Electrified Simulations of Hurricane Rita (2005) with Comparisons to

LASA DataSteve Guimond1,2 , Jon Reisner2,

Chris Jeffery2 and Xuan-Min Shao2

1 Florida State University2 Los Alamos National Laboratory

Motivation• Improve understanding and

forecasting of TC intensification

Latent Heat

Updraft

Background Vortex

Microphysics

Hurricane Intensification

Roadmap

Eddy Heat and

Momentum Fluxes

Balanced response

Adjustment

Symmetric heating

Asymmetricheating

Adjustment

Balanced response

Adjustment

Intensity and

Structure Change

Nolan and Grasso (2003)

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 ?

Latent Heat

Updraft

Background Vortex

Microphysics

Hurricane Intensification

Roadmap

Eddy Heat and

Momentum Fluxes

Balanced response

Adjustment

Symmetric heating

Asymmetricheating

Adjustment

Balanced response

Adjustment

Intensity and

Structure Change

Nolan and Grasso (2003)

Lightning

Collisions &

Charging

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

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

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

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

10log vh

vv

ZLDR

Z

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

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

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

3 Hours Into Simulation

HIGRAD vs. LASA

Model

Observations

Initializing with LASA data

Rainwater mixing ratio

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?

P-3

EDOP

• 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

Conclusions and Future Work

Acknowledgments• LANL Hurricane Lightning Team

References• Reisner et al. (2005)• Mansell et al. (2005)• Molinari et al. (1999)• Squires and Businger (2008)

Some Model Results

4 hours into simulation

Cloud Liquid Water (g/kg)

Vertical Velocity (m/s)

Graupel (g/kg)

Ice (g/kg)