Search

Author Posting. © The Oceanography Society, 2017. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 30, no. 2 (2017): 74–87, doi:10.5670/oceanog.2017.224., The Arabian Sea circulation is forced by strong monsoonal winds and is characterized by vigorous seasonally reversing currents, extreme differences in sea surface salinity, localized substantial upwelling, and widespread submesoscale thermohaline structures. Its complicated sea surface temperature patterns are important for the onset and evolution of the Asian monsoon. This article describes a program that aims to elucidate the role of upper-ocean processes and atmospheric feedbacks in setting the sea surface temperature properties of the region. The wide range of spatial and temporal scales and the difficulty of accessing much of the region with ships due to piracy motivated a novel approach based on state-of-the-art autonomous ocean sensors and platforms. The extensive data set that is being collected, combined with numerical models and remote sensing data, confirms the role of planetary waves in the reversal of the Somali Current system. These data also document the fast response of the upper equatorial ocean to monsoon winds through changes in temperature and salinity and the connectivity of the surface currents across the northern Indian Ocean. New observations of thermohaline interleaving structures and mixing in setting the surface temperature properties of the northern Arabian Sea are also discussed., The authors were funded through NASCar DRI grants. Additional support from the Global Drifter Program, grant NA15OAR4320071 (LC, VH); the CSL Laboratory at the NCAR CISL (Yellowstone ark:/85065/d7wd3xhc) (JMC); and the Department of Energy ACME project DE-SC0012778 (JMC) are gratefully acknowledged.

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 41 (2014): 7584–7590, doi:10.1002/2014GL061637., Two near-surface dye releases were mapped on scales of minutes to hours temporally, meters to order 1 km horizontally, and 1–20 m vertically using a scanning, depth-resolving airborne lidar. In both cases, dye evolved into a series of rolls with their major axes approximately aligned with the wind and/or near-surface current. In both cases, roll spacing was also of order 5–10 times the mixed layer depth, considerably larger than the 1–2 aspect ratio expected for Langmuir cells. Numerical large-eddy simulations under similar forcing showed similar features, even without Stokes drift forcing. In one case, inertial shear driven by light winds induced large aspect ratio large-eddy circulation. In the second, a preexisting lateral mixed layer density gradient provided the dominant forcing. In both cases, the growth of the large-eddy structures and the strength of the resulting dispersion were highly dependent on the type of forcing., Support for the 2004 field experiment was provided by the Cecil H. and Ida M. Green Technology Innovation Fund and Coastal Ocean Institute grant 27001545, both through Woods Hole Oceanographic Institution, and by Office of Naval Research grant N00014-01-1-0984. Support for the 2011 field experiments was provided by ONR grants N00014-09-1-0194, N00014-09-1-0175, N00014-11-WX-21010, N00014-12-WX-21031, and N00014-09-1-0460 and NSF grants OCE-0751734 and OCE-0751653. Simulations were supported under grant N00014-09-1-0268., 2015-05-06

Research during the fouth year of this project has focused on extending the analysis of baroclinic instability and performing a mixed layer experiment to examine dye dispersion.

Investigate tropical convection and upper ocean circulations on scales from 100 m to 200 km. Elucidate specifically how the ocean mixed layer responds to forcing from atmospheric convection such as wind and precipitation, and thus how surface fluxes depend on the history of convective events. Perform high-resolution coupled atmosphere-ocean numerical model simulations, whose fidelity is a benchmark for operational models and parameterizations. Insights gained from these simulations will be used to improve parameterizations used in operational scale models, and to refine hypotheses in collaboration with investigators working on observational field studies in the Indian and West Pacific Oceans.

The long-term goal is to improve operational numerical weather prediction (NWP) models to more accurately simulate the interaction of tropical deep convection and atmospheric and oceanic boundary layers. The objectives are to investigate tropical convection and upper ocean circulations on scales from 100 m to 200 km. Elucidate specifically how the ocean mixed layer responds to forcing from atmospheric convection such as wind and precipitation, and thus how surface fluxes depend on the history of convective events. Perform high-resolution coupled atmosphere-ocean numerical model simulations, whose fidelity is a benchmark for operational models and parameterizations. Insights gained from these simulations will be used to improve parameterizations used in operational scale models, and to refine hypotheses in collaboration with investigators working on observational field studies in the Indian and West Pacific Oceans. Intraseasonal variability in the tropics is dominated by the Madden-Julian Oscillation (MJO), which generates large-scale variability in the structure and organization of deep convective cloud systems. MJO events consist of multiple scales of convective activity, from single kilometer-sized cells to circulations encompassing half of the tropical Pacific. Key factors for tropical convection include sea surface evaporation and large-scale atmospheric moisture convergence, which both depend on sea surface temperature and wind speed. Most numerical models do not resolve turbulent and convective scales, nor do they simulate the MJO accurately. We plan to investigate how convection during the active phase of MJO affects and interacts with the ocean mixed layer.

The long-term goal of this project is to improve our ability to understand, model and predict lateral mixing and the associated submesoscale physical structure and processes in the upper and interior ocean. The main objective of this project is to examine the interaction between baroclinic, mesoscale eddies and turbulence using a large-eddy simulation (LES) model. Cases will focus on strong, baroclinic waves that form in the mixed layer along surface fronts with scales of a few km, and on mesoscale eddies that are imbedded within larger scale frontal regions. Our goal is to quantify, understand, and ultimately parameterize the physical processes that lead to lateral mixing. Simulations will help guide field experiments planned as part of the Lateral Mixing DRI, and provide a tool for understanding observations in the analysis phase of the project. High-resolution simulations of baroclinic instability and the interaction of mesoscale flow with turbulent mixing are conducted and analyzed using a large-eddy simulation model. Our analysis centers on quantifying and understanding the mechanisms by which small-scale turbulent structure develops on the mesoscale field, the physical processes and balances that control lateral mixing of fluid properties across the unstable front, and the transition from strongly horizontal, geostrophic motion on the mesoscale to three-dimensional, quasi-isotropic, non-hydrostatic motion on turbulent scales.

The long-term goal of this project is to improve our ability to understand, model, and predict lateral mixing and the associated submesoscale physical structure and processes in the upper and interior ocean. The main objective of this project is to examine the interaction between baroclinic, mesoscale eddies and turbulence using a large-eddy simulation (LES) model. Cases will focus on strong, baroclinic waves that form in the mixed layer along surface fronts with scales of a few km, and on mesoscale eddies that are imbedded within larger scale frontal regions. Our goal is to quantify, understand, and ultimately parameterize the physical processes that lead to lateral mixing. Simulations will help guide field experiments planned as part of the Lateral Mixing DRI, and provide a tool for understanding observations in the analysis phase of the project. High-resolution simulations of baroclinic instability and the interaction of mesoscale flow with turbulent mixing are conducted and analyzed using a large-eddy simulation model. Our analysis centers on quantifying and understanding the mechanisms by which small-scale turbulent structure develops on the mesoscale field; the physical processes and balances that control lateral mixing of fluid properties across the unstable front; and the transition from strongly horizontal, geostrophic motion on the mesoscale to three-dimensional, quasi-isotropic, non-hydrostatic motion on turbulent scales. A second area of research that we are investigating concerns the dispersion of dye by mixing in the ocean surface boundary layer. Observations of dye taken from aircraft off the coast of Florida in preliminary experiments suggest that dye patches are capable of outlining mixing circulations contained in the ocean boundary layer. Lateral banding in the dye observations suggests that circulations in the mixed layer are actively concentrating the dye along the wind direction.

Long-Term Goal: Improve operational numerical weather prediction (NWP) models to more accurately simulate the interaction of tropical deep convection and atmospheric and oceanic boundary layers. Objectives: Investigate tropical convection and upper ocean circulations on scales from 100 m to 200 km. Elucidate specifically how the ocean mixed layer responds to forcing from atmospheric convection such as wind and precipitation, and thus how surface fluxes depend on the history of convective events. Perform high-resolution coupled atmosphere-ocean numerical model simulations, whose fidelity is a benchmark for operational models and parameterizations. Insights gained from these simulations will be used to improve parameterizations used in operational scale models, and to refine hypotheses in collaboration with investigators working on observational field studies in the Indian and West Pacific Oceans.