The Magnetometer (MAG) onboard the Space Weather Follow On – Lagrange 1 (SWFO-L1) observatory is performing well and has begun sending magnetic-field data back to Earth. SWFO-L1, NOAA’s first spacecraft built exclusively for around-the-clock space weather observations, launched on September 24, 2025. The MAG was activated two days later and has been measuring the magnetic field as it flows by the spacecraft. The field is carried by the solar wind – a hot, ionized gas that leaves the sun and flows past the spacecraft as it expands through the entire solar system.
Magnetic-field Measurements
The SWFO-L1 magnetometer measured the magnetic field at the spacecraft location during the November 12, 2025 geomagnetic storm. Top: magnetic field measurements by MAG before and during the storm. Bottom: The level of the resulting geomagnetic disturbance on the ground is expressed in two scales used in research and operations: the Kp index and NOAA’s G-scale. The SWFO-L1 measurements were taken approximately 40 minutes before the CME started to impact the Earth’s environment. [Image credit: NOAA NCEI, SWPC, and UNH/SwRI.]
The figure shows the magnetic signature of a major space weather event that led to the geomagnetic storm of November 12, 2025.
In the first panel, following a period of strong solar-flare activity on the sun, several clouds of dense plasma, or coronal mass ejections (CMEs) erupted from the sun and traveled toward Earth. The magnetic field measured by the spacecraft was relatively quiet until November 12, 2025, when the first of these CMEs started arriving. The magnetic field is expressed in three components (X, Y, and Z): their time variations reveal the internal structure of the CMEs and other formations as well as shed light on the turbulence of the background solar wind. Then, less than an hour after SWFO-L1 detected the first CME, it reached Earth and started driving a severe geomagnetic storm. The Z component of the magnetic field (green trace) indicates how much energy in the solar wind is driving the intense storm and is a critical observation for forecasting at the Space Weather Prediction Center (SWPC).
The geomagnetic disturbance triggered by the first CME was sustained by subsequent arrivals, producing a severe geomagnetic storm that peaked on November 12, 2025. The second panel shows the ground-based Kp geomagnetic index, measured every three hours. The corresponding NOAA Geomagnetic storm scale (G-scale), shown in the inset, is used for color-coding the storm intensity, which ranges from green (quiet) to red (severe/G4). This unusually powerful storm produced auroras that were visible as far south as Florida and Texas. It also resulted in impacts such as loss of altitude and/or buildup of static electricity on commercial satellites, disruptions in telecommunications, and rerouting of dozens of flights on near-polar routes. Thanks to NOAA’s advance warnings, based on real-time monitoring of the sun and solar wind, these impacts were significantly reduced.
The Magnetometer
MAG consists of two magnetometers mounted on a boom to improve the accuracy of the magnetic field data by minimizing magnetic “noise,” or interference, generated from the spacecraft. Together, they measure the interplanetary magnetic field at the spacecraft in three different axes for abrupt changes, which can trigger geomagnetic storms on Earth that can be harmful to infrastructure and technology. The information provided by MAG, combined with other SWFO-L1 measurements, will be critically important for predicting the severity of geomagnetic storms.
Upcoming Milestones and Data Releases
SWFO-L1 is expected to arrive at the Lagrange point 1 (L1) region in January 2026, and will be renamed as the Space weather Observations at L1 to Advance Readiness – 1 (SOLAR-1) observatory once it reaches its final orbital position. After completing additional testing and validation, SOLAR-1 will become operational in spring 2026, and NOAA's SWPC will begin using the MAG measurements, along with other data, for official space weather watches and warnings. Once fully commissioned, the SWFO-L1 MAG, along with its other instruments, will replace the instruments currently used at L1 and assume a critical role in monitoring solar wind activity. Its data will support SWPC in a wide range of NOAA space weather forecasting models to limit the impacts of geomagnetic storms and other disturbances. Additional information on the instrument, data products, and science results will be shared on the SWFO Data and Science webpage.
Data from SWFO-L1 during the post-launch testing phase should be considered preliminary and non-operational.