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RASS Observations of Island Heating during Nauru99

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Continuous RASS measurements made with a wind profiler radar during the Nauru99 field campaign. The radar was on board the R/V Mirai off the coast of the island of Nauru in the central Pacific. There was a steady easterly breeze throughout the observation period. The color contour plot indicates the temperature observed using RASS as a function of time and altitude. The schematic map at top indicates the location of the Mirai with respect to the island as a function of time. The island is about 5 km across. For the first 15 minutes the Mirai was downwind of the island (about one kilometre off the western coast) slowly steaming north. The vessel cleared the northern coast just before 3 UT, then sailed a large loop before finally gradually appoaching the western coast again (sailing due east) from about 4:30 UT to arrive back at the starting point. The observed temperatures are highest for both the first 15 minutes, and for the last 30 minutes, during which time the Mirai was 500 - 1000 metres downwind of the island. This suggests the island was heating the air above (and downwind) of the island.

It is possible to make a rough estimate of the heat flux from the island. The easterly wind was about 3.5 m/s, and since the island is 5 km across, the heat was imparted over about 1500 seconds. The air was heated by about 0.8K. The rate of heating (assuming from soundings, a 650 meter deep boundary layer) was H = 0.8K * 650m / 1500s = 0.35 K m/s. The heat flux therefore can be approximated as Q = H p Cp = 400 Watts per meter squared (where p and Cp are the density and specific heat of air). This heat flux is around two orders of magnitude greater than the sensible heat flux from the open sea.