| Term: | Polar cap absorption events |
| Definition: |
Episodes of intense absorption of HF and VHF radio waves over the polar caps caused by excess ionization resulting from an influx of solar energetic particles into the upper atmosphere. PCA events have a pronounced diurnal variation, being much more intense during daytime than at night, and typically last for two to three days. (Abbreviated PCA events.) AMSglossary
GCW |
| Term: | Polar cap absorption events |
| Definition: | Episodes of intense absorption of HF and VHF radio waves over the polar caps caused by excess ionization resulting from an influx of solar energetic particles into the upper atmosphere. PCA events have a pronounced diurnal variation, being much more intense during daytime than at night, and typically last for two to three days. (Abbreviated PCA events.) |