xstream is a simple program used to visualize the structure of vector fields by simulating the trajectories of thousands of particles scattered initially on a grid and then advected by the wind, assuming steady (time invariant) flow conditions.
xstream does not have a user interface. It starts with a wind field defined from the calling arguments (file, level, forecast hour) and keeps on animating it until the left mouse button has been pressed.
xstream always interpolate the source grid on a polar stereographic grid. The default grid covers most of the Canada, but the user is free to input any valid PS grid (à la PGSM).
xstream
-IMFLDS RPN_Standard_file
-IP1 level [first level in the standard file]
-IP2 forecast_hour [first forecast hour in the standard file]
-NPTS number of points [2000]
-NPAS number of time steps [25]
-DEET time step (seconds, [1800]
-SEGSTEP [4 - the number of frames on which the particles are followed]
-SEGLEN [3 - the number of adjacent particles in a stream]
-NI number of points of the target grid along the x axis[351]
-NJ number of points of the target grid along the y axis[261]
-GRTYP grtyp (N or S) [N]
-PI X position of the pole on the grid, in grid points [121.5]
-PJ Y position of the pole on the grid, in grid points [281.5]
-D60 grid length in meters [20000.0:20000.0]
-DGRW rotation of the grid wrt Greenwich meridian [21.0:21.0]
xstream -imflds $CMCGRIDF/prog/regpres/1999072912_024 -ip1 500
xstream -imflds $CMCGRIDF/prog/regpres/1999072912_024 -ip1 250 -npas 100
xstream -imflds $CMCGRIDF/prog/regpres/1999072912_024 -ip1 1000 -deet
3600
xstream -imflds $CMCGRIDF/prog/regpres/1999072912_024 -ip1 500 -segstep
16 -seglen 1
xstream -imflds $CMCGRIDF/prog/regpres/1999072912_024 -ip1 500 -segstep
16 -seglen 8
Caveats:
The numerical method used to advect the particles is Eulerian forward (hence pretty crude!). A better method will eventually be employed to guarantee more precise results.
Future work:
This module will eventually be integrated in xrec (or max, if its developers are interested). If you have any suggestion, please correspond with the author!
Author: Yves Chartier
Last updated August 3rd, 1999.