UNDERGROUND METEOROLOGY-“What’s the weather underground?”

The aim of t h is work is to provide a synt h etic outline of some of t h e processes of transient nature occurring in caves, focusing on poorly studied general aspects of underground physics and mainly making use of original experimental data. In the first part, t h e average climatic conditions of a caves, t h eir connection to t h e external climate, and t h e general role played by rock, water, air and external morp h ology are discussed. The variation of t h e internal temperature wit h t h e altitude is a key parameter for t h e cave p h ysics: t h e related energetic consequences are briefly discussed. In t h e second part, transient processes are considered, and a general overview of main meteorological p h enomena occurring underground is given. The p h ysics of t h ermal sedimentation, of underground temperature ranges, of infrasonic oscillations of cave atmosp h eres and, above all, of water vapour condensation in caves is synt h etically described. The experimental study of t h ese processes is extremely difficult, because t h ey are time dependent and h ave very small amplitude; t h e first measurements s h ow, h owever, t h at t h eir variability from one cave to anot h er, and from point to point inside a cave, is surprisingly h ig h . To provide a more correct interpretation of underground climatic measurements, for t h eir speleogenetic role and importance in cave environment protection, a better understanding of t h e processes described h ere is essential.