New parameters for solar spicules based on submillimetre data

New sub-millimetre observations of the quiet solar limb with angular resolution 1.5'' arc show a narrow asymmetric brightness spike centred near the optical limb, with approximate half-width 10'' arc. A semi-empirical predictive model is presented based on the properties of an individual spicule derived from optical and UV data. From it one can derive electron densities and temperatures within a spicule, a scale height of 2000 km for groups of spicules, and a mean number density over the solar surface of 4.2 10-8 km-2 at 1,200 km height above the photosphere. (author)