Midlevel Cloud Formation at Darwin ARM Site
U.S. Department of Energy (DOE) scientists at Pacific Northwest National Laboratory capitalized on the multiple sensors available at DOE’s Atmospheric Radiation Measurement (ARM) Climate Research Facility site in Darwin, Australia, to understand how and when midlevel clouds form in the tropics. Midlevel clouds impact the energy budget and vertical profile of heating in the atmosphere, yet the radiative and latent heating impacts are difficult to calculate because they depend on understanding the frequency and phase of the clouds. The scientists observed cloud formation using a four-year climatology of vertically pointing lidar and radar data to get a complete picture of how clouds at this altitude occur. The team combined this technique with data from radiosondes launched on weather balloons to gather atmospheric measurements and a scanning precipitation radar that observes precipitation. Their results show that thin, midlevel clouds more frequently follow stratiform precipitation during the active monsoon rather than the break monsoon period. Cloud layers are more likely to coincide with warmer, more stable layers during the break period. In the active monsoon phase, when storms come from the ocean, these midlayer clouds are more often found after ice precipitation melts and cools the layer, causing more water vapor to condense into a cloud. In the break monsoon phase, the clouds come primarily from over land. A greater percentage of those midlevel clouds come from direct injection of cloud particles into the layer. This study provides a unique climatology based on four years of observations at the Darwin ARM site.
Riihimaki, L. D., S. A. McFarlane, and J. M. Comstock. 2012. “Climatology and Formation of Tropical Midlevel Clouds at the Darwin ARM site,” Journal of Climate 25(19), 6835-50. DOI: 10.1175/JCLI-D-11-00599.1.