Observed Changes in Cloud Cover from MISR and MODIS over the Southern Oceans

Monday, 15 December 2014
Roger Marchand, University of Washington, Department of Atmospheric Sciences, Seattle, WA, United States
Datasets spanning more than 13 years are now available from the sensors on board the Terra and Aqua satellites, including the Multiangle Imaging Spectro-Radiometer (MISR) and the MOderate Resolution Imaging Spectrometer (MODIS). Among the datasets produced from MISR and MODIS observations are joint histograms of cloud-top-height (CTH) and optical-depth (OD). An examination of monthly CTH-OD histograms shows that while there has been no change in global, total cloud fraction (the sum of all CTH-OD components) over the past decade, there has been a significant change in some of the CTH-OD components. Of particular note is a systematic decrease in the amount of the most reflective, most optically thick cloud (OD > 23). This reduction in optically thick cloud has occurred primarily in the extratropics of both hemispheres. In this presentation, I report on early efforts to attribute the changes in cloud cover over the Southern Ocean near New Zealand to changes in synoptic weather patterns. Preliminary results suggest the reduction in optically thick cloud and other changes in cloud cover in this area are not due to a change in the distribution of synoptic patterns but rather is associated with relatively subtle changes in the pressure and position of baroclinic systems, and is tied to the Southern Annualar Mode.