Recent Results from Storm Electrification Modeling

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Recent Results from Storm Electrification Modeling

• Edward Mansell
• CIMMS/Univ. of Oklahoma/NSSL, Norman, OK
• co-investigators
• Donald MacGorman, Conrad Ziegler
• National Severe Storms Laboratory, Norman, OK
• Jerry Straka, Kristin Kuhlman
• University of Oklahoma, School of Meteorology

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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)

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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)

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Electrification Options

• Five noninductive charging parameterizations
  (graupel-crystal)
• Brooks et. al (1997, AR)
• Saunders and Peck (1998, JGR)
• Saunders et al. (1991)/Helsdon et al. (2001)
• Gardiner et al. (1985)/Ziegler et al. (1991)
• Takahashi (1978,1984, JAS)
• Inductive charging (graupel-droplet)
  (Ziegler et al., 1991, JGR)

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Noninductive Charge Separation
Before
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Inductive Charge Separation
Before
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Stochastic Lightning Model
Segment-by-segment development of lightning
channels Advantage Effect of charge carried by
channels on lightning propagation is included by
recalculating the electric field via Poissons
equation Disadvantage Can become
computationally expensive for high flash rates.
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Lightning Propagation Grid
Negative leader
Positive leader
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Positive CG Flash
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Negative CG flash
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Small storm simulation (Florida)
Positive leaders
Initial Breakdown
Negative leaders
30 flashes in 1 hour
25 km
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Supercell storm simulation (STEPS)
10,000 flashes in 3 hours
80 km
(K. Kuhlman)
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Severe Bow Echo Storm
70,000 flashes in 4 hours
140 km
(J. Straka)
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What effects does inductive charging have? (in
the model, at least) Look at a multicell storm
with and without inductive charging.
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Using Takahashi noninductive charge separation
scheme
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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.
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36 Min
First cell decaying, new cell growing
No Inductive
With Inductive
NIC only
NICIC
Decaying cell
New cell
Charge density
Charge density
Wind vectors
Graupel Mix. Rat.
Inductive charging rate
Noninductive charging rate
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40 Min
New cell growing recylcing graupel from old cell
NIC only
NICIC
Charge density
Charge density
Inductive charging rate
Noninductive charging rate
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44 Min
New cell maturing has dipole charge structure
NIC only
NICIC
Charge density
Charge density
Inductive charging rate
Noninductive charging rate
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48 Min
Mature cell strong inductive charging?LPC
NIC only
NICIC
Charge density
Charge density
Inductive charging rate
Noninductive charging rate
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52 Min
Second cell mature flashes with LPC
NIC only
NICIC
Charge density
Charge density
Inductive charging rate
Noninductive charging rate
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56 Min
Second cell decaying third cell growing
NIC only
NICIC
Charge density
Charge density
Inductive charging rate
Noninductive charging rate
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60 Min
Third cell explosive growth recylces graupel
NIC only
NICIC
Charge density
Charge density
Inductive charging rate
Noninductive charging rate
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64 Min
Strong inductive charging in third cell, -CG
flashes
NIC only
NICIC
Charge density
Charge density
Inductive charging rate
Noninductive charging rate
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Time-height lightning
No inductive charging
With inductive charging

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Lightning correlations
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Positive CG flash
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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)

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Merci!Thank you!Gracias!Danke!Interrogations?
Questions?Preguntas?Fragen?
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