The ETA Forecast Trajectory Model was used to produce forecasts of air-parcel trajectories twice a day at three pressure levels over seven sites in Southern Africa for the period August 14, 2000 to September 23, 2000. These sites are Durban, Middleburg, Pietersburg, and Springbok, South Africa; Maun, Botswana; Mongu, Zambia; and Windhoek, Namibia.
The twice daily three-dimensional wind field (at 0000 and 1200 UTC) was used as input to the trajectory model. By integrating the vertical motion of the air parcels over a period of time, the trajectory model was able to forecast the net vertical displacement of air parcels during 12-hour periods.
The resulting trajectory plots represent the three-dimensional transport of air in time and can be used to examine what is happening in the low-to-mid troposphere during flight and ground-based observations. These levels are most significant in terms of the thermodynamic structure of the troposphere, especially the stable layers and accumulation of material between and below them, as well containing the major levels of subsidence over the subcontinent. The trajectory model output and thermodynamic profiles of the troposphere were used to position aircraft for sampling trace gases, aerosols and other species during the SAFARI 2000 field campaign and to predict regions of high aerosol and trace gas concentrations downwind.
The model output data are daily forward and backward trajectory plots at 850 hPa, 700 hPa, and 500 hPa pressure levels for each location. The plots are provided as JPEG images with coordinate, date, and time stamps.
Cite this data set as follows:
Freiman, T. 2005. SAFARI 2000 Modeled Tropospheric Air Mass Trajectories, Dry Season 2000. Data set. Available on-line [http://daac.ornl.gov/] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A. doi:10.3334/ORNLDAAC/792.
Freiman, M. T., M. R. Jury, and S. Medcalf. 2002. The state of the atmosphere over South Africa during the Southern African Regional Science Initiative (SAFARI 2000). South African Journal of Science, 98: 91-98.
Jury, M. R. and Freiman, M. T. 2002. The climate of tropical Southern Africa during the SAFARI 2000 campaign. South African Journal of Science, 98: 527-540.
South African Weather Service (SAWS). 2004. SAFARI 2000 ETA Atmospheric Model Data, Wet and Dry Seasons 2000. Data set. Available on-line [http://daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A.
The data files are stored as JPEG images, one file per plot, pressure level, and date, with a header displaying pressure level, coordinates, date, and time stamp on the top of each plot. The file naming convention is OUTx_nnn_yymmdd12_Loc#_xrrr.jpg,
|where:||OUTx indicates whether the output is a forward (x=f) or backward (x=b) trajectory,|
|nnn is the pressure level (i.e., 850 hPa, 700 hPa, or 500 hPa),|
|yy are the last two digits of the year of data collection,|
|mm and dd are the month and day of data collection,|
|Loc# indicates the location of data collection (see table below), and|
|xrrr is a file identifier code where x indicates whether the output is a forward (x=f) or backward (x=b) trajectory and rrr is an alphanumeric.|
The JPEG images are organized and zipped and available for downloading by both date and location.
In addition, companion files include a template of each site that illustrates how to read the plots, a composite map of the spatial coverage of all the sites used, and a synoptic analysis of daily meteorological conditions at midday at the three pressure levels for three latitudinal zones (10 to 20 degrees South; 20 to 30 degrees South; and 30 degrees South and southwards) that is provided as a .csv file
The following sites were used to run forward and backward trajectories:
Sites Country Coordinates Plot Number Location Number Pietersburg South Africa 29.5 E, -23.9 S Plot 1 Loc 1 Mongu Zambia 23.2 E, -15.3 S Plot 2 Loc 2 Maun Botswana 23.4 E, -20.0 S Plot 3 Loc 3 Windhoek Namibia 17.1 E, -22.6 S Plot 4 Loc 4 Springbok South Africa 17.8 E, -29.7 S Plot 5 Loc 5 Middleburg South Africa 29.3 E, -25.8 S Plot 8 Loc 8 Durban South Africa 31.0 E, -30.0 S Plot 9 Loc 9
Additional information about the ETA Model, site locations, and trajectory plots is found in the companion file: ftp://daac.ornl.gov/data/safari2k/climate_meteorology/trajectory_images/comp/trajectory_images_readme.pdf.