HMI radial estimates show a larger decrease in net field magnitude at 60–70°N than at 70–90°N between August–September 2025 and August–September 2026

We compared public HMI polar-field estimates for 1 August through 30 September in 2025 and 2026. The northern decrease was known from prior work. We tested its later recovery and its latitude structure with 61 paired daily means at 00 and 12 TAI and QUALITY equal to zero. The mean net field magnitude at 60–70°N decreased from 1.592 G to 0.695 G, or 56.3%. At 70–90°N it decreased from 2.135 G to 1.851 G, or 13.3%. The difference between the band changes is −0.613 G. The lower band supplies 79.4% of the decrease in the observed northern cap mean. A finite-distance projection check shows that a small part near the north pole crossed the image boundary in early August. On the 57 paired days when both selected northern bands pass the complete boundary test, the decreases remain 54.9% and 13.7%. The 60–70° result also persists across primary sampling-hour and viewing-latitude checks. Circular moving-block resampling describes variation within this short season; it does not include full instrument errors. The WSO polar-field page has no numeric row after 9 January 2026 and supplies no check of the target season. The result concerns net radial-field estimates under the HMI radial-field assumption. It does not measure unsigned magnetic flux or establish a cause or a forecast for the next solar cycle. We preserve the input data, source records, code, results, figures, and instructions for reproduction.

solar polar field · HMI · solar cycle 25 · radial magnetic field · latitude bands · viewing geometry · public data · reproducible analysis