ECMWF Trajectories

5 day back trajectories have been computed on a routine basis using analyses from the European Centre for Medium Range Weather Forecasting (ECMWF). Three sets of back trajectories are available:

1. 252 back trajectories which are launched at 900 mb from points on three regular latitude / longitude grids centred over the UK., the mid-Atlantic storm track region and the eastern U.S.A. The dataset runs from 1979 to February 1999. The back trajectories were launched at 12.00. In addition during 1996 and 1997, as part of the ACSOE campaign, the 12.00 releases were supplimented by releases at 00.00, 06.00, and 18.00.
2. Clusters of back trajectories launched from pre-defined instrument sites in the UK - Weybourne (52.95°N, 1.13°E), Great Dunn Fell (54.68°N, 357.55°E), Bush Estate (55.50°N, 356.80°E), Aberystwyth (52.42°N, 356.00°E) Mace Head (53.32°N, 350.10°E) and in the Irish Sea west of Mace Head (53.00°N, 346.00°E). These trajectories are launched 4 times per day from 4 different pressure levels (700, 850, 950 and 1000 mb). The dataset covers the period of the ACSOE campaign (1995-1997).
3. Global back trajectories on a 20 by 36 lat-long grid - the grid is not regular in latitude. This grid is repeated on 9 pressure levels (approx 950, 850, 750, 650, 550, 450, 350, 250, 150 and 50 mb). This dataset covers the period 1997 - February 1999.

The trajectories are calculated at ECMWF using 6 hourly T106 operational analyses of the three components of the wind and surface pressure which are interpolated on to a 1.5° x 1.5° grid. The data are linearly interpolated in time and space. The output data consist of latitude, longitude and pressure of the trajectory every 30 minutes.

Sample plots of the daily trajectories for 1996 are available in GIF form through the World Wide Web interface to provide an overview of the trajectories.

These data are for bona fide research purposes only and access is therefore restricted. For this reason, we do not make the data available to anonymous users through these WWW pages. Additionally, access to data is provided on a per person per project basis (i.e. all members on a same project who will be using the data must individually apply for access to the data).

In order to gain access to the data, please apply for access to the ECMWF Trajectory data. The application includes the Met Office Agreement to be completed online. Subject to eligibility you will then be given access to the data and will be sent a confirmation email.

The data files are held in compressed ASCII form (gzip). Help files are provided to assist in accessing and reading the files. Sample third party software is also available to extract selected trajectories from the files and to plot them using IDL.

A help file is available describing in more detail the method of computation and details of the various changes in methods that have been introduced at certain times. Documentation on the file format is also provided.

The BADC also holds these relevant ECMWF datasets:

• ECMWF Operational data
• ECMWF ERA-15 Re-analyses
• ECMWF ERA-40 Re-analyses and
• ECMWF ERA Interim

Berrisford P, ECMWF Trajectories, [Internet]. NCAS British Atmospheric Data Centre. 2006-, Date of citation. Available from http://badc.nerc.ac.uk/view/badc.nerc.ac.uk__ATOM__dataent_ECMWF-TRJ.

For general queries about these pages or about browsing the data, you should contact the BADC support line. For further information on these trajectories and how they have been calculated, contact Dr. Paul Berrisford at Reading University or the PI Prof. Brian Hoskins.