Joint Science Operations Center (JSOC) Data Products

Linewidth Data

The linewidth observable refers to the FWHM of the (assumed) Gaussian absorption line profile for the 6173.3 Å line on the surface of the sun. The linewidth (L_w) data is in the DRMS series hmi.Lw_45s and hmi.Lw_720s

Keywords:

All the FITS header keywords that appear in the Linewidth data are explained here. Any combination of FITS header keywords CAMERA and T_REC is unique for the both DRMS series hmi.Lw_45s and hmi.Le_720s Further explanation on WCL keyword descriptions can be found in this paper.

Algorithm For Calculation:

HMI samples the Fe I absorption line at 6173.3 Angstrom at six points. Assuming that the "pure" solar Fe I line profile is a Gaussian and the HMI filter filter transmission profiles are delta functions, the first and second Fourier coefficients of the of the Fe I line can be calculated and an estimate of the linedepth is made. More details can be found here.

Processing:

The link to the HMI pipeline processing is here.
The status of the pipeline processing can be checked here.

Calibration:

Look-up tables and polynomial correction have *NOT* been applied to the Linedepth data.

Status Notes and/or Known Problems:

All the Line-of-Sight Observables show fluctuation in the values with a twenty four hour cadence. This is an instrumental effect.