The lower boundary layer is probably the least observed part of tropical cyclones. While much of the rest of the storm has been extensively mapped over the last 50 years, good quality measurements in the lowest few hundred metres are exceedingly rare. Yet it is here, in the "habitation layer", that the storm impacts most directly on humanity, both through direct wind damage, and through the generation of ocean waves and storm surge.
The approach to understanding the tropical cyclone boundary layer has been to extrapolate theories, developed and verified in more benign conditions, and apply them in the severe conditions of the cyclone core. However, there is some evidence to suggest that air-sea interaction at high wind speeds cannot be extrapolated from low wind speed and land-based behaviour.
The experimental site presents a unique opportunity to resolve some of these issues. On flat land at the tip of a peninsula, on one of the most cyclone-prone coasts in the world, are a collection of 13 towers, each over 300 m high, that support the main antenna for a joint Australian-U.S. Naval communication station. Two of these towers have been instrumented at 5 levels each. Instruments consist of conventional electronic temperature and humidity sensors, and cup and vane anemometers, located on the ends of 7 m booms to minimise flow distortion. Data is electronically logged at each level. In addition, one tower supports 4 sonic anemometers, which are logged via radio modems at the ground, and a 920 MHz boundary layer profiler with RASS has been installed adjacent to the site.
The talk will briefly outline the aims of the project, but focus on the techniques used to overcome the many difficulties with the site. These include the need to withstand hurricane strength winds, an extremely hot dry climate, RF interference with electronic equipment (the transmitter power output is 2 MW), remoteness and difficulty of access, wildlife, and the need for long term monitoring to capture a rare event.