It doesnt heat the ionosphere first of all. It causes ot to raise. Radio waves have always bounced down off the ionosphere. That is who AM can travel over the horizon.
"Work [..] has shown that it is possible to raise this temperature by as much as 30% within a small, localized region during an experiment." https://bit.ly/2Ppnyjy
It's not in a controlled manner as far as I know but as I already said, they can easily amplify already occuring events like hurricanes and trigger eathquakes in specific areas.