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Application of MODIS SSTs within WRF

This document discusses the application of high-resolution MODIS SST fields in NWP models, focusing on the influence on coastal mesoscale processes and warm-season precipitation distribution. The differences between RTG and MODIS SSTs along the Florida East Coast are examined, and an experiment design is proposed to isolate impacts associated with altering SST. The study period of May 2004 is analyzed to determine the overall impact on surface energy budget, PBL height, mesoscale convergence, and daily accumulated precipitation. The progress made since the last SAC meeting is also highlighted.

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Application of MODIS SSTs within WRF

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  1. Application of MODIS SSTs within WRF Science Advisory Committee Meeting 13 June 2007 LaCasse, Splitt, Lazarus & Lapenta

  2. cool warm 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 • 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 • 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

  5. SST Difference (MODIS – RTG; K) 14 May 2004 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. observed cumulus convergence zones 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)

  8. 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 Miami’s operational Weather Research and Forecasting (WRF) prediction system forecasts since mid-February 2007

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