This project undertakes investigations of outstanding science questions on the low latitude ionosphere, particularly its electrodynamic phenomena, while providing significant modeling and analysis support for the Low Latitude Ionosphere Sensor Network (LISN). LISN is a distributed ionospheric observatory funded by NSF's Major Research Instrumentation program that monitors conditions over the western half of South America. The research plan consists of a three part effort that will: (1) combine the multi-instrument multi-point observations of LISN with physics-based models of the ionosphere and electrodynamics to produce an optimal representation of the ionosphere, the electrodynamics, and its drivers above the western half of equatorial South America; (2) utilize JRO incoherent scatter radar data in the calibration and verification of the LISN generated specifications and eventually integrate JRO into the LISN system; calibration and verification efforts will also make use of airglow Fabry-Perot interferometers available in the region; (3) use the resulting low-latitude representation to address the following science questions: What is (are) the source(s) that determine the magnitude of the pre-Reversal enhancement of the vertical plasma drift and the shear in the east-west drift in the post-sunset F region? How strong is the longitudinal variation of the (generally) sun-synchronous ionosphere? What controls the longitudinal trends in the electrodynamics/ionosphere? What are the relative roles of the three key post-sunset F region quantities on equatorial spread-F occurrence? These quantities are (a) the post-sunset shear in the zonal plasma drift, (b) the pre-reversal enhancement of the vertical plasma drift, (c) the vertical density gradients below the F-region peak. What are the key states of the ionosphere drivers and what conditions lead to the high variability of the low-latitude F region ionosphere and the occurrence of ESF? If one can identify a key variability then how early can ESF occurrence be forecast if that quantity is measured? There are several broader impacts of the research. These include its contribution to efforts to develop predictive capabilities for the low latitude ionosphere which has important applications for communications and navigation and may aid efforts to mitigate the effects of equatorial spread F and reduce the uncertainties in the global-positioning system. The JRO observations and model results will be incorporated into the LISN database which is used by scientists from 10 different countries. A graduate student at the PI institution will participate in the research.
Weather of the Earth’s upper atmosphere is becoming a more important component of society’s need for weather information. Large space weather events affect a number of technologies such as cell phone networks, navigation instruments, oil & gas pipelines, and electrical grids. The National Science Foundation continues to support basic and applied research in space science to increase understanding of the science, improve modeling capabilities, and potentially forecast significant weather events. The NSF Directorate for Geosciences recently funded the first distributed ionosphere observatory named the Low-Latitude Ionosphere Sensor Network (LISN) to investigate the complex physics of the low-latitude ionosphere. The LISN sensor network consists of a number of different types of instruments spread throughout South America. The LISN project collaborates with other experiments throughout the world to provide multi-faceted observations of upper atmosphere weather. This funded effort provides the physics-based modeling component to the LISN project to generate interpretative insight based on the LISN project observations. First, we combined physic-based models of the ionosphere and electric fields with the LISN observations to produce accurate specifications of the ionosphere, electrodynamics, and neutral wind drivers of the space weather. Second, we utilized data from the large incoherent scatter radar (ISR) at the Jicamarca Radar Observatory to validate the LISN modeling of ionospheric weather. Third, we used the combination of these models and low-latitude observations to address the science questions about the structure and variability in space weather. During the course of this grant, the principal investigator oversaw the research of an Air Force captain as he pursued his PhD in physics at Utah State University. The PhD candidate completed his dissertation work on the development of equations to model three-dimensional electric fields in the earth’s ionosphere and of equations to model atmospheric gravity waves for the seeding of electron density instabilities in the nighttime ionosphere. These studies identified the characteristics of the atmospheric gravity waves that are most efficient in seeding large ionospheric instabilities that affect communications and navigation technologies. The main work of the effort was to combine existing physics-based models into a data-assimilation model that can reveal the drivers of ionosphere/electric field variations in the low-latitude ionosphere. The principal investigator and an undergraduate physics student from Utah State University investigated several methods of combining the models and the LISN data to determine space weather drivers. The data-model inversion methodology to provide the most certain solution was based on the assimilation of multiple data types: including measurements of induced magnetic field variations, the total electron content between GPS satellites and ground GPS monitors, and reflected HF radar signals off the ionosphere. These studies provided a description of the three-dimensional neutral wind pattern of the upper atmosphere. In particular, it was demonstrated that atmospheric tides in phase with the moon were responsible for a significant portion of the observed ionospheric variability during solar minimum conditions (Figure 1). The efficacy of the model-data inversion methods was validated through the comparison of the model predictions with the precise observations of the NSF-funded incoherent scatter radar at the Jicamarca Observatory and with observations of high-altitude airglow observations by all-sky cameras. Additionally, theoretical studies were supported to investigate a longstanding discrepancy between theory and observation of the altitude of the electric current peak of the equatorial electrojet current, a region of strong current flow in the low-latitude ionosphere. The study demonstrated that the earth’s strong magnetic field influence on the electric fields and currents required models to maintain an accurate geometry in the calculation of the fields and currents. The resolution was demonstrated using the ionosphere and electric field models of this effort. This study was in support of a PhD student’s dissertation work at Cornell University. Investigations of theory of electric fields in the ionosphere continues as a result of these studies. Publications Produced as a Result of this Research Chapagain, N. P., M. J. Taylor, and J. V. Eccles (2011), Airglow observations and modeling of F region depletion zonal velocities over Christmas Island, J. Geophys. Res., 116, A02301, doi:10.1029/2010JA015958. Eccles, V., D. D. Rice, J. J. Sojka, C. E. Valladares, T. Bullett, and J. L. Chau (2011), Lunar atmospheric tidal effects in the plasma drifts observed by the Low-Latitude Ionospheric Sensor Network, J. Geophys. Res., 116, A07309, doi:10.1029/2010JA016282. Kelley, M. C., R. R. Ilma, and V. Eccles (2012), Reconciliation of rocket-based magnetic field measurements in the equatorial electrojet with classical collision theory, J. Geophys. Res., 117, A01311, doi:10.1029/2011JA017020.
