New Dataset for Marine Boundary Layer Clouds
Marine boundary layer (MBL) clouds cover large areas of the world’s oceans and coastal areas and play a major role in the global climate system. Feedbacks associated with changes in MBL clouds are one of the largest sources of uncertainty in cloud feedbacks in global climate model simulations. The U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) Climate Research Facility’s Mobile Facility was recently deployed to the Azores and obtained the most extensive (19 months) and comprehensive dataset of MBL clouds to date. The observations show that cumulus and stratocumulus cloud types often occur simultaneously, with each cloud type tied to a distinct thermodynamic layer. Theoretical models of stratocumulus cloud formation often assume that the boundary layer is well mixed, meaning that there are few horizontal or vertical gradients in potential temperature or water vapor mixing ratio. The frequent presence (> 90%) of transition layers in the sounding observations indicates that this well-mixed assumption rarely holds true for the Azores. The percentage of these decoupled layers is much higher than observed in previous studies in the eastern Equatorial Pacific, indicating important differences between MBL clouds in different regions. These findings, as well as statistics on cloud frequency, precipitation occurrence, and cloud updrafts, will be used to improve models of MBL clouds.
Rémillard, J., P. Kollias, E. Luke, and R. Wood. 2012. “Marine Boundary Layer Cloud Observations in the Azores,” Journal of Climate 25, 7381–98. DOI: 10.1175/JCLI-D-11-00610.1