Y. Shen, D. J. Knudsen, J. K. Burchill, A. Howarth, A. Yau, R. J. Redmon, D. M. Miles, R. H. Varney, and M. J. Nicolls. Strong ambipolar-driven ion upflow within the cleft ion fountain during low geomagnetic activity. J. Geophys. Res. Space Physics, issue 121, 2016 .