Solar Soft X-ray irradiance with Yohkoh/SXT

Project description

Using SXT data from this archive, we can study solar activity in terms of sun's radiation in solar soft X-rays. In this project, we will process the SXT full-Sun images taken from 1991 to 2001 to derive solar soft X-ray irradiance during this period. We will learn how to handle Yohkoh/SXT FITS data for quantitative analysis: selection of data files and area of interest, derivation of temperature and emission measure, calculation of the SXT irradiance in the physical unit comparable with other instruments. Since the SXT is an imager, we can derive unique spatial variations of irradiance, which have never be obtained with other instruments that only measure the full-Sun integrated flux. We will characterize dependence of the irradiance on solar latitudes, or its association with particular solar structures, etc.

As a bonus, we will have a few opportunities to watch and learn how an international satellite project like Yohkoh is operated. MSU is participating the operation of Hinode/XRT, which is a succeeding project of Yohkoh/SXT. We will have two duty weeks of Hinode/XRT operation in July and August in which we actually take control of the XRT observation.

Weekly goals

• Week 1 (6/4 -- 6/8) : Get familiar with IDL and Yohkoh/SXT project. Read "Encyclopedia of the Sun" sections 8.4, 8.5, and 8.1.
  facula image. best sunspot from a GBO. sunspot from Hinode/SOT. MSU SSEL web site.
• Week 2 (6/11 -- 6/15) : Start processing SXT data. Read YLA level2 FITS files, display each Al and Am image pair side by side in the window, check quality, save data cubes and indexes for analysis (first for 1991).
  Dagwood_sandwitch.
• Week 3 (6/18 -- 6/22) : Separate the whole project into several steps:
  
  • [step 1] Read Loren's pairs of file names. Create movie array for checking image quality, prepare data cube and indexes for the next step.
  • [step 2] Start from the previous data cube and indexes. Prepare 'masked' data cube and indexes.
  • [step 3] Start from the masked data cube and indexes. Collect total intensity for each image and make a time plot. Save total intensity array.
  • [step 4] Start from the total intensity array. Do temperature(Te) and emission measure(EM) analysis.
  • [step 5] Start from Te and EM, calculate a model coronal spectrum, then derive the irradiance in the unit of W/m^2.
  Confirmed the programs for step 1-3 work for 1991 and 1992.
  Nicole's movie product, the whole Sun intensity plot for 1991.
• Week 4 (6/25 -- 6/29) : Takeda out of town. Nicole will do the step 1-3 for the rest years (1993-2001). If possible, think about how to get intensity variation for the Northern hemisphere and for the Southern hemisphere, separately.
• Week 5 (7/2 -- 7/6) : Learn more about the Filter Ratio Method. Applying FRM code to the intensity arrays.
• Week 6 (7/9 -- 7/13) : Prepare for the mid-term presentation on 7/12 (excellently done!). Added DN adjustment from different space resolution images in Step-3 programs. Watch Hinode operation meeting(7/13 19:00-).
• Week 7 (7/16 -- 7/20) : Complete total & hemispheric Te & EM plot for 1992. Understanding the scheme to convert Te & EM to the irradiance. Applying the code (chianti_spec.pro) to the whole year data turned out to take a few hours and ended with error (short of memory). Needs to accelerate the conversion code (Takeda in charge of this work).
  TEEM plot by Nicole: Old and New calibrations 1992    Total and hemispheric for 1992
• Week 8 (7/23 -- 7/27) : Applying the accelarated code for converting Te & EM to Irrad to 1992 data. A bug report of ISOTHERMAL.PRO sent to P. Young. Connect Te & EM plots of multiple years (required to re-define iarr structures to concatenate). Add year numbers to the annotation of x-axis (with /year,/y2k keywords). Try different size of masking (within 1.1Rs to 1.2Rs).
• Week 9 (7/30 -- 8/3) : Another test on mask size: compare 1.1R, 1.2R & no_mask. Calculate irradiance in different wavelength range: 3-45A (SXT's official spectral range: 1% peak response) instead of 1-30A (read from the Al01 and AlMg filter response plots). Considering bad image removal.
• Week 10 (8/6 -- 8/10) : Complete hemispheric irradaiance for the whole year. Time to learn from our final product (what's our findings). Prepare for the final presentation on 8/8 (great job!). The EM mistery we found: N-hemispheric EM + S-hemispheric EM does not equal to the total EM. The latter is slightly larger than the former. This propergates to the irradiance.
  • plot of N-hem irrad, S-hem irrad, with Total irrad.
  • plot of N-hem irrad, S-hem irrad, and (N-irrad + S-irrad).

Beyond this project

• Calculate 1-8A irradiance to compare with GOES/XRS.
• Assume different elemental abundance set to see how it affects the irradiance.
• Apply filter ratio method to images not to the disk-integrated intensities.
  • This method will make N- + S- equals to total.
  • Averaged Te will be cooler than those derived from the integrated intensities.
  • This method allows to make differential EM plot for the whole mission (suggestion from Dana).
• Prepare for Hinode-12 presentation and for our project paper.

Resources

• about Yohkoh/SXT telescope and filters
• References
• about Synoptic Composite Images
• IDL sample programs
• CHIANTI atomic database

Aki Takeda (Research Scientist, Dept. of Physics at MSU)