Hysplit: TRAJ.CFG

Understanding the HYSPLIT TRAJ.CFG Configuration File

The TRAJ.CFG file is a crucial configuration file that controls advanced settings for the HYSPLIT trajectory model. It defines how calculations are performed and what output is generated.

Here's a breakdown of the TRAJ.CFG file structure and parameters:

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&SETUP tratio = 0.75, delt = 0.0, mgmin = 10, khmax = 9999, kmixd = 0, kmsl = 0, kagl = 1, k10m = 1, nstr = 0, mhrs = 9999, nver = 0, tout = 60, tm_pres = 1, tm_tpot = 0, tm_tamb = 0, tm_rain = 0, tm_mixd = 0, tm_relh = 0, tm_sphu = 0, tm_mixr = 0, tm_dswf = 0, tm_terr = 0, tm_uwnd = 0, tm_vwnd = 0, dxf = 1.00, dyf = 1.00, dzf = 0.01, messg = 'MESSAGE', /

Parameter Explanations

Core Simulation Parameters

• tratio = 0.75 - Time step ratio (stability factor). HYSPLIT adjusts its internal time step so an air parcel doesn't travel more than 75% of a grid cell in one step.
• delt = 0.0 - Fixed time step (minutes). 0.0 means HYSPLIT uses variable time step controlled by tratio.
• mgmin = 10 - Minimum number of grid cells for met data. Sanity check to prevent errors with bad met files.
• khmax = 9999 - Maximum duration (hours) for a trajectory. 9999 means "no limit".

Vertical Motion & Starting Height

• kmixd = 0 - Boundary Layer option. 0 = Ignore mixing depth.
• kmsl = 0 - Input starting height reference. 0 = meters above ground level (AGL).
• kagl = 1 - Output height reference. 1 = meters above ground level (AGL).
• k10m = 1 - Use 10m meteorological data for surface-based trajectories.

Output Control

• nstr = 0 - Number of special starting locations. 0 means not used.
• mhrs = 9999 - Maximum duration for meteorological data. 9999 means "no limit".
• nver = 0 - Vertical motion output flag. 0 = Do not include vertical velocity.
• tout = 60 - Output frequency. 60 = Save trajectory position every 60 minutes.

Meteorological Output Variables (tm_ flags)

These control what additional meteorological data is written to the output file:

• tm_pres = 1 - Pressure (hPa or mb) - INCLUDED
• tm_tpot = 0 - Potential Temperature (K) - Excluded
• tm_tamb = 0 - Ambient Temperature (K) - Excluded
• tm_rain = 0 - Rainfall/Precipitation - Excluded
• tm_mixd = 0 - Mixing Depth (m) - Excluded
• tm_relh = 0 - Relative Humidity (%) - Excluded
• tm_sphu = 0 - Specific Humidity (g/kg) - Excluded
• tm_mixr = 0 - Water Mixing Ratio (g/kg) - Excluded
• tm_dswf = 0 - Downward ShortWave Radiation Flux (W/m²) - Excluded
• tm_terr = 0 - Terrain Height (m) - Excluded
• tm_uwnd = 0 - U-Wind Component (m/s) - Excluded
• tm_vwnd = 0 - V-Wind Component (m/s) - Excluded

Output File Scaling Factors

• dxf = 1.00, dyf = 1.00 - Scaling factors for horizontal components of trajectory dispersion.
• dzf = 0.01 - Scaling factor for vertical component of trajectory dispersion.

Log File Control

• messg = 'MESSAGE' - Names the detailed log file generated by HYSPLIT.

Note: This configuration is set up for a standard, single, backward trajectory with output in meters AGL, saved every 60 minutes, with pressure as the only additional meteorological variable.

HYSPLIT TRAJ.CFG Configuration Guide | Understanding HYSPLIT Model Settings