(Week 47, 1998)
The Soft X-ray Telescope operated well as usual. See the weekly operations report for details. Solar activity underwent a nice sinusoidal oscillation this week, with interesting phenomena, but only C flares up until the very end of the week - then, an X-class flare rose out of a low background.
In the display above (click to enlarge), the colored lines show the times of SXT images that currently are on-line at ISAS. The purple lines are flare mode. The gaps will be considerably reduced when the NASA telemetry arrives and gets reformatted. For a summary index listing of the weekly science reports, click here.
We have started routinely looking at daily difference images, something that we should have done long ago. The Yohkoh data come in daily sets as the Earth, carrying the Kagoshima ground station, rotates underneath its orbit. One day thus is a natural unit for difference-image searches. One motivation for this would be to spot emerging flux as it happens, in order to guide observations of new regions. An example appears below:
This particular difference pair was selected to show some interesting phenomena. It looks rather ugly (hence the title) because we have not corrected for solar rotation - thus new things or brightening things show up as white, whereas old things or dimming things show up as black. Newly emerging flux would be white. The gray-scale is saturated to show faint things; the original images have extremely large dynamic range because they are composed from pairs of long and short exposures. We show the same image below with a heliographic grid for reference, and call out several items. The grid lines are at the usual 15-degree increments; N up and W to the right.
The differences show many other things, and we intend to develop this tool for routine monitoring. Of course, dimming resulting from a CME occurrence would be nice to be able to sense routinely, but this effect is quite subtle and would be difficult to detect with relatively hideous images such as these.
hudson@isass0.solar.isas.ac.jp)