Two types of backward trajectories were calculated.  The first category consists of 
trajectories arriving at the various altitudes of the aircraft during a flight.   
The gif image designated “ALT” shows an example of this category.  The second 
category consists of trajectories arriving at various constant pressure levels 
along the flight track (850, 700, 600, 500, 400, 300, 200, and 100 hPa).  These 
levels typically were either above or below the aircraft altitude, but occasionally 
corresponded to the exact aircraft altitude.  The gif images show example plots of 
these at 300, 500 and 850 hPa.

The zip files contain the tabulated values for both types of trajectories for each 
flight of each aircraft.  Trajectories were calculated at intervals of 5 min of 
aircraft flight time.  For example, at an aircraft speed of 400 kt (206 m s-1), the 
5-min interval corresponds to a horizontal separation of ~ 62 km. Trajectory output 
is at an hourly interval.

Although trajectories extend back a maximum of 10 days, some terminate early due to 
various factors.  Therefore, each trajectory consists of a header number giving the 
total number of hourly time steps along that trajectory.  The header number is followed 
by the latitude (deg), longitude (deg), and pressure altitude (hPa) of positions along 
the trajectory as a function of time from arrival along the flight track.  

A cluster of trajectories was prepared at each location.  That is, a diamond of four 
points was superimposed on the flight track point.  Each point of the diamond is 
separated from the center point by 2 deg lat/long.  The five cluster points also 
were used at 25 mb above and below the flight level.  This results in 15 trajectories 
calculated for every 5-min separation point along the flight track.