R. L. Buckley, A. Dupont, R. J. Kurzeja, and M. J. Parker

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R. 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
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• 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

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• 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

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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

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Standard Meteorogram Forecast Product
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• 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)

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Results
(Over 1700 simulations considered in each line
depicted).
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• 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

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Observed 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
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• 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)

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Sample Comparison (20-Apr-2007,
RAMS43-vs-Observation)
Obs RED Sim 00Z Blue Sim 12Z Green 00Z better
than 12Z (shorter forecast lead time)
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• 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.