Impact of electrified clouds to the GEC - University of Colorado at ...

A Short Review of Thunderstorm 

Electrification 

Impact of electrified clouds to 

the GEC 

Wiebke Deierling

Thunderstorm Electrification 

Strong field, laboratory and modeling evidence suggests that 

precipitation-based charging is the primary candidate for 

thunderstorm electrification. 

Precipitation-based charging can be divided into: 

‣ Inductive charging 

‣ Non inductive charging 

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Inductive charging mechanisms: 

‣ Rebounding collisions between hydrometeors that became 

polarized by an existing vertical electric field. 

‣ Role of inductive 

charging not entierly 

known but it is 

hypothesized that it can 

intensify electrification 

once it is initially achieved 

by other mechanisms. 

From MacGorman and Rust, 1998 

3

Non inductive charging 

mechanism: 

‣ Independent of an ambient 

electric field 

‣ Charging occurs in strong 

updraft within mixed phase 

region 


‣ Rebounding collisions 

between riming ice particles 

(e.g. graupel pellets) and ice 

crystals in presence of 

supercooled liquid water 

From Dye 2011; 

‣ Sign and magnitude of charge transfer depends on effective liquid 

water content, temperature, size of ice, impact velocity, growth regime 

(diffusion or sublimation), contaminants in ice 

4


‣ Inductive charging can generally explain the thunderstorm charge 

structure 

In situations where 

LWC = 1 g/m 3 , then: 

- graupel becomes 

negatively charged 

around -15C and 

ice crystals become 

positively charged 

- reverse occurs between 

0 to -5C 

Gravitational sorting of hydrometeors 

leads to charge separation 

Saunders (1993) 

5

NASA’s Airborne Field Mill Project 2000-01 

Charging without liquid water in thunderstorm anvils 

Flight 

track at 

10 km 

dBZ at FL 

Total lightning 

Reflectivity curtain along 

A/C track. 

Electric Field (kV/m) 

Total Field == bold line 

Vertical E == light line 

The abrupt increase of electric field at ~10 dBZ! 

National Security Applications Program 

Research Applications Laboratory 

ATEC-4DWX Forecasters’ Training 

Courtesy: 29-31 March 2011, Jim Boulder, Dye Colorado 6


From:http://www.nssl.noaa.gov/primer/lightni 

ng/ltg_basics.html 

From Encyclopedia Britannica 

7


from Krehbiel, 1986 

MCS 

Charge structures 

can be more 

complicated…. 

Height of charge 

layers vary by storm 

type and during 

lifecycle of storm 

Inverted polarity 

storms, as observed 

at Tibetean Plateau 

and High Plains 

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Cloud Type 

Inside thunderstorms 

Initiation of natural lightning 

Breakdown in clear air 

Shower clouds (no ltg) 

Anvil and debris clouds 

Layered Clouds (e.g. 

Nimbostratus, Stratocumulus) 

Fair weather electric field close 

to surface, no clouds 

Typical Electric Field Value 

~ 70-200 kV/m 

~ 200 kV/m 

~ 3000 kV/m 

~ 0.1-100 kV/m 

~ 10 - 100 kV/m 

~ 1-30 kV/m 

~ 0.1 kV/m 

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The Role of Electrified Clouds in the Global 

Electric Circuit 

Wiebke Deierling, Tina Kalb 

10

Thunderstorms & Global Electric Circuit 

Beginning of 20 th Century 

- Global electric field measurements 

- Daily variations of fair weather 

electric field with universal time 

- Thunderstorm activity similar trend 

to Carnegie curve 

- Assume that fair weather field is 

proportional to current generator in 

GEC and that current generator is 

supplied by thunderstorms 

11


Thunderstorms thought to play a major role as generators of 

the earth’s fair weather circuit. 

From:http://thunder.msfc.nasa.gov/primer/primer3.html 

12

Global Lightning Map 

Data from space-based optical sensors reveal the 

distribution of worldwide lightning strikes. 

Units: flashes/km 2 /yr. Image credit: NASA/MSFC. 

13


Diurnal variation of the fair weather field (blue curve) derived from ocean measurements 

(Carnegie curve), thunder day statistics (green curve) from Whipple and Scrase [1936], and 

diurnal variation of flash rates (red curve) derived from Lightning Imaging Sensor (LIS) and 

Optical Transient Detector (OTD) data. Note that the phase and shape of the three plots are very 

14 

similar, but the amplitudes are quite different. Figure 1 out of Mach et al. 2011.


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Current Flow in Thunderstorms 

Conduction currents 

from cloud tops, net 

positive current toward 

electrosphere 

Transient currents 

Precipitation, Corona (or point-discharge) 

and Lightning current, negative & positive 

current measured at ground 

Convection current 

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Krider and Muser (1982) propose to measure total current flow in a 

thunderstorm by determining the Maxwell current density, proposing 

that it is directly coupled to the meteorological structure and/or the 

kinematics of the cloud. Three regions: Below, inside and above a storm 

Maxwell current density in thunderstorm: J M =J point_discharge + J convection + 

J precipitation + J lightning + J conduction + e deltaE/deltat(displacement current) 

ER2 conductivity and electric field measurement above T-storm yielded 

average conduction current estimates 1.7A (Blakeslee et al. 1989) 

Muehleisen 1977, Williams and Satori (2004) suggested that this 

number is too large because other non-thunderstorm generators such 

as rain clouds contribute as well 

Still open question: Specific contributions of different types of clouds 

to GEC 

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Recent conduction current estimates from Mach et al.2009,2010 and 

2011, 850 overflights of electrified clouds were obtained from both 

the NASA ER‐2 aircraft and the Altus unmanned aerial vehicle (at 15- 

20 km altitude) 

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The mean total conduction current for the global electric circuit is 2.0 kA. Mach et al. 2011 

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- Mach et al. [2009, 2010] found that land storms had greater lightning rates 

than ocean storms but smaller mean conduction (Wilson) currents. 

- Mach et al. [2009, 2010] also found that electrified, nonlightning‐producing 

storms do make a measureable contribution to the global electric circuit. 

- The results of Mach et al. [2010] indicate that using a single global mean 

for storm current and lightning rate (i.e., one that does not account for land 

and ocean differences), will not likely be able to duplicate the Carnegie 

curve. 

20


Diurnal variation of the fair weather field (blue curve) derived from ocean measurements 

(Carnegie curve), thunder day statistics (green curve) from Whipple and Scrase [1936], and 

diurnal variation of flash rates (red curve) derived from Lightning Imaging Sensor (LIS) and 

Optical Transient Detector (OTD) data. Note that the phase and shape of the three plots are very 

21 

similar, but the amplitudes are quite different. Figure 1 out of Mach et al. 2011.


Mach et al. 2010: “Cloud top heights and flash rates are not 

sufficient to characterize the storm’s Wilson current. More 

complicated rules and analyses, such as those using updraft and 

mixed-phase region characteristics [e.g., Williams et al., 1992; 

Zipser and Lutz, 1994; Hood et al., 2006; Deierling and Petersen, 

2008] are more likely to find strong relationships to storm currents 

and lightning rates.” 

Recall that lightning climatology did not represent Carnegie Curve 

fully 

ER-2 and Altus Wilson current estimates not global 

To get better global representation Mach et al. 2011 combines LIS- 

OTD lightning climatologies and Wilson current estimates from 

overflights


Figure 8. Global electric circuit total generator current. The curves are calculated by 

combining the LIS‐OTD data and our storm overflight data. The mean current for land 

ESCs is 0.04 kA. The mean currents for ocean ESCs and thunderstorms are 0.22 and 

0.65 kA, respectively. The mean current for land thunderstorms is 1.13 kA, and the 

total mean current is 2.04 kA. From Mach et al. 2011 

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Combined Overflight data and OTD/LIS data : Mach et al. 2011 

Storms with lightning 

Storms with and without lightning 

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Fraction differences from Carnegie curve, Mach et al. 2011 

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Underrepresentation of inverted dipole thunderstorms, MCS’s (larger 

scale than 10-30 km, more like 100-200km with two parts to it), winter 

storms, non-lightning producing cloud distribution (some may be larger 

scale too?)? 

Conduction currents computed in Mach et al. around active T-storm part 

(30 km) 

Mach et al. suggest looking at better distribution of non-lightning 

producing clouds 

Can we have a better representation of them to ultimately get a better 

estimates of sources of conduction currents?


Part of NCAR Activities and Plans: 

-Develop model parameterizations for conduction currents for different 

electrified cloud types, 

- Be involved in validating output with available observations and 

- Investigate how the spatial-temporal variability of electrified clouds 

translate to GEC characteristics. 

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Current work: 

- Extend Doug Mach’s study in collaboration with Doug and compare 

coincident storm microphysical and dynamical properties derived 

from radar data with his estimated conduction currents to investigate 

if we can improve characterizations for various electrified clouds 

- Link with CU work that focuses on more global data sets from 

TRMM and model reanalysis data 

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Future work: 

-Produce a 2D global map of current sources from electrified clouds, 

following Mach et al. [2010, 2011], for use in the 3DGSM. 

-WRF- cloud resolving model: investigate the ability of several model 

cloud parameters, such as ice mass fluxes, updraft characteristics, ice 

mass and cloud top height to represent the total electric currents 

-Global non-cloud-resolving model: Investigate the prediction of electric 

currents by a reduced set of model variables and compare them to 

electric currents from the cloud-resolving model (coincident data 

available) 

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Impact of electrified clouds to the GEC - University of Colorado at ...

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