JSOC DRMS segments
In JSOC/DRMS, segments are the named data arrays requested from a data-series record.
An HMI SHARP record is not one file. It can contain many arrays: magnetic components, errors, metadata products, masks, and so on. The segment list says which arrays should be exported as FITS files.
In the NF2 downloader, the segment string is inserted directly into the DRMS query braces:
hmi.{series}[...]{segments}Example:
hmi.sharp_cea_720s[377][2011.02.15_00:00:00_TAI]{Br,Bp,Bt,Br_err,Bp_err,Bt_err}This means: from the SHARP CEA HMI product, get HARP 377 at that time and download those six named FITS arrays.
Segment families
For normal HMI SHARP CEA NF2 work, use:
Br,Bp,Bt,Br_err,Bp_err,Bt_errFor field/inclination/azimuth experiments, use:
field,inclination,azimuth,disambigThese are different representations. The downloader does not automatically convert one into the other.
Mental model
Read the query as:
series[patch][time]{which arrays?}For the smoke run:
hmi.sharp_cea_720s[377][2011.02.15_00:00:00_TAI]{Br,Bt,Bp,Br_err,Bt_err,Bp_err}the braces are the segment selection.
Typos or a wrong segment family become wrong downloaded files. The code is not clever enough to rescue that, which is good: silent magic here would be worse.