Understanding the Dynamics of Upward Propagating Sprite Streamers

Recent high speed photographic images have recorded sprites at 100,000 fps, showing upward propagating sprite streamers interacting with the ionosphere in detail never before seen. These new data, along with the knowledge of streamer dynamics from modeling and experiment, are making it possible to probe the lower ionosphere, or D-region. This is a notoriously difficult region of our atmosphere to study, granting it a nickname in some circles of the ``ignorosphere''. The individual upward sprite streamers, in the observations, accelerate and brighten at rates similar to what was seen in previous studies. As the streamer interacts with the ionosphere, its morphology transitions from compact to diffuse and its upward propagation reaches a stopping point at around 90 km altitude. It is near this time and location that the streamer reaches its maximum optical intensity which then begins to exponentially decay in time. By observing the optical decay time constant to be between 80-100 microseconds, the approximate electron number density of the ionosphere is calculated to be between 2x10^7 -9x10^7
cm^−3, similar to previous predictions. Using a numerical model, we initiate an upward negative streamer near typical sprite initiation altitudes that grows and then interacts with the lower ionosphere. We present a comparison of our results to those obtained from the observations.