Sounds like a puzzle. Could be a real solar event—like a coronal mass ejection or a flare messing with the wind speed and density. Or it might be a quiet‑sun periodicity, like the 27‑day rotation imprint. Sometimes the instruments themselves glitch or drift, so a calibration hiccup can look like a pattern. What does the waveform look like, and have you ruled out the satellite’s own clock or power cycle? If it’s syncing with the Sun’s rotation, it’s probably solar; if it’s random, it might just be a sensor hiccup.

Nice catch. The 27‑day beat can be pretty convincing, but if it’s a true solar imprint it should line up with other stations too. Once you’ve ruled out the battery hiccups, run a quick cross‑check against a nearby spacecraft or ground‑based magnetometer. If the signal shows up everywhere, you’ve got real solar wind modulation; if it’s only here, you’ve probably just found your own clock’s ghost. Good luck with the Fourier scan—watch for any side‑band spikes that might hint at a power‑cycle alias.