NASA Ames Output format for the BADC trajectory service

The BADC trajectory service produces NetCDF files by default which is a binary based output format. It is possible to produce readable output files using the 'View NASA Ames' links on the Output file page, and plot page. The NASA Ames files are a self describing ASCII based files that have seen extensive use in experimental campaigns. Each file begins with a header, which describes the contents of the file, and defines and scaling factors or missing value flags. The data follows the header. For more detailed information on the NASA Ames Data transfer file format refer to the document by Gaines and Hipskind.

The NASA Ames trajectory files are file format index 2110. This file format is appropriate for fields which have two independent variables (or dimesions). In the case of trajectories these dimensions are time and trajectory index which labels each trajectory within the file. Some campaigns use file format index 2160 for trajectory files. In this case the second dimension is a character label for the trajectory start position rather than a trajectory index. For the BADC trajectory service the file format index 2110 has been chosen since the trajectory start positions are arbitray and do not neccessarily coincide with any named station.

The current implementation of the 2110 file format index is minimalist. This will change with time: more primary variables, such as temperature, more auxillary variables, and more comments will be added. All changes will be consistent with the definition of the 2110 file format index.

An example of a typical file, along with explanations follows. The variable names, such as NLHEAD are taken from Gaines and Hipskind.

22 2110                                         [NLHEAD FFI]
BADC User Support (badc@rl.ac.uk)
British Atmospheric Data Centre
WWW Trajectory Service
No Mission: Produced as part of a regular service
1 1
1999 01 01 1999 07 06                           [DATE RDATE]
2400.0 1.0                                      [DX(1) DX(2)]
Time (seconds) from 00 on start date            [XNAME(1)]
Trajectory Index                                [XNAME(2)]
3                                               [NV]
1.0 1.0 1.0                                     [VSCAL(1) VSCAL(2) VSCAL(3)]
999.99 999.99 9999.99                           [VMISS(1) VMISS(2) VMISS(3)]  
Latitude (degrees North)                        [VNAME(1)]
Longitude (degrees East)                        [VNAME(2)]
Pressure (hPa)                                  [VNAME(3)]
1                                               [NAUXV]
1.0                                             [ASCAL(1)]
9999.99                                         [AMISS(1)]
Number of output times along trajectory         [ANAME(1)]
0                                               [NSCOML]
0                                               [NNCOML]
1 5 
      0   50.00    0.00   50.000
   2400   50.60    0.78   49.325
   4800   51.18    1.58   48.738
   7200   51.74    2.41   48.262
   9600   52.31    3.31   47.885

NLHEAD=22: The number of lines in the header
FFI=2110: The file format index
DATE=1999 01 01: The start date of the trajectory run.
RDATE=1999 07 06: The date on which the trajectory model was run.
DX(1)=2400.0: The number of seconds between output times
DX(2)=1.0: The trajectory index will always increment by one
XNAME(1)=Time (seconds) from 00 on start date: The name of the most rapidly varying dimension. In this case time from midnight on the start date. This leads to non-zero initial times, for trajectory integrations that start at any other time, e.g. 12UT.
XNAME(2)=Trajectory Index: The name of the second independant (dimension) variable. In this case it is simply the index of the trajectory in the file. Trajectories are labeled by indices 1, 2, 3, etc.
NV=3: The number of primary dependant variables
VSCALE(1) VSCALE(2) VSCALE(3)=1.0 1.0 1.0: Scale factors for each of the dependent variables.
VMISS(1) VMISS(2) VMISS(3)=999.99 999.99 9999.99: Values for undefines/missing data points for each of the dependent variables.
VNAME(1)=Latitude (degrees North): Name of the first dependent variable.
VNAME(2)=Longitude (degrees East): Name of the first dependent variable.
VNAME(3)=Pressure (hPa): Name of the first dependent variable.
NAUXV=1: Number of auxillary variables.
ASCALE(1)=1.0: Scale factor for the auxillary variable
AMISS(1)=9999.99: Values for undefines/missing data points for each of the auxillary variables.
ANAME(1)=Number of output times along trajectory: For the 2110 format there is always one auxillary variable which gives information on the length of the most rapidly varying dimension. In this case this is the number of output times along the trajectory.
NSCOML=0: In the current, minimalist, implementation of the NASA Ames format for the trajectory files there are no special comments. This will change.
NNCOML=0: In the current, minimalist, implementation of the NASA Ames format for the trajectory files there are no normal comments. This will change.
Data Records:: Each data record begins with the trajectory index, followed by the number of output times for this trajectory. The columns that follow are the time, latitude, longitude, and pressure along that trajectory.

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