Coronal Density Maps
Contact: Huw Morgan, hmorgan@aber.ac.uk
Coronal rotational tomography is used to estimate the electron density of the coronal plasma. The novel tomography method, developed in Aberystwyth, is based on several advanced data processing and calibration steps applied to coronagraph image data (Morgan, 2015); a spherical harmonic-based regularized inversion method (Morgan, 2019); and further refinement steps (Morgan, 2020). Please cite these papers if you plan to use the images or data for your own work.
Morgan 2015: https://iopscience.iop.org/article/10.1088/0067-0049/219/2/23/meta
Morgan 2019: https://iopscience.iop.org/article/10.3847/1538-4365/ab125d/meta
Morgan 2020: https://iopscience.iop.org/article/10.3847/1538-4357/ab7e32/meta
The directory structure is by year and heliocentric distance, e.g. ./2007/distance_4-0/
For each date and distance where a tomography map exists, there is an IDL save file (.dat) and a corresponding JPEG image (.jpg). IDL save files can easily be opened in Python, see https://docs.scipy.org/doc/scipy/reference/generated/scipy.io.readsav.html.
Users should quickly check the JPEG image for any obvious errors. Biggest errors occur during solar maximum - the 'static' tomography method does not agree well with rapid changes and large coronal mass ejections! It is often useful to compare the structure in the tomography maps (the distribution of high-density streamers) against other types of data such as PFSS magnetic models. It is reassuring to see corresponding structures in both types of maps, since they are created using different observations and methods. If you see corresponding structures between the tomography and PFSS, but they disagree in location, then the tomography maps are highly likely to be giving the correct location (since they are more directly based on coronal observations).
Each data file gives the observed brightness on which the tomography is based (variable BOBS). This has dimensions position angle (x) and time (y). We also provide the reconstructed brightness BMOD. Users can compare these - a large residual means a poorer fit to the observation. Qualitatively, one wishes to see a good correlation between the distribution of structures in BOBS and BMOD. A good correlation gives confidence that the density structure in the tomography map is dependable.
The date in the filename is the 'mid-date'. Two weeks of observation are required to create a tomography map, and the mid-date is the center date of this two-week period.
The cor2a archive provided here is based on the STEREO A COR2 coronagraph polarized brightness observations, which currently (2021/10) gives the best results over a long time period (2007-2019). The archive is currently (2021/10) not updated automatically. If you require a more recent date, please contact us.
The variables contained within each .dat file are:
MISSION STRING = 'sta'
INSTR STRING = 'cor2a'
MIDDATE STRING = '2007/03/17'
LON_RAD DOUBLE = Array[540]
COLAT_RAD DOUBLE = Array[270]
RMAIN FLOAT = 4.02525
DENS DOUBLE = Array[540, 270]
BOBS FLOAT = Array[720, 384]
BMOD DOUBLE = Array[720, 384]
PA_RAD FLOAT = Array[720]
DATES STRING = Array[384]
CREDIT STRING = 'If you use these data for your own research, please cite: https://iopscien'...
DESCRIPTION STRING = Array[9]
CONTACT STRING = 'Any problems or queries: Huw Morgan, Aberystwyth University, hmorgan@aber.'...
The DESCRIPTION variable is an array of strings giving more detailed information on each variable:
description=['dens = Electron density as a function of Carrington longitude and co-latitude, in cm^-3', $
'bobs = Observed polarized brightness as a function of position angle (pa) and dates, in mean solar B', $
'bmod = Reconstructed polarized brightness corresponding to bobs, in mean solar B', $
'pa_rad = position angle of the observation in radians, measured counterclockwise from north', $
'rmain = heliocentric distance in solar radii', $
'lon_rad = Carrington longitude in radians', $
'colat_rad = Carrington co-latitude in radians', $
'dates = dates of observations', $
'middate = the target date of the reconstruction, approx. centered in the middle of the observation dates']