A comparison of SEM and GOES data

We chose at random a moderately active 24-hour period to compare the temporal behavior of X-rays observed by the SOHO/SEM sensor with that observed by GOES. The first figure below displays the SEM broadband channel (1 - 500 A), and 2 GOES channels: 1 - 8 A, and 0.5 - 4 A. For convenience, the SEM data has been multiplied by 10^-9, and the Goes 0.5 - 4 A channel has been multiplied by 6.

We then selected 9 events as labeled in the above figure. For each of these 9 events, two ratios were calculated: SEM to GOES (1 - 8 A), and GOES (1 - 8 A) to GOES (0.5 - 4 A). These 2 ratios (with the same normalizations as mentioned above) were then plotted against each other for the 9 events, as shown here:

A linear fit to this data has a correlation coefficient of 0.96, demonstrating that the 2 ratios are statistically highly correlated. The interpretation is simply that a "softer" spectrum (one with relatively more flux at the longer wavelengths) as measured from the 2 GOES channels will produce a higher value of the ratio of SEM (1 - 500 A) to GOES (1 - 8 A).