Lessons learned from THORPEX THORPEX working group on Data Assimilation and Observing Strategies Florence Rabier (Météo-France and CNRS, France, Co-chair) Pierre Gauthier (UQAM, Canada,Co-chair) Carla Cardinali (ECMWF, Int) Ron Gelaro (GMAO, USA) Ko Koizumi (JMA, Japan) Rolf Langland (NRL, USA) Andrew Lorenc (Met Office, UK) Peter Steinle (BMRC, Australia) Mickael Tsyrulnikov (HRCR, Russia) Nonlinear Processes in Geophysics, 15, 1-14, 2008 New WG being formed, including Observing Systems

THORPEX and the DAOS-WG “THORPEX: a Global Atmospheric Research Programme” established in 2003 by WMO.“THORPEX: a Global Atmospheric Research Programme” established in 2003 by WMO. Mission statement: “Accelerating improvements in the accuracy of high-impact 1-14 day weather forecasts for the benefit of society and the economy”Mission statement: “Accelerating improvements in the accuracy of high-impact 1-14 day weather forecasts for the benefit of society and the economy” Design and demonstration of interactive forecast systems: enhancements to the observations usage in “sensitive regions”Design and demonstration of interactive forecast systems: enhancements to the observations usage in “sensitive regions” Perform THORPEX Observing-System Tests and Regional field Campaigns to test and evaluate experimental remote- sensing and in-situ observing systemsPerform THORPEX Observing-System Tests and Regional field Campaigns to test and evaluate experimental remote- sensing and in-situ observing systems DAOS-WG: evaluate and improve the impact of observationsDAOS-WG: evaluate and improve the impact of observations

Outline ContextContext Main objectivesMain objectives –Assess impact of observations and observing system design –Targeting strategies –Improved use of observations Illustrations from field campaigns (AMMA…),Illustrations from field campaigns (AMMA…), the Intercomparison experiment and the WMO Data Impact Workshop (

Large number of data and different data sources

Assessing the impact of observations OSEsOSEs OSSEsOSSEs DFSDFS Error variance reductionError variance reduction Sensitivity to observationsSensitivity to observations

Winter results: Baseline – Control (Z500) Impact of terrestrial, non-climate, observations NH EUR Differences in RMS errors and significance bars for each forecast range ECMWF

Control-Baseline (Z500) Normalised forecast error difference, Day-3 Geographical distribution of error reductionECMWF

Neutral Case impact A few hours 6 hours 12 hours Northern Hemisphere Extra-tropics Radiosonde Aircraft Buoys AIRS IASI AMSU/A GPS-RO SCAT AMV SSMI Tropics Radiosonde Aircraft Buoys AIRS IASI AMSU/A GPS-RO SCAT AMV SSMI Southern Hemisphere Extra-tropics Radiosonde Aircraft Buoys AIRS IASI AMSU/A GPSRO SCAT AMV SSMI Synthesis of all results after WMO workshop

Analysis Nature run (output from high resolution, high quality climate model) Simulator Forecast model Candidate observations (e.g. GEO MW) Initial conditions Reference observations (RAOB, TOVS, GEO, surface, aircraft, etc.) Forecast products Assessment OSSE, conceptual model End products JCSDA

Vertical structure of a HL vortex shows distinct eye- like feature and prominent warm core; low-level wind speeds exceed 55 m/s Reale O., J. Terry, M. Masutani, E. Andersson, L. P. Riishojgaard, J. C. Jusem (2007), Preliminary evaluation of the European Centre for Medium-Range Weather Forecasts' (ECMWF) Nature Run over the tropical Atlantic and African monsoon region, Geophys. Res. Lett., 34, L22810, doi: /2007GL HL vortices: vertical structure Tropical cyclone NR validation Preliminary findings suggest good degree of realism of Atlantic tropical cyclones in ECMWF NR.

DFS: Information content by area M-F DFS= Tr(HK)=Tr(I-AB -1 )

Ensemble variational assimilation at Météo-France Ensemble assimilation : simulation of the joint evolution of analysis, background and observation errors:Ensemble assimilation : simulation of the joint evolution of analysis, background and observation errors:  a = (I – KH)  b + K  o. Observations are explicited perturbed, while backgrounds are implicitly perturbed through cycling.Observations are explicited perturbed, while backgrounds are implicitly perturbed through cycling. (From Ehrendorfer, 2006)

Ensemble  b –  a with energy norm One month statistics (January 2007) at 00UTC 6 member 3D-Var FGAT ensemble Desroziers, M-F

14 Observations move the model state from the “background” trajectory to the new “analysis” trajectory The difference in forecast error norms,, is due to the combined impact of all observations assimilated at 00UTC Sensitivity to Observation ( Langland and Baker, 2004) OBSERVATIONS ASSIMILATED 00UTC + 24h

Forecast error measure (dry energy, sfc–140 hPa): Estimating Observation Impact Taylor expansion of change in due to change in : 3 rd order approximation of in observation space: model adjointanalysis adjoint …summed observation impact Analysis equation allows transformation to observation-space:

Properties of the Impact Estimate …the observation improves the forecast …the observation degrades the forecast …see Langland and Baker (2004), Errico (2007), Gelaro et al. (2007)  The “weight” vector is computed only once, and involves the entire set of observations…removing or changing the properties of one observation changes the weight of all other observations.  Valid forecast range limited by tangent linear assumption for  The impact of arbitrary subsets of observations (e.g. instrument type, channel, location) can be easily quantified by summing only the terms involving the desired elements of.

Forecast error norms and differences e 30 e 24 Forecasts from 0600 and 1800 UTC have larger errors e 24 – e 30 (nonlinear) e 24 – e 30 (adjoint) Global forecast error total energy norm (J kg -1 ) Forecast errors on background-trajectories Forecast errors on analysis-trajectories NRL

NAVDAS-NOGAPS Percent of observations that produce forecast error reduction (e 24 – e 30 < 0) NRL

AMMA RAOB Temperature Ob Impacts May-Oct 2006 TAMANASET:60680 SUM= J kg -1 BANAKO:61291 SUM= J kg -1 NRL

Example : AMV impact problem Date: Jan-Feb 2006 Issue: Non-beneficial impact from MTSAT AMVs at edge of coverage area Action Taken: Data provider identified problem with wind processing algorithm. NRL

Comparison and Interpretation of ADJ and OSE Results  The ADJ measures the impact of observations in each analysis cycle separately and against the control background, while the OSE measures the impact of removing information from both the background and analysis in a cumulative manner  The ADJ measures the impacts of observations in the context of all other observations present in the assimilation system, while the OSE changes/degrades the system ( differs for each OSE member)  Comparison is restricted to the forecast range and metric for which the adjoint results are valid on the one hand (24h-energy in this study) and to the observing systems tested in the OSE on the other …a few things to keep in mind… Gelaro

Removal of AMSUA results in large increase in AIRS (and other) impacts Removal of AIRS results in significant increase in AMSUA impact Removal of raobs results in significant increase in AMSUA, aircraft and other impacts (but not AIRS) Combined Use of ADJ and OSEs (Gelaro et al., 2008) …ADJ applied to various OSE members to examine how the mix of observations influences their impacts NASA, GMAO

Total observation impact at 00 UTC

Targeting strategies

Evaluating and improving targeting strategies Select additional observations or optimize the use of satellite sensors (sampling rate, thinning, chanel selection…) Results depend on method, flow regimes To be extended to Tropics (model error), evaluation at finer scales Observation time Adjoint model or Ensemble Transform Verification time

A-TReC (Atlantic THORPEX Regional Campaign) Oct15-Dec The ATREC was led by EUCOS in the context of THORPEX. It involved UK Met office, ECMWF, Meteo-France, NRL, NASA, U of North Dakota, Meteorological Service of Canada, NCEP, FSL, NCAR and U of Miami A variety of observing platforms were deployed. AMDAR (550), ASAP ships (13), radiosondes (66), GOES rapid-scan winds and dropsondes. Fourrié, et al, M-F Geopotential forecast error for the ATReC area (wrt analyses)

Impact of targeted obs Targeting is possible and successful – mid-latitude targeted observations are about twice as effective as random observations.Targeting is possible and successful – mid-latitude targeted observations are about twice as effective as random observations. Improvements to DA methods should improve the assimilation of all observations in sensitive regions, including targeted obs, but the statistical basis still means that only just over 50% will have a positive impact.Improvements to DA methods should improve the assimilation of all observations in sensitive regions, including targeted obs, but the statistical basis still means that only just over 50% will have a positive impact. Improvements to targeting methods are possible (e.g. longer leads for large areas) but the statistical basis means that impacts on scores will vary. Improvements to targeting methods are possible (e.g. longer leads for large areas) but the statistical basis means that impacts on scores will vary. Thanks to the general improvement of operational NWP, the average impact of individual observing systems is decreasing.Thanks to the general improvement of operational NWP, the average impact of individual observing systems is decreasing. Targeting alone is unlikely to significantly accelerate improvements in the accuracy of 1 to 14-day weather forecasts compared to other improvements over the THORPEX period in NWP and satellites.Targeting alone is unlikely to significantly accelerate improvements in the accuracy of 1 to 14-day weather forecasts compared to other improvements over the THORPEX period in NWP and satellites.

Improving the use of observations Extending the use of satellite dataExtending the use of satellite data Bias correctionBias correction

Improved representation of surface emissivity for the assimilation of microwave observations Dynamical approach for the estimation of the emissivity from Satellite observations over land (Karbou 2006) The estimation of emissivity has been adapted to Antarctica : snow and sea ice surfaces Karbou, M-F

Comparison of the new emissivity calculation with the old one, over sea ice Fg-departure (K) (obs- first guess) histograms for AMSU-A, ch4 (July 2007) Fg-departure (K) (obs- first guess) histograms for AMSU-B, ch2 (July 2007) Old New

Use of additional microwave data AMSUB- Ch3AMSUA- Ch5 CONTROL EXP Density of data Being actively assimilated Bouchard, Karbou, M-F

AMMA: The African Monsoon Multidisciplinary Analysis Better understand the mechanisms of the African monsoon and prevent dramatic situations (Redelsperger et al, 2006) Enhanced observations over West Africa in 2006 In particular, major effort to enhance the radiosonde network (Parker et al, 2008)

Impact of using the AMMA radiosonde dataset New radiosonde stationsNew radiosonde stations Enhanced time samplingEnhanced time sampling AMMA database: additional data which were not received in real time + enhanced vertical resolutionAMMA database: additional data which were not received in real time + enhanced vertical resolution Bias correction for RH developed at ECMWFBias correction for RH developed at ECMWF (Agusti-Panareda et al) Data impact studiesData impact studies With various datasets, With and without RH bias correction Number of soundings provided on GTS in 2006 and 2005 Period: 15 July- 15 September, 0 and 12 UTC

Impact on quantitative prediction of precipitation over Africa Higher scores for AMMABC Lowest scores for NO AMMA CNTR: data from GTS AMMA: from the AMMA database AMMABC: AMMA + bias correction PreAMMA: with a 2005 network NOAMMA: No Radiosonde data Faccani et al, M-F

Work performed and lessons learnt Impact of observationsImpact of observations –Guidance for observation campaigns and the configuration of the Global Observing system –Assessment of the value of targeted observations (papers by Buizza, Cardinali, Kelly, in QJRMS) –Evaluation of observation impact with different systems (A-TReC, AMMA…). Need for relevant bias correction. –Intercomparison experiment for sensitivity to observations Improving the use of satellite dataImproving the use of satellite data –Extend our use of satellite data (density, cloudy/rainy, over land) Important to study different methods and different systems to draw relevant conclusionsImportant to study different methods and different systems to draw relevant conclusions