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) Defining Structure from Satellite Data (C. Velden) Field Experiments (P. Black and S. Chen)

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

Eyewall Replacement Cycle Hurricane Wilma

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

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

Conceptual Models Shear –More than 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

H. Georges: Analysed Surface Wind Factor - Ratio of surface wind speed to higher-level wind |V 50 | / |V 1500 | Largest values (~1) in left eye- wall. Smallest values to right. Secondary max associated with outer rainband. |V 50 | / |V 2500 |

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

Role of the Loop Current

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.

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?