Since I increased graphics settings on my FSX, these spiral appears in the sky. Does anyone know what this means?

 

FSX' desperate attempt to simulate a tornado?

 

Seriously, I have never seen those. Do they appear when you chose a specific aircraft?

 

Cheers

That looks like thermal visualisation to me.  Check your display settings, weather tab, just below the cloud draw distance. 

I saw that spiral only during gliding missions, never in free flight.

Tim is very much spot on in my eyes. You can pick either no visualisation, those circles or some birds to show you the static thermals in FSX. Find the option under the weather tab.

Thanks for the replies guys!

AndyPaul, this happens with any aircraft.

The problem is the thermal visualization. In display settings, weather tab has the option "thermal visualization": none, normal or schematic. It was filled with "schematic". When I change it to "normal", the spirals are gone.

Thanks again to every body!