If you want to visualize the surface air flowing across every meter of the planet Earth, you need to plot nearly three trillion squares of land and sea and space. To do that you need a mind-bogglingly big calculator.Which is why Ioan Hadade, a computational scientist working with vast weather forecasting and climate models, is excited about the machine now online an hour down the road from his lab in Bonn, Germany. Europe’s first exascale supercomputer—called JUPITER, after a much bigger planet ...