“…Ground-based optical, rocket-borne, and, more recently, active lidar soundings of these clouds have provided a wealth of information on their evolution, particle size, wave dynamics, and altitude structure essential for quantifying their variability (Chu et al, 2003;Rapp et al, 2002;Semeter & Mendillo, 1997). They have also established the remarkably consistent and stable altitude of the NLCs in the upper mesosphere over the past century, occurring at a mean height of 83 ± 2.5 km (Baumgarten et al, 2009;Collins et al, 2009;Chu et al, 2004;Gadsden & Taylor, 1994;Gerding et al, 2007;Jesse, 1896;Paton, 1964;Stoȑmer, 1933;Taylor et al, 1984;Thayer et al, 2003;von Zahn et al, 1998). However, most of these measurements are from isolated sites and are naturally limited by the prevailing weather conditions (Gadsden & Schroder, 1989).…”