Detection of the Occurrence and Impacts of the Nauru Island Effect

Chuck Long NOAA Global Monitoring Division/CIRES
Sally McFarlane U.S. Department of Energy

Category: Cloud Properties

Working Group: Cloud Life Cycle

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Time series (September 2005–September 2009) of the daily relative percent of occurrence (red) of an island influence on the measurements at the Nauru ARM site as determined by the McFarlane et al. (2005) methodology. Black line represents a 30-day running mean.

During the Nauru99 Experiment (http://www.arm.gov/campaigns/twp1999nauru), results indicated that Nauru Island had some influence on the Nauru ARM Climate Research Facility measurements that are intended to represent the surrounding oceanic environment. These results spurred the Nauru Island Effect Study campaign (Long 2001) where data were used to determine the character of the Nauru Island influence (Matthews et al. 2007) and develop a methodology given "upwind" measurements to detect when an island influence was occurring (McFarlane et al. 2005). The two largest cloud effects are shown to be a high bias in the frequency of occurrence of low-level cloudiness and a low bias on the downwelling shortwave irradiance (with a corresponding increased variability), both occurring during daylight hours, since the island effect is primarily driven by solar heating of the island. To provide long-term measurements needed for detection of the island effect occurrence, a set of Licor pyranometers were installed at a location near the airport on the southern part of Nauru Island, with the data record starting on September 22, 2005. A system failure resulted in an 8-month data gap from January into August 2007 and another 3-month gap from late November 2008 into mid-February 2009. We have coded up the island effect detection algorithm and processed the available data through October 2009. A plot of the percent of daily daylight-detected island effect occurrence is shown here. A primary intent of these efforts is for the TWP Site Scientist’s office to provide ARM data users with information on the occurrences and impacts of the island effect as an aid in understanding and using the Nauru data. We will present an updated analysis of the occurrence of the Nauru Island effect, as well as analyses of the impact on various measurements at the Nauru ARM site. Long, CN. 2001. The Nauru Island Effect Study (NIES) IOP Science Plan. U.S. Department of Energy. DOE-SC-ARM-0505. http://www.arm.gov. Matthews, S, JM Hacker, J Cole, J Hare, CN Long, and RM Reynolds. 2007. “Modification of the atmospheric boundary layer by a small island: observations from Nauru.” Monthly Weather Review, 135(3): 891–905. 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: 1045–1065.

This poster will be displayed at ASR Science Team Meeting.

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