Coming From Jena STILT

Jena STILT is the stiltR code from the Max Planck Institute for Biogeochemistry, which the ICOS footprint service (stilt.icos-cp.eu) runs. It and PYSTILT drive the same HYSPLIT particle model. They differ in how the particles become a footprint, and in their defaults. This page lists the differences, read from the stiltR code, and the PYSTILT settings that come closest.

How the footprints differ

Topic	Jena STILT	PYSTILT
Resolution	16 grids, from the fine grid to one 32 times coarser in each direction. At each step back in time, the extent of the particle cloud picks the grid, and the grid never gets finer as the steps go further back. A coarse cell’s total is spread evenly over the fine cells it covers.	One grid. Each particle’s influence is spread by a Gaussian kernel whose width grows with the spread of the particles, as in STILT-R (smooth_factor).
Near the receptor	No correction.	The near-field correction of foot (hnf_plume), as in STILT-R.
Mass	Particles whose dmass leaves the range 1e-3 to 1e3 are dropped. foot is weighted by dmass, divided by its mean over the particles at each step.	Not used.
Grid edges	A particle that crosses the western edge is dropped from that step on, since the background is taken there. Steps outside the other edges are left out.	A step outside the grid adds nothing. A particle that comes back counts again.
Time layers	Hourly: layer k holds the steps from k to k + 1 hours back.	Hourly, the same hours: the first hour back is layer -1 (Output Layout).
Particle count	The total is divided by the particles left after the dmass check.	The total is divided by numpar.
Defaults	240 hours and 250 particles.	24 hours and 200 particles.
Meteorology	ECMWF short-term forecasts every 3 hours at about 35 km, in ARL format.	Any ARL meteorology, ERA5 included once converted (Meteorology).

The settings that come closest

Give the run length and particle count of your Jena runs, turn off the near-field correction, and use the same grid:

n_hours: -240
numpar: 250
hnf_plume: false
grid:
  xmin: -15.0      # lon_ll
  xmax: 35.0       # lon_ll + numpix_x * lon_res
  ymin: 33.0       # lat_ll
  ymax: 72.0       # lat_ll + numpix_y * lat_res
  xres: 0.2        # lon_res
  yres: 0.1        # lat_res

The coarsening grids, the dmass weighting, and the western-edge rule have no PYSTILT setting. Footprints from the two will not match cell by cell, most of all far from the receptor, where Jena STILT’s grids are coarsest. Compare totals over regions (Summing Footprints: Areas And The Jacobian), or the modeled mole fractions, rather than single cells.