GNSS Radio Occultation: progress report

1
GNSS Radio Occultationprogress report

• Lidia Cucurull
• Joint Center for Satellite Data Assimilation
• JSDI funded project Further development of the
  assimilation of Global Positioning System (GPS)
  radio occultation (RO) observations

UMBC, Maryland, May 2009
2
Outline

• Recent work
• Assimilation code
• Latency issues
• Early evaluation of new instruments
• Ongoing activities (research-2-operations)
• Future plans

3
Assimilation code

• More accurate forward operator for refractivity
• Three term expression
• Analysis of different sets of refractive indexes
• Update of the quality control procedures
• More observations (in particular in tropical
  latitudes)
• Optimal observation error characterization
• Smoother normalized differences
• No empirical tuning
• Changes resulted in an improvement in model skill
  in SH (mass fields) and reduction of the low- and
  high-level tropical wind errors.
• These changes are under current pre-operational
  testing at NCEP for Fall 2009 implementation
• Detailed description of the changes and results
  can be found in Cucurull 2009, submitted to MWR.

4
(O-B)/O_err
original (ops) QC error
modified QC error
NH
TR
Many more Observations !!
Errors too small
Very few observations
SH
5
Recent impacts with COSMIC
COSMIC provides 8 hours of gain in model
forecast skill at day 4!!!!

• expx (NO COSMIC)
• cnt (operations - with COSMIC)
• exp (updated RO assimilation code - with COSMIC)

6
COSMIC latency

• There was a latency problem with the COSMIC data
  at NOAA
• As a consequence, many observations arrived too
  late to be assimilated in the operational system
• As a collaborative effort between UCAR, NESDIS
  and NWS, this issue was resolved in January 2009
  and many more observations were within the
  assimilation window after the fix
• COSMIC data is being pulled from TNC/TOC instead
  of DDS server since 3 March 2009.

7
Preliminary evaluation of GRAS (gt30N, August 2008)
refractivities

• The JCSDA identified the significant effects of a
  bug in the encoding of the GRAS BUFR files at
  DMI.
• The bug was particularly important in local
  regions where the differences between the geoid
  and the ellipsoid heights are significant.
• The bug assigned a wrong height to the
  observations and introduced a bias in the
  refractivity profiles.
• The results were reported to DMI and they fixed
  the bug in the BUFR files on 11 Nov 2008.
• The same bug affected the GRACE-A and CHAMP BUFR
  files ( GFZ fixed the bug on 14 Nov 2008).

8
Ongoing activities

• UCAR recently identified a bug in the processing
  of the COSMIC observations that modifies the
  statistics of the data (bias and standard
  deviation in stratosphere). We are currently
  testing the impact of the new data to assess if
  additional modifications in the analysis code are
  needed.
• Evaluating impact of Metop/GRAS and GRACE-A data.
  If results look good, the data will be ready for
  operational assimilation (the implementation
  needs to fit NCOs schedule).
• Working on getting SAC-C (Argentinean mission)
  sample data for evaluation and possible
  transition to real-time -currently delivered in
  non-real time- and TerraSAR-X (German mission)
  -data in real-time but not distributed to the
  external community yet.
• Proposal submitted to evaluate ROSA (Italian RO
  receiver) on Oceansat-2

9
Ongoing activities (contd)

• Collaborative project with CWB (Taiwan) to
  accelerate the use of COSMIC into the NCEPs
  regional data assimilation system (NAM). (JCSDA
  project).
• Co-mentoring with UCAR/CDAAC a SOARS (NSF-funded)
  student to improve the use of COSMIC data to
  retrieve PBL heights for assimilation into the
  real-time mesoscale analysis system (RTMA).
  (NCEP/EMC project)
• Got funding from NESDIS/OSD for a 1-year
  (2-year?) post-doc to add the GNSS RO OSSE
  capability into the Joint OSSE project. (JCSDA
  project)
• Test possible satellite configurations to design
  optimal constellation for operational global
  weather forecasting (UCAR will focus on the
  regional component).
• Use of RO for validation of re-calibrated
  radiances and evaluation of the impact of RO
  observations on the bias correction of nadir
  sensors into the CFSRR system (Re-analysis).
  (NESDIS project PI Cheng-Zhi Zou, submitted)
• Coordinating work with Dr. Kursinski on the
  external grant awarded via competitive Federal
  Funding Opportunity (FFO).

10
Scope of Research
Improving the Impact of GPSRO Data Assimilation
at NCEP
E. R. Kursinski, A. Otarola University of
Arizona F. Xie, C. Ao Caltech/JPL

• Improve the impact of GPS RO particularly in the
  lower troposphere
• Two areas of emphasis
• Super-refraction
• Occurs at very sharp PBL top over oceans
• Causes refractivity to be systematically
  underestimated
• Improve GPS RO error covariance
• Create humidity dependent error covariance
• Examine representativeness error

11
Ongoing activities (contd)

• Working with OSD on a follow-on capability beyond
  COSMIC - as NESDIS Program Scientist for GNSS RO
  . This involves NESDIS, NWS and other NOAA line
  offices.
• NOAA is moving forward on a replacement to COSMIC
• COSMIC 2 (conceptual)
• 12 satellites
• Homogeneous global coverage
• GPS and Galileo signals (minimum)
• Higher gain antennas for lower SNR
• 8000 soundings per day
• 30 minutes data latency - from sounding to data
  delivery to the weather/ionospheric centers

12
Future plans

• Monitor current GPS RO observations
  (modifications in the processing of the data
  might require adjustments in the assimilation
  algorithm)
• Evaluate future RO sensors (as early as possible)
  to enable operational assimilation of the new
  data as soon as possible.
• Delivery of a perl-based software to monitor GPS
  RO statistics in real time at NCEP (in
  collaboration with D. Hunt, UCAR)
• Operational assimilation of COSMIC (and other RO
  sensors) into NAM (in collaboration with Yen-Chih
  Shen, CWB)
• Improve the assimilation code
• Transitioning to 1D bending angle
• Explore 2D forward operators
• Support the design requirements for a COSMIC
  follow-on mission
• Collaboration project with Spain IEEC for launch
  of a COSMIC-type receiver for RO and modified
  antennas (multi polarized) to detect
  precipitation