Scripts

remesh_sinlat_to_lat.py: remesh sine-latitude*longitude maps (downloaded from JSOC) to latitude*longitude.
read_*.py: functions to read FITS and IDL sav files and get the vector magnetic field
reproduce_singh18_SOLIS.py: try to reproduce figure 2 of [Singh 18] using SOLIS data from Nishant's IDL sav files.
plot_from_simulation*.py: apply the two-scale technique to a simulation (present in subdirectories of simulation/, and see if it is consistent with the sign of the helicity calculated directly from xy averages (similar to figure 6 of Brandenburg et al., 2017).

Downloading and plotting data

HMI synoptic maps

Downloading

Can use either hmi.b_synoptic (20MB per image) or hmi.b_synoptic_small (1MB per image). Prime key is CAR_ROT for both. Available segments are Br, Bt, Bp, epts

To download required FITS files into the current directory:

import drms
client = drms.Client(email=REGISTERED_EMAIL_HERE, verbose=True)
q = client.export('hmi.b_synoptic_small[2093-2268]{Br,Bt,Bp}', protocol='fits')
q.download(".")

Malformed FITS headers

FITS headers in the files are malformed, so cannot use astropy.wcs.WCS directly. Need to do something like

from astropy.io import fits
from astropy.wcs import WCS

f = fits.open("hmi.b_synoptic.2267.Br.fits")
f[0].header['CUNIT2'] = "" #sine(latitude) is dimensionless

w = WCS(f[0].header)

Handcoded one (to get the coordinate arrays) is like

h = f[0].header
coord = lambda i: (i+1-h['CRPIX?'])*h['CDELT?'] + h['CRVAL?']

SOLIS synoptic maps

Data download links are provided at https://solis.nso.edu/0/solis_data.html. Synoptic vector magnetograms only seem to be available through the "Alternative Interface". Naming scheme for files is described in https://solis.nso.edu/pubkeep/DATAINFO_VSM.txt (saved in images_SOLIS/). If we are interested in Carrington rotations 2177–2186, we need to look at the date range 2016-05-10 to 2017-02-06. Links to the maps we require seem to be directly available at https://magmap.nso.edu/solis/v9g-int-maj_dim-180_cmp-phi-kc.html.

As per https://solis.nso.edu/pubkeep/DATAINFO_VSM.txt, we need kcv9g*t*_int-mas_dim-180.fits.gz. These maps are in coordinates latitude vs longitude. An example of such a file is https://magmap.nso.edu/solis//SV/v9g/201710/kcv9g171023/kcv9g171023t1526c2196_000_int-mas_dim-180.fits.gz. A single file contains all three components of the magnetic field (see hdu.header['IMTYPE{1,2,3}']. hdu.data is a 4x180x360 array, with [[0,1,2],:,:] being r,theta,phi components.

Miscellany

Date for a given Carrington rotation

Sunpy provides the function sunpy.coordinates.sun.carrington_rotation_time.

West and east

On the Sun, 'west' and 'east' are swapped as compared to the ones on the Earth (see https://astronomy.stackexchange.com/questions/2203/how-are-east-and-west-defined-on-other-bodies-of-our-solar-system/2207#2207). This is why many sources (e.g. the headers of the SOLIS synoptic maps) say that the coordinate $\phi$ increases in the westward direction (which is the prograde direction). $r, \theta, \phi$ thus form a right-handed coordinate system, as expected.

Kishore96in/bihelical-mag-fields