Solar Cycle 25 - the Solar Magnetic Field from Solar Minimum to Pole Flip

One advantage of long-lived missions like Solar Dynamics Observatory (SDO) is the ability to see slow but significant changes over long periods of time.

This view from SDO's Helioseismic and Magnetic Imager (HMI) shows the evolution of sunspots on the solar disk starting from solar minimum (around December 2019) and into the maximum solar activity phase. The video ends in September 2024, however this maximum phase is expected to continue into 2025. The peak solar maximum of this solar cycle has not yet been identified. In the first video, the images are sampled uniformly, about every six hours over this time period. Starting at solar minimum, we observe very little detail on the Sun, but for an occasional sunspot. As the Sun evolves further into the cycle, sunspots appear more frequently, and larger.

This version of the video covers the same time frame (December 2019 to September 2024), but starting in January 2023, the image sampling is increased from 6 hours to every 30 minutes. This slows down the motion allowing us to observe the sunspots grow, evolve and move in more detail.

Next we view the Sun in ultraviolet light at 171 ångstroms, covering the December 2019 to September 2024 time frame. At solar minimum, the solar 'surface', or chromosphere, presents itself as a fairly uniform glow. Darker regions near the upper and lower rotation poles reveal the 'open' solar magnetic field lines which carry solar plasma on a 'fast track' to the distant solar system. As the Sun evolves deeper into the solar cycle, active regions form (they appear as sunpots in the visualizations above) with the magnetic poles of the sunspots connected by bright channels of hot plasma. Many of these active regions will launch solar flares to release their pent-up magnetic energy.

The visualizations below present the evolution of the solar magnetic field during this part of the solar cycle, generated from solar magnetograms using the PFSS (Potential-Field Source Surface) model. On the magnetogram representing the solar surface, the gray color represents the weak global magnetic field. As sunspots emerge, they can appear as white or black on the surface -- white being a stronger magnetic field pointing outward to space, while black is a stronger magnetic field directed to the solar interior. White and black regions usually appear close to each other (which form the sunspots in the HMI views above) with closed magnetic field lines (white curves) connecting them. These closed field lines often appear prominently in SDO 17.1 nanometer (171 ångstrom) filter imagery as loops of hot plasma.

'Open' magnetic field lines connect the solar magnetic field to the solar wind and the rest of the solar system. Magenta field lines are directed sunward while green field lines are directed outward.