6 Minutes
Unexpected uptick in solar activity
Recent analyses of long-term solar observations indicate that the Sun's activity has been increasing steadily since about 2008, a trend that extends beyond the familiar 11-year solar cycle. Agencies including NASA and NOAA initially forecast a relatively weak Solar Cycle 25 following the low-activity Cycle 24, but observed sunspot counts, flares, and coronal mass ejections have been higher than expected. Researchers at NASA's Jet Propulsion Laboratory (JPL) now report that multiple measures of the solar wind — including speed, density, temperature, thermal pressure, mass flux, momentum, energy flux, and magnetic field strength — have all risen over the past decade and a half.
Solar cycles, the Hale cycle, and historical context
The Sun's principal rhythm observed by scientists is the approximately 11-year sunspot cycle, which alternates between solar minimum and maximum and is associated with changes in sunspot number, solar flares, and coronal mass ejections (CMEs). Each 11-year cycle is actually half of a 22-year magnetic Hale cycle, during which the Sun's magnetic polarity reverses twice and returns to its original orientation.
Longer-term variability is also documented in historical records. The Maunder Minimum (roughly 1645–1715) and the Dalton Minimum (around 1790–1830) were extended intervals of unusually low sunspot counts. Such episodes demonstrate that the Sun can enter prolonged phases of reduced activity, but the mechanisms that trigger these multi-decade shifts remain poorly understood. As JPL plasma physicist Jamie Jasinski observed, "All signs were pointing to the Sun going into a prolonged phase of low activity. So it was a surprise to see that trend reversed. The Sun is slowly waking up."
New data and what researchers measured
Jasinski and colleagues, including space physicist Marco Velli of JPL, examined multiple solar-wind and heliospheric datasets spanning several solar cycles. Rather than relying solely on sunspot counts, their approach incorporated in-situ spacecraft measurements and remote-sensing indices that quantify the properties of the solar wind and interplanetary magnetic field.
Beginning around 2008, corresponding with the start of Solar Cycle 24, the team found a gradual increase in solar-wind speed, plasma density and temperature, as well as thermal and dynamic pressures. Magnetic field magnitude and energy fluxes also trended upward. Collectively, these parameters point to an overall strengthening of the Sun’s outward influence on the heliosphere.
Implications for space weather and Earth
An extended rise in solar-wind strength and magnetic activity can translate into more frequent or more intense space-weather events. That includes enhanced rates of solar flares and CMEs, stronger geomagnetic storms when such eruptions intersect Earth's magnetosphere, and increased radiation exposure for satellites, astronauts, and high-altitude aviation. The observed changes do not automatically signal an extreme event, but they expand the likelihood window for disruptive solar activity compared with projections based primarily on sunspot forecasts.
Mission planners and satellite operators track these trends using a constellation of observatories and probes, such as Parker Solar Probe, Solar Orbiter, ACE, DSCOVR, SOHO, and STEREO. These spacecraft provide continuous monitoring of the near-Sun environment and the solar wind, improving nowcasts and forecasts of space weather.
Why predicting the Sun remains difficult
The Sun is a highly nonlinear magneto-hydrodynamic engine. Internal flows, differential rotation, and magnetic field generation through the solar dynamo produce variability across multiple time scales. Sunspots are a useful proxy, but they capture only one observable manifestation of deeper processes. The JPL analysis highlights that relying solely on sunspot counts may understate longer-term changes taking place in the heliosphere.
Researchers emphasize the need to broaden diagnostic metrics to include solar-wind properties, open magnetic flux, and energetic-particle populations. Only with a wider observational catalog and improved dynamo models can scientists better anticipate whether current trends will continue, plateau, or reverse.
Expert Insight
Dr. Laura Mendes, an astrophysicist who studies solar magnetism (expert commentary), notes: "The trend since 2008 is a reminder that the Sun behaves on multiple overlapping cycles. Observations from Parker Solar Probe and Solar Orbiter are helping us test whether the increase in solar-wind energy is linked to deeper changes in the solar dynamo. For planners, the practical takeaway is to treat recent predictions with adaptive strategies — expect variability and prepare systems accordingly."
Monitoring and missions
Ongoing and upcoming solar missions enhance our capacity to detect and analyze changes. Parker Solar Probe is sampling the inner heliosphere, Solar Orbiter combines close-up imagery with in-situ plasma measurements, and ground-based observatories monitor sunspots and magnetic topology. Together, these assets feed models that inform NOAA and other space-weather services responsible for satellite drag forecasts, radio blackout warnings, and geomagnetic storm alerts.
Conclusion
Recent analyses indicate the Sun's activity has been increasing since about 2008, with measurable rises in solar-wind speed, density, temperature, pressure, and magnetic field strength. These trends complicate forecasts based only on sunspot counts and underscore the importance of multi-parameter monitoring across the heliosphere. While the solar wind pressure today remains lower than levels observed around the start of the 20th century, persistent observation and improved modeling are essential to determine whether the Sun will continue on this upward trajectory and what that means for space weather and technological systems on and near Earth.
Source: swpc.noaa
Comments