A study was made of the polar cap absorption
(PCA) event on 23-24 March 1991 produced by the largest solar proton event at
E>10 MeV since August 1972. This PCA event was related to a solar flare in
the eastern hemisphere lasting only 2 days and exhibiting a long time delay
between the flare and the increase of ionospheric absorption. Midday recovery
occurred regularly each PCA day near the cut-off latitudes during the noontime
hours and is attributed to the daily variation in the proton cut-off latitudes.
The maximum absorption during the PCA event was observed at high latitudes or
near the cut-off latitudes where ionization may be due to both solar protons and
trapped particles. The minimum in the absorption values during the night-time
hours would appear to be caused by the chemistry of the D-region as well as
access of the solar protons into the polar cap area
Is data on this page outdated, violates copyrights or anything else? Report the problem now and we will take corresponding actions after reviewing your request.