First Solar EUV Irradiances from SOHO by SEM

Authors: Judge, D.L., D.R. McMullin, H.S. Ogawa, D. Hovestadt, M. Hilchenbach, E. Moebius, L.R. Canfield, R. Watts, M. Khne, and P. Wurz
Reference: 17th International Workshop/SOLERS22 1996 Workshop, June 17-21, 1996 National Solar Observatory/Sacramento Peak, Sunspot, New Mexico, USA Group 4&5: contributed

The first results obtained with the Solar EUV Monitor (SEM) aboard the Solar and Heliospheric Observatory (SOHO) will be presented. The SEM has measured absolute solar EUV irradiance since December 16, 1995. The instrumentation consists of a simple, light weight (480 gm) transmission grating (5000 bars/ mm) spectrometer fitted with a free standing aluminum filter immediately behind the SEM entrance aperture to reduce the heat load on the grating and to limit the wavelength range to the aluminum transmission region. The dispersed light is detected by three aluminum coated photodiodes strategically placed 200 mm behind the grating. The zero order detector primarily measures the irradiance within the nominal aluminum wavelength band pass (170 - 800 A), and first order 304 A detectors measure the irradiance within an 80 A band pass centered about the 304 A solar He II emission. The zero order channel is also sensitive to soft x-rays shortward of approximately 120 A, while the first order channels are not. A comparison of the zero order data with the GOES7 x-ray data (1-8 A) will be presented.

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Last Update: April 2, 1999, James Weygand