Solar Scientists Say Cycle 24 is the Weakest in More than a Century
Four leading solar scientists on December 11 told journalists attending the American Geophysical Union (AGU) fall conference in San Francisco that current solar Cycle 24 has demonstrated extremely low sunspot activity and appears to be the weakest cycle of the past 10 cycles — more than 100 years. This already has resulted in milder “space weather” and less-intense geomagnetic storms and “energetic particle events,” such as coronal mass ejections (CMEs), NASA scientist Nat Gopalswamy said.
“The weak activity of Cycle 24 is thought to be due to the weak polar magnetic field in Cycle 23,” an AGU news release explained. “If this trend continues for the next couple of cycles, the Sun may be heading for a global minimum.”
The scientists drew no specific conclusions regarding the impact of the extremely weak Cycle 24 on radio propagation. Stanford University’s Leif Svalgaard said this weak cycle had been predicted based on the behavior of the Sun’s polar magnetic fields, which translate into fewer sunspots. Svalgaard believes that in a few years it will be possible to use polar field data to determine the robustness of Cycle 25. The Sun’s weak polar magnetic field could lead to an increase in cosmic ray activity, which could affect manned spaceflight, the news conference was told.
In addition to Svalgaard and Gopalswamy, the other scientists were Martin Mlynczak of NASA-Langley, and Joe Giacolone of the University of Arizona.
According to Spaceweather.com, since 2004 there have been 821 days without sunspots, compared to 486 days for the “typical” solar minimum, but none of these days fell within 2012 or 2013. On December 17 the sunspot number was 114, while 10.7 centimeter solar flux was 154.
Spaceweather.com reports low solar activity and no active flares. Two current Earth-facing sunspots have “beta-gamma” magnetic fields and hold the potential for “moderately strong solar flares” that most likely would impact Earth.