@Ve3ldj Hahaha. High-Frequency Active Auroral Research Program, but I'm sure you already knew that.

Until HAARP was built, there wasn't much we could do to study the ionosphere (200 miles up, well into space) besides observe the effect of the sun on it. HAARP is composed of a gang of transmitters totalling several megawatts feeding a phased-array antenna system that can focus those megawatts on a small and quickly steerable area of the sky. The gain of the antenna system results in ERP (effective radiated power) as high as 4 gigawatts. This is enough that HAARP is able to induce small effects in tiny areas of the ionosphere which is highly educational.

Over the years there have been some "fun" experiments where the ham radio community all over the world was invited to participate. I participated in one back in 2008 where we did moonbounce in the 40 meter band, haha. HAARP focused full power transmissions at the moon. The reflected radio signals were received by hams all over the world.

https://kw2p.shuttersparks.net/haarp-moon-echo-experiment/

As far as affecting the weather, no. Causing earthquakes, no.