Es and weather?

[KX4QC]

While it's well known to be a mostly summer ionospheric effect, there is some variation, as can be seen in this plot of Es by month compared over several years.

Es_by_month.png

Take a look at "Sporadic E Propagation — The Heart of 6 Meters" at https://k5nd.net/2020/09/sporadic-e-pro ... -6-meters/ to see a fine piece by Jim Wilson.

It goes over the basics of what is known of Es occurrence, and shows evidence for weather effects on the Es clouds.

First thoughts are that the E region is well above any usual weather, so what's going on?

Is the association with weather just association or do we dare suggest causation? If the latter, what the F (or E) is going on?

Any ideas?