Long-Term Observations of the Solar Polar Magnetic Field with the KMAS/STOP Magnetograph: Continuing the WSO Time Series
This study demonstrates that synoptic observations from the KMAS/STOP magnetograph (2014–2026) provide a stable, high-correlation continuation of the Wilcox Solar Observatory's long-term solar polar magnetic field time series, successfully filling the gap left by the termination of regular WSO operations.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
The Sun is not a static ball of fire; it is a churning, magnetic engine that drives the space weather surrounding our planet. At the heart of this engine lies a massive, invisible cycle that repeats roughly every eleven years, flipping the Sun's magnetic north and south poles like a giant bar magnet. Scientists have long known that the strength of these polar fields at the bottom of a quiet period predicts how violent the next cycle will be. To understand this, they need to watch the poles closely, but doing so is difficult. From Earth, the poles are always viewed at a sharp angle near the edge of the solar disk, making them hard to see clearly. For decades, a single observatory in California, the Wilcox Solar Observatory, provided the only consistent, long-term record of these polar fields, creating a continuous timeline that stretches back to the 1970s. This record became the gold standard for predicting solar storms and understanding the Sun's behavior. However, that observatory recently stopped its regular observations, leaving a gap in our historical data just as the Sun enters a new phase of activity.
To fill this gap, researchers Ivan Berezin and Andrey Tlatov turned their attention to a different instrument located high in the mountains of Kislovodsk, Russia. This device, known as the STOP magnetograph, has been scanning the entire face of the Sun since 2014. The team's goal was straightforward: determine if this Russian telescope could pick up the baton from the American one and continue the decades-long story of the Sun's magnetic poles. They spent years analyzing the data from the STOP instrument, which measures the magnetic field by looking at how sunlight splits into different colors when passing through a magnetic field. They compared their new measurements against the historic Wilcox record, as well as against data from modern space telescopes and other ground-based networks. The result is a confirmation that the STOP instrument is not just a backup, but a reliable successor capable of extending our understanding of the solar cycle.
The researchers found that the measurements from the Kislovodsk telescope track the historic Wilcox data with remarkable precision. When they plotted the magnetic strength of the north and south poles over time, the two records moved in lockstep, rising and falling together with a correlation so strong it exceeded 95 percent in the northern hemisphere. This means that despite being built differently and located thousands of miles apart, the two instruments are seeing the same underlying reality of the Sun's magnetic engine. The team also checked the data against other major sources, including the Solar Dynamics Observatory in space and a global network of ground stations. They discovered that the STOP data aligns just as closely with these independent records as the historic Wilcox data does, proving that the new measurements are not an isolated anomaly but part of a consistent global picture.
One of the most interesting discoveries in the study concerns the numbers themselves. While the patterns of change were identical, the actual numbers reported by the STOP telescope were slightly different from those of the Wilcox observatory. The Russian instrument consistently reported slightly stronger magnetic fields than the American one. The researchers investigated whether this was a mistake in the equipment or the software, but they found the difference was real and consistent. It appears to stem from the specific type of light the instruments use to measure the magnetism; the Wilcox telescope looks at one specific color of light, while the STOP telescope looks at two slightly different colors. These different colors react to the magnetic field in slightly different ways, leading to a small, systematic shift in the final numbers. However, because the relationship between the two sets of numbers is so stable and predictable, the scientists can easily adjust the STOP data to match the Wilcox scale.
This ability to translate between the two scales is the key to the paper's success. The researchers showed that by applying a simple mathematical adjustment, they could make the STOP data fit perfectly onto the historic timeline, with an average difference of less than one-tenth of a Gauss, a unit used to measure magnetic strength. Crucially, this adjustment did not need to change over time; the relationship remained steady from 2014 to 2026, with no signs of the instrument drifting or losing accuracy. This stability means that the STOP telescope can now be used to extend the historic record of solar polar fields well beyond the end of the Wilcox observations. The data from Kislovodsk provides a stable, independent ground-based record that ensures scientists will not lose the continuity of this vital long-term dataset.
The study also highlighted that not all instruments are equally ready to take over this role. While the space-based telescope and the global network of stations showed good agreement, one other ground-based instrument from China showed much more erratic behavior, with its data jumping around and failing to match the smooth trends seen by the others. This contrast reinforced the reliability of the STOP telescope, which maintained a steady, consistent performance throughout the study period. The researchers concluded that the Kislovodsk observations provide a robust foundation for the future. By bridging the gap left by the Wilcox observatory, the STOP magnetograph ensures that scientists can continue to monitor the Sun's magnetic heartbeat, keeping our predictions of space weather accurate and our understanding of the solar cycle intact for the decades to come.
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