assimilation of modis winds at ecmwf
DESCRIPTION
Assimilation of MODIS winds at ECMWF. Niels Bormann, Jean-No ël Thépaut, and Graeme Kelly * (ECMWF) ( * now at UK Met.Office) (with contributions from Dave Santek and Jeff Key, CIMSS). Outline. Introduction: Polar winds from MODIS Forecast impact of MODIS winds - PowerPoint PPT PresentationTRANSCRIPT
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
Assimilation of MODIS winds at ECMWF
Niels Bormann, Jean-Noël Thépaut, and Graeme Kelly*
(ECMWF)
(* now at UK Met.Office)
(with contributions from Dave Santek and Jeff Key, CIMSS)
![Page 2: Assimilation of MODIS winds at ECMWF](https://reader036.vdocuments.mx/reader036/viewer/2022070418/56815a66550346895dc7b245/html5/thumbnails/2.jpg)
ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
Outline
1. Introduction: Polar winds from MODIS
2. Forecast impact of MODIS winds
3. Forecast example of MODIS winds impact
4. AVHRR winds
5. Summary
![Page 3: Assimilation of MODIS winds at ECMWF](https://reader036.vdocuments.mx/reader036/viewer/2022070418/56815a66550346895dc7b245/html5/thumbnails/3.jpg)
ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
Outline
1. Introduction: Polar winds from MODIS
2. Forecast impact of MODIS winds
3. Forecast example of MODIS winds impact
4. AVHRR winds
5. Summary
![Page 4: Assimilation of MODIS winds at ECMWF](https://reader036.vdocuments.mx/reader036/viewer/2022070418/56815a66550346895dc7b245/html5/thumbnails/4.jpg)
ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
1) Polar winds from MODIS
• Wind derivation developed at CIMSS (Cooperative Institute for Meteorological Satellite Studies), Madison • Based on feature-tracking in subsequent MODIS swaths (similar to “cloud track winds” from geostationary satellites)
• Height assignment to cloud top: IR brightness temperature/WV-intercept method
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
1) Polar winds from MODIS (cnt’d)
• Primary source of wind observations over the polar regions• Assimilated operationally at ECMWF since 14 January 2003.
Sample of IR winds
Sample of WV winds
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
Outline
1. Introduction: Polar winds from MODIS
2. Forecast impact of MODIS winds
3. Forecast example of MODIS winds impact
4. AVHRR winds
5. Summary
![Page 7: Assimilation of MODIS winds at ECMWF](https://reader036.vdocuments.mx/reader036/viewer/2022070418/56815a66550346895dc7b245/html5/thumbnails/7.jpg)
ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
2) Forecast impact:Data assimilation system
The observations are used to correct errors in the short forecast from the previous analysis time.
Every 12 hours we assimilate 4 – 8,000,000 observations to correct the 100,000,000 variables that define the model’s virtual atmosphere.
This is done by a careful 4-dimensional analysis in space and time of the available observations; this operation takes as much computer power as the 10-day forecast.
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
assimilation window
t0 tnti
yo
yo
yo
yo
previous forecast
xb corrected forecast (analysis)
xa observations
2) Forecast impact:Schematic of 4d variational data assimilation (4DVAR)
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
2) Forecast impact of MODIS winds
Assimilation experiments:- 3DVAR, T159/159 (~125 km res.):
- 5 March—3 April 2001 (30 forecasts)- 4DVAR, T511/159 (~40 km/125 km model/analysis res.):
- 13 July—29 August 2002 (48 forecasts) - 5 March—3 April 2001 (30 forecasts)
CTL: No MODIS winds; otherwise full operational set of observations.MODIS: MODIS winds added to CTL.
MODIS winds used: IR, WV cloudy and clear, Terra data only Over land: IR and WV winds above 400 hPa. Over sea: IR winds above 700 hPa, WV above 550 hPa.
(see also Bormann and Thépaut, 2004, MWR)
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
2) Forecast impact (3DVAR)
Anomaly correlation for 500 hPa geopotential, each experiment verified against its own analysis (25 cases).
Northern Hemisphere Arctic (N of 65N)
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
2) Forecast impact (3DVAR, cnt’d)
Anomaly correlation for 500 hPa geopotential, each experiment verified against its own analysis (25 cases).
Southern Hemisphere Antarctic (S of 65S)
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
2) Forecast impact (4DVAR)
Anomaly correlation for 500 hPa geopotential, each experiment verified against own analysis (58 cases).
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
2) Forecast impact (4DVAR, cnt’d)
Anomaly correlation for 500 hPa geopotential, each experiment verified against own analysis (58 cases).
![Page 14: Assimilation of MODIS winds at ECMWF](https://reader036.vdocuments.mx/reader036/viewer/2022070418/56815a66550346895dc7b245/html5/thumbnails/14.jpg)
ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
Outline
1. Introduction: Polar winds from MODIS
2. Forecast impact of MODIS winds
3. Forecast example of MODIS winds impact
4. AVHRR winds
5. Summary
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
3) Forecast Example
Analysis MODIS
CTL
5 day forecast of 500 hPa geopotential, initialised 15 March 2001, 12 UTC,
3DVAR experiment
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
3) Forecast Example: Snowfall
“Analysis” (corresp. 0-12 h forecast) MODIS
CTL
96-108 h forecast of 12h snowfall [mm water equivalent], initialised
15 March 2001, 12 UTC
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
3) Forecast Example: Difference tracking
Forecast of 500 hPa geopotential [gpdm] initialised 15 March 2001:
blue: MODIS forecastblack: CTL forecast
red/green: Difference MODIS-CTL (positive/ negative)
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
Outline
1. Introduction: Polar winds from MODIS
2. Forecast impact of MODIS winds
3. Forecast example of MODIS winds impact
4. AVHRR winds
5. Summary
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
4) AVHRR AMVs
CIMSS-derived polar AMVs from AVHRR from NOAA-15, -16, -17, -18. No WV channel on AVHRR, so IR winds and height assignment only.
Assimilation experiments:
12-hour 4DVAR
Resolution: T511L60 (~40 km, model), T159 (~125 km, analysis)
1 January 2007 – 14 February 2007 (45 forecasts)
Control: Conventional observations + NOAA-18 AMSU-A
AVHRR: As Control, but plus AVHRR winds
AMVs used over land above 400 hPa, over sea/ice above 700 hPa.
MODIS: As Control, but plus MODIS winds
IR AMV usage as for AVHRR;
WV AMVs used over land above 400 hPa, over sea/ice above 550 hPa.
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
4) AVHRR AMVs: Coverage Number of used winds (all levels), 1 Jan – 14 Feb 2007:
AVHRR N.Pole AVHRR S.Pole
MODIS N.Pole(IR & WV)
MODIS S.Pole(IR & WV)
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
U-component:
V-component:
Std.dev [m/s] Bias [m/s]
Std.dev [m/s] Bias [m/s]
• Statistics for used AMVs over Antarctica for AVHRR and MODIS (IR & WV).
• AVHRR winds show larger departures and worse biases against the FG than MODIS winds.
Obs-FG MODISObs-FG AVHRRObs-AN MODISObs-AN AVHRR
4) AVHRR AMVs
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
Normalised
differences in RMS of
48-hour forecast
errors for the 500 hPa
geopotential
(negative = polar
winds “good”)
AVHRR – Control
MODIS – Control
4) AVHRR AMVs
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
Outline
1. Introduction: Polar winds from MODIS
2. Forecast impact of MODIS winds
3. Forecast example of MODIS winds impact
4. AVHRR winds
5. Summary
![Page 24: Assimilation of MODIS winds at ECMWF](https://reader036.vdocuments.mx/reader036/viewer/2022070418/56815a66550346895dc7b245/html5/thumbnails/24.jpg)
ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
5) Summary
MODIS winds provide important upper air wind observations over polar regions.
Significant positive forecast impact when first introduced, also outside high-latitudes.
Used by all main NWP centres.
ECMWF plans to re-evaluate MODIS winds impact to provide input to Arctic imager initiatives.
WV winds provide 2/3 of the number of MODIS winds; lack of WV channel on AVHRR means fewer AVHRR winds with poorer quality.
AVHRR winds will provide only limited polar wind coverage after the lifetime of the MODIS instruments.
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ECMWFArctic Imaging Workshop, Copenhagen, 20/21 August 2008
Arrival time
4 Z extraction time for early delivery
Timeliness of MODIS AMVs
Direct broadcast MODIS winds
NESDIS MODIS winds
Nu
mb
er
of o
bse
rva
tion
sAccumulated number of data for 21-3 Z early delivery data window vs arrival time
Data window for early delivery analysis