The North American Thermosphere Ionosphere Observing Network (NATION), comprising a new network of Fabry-Perot interferometers (FPIs), will be deployed in the Midwest of the United States of America. FPIs will initially be deployed to four sites to make coordinated measurements of the neutral winds and temperature in the Earth’s thermosphere using measurements of the 630-nm redline emission. The observing strategy of the network will take in to account local observing conditions and common volume measurements from multiple sites will be made in order to estimate local vector wind quantities. The network is expandable, and as additional FPI sites are installed in North America, or elsewhere, the goal of providing the upper atmospheric research community with a robust dataset of neutral winds and temperatures will be achieved.
Each site in the initial NATION deployment has been chosen for having relatively good observing conditions as well as ease of access. The sites each have Internet access, allowing for their operation as a single distributed sensing network. The typical observing strategy will be to coordinate observations of the CV locations shown in the Figure. Typical integration times will be on the order of 3 minutes for each operation, but will be dynamically determined based on the actual observing conditions. The sequences of observations will be specified depending on the goals of a given experiment. High temporal resolution (~3 minutes) could be obtained by continually observing the same common volume points. The resulting temporal resolution would allow for the tracking of dynamic features in the thermosphere, such as TADs or gravity waves. Alternately, observing all of the available orthogonal common volume locations, resulting in the largest spatial coverage, could be achieved in a sequence taking less than 30 minutes. Thus, there is a trade off between spatial coverage and temporal resolution.
The initial NATION sites are located at the University of Illinois (UI), the Pisgah Astronmoical Research Institute (PARI), Peach Mountain near the University of Michigan (UM), and Eastern Kentucky University (EKU).It is important to note that the NATION concept is fully scalable and is expected to expand as additional instruments are deployed to new sites. Additional FPIs will soon be deployed in New Jersey and New Mexico, providing important longitudinal diversity to the NATION measurements that will be useful in studying, among other topics, the penetration of mid-latitude tidal structure into thermospheric dynamics.
Each site will also have a Boltwood cloud sensor, from which the local viewing conditions can be made. These conditions will be taken in to account as the realtime observing strategy for NATION is determined. For example, if one site is determined to be clouded over, a common volume (CV) observing strategy involving that site will not be made, allowing for a higher temporal cadence for the other CV locations. In the event that no CV observations are possible from a given site due to cloud conditions at the other sites, a site would revert to a cardinal direction observing mode.