In order to fully characterize the effect of lightning on ionospheric density structures, this project will deploy co-located ionosphere and lightning RF arrays at HF (1-30 MHz) for D- and E-region imaging, and VLF (0-500 kHz) and VHF (120-150 MHz) radars for lightning studies. The observational program will be augmented by computations from the Ionospheric Data Assimilation Four-Dimensional (IDA4D) model. The model will perform tomographic reconstruction of the ionosphere for heights extending from the E region to above using the observations obtained as well as other opportunistic E region data sources, most notably from the Los Alamos Portable Pulser (LAPP) with the Cibola Flight Experiment (CFE) satellite. The goal of these activities is to elucidate coupling processes between the troposphere and ionosphere, in particular the interaction between lightning and E region ionization enhancements known as sporadic-E. Current thinking suggests that there are two primary mechanisms that transport energy from the troposphere to the lower ionosphere: the first is mechanical wave activity and the second is electrical effects associated with lightning, including electromagnetic pulses and relativistic electrons. The mechanical coupling of waves may increase the peak plasma densities of sporadic-E layers before propagating into the F-region. Discharges from lightning couple electromagnetically and may increase the peak plasma densities by creating more long-lived metal ions from the ambient population of meteoric metal atoms found at these altitudes. However, very little is known about the electromagnetic coupling between lightning and the ionosphere, even though observations of Transient Luminous Events (TLE) indicate that interactions between thunderstorms and the middle and upper atmospheres do occur. The goal is to make significant progress in answering the following questions on ionosphere/troposphere coupling: (1) What is the coupling mechanism between lightning emissions and the development of sporadic E layers? (2) What is the relationship between lightning emissions and the variations of conductances in the ionosphere? (3) To what degree can we use measured RF values of the lightning emissions and characterization of the ionosphere to simultaneously model and analyze the physical characteristics of lightning emissions and the detailed structuring of the ionospheric response?
", was designed to increase our understanding of coupling processes between lightning and the lower ionosphere. In particular, previous research had shown that lightning and thunderstorm activity generated sporadic-E layers in the lower ionosphere, which are high density localized structures that can persist for many hours. These sporadic-E layers have plasma densities that can be an order of magnitude larger than the background ionosphere and therefore disrupt ground-to-satellite communication either through reflection or dispersion and interference. The mechanism for this coupling between lightning and sporadic-E has yet to be definitively established, though much emphasis has been placed on traveling ionospheric disturbances (TIDs) as a possible link. We executed an experimental campaign by collecting total electron content (TEC) data using ground-based receivers in New Mexico, as well as lightning data using a lightning mapping array (LMA). The LMA provides 3D images of lightning within the cloud and can help distinguish between different lightning types. Additionally, we modified the IDA4D tomographic inversion algorithm to incorporate data from the lower ionosphere in order to generate 4D maps of the ionosphere. Our results showed a correlation between thunderstorms and TID generation during the late summer months; in particular, higher frequency (shorter wavelength) TIDs with low amplitude were correlated with thunderstorm activity. Future research will focus on winter data.
