[Note that the question and the answer below are recreated from a HYSPLIT FAQ site that predates this forum site. The original posting date is unknown.]
Question:
When I ran a backward trajectory from a location on a previously computed forward trajectory, I did not return to the starting location of my forward trajectory. Why?
Answer:
A backward trajectory from the forward end-point will rarely end up at the starting location due to the accumulation of various numerical integration errors. It depends upon the complexity of the wind field and the integration time step. The existing error tolerance is a compromise for speed and accuracy (concentration and trajectory models run with the same criterion) such that a point will not be advected more than 75% of the grid cell size in one time step. You can reduce the numerical error by reducing TRATIO from 0.75 to a smaller value, such as 0.25. TRATIO is defined in the SETUP.CFG namelist file that should be located in the root startup directory, either \working from the GUI or \trajmdl from the command line. This option will be available on the next Hysplit revision (coming within a few weeks).
Roland Draxler
When I ran a backward trajectory from a location on a previously computed forward trajectory, I did not return to
Post any questions or comments regarding the Desktop PC version of HYSPLIT. This includes the model execution, GUIs, results, or graphics. Be sure to include the operating system you are using (Windows XP, Windows Vista, Windows 7, Windows 8, etc.
-
- Posts: 361
- Joined: May 8th, 2019, 1:31 pm
- Registered HYSPLIT User: Yes
Jump to
- HYSPLIT
- ↳ Users
- ↳ Developers
- ↳ Bugs
- ↳ Announce
- ↳ General Comments
- ↳ Trajectory Model
- ↳ Dispersion Model
- ↳ User Applications
- ↳ In-line WRF-HYSPLIT coupling
- HYSPLIT Platform Specific
- ↳ HYSPLIT for PCs
- ↳ HYSPLIT for Mac OS X
- ↳ HYSPLIT for LINUX
- ↳ HYSPLIT on the READY Server
- Meteorological Data
- ↳ General questions on meteorological data needed for HYSPLIT
- ↳ Conversion programs
- ↳ Repositories of HYSPLIT formatted data
- ↳ MeteoInfo Software
- HYSPLIT Research
- ↳ Volcanic Ash
- ↳ Wildfire Smoke
- ↳ Dust
- ↳ Chemicals
- ↳ Radiological
- ↳ Cluster Analysis
- HYSPLIT Workshop
- ↳ 2022 HYSPLIT Workshop Questions
- ↳ 1. Installing HYSPLIT
- ↳ 2. Testing the installation
- ↳ 3. Gridded meteorological data files
- ↳ 4. Trajectory calculations
- ↳ 5. Trajectory options
- ↳ 6. Trajectory statistics
- ↳ 7. Air concentration calculations
- ↳ 8. Configuring the CAPTEX simulation
- ↳ 9. Air concentration parameter sensitivity
- ↳ 10. Alternate display options
- ↳ 11. Pollutant transformations and deposition
- ↳ 12. Air concentration uncertainty
- ↳ 13. Source attribution methods
- ↳ 14. Wildfire smoke and dust storms
- ↳ 15. Radioactive pollutants and dose
- ↳ 16. Volcanic eruptions with gravitational settling
- ↳ 17. Custom simulations
- ↳ 2021 HYSPLIT Workshop Questions
- ↳ 1. Installing HYSPLIT
- ↳ 2. Testing the installation
- ↳ 3. Gridded meteorological data files
- ↳ 4. Trajectory calculations
- ↳ 5. Trajectory options
- ↳ 6. Trajectory statistics
- ↳ 7. Air concentration calculations
- ↳ 8. Configuring the CAPTEX simulation
- ↳ 9. Air concentration parameter sensitivity
- ↳ 10. Alternate display options
- ↳ 11. Pollutant transformations and deposition
- ↳ 12. Air concentration uncertainty
- ↳ 13. Source attribution methods
- ↳ 14. Wildfire smoke and dust storms
- ↳ 15. Radioactive pollutants and dose
- ↳ 16. Volcanic eruptions with gravitational settling
- ↳ 17. Custom simulations
- ↳ 2020 HYSPLIT Workshop Questions
- ↳ 1. Installing HYSPLIT
- ↳ 2. Testing the installation
- ↳ 3. Gridded meteorological data files
- ↳ 4. Trajectory calculations
- ↳ 5. Trajectory options
- ↳ 6. Trajectory statistics
- ↳ 7. Air concentration calculations
- ↳ 8. Configuring the CAPTEX simulation
- ↳ 9. Air concentration parameter sensitivity
- ↳ 10. Alternate display options
- ↳ 11. Pollutant transformations and deposition
- ↳ 12. Air concentration uncertainty
- ↳ 13. Source attribution methods
- ↳ 14. Wildfire smoke and dust storms
- ↳ 15. Radioactive pollutants and dose
- ↳ 16. Volcanic eruptions with gravitational settling
- ↳ 17. Custom simulations
- ↳ 2019 HYSPLIT Workshop Questions