30 th Conference on Hurricanes Summary

1. 30th Conference on Hurricanes Summary www.cawcr.gov.au Jeff Kepert, Kevin Tory and Sally Lavender HIW Team Meeting 6 June 2012

2. Overview • Climate Stuff • Climate change • Seasonal prediction • TCs role in climate • Intensity change • Catastrophe modelling • Structure and structure change • Environmental interaction • BL & surface wind, eyewall, eye • Size change, symmetric/asymmetric • Extratropical transition • Ensemble forecasting, data assimilation and targeting (IFEX, HFIP) • Tropical cyclogenesis • Historical perspectives • Tropical cyclone landfall and land interaction • Concentric eyewalls and eyewall replacement cycles • Operational issues • Numerical modelling • Field experiments • PREDICT, GRIP, DYNAMO, CINDY, ITOP • Rainbands and precipitation • Remote sensing The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

3. Secondary eyewall formation • Prevailing theory: • vortex Rossby waves transfer momentum out to their stagnation radius (~3xRMW) and accelerate the flow there • Agree: • Menelaou: Empirical normal modes and EP flux => acceleration at radius where SEF occurs. • Gadoury: Need high grid resolution as this allows a thinner PV ring at the eyewall, which affects the VRWs • Disagree: • Huang, Abarca: Expansion of outer wind max, nonlinear BL processes • Corbosiero: VRWs matter but because they redistribute PV to the SEF radius, not because they accelerate the wind. • Leroux: Environmental interaction initiated the ERC • Fence-sit: • Wu: Successful simulation but sensitive to DA, data denial experiments can weaken or eliminate the SEF. The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

4. Data assimilation and NWP for TCs • Two years ago, this session was awful! Now much better • there is a lot to be said for not violating theory! • Lots of talks on ensemble-based DA • We are almost unique in using 4D-Var • ACCESS-TC is extremely good • No-one is doing better on track stats (although different basins) • Many are doing significantly worse at track forecasting • We lag significantly on diagnostics/verification • Number of available people • Should we collaborate (shamelessly borrow) and use others’ packages? • Opportunities for collaboration • PME with NRL, ONR • Exchange of forecasts, initial conditions, observations, … (resources!) The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

5. Boundary layer and air-sea exchange • Turbulence parameterisation: • Gopal: Halves K and significantly improves HWRF forecasts (but introduces internal inconsistency) • Gao BL rolls: Uses 2D-LES “superparameterisation” to get rolls when Ri<1/4, does not couple back to simulation • Surface layer: • Zachry: near-shore CD is higher than deep water (younger waves), inundation reduces “land” CD • Rastigejev: CD cap is because spray quashes TKE • Powell: used asymmetry in “white water” to estimate stress and CD; CD highest on left of storm, and possibly stress also The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology

6. Observations • N Atlantic reconnaissance • Airborne Doppler radar wind retrievals are on the web! • Resource for assimilation, verification, diagnostic studies • E.g. Rogers RI study: RI is favoured by • ring vorticity, not monopole • low outer core vorticity and inertial stability • deeper inflow layer • stronger eyewall updraft especially above 6 km • longer tail on pdf of eyewall updrafts (more convective bursts in eyewall) • E.g. Reasor environmental impacts on TC structure and intensity using P3 tail Doppler radar The Centre for Australian Weather and Climate ResearchA partnership between CSIRO and the Bureau of Meteorology