Densitometer for geophysical fluid dynamics experiments

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Just as surface waves move on the ocean, so can internal waves move within the atmosphere and ocean where the effective density decreases with height.  These waves transport momentum and energy and accelerate the flow at levels where they break.  Downslope windstorms are an example of the intense winds that can result from the waves when generated by mountains.  Cumulatively, the action of internal waves changes atmospheric and oceanic circulation patterns with important consequences for weather and climate. Despite their importance, little is known about the generation, propagation and breaking of internal waves beyond simplified theories and relatively coarse-resolution numerical simulations.   In Sutherland's experimental laboratory, substantial progress has been made through examining simplified systems in which the effective density decreases linearly with height.  In particular, an empirical prediction for wave generation above rough topography has now been developed and is being used to calibrate numerical simulations that cannot simultaneously resolve both turbulence and waves.   In the past density fluctuations were measured in the laboratory using probes, refractometers and scales.  Though the measurements were not accurate, the linearity of the density variations in idealized studies allowed statistical methods to improve the data.  In reality, however, the density of the atmosphere and ocean does not vary linearly but can exhibit rapid changes (eg, at an atmospheric inversion) together with slow variations. To extend the research to more realistic situations, we are requesting funds to purchase a densitometer, which will measure density accurate to 5 digits, two orders of magnitude more accurate than currently possible. The resulting research will determine the characteristics of waves generated from storms, winds and turbulence.