Inconsistent back trajectory using HRRR Met data

Topics about the HYSPLIT trajectory model.
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Posts: 2
Joined: March 3rd, 2021, 3:43 pm
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Inconsistent back trajectory using HRRR Met data

Post by xiangyuj »

Dear HYSPLIT users,

I was using HYSPLIT trajectory model to compute back trajectory starting at UTC 5:00 on Feb 28, 2021 in Georgia state (Number of Trajectory Starting Locations is 1). However, I couldn't replicate the back trajectories when I set different number of level heights using the same HRRR 3k Met data, . Please see the attached figure for the details:
The parameter settings for Fig 1-Fig 3 are exactly the same except the level height. Fig1 sets the level height of 100m. Fig2 sets two level heights, 100 and 500, while Fig3 sets three level heights 100, 500, and 1000 m. If we compare the back trajectory at level height of 100 m (red line), the three figures show different results. However, if I use NAM met data instead of HRRR 3k Met data to run the trajectory model, it will give us identical results at 100 meter height.

Does anyone know what causes the differences by using the HRRR 3k Met data?

Thank you! :)

Posts: 660
Joined: November 7th, 2012, 3:14 pm
Registered HYSPLIT User: Yes

Re: Inconsistent back trajectory using HRRR Met data

Post by ariel.stein »

Please try setting the timestep (delt) to a fix value (e.g. 5 or 1). The model is using different time steps when calculating the trajectories at different heights and that causes the observed discrepancies.
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