Recent Results from Storm Electrification Modeling

Edward MansellCIMMS/Univ. of Oklahoma/NSSL, Norman, OK

co-investigators Donald MacGorman, Conrad Ziegler National Severe Storms Laboratory, Norman, OK

Jerry Straka, Kristin KuhlmanUniversity of Oklahoma, School of Meteorology

Objectives:• Study electrification of thunderstorms• Examine differences in lightning for a

spectrum of severe storms (supercell and non-supercell)

• Compare and evaluate charge separation parameterizations

• Investigate conditions for Cloud-to-ground (CG) lightning (especially +CG)

Model Features:• Micophysics parameterization has 12

hydrometeor categories (bulk): • 2 Liquid: cloud droplets, rain• 10 Ice: cloud ice (columns, plates,

rimed), snow (aggregates), frozen drops, 3 graupel densities, 2 hail size ranges

• Explicit treatment of small ion processes (attachment, diffusion, corona emission at ground)

• 3-D Branched lightning (Mansell et al. 2002)

Electrification Options:• Five noninductive charging

parameterizations (graupel-crystal):5. Brooks et. al (1997, AR)6. Saunders and Peck (1998, JGR)7. Saunders et al. (1991)/Helsdon et al. (2001)8. Gardiner et al. (1985)/Ziegler et al. (1991)9. Takahashi (1978,1984, JAS)

• Inductive charging (graupel-droplet) (Ziegler et al., 1991, JGR)

Noninductive Charge Separation

Before After

–

+

Inductive Charge Separation

Before After

E

Segment-by-segment development of

lightning channelsAdvantage: Effect of charge carried by channels on lightning propagation is included by recalculating the electric field via Poisson’s equation:

Disadvantage: Can become computationally expensive for high flash rates.

Stochastic Lightning Model:

−∇2φ=ρε

Lightning Propagation Grid

Positive leader

Negative leader

InitialBreakdown

Intracloud flash

Positive CG Flash

Negative CG flash

Small storm simulation (Florida)

Positiveleaders

Negativeleaders

InitialBreakdown

25 km

30 flashes in 1 hour

Supercell storm simulation (STEPS)

(K. Kuhlman)80 km

10,000 flashes in 3 hours

Severe Bow Echo Storm

(J. Straka)140 km

70,000 flashes in 4 hours

What effects does inductive charging have?(in the model, at least)

Look at a multicell storm with and without inductive charging.

Using Takahashi noninductive charge separation scheme:

Environment is for a continental storm.

High CCN concentration shuts off warm rain process, so the initial precipitation develops from ice crystals.

Inductive charging causes Lower Positive Charge region, resulting in negative CG flashes.

Charge density

No Inductive

Charge density

Noninductive charging rate Inductive charging rate

36 Min With Inductive

Decaying cell

New cell

Neg. Charge to graupel

Pos. Charge to graupel

NIC only NIC+IC

Graupel Mix. Rat.

Wind vectors

First cell decaying, new cell growing

Charge density Charge density

Noninductive charging rate Inductive charging rate

NIC only NIC+IC40 Min

New cell growing; recylcing graupel from old cell

Charge density Charge density

Noninductive charging rate Inductive charging rate

NIC only NIC+IC44 Min

New cell maturing; has ‘dipole’ charge structure

Charge density Charge density

Noninductive charging rate Inductive charging rate

NIC only NIC+IC48 Min

Mature cell; strong inductive chargingLPC

Charge density Charge density

Noninductive charging rate Inductive charging rate

NIC only NIC+IC52 Min

Second cell mature; flashes with LPC

Charge density Charge density

Noninductive charging rate Inductive charging rate

NIC only NIC+IC56 Min

Second cell decaying; third cell growing

Charge density Charge density

Noninductive charging rate Inductive charging rate

NIC only NIC+IC60 Min

Third cell explosive growth; recylces graupel

Charge density Charge density

Noninductive charging rate Inductive charging rate

NIC only NIC+IC64 Min

Strong inductive charging in third cell, -CG flashes

Time-height lightningNo inductive charging

With inductive charging

Positive leaders

Negative leaders

Lightning correlations

Positive CG flash

Conclusions• Wide range of storms can be simulated• Possible importance of Inductive

Graupel-droplet charging for lower positive charge development.

• CG time-delay potentially related to graupel recycling time.

• Correlations between lightning flash rates (IC/CG) and storm properties (e.g. graupel mass, updraft volume)

Merci!Thank you!

Gracias!Danke!

Interrogations?Questions?¿Preguntas?

Fragen?