SRCTRAJECTORIES.txt

WHAT IS AN AIR PARCEL ?
An imaginary body of air to which may be assigned any or all of the basic dynamic and thermodynamic properties of atmospheric air. A parcel is large enough to contain a very great number of molecules, but small enough so that the properties assigned to it are approximately uniform within it and so that its motions with respect to the surrounding atmosphere do not induce marked compensatory movements. It cannot be given precise numerical definition, but a cubic foot of air might fit well into most contexts where air parcels are discussed, particularly those related to static stability.


HYSPLIT
The Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) is a computer model that is used to compute air parcel trajectories and deposition or dispersion of atmospheric pollutants. It was developed by NOAA and Australia's Bureau of Meteorology.

One popular use of HYSPLIT is to establish whether high levels of air pollution at one location are caused by transport of air contaminants from another location. HYSPLIT's back trajectories, combined with satellite images (for example, from NASA's MODIS satellites), can provide insight into whether high air pollution levels are caused by local air pollution sources or whether an air pollution problem was blown in on the wind.

HYSPLIT is rather unusual in that it may be run in client-server mode (HYSPLIT-WEB) from the NOAA website, allowing members of the public to select gridded historical or forecast datasets, to configure model runs, and retrieve model results with a web browser.

PySPLIT includes a method that repeatedly calls HYSPLIT in a subprocess to generate arbitrarily large numbers of
trajectories launched from a single location over as many months and years as desired, limited
only by the availability of meteorological data.


LINK:
https://www.youtube.com/watch?v=2mzhTC4Kp-Y

PySPLIT
PySPLIT enables fully reproducible workflows, with orders of magnitude superior
efficiency compared to what was previously possible with HYSPLIT alone, and
leverages the capabilities of the scientific Python ecosystem and matplotlib to
generate reproducible, publication-quality figures.

Prior to performing trajectory generation with PySPLIT, the user must have a working installation of the desktop
version of HYSPLIT. Users must also have meteorology files corresponding to the time and general location of interest. 

The call for bulk Trajectory generation contains 10 required arguments indicating various directories and initialization parameters:
• basename String, first characters in trajectory file names;
• hysplit working String, full or relative path to the HYSPLIT working directory;
• output_dir String, full or relative path to the trajectory storage location;
• meteo_dir String, full or relative path to directory of meteorology files required to calculate trajectories;
• years List of ints;
• months List of ints;
• hours List of ints, in Universal Coordinated Time;
• altitudes List of ints, in meters (HYSPLIT defaults to meters above ground level);
• coordinates Tuple of floats, launch location in decimal degrees; and
• run Int, the length in hours of simulation. Sign indicates forward (+) or backward (-) trajectories.