Impact of Island-Induced Clouds on Surface Measurements: Analysis of the ARM Nauru Island Effect Study Data
McFarlane SA, CN Long, and DM Flynn. 2005. "Impact of Island-Induced Clouds on Surface Measurements: Analysis of the ARM Nauru Island Effect Study Data." Journal of Applied Meteorology 44(7):1045-1065.
The Department of Energy's second Atmospheric Radiation and Cloud Station (ARCS) site in the tropical western Pacific (TWP) region was established on the island of Nauru as part of the Atmospheric Radiation Measurement (ARM) Program. Analysis of data taken during the Nauru99 intensive field experiment indicated that the cloud and radiation measurements at the ARCS site were being affected by a cloud plume, which was induced by the island due to diurnal heating relative to the ocean and the predominantly easterly flow of the tradewinds. The Nauru Island Effects Study (NIES) was developed to identify times when the island cloud effect occurs and to quantify the effect on the ARCS measurements. The Nauru cloud plume is found to be highly correlated with surface wind direction. During suppressed conditions the plume heading is predominantly to the west because of the consistency of the easterly trade winds. During El Nino conditions, the cloud plume can occur with almost any heading due to the variability of the surface winds. During suppressed conditions the cloud plume was observed in 60% of the visible satellite images after 10:30 LST. During active conditions, the plume was observed in only 25% of the satellite images and only half of the observed plumes were downwind of the ARCS site. This study indicates that the absolute increase in low cloud frequency due to the cloud plume is on the order of 10% and the effect of the cloud plume on the average daily surface radiation is around 50-60 wm. By installing a simple measurement platform consisting of surface meteorological instruments and a global shortwave radiometer at a site on the opposite side of the island, the effect of the cloud plume on the radiation field at the ARCS site can be quantified on a long term basis.