Flows of Mass , Momentum and Energy in the Solar

This work is dedicated to the study, in the framework of known models of coronal loops, of cold long loops observed in several spectral lines by SOHO. In particular an observation made by SOHO/CDS in the O V (629.73 A) line show a very high speed ow along a loop. The comparison with steady state siphon ow loop models leads to the conclusion that such loop cannot be in steady state; in particular no steady state solution with maximum temperature in the range of a few 10 5 K can be obtained. Some suggestions on the possible characteristics of the loop dynamic state are discussed and a preliminary analysis, in terms of a loop dynamically heated by mi-crooares and alternating between coronal conditions and chromospheric temperatures, is presented. Suggestions on how to observe the dynamic behaviour of such cold loops are also discussed. The cold EUV loops observed in detail by SOHO instruments can provide information on a less known aspect of solar loop physics, one which may be quite important in the overall balance of ows of mass, momentum and energy in the solar atmosphere.