- Slides: 22
Sixth International Workshop on Tropical Cyclones Topic 3. 3: Targeted observations and data assimilation in track prediction Rapporteur: Chun-Chieh Wu PSA Working Group: Sim Aberson, Brian Etherton, Sharanya J. Majumdar, Seon Park, Melinda S. Peng, Zhaoxia Pu, Michael Morgan, Steve Tracton, Samuel Westrelin, and Munehiko Yamaguchi
Outline Introduction p Surveillance programs using the dropwindsondes p Targeted observations for tropical cyclones p Comparison of targeted observing methods p Other data to be targeted and assimilated p Issues and concerns p Recommendations p
Improving the understanding and forecasting of TCs Dynamics of the typhoon system Cost effective? Initial condition New Observation Data assimilation and/or Initialization Dynamics of the model Multi-scale interaction Air-sea interaction Terrain/PBL effect
Introduction • Accurate forecast of tropical cyclones – Realistic numerical models – Accurate representation of meteorological fields • Observation data – Surface observations, soundings, and ships – Dropwindsonde data – Satellite data – Radar data • Data assimilation
Surveillance programs using the Dropwindsondes • The impact of dropwindsonde data – Between 1982 and 1996, the HRD conducted 20 “synoptic flow” experiments. • Burpee et al. (1996) – The average error reductions in the consensus forecasts from three dynamical models varied from 16% to 30%.
Dropwindsondes • In 1997, the HRD began operational synoptic surveillance mission with the G-IV jet aircraft. • Aberson and Franklin (1999) – The dropwindsonde observations improved the mean track forecasts of the GFDL model by as much as 32%. No drop with drop
Dropwindsondes • Aberson (2002) – The additional dropwindsonde data from the synoptic surveillance missions provided statistically significant improvements in the GFDL forecast only at 12 h. • TC vortex initialization schemes • The amount of data coverage • Aberson (2003) and ongoing… – The improvement through targeted observations
DOTSTAR (Dropwindsonde Observations of Typhoon Surveillance near the Taiwan Region) 69 69 Astra jet of AIDC (Wu et al. 2005 a, BAMS) JMA, UKMO, ….
DOTSTAR observations Up to 2006, 24 missions have been conducted in DOTSTAR for 20 typhoons, with 386 dropsondes deployed during the 129 flight hours. 18 typhoons affecting Taiwan 8 typhoons affecting mainland China 4 typhoons affecting Japan 2 typhoons affecting Korea 5 typhoons affecting Philippines 20. Bilis 21. Kaemi 22. Bopha 23. Saomai 24. Shanshan
The impact of DOTSTAR data on global models in 2004 Melinda Peng Sim Aberson NCEP GFS : 14% NOGAPS : 14% JMA GSM : 19% ENSEMBLE : 22% Tetsuo Nakazawa (Wu et al. 2006 a, WF)
Background on targeted observations • Adaptive observations : observations targeted in sensitive regions can reduce the initial condition’s uncertainties, and thus decrease forecast error. • Targeted observation is an active research topic in NWP, with plans for field programs, programs tests of new observing systems, systems and application of new concepts in predictability and data assimilation (Langland 2005) • Factors associated with adaptive observations - Observation density, variables and errors - Magnitude of uncertainty - Data assimilation system - Growth of uncertainty
Adaptive observation strategies • Dynamics-based strategy • SV, adjoint sensitivity, and PV. • Uncertainty-based strategy. • Ensemble variance • Joint dynamics-uncertainty based strategy. • The ideal one would be the strategy that use both of dynamics and uncertainty information (e. g. , ETKF, VARSV). • (Since 1997, developed for mid-lat, FASTEX)
• Since 2003, several objective methods, have been proposed and tested for operational surveillance missions in the environment of Atlantic hurricanes conducted by HRD/NOAA (Aberson 2003) and NW Pacific typhoons by DOTSTAR (Wu et al. 2005). (Aberson 2003, MWR) – NCEP/GFS ensemble variance (collaborating with Aberson) (Majumdar et al. 2006, MWR) – ETKF (collaborating with Majumdar) – NOGAPS Singular Vector (Peng and Reynolds 2006, (collaborating with Reynolds. JAS) and Peng) – Adjoint-Derived Sensitivity Steering Vector (ADSSV) (Wu et al. 2006 b, JAS) – JMA moist Singular Vector (collaborating with Yamaguchi)
Comparison of targeted observations in DOTSTAR Ensemble Variances, Toth and Kalnay (1993) FNMOC SV, Palmer et al. (1998) ETKF, Bishop and Majumdar (2001) ADSSV, Wu et al. (2006) • DOTSTAR (Wu et al. 2006 b) • G-IV surveillance Comparison of targeted techniques (Etherton et al. 2006) Maumdar et al. 2006 Reynolds et al. 2006 More comprehensive comparisons are ongoing.
How the dropsonde data improve the forecast? Typhoon Conson (2004) as an example (Nakazawa 2004, THORPEX meting) JMA-GSM Typhoon Conson (2004) 8 June 1200 UTC
Evaluate a SV method as a strategy for Targeting Observation JMA has executed Observing System Experiments (OSEs) to investigate the usefulness of the singular vector method as a strategy for sensitive analysis. For the initial time of 12 UTC 08 June 2004 when totally 16 dropsondes were dropped into typhoon CONSON by the DOTSTAR (Dropsonde Observation for Typhoon Surveillance near the Taiwan Region) project, 4 predictions with JMA Global Spectral Model (TL 319 L 40) about the use of the dropsondes in the global 4 D-Var analysis are executed. (I) all dropsonde observations are used for making the initial condition (II) dropsondes are not used at all (From (III) only 3 data within a sensitive region are used (4, 9, 12) (IV) only data outside of a sensitive region are used (6, 8, 10, 13, 15, 16) Yamaguchi) Sensitive analysis result l. The distribution means vertically accumulated total energy by the 1 st moist singular vector. x l. Targeted area for the SV calculation is N 25 -N 30, E 120 -E 130. CONSON’s center position l. Optimization time interval is 24 hours.
OSEs result on CONSON’s track forecast Red: (I) all dropsonde observations are used for making the initial condition Blue: (II) dropsondes are not used at all Green: (III) only 3 data within a sensitive region are used (4, 9, 12) Water: (IV) only data outside of a sensitive region are used (6, 8, 10, 13, 15, 16) (III) (I) similar (From Yamaguchi) (IV) (II) is almost same with (IV)
Other data to be targeted and assimilated • Observations for data assimilation – To date, “Targeted” observations for TCs are mainly dropwindsondes deployed from the aircraft. – There is considerable scope for extending targeted observing strategies to include other types of data, most prominently from satellites. • GOES (Zou et al. 2001) and TRMM (Pu et al. 2004) • Microwave radiances (Bauer et al. 2006 a, b). – The collection of satellite and in-situ data from field programs (e. g. CAMEX-4, Kamineni et al. 2006) with different spatial and temporal resolutions and error characteristics (Fisher 2003; Berre et al 2006, Westrelin et al 2006) will continue to play a very important role in improving tropical cyclone track
Other data o be targeted and assimialted – Questions more specific to targeted observations can be addressed over the next decade: • Given the abundance of satellite data that will be available for assimilation, what subsets of the data are the most necessary for assimilation to improve the tropical cyclone forecast? (satellite data thinning) • What are the optimal variables, three-dimensional structures, and spatial and temporal density that are necessary for observation?
Issues of concerns (Langland 2005 and THORPEX) • Although the impact of observations is greater when selected in a sensitive area, the few observations deployed may not make a substantial impact on the forecasts. • The statistical evaluation of the significance of the measured impact requires a large number of cases. • Current diagnostics used to evaluate forecasts provides a good assessment of the validity of forecasts (skill), but it may not be sufficient to reveal whether these improvements are relevant to applications (value). • The use of climatological sensitivities may lead to improvements on average and be more cost effective than targeted observations on demand. • Overall, there was a considerable question as to the value of targeting, especially when isolated from the more general issues of observing system sensitivities in design of an “optimal” mix of available observing platforms.
Recommendation • • Need to assess the influence of the data assimilation scheme on the effectiveness of targeted observations. More studies of varying definitions, interpretations, and significance of sensitive regions (e. g. , different methods, metrics) More work on sampling strategies in sensitive areas, e. g. , immediate storm environment for shorter range prediction versus remote areas relevant to longer range forecasts – including the impact of large scales in meso-scales models. More work on metrics to assess the impact of targeting – or more generally on any changes in the observation network. Emphasis of the potential value of OSEs and OSSEs in assessing potential observing system impacts prior to actual field programs. Stronger efforts to develop alternative observing platforms (other than the dropwindsondes) for targeting, especially adaptively selecting satellite observations by revising the data thinning algorithms currently used. Improvement and continuous refinement of targeted observing strategies.
THORPEX-PARC Experiments and Collaborating Efforts (from Dave Parsons) Upgraded Russian Radiosonde Network for IPY Winter storms reconnaissance and driftsonde NRL P-3 and HIAPER with the DLR Wind Lidar JAMSTEC/IORGG