A new data set that identifies periods when Nauru data may be affected by island-influenced clouds has been produced by Chuck Long, site scientist for the ARM Tropical Western Pacific site. The Nauru island effect (NIE) data set currently covers the period from September 2005 to May 2010 and will be updated periodically as new data are obtained. This data set will help scientists in their analysis of cloud and radiation data at Nauru and will enable them to perform more relevant comparisons of observations and model results.

Due to logistical constraints, the observational site on Nauru was located on the western side of the island, which is the leeward-side relative to the prevalent easterly trade winds. Observations during the Nauru99 field experiment found that low-level cloud plumes were frequently induced by heating of the island, advected downwind, and measured by the ARM instruments. Thus, at times the ARM measurements may not be representative of the surrounding oceanic area. To develop a methodology for identifying periods when this “island effect” influences the cloud and radiation measurements, a set of radiometers were installed on the eastern (upwind) side of the island during the Nauru Island Effect Study.

Based on the algorithm developed by McFarlane et al. (2005), statistical analysis of the wind direction and air temperature at the site and downwelling shortwave radiation at the two sites now can be used to identify likely occurrences of an island influence on the Nauru data. Subsequently, a permanent set of Licor pyranometers have been installed near the airport on the southern end of the island for use in applying the island effect detection methodology.

Affected ARM data will be periodically identified and made available through the Nauru Island Effect Detection Data Set available at the ARM Data Archive; a user login is required. Questions? Contact Chuck Long (chuck.long@pnl.gov) or Sally McFarlane (sally.mcfarlane@pnl.gov).