Lightning-Driven Electric Fields in the
Stratosphere: Comparisons Between In-Situ
Measurements and Quasi-Electrostatic
Field Model
Jeremy N. Thomas, Robert H. Holzworth, Michael P.
McCarthy, Nimisha Ghosh Roy, Natalia N. Solorzano,
Osmar Pinto, Jr., and Mitsuteru Sato
UW – USU – INPE collaboration
Supported by US: NSF and Brazil: FAPESP
ELF Data supplied by Tohoku University Japan
Outline
I.
The Data Set: In-Situ Balloon Measurements
During the Brazil Balloon Campaign 2002-2003
II. Case Study: A quasi-electrostatic field (QSF)
model to simulate a measured lightning-driven
electric field perturbation (+CG)
III. Prediction: Use the QSF model to predict the
lightning-driven electric field at sprite altitudes
IV. Sprite Production: How does this predicted
electric field compare to the magnitude and
duration needed to produce sprites?
Data Set: In-Situ Balloon Measurements
• 38 electric field changes greater
than 10 V/m were measured above
30km in alt.
• Location of strokes: Brazilian
Integrated Ground Based Lightning
Network (BIN)
• Sprites not ruled out, although none
were confirmed optically
• The balloon payload also measured
Flight 1 Trajectory and BIN CGs
the conductivity
Case Study: A Large +CG Event
• Two positive cloud-to-ground (+CG) strokes 150ms apart
34 km hor. distance from the balloon payload (alt=34km)
• Charge moment: 436 C-km estimated from remote ELF
(extremely low frequency) magnetic field measurements
(M. Sato)
ELF Data from Syowa, Antarctica
Case Study: Simulating A Large +CG Event
From Pasko et al. 1997
• An axi-symmetric stroke
centered numerical simulation
of the quasi-static electric field
change after a +CG based on
the work of Pasko et al., JGR,
102, 4529, 1997
• Important input parameters:
charge moment, cloud charge
distribution, discharge time,
and atmospheric conductivity
profile
Case Study: Simulating A Large +CG Event
Equations Solved Numerically:
Model assumptions:
• No horizontal currents: The
cylindrical symmetry prevents
this.
• The atm. conductivity is not
affected by the lightning stroke
• No magnetic field perturbations
• Only the change in electric field
due to +CG is modeled, not the
background field before and after
the +CG
Vertical Electric Field Pulse for +CG
data
2 sec
model
model
data
2 sec
Radial Electric Field Pulse For +CG
Predicting Electric Fields at Sprite Altitudes
• The parameters that best fit the quasi-static field
model to the balloon data are used to predict the
electric field perturbation at sprite altitudes (5080km)
• These electric field pulses are compared to the
electrical breakdown thresholds (conventional and
relativistic)
• The duration of the pulse is compared to the
duration of observed sprites
Model Output: Predicted lightning-driven electric
fields at sprite altitudes (Z=60km)
220 ms
Model Output: Predicted lightning-driven electric
fields at sprite altitudes (Z=70km)
22 ms
Comparison to breakdown
thresholds
Conclusions
• For the +CG event studied, the electric field never
surpasses the conventional electrical breakdown
threshold at sprite altitudes but does surpass the
relativistic breakdown threshold.
• The duration of the electric field pulse at sprite altitudes
(22 ms at 70km) is comparable to the time duration of
sprites.
• Better electron conductivity profiles (dependent on
location, weather, and solar activity) are needed to more
accurately model these electric field pulses at sprite
altitudes
Contact info:
E-mail: jnt@u.washington.edu
Webpage: http://www.ess.washington.edu/students/jnt/