Subversion Repositories lagranto.um

.TH trace

.SH NAME

.B trace - trace meteorological fields along trajectories

.SH SYNOPSIS

.B trace

.I inpfile

.I outfile

[

.I optional arguments

]

.SH DESCRIPTION

Trace meteorological fields along the trajectories given in the input file 

.I inpfile

and write a new trajectory file

.I outfile

. The meteorological fields to trace are listed in a 

.I

tracing 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 inpfile

input trajectory file; the appendix determines the format (see

.B reformat 

for details).

.TP 15

.I  outfile

output trajectory file; the appendix determines the format (see

.B reformat 

for details).

.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[:shift]

.I scale

.I computation 

.I prefix  

.TP 5

Shifts (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 5 

Examples

.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 P :

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 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 -notimecheck

take the first time on the netCDF file - do no explicit test that the requested 

time is available on the file. This is particularly helpful if you have no write

 permission for the P files.

.SH ONLINE CALCULATIONS

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:

.TP 5

.B - TH

potential temperature (in K).

.TP 5

.B - RHO

density (in kg/m^-3).

.TP 5

.B - RH

relative humidity (in %).

.TP 5

.B - THE

equivalent-potential temperature (in K).

.TP 5

.B - LHR

latent heating rate (K per input time step, typically K/6h). 

.TP 5

.B - D[U,V,T,TH]DX

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). 

.TP 5

.B - D[U,V,T,TH]DY

horizontal 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]DP

vertical derivative d[U,V,T,TH]/dp - pressure p in Pa.

.TP 5

.B - NSQ

squared Brunt-Vaisala frequence (in m^-2).

.TP 5

.B - RELVORT

relative vorticity (in s^-1) - RELVORT = DVDX - DUDY.

.TP 5

.B - ABSVORT

absolute vorticity (in s^-1) - ABSVORT = DVDX - DUDY + F, F being the Coriolis parameter.

.TP 5

.B - DIV

horizontal divergence of the velocity field (in s^-1) - DIV = DUDX + DVDY.

.TP 5

.B - DEF

horizontal deformation of the velocity field (in s^-1) - DEF = SQRT( ( DVDX + DUDY )^2 + (DUDX-DVDY)^2 ).

.TP 5

.B - PV

Ertel potential vorticity (in PVU) - PV = g * ( ABSVORT * DTHDP + DUDP * DTHDY - DVDP * DTHDX ).

.TP 5

.B - RI

Richardson number - RI = NSQ / (DUDP^2 + DVDP^2 ).

.TP 5

.B - TI

tubulence indicator according to Ellrod & Knapp - TI = DEF * SQRT( DUDP^2 + DVDP^2 ) * ( RHO * G).

.TP 5

.B - DIR

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. 

.TP 5

.B - DIST0

spherical distance (in km) from starting position.

.TP 5

.B - DIST

length of the trajectory (in km): integrated along great circle sections between the trajectory vertices.

.TP 5

.B - HEAD

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. 

.SH EXAMPLES

.TP 5

.B [1] /home/sprenger/lagranto/bin/trace TRAJECTORY.1 TRAJECTORY.1 -changet

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.

.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 AUTHOR

Written by Michael Sprenger and Heini Wernli (January 2011).