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Results and status of assimilation of GPS-Derived Integrated … · 2016. 12. 20. · Assimilation of GPS-derived IWV Nudging of GPS data in LM ( ) q (k)IWV IWV q k v obs obs v mod

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Page 1: Results and status of assimilation of GPS-Derived Integrated … · 2016. 12. 20. · Assimilation of GPS-derived IWV Nudging of GPS data in LM ( ) q (k)IWV IWV q k v obs obs v mod

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Page 2: Results and status of assimilation of GPS-Derived Integrated … · 2016. 12. 20. · Assimilation of GPS-derived IWV Nudging of GPS data in LM ( ) q (k)IWV IWV q k v obs obs v mod

Results and status of assimilation of GPS-Derived Integrated Water Vapour in LM

M. Tomassini and Ch. SchraffDeutscher Wetterdienst

This work was carried out within theGPS Atmospheric Sounding Project

http://www.gfz-potsdam.de/pb1/GASP/

Page 3: Results and status of assimilation of GPS-Derived Integrated … · 2016. 12. 20. · Assimilation of GPS-derived IWV Nudging of GPS data in LM ( ) q (k)IWV IWV q k v obs obs v mod

Assimilation of GPS-derived IWV

Nudging of GPS data in LM

( ) ( )kqIWV

IWVkq v

obsobsv

modmod

⋅=

( ) ( ) ( )( )[ ]kw

kpkqkw

satv

max

∆=

GPS specific humidity at model level k:

Quality weight assigned to GPS obs:(w(k) ~ 1 between 700-800 hPa)

Retrieved GPS humidity profiles are treated as radiosonde except:• used only below 500 hPa• smaller horizontal radius of influence (~ 50 km at 850 hPa)

Integrated Water Vapour IWV derived from total zenith delay using pressureand temperature from synop, if not available from model fields.

Page 4: Results and status of assimilation of GPS-Derived Integrated … · 2016. 12. 20. · Assimilation of GPS-derived IWV Nudging of GPS data in LM ( ) q (k)IWV IWV q k v obs obs v mod

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Page 5: Results and status of assimilation of GPS-Derived Integrated … · 2016. 12. 20. · Assimilation of GPS-derived IWV Nudging of GPS data in LM ( ) q (k)IWV IWV q k v obs obs v mod

Bias of GPS relative to LM IWV› positive in summer, almost zero in winter› in summer different IWV daily cycle==> daytime-dependent bias correction of GPS IWV (Aug. 2002)

Diurnal cycle Aug 2002: IWV hourly mean at 103 GPS stations

Assimilation of GPS-derived IWV

26,50

27,00

27,50

28,00

28,50

29,00

0 3 6 9 12 15 18 21 24

time (hour)

IWV

(m

m)

GPS LM1MO GPS correc LM1AN

Page 6: Results and status of assimilation of GPS-Derived Integrated … · 2016. 12. 20. · Assimilation of GPS-derived IWV Nudging of GPS data in LM ( ) q (k)IWV IWV q k v obs obs v mod

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12 h FORECAST GPS 12 h FORECATS CNT

Page 7: Results and status of assimilation of GPS-Derived Integrated … · 2016. 12. 20. · Assimilation of GPS-derived IWV Nudging of GPS data in LM ( ) q (k)IWV IWV q k v obs obs v mod

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Page 8: Results and status of assimilation of GPS-Derived Integrated … · 2016. 12. 20. · Assimilation of GPS-derived IWV Nudging of GPS data in LM ( ) q (k)IWV IWV q k v obs obs v mod

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Page 9: Results and status of assimilation of GPS-Derived Integrated … · 2016. 12. 20. · Assimilation of GPS-derived IWV Nudging of GPS data in LM ( ) q (k)IWV IWV q k v obs obs v mod

Assimilation of GPS-derived IWV

Summary of Results

� clear positive statistical impact on IWV�

upper-air humidity

slight positive statistical impact on upper-air temperature�

wind

in forecasts up to about +15 h

� mixed (Aug. 01) or slightly positive (Aug. 02) overall impact on

analyzed and predicted precipitation

� negative impact on cloud cover of low stratus

Deutscher Wetterdienst

Page 10: Results and status of assimilation of GPS-Derived Integrated … · 2016. 12. 20. · Assimilation of GPS-derived IWV Nudging of GPS data in LM ( ) q (k)IWV IWV q k v obs obs v mod

Assimilation of GPS-derived IWV

Important Issues in View of the Operational Application

� bias of GPS IWV relative to LM IWV with a diurnal cycle in summer� daytime-dependent bias correction� potential problem: adaptation of the bias correction to changes in

the error characteristics of the IWV observations(and of the LM � convection parameterization)

� vertical distribution of vertically integrated observational information� no general solution � open question :

What is the impact of assimilating IWV in combination with other typesof data (e.g. cloudiness, radar reflectivity) that are not used operationallyyet ?

Deutscher Wetterdienst