The Advantages and Challenges of Ground-based Interferometer Arrays for Measurements of Thermospheric Winds and Temperatures

Data from a coordinated chain of Doppler imaging Fabry-Perot interferometers (FPIs), specializing in the measurement of neutral temperatures and winds in the nocturnal F-region thermosphere, are used to illustrate the advantages and challenges of distributed ground-based arrays for Space Weather diagnostics. Five instruments have been deployed near a common magnetic meridian extending from Westford Massachusetts U.S.A. to Cachoeira Paulista, Brazil. Each instrument in the chain has been remotely and automatically operated and wavelength calibrated, with statistical line-of-sight wind vector errors typically < 1 m/s, and OI 630 nm linewidth temperature errors < +/- 15 K. Systems maintaining FPI etalon and interference filter temperature to < +/- 0.1 C, and pressure systems used to maintain FPI etalon wavelength stability are described. Close instrument access has permitted the identification and isolation of insidious spectral contamination from OH airglow, with evolving instrument design improving data reliability into the future. Relative to space-based platforms, other clear advantages of ground-based deployments are data precision and accuracy, low costs amortized to multi-decade service lifetimes, local time coverage, and a provision of hands-on student training in Space Weather instrumentation. State-of-the-art regional FPI chains, accompanied by all-sky 630 nm imagers, are aptly suited for sampling regional storm time dynamic response, ionospheric irregularity genesis, medium scale traveling ionospheric disturbance morphology, equatorial anomaly climatology and upper atmospheric tidal response, among other topics. Disadvantages of these arrays include both scientific and logistic limitations. These currently include restrictions to nighttime, mostly clear sky conditions, and the uncertain reliability of basic maintenance and hospitality at host sites, including federal facilities.