Lots of information about Sporadic E On the web.
https://www.electronics-notes.com/ar...radic-e-es.php
Information on tropospheric propagation
https://www.bbc.co.uk/reception/help...ng-on-freeview
Sporadic E was a common problem for Band 1 interference and can cause problems for VHF radio. Tropospheric seems to cause problems with the higher UHF frequencies.