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The principle dynamical components in the large scale ocean (i.e. spatial scales larger than O(100m)) are dominated by mesoscale eddies, submesoscale currents and interia gravity waves comprising both storm-forced Near-Inertial Waves (NIWs) and tidally generated internal waves (TIWs).  While mesoscale eddies (length scales of 10s of kms), generated primarily through baroclinic instability are the principal reservoir of kinetic energy in the world oceans, submesoscale currents (O(1-10 km)) comprising mixed layer eddies and fronts interact strongly with mesoscales and are critical for  regulating biogeochemical and air-sea fluxes. Here we use the so-called coarse-graining approach to compute cross-scale energy fluxes that shed light on dynamical interactions between these three components and their impact on the upper ocean. By first decomposing the oceanic velocity field into rotational and divergent components on one hand (i.e. a Helmholtz decomposition) and separately using an eddy-IG...

Mesoscale Eddies are rotating structures found in the ocean with size of 50 to 500 km with a lifespan of 10 to 100 days. Eddies can be detected from Sea Surface Height (SSH) data. These circulations play a major role in transportation of heat, salt, carbon and nutrients throughout the ocean and are also associated with complex atmosphere-ocean interactions. That is why the detection of the eddies is extremely important to understand the big picture of the climate. Various, physics based methods were used for eddies detection but dependent upon the threshold values and human expertise which leads to the false detection. Therefore, advance techniques of artificial intelligence are needed to overcome these challenges. Various Deep Learning based works were done over the South China Sea and South Atlantic Ocean but Bay of Bengal is less explored. In this study we trained deep learning models, U-Net and Attention U-Net, for detecting the mesoscale ocean eddies over Bay of Bengal from daily ...

We use the ocean-only global circulation model (gcm) ICON-O with very high horizontal (5km), vertical and temporal resolution including the astronomical tidal forcing to study the effects of mesoscale eddies on the low-mode internal tide. This is the first study using a high-resolution gcm to study these interactions.
The diagnosed lunar semidiurnal (M2) internal tide reveals wavy patterns with horizontally varying wavelengths, which do not correspond to plain waves.
We therefore propose a new modal decomposition method based on spatial empirical orthogonal functions. Using this method we observe enhanced dissipation of the internal tide kinetic energy inside and in the lee area of the eddy, which can be attributed to enhanced weakening of the low mode internal tide. We also observe that eddies can significantly alter the propagation pathways of the low-mode internal tide by refracting the beam southwards.
We also find that the high-modes of the internal tide are trapped inside and ...

Baroclinic instability is a phenomenon in rotating stratified systems, and is known to play an important role in the Earth's atmosphere and ocean. The Eady problem is a text book example of baroclinic instability widely invoked for various applications (along with the Charney and Phillips problem). In the first part we recap some of the features of the standard geostrophic Eady problem (e.g., as described in most standard GFD textbooks), such as the linear instability characteristics, method of solution by analytical means, instability mechanism in terms of Counter-propagating Rossby Waves (CRWs), relations to baroclinic lifecycles, and its parameterisation in atmospheric and/or oceanic systems (e.g., works of Green, Gent-McWilliams and/or Greatbach-Lamb schemes). In the second part, we proceed to highlight and/or clarify some features of a modified Eady linear instability problem in the presence of a slope, namely (i) links of the Eady problem with quantum mechanics under the umbrella...

Baroclinic instability is a phenomenon in rotating stratified systems, and is known to play an important role in the Earth's atmosphere and ocean. The Eady problem is a text book example of baroclinic instability widely invoked for various applications (along with the Charney and Phillips problem). In the first part we recap some of the features of the standard geostrophic Eady problem (e.g., as described in most standard GFD textbooks), such as the linear instability characteristics, method of solution by analytical means, instability mechanism in terms of Counter-propagating Rossby Waves (CRWs), relations to baroclinic lifecycles, and its parameterisation in atmospheric and/or oceanic systems (e.g., works of Green, Gent-McWilliams and/or Greatbach-Lamb schemes). In the second part, we proceed to highlight and/or clarify some features of a modified Eady linear instability problem in the presence of a slope, namely (i) links of the Eady problem with quantum mechanics under the umbrella...

Submesoscale density fronts (1s-10s km wide) are a common feature of the ocean’s surface layer and are thought to be important for mediating buoyancy, heat, and energy exchanges which in turn have a substantial impact on the biogeochemistry. These fronts are challenging to observe due to their fast time and short length scales, so to date observations on regional and global scales have been limited. To fill this gap, this study uses a global database of along-track salinity and temperature data in combination with satellite data to identify 250,000 submesoscale density fronts across the globe.  On average, frontal buoyancy gradients scale with the frontal width, which is consistent with the expected dynamics. The submesoscale frontal gradients also exhibit global geographic variability that is correlated with the large scale density gradient, and inversely correlated with the large scale horizontal Turner angle and the mixed layer depth. Potential future research trajectories that coul...

Comprehending how submesoscale dynamics and their potential interplay with tides affect climate models is challenging due to their small scales and high computational demands. To address this challenge, our approach integrates modelling and observational methods. In this study, we investigate the impact of internal tides, eddies and submesoscale currents on the frequency energy spectrum of the ocean. To this end, we apply a novel simulation with telescopic grid refinement to achieve a horizontal resolution finer than 600 m over large regions of the South Atlantic. This refined resolution allows us to accurately capture submesoscale turbulence and a relatively large part of the internal wave spectrum under realistic atmospheric conditions. By comparing simulations with and without tides, we find that without tidal forcing there is significantly less energy at the high frequency end of the spectrum. Validation with mooring and Pressure Inverted Echo Sounder data sets deployed over a two ...

 Batchelor's self-similarity and Kraichnan's inertial range work on two-dimensional turbulence are unsuccessful due to the formation of coherent vortices which generate spatial hierarchical structures with time. In particular, the vortices create spatial intermittency and non-Gaussianity, and mechanisms for inverse energy cascade and direct enstrophy transfer are still open to probe. Via numerical simulations and self-similar vortex theory, we quantified the vortex populations and found the energy spectrum at high wave numbers follows a steeper slope than that predicted by the Batchelor and Kraichnan theories. Also, we discuss the reasons for the decay of enstrophy, which is due to the debris that is created by the vortex collisions.