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

COMET Faculty Course on Numerical Weather Prediction

10 June 1999

Presented by Eric Rogers

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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

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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)

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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

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

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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

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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!

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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 atmosphericvariables (T,q,u,v,sfc p) at the start of the 12-hEDAS obtained from GDAS; soil moisture /temperature, cloud water, turbulent kinetic energy from the previous EDAS cycle

* http://www.nws.noaa.gov/om/tpb/447.htm

- Meso Eta-29 unchanged

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ETA 3DVAR ANALYSIS (Parrish et.al1996 NWP Preprint Volume)

• Loosely patterned after NCEP global SSI analysis

• Analysis variables: - Stream function- Potential function

- Temperature- 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)

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

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

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3DVAR vs. OI

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WHY DO CYCLING?

• Initial conditions more consistent with forecast model

• Less spinup of divergence, cloud, precipitation, and TKE

• More accurate representation of soil moisture

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IMPACT OF CYCLING ON SOIL MOISTURE

48km EDAS : 12-h cycle 32km EDAS : 3 week cycle

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48-h Eta forecast 2-m temperature - sfc T obs : Model shows no disquieting drift from cycled EDAS

Bia

s (d

eg

C)

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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

- Robust backup system in place to ensure that EDAS soil moisture is never reinitialized from the GDAS

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

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DATA DUMP TIMES

Cycle Dump Time

00Z 0111Z

03Z 0340Z

12Z 1313Z

18Z 1835Z

Cycle AnalysisTimes

Dump Time

00Z 18,21Z 2243Z

12Z 00,03,06,09Z

1002Z

18Z 12,15Z 1720Z

Early Eta EDAS

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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

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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”)

• 3DVAR : Analysis performs gross check vs. first guess:

- Temperature : +/- 15oC- Wind :+/- 25 ms-1

- RH : +/- 90%- Precipitable water : +/- 12 g/kg- Height : +/- 100 m

• SDMEDIT : NCEP Senior Duty Meteorologist can flag all or parts of suspect raobs

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

Eta OI Analysis

Eta 3DVAR Analysis

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

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EXAMPLE : 00Z 7/13/98 at Rapid City, SD

Solid = RAOBDashed = 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 = RAOBDashed = 80 km Modified 3DVAR

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• 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……..

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Solid = Eta Short Dash = NGM Long Dash = AVN/MRF

24-H ACCUMULATED PRECIPITATION EQUITABLE THREAT SCORES: ALL FCSTS

12/1/97 - 2/28/98 12/1/98 - 2/28/99

10-15% drop in Eta skill between 1997-98 and 1998-99

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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

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AVN had much better SLP forecast then Eta :

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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)

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SOLUTION : Improve geostrophic coupling of mass/wind analysis corrections in 3DVAR Operational 3DVAR analysis Modified 3DVAR analysis

Note: Improved height/wind coupling near Aleutians

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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

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Operational 32-km 3DVAR

Modified 32-km 3DVAR

200 mb

900mb

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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

Equ

itabl

e T

hrea

t Sco

re

Threshold (in)

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00-h

24-h

48-h

00,24,48-h forecast vector RMS wind error vs RAOBSDashed = Modified 3DVAR Solid = Operational 3DVAR

Vec

tor

RM

S e

rror

(m

/s)

Pressure (mb)

NOTE = 200 mb 24-h modified 3DVAR error = 00-h error in operational 3DVAR!

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NEW 3DVAR IMPLEMENTED 13 MAY 1999* : IMPACT

* Further documentation at http://www.nws.noaa.gov/om/tpb/3d-eta.htm

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

RM

S V

ecto

r W

ind

Err

or (

m/s

)

Rog

ers

on le

ave;

sof

twar

e br

eaks

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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

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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)

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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)

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Cloud Data Assimilation(Zhao et al, 1998, 12th NWP, Phoenix, AZ)

• Data sources– real-time Neph Analyses (USAFGWC)– hourly radar/gauge observations