sean healy presented by erik andersson
DESCRIPTION
Outline Performance of GPSRO in a recent adjoint-based impact study: forecast error sensitivity to observations (FSO) Investigating the surface pressure information derived from GPSRO measurements GRAS/COSMIC consistency Summary COSMIC in Global NWPTRANSCRIPT
Sean Healy Presented by Erik Andersson
Use of COSMIC data in ECMWFs global data assimilation system for
numerical weather prediction Sean Healy Presented by Erik Andersson
COSMIC in Global NWP Outline Performance of GPSRO in a recent
adjoint-based impact study:forecast error sensitivity to
observations (FSO) Investigating the surface pressure information
derived fromGPSRO measurements GRAS/COSMIC consistency Summary
COSMIC in Global NWP Forecast Error Sensitivity to Observations
(FSO)
Data assimilation scientists have developed adjoint-basedtools to
estimate by how much various observation typescontribute to the
reduction of 24-hour forecast error. Carla Cardinali has recently
completed this type of calculationfor the ECMWF 4D-Var data
assimilation system GPSRO has performed well COSMIC in Global NWP
Forecast sensitivity to observations (FSO)
J is a measure of the forecast error (dry energy norm, ps, T, u,v)
Forecast error sensitivity to the analysis Analysis solution Rabier
F, et al Analysis sensitivity to observation and background The
tool provides FSO for each assimilated observation, which can be
accumulated by observation type, subtype, variable or level The
forecast sensitivity (J is a scalar of the forecast error) equation
can be expressed as a product of the forecast sensitivity with
respect to the initial conditions and theanalysis sensitivity with
respect to the observations. The analysis solution can be expressed
as the contribution of the background information plus the
innovation vector. If we take the analysis rel xa=xb+Kdy and
compute the analysis sensitivity with respect to the observation we
obtain the transpose of the K-matrix gain. After some substitutions
and applying numerical techniques to solve dJ/dy (Krylov solution).
Once dJ/dy is computed we can now take the delta J and rearrange it
by substituting the xa= solution. The forecast error can be
gathered over different subsets (type, subtype, variable and level)
y COSMIC in Global NWP Observations contributions to decreased
forecast error Operational FC system, Sept-Dec 2008
COSMIC in Global NWP Observations contributions to decreased
forecast error Operational FC system, Sept-Dec 2008
GPS-Radio Occultation COSMIC in Global NWP Summary statistics by
observation type
Mean sensitivity of An to Obs Global observation influence on
analysis: GI=7% Global background influence I-GI=93% Information
content (DFS) COSMIC in Global NWP Surface pressure information
derived from GPSRO measurements
The integration of the hydrostatic equation is part ofthe GPSRO
observation operator because the bendingangle and refractivity
values are given as a function ofa height co-ordinate. 1D-Var
studies (Healy and Eyre, 2000) suggest that itshould be possible to
derive useful surface pressureinformation from the GPSRO
measurements. We have recently performed experiments where
allsurface pressure information is blacklisted to see ifCOSMIC and
GRAS can constrain the surface pressurefield. Period June-July,
Verified against ECMWFoperations. COSMIC in Global NWP Just to show
the number of conventional Ps obs.
COSMIC in Global NWP Southern Hemisphere results (24 hour forecast
mean error)
GPSRO bias quite stable The GPSRO seems to constrain the Ps bias.
Control is the full observing system. Similar temporal evolution in
NH and tropics COSMIC in Global NWP SH sigma of 24 Hour error
COSMIC in Global NWP 500Z height score (SH) The Ps measurements
dont have much impact from ~day-4 when GPSRO assimilated. HOWEVER,
Im currently looking at another period to see if I can reproduce
this result. COSMIC in Global NWP GRAS-COSMIC mean
differences
We expect GPSRO measurements from differentinstruments to have
similar bias characteristics, butoperational monitoring has shown
that the GRAS andCOSMIC bending angle biases differ by about 0.2%
in thelower-mid stratosphere. In operations, the COSMIC departures
were in betteragreement with ECMWF forecasts and we initially
assumedthat the problem was with the GRAS processing. However,
Christian Marquardt (EUMETSAT) demonstrated atthe January 2009 AMS
meeting that the problem was causedby the smoothing of the COSMIC
phase delays at UCAR. UCAR proposed modifications to their
processing and made3 months (Nov, Dec, 08 and Jan 09) data
available to theNWP centres. We used this data to investigate the
GRASCOSMIC consistency. Revised data processing at UCAR has been
operationalsince October 11, 2009. COSMIC in Global NWP Global
bending angle (o-b)/b departure statistics from ECMWF operations
for Aug. 20 to Sept. 20, 2009 GRAS COSMIC-6 COSMIC-4 This is a
typical result derived from operations before UCAR made the change.
The COSMIC instruments agree with each Other but not with GRAS.
COSMIC in Global NWP Experiments with Modified COSMIC data
Statistics for Dec 08 (NH)
GRAS Much better consistency after UCAR processing change. But what
causes the biases? Good agreement between GPSRO instruments, but
what causes the ve bias? COSMIC in Global NWP Dec 08 Statistics
when aircraft temperatures are blacklisted
Aircraft T values bias the analyis warm, peaking at 200 hPa by ~0.5
K. This shifts all the stratospheric model levels upwards,
Increasing the forward modelled bending angles. Part of the bias is
caused by aircraft temp measurementswhich are known to be biased
warm stratospheric modellevels too high, so the simulated bending
angles are biased high. COSMIC in Global NWP Summary FSO
diagnostics show that GPSRO is an important observingsystem. We are
currently investigating the surface pressureinformation content of
GPSRO. Consistency between GRAS and COSMIC measurements muchbetter
since the processing change at UCAR. Part of thenegative bending
angle bias is caused by biased Aircraft Tmeasurements. We plan to
bias correct the aircraft Temperaturemeasurements. COSMIC in Global
NWP