We have combined analyses of over 1000 high altitude aircraft observations of electrified clouds with diurnal lightning statistics from the Lightning Imaging Sensor (LIS) and Optical Transient Detector (OTD) to produce an estimate of the diurnal variation in the global electric circuit. Using basic assumptions about the mean storm currents as a function of flash rate and location, and the global electric circuit, our estimate of the current in the global electric circuit matches the Carnegie curve diurnal variation to within 4% for all but two short periods of time. The agreement with the Carnegie curve was obtained without any tuning or adjustment of the satellite or aircraft data. Mean contributions to the global electric circuit from land and ocean thunderstorms are 1.1 kA (land) and 0.7 kA (ocean). Contributions to the global electric circuit from ESCs are 0.22 kA for ocean storms and 0.04 kA for land storms. Using our analysis, the mean total conduction current for the global electric circuit is 2.0 kA

Bailey, J. C.

Bateman, M. J.

Blakeslee, R. J.

Mach, Douglas M.

NASA Technical Reports Server

XIV International Conference on Atmospheric Electricity, August 08-12, 2011, Rio de Janeiro, Brazil 
 
  
Global Electric Circuit Diurnal Variation Derived From 
Storm Overflight and Satellite Optical Lightning Datasets∗
 
 
D. M. Mach1*, R. J. Blakeslee2, M. J. Bateman3, J. C. Bailey
 
4  
1. University of Alabama in Huntsville, Huntsville, Alabama 35899, USA, e-mail dmach@nasa.gov  
2. NASA Marshall Space Flight Center, Huntsville, Alabama 35812, USA, e-mail rich.blakeslee@nasa.gov 
3. Universities Space Research Association, Huntsville, Alabama 35803, USA, e-mail monte.bateman@nasa.gov 
4. University of Alabama in Huntsville, Huntsville, Alabama 35899, USA, e-mail jeffrey.c.bailey@nasa.gov  
 
ABSTRACT: We have combined analyses of over 1000 high altitude aircraft observations of electrified clouds 
with diurnal lightning statistics from the Lightning Imaging Sensor (LIS) and Optical Transient Detector (OTD) 
to produce an estimate of the diurnal variation in the global electric circuit.  Using basic assumptions about the 
mean storm currents as a function of flash rate and location, and the global electric circuit, our estimate of the 
current in the global electric circuit matches the Carnegie curve diurnal variation to within 4% for all but two 
short periods of time.  The agreement with the Carnegie curve was obtained without any tuning or adjustment 
of the satellite or aircraft data.  Mean contributions to the global electric circuit from land and ocean 
thunderstorms are 1.1 kA (land) and 0.7 kA (ocean).  Contributions to the global electric circuit from ESCs are 
0.22 kA for ocean storms and 0.04 kA for land storms.  Using our analysis, the mean total conduction current 
for the global electric circuit is 2.0 kA.  
1. INTRODUCTION 
We have been measuring the electric field and atmospheric conductivity over electrified clouds for many 
years [e.g., Blakeslee et al, 1989; Bailey et al., 1999; Bateman et al., 2010].  By combining the mean currents 
and flash rates associated with land/ocean storms derived from aircraft overflights [Mach et al., 2010] with the 
diurnal variations in global lightning rates derived from satellite observations [e.g., Bailey et al., 2007], we are 
able to estimate the total current and diurnal variation in the global electric circuit [Mach et al., 2011].  The 
resultant diurnal variation closely matches the Carnegie curve.  The two datasets used to derive our estimate of 
the global electric circuit are totally independent and the analysis and results include the contributions from both 
thunderstorms and electrified shower clouds (ESCs). 
2. INSTRUMENTATION 
2.1 Overflight dataset 
The 1040 overflights of electrified clouds were obtained by three different aircraft.  The first was the 
NASA ER-2 aircraft [Heymsfield, et al., 2001], the second was the Altus unmanned aerial vehicle [Farrell et al., 
2006], and the third was the NASA Global Hawk [Bateman et al., 2010].  All aircraft were directed to target 
storms based on mission objectives and remote sensing data.   
The electric field vector (e.g., EX, EY, EZ
                                                        
∗ Correspondence to:  
, and Q) was determined by the analysis of observations from the 
field mills (electric field meters) [Bateman et al., 2007] on the aircraft.  The conductivity data were derived 
Douglas Mach, UAHuntsville, NSSTC, 320 Sparkman Drive, Room 4001, Huntsville, AL 35805, USA, Email: dmachr@nasa.gov 
https://ntrs.nasa.gov/search.jsp?R=20110016037 2019-08-30T17:27:12+00:00Z
XIV International Conference on Atmospheric Electricity, August 08-12, 2011, Rio de Janeiro, Brazil 
 
  
from atmospheric model data [Blakeslee, personal communication, 2011] (Global Hawk) or from Gerdien 
capacitor conductivity probes [Mitchell et al., 1990; Bailey et al., 1999] (ER-2 and Altus).  More detailed 
information about the instrumentation is contained in Mach et al. [2009; 2010]. 
2.2 Satellite Dataset 
The satellite-based data are from the Lightning Imaging Sensor (LIS) and Optical Transient Detector (OTD) 
instruments.  Details of the instruments are contained in other studies [e.g., Christian et al. 1996; Koshak et al., 
2000].  The global lightning diurnal variation (in UTC) from the LIS/OTD satellite data comes from Bailey et 
al. [2007]. 
3. RESULTS 
3.1 Overflight data 
We analyzed 1040 overflights of electrified clouds collected over a 17 year period from 1993 to 2010 (Table 
1).  The overflights were divided into four groups depending on their location (land, ocean) or electrical activity 
(lightning, ESC).  Land storms with lightning have a mean current of 0.95 A while ocean storms with lightning 
have a mean current of 1.7 A.  The mean flash rate for land storms with lightning is 2.2 flashes min-1 and the 
mean flash rate for ocean storms with lightning is 0.8 flashes min-1
 
 [Mach et al., 2010].  Land ESCs have a 
mean current of 0.17 A and ocean ESCs have a mean current of 0.41 A [Mach et al., 2010]. 
Table 1 Field program overflight statistics 
Campaign (month, year) Lightning No Lightning Land Ocean 
TOGA-COARE (Jan-Mar, 1993) 14 64 19 59 
CAMEX-1 (Sep-Oct, 1993) 13 25 15 23 
CAMEX-2 (Aug-Sep, 1995) 29 7 11 25 
TEFLUN-A (Apr-May, 1998) 39 8 43 4 
TEFLUN-B (Aug-Sep, 1998) 35 3 35 3 
CAMEX-3 (Aug-Sep, 1998) 37 38 19 56 
TRMM-LBA (Jan-Feb, 1999) 192 63 255 0 
CAMEX-4 (Aug0Sep, 2001) 52 35 22 65 
ACES (Aug, 2002) 76 22 80 18 
TCSP (Jul, 2005) 55 43 15 83 
GRIP (Aug-Sep, 2010) 65 125 14  176 
Totals 607 433 528 512 
 
3.2 Satellite data 
To create the diurnal lightning rate data, Bailey et al. [2007] analyzed 5 years (April 1995 to March 2000) of 
OTD data and 8 years (December 1997 to December 2005) of LIS data.  Gridded flash products (2.5º x 2.5º 
resolution bins) are used in the analyses.  The flash locations and rates were divided into the major continents 
(i.e., land) and ocean data.  For our analysis, we combined the UTC diurnal variation of all continents into a 
single “land” diurnal variation and used the remaining ocean contribution as our “ocean” diurnal variation. 
3.3 Combined data 
Combining our mean flash rates for all ocean and land storms with the global diurnal flash rate statistics 
from LIS/OTD, we can estimate the number and total currents produced by land and ocean storms with and 
XIV International Conference on Atmospheric Electricity, August 08-12, 2011, Rio de Janeiro, Brazil 
 
  
without lightning (Figure 1).  The mean conduction current from lightning producing land storms is 1.1 kA 
while the mean conduction current from lightning producing ocean storms is 0.7 kA.  The mean current from 
ocean ESCs is 0.22 kA and the mean current from land ESCs is 0.04 kA.  The total mean conduction current is 
2.0 kA.  Our analysis indicates that the largest contributing group of storms is land thunderstorms which have 
an average count of about 1100.  The next largest group of storms is ocean ESCs (mean storm count of 530).  
This is followed by ocean thunderstorms (mean storm count of 390).  The smallest group is land ESCs (mean 
storm count of 330). 
3.4 Comparison to Carnegie curve 
Comparing the relative magnitudes of the 
Carnegie curve with the total current diurnal 
variations produces an interesting result 
(Figure 1).  The two diurnal variations agree 
to within 4% except during two brief periods.  
We assume that the diurnal variation of ESCs 
(not measured by LIS/OTD) follows the 
diurnal variation of lightning storms (measured 
by LIS/OTD) and that the relative occurrence 
of lightning storms and ESCs are close to what 
we found in our overflight data. 
4. DISCUSSION 
Using these data sets (LIS/OTD land/ocean lightning diurnal variations and storm overflight mean currents 
and lightning rates) alone, we are able to create an estimate of the diurnal variation in the global electric circuit 
generator that is mostly within 4% of the Carnegie curve without any ad hoc assumptions or other datasets.  As 
past studies have demonstrated [e.g., Whipple, 1929; Bailey et al. 2007; Williams, 2009], lightning alone is a 
poor proxy for the global electric circuit, producing a diurnal variation (35%) that is much greater than the 
variation in the fair weather field (10-20%).  However, as our results show, most of the observed amplitude 
variation of the Carnegie curve is accounted for by correctly including the differences that exist in the mean 
currents and flash rates between land and ocean thunderstorms [e.g., Mach et al., 2009; 2010; 2011].   
Although the mean current values from electrified storms without lightning are much less than either land or 
ocean thunderstorms, the mean current from ESCs is still significantly different than zero (0.13 A for land storm 
and 0.41 A for ocean storms).  Overall, ESCs contribute 13% of the total current, with 11% due to ocean storms 
and only 2% from land-based storms.  When we rank the contributions of the four categories (land with 
lightning, ocean with lightning, ocean without lightning, land without lightning), the dominant source of current 
is from land thunderstorms, which can explain why prior estimations of the global circuit using only lightning 
producing land storms matched the phase of the Carnegie curve but not the amplitude variation. 
5. CONCLUSIONS 
To reconcile the past differences found between the diurnal variations in the fair weather electric field (i.e., 
Carnegie curve) and lightning based estimates of the global electric circuit [e.g., Whipple, 1929; Williams, 2009], 
we included the differences between land and ocean storms and the contributions from ESCs.  Ocean storms 
have less lightning than land storms, but have greater currents on a storm-by-storm basis.  The differences 
between land and ocean storms account for nearly all of the amplitude differences between the Carnegie curve 
and the purely lightning-based diurnal variation.  ESCs account for the rest of the amplitude variation between 
Figure 1. Global electric circuit total generator current (left 
axis) plus Fair Weather Electric Field (Carnegie curve, 
right axis).  
 
XIV International Conference on Atmospheric Electricity, August 08-12, 2011, Rio de Janeiro, Brazil 
 
  
the Carnegie curve and single parameter lightning based diurnal variations.  We found that ESCs produce mean 
currents one-fourth to one-fifth the amplitude of the mean current of storms with lightning [Mach et al., 2010].  
Once these storms are included in the global electric circuit estimation, the resultant global circuit diurnal 
variation derived from the combined aircraft storm electric current measurements and the satellite-based diurnal 
lightning statistics is mostly within 4% of the Carnegie curve.  When we increase the ESC contribution by a 
factor of between 3 and 4, our diurnal curve has a slightly better match to the Carnegie curve than our “untuned” 
data.  One thrust of any future work will be in the area of determining the distribution and diurnal variation in 
ESCs. 
ACKNOWLEDGMENTS 
The authors gratefully thank NASA’s Earth Science Enterprise (ESE) for support of this research.  Data used 
in this study were taken from the LIS/OTD gridded climatologies, available for order from the Global Hydrology 
Resource Center (http://ghrc.msfc.nasa.gov). The LIS/OTD instrument team was funded by the NASA Earth 
Science Enterprise (ESE) Earth Observing System (EOS) project. 
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Global Electric Circuit Diurnal Variation Derived from Storm Overflight and Satellite Optical Lightning Datasets

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