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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

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  1. 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

  2. Outline • The Data Set: In-Situ Balloon Measurements During the Brazil Balloon Campaign 2002-2003 • Case Study:A quasi-electrostatic field (QSF) model to simulate a measured lightning-driven electric field perturbation (+CG) • Prediction: Use the QSF model to predict the lightning-driven electric field at sprite altitudes • Sprite Production: How does this predicted electric field compare to the magnitude and duration needed to produce sprites?

  3. 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 the conductivity Flight 1 Trajectory and BIN CGs

  4. 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

  5. Case Study: Simulating A Large +CG Event • 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 From Pasko et al. 1997

  6. Case Study: Simulating A Large +CG Event Model assumptions: Equations Solved Numerically: • 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

  7. Vertical Electric Field Pulse for +CG data 2 sec model

  8. model data 2 sec Radial Electric Field Pulse For +CG

  9. 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 (50-80km) • 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

  10. Model Output: Predicted lightning-driven electric fields at sprite altitudes (Z=60km) 220 ms

  11. Model Output: Predicted lightning-driven electric fields at sprite altitudes (Z=70km) 22 ms

  12. Comparison to breakdown thresholds

  13. 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

  14. Contact info: E-mail: jnt@u.washington.edu Webpage: http://www.ess.washington.edu/students/jnt/

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