Vista

Vista (Q, pron. [ˈvista]) or Wista (pron. [ˈwista]) was a part of the atmosphere that surrounded the world of Arda before the cataclysm at the end of the Second Age. Vista formed the inner layer of normal air: above it was Ilmen, and above that Vaiya.

Vista was the breathable air, with in the top part the clouds, and in the lower parts the paths of birds.