For 32 of the past 33 days, the sun has lacked a single spot as the current Solar Cycle, numbered 24, nears its end. SpaceWeather.com said it has been almost a decade (since 2009) with so little activity on the sun.
About a year from now, the first spots of newly emerging Solar Cycle 25 are expected to appear, initiating a new 11-year sequence in which the sun’s energy rises to a peak and then falls before the next cycle begins.
Solar Cycle 24 was average size but significantly smaller than its predecessors of the past 30 years.
So how strong will the next cycle be? And how will the magnetic field evolve, which forms sunspots and fuels eruptions on the sun’s surface, such as solar flares and coronal mass ejections, that affect electric power grids, GPS, and other technologies on which we depend?
Predicting the strength of the next solar cycle
Scientists, employing three different techniques, have made predictions. This small sample illustrates the complexity of the task of understanding how the sun renews its magnetic fields and molts into the new cycle.
Frank Hill, of the National Solar Observatory, and co-workers have measured the subsurface zonal flow of the solar plasma as an indicator of the processes that build the upcoming cycle. They believe that Cycle 25 will be smaller than the current cycle by approximately 25 percent.
A second technique, studying the occurrence of bright points in the solar corona, has been employed by Scott McIntosh, director of the High Altitude Observatory of the National Center for Atmospheric Research, and colleagues. They believe these bright points serve as buoys connected magnetically further down in the solar atmosphere that indicate evolving magnetic field. Their predictions align with Hill’s and predict a new cycle about 25 percent weaker than the current.
W. Dean Pesnell, project scientist of the Solar Dynamics Observatory at NASA, believes that studying the strength of the solar polar magnetic fields before the onset of the new cycle tells how much flux will be available to build sunspots. He finds the polar fields to be on par with the now waning cycle, and predicts that Cycle 25 to be at least as strong as Cycle 24, maybe larger, if the polar fields strengthen in the next year.
Solar eruptions, which tend to increase as the solar cycle moves toward its maximum, can have important consequences for critical systems. For example, a study in the journal Space Weather published Monday discussed how strong solar flares disrupted radio communications during the 2017 Atlantic hurricane season.
When Hurricane Irma slammed into Barbuda on Sept. 7, “radio communications went down for most of the morning and early afternoon on September 6 because of the Sun’s activity,” the study’s press release reports. “French civil aviation reported a 90-minute loss of communication with a cargo plane, according to the study’s authors, and … high frequency radio, used by aviation, maritime, ham radio, and other emergency bands, was unavailable for up to eight hours.”
The powerful flares that erupted in September were an important reminder that, even during the solar minimum, the sun can have profound effects on systems on Earth.
To prepare for future inclement space weather, the United States has embarked upon a multiagency program called Space Weather Operations, Research, and Mitigation to lay out roles and responsibilities for government agencies.
The U.N. International Civil Aviation Organization is introducing Standards and Recommended Practices for international commercial aviation, beginning November 2018. In both cases, the focus is on mitigating the effects of a very active sun.
The current solar minimum and effects on the weather
The strength of the solar cycle is not expected to have noticeable effects on the weather, but research has shown that during the solar minimum, which we are in now, we tend to see more zones of high pressure at the high altitudes, which tend to slow down the progress of weather systems.
For example, research has shown strong high pressure over Greenland, sometimes called the Greenland Block, is more prevalent during solar minimums. Greenland Blocks are known to favor periods of cold, snowy weather in the eastern United States and during winter.
During the last solar minimum in 2010, a measure of the strength of the Greenland Block, known as the negative phase of the North Atlantic Oscillation, hit a record low. “It was pretty impressive during that window,” said Capital Weather Gang’s Matt Rogers, a long-range forecasting specialist.
The last solar minimum coincided with the snowiest winter on record in Washington, in 2009-2010.
Capital Weather Gang’s Jason Samenow contributed to this report.