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 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.
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
from Heffter, 1980
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.
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.
Well, at times, pretty different!
Atad most southerly, EDAS most easterly with FNL in between.
7/18-7/28, first few days in August, and end of August
June - September, 1999
ATAD, EDAS, FNL
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
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.
Maybe Not Real
TX/MX Border with ATAD saying Mexico
High Concentration Source Contribution Function for CSU Sulfate Ion, July-Oct,
ATAD, EDAS & FNL started at 1000 m.
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.