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SAS: NCAR ACD FLEXPART Backtrajectories (Ground Sites)


This dataset contains output of FLEXPART, a Lagrangian Particle Dispersion Model (LPDM) for the time period 1 June to 14 July 2013. It provides information on the history of air sampled at the ground sites by releasing "particles" (infinitesimally small parcels of air) from the field site location and following its path backwards in time. Advection, turbulence and convection are the processes considered. A particle itself is "inert", processes like deposition, emission or chemical conversion are not considered. Thereby the result could be called "airmass history", as the particles behave like air. Its location back in time and space since released is called "backtrajectory". The chaotic nature of the atmosphere and uncertainties in model estimates of wind vector, turbulence and convection requires a statistical approach to estimate all probable backtrajectories. Hence not only one, but a large number of particles (1e5 - 1e6) are released over a short time period (1 hr) and followed back in time. While the exact trajectory for each particle is used internally, the main model result is the number of particles and the time they spent within a 3D latitude / longitude / altitude grid, called a "sensitivity" or "residence time" field. This is calculated at discrete intervals (every hour) in time since release. These fields are the raw output of the model calculations. For ease of use, deterministic backtrajectories as mass weighted mean of the plume at each hour, and 5 plume cluster centroids (Stohl et al., Atm. Env., 2002) are calculated as well. The dataset consists of three types of data: png - overview plot, icartt - trajectories as text, nc - raw (and most accurate) model output. The data were collected from 5 sites:

CTR - Centreville, AL, SEARCH site at -87.2499, 32.9039
AABC - Alabama Aquatic Biodiversity Center (tower) at -87.2490, 32.6942
Lookrock - Look rock, TN, at -83.9416, 35.6334
RTP - Research Triangle Park, NC, at -78.8791, 35.8880
BHM - Birmingham, AL, at -86.8147, 33.5530

Note that the NetCDF portion of this dataset was updated on 31 July 2014. Please make sure to properly acknowledge this dataset in publications or presentations, or consider offering co-authorship if you deem it to be a substantial contribution to your work.

Data access

  • ORDER data for delivery by FTP

Additional information

Data Quality final
  • 1.0 (2013-10-29)
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Related projects
Spatial Type grid
Frequency hourly
Language English
Related links

Temporal coverage

Begin datetime 2013-06-01 00:00:00
End datetime 2013-07-14 23:59:59

Spatial coverage

Map data from IBCSO, IBCAO, and Global Topography.

Maximum (North) Latitude: 45.00, Minimum (South) Latitude: 24.00
Minimum (West) Longitude: -105.00, Maximum (East) Longitude: -72.00

Primary point of contact information

EOL Data Support <>

Additional contact information


Knote, C. 2013. SAS: NCAR ACD FLEXPART Backtrajectories. Version 1.0. UCAR/NCAR - Earth Observing Laboratory. Accessed 28 May 2024.

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