SCATTERING MODELS FOR THE SOLAR INFRARED F-CORONA BRIGHTNESS

Model calculations are made of the infrared brightness in the solar F- corona motivated by recent infrared solar eclipse observations. Two di fferent approaches are employed to describe the scattering properties of interplanetary dust: Mie scattering theory and diffraction theory, with and without and isotropic scattering term. In addition, two diffe rent particle size distributions are used in the calculations and the resultant line of sight brightness is compared with observational data of the solar F-corona between 3 and 8 solar radii (R.) in the eclipti c plant. It is found that the use of diffraction theory without and is otropic scattering contribution gives a very poor match with the obser vations, for both assumed particle size distribution. However, both th e diffraction theory including isotropic scattering and the Mie scatte ring theory agree reasonably with the observed brightness, and especia lly its radial slope within the corona, for the model size distributio n which is dominated by large particles. Only Mie theory may be employ ed in describing the second model size distribution because diffractio n theory poorly describes the scattering due to the small particles wh ich dominate this size distribution. It is concluded that the derivati on of particle size distributions from the F-coronal brightness is sti ll ambiguous and a further analysis needs either improved observations , or the application of further reasonable physical assumptions.