The package traj

The package traj allows to determine the trajectories of an ensemble of air parcels. Using assimilated winds and temperatures derived from meteorological data (currently UKMO or ECMWF), both forward and backward can be calculated. The numerical integration is based on the 4th order Runge-Kutta schema.

Initial positions of air parcels

This file includes the starting positions of the trajectories (longitudes, latitudes and theta) and the corresponding starting times. To create it the package pos can be used. It has to be a file in NetCDF data format with the following variables:

• LAT: latitudes in deg N, valid range [-90,90]
• LON: longitudes in deg O, valid range [0,360]
• THETA: potential temperature in K
• TIME_INIT: time in Julian Seconds

The filename must correspond to the following format:

• pos_xxx_yymmddhh.nc
  xxx : 1-3 characters
  yymmddhh : starting time
  e.g.: pos_ABC_99022812.nc

Meteorological data

The data files with meteorological data used by the trajectory program must contain the coordinate variables

• LAT: latitudes in deg N, valid range [-90,90]
• LON: longitudes in deg O, valid range [0,360]
• THETA: potential temperature in K
• time: time in julian seconds

Besides they must include at least the four-dimensional data sets for the variables

• U: westerly wind
• V: southerly wind
• OMEGA: vertical velocity
• TEMP: temperature
• PRESS: pressure
• PV: potential vorticity

The filenames must correspond to the format:

• isen_xxx_yymmddhh.nc
  xxx : 3 characters
  yymmddhh : valid time
  e. g.: isen_ABC_99022812.nc

Configuration file

The options for the execution of traj can be set in the configuration file traj.inp:

/arch/jicg11/jicg1108/traj_input/pos_EXP_97032512.nc    ! Name of initial positions file
/arch/jicg11/jicg1108/traj_input                        ! Input directory
I3U                                                     ! Prefix of wind files
/usr_FZJ/jicg11/jicg1108/traj/t90                       ! Output directory
TRU                   ! Prefix for output file
24                    ! 1/2/3/4/6/8/12/24 -> Data every n hours 
y                     ! y/n - Backward/Forward trajectories 
y                     ! y/n - 3d(with theta_dot)/2d(without theta_dot) run
1                     ! eq. starts (a=0) diff. starts: a=1/2 same end/length
12 23 03 1997         ! Endtime(hh dd mm yy) for a=0/1, lenght (hrs) for a=2
1800                  ! First timestep in seconds
60                    ! Second timestep in seconds
0 1 0                 ! Writing frequency (minutes hours days) 
N.Thomas              ! user name
4                     ! number of output parameters
TEMP                  ! output parameters (one short name per line) 
PRESS                 ! possible parameters are: TEMP,PRESS,U,V,PV, and SZA
PV
SZA