HYSPLIT Forum: hysplitbbs.arl.noaa.gov

Hi everyone,

I need the documents explaining the detailed equations of backward analysis (both advection only and dispersion) in Hysplit. I took a look at user_guide and arl_224, but I couldn't find how the backward analysis is done. For example, we know the forward trajectory analysis is:

P'(t+Δt) = P(t) + V(P,t) Δt
P(t+Δt) = P(t) + 0.5 [ V(P,t) + V(P',t+Δt) ] Δt,

What about the backward analysis?

The same question I have about the backdispersion.

Cheers,
Hooman

The trajectory calculations are the same, just time is reversed.

P'(t-Δt) = P(t) + V(P,t)(-Δt)
P(t-Δt) = P(t) + 0.5 [ V(P,t) + V(P',t-Δt) ] (-Δt),

The turbulent dispersion calculation just stays the same. I would recommend this paper to
understand this better.

Utility of atmospheric transport runs done backwards in time for source term estimation
By:Eslinger, PW (Eslinger, Paul W.)[ 1 ] ; Schrom, BT (Schrom, Brian T.)[ 1 ]
JOURNAL OF ENVIRONMENTAL RADIOACTIVITY
Volume: 203 Pages: 98-106
DOI: 10.1016/j.jenvrad.2019.03.006