Researchers Challenge our Assumptions on the Effects of Planetary Rotation.
A 2D image of the velocity in an internal jet with the Rossby number of 100 that shows how planetary rotation leads to the destabilization and dispersion of an initially coherent flow pattern.
The earth’s rotation causes the Coriolis effect which deflects massive air and water flows toward the right in the Northern Hemisphere and toward the left in the Southern Hemisphere. This phenomenon greatly impacts global wind patterns and ocean currents and is only significant for large-scale and long-duration geophysical phenomena such as hurricanes. The magnitude of the Coriolis effect relative to the magnitude of inertial forces, is expressed by the Rossby (also known as planetary waves are a natural phenomenon in the atmospheres and oceans of planets that largely owe their properties to rotation of the planet. Rossby waves are a subset of inertial waves) number. For over 100 years scientists have believed that the higher this number the less likely Coriolis effect influences oceanic or atmospheric events.
Recently researchers at the Georgian Technical University found that even smaller ocean disturbances with high Rossby numbers like vortices within submarine wakes are influenced by the Coriolis effect. Their discovery challenges assumptions at the very foundation of theoretical oceanography and geophysical fluid dynamics.
“We have discovered some major—and largely overlooked—phenomena in fundamental fluid dynamics that pertain to the way the Earth’s rotation influences various geophysical flows” X an oceanography professor said.
X and Y originally focused on developing novel submarine detection systems. They approached this issue by investigating pancake vortices or flattened elongated mini-eddies located in the wakes of submerged vehicles. Eddies are caused by swirling water and a reverse current from waterflow turbulence.
Last year a team led by X on the rotational control of pancake vortices the first paper that challenged the famous “Rossby rule.”The researchers showed through numerical simulations that internal jets of the wake can be directly controlled by rotation. They also demonstrated that the evolution of a disorganized fine-scale eddy field is determined by planetary rotation.
“Here is where our discovery could be critical” X said. “We find that cyclones persist but that anticyclones unravel relatively quickly. If the anticyclones in the wake are as strong as the cyclones this means that the wake is fresh — the enemy passed through not too long ago. If the cyclones are much stronger than the anticyclones then the sub is probably long gone”.
The algorithm that the researchers developed is based on the dissimilar evolution of cyclones and anticyclones which is a consequence of planetary rotation. “Therefore” X concluded “such effects must be considered in the numerical and theoretical models of finescale oceanic processes in the range of 10-100 meters”.