Shikhar Rai
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Research Subjects
Shikhar Rai has a total of 26 co-authors. Here are the top co-authors by number of shared publications:
- Hussein Aluie
University of Rochester
5 shared publications - Jessica K. Shang
University of Rochester
2 shared publications - Matthew W. Hecht
Los Alamos National Laboratory Los Alamos NM USA
2 shared publications Aarne Lees
Department of Mechanical Engineering, University of Rochester, Rochester, New York 14625, USA
1 shared publication- Aarne Lees
Laboratory for Laser Energetics, University of Rochester 1 , Rochester, New York 14623
1 shared publication - Alistair Adcroft
Princeton University Princeton NJ USA
1 shared publication
Latest Publications
- Open Access
- 2 December 2025
- Published by Wiley
Sampling Scale Mismatch Drives Discrepancies between Satellite and TAO Buoy Measurements of Ocean Surface Winds
Satellite (QuikSCAT and ASCAT) and buoy winds measurements at TAO mooring sites generally agree, with 80\% of vector-wind comparisons falling within $\pm 2~\mathrm{m/s}$ and $\pm 25\degree$. We investigate the environmental conditions for the discrepancies in the remaining 20\% of mismatches, identified using Density-Based Spatial Clustering of Applications (DBSCAN). These discrepancies are concentrated in the ITCZ and the western Pacific, regions of frequent precipitation, yet the mismatches are not caused by rain contamination. Instead, the discrepancies are associated with higher relative humidity and sea-air temperature differences, along with lower winds, reduced Stokes drift velocity, and lower wind-wave significant height. The discrepancies also exhibit greater hourly variability in vector-winds, relative humidity, and sea-air temperature difference. Using a random forest model, we demonstrate that these discrepancies are systematically predictable from buoy-measured meteorological variables and wave reanalysis data. The results indicate that differences in the spatial and temporal sampling scales between satellites and buoys primarily drive the discrepancies, which can be slightly reduced by temporal smoothing of buoy winds and spatial smoothing of satellite winds. This implies that most mismatches arise from sampling scale differences rather than deficiencies in either observing system.- 2 December 2025
- Published by Wiley
Open AccessSampling Scale Mismatch Drives Discrepancies between Satellite and TAO Buoy Measurements of Ocean Surface Winds
Satellite (QuikSCAT and ASCAT) and buoy winds measurements at TAO mooring sites generally agree, with 80\% of vector-wind comparisons falling within $\pm 2~\mathrm{m/s}$ and $\pm 25\degree$. We investigate the environmental conditions for the discrepancies in the remaining 20\% of mismatches, identified using Density-Based Spatial Clustering of Applications (DBSCAN). These discrepancies are concentrated in the ITCZ and the western Pacific, regions of frequent precipitation, yet the mismatches are not caused by rain contamination. Instead, the discrepancies are associated with higher relative humidity and sea-air temperature differences, along with lower winds, reduced Stokes drift velocity, and lower wind-wave significant height. The discrepancies also exhibit greater hourly variability in vector-winds, relative humidity, and sea-air temperature difference. Using a random forest model, we demonstrate that these discrepancies are systematically predictable from buoy-measured meteorological variables and wave reanalysis data. The results indicate that differences in the spatial and temporal sampling scales between satellites and buoys primarily drive the discrepancies, which can be slightly reduced by temporal smoothing of buoy winds and spatial smoothing of satellite winds. This implies that most mismatches arise from sampling scale differences rather than deficiencies in either observing system. - Open Access
- 30 January 2025
- Published by Springer Nature in Nature Communications
- Vol. 16 (1) , 1-9
Atmospheric wind energization of ocean weather
Ocean weather comprises vortical and straining mesoscale motions, which play fundamentally different roles in the ocean circulation and climate system. Vorticity determines the movement of major ocean currents and gyres. Strain contributes to frontogenesis and the deformation of water masses, driving much of the mixing and vertical transport in the upper ocean. While recent studies have shown that interactions with the atmosphere damp the ocean’s mesoscale vortices O (100) km in size, the effect of winds on straining motions remains unexplored. Here, we derive a theory for wind work on the ocean’s vorticity and strain. Using satellite and model data, we discover that wind damps strain and vorticity at an equal rate globally, and unveil striking asymmetries based on their polarity. Subtropical winds damp oceanic cyclones and energize anticyclones outside strong current regions, while subpolar winds have the opposite effect. A similar pattern emerges for oceanic strain, where subtropical convergent flow is damped along the west-equatorward east-poleward direction and energized along the east-equatorward west-poleward direction. These findings reveal energy pathways through which the atmosphere shapes ocean weather.
- 30 January 2025
- Published by Springer Nature in Nature Communications
- Vol. 16 (1) , 1-9
Open AccessAtmospheric wind energization of ocean weather
Ocean weather comprises vortical and straining mesoscale motions, which play fundamentally different roles in the ocean circulation and climate system. Vorticity determines the movement of major ocean currents and gyres. Strain contributes to frontogenesis and the deformation of water masses, driving much of the mixing and vertical transport in the upper ocean. While recent studies have shown that interactions with the atmosphere damp the ocean’s mesoscale vortices O (100) km in size, the effect of winds on straining motions remains unexplored. Here, we derive a theory for wind work on the ocean’s vorticity and strain. Using satellite and model data, we discover that wind damps strain and vorticity at an equal rate globally, and unveil striking asymmetries based on their polarity. Subtropical winds damp oceanic cyclones and energize anticyclones outside strong current regions, while subpolar winds have the opposite effect. A similar pattern emerges for oceanic strain, where subtropical convergent flow is damped along the west-equatorward east-poleward direction and energized along the east-equatorward west-poleward direction. These findings reveal energy pathways through which the atmosphere shapes ocean weather.
- Open Access
- 1 February 2023
- Published by Wiley
Scale-dependent Air-Sea Mechanical Coupling: Resolution Mismatch and Spurious Eddy-Killing
Mechanical coupling of the atmosphere to the ocean surface in general circulation models is represented using bulk wind stress formulations. The stress is often based on either absolute wind velocity, τa, or the more correct wind velocity relative to the ocean surface currents, τr. Here, we use coarse-graining to disentangle wind work by these formulations at different length-scales. We show that both can be reasonably accurate in forcing the ocean at length-scales larger than the mesoscales, with τa overestimating wind work by 10%. However, τa and τr show stark and opposing systematic biases in how they drive the mesoscales; τa does negligible (albeit positive) work on the mesoscales, while τr yields eddy-killing (negative work) that is artificially exaggerated by a factor of ≈4. We derive an analytical criterion for eddy-killing to occur, which shows that exaggerated eddy killing is due to resolution mismatch between the atmosphere and ocean. Our criterion highlights the disproportionate effect small-scale winds Ο(100)km can have on the dynamics of mesoscale ocean eddies, despite the dominant atmospheric motions being at length-scales larger than Ο(103) km. The eddy-killing criterion shows that large-scale winds do not necessarily cause eddy-killing but are merely an amplification factor for wind work on the mesoscales, which can be either positive or negative depending on the local alignment of small-scale winds with the ocean eddies. We propose a simple reformulation of τr, without introducing tuning parameters, to remove spurious eddy-killing from air-sea resolution mismatch that is often present in climate models.
- 1 February 2023
- Published by Wiley
Open AccessScale-dependent Air-Sea Mechanical Coupling: Resolution Mismatch and Spurious Eddy-Killing
Mechanical coupling of the atmosphere to the ocean surface in general circulation models is represented using bulk wind stress formulations. The stress is often based on either absolute wind velocity, τa, or the more correct wind velocity relative to the ocean surface currents, τr. Here, we use coarse-graining to disentangle wind work by these formulations at different length-scales. We show that both can be reasonably accurate in forcing the ocean at length-scales larger than the mesoscales, with τa overestimating wind work by 10%. However, τa and τr show stark and opposing systematic biases in how they drive the mesoscales; τa does negligible (albeit positive) work on the mesoscales, while τr yields eddy-killing (negative work) that is artificially exaggerated by a factor of ≈4. We derive an analytical criterion for eddy-killing to occur, which shows that exaggerated eddy killing is due to resolution mismatch between the atmosphere and ocean. Our criterion highlights the disproportionate effect small-scale winds Ο(100)km can have on the dynamics of mesoscale ocean eddies, despite the dominant atmospheric motions being at length-scales larger than Ο(103) km. The eddy-killing criterion shows that large-scale winds do not necessarily cause eddy-killing but are merely an amplification factor for wind work on the mesoscales, which can be either positive or negative depending on the local alignment of small-scale winds with the ocean eddies. We propose a simple reformulation of τr, without introducing tuning parameters, to remove spurious eddy-killing from air-sea resolution mismatch that is often present in climate models.
- 3 October 2022
- Published by American Physical Society (APS) in Physical Review Fluids
- Vol. 7 (10) , 104601
Effective drift velocity from turbulent transport by vorticity
We highlight the differing roles of vorticity and strain in the transport of coarse-grained scalars at length scales larger than by smaller scale (subscale) turbulence. We use the first term in a multiscale gradient expansion due to Eyink [ J. Fluid Mech. 549, 159 (2006)], which exhibits excellent correlation with the exact subscale physics when the partitioning length is any scale smaller than that of the spectral peak. We show that unlike subscale strain, which acts as an anisotropic diffusion/antidiffusion tensor, subscale vorticity's contribution is solely a conservative advection of coarse-grained quantities by an eddy-induced nondivergent velocity, , that is proportional to the curl of vorticity. Therefore, material (Lagrangian) advection of coarse-grained quantities is accomplished not by the coarse-grained flow velocity, , but by the effective velocity, , the physics of which may improve commonly used LES models.- 3 October 2022
- Published by American Physical Society (APS) in Physical Review Fluids
- Vol. 7 (10) , 104601
Effective drift velocity from turbulent transport by vorticity
We highlight the differing roles of vorticity and strain in the transport of coarse-grained scalars at length scales larger than by smaller scale (subscale) turbulence. We use the first term in a multiscale gradient expansion due to Eyink [ J. Fluid Mech. 549, 159 (2006)], which exhibits excellent correlation with the exact subscale physics when the partitioning length is any scale smaller than that of the spectral peak. We show that unlike subscale strain, which acts as an anisotropic diffusion/antidiffusion tensor, subscale vorticity's contribution is solely a conservative advection of coarse-grained quantities by an eddy-induced nondivergent velocity, , that is proportional to the curl of vorticity. Therefore, material (Lagrangian) advection of coarse-grained quantities is accomplished not by the coarse-grained flow velocity, , but by the effective velocity, , the physics of which may improve commonly used LES models.- Open Access
Effective Drift Velocity from Turbulent Transport by Vorticity
We highlight the differing roles of vorticity and strain in the transport of coarse-grained scalars at length-scales larger than $\ell$ by smaller scale (subscale) turbulence. %subscale flux/stress which appear in the evolution of coarse-grained (resolved) scalars/momentum account for the effect of (subgrid) scales smaller than the coarse-graining length $\ell$. We use the first term in a multiscale gradient expansion due to Eyink \cite{Eyink06a}, which exhibits excellent correlation with the exact subscale physics when the partitioning length $\ell$ is any scale smaller than that of the spectral peak. We show that unlike subscale strain, which acts as an anisotropic diffusion/anti-diffusion tensor, subscale vorticity's contribution is solely a conservative advection of coarse-grained quantities by an eddy-induced non-divergent velocity, $\bv_*$, that is proportional to the curl of vorticity. Therefore, material (Lagrangian) advection of coarse-grained quantities is accomplished not by the coarse-grained flow velocity, $\OL\bu_\ell$, but by the effective velocity, $\OL\bu_\ell+\bv_*$, the physics of which may improve commonly used LES models.Open AccessEffective Drift Velocity from Turbulent Transport by Vorticity
We highlight the differing roles of vorticity and strain in the transport of coarse-grained scalars at length-scales larger than $\ell$ by smaller scale (subscale) turbulence. %subscale flux/stress which appear in the evolution of coarse-grained (resolved) scalars/momentum account for the effect of (subgrid) scales smaller than the coarse-graining length $\ell$. We use the first term in a multiscale gradient expansion due to Eyink \cite{Eyink06a}, which exhibits excellent correlation with the exact subscale physics when the partitioning length $\ell$ is any scale smaller than that of the spectral peak. We show that unlike subscale strain, which acts as an anisotropic diffusion/anti-diffusion tensor, subscale vorticity's contribution is solely a conservative advection of coarse-grained quantities by an eddy-induced non-divergent velocity, $\bv_*$, that is proportional to the curl of vorticity. Therefore, material (Lagrangian) advection of coarse-grained quantities is accomplished not by the coarse-grained flow velocity, $\OL\bu_\ell$, but by the effective velocity, $\OL\bu_\ell+\bv_*$, the physics of which may improve commonly used LES models. - Top Cited PapersOpen Access
- 9 July 2021
- Published by American Association for the Advancement of Science (AAAS) in Science Advances
- Vol. 7 (28) , eabf4920
Scale of oceanic eddy killing by wind from global satellite observations
While wind is the primary driver of the oceanic general circulation, it kills the ocean’s most energetic motions.
- 9 July 2021
- Published by American Association for the Advancement of Science (AAAS) in Science Advances
- Vol. 7 (28) , eabf4920
Top Cited PapersOpen AccessScale of oceanic eddy killing by wind from global satellite observations
While wind is the primary driver of the oceanic general circulation, it kills the ocean’s most energetic motions.
- 1 March 2016
- Published by Elsevier in Renewable Energy
- Vol. 87, 307-316
A methodology for designing Francis runner blade to find minimum sediment erosion using CFD
- 1 March 2016
- Published by Elsevier in Renewable Energy
- Vol. 87, 307-316
A methodology for designing Francis runner blade to find minimum sediment erosion using CFD