Models for solar magnetic loops - I. A simple theoretical model and diagnostic procedure

In the present paper the quasi-static model of Landini & Monsignori Fossi (1975) for coronal loops is improved and a simple diagnostic procedure is developed to compare the most important physical properties of the model with a set of spectral observations of loops such as those obtained by the CDS and SUMER instruments on SOHO. The model assumes quasi-static and isobaric conditions and solves the energy equation among radiative losses, a constant heating function and heat conduction. The model is allowed to have a variable loop section. To better match the latest observational results, an isothermal section of the loop is added at the top of the loop model; its effects on the diagnostic technique and on the shape of the unknown heating function are discussed. A numerical simulation is shown and the effect of the isothermal region is discussed. In a second paper (Brkovic et al. 2002, Paper II) the present model will be compared with observations from the SOHO satellite.