On the dynamics of flow past a cylinder: Implications for CTD package motions and measurements

Abstract

During the collection of ship‐based observations, heaving of the vessel may lead to variation in the descent rate of a CTD package. This can result in the package being pulled upward through previously sampled water, leading to difficult to quantify errors due to the complex wake. To reduce this problem to one of manageable stature, we use the simple paradigm of two‐dimensional flow past a cylinder. By using a tracer with a gradient along the flow, we quantify the effect of the cylinder on its distribution and the impact of postprocessing. At high Reynolds numbers, over 200, uniform translation leads to a small error in the tracer value. This error is likely negligible at the much higher Reynolds number of the ocean. When the flow is oscillated longitudinally, there are two main sources of error; attached vortices may propagate around the cylinder and/or shed vortices may translate into the path of the cylinder. Postprocessing by removing records from previous pressure levels removes much of the first error, due to it occurring as the package ascends. However, the second source of error is more difficult to remove, due to it occurring when the package is once again descending. In general, results indicate that long‐period oscillations are preferable. While the magnitude of the errors are comparable to those from short‐period oscillations, they are spread farther apart in time and space and the overall effect is to localize the errors in small regions of the final depth profile.

Finale: impact of the ORCHESTRA/ENCORE programmes on Southern Ocean heat and carbon understanding

“…The models developed have provided new insights into ocean processes, such as mode water variability, eddy dynamics and ocean heat uptake in response to wind stress, and also into vertical coordinate system development and the advantages of combined adjoint-forward model experimental design. This is of course an immensely compressed summary of the activities of several dozens of researchers over 6 years and, for example, O/E also delivered novel work using machine learning to classify Southern Ocean profile types [ 75 ], defined a new probabilistic metric for fronts [ 76 ], undertook diffusive flux analysis [ 77 ], produced chapters in textbooks on subduction [ 78 ], satellite altimetry [ 79 ] and mixing [ 80 ], and even investigated the hydrodynamics of induced CTD package oscillations [ 81 ].…”

CTD Sensors for Ocean Investigation Including State of Art and Commercially Available

“…Data correction algorithms are another factor affecting the authenticity of CTD data. Measurement results of individual sensors are always affected by environments and the method of measurement, such as thermal lag, effects of temperature measurement, temperature drift of pressure sensor [ 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 ], etc. These errors can be partly corrected via compensation algorithm [ 106 , 107 , 108 , 109 , 110 , 111 ].…”