Which GRIB2 inputs are used to build NOAA’s HRRR sigma ARL files?

[ggreen98]

Hi there,

I am trying to download a whole batch of ARL files for use in a multi-year HYSPLIT back-trajectory pollution analysis. To avoid speed limitations on the ARL archive server, I’m attempting to construct ARL files locally from HRRR GRIB2 data.

Goal:
Convert HRRR GRIB2 to HYSPLIT ARL (sigma, as described here: https://www.ready.noaa.gov/hypub/hysp_meteoinfo.html) so that the results match the READY server files named like:
YYYYMMDD_00-05_hrrr
YYYYMMDD_06-11_hrrr
YYYYMMDD_12-17_hrrr
YYYYMMDD_18-23_hrrr
(READY/HYSPLIT docs indicate these four daily sigma files correspond to 6-hour chunks, with “00-05” covering forecast hours 0–5 from one cycle.)

Question:
Which GRIB2 inputs exactly are used to build these sigma ARL files?
From what I understand, HRRR GRIB2 comes in three main families:
wrfnat (native, 3-D)
wrfsfc (surface, 2-D)
wrfprs (pressure levels)
My assumption is that for sigma-level ARL files with surface fields (e.g., PRSS) and 3-D fields on sigma/native coordinates, you’d need wrfnat + wrfsfc, while wrfprs would only be used for the pressure-level ARLs. Is this correct, or does READY build the sigma files a different way?
I am currently using api2arl_v6 — is this the right tool? I realize my outputs might differ slightly from NOAA’s pre-made sigma ARLs, but I’m hoping they’ll be comparable and reliable for trajectory work.
Also, regarding hourly composition: READY documentation lists filenames like hysplit.tXXz.hrrrf00 (hours 0–5 from cycle XX). Does that mean each of the four daily ARL files is built from the forecasts of a single cycle? For example, is 00-05_hrrr comprised of t00z f00..f05? Or is there cross cycle stitching like t00z-t06z?

Thanks for any clarification!