Comparison of nonflare solar soft X ray flux with 10.7‐cm radio flux

The similarities and differences of the nonflare solar 1‐ to 8‐Å X ray flux and the daily 10.7‐cm Ottawa solar radio flux are examined. The radio flux is shown to be much less sensitive than the soft X ray flux on the average to the coronal emission of active regions located near or beyond the solar chromospheric limb relative to regions near the center of the solar disk. This is caused by the solar soft X ray emission's being optically thin while much of the 10.7‐cm active region emission is from optical depths of τ ∼ 1. The radio flux includes a large quiet sun flux which is emitted mostly from the tenuous chromosphere‐corona transition region ( T ∼ 10 4 –10 6 °K) and partly from the cooler portions of the quiet corona T ∼ 1.5×10 6 °K. Conversely, the solar soft X ray flux has a very small quiet sun component.