BRAVO Back-Trajectory Analyses

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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 gt 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 HysplitHow Different Can They Be?
Well, at times, pretty different!
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And at Other TimesQuite Similar
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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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Height Differences Between EDAS FNL can be
large - even on order of Km
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Directional Differences Between EDAS FNL can be
large (See 1000m traj.)
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Even When Heights match, Directions can Differ
Between EDAS FNL (See 2000 m)
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Overall Residence Time June - September,
1999 ATAD, EDAS, FNL
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2 Wind Fields and 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 DifferencesClosest Comparison to Atad
FNL 1000m
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EDAS vs FNL 1000m
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EDAS at 2 Heights
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Which is Right? Why? Does it Matter?
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
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TX/MX Border
Maybe Not Real
E. Texas
TX/MX Border with ATAD saying Mexico
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Example of TX/MX Border Trajectories
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Example of East Texas Trajectories
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Example of ATAD saying Mexico while Hysplit is
along the border.
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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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High Concentration Conditional Probability
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Whats Next?
1. To use Hysplit in the usual ATAD residence
time-type analyses requires some consideration of
trajectory height. 3-D residence time? 2. If
ATADs 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.