A study on natural and manmade global interannual fluctuations of cirrus cloud cover for the period 1984-2004 - Elefthreratos, K.; Zerefos, C. S.; Zanis, P.; Balis, D. S.; Tselioudis, G.; Gierens, K.; Sausen, R. (Atmos. Chem. Phys., 2007)