This project is a 3-year collaborative effort between University of Illinois and Clemson University. The objective is to utilize observations from a suite of instruments newly deployed in northeastern Brazil to study the effects caused by thermosphere-ionosphere (TI) coupling and equatorial plasma instabilities, particularly those effects that are initiated by thermospheric gravity wave (GW) activity. The Remote Equatorial Nighttime Observatory for Ionospheric Regions (RENOIR) consists of two Fabry-Perot interferometers (FPI), a single wide-field imaging system, a dual-frequency GPS receiver, and two arrays of single-frequency GPS scintillation monitors. The two FPI instruments will be used in a bi-static configuration to measure thermospheric wind and temperature fluctuations within a common volume region. This will provide evidence for gravity wave activity that is one of the suggested trigger mechanisms for the production of equatorial spread-F (ESF) and plasma bubbles. ESF activity will be documented through two-dimensional maps of 630.0-nm and 777.4-nm nightglow intensities using the wide-field airglow imaging system. In addition, as part of these routine observations, GPS measurements of the total electron content (TEC) and scintillation properties associated with ionospheric irregularities will be made.
RENOIR in Brazil represents an international collaboration between Clemson University, the University of Illinois, the Instituto Nacional de Pesquisas Espaciais (INPE), and the Federal University at Campina Grande. Students from institutions in both the United States and Brazil will be involved in all aspects of this project, enhancing their education while training the next generation of scientists and engineers. The results of this project will advance the understanding of equatorial ionospheric irregularities, which has direct societal benefits through the adverse effects these irregularities can have on trans-ionospheric radio wave propagation
This project focused on the operation of two suites of instrumentation in northeastern Brazil for the study of thermospheric/ionospheric dynamics. The instruments comprise the Remote Equatorial Nighttime Observatory of Ionospheric Regions (RENOIR) program. The primary instrumentation consists of a Fabry-Perot interferometer at each site and an imaging system at one of the sites. In addition, GPS equipment is at each site to characterize the effects of ionospheric dynamics on radio wave propagation. The goal of the project is to study thermosphere/ionosphere coupling and equatorial plasma instabilities. Specific goals of the project included studying: 1) irregularities in the equatorial ionosphere and there relation to background thermospheric neutral winds; 2) the effect of the neutral wind on irregularity development; 3) if thermospheric gravity waves can be identified in the wind and temperature data collected by the FPIs; and 4) the occurrence of the midnight temperature maximum. The following major activities were completed during the project: 1) Two new optical aeronomy field sites were created in northeastern Brazil. One of the sites (Cajazeiras) was upgraded to a permanent building on the campus of the Federal University of Campina Grande in Cajazeiras. 2) The instrumentation installed at these two sites were operated and maintained through a new collaboration with a faculty member at the Federal University of Campina Grande in Brazil. Several Brazilian students and postdocs were involved in operation of the equipment. One Brazilian student was accepted and is currently a graduate student at Clemson University. 3) The operations of the instruments at the sites was upgraded to allow for higher cadence observations, required to search for signatures of phenomena, such as gravity waves. 4) Data were collected over the duration of the project creating the most complete, multi-year dataset of ground-based measurements of thermospheric neutral winds and temperatures compiled at low latitudes. 5) With the assistance of students at the University of Illinois, Clemson University, and the Federal University of Campina Grande, the collected data were analyzed to study: a) the coupling of the ionosphere and thermosphere through coincident observations of equatorial plasma bubbles and neutral winds (goals 1 and 2); b) whether gravity waves can be observed in the FPI neutral wind and temperature data (goal 3); and c) the occurrence and properties of the midnight temperature maximum, both in the collected data and state-of-the art numerical models (goal 4). Results from these studies have been included in at least 45 presentations given by team members at a variety of venues (both domestic and international) and have been published in 8 peer-reviewed articles. Significant results from these publications include: 1) The dependence of the neutral temperature on solar flux conditions, the properties of the midnight temperature maximum, and the climatologies of the neutral winds were detailed in Makela et al. (2013) based on the complete FPI data set collected during this project. This paper extends the previous paper presenting the first year of observations (Meriwether et al., 2011). The data set presented in this paper has been shared with the community and has been instrumental in improving the forthcoming release of the new Horizontal Wind Model. 2) The response of the low-latitude thermosphere to magnetic storms was presented in Earle et al. (2013) using satellite data as well as the FPI data from this project. Enhanced meridional neutral flow was observed in both the satellite and ground-based data sets occurring about 5-7 hours after the storm onset. 3) Ion-neutral coupling effects, studied through coincident measurements of neutral winds and the drifts of equatorial plasma bubbles were studied in detail by Chapagain et al. (2013; 2012). The plasma and neutrals were observed to be tightly coupled several hours after local sunset. Prior to this time, the wind can sometimes exceed the plasma drift speed, indicating that the F-region dynamo is not yet fully in effect. 4) The FPI wind and temperature data were used to validate the Whole Atmosphere Model (WAM) in Meriwether et al. (2013). Although the general agreement between the data and model was high, there were certain details (such as the timing of the midnight temperature maximum) that did not compare as well, requiring further study. 5) A simulation study was performed by Huang et al. (2012) to investigate whether the signature of thermospheric gravity waves would be evident in the FPI data collected. The results of this study guided the development of new observing strategies to enhance the temporal cadence of measurements. 6) The technique for reducing two-dimensional imaging FPI data to estimates of thermospheric neutral winds and temperatures was published in Makela et al. (2011). The related source code for the algorithm is available for the community to use and it is our hope that this becomes the standard analysis routine for imaging FPI datasets.
