I'm afraid that's a new one on me. Was that aone off or did the locals tell you it was a regular occurence?

Cloud to cloud lightning is not unusual. I have never heard of it occuring without sound. The sound would not travel much more than a few miles. Less than five I think. It would depend on how high the cloud and how far away but I presume it was all around you?

Interesting. Thunderheads reach 10 to 15 miles though don't they?

I asked Shan to get me some info on Monsoons. My weather forecasts are based on the time of the phase of the moon. In an hour the sun or moon would travel about 15*.

I don't know how the system works but I've an idea that mascons are involved. Mascons are minute variations gravitational attraction in the surface of the earth caused by changes in the density of the strata.

The orbits of satellites for instance are degraded by them. They are also the same regions as the so called "tectonic plate boundaries."

Is there a chance that the region you were in was near such a mascon / tectonic-plate margin?

In which case the phenomenon is related to earthquake lights not uncommon in the Andies I believe. And St Elmo's fire....

But I am only guessing.

Whilst here may I take the opportunity to say anyone can copy and post my stuff.