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seeking guidance on how to use the trajectory runtime option

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New member
Hi all,

To my understanding, the WRF-ARW model since V3.5 has had the capability to run forward trajectories during model runtime.

I would be interested in trying to run WRF V3.9.1 using this option as part of a quadruply-nested tropical cyclone simulation configuration. According to my README.namelist, there are just two trajectory related namelist variables:

traj_opt --> to turn trajectory calculation on or off
num_traj --> number of trajectories to be released

Is there any additional documentation available for using this option? I cannot find any in the V3.9.1 User Guide.
For instance, how can I control the trajectory seed positions? And how are the trajectory coordinates output?

Any additional help would be appreciated

Unfortunately there isn't any official documentation out there on this option; however, take a look at this presentation given at our WRF tutorial. There are a couple of slides that discuss the option and may provide more insightful information for ways to manipulate the code:

Thank you, Kelly

The main reason why I am interested in using this runtime trajectory option is that I have developed code for computing trajectories from post-processed WRF output (binary .dat files generated by ARWpost). I have implemented an experimental time interpolation scheme that aims to be an improvement over the standard linear interpolation in time used by most publicly available codes that compute trajectories from model output - especially for applications with complex, nonlinearly evolving flows. My scheme also corrects the parcel positions on moving nested domains commonly used for tropical cyclone simulations.

I have submitted a manuscript describing my trajectory computation algorithm to Monthly Weather Review and it is currently under revision. As part of my verification work, I would like to, if possible compare backward trajectories generated by my code against forward "truth" trajectories computed during WRF model runtime that have endpoints at the backward trajectory seed positions.

If my work is accepted for publication, I plan to share my trajectory code publicly with other users.

Anyone on the forum is welcome to contact me offline at if they have other suggestions.


Will Miller
PhD Candidate, University of Maryland College Park
Hi Will,
Thank you for that information. Hopefully it will be useful to someone in the future!