SHIMMER Graph (IMAGE) Naval Research Laboratory Caption Number of PMCs observed by SHIMMER between 50-58°N versus local time. The red line (2007) shows a clear semidiurnal behavior, whereas the black line (2008) illustrates that in 2008 diurnal behavior is observed. How this difference in cloud occurrence is related to other meteorological data, such as winds and temperatures, is subject to ongoing and proposed work. Credit Naval Research Laboratory Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.