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.TH trace.SH NAME.B trace - trace meteorological fields along trajectories.SH SYNOPSIS.B trace.I inpfile.I outfile[.I optional arguments].SH DESCRIPTIONTrace meteorological fields along the trajectories given in the input file.I inpfileand write a new trajectory file.I outfile. The meteorological fields to trace are listed in a.Itracing file(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..SH PARAMETERS.TP 15.I inpfileinput trajectory file; the appendix determines the format (see.B reformatfor details)..TP 15.I outfileoutput trajectory file; the appendix determines the format (see.B reformatfor details)..SH TRACING FILENormally 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 5Format.I field[:shift].I scale.I computation.I prefix.TP 5Shifts (optional).B - field:+100km[lat]- get field at trajectory position + 100 km shifted to north. A shift to south is obtained with field:-100km[lat]..br.B - field:+100km[lon]- get field at trajectory position + 100 km shifted to east. A shift to west is obtained with field:-100km[lon]..br.B - field:+2[dlat]- get field at trajectory position + 2 grid spacings dlat shifted to north. A shift to south is obtained with field:-2[dlat]..br.B - field:+2[dlon]- get field at trajectory position + 2 grid spacings dlon shifted to east. A shift to west is obtained with field:-2[dlon]..br.B - field:+50hPa- get field at trajectory position + 50 hPa shifted in vertical. A shift to lower pressures is obtained with field:-50hPa..br.B - field:+1dp- 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..br.B - field:+6h- 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)..TP 5Examples.B - TH 1. 0 S :trace 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 :trace specific humidity (Q), scale it with 1000 to have g/kg; it is available on the P file (no computation is needed: 0)..br.B - RH 1. 1 * :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)..br.B - TH:100hPa 1. 0 S :As in the first example, but now the potential temperature is taken 100 hPa below the air parcel position..SH OPTIONAL ARGUMENTS.TP 15.TP 15.I -i hourstime increments (in hours) for input P and S files. If not explicitely specified, this is determined from the P and S files in the current directory..TP 15.I -v varfileChange the name of the tracing file from its default value "tracevars" to "varfile"..TP 15.I -f field scaleTrace 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 -changetflag whether the times of the P and S files should be changed or not before a calculation; the default is that thetimes are.B notchanged..TP 15.I -nocleanflag whether parameter and criterion files should be kept; this is particularly helpful for debugging..TP 15.I -timecheckenforce a time check for the data file.SH SPECIAL INTERPOLATION MODES.TP 15.I -nearestDo 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 -circle_avg radiuscalculate 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..TP 15.I -circle_max radiuscalculate maximum within a circle of a radius [km]. e.g. -circle_max 200.TP 15.I -circle_min radiuscalculate minimum within a circle of a radius [km]. e.g. -circle_min 200.TP 15.I -clusteringspecial 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..SH ONLINE CALCULATIONSIf 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:.TP 5.B - THpotential temperature (in K)..TP 5.B - RHOdensity (in kg/m^-3)..TP 5.B - RHrelative humidity (in %)..TP 5.B - THEequivalent-potential temperature (in K)..TP 5.B - LHRlatent heating rate (K per input time step, typically K/6h)..TP 5.B - D[U,V,T,TH]DXhorizontal 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)..TP 5.B - D[U,V,T,TH]DYhorizontal derivative d[U,V,T,TH]/dy in south-north direction along pressure surfaces -meridional distance in m..TP 5.B - D[U,V,T,TH]DPvertical derivative d[U,V,T,TH]/dp - pressure p in Pa..TP 5.B - NSQsquared Brunt-Vaisala frequence (in m^-2)..TP 5.B - RELVORTrelative vorticity (in s^-1) - RELVORT = DVDX - DUDY..TP 5.B - ABSVORTabsolute vorticity (in s^-1) - ABSVORT = DVDX - DUDY + F, F being the Coriolis parameter..TP 5.B - DIVhorizontal divergence of the velocity field (in s^-1) - DIV = DUDX + DVDY..TP 5.B - DEFhorizontal deformation of the velocity field (in s^-1) - DEF = SQRT( ( DVDX + DUDY )^2 + (DUDX-DVDY)^2 )..TP 5.B - PVErtel potential vorticity (in PVU) - PV = g * ( ABSVORT * DTHDP + DUDP * DTHDY - DVDP * DTHDX )..TP 5.B - RIRichardson number - RI = NSQ / (DUDP^2 + DVDP^2 )..TP 5.B - TItubulence indicator according to Ellrod & Knapp - TI = DEF * SQRT( DUDP^2 + DVDP^2 ) * ( RHO * G)..TP 5.B - DIRwind 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..TP 5.B - DIST0spherical distance (in km) from starting position..TP 5.B - DISTlength of the trajectory (in km): integrated along great circle sections between the trajectory vertices..TP 5.B - HEADheading 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..SH EXAMPLES.TP 5.B [1] trace TRAJECTORY.1 TRAJECTORY.1 -changetRead 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..TP 5.B [2] trace INPTRA.1 OUTTRA.1 -f PV 1.Trace PV (with scaling factor 1.) along the trajectories in trajectory file "INPTRA.1" and write a new trajectory file "OUTTRA.1"..TP 5.B [3] trace INPTRA.1 OUTTRA.1 -f PV:-100HPA 1.As in example [2], but the PV is taken at a position 100 hPa higher (lower pressure) than the air parcel's position..TP 5.B [4] trace INPTRA.1 OUTTRA.1 -f DIST0 1.Get the spherical distance (in km) of the air parcel from its starting position..SH AUTHORWritten by Michael Sprenger and Heini Wernli (January 2011).