W. K. Hocking and G. K. Kumar. Long term behaviour of the MLT quasi-7-day wave at two radar-sites at northern polar latitudes. J. Atmos. Solar-Terr. Phys., volume 73, pages 1616-1628, 2011 . G. K. Kumar and W. K. Hocking. Climatology of northern polar latitude MLT dynamics: mean winds and tides. Ann. Geophys., volume 28, issue 1, pages 1859-1876, 2010 .