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J.W. Cook (Naval Research Lab), J.S. Newmark (GSFC), A. Vourlidas (George Mason U.)
We have modeled the contribution to solar radio emission at 328 and 1446 MHz from free-free thermal bremsstrahlung emission, using a full disk differential emission measure (DEM) map of the Sun. The DEM map is produced from four EUV images (171 A, 195 A, 284 A, and 304 A) for a selected day from the EIT instrument on the SOHO satellite, using a method developed previously by Cook, Newmark, and Moses. The EIT instrument images the Sun out to 1.4 R, with a pixel size of 2.6 arc sec and spatial resolution of 2 pixels. We perform the radiative transfer calculation, determining the optical depth scale for free-free emission and the emergent absolute intensity for each pixel in the field-of-view using the individual DEM of that pixel, and transforming integrals over the line-of-sight into integrals over temperature via the DEM. We can compare our model calculation with the VLA radio observations of Vourlidas from 1998 January 31. Our model is in good agreement outside of active regions, where free-free emission should truly be the dominant emission mechanism. In areas such as sunspots, where the strong magnetic field leads to additional gyro resonance radiation, the difference between the observed total intensity and our calculated thermal component should be a good estimate of the nonthermal gyro radiation. This work is supported by NASA under W-19,348 and by the Office of Naval Research.
The author(s) of this abstract have provided an email address for comments about the abstract: cook@hrts.nrl.navy.mil