(BRAVO) Study: Final Report. - Desert Research Institute
(BRAVO) Study: Final Report. - Desert Research Institute
(BRAVO) Study: Final Report. - Desert Research Institute
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
<strong>Final</strong> <strong>Report</strong> — September 2004<br />
of trajectories in HYSPLIT during time periods when there is significant directional wind<br />
shear with height. Trajectories produced by the Monte Carlo model can also be somewhat<br />
sensitive to height if a particle moves from within the mixed layer to above. Average<br />
differences caused by occasional bumping of a trajectory from one grid cell and/or horizontal<br />
layer to a neighboring one will be minimized as more trajectories are aggregated. Thus,<br />
longer analysis periods, more start heights and times are all desirable. Both HYSPLIT and<br />
the Monte Carlo model allow trajectories to get as high as 10 km. Due to its different design,<br />
ATAD does not have trajectories above the mixed layer, with a maximum of 3 km.<br />
9.2.3 Effect of Back Trajectory Start Height<br />
Figure 9-6 illustrates the effect of start height (i.e., the chosen trajectory height at Big<br />
Bend), which affects the mean trajectory height and hence the mean trajectory speed and<br />
trajectory direction, for back trajectories in HYSPLIT. The higher speeds typically<br />
associated with greater heights will tend to implicate more distant source areas, while lower<br />
speeds and heights give more weight to nearer sources, but this generalization may not<br />
always hold. For example, on July 15 th (the left panel of Figure 9-6), trajectories group<br />
according to start height. Back trajectories from 10, 100, and 200 m all follow the same<br />
general path into the Gulf of Mexico, with the effect of increasing wind speed with height<br />
reflected in the trajectory lengths. Trajectories from 500 and 1000 m are farther south and<br />
pass over the Yucatan Peninsula. The 200-m trajectory starts out like the lowest trajectories<br />
but has a completely different looping path in the last 30 hours. On September 20 th (the right<br />
panel), on the other hand, the low altitude back trajectories all follow the same path to the<br />
Jul. 15, 1999 hr 18 (JD 196)<br />
Sep. 20, 1999 hr 6 (JD 263)<br />
HYSPLIT-EDAS<br />
Orange = 2000m<br />
Green = 1000m<br />
Cyan = 500m<br />
Blue = 200m<br />
Magenta = 100m<br />
Red = 10m<br />
HYSPLIT-EDAS<br />
Orange = 2000m<br />
Green = 1000m<br />
Cyan = 500m<br />
Blue = 200m<br />
Magenta = 100m<br />
Red = 10m<br />
Height(Km)<br />
0 2 4 6 810<br />
0 20 40 60 80 100 120<br />
Hours<br />
Height(Km)<br />
0 2 4 6 8 10<br />
0 20 40 60 80 100 120<br />
Hours<br />
Figure 9-6. Examples of the effect of start height on the trajectories produced by the<br />
HYSPLIT model with the EDAS wind field.<br />
9-16
Change language