6B.2
Cirrus generation and maintenance in the Tropical Western Pacific
James H. Mather, PNNL, Richland, WA; and J. M. Comstock and T. P. Ackerman
The Department of Energy's Atmospheric Radiation Measurement (ARM) program maintains two sites in the equatorial Pacific, one in Papua New Guinea (147.4 East) and one on Nauru (166.9 East). These sites are equipped with millimeter radar and lidar to provide continuous observations of cloud properties. The sites also include upper air soundings and a comprehensive array of radiometric measurements. The frequency and depth of convection are very different at Manus and Nauru and consequently, cirrus properties also differ. Cirrus over Manus appear to be generated locally by convective outflow. They tend to have a depth of several kilometers and considerable structure. Over Nauru, the cirrus are often not directly tied to local convection. They also tend to be thinner and exhibit less internal structure. We will examine the environmental conditions that control convection in these two regions and the upper tropospheric conditions that affect cirrus formation, structure, and lifetime. Over Nauru, where deep convection is rare, dynamical processes such as the horizontal transport of water vapor and dynamically forced vertical motion become more important for the generation and maintenance of cirrus.
Session 6B, Large-scale dynamics and convection (Parallel with Sessions 6A, 6C, and 6D)
Tuesday, 30 April 2002, 2:00 PM-3:30 PM
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