Polar Cap Absorption

A polar cap absorption event results from the ionisation of the D-layer of the polar ionosphere by high energy protons. A PCA causes a HF radio blackout for trans polar circuits and can last several days. PCAs are almost always preceded by a major solar flare with the time between the flare event and the onset of the PCA ranging from few minutes to several hours.

See Real Time Riometer Data from Antarctic Stations.

The icon below indicates the estimated absorption in db of a 30 MHz riometer from Casey station in Antarctica. These figures give an indication of the severity of the PCA. The background colour of the icon is red when absorption exceeds 1db and green otherwise.

Details of any current proton event are given below:

(last updated 21 May 2025 03:25 UT)

10MeV (S1) Proton/PCA Event Began 04 01 2025 2220UT and is in progress 10MeV (S1) Proton/PCA Event Ended 05 01 2025 0930UT 10MeV Maximum proton flux of 2.00E+01 PFU (S1) observed at 05 01 2025 0055UT 10MeV (S1) Proton/PCA Event Began 25 02 2025 0010UT and is in progress 10MeV (S1) Proton/PCA Event Ended 25 02 2025 0830UT 10MeV Maximum proton flux of 3.71E+01 PFU (S1) observed at 25 02 2025 0240UT 10MeV (S1) Proton/PCA Event Began 31 03 2025 1425UT and is in progress 10MeV (S2) Proton/PCA Event Began 01 04 2025 0200UT and is in progress 10MeV (S2) Proton/PCA Event Ended 01 04 2025 0850UT 10MeV Maximum proton flux of 1.47E+02 PFU (S2) observed at 01 04 2025 0425UT 10MeV (S1) Proton/PCA Event Ended 02 04 2025 0810UT 10MeV Maximum proton flux of 1.47E+02 PFU (S2) observed at 01 04 2025 0425UT

(last updated 21 May 2025 03:25 UT)

No proton event in progress

Note: Proton event descriptive text will lag realtime due to data smoothing.

Current proton fluxes are as follows:

(last updated 21 May 2025 03:25 UT)

GOES (Gp18) satellite energetic Proton Flux (Courtesy of SWPC, Boulder Colorado, USA) Proton event detection will lag data time by approximately 1 hour due to data smoothing. Data Date/Time: 21 05 2025 0315 UT Proton Energy Current Proton Level Flux Event Status 10MeV 1.73e-01PFU No proton event in progress 100MeV 1.53e-01PFU No proton event in progress 500MeV 1.49e-01PFU No proton event in progress Units: PFU = protons/cm2/sec/ster MeV = million electron volts Proton energy levels and PFU event thresholds: Proton Energy Proton Flux Level Threshold 10MeV 10PFU 100MeV 1PFU 500MeV 1PFU Gp: GOES primary Gs: GOES secondary Solar proton events can impact satellite operations and transpolar HF communications.

GOES satellite proton flux data for this page are provided by US Space Weather Prediction Center in Boulder.