Densitometer for geophysical fluid dynamics experiments

就像表面波在海洋上移动一样，内波也可以在大气和海洋中移动，有效密度随着高度的增加而减少。因此，这些波传输动量和能量，并在其破裂的水平上加速流动。下坡风暴是海浪在山脉产生时可能产生的强风的一个例子。总体而言，内波的作用改变了大气和海洋环流模式，对天气和气候产生了重要影响。尽管内波的产生、传播和破裂很重要，但除了简化的理论和相对较粗分辨率的数值模拟外，人们对内波的产生、传播和破裂知之甚少。在萨瑟兰的实验室里，通过研究有效密度随高度线性下降的简化系统，已经取得了实质性的进展。尤其是，对于粗糙地形上的波浪产生的经验预测现在已经开发出来，并被用于校准无法同时解决湍流和波浪的数值模拟。过去，密度波动是在实验室中使用探头、折射仪和标尺测量的。尽管测量不准确，在理想化的研究中，密度变化的线性使统计方法能够改进数据。然而，在现实中，大气和海洋的密度不是线性变化的，而是可以表现出快速变化(例如，在大气逆温时)和缓慢变化。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出两个数量级。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.