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Structure & Structure Change IWTC VI, Topic 1

Structure & Structure Change IWTC VI, Topic 1. Chair: Jeff Kepert (Substituting for Hugh Willoughby) Rapporteurs Environmental Effects (E. Ritchie) Inner Core Dynamics (J. Kepert) Ocean Interaction (N. Shay) Operational Definition (M. Lander) Operational Guidance and Skill (J. Knaff)

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Structure & Structure Change IWTC VI, Topic 1

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  1. Structure & Structure ChangeIWTC VI, Topic 1 Chair: Jeff Kepert (Substituting for Hugh Willoughby) Rapporteurs Environmental Effects (E. Ritchie) Inner Core Dynamics (J. Kepert) Ocean Interaction (N. Shay) Operational Definition (M. Lander) Operational Guidance and Skill (J. Knaff) Defining Structure from Satellite Data (C. Velden) Field Experiments (P. Black and S. Chen)

  2. Observations • Passive microwave sensors • SSMI, AMSU, AMSR-E, Windsat, TRMM/TMI • Active microwave sensors • TRMM/PR, Cloudsat, QuikScat, ASCAT • Ground and airborne radar • VIS, IR & Water vapor channels • Satellite altimetry • Aircraft: In-situ & expendable probes • Conventional synoptic observations

  3. Eyewall Replacement Cycle Hurricane Wilma

  4. Observation Use & Interpretation • Web-based resources, e.g. NRL Satellite Imagery Site • Transition to operations: e.g. JHT in the US • Dvorak • Main intensity tool worldwide • Historical data & standardization • Extension to use new sensors — e.g. SSMI • Data assimilation • Dynamically consistent fusion of data from multiple sensors • Time scales and dynamical constraints • Error characterisation • Forward models for individual sensors • Surface Winds • Definition in terms of averaging period, gusts, … • Models & Measurements (remote and in situ) • Calibration to damage • Oceanographic

  5. Sampling Pattern: AXCTDs and Drifters relative to OHC and Rita’s track. Pre and Post Rita WCR/CCR/ LC OHC and 26oC isotherm depth. Vertical structure of the thermal layers from AXCTDs. (Shay et al. 2006)

  6. Conceptual Models • Shear • More than 8 -10 m/s implies weakening (but not immediately?) • Downshear-right convection & rainfall asymmetry (NH) • Tilted vortex dynamics • Physical mechanism of interaction (dynamic or thermodynamic?) • Annular Hurricanes • Low (or easterly) shear • Weaken gradually despite constant or cooling SST • Weaken more slowly than average • Eyewall mesovortices • Impact on pressure and wind fields • Superintensity • Boundary layer • Surface wind reduction -- mean values, variation within and between storms • Longitudinal rolls • Supergradient winds

  7. H. Georges: Analysed Surface Wind Factor - Ratio of surface wind speed to higher-level wind • Largest values (~1) in left eye-wall. • Smallest values to right. • Secondary max associated with outer rainband. |V50| / |V1500| |V50| / |V2500|

  8. More Conceptual Models • Eyewall replacements • Weakening as old eyewall dissipates • Timing and amount of weakening • Good and bad troughs • Eddy momentum transports • Associated shear • Spiral bands • Vortex Rossby Waves • Fine scale / boundary layer rolls • Potential intensity & superintensity • Oceanic heat source • Ocean heat content • Mixing and upwelling • Warm currents and eddies • Simple vs. elaborate models

  9. Role of the Loop Current

  10. Forecast Needs • Intensity • Rapid intensification or weakening • Surface wind structure • Radii to gales etc, size, asymmetry, … • Effect of small scales on damage, risk assessment, design, … • Impact on surge, wave forecasts • Rainfall distribution and amount • Track • Trochoidal oscillation, convective asymmetry, tilted vortex effects.

  11. Numerical Weather Prediction • Driving strong and sustained track improvements • Intensity • NWP slowly catching up to statistical methods. • Rapid intensification. • Structure • Fantastic research tool. • RAINEX simulations (~2 km resolution). • Ensembles • Using/interpreting/communicating the information? • How to generate? • THORPEX and TIGGE • Assimilation • Vortex initialisation (bogussing vs forward modelling). • Technical issues (balance, quality control, scales, …) • Remotely sensed data only (no recon) for much of world?

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