AIR WATCH: a space mission to observe the UV fluorescence induced in the Earth atmosphere by extreme-energy cosmic radiation

One of the most challenging tissues in Astroparticle Physics is represented today by the observation of the energy spectrum of the Extreme Energy Cosmic Radiation. The very existence of particles with energy above 1020 eV and of neutrinos of comparable energy raises fundamental scientific questions in connection with their origin and propagation in the interstellar/intergalactic space. These particles can be detected through the gain showers produced in the Earth Atmosphere. The shower development is accompanied by emission of fluorescence in the atmosphere, in particular that induced in Nitrogen with characteristics spectral lines in the UV. Following a first suggestion by J. Linsley in the early 1980's, taken over by Y/ Takahashi, the fluorescence observation can be advantageously carried out by space. By using wide angel optics with large collecting surface, we can monitor a target area of atmosphere of the order of millions square kilometers x sr and corresponding mass above 1013 tons, allowing the detection of the very small flux values typical of the EECR and making possible the search of the elusive high energy neutrinos. AIRWATCH follows this approach. We describe the main scientific goals for the investigation of the EECR, High Energy neutrinos and of the Gamma Ray Bursts, together with the relevant connections to the problem of their origin. The experimental framework is outlined and a description is given of the space mission and of the observational strategy.