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THE NCEP ETA DATA ASSIMILATION SYSTEM (EDAS) : AN OVERVIEW

THE NCEP ETA DATA ASSIMILATION SYSTEM (EDAS) : AN OVERVIEW. COMET Faculty Course on Numerical Weather Prediction. 10 June 1999. Presented by Eric Rogers. OUTLINE. Philosophy. General Description / History. Current Operational 32-km EDAS. - Impact of 3DVAR analysis and cycled

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THE NCEP ETA DATA ASSIMILATION SYSTEM (EDAS) : AN OVERVIEW

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  1. THE NCEP ETA DATA ASSIMILATION SYSTEM (EDAS) : AN OVERVIEW COMET Faculty Course on Numerical Weather Prediction 10 June 1999 Presented by Eric Rogers

  2. OUTLINE • Philosophy • General Description / History • Current Operational 32-km EDAS - Impact of 3DVAR analysis and cycled EDAS - Observations - Recent Performance : The Good, the Bad, and the Ugly • Future Plans

  3. GOAL : PRODUCE BEST POSSIBLE INITIAL CONDITIONS FOR ETA MODEL FORECAST* • KEY COMPONENTS - State of the art analysis (variational) - Consistency between assimilating and forecast model (resolution, physics, dynamics) - Intelligent selection and use of observations * NOT necessarily the same as fitting all the observations exactly (more to come on this)

  4. EDAS : PAST CONFIGURATION MILESTONES • June 1993 : Eta-80 (Early Eta) replaces LFM; initialized with single Eta Optimum Interpolation (OI) analysis at 00/12Z using GDAS first guess • March 1995 : Eta-29 (Meso Eta) ; 3-h EDAS with OI analysis used as first guess for 03/15Z forecasts • October 1995 : Eta-48 replaces Eta-80 in Early Eta slot, initialized by a 12-h intermittent EDAS cycle with 3-h OI analysis updates

  5. EDAS Original Configuration : Eta-48 forecast 00Z/12Z, Eta-29 forecast from 03Z/15Z

  6. 48KM EDAS : PROBLEMS AND CONCERNS • Forecasters wanted higher resolution run earlier • Starting the EDAS using a GDAS first guess still caused inconsistencies (e.g., soil moisture) • Eta OI analysis not easily adaptable for use of non-traditional data sets (satellite radiances, NEXRAD radial velocity) • Eta OI analyses heights, not temperatures, so it can’t use aircraft mass information

  7. Eta-48 Surface Meteogram at Riyadh, Saudi Arabia from 12Z 6/25/97 Solid = Observations Dashed = Forecast 2-m T 2-m Td 12Z 6/25 00Z 6/26 12Z 00Z 6/27 12Z • Ran operational EDAS/Eta-48 system over Saudi Arabia • - Forecast surface temperature 4-10oC too cold • - 00-h analysis Td = 19oC, observed Td = -6oC!

  8. SOLUTION : ETA-32 UPGRADE • Stage 1 : Implemented 9 February 1998* - Resolution of 00Z/12Z EDAS and Early Eta changed from 48km/38levs to 32km/45levs - Eta OI analysis replaced by Eta 3-d variational analysis (3DVAR) - “Partially” cycled EDAS : Basic atmospheric variables (T,q,u,v,sfc p) at the start of the 12-h EDAS obtained from GDAS; soil moisture / temperature, cloud water, turbulent kinetic energy from the previous EDAS cycle - Meso Eta-29 unchanged * http://www.nws.noaa.gov/om/tpb/447.htm

  9. ETA 3DVAR ANALYSIS (Parrish et.al 1996 NWP Preprint Volume) • Loosely patterned after NCEP global SSI analysis • Analysis variables: - Stream function - Temperature - Potential function - Specific humidity - Surface pressure - Geopotential height • More adaptable for use of new data types than OI (e.g., NEXRAD radial velocities used in Eta-10 runs during 1996 Olympics)

  10. 3DVAR vs. OI : 00Z/12Z First Guess Temperature vs RAOBS

  11. 3DVAR vs. OI : 00Z/12Z first guess vector wind RMS vs. RAOBS

  12. 3DVAR vs. OI

  13. WHY DO CYCLING? • Initial conditions more consistent with forecast model • Less spinup of divergence, cloud, precipitation, and TKE • More accurate representation of soil moisture

  14. IMPACT OF CYCLING ON SOIL MOISTURE 48km EDAS : 12-h cycle 32km EDAS : 3 week cycle

  15. 48-h Eta forecast 2-m temperature - sfc T obs : Model shows no disquieting drift from cycled EDAS Bias (deg C)

  16. ETA-32 UPGRADE • Stage 2 : Implemented 3 June 1998 - EDAS converted to “full” cycling mode with atmospheric variables cycled from the previous EDAS as well as soil/cloud/TKE - Meso Eta-29 converted to 32km 1) 03Z Eta-29 ----> 03Z Eta-32 (33-h fcst) 2) 15Z Eta-29 ----> 18Z Eta-32 (30-h fcst) 3) Both off-time runs connected to fully cycled EDAS - Robust backup system in place to ensure that EDAS soil moisture is never reinitialized from the GDAS

  17. DATA DUMP TIMES EDAS Early Eta

  18. OBSERVATIONS USED BY ETA 3DVAR • Upper air data - Rawinsonde height/temperature/wind/moisture - Dropwindsondes - Wind Profilers - NESDIS thickness retrievals from polar orbiting satellites (oceans only) - VAD winds from NEXRAD - Aircraft (conventional and ACARS) winds/temps - Satellite cloud drift winds - SSM/I and GOES precipitable water retrievals - Synthetic tropical cyclone data • Surface data - Surface land wind/temperature/moisture - Ships and buoys - SSM/I oceanic surface winds

  19. DATA QUALITY CONTROL • CQC: Complex QC of raob height/temps (baseline, hydrostatic, lapse rate, radiation correction, etc.) • ACQC : Quality control of conventional aircraft data (remove duplicates, track checks, create “superobs”) • SDMEDIT : NCEP Senior Duty Meteorologist can flag all or parts of suspect raobs • 3DVAR : Analysis performs gross check vs. first guess: - Temperature : +/- 15oC - Wind :+/- 25 ms-1 - RH : +/- 90% - Precipitable water : +/- 12 g/kg - Height : +/- 100 m

  20. Use of Surface Data: Eta OI vs. Eta 3DVAR Eta OI Analysis Eta 3DVAR Analysis

  21. RECENT ETA/EDAS PERFORMANCE • Original 3DVAR in Eta-32 : degraded surface analysis (especially moisture)

  22. EXAMPLE : 00Z 7/13/98 at Rapid City, SD Solid = RAOB Dashed = 80 km OPNL 3DVAR 5oC analysis error in Td at 850 mb ! Problems : 1) 3DVAR tuned to give too much weight to first guess; 2) code error excluded all surface data! Solid = RAOB Dashed = 80 km Modified 3DVAR

  23. New 3DVAR tested in July 1998 and showed improved fit to surface and raobs (especially moisture) • Re-tuned 3DVAR implemented on 3 November 1998 • We thought everything was OK….. BUT……..

  24. 24-H ACCUMULATED PRECIPITATION EQUITABLE THREAT SCORES: ALL FCSTS Solid = Eta Short Dash = NGM Long Dash = AVN/MRF 12/1/97 - 2/28/98 12/1/98 - 2/28/99 10-15% drop in Eta skill between 1997-98 and 1998-99

  25. Persistent synoptic error in Eta-32 during winter of 98-99: weaker and faster Eastern Pacific troughs/cyclones than observed Example : 48-h Forecasts valid 1200 UTC 17 March 1999

  26. AVN had much better SLP forecast then Eta :

  27. PROBLEM 1: November 98 change degraded mass/wind balance in 3DVAR • If mass / wind balance well-behaved, positive height correction is coincident with center of anticyclonic wind correction 850 mb ANL-GUESS height/wind 80KM EDAS valid 00Z 3/15/99 • Note 10 degree longitude displacement between centers of wind and height correction • Problem is most severe in regions and at analysis times without widespread raob data but with large amounts of wind or mass only data (e.g., satellite winds)

  28. SOLUTION : Improve geostrophic coupling of mass/wind analysis corrections in 3DVAR Operational 3DVAR analysis Modified 3DVAR analysis Note: Improved height/wind coupling near Aleutians

  29. PROBLEM 2: Horizontal/vertical correlations too narrow : observation had VERY limited impact on analysis away from its level • One observation test : Insert one height observation 10 m greater than first guess at 200, 500, 900 mb and measure impact in horizontal/vertical

  30. Operational 32-km 3DVAR Modified 32-km 3DVAR 200 mb 900 mb

  31. Performance of new 3DVAR : 3 December 1998 to 16 January 1999 test at 80 km resolution 24-h accumulated precipitation threat scores: All forecasts Dashed = Modified 3DVAR Solid = Operational 3DVAR Equitable Threat Score Threshold (in)

  32. 00,24,48-h forecast vector RMS wind error vs RAOBS Dashed = Modified 3DVAR Solid = Operational 3DVAR 48-h 24-h Vector RMS error (m/s) 00-h Pressure (mb) NOTE = 200 mb 24-h modified 3DVAR error = 00-h error in operational 3DVAR!

  33. NEW 3DVAR IMPLEMENTED 13 MAY 1999* : IMPACT 200 mb Vector Wind RMS error vs RAOBS : 3/1/99-5/31/99 Blue = 48-h Eta-32 fcst Purple = 48-h AVN fcst Old 3DVAR New 3DVAR RMS Vector Wind Error (m/s) Rogers on leave; software breaks * Further documentation at http://www.nws.noaa.gov/om/tpb/3d-eta.htm

  34. FUTURE EDAS DEVELOPMENT • 0-6 months (Day 1 on IBM) - Move 03Z Eta to 06Z; run 12-h EDAS for 00/12Z cycle; 06-h EDAS for 06/18Z cycle - Use of GOES/TOVS radiances in Eta 3DVAR • 6-12 months - Increase resolution to 22km/50levs - Assimilation of observed precipitation (Lin et.al, 1998 NWP Conference, 1999 Mesoscale Conference) • 12-18 Months - Initialization of cloud water (Zhao et.al 1998 NWP Conference) - Use of NEXRAD radial velocity and surface mesonet data in Eta 3DVAR; switch from 3-h to 1-h analysis cycle in EDAS

  35. Impact of precip assimilation on Eta-80 24-h forecast valid 12Z 7/5/98 Control forecast Forecast w/precip assimilation 24-h observed precip (RFC analysis)

  36. Rainfall Data Assimilation (Lin et.al, 1998 NWP Conference, Phoenix, AZ) • During the 12h pre-forecast assimilation period at each timestep compare the model predicted rainfall to observed • Adjust the model’s latent heating profile accordingly (Carr and Baldwin, 1991)

  37. Cloud Data Assimilation(Zhao et al, 1998, 12th NWP, Phoenix, AZ) • Data sources • real-time Neph Analyses (USAFGWC) • hourly radar/gauge observations

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