Cloud properties and associated radiative heating rates in the tropical western Pacific

Calculations of radiative flux profiles require measurements of thermodynamic and cloud properties (temperature, humidity, liquid and ice water content). Instruments capable of making these measurements have only recently become available. The U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program operates a comprehensive set of atmospheric remote sensing instruments at sites around the world, including three in the tropical western Pacific region. We have processed several months of ARM observations from two of these sites, Manus and Nauru, to calculate time series of vertical cloud property profiles and associated radiative fluxes and heating rates. Maxima in cloud occurrence are found in the boundary layer and the upper troposphere at both sites. Manus, which was much more convectively active than Nauru during the study period, also exhibits a midlevel cloud feature near the melting level. The two sites exhibit very different diurnal cycles. Manus experiences an afternoon maximum in high clouds while Nauru experiences a weak afternoon minimum. Nauru experiences a strong afternoon maximum in boundary layer clouds. Calculated fluxes at the surface and the top of the atmosphere are found to be in reasonable agreement with measurements. Below 15 km, radiative processes lead to cooling in the average profile, with local maxima near the surface and approximately 8 km. On average, high and midlevel clouds have a net warming effect though not enough to offset the clear‐sky cooling. The prevalent boundary layer clouds at Nauru have a net cooling effect in and above the cloud layer and a net warming below. This data set will be an important tool for describing radiative processes in the tropics and assessing the simulation of these processes in dynamical models.