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

COMET Mesoscale Analysis and Prediction Course 1999

16 September 1999

Presented by Eric Rogers

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

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)

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

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

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

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!

INITIAL VOLUMETRIC SOIL MOISTURE FROM GDAS IS TOO HIGH --> EVAPORATION OF SOIL MOISTURE LED TO ERRONEOUSLY HIGH SURFACE Td

INITIAL GDAS SOIL MOISTURE SOIL MOISTURE AFTER 48H FCST

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

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)

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

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

3DVAR vs. OI

WHY DO CYCLING?

• Initial conditions more consistent with forecast model

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

• More accurate representation of soil moisture

IMPACT OF CYCLING ON SOIL MOISTURE

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

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

Bia

s (d

eg

C)

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

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

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

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

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

Eta OI Analysis

Eta 3DVAR Analysis

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

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

• 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……..

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

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

AVN had much better SLP forecast then Eta :

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)

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

Note: Improved height/wind coupling near Aleutians

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

Operational 32-km 3DVAR

Modified 32-km 3DVAR

200 mb

900mb

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)

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!

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 : 3/1/99-8/31/99 Red = 48-h Eta-32 fcst Green = 48-h AVN fcst

Old 3DVAR New 3DVAR

RM

S V

ecto

r W

ind

Err

or (

m/s

)

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

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)

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)

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

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