Tips for finding the perfect data-set#

The nature of EIS observations means that it can be quite difficult to find the data you want. For example, suppose you would like to study an active region loop and measure velocities in the Fe IX 197.86 line. How would you go about trying to find suitable data-sets?

Using eis_filter_studies#

The procedure described here starts by first narrowing down the large list of EIS rasters to those that are likely to be useful for the work. In IDL do:

IDL> s=fix_zdbase(/eis)
IDL> eis_filter_studies

The first command simply sets up the official EIS databases, and the second starts up a widget-based routine for filtering the complete set of EIS rasters to a more manageable list.

For velocity work we need to use 1" or 2" slit data and we also want to make sure that the raster covers a large range in Y to maximise the chances for obtaining good quiet Sun data (for wavelength calibration purposes). We will take a minimum raster height of 300". It is also useful to have a good range in X to make it easy to search for loop footpoints. We will use 200".

In the widget, select 'Raster type' to be 'Scanning', and 'Slit/Slot' to be 1". Also set the minimum raster height and width to be the values given above. Finally in the list of lines choose the Fe IX 197.86 line.

You will find only 3 rasters that satisfy the criteria. Switching to the 2" slit gives 6 rasters. Note down the names of each raster.

Browsing thumbnails#

The next step in finding the perfect data-set is to browse thumbnails from the 9 rasters. Go to the NRL thumbnail gallery where you will see a long list of rasters. Scroll down the list until you find the first of the rasters you identified earlier, and click on the raster name.

You will now see a long list of html filenames. Each of the runs of the raster has two filenames: one contains thumbnail images from the Oslo archive, the other (identified by 'mssl' in the filename) contains images from the MSSL archive. The velocity maps seem to be a little better in Oslo archive so generally you should click on this file. Sometimes, however, the Oslo thumbnails may be missing in which case it's worth checking the MSSL page.

Choose the filename at the top of the list and you will see a page appear with an EIT context image, and thumbnail images (intensity, velocity and line width) from each wavelength window of the EIS raster. Clicking on any thumbnail will bring up a larger version.

To move onto the next run of the raster, click on the link in the top-left of the html window to take you to the next set of thumbnails.

By repeating this for all the rasters you can fairly quickly browse the available data-sets and find that perfect loop.