Second-Order Velocity Structure Functions at Submesoscales.
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| Title: | Second-Order Velocity Structure Functions at Submesoscales. |
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| Authors: | Hypolite, Delphine1 (AUTHOR) dhypolite@atmos.ucla.edu, Srinivasan, Kaushik1 (AUTHOR), McWilliams, James C.1 (AUTHOR), Barkan, Roy1,2 (AUTHOR), Rodriguez, Ernesto3 (AUTHOR), Wineteer, Alex3 (AUTHOR), Molemaker, M. J.1 (AUTHOR), Torres, Hector3 (AUTHOR), Rocha, Cesar4 (AUTHOR) |
| Source: | Journal of Physical Oceanography. Jan2026, Vol. 56 Issue 1, p225-244. 20p. |
| Subjects: | Ocean currents, Ocean dynamics, Acoustic wave effects, Doppler radar, Turbulence, Kinetic energy |
| Abstract: | Observations of ocean surface currents from the JPL Doppler Scatterometer (DopplerScatt) during the Submesoscale Ocean Dynamics Experiment (S-MODE) campaigns reveal unexpectedly shallow second-order velocity structure function (SF) slopes at submesoscale separation scales (r < 10 km), deviating from classical turbulence theory and prior modeling results. This discrepancy suggests missing physics in current submesoscale-resolving numerical ocean models or an incomplete interpretation of the DopplerScatt observations. To investigate this, we analyze high-resolution Regional Ocean Modeling System (ROMS) simulations across a range of configurations that isolate the influence of model resolution, season, high-frequency forcings, and surface gravity wave effects on currents. We find that high-frequency motions associated with near-inertial waves reduce the transverse SF amplitude, driving the ratio of longitudinal to transverse SFs close to unity at submesoscales independently of the season. Additionally, the inclusion of wave–current interactions, often omitted in standard submesoscale-resolving models, can produce energetic small-scale motions, leading to broadband shallow structure function slopes. These results reveal a broader mechanism by which shallow structure function slopes can emerge: Any process that injects kinetic energy at small scales over a narrow range of wavenumbers will appear broadband in structure function space and produce shallow scalings. Wave effects are one such candidate and offer a plausible interpretation of the DopplerScatt observations under energetic wave conditions. However, under low wave conditions, other processes with similar spectral characteristics are required to account for the observed shallowness. Finally, the relatively large transverse-to-longitudinal SF ratio in DopplerScatt may reflect its lateral averaging over part of an inertial period, a sampling strategy not replicated in models and warranting further study. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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| Abstract: | Observations of ocean surface currents from the JPL Doppler Scatterometer (DopplerScatt) during the Submesoscale Ocean Dynamics Experiment (S-MODE) campaigns reveal unexpectedly shallow second-order velocity structure function (SF) slopes at submesoscale separation scales (r < 10 km), deviating from classical turbulence theory and prior modeling results. This discrepancy suggests missing physics in current submesoscale-resolving numerical ocean models or an incomplete interpretation of the DopplerScatt observations. To investigate this, we analyze high-resolution Regional Ocean Modeling System (ROMS) simulations across a range of configurations that isolate the influence of model resolution, season, high-frequency forcings, and surface gravity wave effects on currents. We find that high-frequency motions associated with near-inertial waves reduce the transverse SF amplitude, driving the ratio of longitudinal to transverse SFs close to unity at submesoscales independently of the season. Additionally, the inclusion of wave–current interactions, often omitted in standard submesoscale-resolving models, can produce energetic small-scale motions, leading to broadband shallow structure function slopes. These results reveal a broader mechanism by which shallow structure function slopes can emerge: Any process that injects kinetic energy at small scales over a narrow range of wavenumbers will appear broadband in structure function space and produce shallow scalings. Wave effects are one such candidate and offer a plausible interpretation of the DopplerScatt observations under energetic wave conditions. However, under low wave conditions, other processes with similar spectral characteristics are required to account for the observed shallowness. Finally, the relatively large transverse-to-longitudinal SF ratio in DopplerScatt may reflect its lateral averaging over part of an inertial period, a sampling strategy not replicated in models and warranting further study. [ABSTRACT FROM AUTHOR] |
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| ISSN: | 00223670 |
| DOI: | 10.1175/JPO-D-25-0038.1 |
