Title: R. L. Buckley, A. Dupont, R. J. Kurzeja, and M. J. Parker
1R. L. Buckley, A. Dupont, R. J. Kurzeja, and M.
J. Parker Atmospheric Technologies Group Savannah
River National Laboratory Palmetto American
Meteorological Society Mini-Technical Meeting, 03
April 2009
2- Background
- Daily weather forecasts provided for worker
safety - Prescribed fires conducted at the Savannah River
Site (SRS) on routine basis to reduce potential
fire hazards - Fire-weather forecasts are part of daily forecast
package - Mixing depth is an important factor in
determining altitude and dilution of smoke plumes -
3- Description of Work
- This work examines trends in average maximum
mixing depths at SRS for 5 years using mesoscale
model (RAMS) - Compare results between two versions of the model
and examine seasonal trends - Compare simulations with specific days in which
special balloon soundings were released -
4 Standard Regional Simulations
- Horizontal grid spacing 20 km. Lowest level above
ground (25 m AGL). - Initialize model with ETA (NAM) and nudge to
lateral BCs every 3 hours - Simulate 48 hours (keeping final 36 hours),
updating twice per day - Basis for fire weather forecasts
5Standard Meteorogram Forecast Product
6- Assumptions to Determine Trends
- Use potential temperature gradient derivation
- Limit to earliest 12-hr daylight period (i.e. 12Z
to 00Z ? starting 07 or 08 LST) - Discard periods when RAMS did not run properly,
or when windy and overcast or foggy conditions
were predicted - Average maximums determined monthly
- Time period considered (Jan. 2003Sep. 2007)
7Results
(Over 1700 simulations considered in each line
depicted).
8- Comments on Mixing Depth Trends
- Mixing depths for RAMS43 greater than RAMS3a
- RAMS43 tends to predict higher surface
temperature daily maximums - Surface parameterization differences
- Maximum averages lower in 2003 than later years
- SRS measurements support this trend
9Observed Quantities Averaged over Summer (May-Sep)
P Total Precipitation S Incoming solar
radiation (average every 15-min from 12 to 00
UTC) T Temperature (average every 15-min from 12
to 00 UTC) HS3 Number of 15-min periods with
heat stress category 3
10- Comparison with Specific Observed Soundings
- 50 SRS balloon-borne soundings released from
20032007 - Simulated mixing depth within 20 of observed
mixing depth roughly 40 of all times - Better agreement with RAMS43 than RAMS3a
- Difficulties seen in estimating mixing depth
during mid- morning (transition)
11Sample Comparison (20-Apr-2007,
RAMS43-vs-Observation)
Obs RED Sim 00Z Blue Sim 12Z Green 00Z better
than 12Z (shorter forecast lead time)
12- Conclusions
- Simulated mixing depths calculated for 5 year
period. Daily maximums recorded using two
versions of RAMS. - Monthly averages indicate expected seasonal
trends. Lower summer maxima predicted in 2003
agree with SRS observations of temperature,
precipitation, solar radiation, and heat stress. - RAMS43 mixing depths tend to be higher than
RAMS3a mixing depths due to higher surface
temperature predictions from differences in
surface parameterizations. - Comparison with 50 balloon-borne soundings
released over SRS indicate better overall
agreement with RAMS43 simulations.