Few things in nature are as predictable as ocean tides. These persistent, short-lived phenomena of large magnitude, caused by the gravitational pull of the Moon and the Sun, can be seen in almost all oceanographic and satellite observations. They directly affect the rhythm of life of millions of people and countless ecosystems.
But recently researchers have noticed subtle changes in surface tide measurements that do not coincide with changes in the gravity of the Moon and Sun. Instead, accumulating data and theory suggest that warming of the ocean surface may be behind the observations.
from the University of Bonn. To investigate this phenomenon, Michael Schindelegger improved the accuracy of three-dimensional (3D) ocean circulation by better understanding observational data collected between 1993 and 2020, using the supercomputing resources of the Jülich Supercomputing Center (JSC). . models are being developed.
The study was published in the journal Contact Earth and Environment .
“Tides often mask other potentially interesting and less predictable signals, such as the general circulation of the ocean or the effects of climate change,” explains Schindelegger. “Getting climate signals from oceanographic observations also depends on the accuracy with which we can model tides, including potential changes over time.”
Internal currents increase complexity
Scientists estimate that the upper 700 meters of the ocean absorbs approximately 90% of the excess heat trapped in the climate warming system. As this area of the ocean warms, it expands and becomes less dense, resulting in a greater contrast in water density compared to the lower levels of the ocean that remain cooler and denser.
Specifically, Schindelegger and his colleagues are investigating the relationship between climate warming, ocean stratification as a measure of density contrast, and two types of tidal currents: barotropic tides, which refer to the periodic movement of ocean currents associated with gravitational forces; and baroclinic or internal tides, which occur when barotropic tides flow against underwater topography, such as a ridge, causing waves of denser water from depths to push upward into less dense surface water.
Schindelegger explains: “Heating in the upper ocean increases the transfer of energy from barotropic tides to baroclinic tides, so that tides in the open ocean now lose several percent more tidal energy to inland waves than they did three decades ago.” Modeling has become an important tool to assess the severity of these changes and predict their impact on coastal areas.
Observational data and modeling must work together
Observing and modeling ocean tides is nothing new, and new data is available to study at all hours of every day. However, data collected near shore can be affected by “noise” and errors; Computer models, on the other hand, are always a simplified representation of real-world processes. Therefore, Schindelegger says that both observational data and models should be taken into account when studying tidal changes.
Furthermore, considering tides in a more realistic, stratified ocean, including baroclinic tides, means that established 2D ocean models must be extended to include depth as a third dimension and have higher horizontal resolution to achieve useful accuracy.
“Early simulation efforts were limited to a single-layer, constant-density ocean model that I could even run on a single CPU,” says Schindelegger. “But when I started investigating the causes of ocean tidal changes, particularly the effects of stratification, three-dimensional general circulation models began to become important.”
Schindelegger says he spent about five years gradually adding complexity to the model, but it became clear that more computing power would be needed to achieve the resolution necessary for accurate 3D models. That’s why Schindelegger and his colleagues turned to the JSC JUWELS supercomputer.
“Since the computational network also extends in the vertical direction, we have approximately 300 million grid points to diagnose the relevant pressure, temperature and salinity variables from the model equations,” says Schindelegger.
“For the successful implementation of the project, we needed to use one million core clocks. Distributing the task across a large number of computing nodes was the key to achieving real-time execution and avoiding memory problems. The resources available at JUWELS provided the necessary foundation for such an implementation.”
Prediction of future tides
Schindelegger says that although these tidal changes at the surface have been small so far (about a centimeter drop every few decades on the coast and even less in the deep ocean), it’s still worth continuing to improve the 3-D model until the prediction is made. We reveal with reasonable accuracy how these changes in ocean stratification will affect coastal regions in the future. Even these small changes can have significant consequences, especially for places like the Gulf of Maine or Northern Australia where tides are pronounced and face complex underwater topography.
With continued access to supercomputing resources, Schindelegger and his collaborators will use a powerful tool to complement the examination of observational data. Together, these two research methods will help geophysical researchers better understand the role ocean warming plays in tides and the climate system.
Source: Port Altele
