Guide to HMI HARP data


This document contains some notes I made when trying to use a HARP data-set. More details about HARPs are available at the JSOC.

HARPs are HMI vector magnetogram data products for active regions. The data I need (parameters for a specific active region) are part of the Space-weather HARP (SHARP) series, hmi.sharp_720s.

Note that vector magnetic field at a higher cadence of 90 or 135s are possible, and have been produced for some periods (mainly big flares). See Sun et al. (2017, ApJ) for more details. The JSOC series has the form hmi.B_135s.

JSOC query

The following is a query for a specific active region number that can be input to the JSOC data export page.

hmi.sharp_720s[][2013.10.22_20:30/91m@12m][? NOAA_ARS ~ "11875" ?]

It returns 31 data products for each time step (7 in this case). These products are listed in Table 10 of Hoeksema et al. (2014).

It's not possible to perform cutouts of the SHARP series. The images are cutouts already (of the AR) and "sub-cutouts" are not possible.

Solarsoft routines

The  SHARP data products can be read with read_sdo. I notice the sizes of the images in the sequences are not necessarily the same size, so they can't be read directly into a map array with index2map.

Magnetic field orientation

The relevant parameters are 'azimuth' and 'inclination'. The latter is the angle between the line-of-sight and the magnetic field and takes values of 0 to 180 degrees, where 0 points towards the observer. The azimuth is the angle of the field in the image plane, but I don't know in which direction it is measured (clockwise or anticlockwise), nor what the zero angle is.


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