Dear alicec,
Thank you very much for your reply.
I attempt to specify a value for the deposition velocity, rather than calculating it from the particle diameter and density.
From what I understand, for particle dispersion, if a dry deposition velocity is specified, then that value is used as the particle gravitational settling velocity rather than the value computed from the particle diameter and density.
In gravitational deposition, the deposition velocity is the settling velocity due to the gravity-induced drag. Therefore, the gravitational settling velocity and the deposition velocity are the same thing.
More importantly, this value (deposition velocity) will be added to the vertical velocity in the particle trajectory advection computation. This probably means adding a settling velocity to computational particles motion throughout the atmosphere (not just in the surface/ground layer), so that computational particles will slowly settle toward the ground.
Once the computational particles are in the surface/ground layer, the dry deposition occurs. HYSPLIT will calculate dry deposition (the flux: mass/m^2/s) using the given deposition velocity (m/s) and the computational particles concentration (mass/m^3) above the ground layer.
Am I correct? Please confirm.
Another question:
According to the tutorial, there is an equation to calculate the deposition/setting velocity.
Vg = dp2 g (ρg - ρ) (18 μ)-1
μ is the viscosity of air. It should change with height in the atmosphere.
I am just wondering how HYSPLIT handles it, if the setting velocity is a constant for all computational particles in all layers. Does HYSPLIT use a constant to represent the viscosity, regardless of height?
My apologies for asking too many questions. I am just trying to understand how HYSPLIT works.
Your help would be much appreciated. Thanks.
Kind Regards,
Ming