their associated ‘filaments’ or ‘prominences,’ which are relatively cool plasmas trapped in the flux ropes in the corona. When these flux ropes erupt from active regions on the Sun (regions associated with sunspots and very strong magnetic fields), they are often accompanied by large solar flares.”

The September 10 flare wreaked havoc with HF nets activated for the Hurricane Irma response, including the Hurricane Watch Net, which operates on 20 meters and 40 meters.

As of 1400 UTC today, the solar flux index was at 78, and the sunspot number at 23. The A index was 11, while the K index was 2. Conditions on the HF bands, in general, remain in the fair-to-poor range, but that should not necessarily deter anyone from turning on the radio and seeing what can be worked — even on the higher bands.





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