The 2009 Europhysics Conference on High Energy Physics

The detection of vertical High Energy Cosmic Rays is blurred in ground arrays by Coulomb spread of air-shower secondaries. These showers grows in a well knon conic random tree. High Altitude horizontal airshowers are totally different: the low air density allows the spread of the shower in a thin fan-like shape of huge lenghts. Their arrival angle at horizons select, in a fine- tuning, their slath-depth and energy ; their shower distances inferr their primary compositions. Electron pair fingers opens in a wide forked tails differently on Earth: At geomagnetic equator the spread is vertical while at Poles the fan spread are horizontally tangent to the Earth atmosphere. At equator long array of element from balloons or satellites may reveal the thin twin spread of HECR skimming showering. Below the Earth edge, rarest but significant EeV tau air-shower may finally reveal the UHE GZK (few EeV ) tau neutrino whose skimming tau are escaping and decaying from Earth edge in high quotas air.