We acknowledge the developers of the NIGTEC model and the Centre for Atmospheric Research of National Space Research and Development Agency for making the NIGTEC model available.The GUVI data used in this study are provided through support from the NASA MO&DA program.The GUVI instrument was designed and built by the Aerospace Corporation and the Johns Hopkins Uni-versity.The Principal Investigator is Dr.Andrew B.Christensen and the Chief Scientist and co-PI is Dr.Larry J.Paxton.The authors also thank the INTERMAGNET team(www.intermagnet.com),Yizen-gaw,E.Zesta,M.B.Moldwin,and the rest of the AMBER and SAMBA teams for the magnetometer data,as well as UNAVCO(htpp://www.unavco.org/data/data.html)for the GNSS observables.The authors finally appreciate the ISGI for the SYM-H and Polar cap index.Author P.O AMAECHI thanks the editor and two anonymous reviewers for their comments,which have substantially improved the quality of the present manuscript.The authors thank the editor and anonymous reviewers for their comments,which have signif-icantly improved the quality of this manuscript. （www.intermagnet.com）