No one has a firm grasp on the dimensions and activity of the lowest part of our upper atmosphere, known as the ionospheric D region, because it’s literally a moving target. Located 40 to 60 miles above the Earth’s surface, the region moves up and down, depending on the time of day. And it’s nearly impossible to monitor: it’s too high for airplanes and research balloons, too low for satellites, and not dense enough for direct radio sounding.
Original Title: Researcher uses lightning storms to measure the density of Earth's upper atmosphere
Full Text of the Original Article: https://phys.org/news/2019-04-lightning-storms-density-earth-upper.html