Boundary Layer Dynamics (1997) / Chapter Skim
Currently Skimming:
Chapter 2 - Scientific Opportunities and Recommendations
Chapter 2 - Scientific Opportunities and Recommendations
Pages 7-26
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 7... ...
Understanding the spatial and temporal 7 variability of these fluxes, particularly in coastal regions, is essential to evaluating the uncertainty of weather and undersea forecasts and, consequently, to predicting the performance of a variety of weather and sea-state-sensitive surveillance, mobility, and weapons systems. Characterizing fluxes of mass, momentum, heat, moisture, and gases across the oceanatrnosphere interface, and the dependence of these physical processes on mean conditions of the ocean and atrno sphere, is critical to understanding the vertical mixing of mass and material components, momentum, and heat within the upper layer of the ocean; air-sea interaction and its effects on wind stress; and the results of remote sensing of the ocean surface.
|
From page 8... ...
How do ocean surface waves affect marine surface fluxes? When can the standard Reynolds averaging techniques be applied to define marine surface fluxes?
|
From page 9... ...
Research Status Marine Atmospheric Boundary Layer A major challenge in large-scare atmospheric modeling is to adequately represent the unresolved physics of the boundary layer. Current problems include extending the influence of surface fluxes properly in the vertical; modeling the correct amount of wind veering through the baroclinic boundary layer; providing the information required to mode!
|
From page 10... ...
A significant fraction of the momentum flux from the atmosphere passes through the wave field before surface wave breaking transfers it to currents. Breaking surface waves almost certainly are the direct source of much of the turbulent mixing in the ocean near the surface.
|
From page 11... ...
If this cannot be accomplished by hiring new experts or transferring existing skilled personnel, a cooperative program with one or more of the leading university groups could be established. OCEAN DATA ASSIMILATION Definition Assimilation of ocean data depends on developing and validating the methods necessary to optimally utilize diverse in situ and remote sensing measurements for the purposes of better initializing, updating, and evaluating oceanic and marine atmospheric analysis and prediction models.
|
From page 12... ...
Satellites observe many different oceanic and atmospheric parameters with sensors operating in different frequency bands of the electromagnetic spectrum. Some satellite observations are direct measurements of the oceanic parameters (e.g., sea surface and wave height from altimeters, or directional spectrum from synthetic aperture radar)
|
From page 13... ...
13 SURFACE WAVE DYNAMICS Definition and Introduction Surface wave dynamics describes the forcing and characteristics of wind- and currentgenerated waves on the ocean surface. Understanding surface wave dynamics requires information on the overlying turbulent atmosphere, on waves and turbulence in the ocean mixed layer, on the many nonlinear interactions that occur between wave modes, and on the processes of forcing and dissipation.
|
From page 14... ...
The difficulties of long-term measurements have been well illustrated by the surface wave dynamics experiment (SWADE) on waves, in which buoys pulled loose from their moorings and were lost at sea.
|
From page 15... ...
Furthermore, many aspects of surface wave theory, especially those dealing with strong nonlinearities, are not amenable to a spectral approach. In fact, surface wave interactions at disparate scales may be fast and strong, and can modulate the wave field to leading order in times comparable to a wave period.
|
From page 16... ...
This range cannot be continuously covered by any existing techniques. In fact, one of the most challenging problems in surface wave studies is the development of techniques for measuring the spatio-temporal structure of the surface wave field.
|
From page 17... ...
Thus there is a real opportunity to make progress by exploiting progress in surface wave dynamics to develop improved deterministic and statistical models for, and to guide advanced experiments on, ocean wind-waves. The NRL optics group could be particularly encouraged to address instrumentation issues related to surface wave measurement.
|
From page 18... ...
physical mechanisms, including SAR imaging and microwave backscatter at intermediate incidence angles and at low grazing angles; (2) improved sensors for active microwave sensing; and (3)
|
From page 19... ...
This capability is important in its own right for wave studies, and also for verification of electromagnetic and acoustic scattering studies. Physics of Synthetic Aperture Radar Imagery of the Ocean Imaging the ocean surface using synthetic aperture radar (SAR)
|
From page 20... ...
Can ocean currents be measured using backscatter in the intermediate incidence angle regime? Can one apply Bragg scattering and composite surface theory to understand surface features seen in real and synthetic aperture radar images?
|
From page 21... ...
Their main use at present is for determining limitations on the approximations made in analytical theories. Physics of Microwave Backscatter from the Sea at Low Grazing Angles Understanding of the physical processes involved in microwave backscatter from the sea at incidence angles above 70 degrees is not as well developed as that in the lower incidence angle regime.
|
From page 22... ...
Without such characterization, many low-grazing-angle scattering theories will remain unconfirmed. Development of Improved Sensors for Active Microwave Remote Sensing The development of better sensors for actively sensing the ocean surface with microwaves is a continuing pursuit.
|
From page 23... ...
The pane! anticipates that the use of microwave radiometry to obtain vector wind data will prove feasible in the next few years and will be based solidly on theoretical developments, especially those involving polarimetric properties of the ocean surface.
|
From page 24... ...
and active and passive undersea probing of the ocean surface and mixed layers. Interpreting structural, chemical, and biological properties of the uppermost ocean requires knowledge of the environmental factors that control bubble size spectra: the acoustical and optical scattering by bubbles; and the species and populations of color-modifying, photosynthesizing dependent marine organisms.
|
From page 25... ...
The frequency of the sound radiated is a strong function of the bubble size; thus the spectrum of sound at 500 Hz or more is a function of the bubble size distribution. Rain striking the ocean surface generates sound.
|
From page 26... ...
Also,N^-W could make use of this work and these data, becoming involved in the coupling of ocean models to the optical data. Recommendation The panel recommends that NRL undertake a strong, coordinated research program that includes simultaneous underwater acoustic, electromagnetic, and optical measurements of the oceanic and marine atmospheric boundary layers in carefully selected coastal zone and continental shelf environments, in which different conditions of atmospheric forcing and the influence of surface slicks can also be quantitatively documented.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.