A trajectory file consist of a number of subsequent trajectories
each with one header line and a body (a number of data lines).

Example of a header for backward trajectories with a timestep of 1 h:

TRA240 1998031318 1998031418 1998030318 -1 241 3051   59  975  99
name   yyyymmddhh yyyymmddhh yyyymmddhh hh npt  LON  LAT PRES ZER
string date1      fcdate     date2
   
       string is the trajectory program name "TRA240"
       date1 is the first date of the trajectories
          (for backward trajectories the enddate, date when they
           are at the requested point)
       fcdate is the date of the forecast or analysis used
           in this example it is later than date1 so analysis date were used.
       date2 is the last date of the trajectories
          (for backward trajectories the begindate)
       hh : timestep in hours (negative implies backward trajectories)
       npt: number of points = the number of lines in the body
            this is one more than the number of time steps.
       LON, LAT, PRES = coordinates of begin point trajectory
                        LON and LAT are in 0.1 degrees
       ZER : an administrative number
       The format of the header is:
          '(A6,X,i10,x,i10,x,i10,I3,I4,3I5,I4)'

The body consists of lines describing each one trajectory position:
   Here follows an example of the first three lines (traj. positions):
          0 10077 3051   59  9750    -73    -47    -13
         -1 10084 3053   61  9791    -78    -47    -10
         -2 10083 3056   62  9819    -82    -47     -6

       TTTT PRES0  LON  LAT  PRES      U      V      W

       TTTT : time step number
       PRES0: pressure at the bottom of the model (the surface)
       LON, LAT: horizontal trajectory position (in 0.1 degrees E and N)
       PRES : vertical trajectory position (in 0.1 hPa)
       U, V : horizontal winds in EW resp. NS direction at trajectory position
              in 0.1 m/s)
       W : vertical wind at trajectory position 

   The format of a line is:
        (7X,I4,I6,2I5,I6,3I7)