I took this photograph on the 22nd April. The dust on the car was said to be from the Sahara. Since then there have been two further events where blobs of hot air have moved north from the Sahara into Europe. I found
https://www.eurekalert.org/pub_releases/2018-10/rai-pjc100218.php which suggests that it is to do with the jet stream. Weather forecasters refer to the jet stream a lot at the moment. Winds on Earth are driven by convection. At the equator, the Sun heats the air so that it expands and rises. This causes low pressure at ground level. The opposite happens at the poles. In between, the air from the equator falls down to the ground creating high pressure around the latitudes that contain deserts like the Sahara. At our sort of latitude, it is warmer than the poles so air pushed down from the Arctic by high pressure there can be warmed and rises. This means that in each hemisphere there are 3 convection cells. The polar jet stream occurs along the boundary between the two most northerly of the large scale convection cells in this hemisphere. I'm interested that it flows along the boundary rather than from one side to the other. This seems a bit like one of the hand rules for electromagnetism. Hot air is rising but the fast flow is perpendicular to this upwards flow.
https://en.wikipedia.org/wiki/Jet_stream#Polar_jet_stream
