PNNL

Abstract

Convection in the Tropical Western Pacific (TWP) region plays an important role in driving global-scale atmospheric circulation. While the TWP is very important, climate models have a difficult time capturing the intricacies of convection in this region. For these reasons, the Atmospheric Radiation Measurement (ARM) program has made the TWP one of its concentrated areas of study. The ARM program now has three sites in the tropical Pacific region: Manus, Nauru, and Darwin. An examination of cloud frequency and radiation data from theses sites reveals variability on a wide range of time scales. At Manus, variability due to intraseasonal processes, including the Madden-Julian Oscillation, is most pronounced but intraseasonal effects are modulated by the annual monsoon cycle as well as by ENSO. In particular, the relative frequency of convection over the large islands of the maritime continent and over the ocean depends on the stage of the monsoon cycle. An important element of ARM's interest in tropical Pacific convection is to characterize cloud optical properties. Because cloud properties are likely to be different for maritime and island-based convection, it is important to understand the dynamical processes that govern the frequency with which each occurs. This paper attempts to attribute variability observed at the tropical Pacific ARM sites to dynamical processes on a range of spatial scales.