Application of MODIS SSTs within WRF

1
Application of MODIS SSTs within WRF
Science Advisory Committee Meeting 13 June
2007 LaCasse, Splitt, Lazarus Lapenta
2
Motivation for using High-Resolution MODIS SST
Fields in NWP Models

• SST known to influence coastal mesoscale
  processes
• Can impact warm-season precipitation distribution
• Sea breeze circulations important to heavily
  populated areas (HOU, NYC)
• Strong influence on height of marine boundary
  layer

3
Differences Between RTG and MODIS SSTsAlong the
Florida East Coast
Better definition of mesoscale SST gradients
4
Experiment Design to Isolate Impacts Associated
with Altering SST

• ARPS Data Analysis System (ADAS) provides ICs for
  WRF
• ADAS uses the Bratseth assimilation scheme
• 20 km RUC used as background field for ADAS
• Measurements ingested include surface and
  upperair observations and radar radial winds
• Direct insertion of SST fields

• Weather Research and Forecasting (WRF) model used
  for simulations
• 3h Eta forecasts used for LBCs
• Dynamics and Physics
• Eulerian mass core
• Dudhia shortwave radiation
• RRTM longwave radiation
• Noah land surface model
• YSU planetary boundary layer scheme
• Explicit convection
• WSM 6-class microphysics scheme

5
May 2004 Study Period

• Methodology
• 24 h WRF-ARW simulations run daily for May 2004
• 2 km resolution 51 vertical levels
• Parallel runs using either the ½ RTG SST
  analyses or the 1 km MODIS SST composites

• Determine overall impact
• Average similar flow regimes
• Easterlies (9 - 19 May)
• Westerlies (27 - 31 May)
• Focus on the nighttime hours (5 - 11 UTC)

6
Surface Energy Budget
A positive net sensible heat flux associated with
the warmer SSTs
Increased mixing over the warmer MODIS SSTs also
led to an increase in PBL height over the Florida
Current
Sensible heat flux difference (MODIS RTG
Wm-2) 05 to 11 UTC, westerly cases
PBL height difference (MODIS RTG m) 05 to 11
UTC, westerly cases
7
Mesoscale Convergence
Enhanced regions of convergence were seen when
using the MODIS SSTs While the locations were not
exactly correct, simulations with the RTG SSTs
did not have these features
MODIS WRF simulations produced 6 more daily
accumulated precipitation (27 more along the
Florida Current) when averaged over May 2004
Visible GOES image from 1130 UTC 06 May
2004 MODIS WRF 10 m convergence (contours, every
0.5 s-1 106) valid at 1200 UTC (12 h simulation)
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Progress since last SAC Meeting

• Concluded the May 2004 study period
• Presented preliminary results at the 2006 AMS
  Annual Meeting and the June 2006 WRF Users
  Workshop
• Prepared a manuscript for Monthly Weather Review
  (revised version submitted May 2007)
• Began project with the Miami Weather Forecast
  Office (WFO)
• SPoRT has run a parallel version of Miamis
  operational Weather Research and Forecasting
  (WRF) prediction system forecasts since
  mid-February 2007