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michaesp |
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.TH trace
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.SH NAME
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.B trace - trace meteorological fields along trajectories
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.SH SYNOPSIS
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.B trace
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.I inpfile
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.I outfile
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[
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.I optional arguments
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]
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.SH DESCRIPTION
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Trace meteorological fields along the trajectories given in the input file
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.I inpfile
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and write a new trajectory file
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.I outfile
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. The meteorological fields to trace are listed in a
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.I
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tracing file
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(default: tracevars). Partly they can be computed "online" (see ONLINE CALCULATIONS below), normally they are availbale on the primary and secondary P and S files.
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.SH PARAMETERS
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.TP 15
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.I inpfile
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input trajectory file; the appendix determines the format (see
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.B reformat
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for details).
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.TP 15
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.I outfile
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output trajectory file; the appendix determines the format (see
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.B reformat
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for details).
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.SH TRACING FILE
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Normally the meteorological fields for tracing are listed in a file with name
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.B "tracevars".
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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:
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.br
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.TP 5
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Format
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.I field[:shift]
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.I scale
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.I computation
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.I prefix
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.TP 5
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Shifts (optional)
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.B - field:+100km[lat]
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- get field at trajectory position + 100 km shifted to north. A shift to south is obtained with field:-100km[lat].
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.br
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.B - field:+100km[lon]
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- get field at trajectory position + 100 km shifted to east. A shift to west is obtained with field:-100km[lon].
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.br
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.B - field:+2[dlat]
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- get field at trajectory position + 2 grid spacings dlat shifted to north. A shift to south is obtained with field:-2[dlat].
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.br
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.B - field:+2[dlon]
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- get field at trajectory position + 2 grid spacings dlon shifted to east. A shift to west is obtained with field:-2[dlon].
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.br
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.B - field:+50hPa
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- get field at trajectory position + 50 hPa shifted in vertical. A shift to lower pressures is obtained with field:-50hPa.
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.br
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.B - field:+1dp
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- get field at trajectory position + 1 grid spacing DP shifted in vertical. A shift to lower pressures is obtained with field:-1dp. Note that DP is not fixed but varies with height.
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.br
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.B - field:+6h
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- get field at trajectory position, but 6 h in the future. Shifts to the past are poeeible with field:-6h. In addition to hours (h), the time shift can be specified in minutes (min).
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.TP 5
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Examples
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.B - TH 1. 0 S :
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trace potential temperature (TH), scale it with 1 (no scaling); it is available on the S file (no computation is needed: 0).
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.br
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.B - Q 1000. 0 P :
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trace specific humidity (Q), scale it with 1000 to have g/kg; it is available on the P file (no computation is needed: 0).
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.br
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.B - RH 1. 1 * :
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trace relative humidity (RH), no scaling is needed (1.); relative humidity is not available on either P or S file and must be computed (1).
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.br
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.B - TH:100hPa 1. 0 S :
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As in the first example, but now the potential temperature is taken 100 hPa below the air parcel position.
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.SH OPTIONAL ARGUMENTS
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.TP 15
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.TP 15
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.I -i hours
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time increments (in hours) for input P and S files. If not explicitely specified, this is determined from the P and S files i
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n the current directory.
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.TP 15
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.I -v varfile
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Change the name of the tracing file from its default value "tracevars" to "varfile".
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.TP 15
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.I -f field scale
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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.
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.TP 15
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.I -changet
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flag whether the times of the P and S files should be changed or not before a calculation; the default is that the
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times are
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.B not
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changed.
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.TP 15
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.I -noclean
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flag whether parameter and criterion files should be kept; this is particularly helpful for debugging.
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.TP 15
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.I -timecheck
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enforce a time check for the data file
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.SH SPECIAL INTERPOLATION MODES
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.TP 15
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.I -nearest
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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.
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.TP 15
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.I -circle_avg radius
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calculate area-weighted average over all grid points within a circle of the specified radius [km]. e.g. -circle_avg 200; note that the tracing of fields within a circle is quite slow.
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.TP 15
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.I -circle_max radius
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calculate maximum within a circle of a radius [km]. e.g. -circle_max 200
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.TP 15
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.I -circle_min radius
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calculate minimum within a circle of a radius [km]. e.g. -circle_min 200
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.TP 15
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.I -clustering
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special mode to trace strat/trop label; the labels are attributed according to the program (tropopause), which clusters the atmosphere into five distinct classes according to the definition of the tropopause: PV (2 PVU) and potential temperature (380 K). The clustering mode is a refined version of the nearest mode, where all surrounding eight grid points vote for the final value.
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.SH ONLINE CALCULATIONS
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If the computation flag in the tracing file is set to 1, a meteorological field is calculated based upon the already traced fields and/or based on the fields on the primary and secondary P and S files. The following fields are implemented for online calculations:
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.TP 5
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.B - TH
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potential temperature (in K).
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.TP 5
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.B - RHO
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density (in kg/m^-3).
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.TP 5
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.B - RH
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relative humidity (in %).
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.TP 5
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.B - THE
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equivalent-potential temperature (in K).
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.TP 5
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.B - LHR
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latent heating rate (K per input time step, typically K/6h).
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.TP 5
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.B - D[U,V,T,TH]DX
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horizontal derivative d[U,V,T,TH]/dx in west-east direction along pressure surfaces - zonal distance in m. U=zonal wind component (m/s), V=meridional wind component (m/s), T=temperature (deg C or K), TH=potential temperature (K).
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.TP 5
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.B - D[U,V,T,TH]DY
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horizontal derivative d[U,V,T,TH]/dy in south-north direction along pressure surfaces -meridional distance in m.
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.TP 5
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.B - D[U,V,T,TH]DP
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vertical derivative d[U,V,T,TH]/dp - pressure p in Pa.
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.TP 5
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.B - NSQ
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squared Brunt-Vaisala frequence (in m^-2).
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.TP 5
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.B - RELVORT
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relative vorticity (in s^-1) - RELVORT = DVDX - DUDY.
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.TP 5
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.B - ABSVORT
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absolute vorticity (in s^-1) - ABSVORT = DVDX - DUDY + F, F being the Coriolis parameter.
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.TP 5
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.B - DIV
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horizontal divergence of the velocity field (in s^-1) - DIV = DUDX + DVDY.
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.TP 5
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.B - DEF
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horizontal deformation of the velocity field (in s^-1) - DEF = SQRT( ( DVDX + DUDY )^2 + (DUDX-DVDY)^2 ).
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.TP 5
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.B - PV
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Ertel potential vorticity (in PVU) - PV = g * ( ABSVORT * DTHDP + DUDP * DTHDY - DVDP * DTHDX ).
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.TP 5
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.B - RI
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Richardson number - RI = NSQ / (DUDP^2 + DVDP^2 ).
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.TP 5
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.B - TI
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tubulence indicator according to Ellrod & Knapp - TI = DEF * SQRT( DUDP^2 + DVDP^2 ) * ( RHO * G).
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.TP 5
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.B - DIR
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wind direction relative to zonal flow: (U,V)=(1,1) -> 45 deg; (U,V)=(1,-1) -> -45 deg; (U,V)=(-1,-1) -> -135 deg; (U,V)=(-1,1) -> 135 deg. A westerly flow has 0 deg, a southerly flow 90 deg, and a northerly one -90 deg.
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.TP 5
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.B - DIST0
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spherical distance (in km) from starting position.
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.TP 5
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.B - DIST
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length of the trajectory (in km): integrated along great circle sections between the trajectory vertices.
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.TP 5
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.B - HEAD
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heading of the trajectory: (DX,DY)=(1,1) -> 45 deg; (DX,DY)=(1,-1) -> -45 deg; (DX,DY)=(-1,-1) -> -135 deg; (DX,DY)=(-1,1) -> 135 deg. A path increment to east has heading of 0 deg; to the north 90 deg; to the south -90 deg; and to the west -180 deg.
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.SH EXAMPLES
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.TP 5
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.B [1] trace TRAJECTORY.1 TRAJECTORY.1 -changet
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Read the trajectory file TRAJECTORY.1, trace all fields in the file "tracevars" along the trajectories and overwrite the existing trajectory file. In preparation, all times on the P and S files are changed prior to the tracing.
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.TP 5
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.B [2] trace INPTRA.1 OUTTRA.1 -f PV 1.
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Trace PV (with scaling factor 1.) along the trajectories in trajectory file "INPTRA.1" and write a new trajectory file "OUTTRA.1".
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.TP 5
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.B [3] trace INPTRA.1 OUTTRA.1 -f PV:-100HPA 1.
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As in example [2], but the PV is taken at a position 100 hPa higher (lower pressure) than the air parcel's position.
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.TP 5
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.B [4] trace INPTRA.1 OUTTRA.1 -f DIST0 1.
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Get the spherical distance (in km) of the air parcel from its starting position.
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.SH AUTHOR
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Written by Michael Sprenger and Heini Wernli (January 2011).
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