Interaction of Lightning Electromagnetic Pulse with the Ionosphere

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The effect of lightning at the ground is obvious, such as when a tree is struck. In the other direction, lightning also can have an impact on the layer of the upper atmosphere known as the ionosphere. The ionosphere is high above the Earth's surface and is strongly affected by solar radiation. One of the practical impacts of the ionosphere from the human perspective is the ionosphere's role in affecting the propagation of radio waves. Studies have determined that lightning can affect the ionosphere through perturbations known as elves, halos, and sprites. The research funded by this award will focus on the impact that lightning has on lowering the height of the ionosphere. A graduate student will be funded by this award, furthering the development of the next generation of scientists.The researchers propose to examine the occurrence of different patterns in ionospheric reflection height change within individual lightning flashes under both daytime and nighttime conditions. This will require acquisition of additional data (at least several hundreds of events), particularly at night. The researchers expect that many observed effects are influenced by lightning discharge intensity. The work will contain an attempt at modeling elves in order to explain the inferred lowering of the reflection height. A number of other issues will also be examined: (1) changes in reflection height as a function of causative-return-stroke peak current and preceding interstroke interval, (2) correlation between magnitudes of the first sky wave and ground wave, and (3) effect on ionospheric reflection height of compact intracloud discharges (in cases when they occur in pairs). The researchers will also search for differences in E field frequency spectra that could be attributed to the inferred differences in effective reflection heights.