# Are backward pathlines possible in VAPOR?

**URL:** <https://vapor.discourse.group/t/are-backward-pathlines-possible-in-vapor/195>\
**Category:** Uncategorized\
**Created:** [June 13, 2022, 3:43pm UTC](https://vapor.discourse.group/t/are-backward-pathlines-possible-in-vapor/195 "2022-06-13T15:43:51Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![michael](https://avatars.discourse-cdn.com/v4/letter/m/4bbf92/32.png) [@michael](https://vapor.discourse.group/u/michael)\
**Post date:** [June 13, 2022, 3:43pm UTC](https://vapor.discourse.group/t/are-backward-pathlines-possible-in-vapor/195/1 "2022-06-13T15:43:51Z")

</div>

Hello,

I am analysing the flow over mountain ranges using WRF output in VAPOR. My goal is to specify target area and find the source region of air parcels (e. i. to compute backward trajectories). It works fine for time-invariant streamlines but I only could perform forward computation with time-variant pathlines. Streamlines are probably fine as I am working in a relatively short time window but I guess that having updated flow field during computation may improve accuracy of the trajectories.

Thank you!  
Michael

---

<div class="post-metadata">

**Author:** ![pearse](https://yyz2.discourse-cdn.com/free1/user_avatar/vapor.discourse.group/pearse/32/177_2.png) [@pearse](https://vapor.discourse.group/u/pearse)\
**Post date:** [June 15, 2022, 5:13pm UTC](https://vapor.discourse.group/t/are-backward-pathlines-possible-in-vapor/195/2 "2022-06-15T17:13:30Z")

</div>

Yes, they are. Check out the “Flow Direction” parameter in the Seeding tab in your Flow Renderer.

This will show you where:

[![](https://global.discourse-cdn.com/free1/uploads/vapor/original/1X/418d9e82a8f38dc1e9f165a7168f04df14643836.jpeg "VAPOR: Backward Wind Trajectories") ](https://www.youtube.com/watch?v=czGVczj6VMY)

---

<div class="post-metadata">

**Author:** ![michael](https://avatars.discourse-cdn.com/v4/letter/m/4bbf92/32.png) [@michael](https://vapor.discourse.group/u/michael)\
**Post date:** [June 15, 2022, 7:31pm UTC](https://vapor.discourse.group/t/are-backward-pathlines-possible-in-vapor/195/3 "2022-06-15T19:31:10Z")

</div>

Thank you for your response. However, these are backward streamlines (time invariant trajectories) and I am looking if there is a possibility to compute pathlines (time variant trajectories) respecting evolving flow between time steps…

---

<div class="post-metadata">

**Author:** ![clyne](https://avatars.discourse-cdn.com/v4/letter/c/b9e5f3/32.png) [@clyne](https://vapor.discourse.group/u/clyne)\
**Post date:** [June 15, 2022, 9:15pm UTC](https://vapor.discourse.group/t/are-backward-pathlines-possible-in-vapor/195/4 "2022-06-15T21:15:35Z")

</div>

Sorry, no, backward pathline integration is not currently supported. Please feel free to open a GitHub [issue](https://github.com/NCAR/VAPOR/issues) requesting it in a future release.