Detecting Ultra High Energy Neutrinos by Upward Tau Airshowers and Gamma   Flashes
  Tau Air-showers are the best trace of rarest Ultra High Energy neutrinos UHE $\nu_{\tau}$, $\bar\nu_{\tau}$ and $\bar{\nu}_e$ at PeV and higher energy. $\tau$ Air-showers may generate billion times amplified signals by their secondaries . Horizontal amplified $\tau$ air-showers by $\nu_{\tau} N$ and UHE $\bar\nu_{e} e$ at PeV emerging from mountain chain might be the most power-full imprint. Upward UHE $\nu_{\tau} N$ interaction on Earth crust at horizontal edge and from below, their consequent UHE $\tau$ air-showers beaming toward high mountains should flash $\gamma$,$\mu$,X and optical detectors on the top.   Upward $\tau$ air-shower may hit nearby satellite flashing them by short, hard, diluted $\gamma-$burst at the edge of Gamma Ray Observatory BATSE threshold. We identify these events with recent (1994) discovered upward Terrestrial Gamma Flashes (TGF) and we probed their UHE $\tau$ - UHE $\nu_\tau$ origin. From these TGF data approximated UHE $\nu_\tau$ flux and $\Delta m_{\nu_\mu \nu_\tau}$ sever lower bound are derived. Partial TGF Galactic signature is also manifest within known 47 TGF events clustered within three degrees from the Galactic plane at ${\simeq 2\cdot 10^{-3}}$probability. Well known $X-\gamma-\mathrm{TeV}$ active galactic and extragalactic sources have found probable counterpart in TGF arrival directions. Detection of elusive UHE $\nu_\tau$ seem finally achieved. 
Daniele Fargion (Physics Department, and INFN, Rome 1, Pl.A.Moro,2,   Italy)