Observations by a Solar Spacecraft Flotilla!

Science Nugget: May 15, 1998

First on SOHO's JOP 059; then on SOHO's JOP 080 - for perhaps the first time in the history of the universe, three solar-observing satellites whizzing around the Earth in completely different orbits pointed their telescopes at the same solar target. This no doubt is the right way to characterize the solar atmosphere, which exhibits such a wide range of temperatures and other physical properties that no single kind of observation can hope to be definitive. To counterbalance this observer's dream, we now face a data analyzer's nightmare, consisting of many "data cubes" of data that are asynchronous and (initially) unregistered.

From the point of view of Yohkoh, things worked out very well indeed. Our planning and summary pages for JOP 059 and JOP 080 show off some of the details. The image below (click to enlarge a bit) shows one frame from the SXT movie for JOP 080:


This shows a typical active region (NOAA 8218), viewed nearly from above. For these observations the SXT observations consisted of one AlMg image every 8 seconds at full resolution, because we were in "PFI-dominant" observing mode; after every tenth frame we got one Al.1 image and one dark image. The exposure times were fixed. The FOV frames the left part of the region, and late in the time series a bright microflare appeared at the right edge. This and one or two other microflares saturated the brightest pixels, but in general the exposures came out just right for time-series analysis of the AR loops.

2. Instrument status report: all's well

SXT continues in good health. This week was again exciting, with medium-level activity including M-class flares. The GOES background level dropped below "C" on the 9th. A rather amazing and huge filament complex at the S had failed, as of May 16, to erupt as predicted by many.

SXT took part in two Joint Observing Programs (JOPs) this week: JOP 059 ("High Cadence Activity Studies and the Heating of Coronal Loops", Robert Walsh coordinating), and JOP 080 ("High Time Resolution Imaging Study of Coronal and Transition Region Dynamics (EIT Shutterless-mode Campaign)", Frederick Clette coordinating). These campaigns were the first, to our knowledge, where solar telescopes on three independent spacecraft (Yohkoh, SOHO, and TRACE) simultaneously observed the same target.

David McKenzie and Hugh Hudson, 15-May-98 (email mckenzie@isass0.solar.isas.ac.jp).