Hi i do have some confusion regarding back trajectory analysis
1. Does HYSPLIT consider the air parcel while calculating back trajectory as a closed parcel, meaning it doesn't pick up any pollutant emission during the course of it's journey? If that is so then how come CWT plots gives region of high concentration (considering i have fused observed daily pollutant concentration at the affected area with trajectory endpoint data) other than the origin point of trajectory. (Since CWT plots also considers the grids through which high concentration pollutant passes and provides weight according to it's residence time).
2. Why do the starting height differ along the course of a trajectory? Is it because of changing PBL or is it because of change in elevation?
Thanks
HYSPLIT air mass back trajectories
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barbara.stunder
- Posts: 451
- Joined: November 9th, 2012, 4:23 pm
- Registered HYSPLIT User: Yes
Re: HYSPLIT air mass back trajectories
1. Air parcels in trajectory calculations are closed. Trajectories are calculated using 3-dimensional wind field data with time. Trajectories have no information about pollutant concentrations.
If you run back-trajectories only from locations beginning at the time of high pollutant concentrations, then that is indicating possible emissions areas, but there are many limitations. You don’t know where along the trajectory the emissions are, turbulent transport is not accounted for, nor wet or dry deposition, if the concentration is over a 24-h period, then the winds can be changing over that 24-h, the starting height of the back-trajectories can affect the trajectories, etc.
2. There is only one trajectory starting height. Thereafter the altitude is determined by the atmospheric vertical air motion.
See the trajectory sections in the Tutorial - https://ready.arl.noaa.gov/documents/Tu ... index.html
If you run back-trajectories only from locations beginning at the time of high pollutant concentrations, then that is indicating possible emissions areas, but there are many limitations. You don’t know where along the trajectory the emissions are, turbulent transport is not accounted for, nor wet or dry deposition, if the concentration is over a 24-h period, then the winds can be changing over that 24-h, the starting height of the back-trajectories can affect the trajectories, etc.
2. There is only one trajectory starting height. Thereafter the altitude is determined by the atmospheric vertical air motion.
See the trajectory sections in the Tutorial - https://ready.arl.noaa.gov/documents/Tu ... index.html