Densitometer for geophysical fluid dynamics experiments

正如表面波在海洋中移动一样，内波也可以在大气和海洋中移动，其中有效密度随高度而减小。 这些波传递动量和能量，并在它们破碎的地方加速流动。 下坡风暴是一个例子，强风可能导致从海浪时，产生的山脉。 内波的作用逐渐改变大气和海洋环流模式，对天气和气候产生重要影响。尽管它们的重要性，很少有人知道的产生，传播和破碎的内波超越简化的理论和相对粗糙的分辨率数值模拟。 在萨瑟兰的实验室中，通过检验有效密度随高度线性下降的简化系统，已经取得了实质性进展。 特别是，一个经验性的预测波浪生成以上粗糙的地形现已开发，并被用来校准数值模拟，不能同时解决湍流和波浪。 在过去，密度波动是在实验室里用探针、折射计和天平测量的。 虽然测量不准确，但理想化研究中密度变化的线性允许统计方法改进数据。 然而，在现实中，大气和海洋的密度并不是线性变化的，而是可以表现出快速的变化（例如，在大气逆温时）和缓慢的变化。为了将研究扩展到更现实的情况，我们正在申请资金购买一台密度计，它将测量精确到5位数的密度，比目前可能的精度高两个数量级。由此产生的研究将确定风暴、风和湍流产生的波浪的特征。

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.