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.TH trace

.SH NAME

.B lidar - lidar of meteorological fields along trajectories

.SH SYNOPSIS

.B trace

.I inpfile

.I outfile

[

.I optional arguments

]

.SH DESCRIPTION

Get pseudo-lidar of meteorological fields along the trajectories given in the input file 

.I inpfile

and write the field to a netCDF file

.I outfile.

The horizontal axis in the netCDF file corresponds to the trajectory times, the vertical axis gives the pressure in hPa (by default, from 100 to 1000 hPa: it can be changet with optional argument '-pmin', '-pmax', '-centering'). By default, the pseudo lidar is taken at a fixed set of pressure levels between 100 and 1000 hPa. If the option '-centering' is selected, the pressure levels are relative to the trajectory position.

The meteorological fields for the pseudo lidar are listed in a 

.I

tracing file 

(default: tracevars).  Note that the tracevars file has the same format as for 

.I trace

but that all online calculations in the tracing file are neglected.

.SH PARAMETERS

.TP 15

.I inpfile

input trajectory file; the appendix determines the format (see

.B reformat 

for details).

.TP 15

.I  outfile

output netCDF file for the pseudo-lidar fields. 

.SH OUTPUT FIELDS

.TP 5

.B - [ FIELD_SUM | FIELD_MEAN ]

Sum or mean of the lidar field FIELD, depending on the optional parameter '-sum' (default) or '-mean'. For instance, if potential temperature TH is passed as a lidar field, then TH_MEAN would contain the mean over all trajectories. The horizontal axis coincides with the times on the trajectory file; the vertical axis depends on the mode. By default, it goes from 100 hPa to 1000 hPa, within 100 steps. If '-centering' is passed as argument, the pressure levels are always relative to the trajectory position.

.TP 5

.B - FIELD_CNT

Number of values contributing to FIELD_SUM and FIELD_MEAN. This value is variable because the following cases do not contribute to the output field FIELD_SUM/MEAN: (a) if the position is outside the data domain of the input P files; (b) if the position falls below topography; (c) if the trajectory position is invalid; and (d) if the lidar field has a missing value flag set.

.TP 5

.B - POSITION

Position of all trajectories contributing to the lidar composite. By default, the vertical position of the trajectories between 100 hPA and 1000 hPa can be visualised in this way. If '-centering' is selected, the POSITION corresponds to a single line because then all pressure positions are relative to the trajectory height, i.e. a pressure of 0 hPa on tghe vertical axis corresponds to the trajectory position.

.SH TRACING FILE

Normally the meteorological fields for tracing are listed in a file with name 

.B "tracevars". 

The name of the tracing file can be changed with the optional argument "-v" (see below). The format of the tracing file is as follows:

.br

.TP 5

Format

.I field

.I scale

.I computation 

.I prefix  

.TP 5 

Examples

.B - TH 1. 0 S : 

pseudo lidar of potential temperature (TH), scale it with 1 (no scaling); it is available on the S file (no computation is needed: 0).

.br

.B - Q 1000. 0 P :

pseudo lidar of specific humidity (Q), scale it with 1000 to have g/kg; it is available on the P file (no computation is needed: 0).

.SH OPTIONAL ARGUMENTS

.TP 15

.TP 15

.I -i hours

time increments (in hours) for input P and  S files. If not explicitely specified, this is determined from the P and S files i

n the current directory.

.TP 15

.I -v varfile

Change the name of the tracing file from its default value "tracevars" to "varfile".

.TP 15

.I -f field scale

Trace field (with scaling scale) along the trajectories; the computation flag and the prefix for the data file is automatically set. This options allows the quick tracing of a field, without specifying a tracing file.

.TP 15

.I -changet

flag whether the times of the P and S files should be changed or not before a calculation; the default is that the

times are 

.B not 

changed. 

.TP 15

.I -noclean

flag whether parameter and criterion files should be kept; this is particularly helpful for debugging.

.TP 15

.I -timecheck

enforce a time check on the data files

.TP 15

.I -nearest

Do no interpolation between grid points; just take the nearest neighbor! This option is useful, if a discrete input field is given (e.g. labels), where interpolated values are meaningless.

.TP 15

.I [-sum|-mean]

If '-sum' (the default) is chosen and several trajectories are on the input file, then the sum of all pseudo lidar fields is written to the output file; otherwise, for '-mean', the mean of all pseudo lidar fields is written.

.TP 15

.I -zmin value

Set the lower limit for the pseudo lidar. Default is 100 m. 

.TP 15

.I -zmax value

Set the upper limit for the pseudo lidar. Default is 10'000 m.

.TP 15

.I -nlev value

Set the number of pressure levels between 'zmin' and 'zmax. Default is 100.

.TP 15

.I -centering

Select the pressure levels relative to the trajectory position; by default the pressure levels are given as absolute heights between 100 and 1000 hPa. If '-centering' is chosen and no explicit limits are specified with 'pmin' and 'pmax', the limits are set to pmin=-500 hPa and pmax=500 hPa.

.SH VECTOR FIELDS

Note for lidaring of vector fields, e.g wind (U,V), there are two options:

.TP 5

- the lidar variable in the tracing field can be given as U, for instance, and then the component U will be lidared along the trajectory; but this U is the wind component in the rotated coordinate system, i.e. the z

onal wind along the rotated latitude circles!

.TP 5

- if the lidar variable is specified as U.V, a vectorial transformation is applied, i.e. the wind components are transformed into true zonal and meridional wind components. This option is physically more meaningful!  

.SH EXAMPLES

.TP 5

.B [1] lidar TRAJECTORY.1 LIDAR 

Read the trajectory file TRAJECTORY.1 and get a composite pseudo-lidar from 100 to 1000 hPa along the the trajectories. If there are several trajectories on TRAJECTORY.1, the sum is written to the netCDF file LIDAR. The fields of which a pseudo lidar is calculated are listed in the file 'tracevars'. 

.TP 5

.B [2] lidar TRAJECTORY.1 LIDAR -zmin 200 -zmax 500

As in [1], but the upper and lower limits of the pseudo lidar are set to 200 and 500 m.

.TP 5

.B [3] lidar TRAJECTORY.1 LIDAR -centering 

As in [1], but the lidar pressure levels are not fixed: They are taken relative to the trajectory height.

.TP 5

.B [4] lidar TRAJECTORY.1 LIDAR -f U.V 1.

The wind (U,V) is 'lidared' along the trajectory; the two component U and V are treated as part of a vector (U,

V) and the components are transformed into true zonal and meridional winds. 

.SH AUTHOR

Written by Michael Sprenger and Heini Wernli (April 2012).