Large solar flares release high intensity radiation which heavily ionizes the lower D layer and increases its absorption.
Short wave fadeouts (SWF) last for about 2 hours and occur simultaneously with the observation of the flare.
Large flares eject clouds of solar material "fast protons" which can arrive a few minutes after the flares , and a slower flare cloud of particles which arrrive days later.
The earths magnetic field guides the electrically charged protons to the poles where they ionize the D region of the ionosphere through collision.
This is termed a PCA (polar cap absorption) which can last for several days.
The large flare cloud arrives up to 3 days later carrying a strong magnetic field which can cause ionospheric and geomagnetic storms.
An ionospheric storm is a redistribution of electron density in the atmosphere.
In a geomagnetic storm the magnitude and direction of the geomagnetic field fluctuates by up to 10% from the average.
This disrupts geological surveys and causes power surges in powerlines.
Interaction of solar material with the atmosphere causes the Aurorae.
Ex Amateur Radio Action Mag (Aust) April 1989