P2.67 Modelling the Transient Response of the Dines Anemometer in Tropical Cyclone Winds Jeffrey D. Kepert Centre for Australian Weather and Climate Research, Bureau of Meteorology, 700 Collins St, Melbourne Vic 3000. Email: J.Kepert@bom.gov.au 29th AMS Conference on Hurricanes and Tropical Meteorology, Tucson, Arizona, May 10 – 14, 2010. 1. Introduction The Dines, or pressure-tube, anemometer, consists of a large-diameter pitot tube mounted on a vane, connected to a unique manometer. This manometer consists of an open-bottomed tapered float in a water tank, with the pressure tube from the pitot head feeding into the air space in the float. As the wind speed rises, the pressure inside the float increases and the float rises, moving the recording pen. Further information on the instrument may be found in Dines (1892) and Gold (1936). The Dines anemometer is now obsolete in Australia, having been largely replaced by cup anemometers. Nevertheless, historical records from the instrument are important to understanding the wind risk climate, not least since the two strongest gusts ever recorded on the Australian mainland, in Tropical Cyclones Tracy of 1974 and Vance of 1999, were on Dines instruments. The behaviour of cup anemometers in turbulence has been extensively studied, but comparatively little similar work has been done on the Dines, and none recently. Some studies have compared cup to Dines anemometers (e.g. Mattice 1938; Dyck 1941; Handcock 1963; Logue 1986; Smith 1981) or looked at the Dines anemometer in isolation (e.g. Wieringa 1980; Bureau of Meteorology 1987) but these have mostly focussed on the mean, rather than the transient, response. Here, we present and analyse a newly developed physical model of the transient response of the Dines anemometer. Two previously observed resonances are confirmed, and their physical mechanism described. A third low-frequency oscillation, not previously known, is found in the model. Observations that may indicate this oscillation are briefly discussed. In addition, it is shown that the instrument may overspeed, albeit for different reasons to cup anemometers. Further work, in collaboration with the Cyclone Testing Stations at James Cook University and Geo- sciences Australia, will involve verification and calibration of the physical model by experiments on a remnant functioning Dines instrument, and reinterpretation of the historic gust record. 2. Modelling the Float Chamber The manometer of the Dines anemometer is illustrated in Fig. 1 has a complicated geometry, designed to produce a steady-state float displacement that is linear in the applied wind speed. This geometry com- plicates the analysis, so for convenience a simpler geometry will be temporarily assumed. In particular, the following simplifying assumptions are made: 1. The cross-sectional areas of the water inside and outside of the float are equal. 2. The float and containing vessel have parallel sides. 1