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BRAVO Back-Trajectory Analyses. BRAVO Meeting, San Antonio, TX, 23 March 2001. Why Consider ATAD? History of use at Big Bend - How Good is our past? History of comparison to other wind fields. ATAD vs Hysplit with EDAS & FNL Wind Fields

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BRAVO Back-Trajectory Analyses

BRAVO Meeting, San Antonio, TX, 23 March 2001

Why Consider ATAD?

History of use at Big Bend - How Good is our past?

History of comparison to other wind fields.

ATAD vs Hysplit with EDAS & FNL Wind Fields

How different are they and why

Results of preliminary qualitative back-trajectory analyses.


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How are ATAD and Hysplit Different?

1. Input data

Raw sounding data for ATAD

Modeled EDAS or FNL wind fields for Hysplit

2. Length of time data is obtainable

1946 - present for ATAD

1997 - present for Hysplit

3. Model methodology

Average wind in a transport layer and radius for ATAD

“Data following” for Hysplit (other options also)

4. Frequency of Output

4 starts/day, endpoints 8 times/day for ATAD, 5 day max length

hourly starts, hourly endpoints for Hysplit, max length > 10 days


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ATAD Methodology

from Heffter, 1980


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EDAS Meteorological Data Archive

The EDAS (Eta Data Assimilation System) data are a product of the NWS' National Centers for Environmental Prediction (NCEP). EDAS is a data assimilation system consisting of successive 3-h Eta model forecasts and Optimum Interpolation (OI) analyses.

  • 79 by 55 Lambert Conformal grid ~ 80 km resolution.

  • 22 vertical layers on constant pressure surfaces from 1000 to 50 mbar

  • 3 hour time increment

  • Upper Air Data: 3-D winds, Temp, RH

  • Surface Data includes: pressure, 10 meter winds, 2 meter Temp & RH, Momentum and heat flux

  • Data is available from 1/97 to present. Note Oct. 1999 data is unavailable due to a fire at NCEP


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FNL Meteorological Data Archive

The FNL data is a product of the Global Data Assimilation System (GDAS), which uses the Global spectral Medium Range Forecast model (MRF) to assimilate multiple sources of measured data and forecast meteorology.

  • 129 x 129 Polar Stereographic Grid with ~ 190 km resolution.

  • 12 vertical layers on constant pressure surfaces from 1000 to 50 mbar

  • 6 hour time increment

  • Upper Air Data: 3-D winds, Temp, RH

  • Surface Data includes: pressure, 10 meter winds, 2 meter Temp & RH, Momentum and heat flux

  • Data is available from 1/97 to present.


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ATAD vs Hysplit…How Different Can They Be?

Well, at times, pretty different!



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A common pattern in July & Aug...

Atad most southerly, EDAS most easterly with FNL in between.

7/18-7/28, first few days in August, and end of August





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Overall Residence Time & FNL (See 2000 m)

June - September, 1999

ATAD, EDAS, FNL


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2 Wind Fields and & FNL (See 2000 m)

2 Heights


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Correlations between Overall Residence Times 3-Day Trajectories June-Sep 1999

atad EDAS2000 EDAS1000 EDAS100 EDAS10 FNL2000 FNL1000 FNL100 FNL10

atad 1.000 0.732 0.769 0.648 0.662 0.790 0.806 0.653 0.644

EDAS2000 0.732 1.000 0.878 0.753 0.787 0.962 0.811 0.714 0.730

EDAS1000 0.769 0.878 1.000 0.942 0.945 0.903 0.956 0.933 0.927

EDAS100 0.648 0.753 0.942 1.000 0.994 0.780 0.870 0.973 0.986

EDAS10 0.662 0.787 0.945 0.994 1.000 0.812 0.867 0.955 0.977

FNL2000 0.790 0.962 0.903 0.780 0.812 1.000 0.860 0.751 0.762

FNL1000 0.806 0.811 0.956 0.870 0.867 0.860 1.000 0.893 0.866

FNL100 0.653 0.714 0.933 0.973 0.955 0.751 0.893 1.000 0.989

FNL10 0.644 0.730 0.927 0.986 0.977 0.762 0.866 0.989 1.000


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Average Differences Trajectories June-Sep 1999Closest Comparison to Atad: FNL 1000m


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EDAS vs FNL 1000m Trajectories June-Sep 1999


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EDAS at 2 Heights Trajectories June-Sep 1999


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Which is “Right”? Why? Does it Matter? Trajectories June-Sep 1999

1. Transport heights matter. ATAD “transport layer” vs Hysplit vertical wind speed driven transport height. To do “standard” residence time analyses with Hysplit may require 3-D analysis.

2. Tracer concentrations should help on days with large differences.

3. MM5 Winds should help.

4. Qualitative results for some residence-time-type analyses suggest similar results no matter which is used.


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Maybe Not Real Trajectories June-Sep 1999


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TX/MX Border Trajectories June-Sep 1999

Maybe Not Real

E. Texas

TX/MX Border with ATAD saying Mexico


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Example of “TX/MX Border” Trajectories Trajectories June-Sep 1999


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Example of “East Texas” Trajectories Trajectories June-Sep 1999



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High Concentration Source Contribution Function for CSU Sulfate Ion, July-Oct,

ATAD, EDAS & FNL started at 1000 m.



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What’s Next? Sulfate Ion, July-Oct,

1. To use Hysplit in the “usual” ATAD residence time-type analyses requires some consideration of trajectory height. 3-D residence time?

2. If ATAD’s directions are wrong, choices…..

Modify ATAD to use EDAS and/or FNL winds

Switch to Hysplit with some height consideration.

Abandon ATAD in favor of Monte Carlo model

3. Further analyses of BRAVO data, measured sfc & upper air winds, tracer, MM5 winds, spatial patterns in chem data should all help in deciding which model to use and why.

4. Continue with analyses of other species and other types of trajectory-based analyses.