The size of clouds can vary under the influence of a global 'electrical heartbeat' in the atmosphere, University of Reading researchers have claimed. They looked at ten years of data fron the north and south poles, after becoming aware of the daily global ebb and flow of an electrical current in the atmosphere, the so called Carnegie Curve. The electricity came from electrified storms across the world and appears to affect the formation of clouds, or their thickness. The story is at http://phys.org/print281866073.html but see also http://tallbloke.wordpress.com/2013/03/08/cloud-height-is-affected-by-th… … where the commenters are a bit stumped. What is this electrical current is the big question- but see iopscience.iop.org/1748-9326/8/1/015027/article, Harrison and Aubaum (2013), Environmental Research Letters.