23rd Conference on IIPS
11th Symposium on Integrated Observing and Assimilation Systems for the Atmosphere, Oceans, and Land Surface (IOAS-AOLS)


The PACRAIN/PI-GCOS automated rain gauge initiative

Michael D. Klatt, University of Oklahoma, Norman, OK; and M. L. Morrissey and J. S. Greene

The Comprehensive Pacific Rainfall Database (PACRAIN) project at the University of Oklahoma (OU) maintains an extensive database of tropical Pacific rainfall data and is also involved in collecting data. PACRAIN is collaborating with the Pacific Islands Global Climate Observing System (PI-GCOS) to expand the rain gauge networks in that region. An increase in the number of gauges is important not only for PACRAIN and PI-GCOS, but also for the local meteorological agencies who use the data operationally. Many of the nations and territories occupy a number of widely-spaced islands. Even on individual islands, complex terrain may create multiple climate zones which require multiple rain gauges. The manual gauges favored in this region are easy to use, reliable, and inexpensive. However, the limited personnel resources of local agencies makes using large numbers of these gauges impractical. Thus, PACRAIN and PI-GCOS are working with the local agencies to install automated gauges.

To date, a total of 33 automated rain gauges have been sent to the Cook Islands, Guam, Niue, Samoa, Tonga, and Vanuatu. All of the gauges are Met One 380 tipping bucket gauges. Each gauge is paired with an Onset HOBO H7 event logger which records tips at a resolution of 0.5 seconds. Onset's BoxCar software is used to retrieve, display, and analyze the tip data. For additional analysis the data can be exported to several formats, including a Microsoft Excel file. An Excel add-in developed by PACRAIN can be used to examine the exported data. The current version of the add-in has tools for converting the tip times into rainfall amounts for various frequencies (hourly, daily, etc.) and individual rain events. The duration and intensity of each rain event are also calculated. Documentation is being assembled for the local meteorological agencies that will detail the installation and use of the rain gauges, data loggers, and software tools. PACRAIN is also working with these agencies to maintain a database of metadata for each gauge installation.

Data from gauges at Afiamalu, Samoa; Fua'amotu, Tonga; and Port Vila, Vanuatu are currently being analyzed prior to integrating them into the PACRAIN database. Data from these gauges will be compared to high-resolution satellite data, and to nearby gauges where possible. A preliminary comparison of daily amounts with satellite estimates yields a correlation of 0.76 for Fua'amotu, 0.74 for Afiamalu, and 0.61 for Port Vila. These data will be used to refine the Excel analysis tools, such as determining the optimum rainfall intensity threshold for defining rainfall events. The data will also be used to develop quality assurance procedures specific to tipping bucket gauge observations.


Joint Session 4, Global Earth Observations (Joint between 11 IOAS-AOLS and 23 IIPS)
Wednesday, 17 January 2007, 1:30 PM-5:30 PM, 216AB

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