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© Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The impact of various observing systems on NWP“; Geneva; 19-21 May 2008
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© Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

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Page 1: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Impact studies with satellite observations at the Met Office

John Eyre and Steve English Met Office, UK

4th WMO Workshop on "The impact of various observing systems on NWP“; Geneva; 19-21 May 2008

Page 2: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Impact studies with satellite observations at the Met Office

Focus on results with implications for design of the GOS

• ATOVS – 1, 2, 3 satellites (reminder) Steve English

• ATOVS RARS Brett Candy

• ATOVS MetOp Brett Candy

• MetOp – IASI and ASCAT Fiona Hilton, Simon Keogh

• Cloudy AIRS radiances Ed Pavelin

• Windsat Brett Candy

• GPS-RO – COSMIC and others Mike Rennie

• AMVs Mary Forsythe

• Ground-based GPS Adrian Jupp

Page 3: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

How many microwave sounders?Reduction in forecast rms error

Impact

Amount of data0% 50% 100%

0%

50%

100% 1st ATOVS

~75% of impact at 45% of data coverage 2nd ATOVS

~95% of impact at 85% of data coverage

3rd ATOVS 100% of impact at 100% of data coverage

Albach Workshop results: summary from 10 experiments

Page 4: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

How many microwave sounders?Conclusions

• First and second AMSU are very important to NWP

• Third satellite has positive impact overall, but its main role is robustness and mitigating data delays

• Complete global coverage is very important – more data improve forecasts if they fill gaps in data coverage

• Impact of 4th satellite demonstrated with 4D-var

• … but it is still most important to fill the gaps!!

Page 5: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Regional ATOVS Retransmission System (RARS)

forecast impactForecast benefit of

timely ATOVS data

2 experiments:

• All ATOVS: data

assimilated regardless of

arrival time

• RARS: ATOVS global +

fast delivery data from 14

RARS stations

• Baseline: operations with

cut-off = 2h45

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

24 48 72 96 120 24 48 72 96 120

Forecast Time (Hours)

imp

rove

men

t in

PM

SL

fo

reca

st e

rro

r (%

)

All ATOVSG RARS

NH SH

Page 6: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

500 hPa height. RMS difference between analyses with all ATOVS and operationally-available ATOVS

ATOVS data missing cut-off would benefit N Pacific and S Hem.

Regional ATOVS Retransmission System (RARS)

forecast impact

Page 7: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Met Office global NWP index

• Skill score:

S = 1 – rf2/rp

2

• rf = rms forecast error

• rp = rms persistence error

• Weighted as table Smean

• N = (1 – Smean)-½

• Index = 100 x N / N0

• N0 = value on 31 March 2000

June 2007 value = 130

1% reduction in r.m.s. error 1% increase in Index

WeightsForecast period

T+24 T+48 T+72 T+96 T+120

NH

PMSL 10 8 6 4 4

H500 6 4 2

W250 12

TRW850 5 3 2

W250 6

SH

PMSL 5 4 3 2 2

H500 3 2 1

W250 6

Page 8: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

MetOp ATOVS

• Switch from NOAA-15 to MetOp improved forecast skill:

• +0.6 on Met Office global NWP index

• Switch to operations was made on 17 January 2007 only 90 days after launch!

• Rapid access to new data is important to users

Page 9: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

MetOp IASI

Red – Used (Sea/Land, Clear/MWcloud)

Yellow – Used (Sea/Clear only)

Blue – Used(1D-Var preprocessor only)

Cyan – Rejected

Green / Lime – Rejected water vapour channels

Channel selection

Page 10: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

24 May – 24 June 2007

Preferred configuration • include water vapour channels• obs errors in 4D-Var: 0.5K / 1K / 4K

Met Office global NWP index• +1.21 v obs , +0.80 v analysis• +1.0 overall

Compare with AIRS for same period• +0.63 v obs, +0.12 v analysis• +0.37 overall• normally see more impact from AIRS

MetOp IASIimpact trial results

Page 11: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

H100,H50

H50 shortrange

PMSL

H500,Winds

T100,T50H500,

Winds

Down isGood!

MetOp IASIChange in rms forecast error v observations

Page 12: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

• IASI initial impact of +1.0 is top of:• 3 x ATOVS on NOAA platforms + ATOVS on MetOp• AIRS• SSMIS

• Current use of data is cautious

• cloud-free fields of view over sea

• restricted channel set

• high observation errors

• Much more impact to come …

MetOp IASIsummary

Page 13: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Cloudy AIRS radiances

• In current assimilation of AIRS and IASI, cloud-affected obs are rejected

• only a small proportion of observations retained

• Moving towards assimilation of cloud-affected radiances

• simple cloudy RT models allow careful use of channels peaking above cloud

Cloud top

Weighting functions of channelspeaking above cloud

Page 14: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Cloudy AIRS radiancesIncreased AIRS usage in cloudy regions

Page 15: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Cloudy AIRS radiancesImpact of assimilating AIRS in cloudy areas

• twice as many observations assimilated

• observations assimilated in meteorologically active areas

• +1.0 points on Met Office global NWP index

• equivalent to doubling overall impact of AIRS

NWP index change with cloudy AIRS assimilation

Page 16: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

MetOp ASCAT

• C-band scatterometer

• Geophysical model function to transform wind vectors to backscatter coefficients

• Ambiguous wind vector retrievals - typically 180 degree ambiguity in wind direction

Page 17: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Typical U component 10m wind RMS O-B values for various observation types

0

0.5

1

1.5

2

2.5

3

Ships Buoys ERS-2 AMI WindSat QuikScat MetopASCAT

RM

S(O

bserv

ed

- B

ackg

rou

nd

) m

/sMetOp ASCAT

wind speed performance

Page 18: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

MetOp ASCAT

• Tropical Cyclone Gonu, June 2007

• ASCAT + MSG IR

• C-band - far less rain-contaminated data than for Ku-band instruments

Page 19: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

MetOp ASCAT impact trial results

• 24 May – 24 June 2007

• Met Office global NWP index:

• +0.35 +0.35 v obsv obs• neutral v analysis

• in presence of QuikSCAT

and ERS-2 data

Page 20: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Scatterometers impact on Met Office global forecasts

• ASCAT is giving approx. same impact as Seawinds• 2 global-coverage scatterometer missions provide

significantly more benefit to NWP than oneMet Office, Met R&D Technical Report 511, 2008

Trial compared with NO-SCAT control

NWP indexv obs

NWP index v analysis

All scatterometers +0.97 -0.07

ASCAT only +0.61 +0.29

QuikSCAT only +0.66 -0.08

Page 21: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

WindSat wind vectors

QuikScat WindSat

• WindSat-specific quality control developed

• In particular, low wind speeds rejected due to low information content

• Ambiguous wind vectors assimilated in similar manner to Quikscat

Page 22: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Windsat wind vectorsanalysis increments and forecast impact

QuikScat

WindSat

PMSL improvements (%)

0

0.5

1

1.5

2

2.5

3

24 48 72 96 120 144

Forecast time (hours)

QuikScat WindSat

relative forecast impact

1-month trial, Aug 2005

Page 23: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

GPS radio occultationMet Office operational use

Sep 2006 1st assimilation of CHAMP + GRACE-A (GFZ) refractivities

Nov 2006 CHAMP and GRACE-A withdrawn – GFZ qc problems

May 2007 4 COSMIC satellites assimilated

Nov 2007 4 6 COSMIC satellites

Apr 2008 Increase vertical range: 4-27 km 0-40 km

Jul 2008? Plan to re-introduce CHAMP and GRACE-A

Page 24: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

COSMIC radio occultation dataforecast temperature v sondes

S.Hem., Dec 2006, 6 COSMIC v no GPS-RO

24h temperature forecast 200 hPa temperature

Mean error

RMS error

bias bias

rmsrms

0.8

0.4

K

0

4

2

K

0

10

100

1000 0 48 96 120h

10

100

1000 0 1 2 3K

Page 25: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Stratospheric bias is reduced by assimilating refractivities up to 40 km.

Results shown in bending angle space

Without RO

Mean O-B

St. Dev. O-B

With RO

COSMIC radio occultation dataadding data up to 40 km

Page 26: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Forecast rms % difference v radiosondes, June 07

better worse

4 COSMICAll GPSRO

Radio occultation: Increasing the number of occultations

23 May – 24 June 2007

Page 27: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

GPS radio occultationimpact of increased vertical range

• Increased vertical range of refractivity assimilation:

• from 4-27 km

• to 0-40 km

• Small benefit:

• non-tropical RH

• low level winds

• temperature bias in lower stratosphere

Page 28: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

GPS radio occultationoverall impact - refractivity assimilation

• Large impact in SH forecasts at all ranges for T, H and wind• > 6 % improvement in rms error v sondes, for T100, T250

• Useful improvements in Tropics in same fields:• ~3% improvement in rms error for T50, T100 and T250.

• NH impacts small but positive • Small improvements in RH

• Impact of 6 COSMIC on Met Office global NWP index:

• 1.3 v observations, 0.8 v analysis

• More impact: 4 6 8 satellites

Page 29: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

AMV impacts

Tested in 2 seasons:

12 Dec 05 – 11 Jan 06 4D-Var N216 L50

1. Control (operational observations, March 06)

2. All AMV data removed

3. All satellite data removed

4. AMVs added on no satellite baseline

12 Dec 07 – 12 Jan 08 4D-Var N216 L50

1. Control (operational observations, Nov 07)

2. All AMV data removed

Page 30: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

Met Office Global NWP Index• Measure of model forecasting skill• Forecasts are verified by comparison with observations and analyses• Calculated from a range of parameters (PMSL, H500, W850, W250), over different areas and forecast ranges.

AMV impact Results from Dec 2005

1.5

18.8

8.6

Operational baseline

No satellite baseline

1. AMV denial

2. No Satellite + AMV

wind at 850 hPa v sondes

Tropics

NH

SH

AMVs improve forecasts, although impact is modest compared to ATOVS radiance data.

Page 31: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

TR NH

12 Dec 05 – 11 Jan 06 12 Dec 07 – 12 Jan 08

Poor impact on TR PMSL

Poor impact on TR height fields

Overall similar pattern of impacts, but generally smaller in Dec 07 season.

Possibly due to model and observation usage improvements (e.g. IASI, GPSRO), but may be partly seasonal variation.

NWP index = -1.8 NWP index = -0.9

NH SH SHTR

Mostly positive impact from AMVs (bars above line)

AMV impactcomparing Dec 2005 with Dec 2007

Verification versus observations

Page 32: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

AMV impact MODIS polar winds

T+48 500 hPa height forecast error, Dec 07 – Jan 08:

difference between control and trial

Control - No AMVs

Improved RMS in H500 over NH polar region

also seen in original MODIS polar wind experiments

Page 33: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

zenith total delay, ZTD

62

0

10z

W

z

bpapZTD dz

T T

• Observations from E-GVAP near real-time GPS network

• very high time resolution - often several per hour - potentially useful in 4D-Var

• At the Met Office:•assimilating ZTD into regional (12 km)

and UK (4 km) models•assimilating one per hour in 4D-Var•small positive impacts on cloud,

surface temperature, visibility and precipitation

•operational since March 2007

Ground-based GPS

Page 34: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Impact studies with satellite observations at the Met Office: Conclusions

Results with implications for design of the GOS:

• MW sounders in 3 well-space orbits are close to optimal

• ATOVS RARS – improved timeliness is beneficial for global NWP

• MetOp ATOVS – an excellent example of early availability

• MetOp IASI – substantial impact from cloud-free radiances

• … and more expected from cloudy radiances (IASI and AIRS)

• MetOp ASCAT – highest quality scatterometer; impact demonstrated

• Windsat – impact comparable to scatterometers (for global NWP)

• GPS-RO – good impact from 6 COSMIC; more impact from >6

• AMVs – useful impact; qc and error characterisation problems remain

• Ground-based GPS – small positive impact in regional/UK models

Page 35: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Questions?

Page 36: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

-14

-12

-10

-8

-6

-4

-2

0

2

Perc

enta

ge c

hange in R

MSE

Z250

Z500

Z700

Z850

Ship

&buoy

pm

sl

Syn

op

pm

sl

3-> 0 ATOVS 3-> 1 ATOVS 3-> 2 ATOVS

How many microwave sounders?Impact on analysis accuracy:

change in fit to backgroundAlbach Workshop results

Page 37: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

IASI - Data Selection

1 pixel in 4• collocated-AVHRR “Most Homogeneous” field of

view

No data used over sea iceNo data used where IR cloud tests failed

• Cost test (English et al. 1999)

• Compare IASI with AMSU (Cheng et al. 2006)

• Threshold on SD of 4 IASI pixels (Cheng et al. 2006)

Page 38: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

IASI - Channel selection for data storage

300 channels selected with information content method (Collard 2007, submitted to QJRMS)Choose successive channels which contain most information content for atmospheric profileAvoid adjacent channels to reduce correlated error

• (only use diagonal error covariance matrix in VAR)

Avoid channels affected by trace gases we don’t modelAdd 14 extra channels for monitoring to give 314 in total(cf AIRS: 324 channels)

Page 39: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

IASI - Channel selection for data processing

Reject some problematic channels (inc highest peaking)Reduce number of water vapour channels used

• (will come back to this later)• But note we are using water vapour channels!

Left with 183 channels used in 1D-Var retrievalReject low-peaking channels

• over land• where AMSU detects cloud (by-product of surface

type test)138 used in 4D-Var where high-peaking channels are removed to avoid stratospheric ringing(cf AIRS: 63 channels)

Page 40: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

IASI - Data Processing

We use RTTOV 7• kCARTA coefficients

Observations are processed through a 1D-Var scheme before assimilation in 4D-VarObservation error (SD) of

0.5K 15μm CO2 band (c.f. O-B fit of ~0.3K)1K window channels (c.f. O-B fit of

~0.6K)4K water vapour channels (c.f. O-B fit of

~1.4K – see later!)

Page 41: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

IASI - Assimilation trials

Pre-operational testing via one-month trials 24th May to 24th June 2007Processing very similar to existing ATOVS/AIRS processingEight different configurations tested with

• Differing channel selections• Different model resolutions (N216,N320; 50L,70L)• Recalculated bias corrections• Different observation errors• It has also been tested with two different model

physics packages

Page 42: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

IASI - Trial results

Results fairly stable throughout trial period which was a difficult period for the Met Office Unified Model operationally

Results proved robust to different trial configurations

We measure trial performance using the “NWP Index”

• Combines 22 key variables of interest to our customers

• Weighted mean skill relative to persistence

• Measured using both observations and analyses as verification, and the two values averaged

All trials showed positive impact

Page 43: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

MetOp IASIChange in rms forecast error v analyses

T700, T500, T100

T250,T50

HeightsHeights

Down isGood!

Page 44: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

IASI Improvement to model fields

I wanted to show some nice plots of improvements to model fields……but the changes are minor improvements across the board adding up to a good increase in the index overall. They don’t show up in plots!Results are more robust to changes in configuration and model physics

Page 45: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

IASI – S.Hem. Height Profile T+24,Mean Forecast Error – Verification vs Sonde

Page 46: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Tropics Relative Humidity 500hPa T+24 timeseries RMS Forecast Error – Verification vs Sonde

Control IASI

Page 47: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Improvement in fit to other satellite dataNOAA-18 AMSU-A Channel 5 (750hPa)

VA

R R

MS

(ob-

calc

) tr

ial-c

ontr

ol [

%]

Initial Fit Final Fit

Page 48: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Improvement in fit to other satellite dataNOAA-16 AMSU-A Channel 14 (stratosphere)

VA

R R

MS

(ob-

calc

) tr

ial-c

ontr

ol [

%]

Initial Fit Final Fit

Page 49: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

Improvement in fit to other satellite dataMetOp HIRS Channel 11 (water vapour)

VA

R R

MS

(ob-

calc

) tr

ial-c

ontr

ol [

%]

Initial Fit Final Fit

Page 50: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

MetOp ASCAT wind speed performance

Scatterometer RMS O-B wind speeds for 30/3/2007 - 7/6/2007

1

1.05

1.1

1.15

1.2

1.25

1.3

1.35

1.4

1.45

ERS2AMI SEAWINDS ASCAT

Scatterometer

RM

S O

-B (

m/s

)

after Met Office quality control applied

Page 51: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

COSMIC-1 Global model biases

Monitoring bending angle (O-B) statistics (using 6 hour forecast) shows a distinct ‘S’ shape bias in the global model at higher than 50 hPa (~22km, around model level 35).Note ECMWF mean and standard deviation also shown for comparison.

Page 52: © Crown copyright 2007 Impact studies with satellite observations at the Met Office John Eyre and Steve English Met Office, UK 4th WMO Workshop on "The.

© Crown copyright 2007

40 km upper range

‘S’ shape bias can be reduced by refractivity assimilation up to 40 km. Note result on right in bending angle space

Without RO

Mean O-B

St. Dev. O-B

With RO