Electrified Simulations of Hurricane Rita (2005) with Comparisons to LASA Data

1. Electrified Simulations of Hurricane Rita (2005) with Comparisons to LASA Data Steve Guimond1,2 , Jon Reisner2, Chris Jeffery2 and Xuan-Min Shao2 1 Florida State University 2 Los Alamos National Laboratory

2. Motivation • Improve understanding and forecasting of TC intensification

3. Background Vortex Hurricane Intensification Roadmap Updraft Latent Heat Microphysics Eddy Heat and Momentum Fluxes Adjustment Balanced response Asymmetric heating Nolan and Grasso (2003) Intensity and Structure Change Adjustment Adjustment Balanced response Symmetric heating

4. Motivation • Improve understanding and forecasting of TC intensification • Convective obs hard to come by over ocean • Doppler radar coverage very sparse • Lightning fills gaps in convective monitoring ?

5. Background Vortex Hurricane Intensification Roadmap Updraft Collisions & Charging Lightning Latent Heat Microphysics Eddy Heat and Momentum Fluxes Adjustment Balanced response Asymmetric heating Nolan and Grasso (2003) Intensity and Structure Change Adjustment Adjustment Balanced response Symmetric heating

6. Motivation • Improve understanding and forecasting of TC intensification • Convective obs hard to come by over ocean • Doppler radar coverage very sparse • Lightning fills gaps in convective monitoring ? • Understand relationship between latent heating and lightning • When/where to add energy to system

7. New Research Tools • Observational component • Los Alamos Sferic Array (LASA; Shao et al. 2000) • Existing VLF/LF array • Records full EMP (allows detection of intracloud and cloud-to-ground strokes) • Lat/Lon, time • New Dual VLF-VHF 4-D lightning mapping array • Deployed along banks of Gulf of Mexico • VLF (~2000 km range) • VHF (~500 km range) • Provides precise height retrieval

8. New Research Tools • Theoretical component • Advanced atmospheric model HIGRAD (Reisner et al. 2005) • Compressible Navier-Stokes, non-hydrostatic, bulk or explicit microphysics • Differentiable (smooth) numerics with greatly reduced time errors (option) • Coupled to electrification model (Mansell et al. 2005) • Non-inductive collisional charge separation (Saunders) • Lightning discharge model requires significant tuning • Flash initiated when EF exceeds “floor” • What is a good “floor” for hurricanes? • Limit “floor” to ~50 kV/m for reasonable results

9. Do Eyewall Hot Towers Produce Lightning? • Next slides… • ER-2 Doppler Radar observations of Hot Towers • Linear Depolarization Ratio (LDR) • particle canting angle or asymmetry • dielectric constant (i.e. wet or dry) • Retrieved vertical velocities (nadir beam) • Lightning Instrument Package (LIP) • Aircraft (20 km) electric field mills (x,y,z components) • ~1 s sampling, ~200 m horizontal resolution

10. Hot Tower #1: CAT 2 Dennis (2005) -8 to -15 dB large, wet, asymmetric ice to large, wet snow aggregates -13 to -17 dB  medium, wet graupel or small hail -18 to -26 dB  small, dry ice particles to dry, low density snow

11. Hot Tower #2: CAT 4 Emily (2005) -8 to -15 dB large, wet, asymmetric ice to large, wet snow aggregates -13 to -17 dB  medium, wet graupel or small hail -18 to -26 dB  small, dry ice particles to dry, low density snow

12. 3 Hours Into Simulation Hurricane Rita Simulations • Current configuration • Grid • 1,980 km on a side; 4 km inner mesh, stretch to 20 km • 35 m stretching to 15 km • Relaxation boundary conditions • Weak, top gravity wave absorber • F plane • Initialization procedure • Barotropic vortex, max wind of 40 m/s • Initialize mass from Key West 88D reflectivity • Storm-centered, gridded, native 1 km • Below melting  rainwater  saturate lower levels • Above melting  graupel or snow  hydrometeor drag, phase changes • Gaussian water vapor function from eyewall to ~200 km radius • ECMWF operational analyses for large scale • Satellite SSTs, High-res topography

13. HIGRAD vs. LASA Observations Model

14. Rainwater mixing ratio Initializing with LASA data

15. Potentially relevant work • Understand the non-linear response of observed vortices to retrieved heating • Airborne Dual-Doppler Radar: Hurricane Guillermo (1997) • Latent heat retrieval (Guimond 2008) • What spatial/temporal scales of heating does the hurricane “feel” ? • Balanced adjustment at 100 m vs. 2 km • Are small scale details of lightning necessary to capture intensification? • Governed by model grid cells • Is bulk heating sufficient?

16. EDOP P-3

17. Conclusions and Future Work • New area of research with physics not well understood • Not all deep convection is created equal • Lightning discharge processes? • How to correctly initialize hurricane? • Radar is good, but impractical • Use LANL data (initialization and assimilation) • How is lightning tied to latent heating? • Comparisons shed light on future simulations • Need broader wind field • Need better rainband initialization • Beta plane

18. Acknowledgments • LANL Hurricane Lightning Team References • Reisner et al. (2005) • Mansell et al. (2005) • Molinari et al. (1999) • Squires and Businger (2008)

19. 4 hours into simulation Vertical Velocity (m/s) Ice (g/kg) Graupel (g/kg) Cloud Liquid Water (g/kg) Some Model Results