Geoscience Reference
In-Depth Information
nudging and the TCOON (Texas Coastal Ocean Observation Network) data
for observation-based nudging along the coast. The MM5 model consists of
28 half-sigma levels in the vertical. Details regarding the meteorological
model simulations have been presented in the report by Emery
et al.
15
3. Methods
The base case modeling simulations for the September ozone episodic
period were evaluated using statistical metrics prescribed by USEPA,
1
for the daily 8-h averaged and the maximum 8-h ozone concentrations.
A series of additional sensitivity simulations were performed in which the
surface and upper air temperatures were perturbed from 1
◦
Cto6
◦
Cin
accordance with the anticipated global temperature changes as predicted
in the IPCC report by Meehl
et al.
2
The perturbations were applied over the
entire nested modeling domain while maintaining the other meteorological
variables constant. This analysis was conducted for the future case with the
high ozone episode days of 16-19 September 1999 after allowing for a spin-
up of 3 days. Only data from the surface grid cells of the 4 km modeling
domain covering the South Texas region was used in the analysis. The
main metrics used for comparison in the study include spatial variations of
differences of 8-h ozone maxima, the 8-h ozone exceedances, the number of
8-h ozone exceedances, and the number of surface grid cells exceeding the
average 8-h ozone standard in these regions.
4. Results and Discussion
4.1
. Base case model evaluation
The model evaluation for the base case model run was undertaken using
USEPA
1
statistical criteria. It was found that all the performance metrics
were within the limits set by the EPA performance criteria. Further
details of model evaluation and validation can be obtained from the
model evaluation report by ENVIRON.
16
The model does underpredict
ozone concentrations at an observational site in the coastal region of
Corpus Christi but on the days of highest ozone concentrations it performs
relatively well as shown in Fig. 2. The model behaves satisfactorily in
the inland areas of San Antonio and Austin, and it meets the EPA-
prescribed performance metrics. The future case modeling simulations were
accomplished after base case validation to test the impact of emission
control strategies.
