proton Polar Cap Absorption vs. Proton Event

[Kaimbridge]

What defines a “polar cap absorption event” vs. just a “regular” “proton event”?

I know that it involves the polar cap, but donʼt all proton events affect the polar caps, such as the current event?

Yesterdayʼs SWPC Activity Report and Forecast, part III, shows proton event probabilities for the next three days as 80/80/60 and PCAF status as “yellow”.

Or, is a “regular” event an elevation of the 10 MeV wave, while the polar cap event follows the less common 100 MeV elevations?

Is there a SWPC (or other space weather site) page that shows PCAE times?

I remember back under the old system—when flares were called “flares” and not “radio blackouts”!—WWV used to give PCAE times (which were always within and shorter than the PrE times) during the :18 report.  But at :16, there was also a navigation status report that also included PCAEs with times and they lasted a lot longer—days and sometimes even weeks (I believe they involved lower frequency events?)!

[Vancanneyt Sander]

Proton events refer to the >10MeV solar protons, those reached S1 Space Radiation Storm level a few days ago due to a flare to the limb. During the flare such protons get accelerated and are send out in every direction. Chances for new proton event are getting lower so as for now code yellow (because it's still elevated) but will soon return to green.

During flares the radio blackouts occur and indeed polar regions are always affected and are associated with flares > M1, during the flare the polar cap high frequency radio connections will be interrupted, the bigger the blackout how more global it gets. These events happen immediately as the flare progresses, a regular proton event starts also with the flare but particles take longer to reach us (that's also the cas for low energy protons and electrons).

[Kaimbridge]

Okay, but that doesnʼt really address defining a PCAE—the proton absorption chart has been steadily red (sometimes dropping to yellow, then rebounding) at least at one of the poles for the past few days, but the official PCAF returned to green a couple of days ago.

So are we still in a PCA event, or are there different baseline measurement defined event catagories like the proton 10MeV ≥ 10pfu and 100MeV ≥ 1pfu events?  And what would be the “10MeV ≥ 10pfu” type definition for a PCAE?

Does the SWPC (or other space wx agency) have a “polar cap flux” type graph chart (like the X-ray and proton charts) or is the above D-Region Absorption Map the closest thing?

 

[Guest Harry Twinotter]

Polar cap events are caused by ionisation of the polar ionosphere by high energy protons. I think low energy protons won't penetrate that far - that is why you only see polar cap events when high energy protons are elevated.

The protons get concentrated there by the earth's magnetic field.

[Kaimbridge]

Polar cap events are caused by ionisation of the polar ionosphere by high energy protons. I think low energy protons won't penetrate that far - that is why you only see polar cap events when high energy protons are elevated.

Ah, okay, so basically then, a “proton event” is 10MeV ≥ 10pfu proton elevation, while a “polar cap absorption event” is 100MeV ≥ 1pfu, or maybe even 50MeV ≥ 1(?)pfu?:

The official PCAF was yellow from the 21st-23rd (in the original, “live” report, the 22nd was red, as SpaceWeatherLive.comʼs archived copy shows) and the proton graph only shows the 50MeV scribble elevated on the 22nd, approaching 1pfu.