IntroductionLightning discharges are known to be a source of high amplitude, broadfrequency electromagnetic radiation. These electromagnetic waves cancause perturbations in electron densities in a region of the upperatmosphere called the ionosphere. The changes in electron density arecaused by either ionization from quasi-electrostatic fields or from inducedenergetic electron precipitation from the magnetosphere. The effect ofthese variations is more pronounced at nighttime due to nighttimeelectron densities being much lower when compared to daytime levels.Because changes in electron density affect the conductivity of theionosphere, nighttime lightning discharges can perturb the amplitude andphase of VLF communication signals propagating through the Earth-ionosphere waveguide. Most past work in this area has involved uniquepropagation paths between a transmitter and receiver. Modeling of suchperturbation events often involves uncertainty since the perturbedionospheric profile cannot be uniquely determined. In this work wefocused on overlapping VLF propagation paths where signals from twodifferent VLF transmitters share a common path to a receiver. This allowsfor the geographic area of the overlapping path to be simultaneouslydiagnosed with two signals with different mode content. Observationsshow that a lightning induced perturbation on the overlapping path canhave a large effect on the amplitude or phase of one signal, while leavingthe other wave relatively unaffected. The Long Wave Prediction Capability(LWPC) software package is used to simulate this phenomenon by alteringthe effective conducting height of the ionosphere near the location of aknown nighttime lightning strike.

LWPC Modeling of Lightning Induced Energetic Electron Precipitation Ionospheric Perturbations Using Overlapping VLF Propagation PathsChad Renick, Mark Golkowski

Department of Electrical EngineeringCU Denver Electromagnetics and Plasma Physics Group

Image of Solar Terminator on Earth

ConclusionsGood agreement has been found between the results of LWPC simulation andobservational measurements. It has been shown that using VLF remote sensingtechniques on overlapping paths of propagation provides additional constraintsto determine the condition of the perturbed ionosphere and a more accuratemodel of how lightning affects ionospheric electron densities. Using LWPCsimulation to analyze the how the effective conducting height of the ionosphereand the sharpness of the ionospheric profile effect the amplitude and phase ofVLF waves propagating in the earth-ionosphere waveguide has led to a morecomplete understanding of why ionospheric disturbances often have differenteffects on individual VLF waves traveling on similar paths. Thus, usingoverlapping paths of propagation has more definitively modeled dynamicionospheric conditions caused by early-fast lightning events and lighteninginduced electron precipitation events.

Image 2: Depiction of VLF waves bouncing off of the ionosphere

June 13th, 2016 06:41:27.818 385 [kA] Event

Lightening Induced Electron Precipitation Event

Early – Fast Lightening Event

Observations from April 26th, 2016

Event #1: 08:03:55.792 +222 [kA] Event #2: 08:50:44.463 -220 [kA]

Observations from June 13th , 2016

Event #3: 08:41:27.818 -385 [kA]