Nauru99 continued a series of intensive field studies in support of the DOE/Atmospheric Radiation Measurement (ARM) program in the tropical Western Pacific (TWP). Centered around the island of Nauru, the NOAA R/V Ronald H. Brown and the JAMSTEC R/V Mirai measured surface and radiation fluxes at sea, for comparison with the land-based ARCS systems and the TAO buoy array.