The University of Melbourne

Parcel Trajectory Software

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3D 3-day trajectories

 

This is the home page for the University of Melbourne Parcel Trajectory Software.

 

Introduction

Parcel trajectories are often calculated to obtain an appreciation of the history of air masses (e.g. Fuelburg et al., 1996). The direction and length of trajectories are useful in diagnosing processes that may affect particular air masses under certain conditions. In this regard it is important that parcel trajectories are determined accurately.

††††††††††† The three-dimensional (3D) algorithm presented here (traj3d) builds on the two-dimensional (2D) model of Law (1993) and reported in application by Perrin and Simmonds (1995). From a specified parcel location in the atmosphere, xn at time n, a finite integral is solved to advect the parcel and generate the trajectory path. Given the 3D wind v(xn) the governing prognostic equation for the trajectory path over a short time interval Δt isxn+1 = xn + v Δt . The wind at a given point is found by cubically interpolating from a spatial grid then linearly in time. For back trajectories the wind direction is reversed. The finite integral is solved using a fourth-order Runge-Kutta scheme to obtain an estimate of the wind. This method is considerably more accurate for trajectory calculations than a simple first-order approach. For mathematical details about the 3D algorithm see Noone and Simmonds (1999) and Barras and Simmonds (2009).

††††††††††† We present an implementation of the 3D algorithm in Fortran 77 that is suitable for any platform given an appropriate compiler. A precompiled Linux version is also available. The input to the program is a simple binary format referred to as CMP. At present the input data (usually 3D winds) are limited to constant pressure levels (e.g. 1000, 925, 850 hPa etc) as is the case with the commonly available reanalysis products e.g. NCEP reanalysis. The output of the program is a NetCDF file (and therefore NetCDF libraries need to be accessible for compilation) and this may be imported into many software packages e.g. Matlab, NCL, for subsequent analysis and plotting. We include some utilities to convert from NetCDF (a common format for 3D meteorological fields like winds) to CMP as well as plotting the trajectories based on NCAR Graphics/NCL.

††††††††††† Although intended for computing 3D trajectories the algorithm is equally applicable to 2D trajectory studies e.g. 10 m winds, or a single pressure level e.g. 500 hPa. Finally, it is possible to interpolate auxiliary variables e.g. air temperature, to the trajectory positions and include these in the output NetCDF file.

 

Obtaining the University of Melbourne trajectory software

The trajectory software (traj3d) is freely available from our group. It is written in Fortran 77 and should compile correctly on any platform with a suitable compiler e.g. the GNU g77 compiler. To date it has been compiled successfully on systems running Solaris, Linux and Cygwin under Microsoft Windows XP. We also provide a Linux binary version of the software which should work on many Linux systems. In addition we plan to provide a version suitable for Cygwin under Microsoft Windows XP that presumably also works with Vista.

The present version is intended for 3D wind data from the common reanalysis projects. The input data should be zonal and meridional winds (u,v) plus omega (w) on a set of pressure levels e.g. 1000, 850, 500, 200 hPa.However it may equally be used for computing 2D (single level) trajectories e.g. 500 hPa, 10 m winds. Furthermore the software will work on either a global or regional grid. The input data are expected to be in a simple binary format that we refer to as Ďconmapí (CMP). Details of this format are given in the software documentation.

We provide some additional Fortran 77 software (read_nc2cmp) to assist in converting GRIB or NetCDF data to the CMP format. The trajectory data is output in NetCDF and this may be processed further by the user or input to a suitable plotting package. We include a utility based on NCAR Graphics (kmapline) as well as an elementary plotting script for NCL. Note that the actual trajectory software does not require any graphics libraries: the only external libraries required for compilation are NetCDF (version 3+).

 

 

The software may be obtained by contacting: Ian Simmonds

 

 

 

Please indicate the platform that you intend to run the software on. We recommend the g77 compiler but the software should compile with others but we canít test these ourselves.

 

Documentation

A detailed description of the software package including compilation and examples is given in the Documentation.

Please direct any questions or report any problems to Kevin Keay.

 

 

The animation at the top of this page

 

The animation at the upper right of this page shows 3-day back trajectories arriving in Melbourne, Australia on April 20 1996 00 UTC that were computed from 3D six-hourly wind fields from the NCEP Reanalysis. The analysis is based on seven pressure levels: 1000, 925, 850, 700, 500, 300 and 200 hPa.Only the trajectories which arrive in Melbourne at the five lower levels (1000 to 500 hPa) are shown in the animation. For aesthetic reasons the two highest levels are omitted since these trajectories start outside of the map region. Note that any desired arrival level could be selected e.g. 425 hPa, not just the a member of the set of input levels.

The trajectories begin on April 17 1996 00 UTC and end on April 20 1996 00 UTC. These are computed at a one hour interval and the evolution is shown every six hours in the animation. The symbols indicate the times 00, 06, 12 and 18 UTC but the intermediate (hourly) points are also present in the plotted trajectories.Different colours correspond to the different arrival levels of the trajectories as shown in the key.

Note that each 3D trajectory is moving through different levels in the atmosphere during the journey from source to arrival location. Below is the final frame of the animation:

 

 

 

1000 hPa††††††††† 925 hPa††††††††††† 850 hPa††††††††††† 700 hPa††††††††††† 500 hPa

 

 

Click here for a larger animation (0.4 MB).

 

 

 

Copyright and Disclaimer

 

We use the parcel trajectory software that is presented here in our published research. Although every effort has been made to ensure that the software is correct we can not guarantee it is free from errors. Hence we take no responsibility for any negative consequences arising from its use by any party external to our group at the University of Melbourne.

 

The output of the trajectory software, as data files or images, may be freely used for research and publications including journals and books. It would be appreciated that you include an appropriate reference to this web site. For instance:

 

The parcel trajectory software (traj3d) was obtained from the University of Melbourne Parcel Trajectory Software web page (http://www.earthsci.unimelb.edu.au/trajectories/trajhome.htm). A discussion of the algorithm is given by Noone and Simmonds (1999) and Barras and Simmonds (2009).

Noone, D., and I. Simmonds, 1999: A three-dimensional spherical trajectory algorithm. Research Activities in Atmospheric and Oceanic Modelling, Report No. 28, WMO/TD-No. 942. H. Ritchie, Ed., World Meteorological Organization, 3.26-3.27.

Barras, V., and I. Simmonds, 2009: Observation and modeling of stable water isotopes as diagnostics of rainfall dynamics over southeastern Australia Journal of Geophysical Research, 114, D23308, doi:10.1029/2009JD012132, 2009.

 

 

 

Meteorology at the University of Melbourne

Details about our group are available here:

Meteorology Group, School of Earth Sciences, University of Melbourne

 

 

References

 

Fuelburg, H.E., R.O. Loring Jr., M.V. Watson, M.C. Sinha, K.E. Pickering, A.M. Thomson, G.W. Sachse, D.R. Blade and M.R. Schoeberl, 1996: TRACE: A trajectory intercomparison 2. Isentropic and kinematic methods. Journal of Geophysical Research, 101, 23927-23939.

 

Noone, D., and I. Simmonds, 1999: A three-dimensional spherical trajectory algorithm. Research Activities in Atmospheric and Oceanic Modelling, Report No. 28, WMO/TD-No. 942. H. Ritchie, Ed., World Meteorological Organization, 3.26-3.27.

 

Law, R.M., 1993: Modelling the global transport of atmospheric constituents. PhD thesis, School of Earth Sciences, The University of Melbourne.

 

Perrin, G. and I. Simmonds, 1995: The origins and characteristics of cold air outbreaks over Melbourne. Australian Meteorological Magazine, 44, 41-59.

 

Barras, V., and I. Simmonds, 2009: Observation and modeling of stable water isotopes as diagnostics of rainfall dynamics over southeastern Australia Journal of Geophysical Research, 114, D23308, doi:10.1029/2009JD012132, 2009.

 

 
 
 
 
 
 
 
 
 
 
 
 



 
 
 
 
 
 
 
 
 
 
 
 

Last Update: December 22 2009

Maintained by: Kevin Keay