Extremely high frequency paths. They are not reflected by the ionosphere nor do they travel along the Earth as ground waves as lower frequency radio waves do. At typical power densities they are blocked by building walls and suffer significant attenuation passing through foliage. Absorption by atmospheric gases is a significant factor throughout the band and increases with frequency. However, it is maximum at a few specific absorption lines, mainly those of oxygen at 60 GHz and water vapor at 24 GHz and 184 GHz. At frequencies in the "windows" between these absorption peaks, millimeter waves have much less atmospheric attenuation and greater
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