COMPARISON OF 10.7 CM RADIO FLUX WITH SME SOLAR LYMAN ALPHA FLUX

Measurements of the solar Lyman alpha flux that were made over a seven‐and‐one‐half‐year period between October 11, 1981 and April 13, 1989 have been compared with ground‐based measurements of the solar 10.7 cm radio flux made over the same time period. There is a long‐term correlation between these two measures of solar flux during the declining part of the solar cycle. During the solar minimum period, there is only a poor correlation between the two solar fluxes because the 10.7 cm radio flux reaches a minimum of 65 × 10−22 W m−2 Hz−1 and does not vary below this value while the Lyman alpha flux continues to decline and show long‐term and short‐term variations. During the early ascending phase of the new solar cycle, there is again a correlation between the two fluxes, although the constant of proportionality between the two is different from the constant during the declining phase of the previous solar cycle. Somewhat later, during the period November 25, 1988 — April 13, 1989 (last period when observations of Lyman alpha were made) a medium‐term correlation exists and the proportionality of the two indices is once again similar to what it was during the declining phase of the previous solar cycle. A study of the correlation of the 10.7 cm flux with the Lyman alpha for a 999‐day period during the declining phase showed that for the short‐term (27‐day) variation there is a correlation between the two fluxes but the proportionality between them varies from one solar rotation to the next. The conclusion is that the solar 10.7 cm radio flux is not a useful index for the prediction of solar Lyman alpha flux for the short‐term, 27‐day variations. Copyright 1990 by the American Geophysical Union.