Latitudinal dependence of low cloud amount on cosmic ray induced ionization
Article first published online: 21 AUG 2004
Copyright 2004 by the American Geophysical Union.
Geophysical Research Letters
Volume 31, Issue 16, August 2004
How to Cite
2004), Latitudinal dependence of low cloud amount on cosmic ray induced ionization, Geophys. Res. Lett., 31, L16109, doi:10.1029/2004GL019507., , , , and (
- Issue published online: 21 AUG 2004
- Article first published online: 21 AUG 2004
- Manuscript Accepted: 13 JUL 2004
- Manuscript Revised: 29 JUN 2004
- Manuscript Received: 16 JAN 2004
 A significant correlation between the annual cosmic ray flux and the amount of low clouds has recently been found for the past 20 years. However, of the physical explanations suggested, none has been quantitatively verified in the atmosphere by a combination of modelling and experiment. Here we study the relation between the global distributions of the observed low cloud amount and the calculated tropospheric ionization induced by cosmic rays. We find that the time evolution of the low cloud amount can be decomposed into a long-term trend and inter-annual variations, the latter depicting a clear 11-year cycle. We also find that the relative inter-annual variability in low cloud amount increases polewards and exhibits a highly significant one-to-one relation with inter-annual variations in the ionization over the latitude range 20–55°S and 10–70°N. This latitudinal dependence gives strong support for the hypothesis that the cosmic ray induced ionization modulates cloud properties.