HYSPLIT Forum: hysplitbbs.arl.noaa.gov

In regards to the HYSPLIT, I do have some questions, please i'd appreciate to help me with them, as follows:
If there is a volcan near the Andes (ca. 5000 m asl) and there was detected some volcanic ashes at 170 km away to the Pacific coast at 4 m asl, I would like to run a backward trajectory BT from the city to the volcano to estimate the path and the estimate time of arrival. Which approach would be the best to choose: 1000 m BT or 5000 m BT? i have run both but the pollution path differs from altitude. I pay attention to your talks and you mentioned no matter the choose altituted the model always run the calculation at 25 km and it is more important the boundary layer PBL.
I'd seen that most of the examples are running with forward trajectories, but from experience abroad, particularly in latin america, it worked for us using meterological data from GDAL 1 degree and backward trajectories, at least to explain Saharan dust plumes and volcanic emissions. Do you have any experience outside US?

HYSPLIT can run a backward trajectory starting at any height, as long as it is not higher than the model top. The model top is the vertical limit of the internal meteorological grid. It tells the model how much the calculation can go vertically. Usually, it is set no higher than the top of your met data.
So, in your application, the BT starting height is 1000 m or 5000 m. Go to Trajectory/Setup Run/Setup starting locations. Then put in the starting height together with the lat-lon location. And in the Trajectory Setup menu, put 25,000 m for the box of "Top of model". The description of these two terms is available in the HYSPLIT user's guide: https://www.ready.noaa.gov/hysplitusersguide/S262.htm

For the trajectory analysis, you may follow section 6.1 to do the frequency plots
https://www.ready.noaa.gov/documents/Tu ... _freq.html

The following webpage gives an overview of volcanic ash studies using HYSPLIT and lists publications related to that.
https://www.arl.noaa.gov/hysplit/volcanic-ash-model/
https://egusphere.copernicus.org/prepri ... -2022-290/

The HYSPLIT BAMS paper has an example of using HYSPLIT to simulate the eruption of the Cordón Caulle volcano in South America. https://journals.ametsoc.org/view/journ ... 0110.1.xml