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== The package pos ==

The package '''pos''' helps to create an ensemble of ''n'' APs. 
Especially, their initial special positions (described in
isentropic coordinates spanned by longitude, latitude and the potential temperature) and their initial times (in Julian seconds) can be created. The geometric properties (positions, Voronoi areas,...) and the dynamical properties (PV, EQLAT, TEMP, PRESS,....) 
of the APs are derived from the meteorological input files using the ''pos''***-family of the programs.


=== Available programs ===

The subdirectory ''source'' contains the following programs: 

 * add_flightpath.f90: Add positions of a flightpath to a pos file

 * [[/pos_3d.f90 | pos_3d.f90]]: Different 2d or 3d initial configurations

 * [[/pos_area.f90 | pos_area.f90]]: 2d or 3d initial positions of APs with equal isentropic areas (+ PV_INIT)
 
 * [[/pos_chem.f90 | pos_chem.f90]]: modifies chemical fields (O3, HCL etc) in init-files on lower and upper bound

 * [[/pos_dyn.f90 | pos_dyn.f90]]: This program completes the geometric positions of the APs with their dynamical properties, i.e.~PV, EQLAT, TEMP, PRESS,...
 
 * pos_example.f90: An easy example how to create the initial positions of APs

 * pos_flightpath.f90: Create pos file with positions along flightpath
  
 * [[/pos_voronoi.f90 | pos_voronoi.f90]]: Voronoi areas are calculated and added to the pos/init-file


=== Output Files ===

Each ''pos_*'' program creates an output file in NetCDF data format. It is named:

        ''pos_xxx_yymmddhh.nc'' 

        ''xxx'' : prefix, 1-3 characters <<BR>>
        ''yymmddhh'' : year, month, day, hour <<BR>>
        e. g.:  ''pos_ABC_99022812.nc''<<BR>>


In this file the starting positions of the trajectories (longitudes, latitudes and theta) are stored on the variables LAT, LON and THETA. The corresponding starting times are saved on the variable TIME_INIT. Furthermore, the variables PV_INIT, EQLAT, TEMP, PRESS, TND (density) and VORONOI_AREA can be created.

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[[/Changes|History of Changes]]