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This page only contains basic information about using this service, and it is work in progress. Please refer to the JSOC page directly for full details.
For information about HMI Active Region Patches (HARPs) and, in particular, the difference between HARPs, SHARPs and MHARPs please visit the [JSOC HARP page|http://jsoc.stanford.edu/HMI/HARPS.html]. Below I describe ways of accessing some useful information from the HARPs.
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The following Open Access paper has more information about the HMI pipeline that generates the HARP data:
[Hoeksama et al. (2014, Solar Physics, 289, 3483)|https://ui.adsabs.harvard.edu/link_gateway/2014SoPh..289.3483H/doi:10.1007/s11207-014-0516-8]
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The first thing to note is that active regions are assigned a HARPNUM, but this is different from the NOAA active region number. The chances are you will know your active regions NOAA number, but not its HARPNUM.
The first thing to note is that active regions are assigned a HARPNUM, but this is different from the NOAA active region number. The chances are you will know your active region's NOAA number, but not its HARPNUM.
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To construct a query for the NOAA number, go to the [LookData page|http://jsoc.stanford.edu/ajax/lookdata.html] and enter, e.g.,
To construct a query for the NOAA number, go to the [LookData page|http://jsoc.stanford.edu/ajax/lookdata.html] and enter, click on the 'RecordSet Select' tab, and type the following in the text box,
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!!Total magnetic flux
!!Average active region properties
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One useful quantity to extract from the HARPs is the total magnetic flux: either positive (MPOS_TOT), negative (MNEG_TOT) or absolute (MTOT). To get these, go to Box 4 on the LookData page and find the keywords in the list. Select them, and then look in the bottom-left of the LookData page and click on the 'Prepare keyword table in plain text format', and then click the 'Fetch keyword values for RecordSet' button. You will then a see a plain ascii file containing the values.
There are a number of parameters that are averaged or summed over the active region as a whole. It is then easy and quick to extract these for a time period (e.g., the passage of the AR across the disk). Each parameter is assigned a keyword, and you see the complete list by clicking on the 'Series Content' tab of the LookData page. Useful ones are:
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Note that the flux is given in units of Webers, and also note that is for the whole HARP area. To get the area, you will also need to get the keyword SIZE for the projected area of the region. Dividing by SIZE gives the magnetic flux density (measured in Tesla or Gauss). Note that the unit of SIZE is micro-hemispheres (mH), which I guess is 2*pi*R_sun^2*10^-6.
USFLUX - total, unsigned magnetic flux in Maxwells.\\
MEANGAM - angle of the average magnetic field vector in degrees (90 corresponds to radial field).\\
AREA - area in micro solar hemispheres (mH). To convert to cm%%sup 2/%, multiply by 3.044 x 10%%sup 16/%.\\
T_OBS - time of observation.\\
HARPNUM - it's a good idea to print your region's HARP number.
Be careful with the following parameters:
MTOT - total line-of-sight magnetic flux density (G), but JSOC lists it as magnetic flux in Wb.\\
SIZE - projected area in mH/2 units, i.e., SIZE = 2 x AREA for region at disk center.
From the 'Series Content' page, you can de-select all keywords and then select just the ones you want. After doing this, go to the 'RecordSet Select' tab. In Box 4 you will see the keywords you selected. Select these with your mouse. In the bottom-left, click on 'Prepare keyword table in plain text format', and then click on the 'Fetch keyword values...' button. You'll then see an ASCII table containing your parameters as a function of time.
!!SHARP files
Once you know your HARP number (HARPNUM), then you can download the SHARP data from the JSOC. Go to the usual [ExportData page|http://jsoc.stanford.edu/ajax/exportdata.html] and type the following into the RecordSet box:
{{{
hmi.sharp_720s[7237][2018.02.11_07:00/3h]
}}}
which downloads three hours of data for AR 12699 (HARPNUM=7237) from 11-Feb-2018. For each time step you'll receive 31 FITS files. Each file contains a rectangular image containing the active region. Note that the pixel map that defines the active region area is stored in the 'bitmap' file. This image has 3 levels defining: the active region pixels for that particular image (highest value); the active region pixels for the complete evolution (middle value); and the pixels not part of the active region definition (lowest level).
This page (revision-3) was last changed on 29-Jun-2021 19:57 by Peter YoungTop