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2. Solar Geophysical Data (U.S. Department of Commerce).
3. Quarterly Bulletin on Solar Activity.
4. Landolt-Börnstein, N.S., Vol. VI/1 (1965).
5. Covington, E.: A Working Collection of Daily 2800 MHz Solar Flux Values, Nat. Res. Coun. Canada, Report No. ARO-5 (1977).