More details on the analysis here: bsky.app/profile/lemo...

Yes, I know NACp is a categorical value. I said I was speaking very roughly!

14/ bsky.app/profile/csan...

13/ This is a nice one too. (Thanks, @russ.garrett.co.uk)

12/ Then for the data, compute mean NACp and subtract the baseline NACp for that minute of the day and 10° latitude band. Chart that difference.

11/ Analysis details: For each 60 second period, take the median NACp reported by an aircraft. Use the mean latitude it reported, and assign the NACp to a 10° band of latitude. Use the data from before the storm to compute a baseline: Each minute of a day and latitude band has an avg NACp.

10/ But also look at this crazy animated map of the last 6 hours of the ionosphere from www.sws.bom.gov.au/HF_Systems/6/5 (thanks, @grajohnt.bsky.social).

9/ My guess is a lot of this repeated diurnal structure has to do with reliable daily changes in aircraft distribution. Waves of aircraft crossing the Atlantic & Pacific, etc. bsky.app/profile/lemo...

8/ There seems to be a delay between solar storm onset and anomalous decrease in NACp (the temporal resolution of the time axis is 60 seconds). Does it take time for the ionosphere to "heat up"?

7/ You might also wonder if my analysis is correct. Well, I can pretty much guarantee there are mistakes somewhere, but I think this result is pretty plausible. "Solar storm caused GPS issues" isn't a surprise.

Right! I wonder if the big east west waves might explain some of the finer structure of the daily signal–e.g., see how there's a pretty strong double-peak (maybe even triple-) at the leading edge of the larger daily peak?

6/ Yes, but aircraft and ADS-B receivers aren't equally distributed around the world. They're mostly in the Western hemisphere, and also in some specific latitude and longitude ranges. So I'm not surprised you can see daily variation.

5/ You may be wondering: “If the daily variation in NACp reflects ionospheric changes driven by sunlight, why would you see a clear 24-hour cycle in global NACp? Aircraft are distributed around the world at all times, so daylight effects should average out—shouldn’t they?”

4/ This chart subtracts the daily periodic baseline from NACp measurements so anomalies caused by the solar storm are more obvious. NACp ranges from 0 (lowest GPS accuracy) to 10 (highest), and the storm seems to have caused an average drop of less than 0.8.

3/ This chart shows avg NACp (a GPS-accuracy indicator) for all aircraft worldwide starting Jan 16. You can see the ionosphere’s daily rhythm, which affects GPS signals. Kp: geomagnetic activity. The dashed line marks the solar storm peak; shortly after, there appear to be anomalous effects in NACp.

2/ There's no obvious effect from the solar flare shown on GPSJAM. The places that are usually green are still green. But the default GPSJAM map is tuned to show interference that makes GPS unusable, so maybe it's not sensitive enough. gpsjam.org?lat=37.44890...