Inquiry About Adjusting Air Parcel Velocity in HYSPLIT

[asianrosyfinch]

I use HYSPLIT to estimate the potential source regions of migratory and vagrant birds, as well as to help determine suitable release locations when rescued birds are to be released back into the wild.
However, birds do not simply move at the speed of the wind.
They have their own airspeed relative to the surrounding air, and therefore may travel somewhat faster than the wind speed when flying with a tailwind.
For this reason, I would like to know whether HYSPLIT has an option that allows trajectories to be calculated using a velocity that is, for example, 1.2 or 2 times the actual wind speed.
If such an option is not currently available, would it be technically possible to develop or modify HYSPLIT to allow users to specify a multiplier for wind speed when calculating trajectories?
I would greatly appreciate any information or advice you could provide regarding this possibility.
Thank you very much for your time and consideration.

[christopher.loughner]

Hi. You can use the VBUG option in SETUP.CFG to increase or decrease the horizontal speed. The units are m/s. If you have the following line in your SETUP.CFG file:

VBUG = 1.0,

for your case, it will represent a bird traveling 1 m/s faster than the wind. The direction of the speed increase is always in the direction of the mean flow. A negative value for VBUG will result in the bird flying against the wind.

Let me know if you would like HYSPLIT to do something else for your scenario (i.e., a multiplication factor). We may be able to modify the code to work for your specific scenario.

Chris