2 nd gras-saf user workshop assimilation of gps radio occultation measurements at dao (soon gmao) p....

2nd GRAS-SAF USER WORKSHOP

Assimilation of GPS radio occultation measurements at DAO (soon GMAO)

P. Poli1,2 and J. Joiner3

Data Assimilation Office (DAO)NASA Goddard Space Flight Center

Greenbelt, MD 20771 USA

Effective June 15, 2003: DAO becomes GMAO

Acknowledgments:We would like to thank EUMETSAT and the Organizing Committee of the Workshop

Some of the work presented was done in collaboration with the Radio Occultation group at JPL

1 Joint Center for Earth Systems Technology, University of Maryland Baltimore County 2 Permanent Affiliation: Meteo France Centre National de Recherches Meteorologiques, Toulouse, France 3 NASA Laboratory for Atmospheres

OUTLINE

1st-generation Data Assimilation System for GPS Radio Occultation: DAOGPS (1999-2002)– Review– Analysis and forecast impact studies with GPS/MET

Next-generation Data Assimilation System for GPS Radio Occultation: (2002-...)– Work in progress

2nd GRAS SAF User Workshop, 11-13 June 2003 Elsinore DenmarkPoli and Joiner

1st generation DAS for GPSRO at DAO: DAOGPS

Radiosonde-like assimilation in two steps:– 1DVAR retrievals of temperature, humidity, and

surface pressure from GPS refractivity and latest available 6-hour forecast (Poli, Joiner, and Kursinski, 2002)

– Assimilation of 1DVAR geopotential heights into the Finite Volume Data Assimilation System (FVDAS) (Poli and Joiner, 2003)


1st generation DAS for GPSRO at DAO: DAOGPS

With assimilationof GPS/MET refractivity

CONTROL

Forecast Day

Forecast Day

Ano

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orre

lati

on

CONTROL

With assimilationof GPS/MET refractivity

Ano

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Indiv. Forecast19950630_00Z+19950630_06Z-19950705-00Z

Average over 14 forecasts19950621-19950704

Height Anomaly Correlation at 500hPa

Northern Hemisphere(pre-AMSU era)


Next-generation DAS for GPSRO at GMAO:(1) Next-generation GPSRO data

Geom. Optics

(Obs-Analysis) Refractivity Biases(Obs-Analysis) Refractivity Biases

(Obs-Analysis) Refractivity Stdev.(Obs-Analysis) Refractivity Stdev.

Back-Prop. Canon. Transf.


Next-generation DAS for GPSRO at GMAO:(2) Next-generation 1DVAR retrievals

Canonical Transform Refractivity data -> Reduced Bias in lower Trop.


Assume: tangent point location (lat, lon) is known, occultation plane remains the same

Simulated 288 occultations with FVDAS analysis fields (1ox1.25o) and 2D ray-tracing

Next-generation DAS for GPSRO at GMAO:

(3) Next-generation obs. operator: FARGO

2D ray-tracing

Integration of[dn/dr(r,) cosalong ray path

obtained by 2D r.t.


obtained by 1D r.t

Integration of[dn/dr(r) cosalong ray path

obtained by 1D r.t Equivalent to:

1D inverse Abeltransform

Problem: slow because each step requires knowledge of the previous step and three 2D interpolations (n,dn/dr,dn/d)Advantage: accurate solution to the forward problem

Problem: requires 2D ray-tracing to calculate ray pathAdvantage: once ray path is known, 2D interpolations (dn/dr only) can be done afterwards (hence parallelized)

Problem: still requires 1D ray-tracing all the way through the atmosphere (from transmitter to receiver) to get ray pathExtra Advantage: ray determination is fast (requires only 1D interp)

Problem: does NOT account for horizontal gradients of refractivityAdvantage: fast


Define our Fast Atmospheric Refractivity Gradient Operator (FARGO):

Advantages of the scheme: require 1D ray-tracing along a reduced portion of the ray (many less interpolations required), and dn/dr(r,) 2D interpolations are fast (can be parallelized)

Other advantage for data assimilation: scheme clearly separates vertical structure from the 2D correction -> possible to derive a computationally inexpensive Adjoint for vertical structure only

Next-generation DAS for GPSRO at GMAO:(3) Next-generation obs. operator FARGO

Integration of[(dn/dr(r,)-dr/dn(r)) cos

along ray path obtained by 1D r.t

+1D inverse Abeltransform


obtained by 1D r.t

Integration of[(dn/dr(r,)-dr/dn(r)) cosalong section L ray path

obtained by 1D r.t

+1D inverse Abeltransform

1200kmL2nd GRAS SAF User Workshop, 11-13 June 2003 Elsinore DenmarkPoli and Joiner

1D INVERSE ABEL TRANSFORM minus 2D RAY-TRACING

(errors due to horizontal gradients)

FARGO minus 2D RAY-TRACING



288 occultations simulated fromDAO analyses horizontal resolution 1ox1.25o

2001-05-31 at 00GMT

1D INVERSE ABEL TRANSFORM minus 2D RAY-TRACING

(errors due to horizontal gradients)

FARGO minus 2D RAY-TRACING


hor. resol. 0.5ox0.625o

hor. resol. 1ox1.25o

hor. resol. 2ox2.5o


(retained only the rays that did not undergo critical refraction)

288 occultations simulated fromDAO analyses fields 2002-01-31 at 00GMT

Conclusions Limited impact with radiosonde-like assimilation of refractivity

data (biases in GPS/MET refractivities, few profiles per day, 1D approach, intermediate 1DVAR step, assimilation of temperature only)

CHAMP and SAC-C GPS RO data processed with advanced methods show better fit with DAO (GMAO) analyses

Developed a Fast model for bending angle: FARGO: (2D integral operator + inverse Abel transform)

Look forward to testing FARGO with real data in order to determine relevance of 2D approach

Future GRAS data: access to occultation geometry parameters (transformation matrix ECF 3D -> 2D plane, local center of curvature), orbital parameters


2 nd gras-saf user workshop assimilation of gps radio occultation measurements at dao (soon gmao) p....

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