The geometry is built using two truncated cones (TRC) whose vertex is in the centre of the Earth, the base is out of the atmosphere and the altitude (considering a geographical location in the northern hemisphere) is in the direction of the Earth radius which passes through the North Pole. The angular span between the two cones contains the atmosphere of interest for the latitude of interest. In addition there is a third cone placed in the opposite direction: its vertex is where the other two cones have the base, its base is out of the atmosphere and its height is in the direction of the Earth radius which passes through the South Pole. A similar geometry can be built for a requested latitude in the southern emisphere. So the complete geometry of the local model, built with the auxiliary program atmloc_2011.f, is made of: - a main series of layers made from the part of the atmospheric shells between the two cones (this is the part where the scoring takes place), - two series of side layers made from the part of the atmospheric shells between one of the two cones and the third one. These additional layers are needed to take into account the primary and secondary particles which don't come from the vertical direction but can anyway reach the region of interest.
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