AATR an ionospheric activity indicator specifically based on GNSS measurements José Miguel Juan, Jaume Sanz, Adrià Rovira-Garcia, Guillermo González-Casado, D. Ibáñez and R. Orus Perez J. Space Weather Space Clim., 8 (2018) A14 Published online: 01 March 2018 DOI: 10.1051/swsc/2017044