Kennelly–Heaviside layer Kennelly–Heaviside layer The Kennelly–Heaviside layer, named after Arthur E. Kennelly and Oliver Heaviside, also known as the E region or simply the Heaviside layer, is a layer of ionised gas occurring between roughly 90–150 km (56–93 mi) above the ground — one of several layers in the Earth's ionosphere. It reflects medium-frequency radio waves. Because of this reflective layer, radio waves radiated into the sky can return to Earth beyond the horizon. This "skywave" or "skip" propagation technique has been used since the 1920s for radio communication at long distances, up to transcontinental distances. Propagation is affected by time of
Atmospheric Circulation Reconstructions over the Earth Atmospheric Circulation Reconstructions over the Earth The Atmospheric Circulation Reconstructions over the Earth, ACRE, is an international science project, began in 2008, that recovers historical weather observations to reconstruct past global and local weather patterns and so support meteorological reanalysis. The project aims to collect weather data from the past 250 years by linking international meteorological organisations to support data recovery projects and the imaging and digitisation of historical meteorological observations made at, for example, inland stations, lighthouses, or by ships at sea or in ports. The project aims to create historical datasets that are spatially and temporally complete, so