Does the scatterometer see wind speed or friction velocity?

Studies of radar backscatter from the sea surface are referred either to the wind speed, U, or friction velocity, u(sub *). Bragg scattering theory suggests that these variations in backscatter are directly related to the height of the capillary-gravity waves modulated by the larger waves in tilt and by straining of the short wave field. The question then arises as to what characteristic of the wind field is most probably correlated with the wave number spectrum of the capillary-gravity waves. The justification for selecting U as the appropriate meteorological parameter to be associated with backscatter from L-band to Ku-band are reviewed. Both theoretical reasons and experimental evidence are used to demonstrate that the dominant parameter is U/C(lambda) where U is the wind speed at a height of about lambda/2 for waves having a phase speed of C(lambda)

Gravity wave turbulence in a laboratory flume

We present an experimental study of the statistics of surface gravity wave turbulence in a flume of a horizontal size 12×6  m. For a wide range of amplitudes the wave energy spectrum was found to scale as Eω∼ω-ν in a frequency range of up to one decade. However, ν appears to be nonuniversal: it depends on the wave intensity and ranges from about 6 to 4. We discuss our results in the context of existing theories and argue that at low wave amplitudes the wave statistics is affected by the flume finite size, and at high amplitudes the wave breaking effect dominates

The role of meteorological focusing in generating rogue wave conditions

Abstract. Rogue waves are believed to be the consequence of focusing of wave energy. While there are several ways that energy may be focused, we concentrate here on the role of meteorological patterns in generating mixed sea conditions. We demonstrate the sharp increase in the probability of high wave crests for a given significant height when the sea is mixed, i.e., consists of wave trains arriving from very different directions. Then, using a full spectral wave prediction model forced by NCEP winds on the Atlantic Ocean, we illustrate the role of meteorological focusing in enhancing the probability of occurrence of rogue waves

Observation of gravity-capillary wave turbulence

We report the observation of the cross-over between gravity and capillary wave turbulence on the surface of mercury. The probability density functions of the turbulent wave height are found to be asymmetric and thus non Gaussian. The surface wave height displays power-law spectra in both regimes. In the capillary region, the exponent is in fair agreement with weak turbulence theory. In the gravity region, it depends on the forcing parameters. This can be related to the finite size of the container. In addition, the scaling of those spectra with the mean energy flux is found in disagreement with weak turbulence theory for both regimes

Using Asymmetry to Your Advantage: Learning to Acquire and Accept External Assistance During Prolonged Split-belt Walking

People can learn to exploit external assistance during walking to reduce energetic cost. For example, walking on a split-belt treadmill affords the opportunity for people to redistribute the mechanical work performed by the legs to gain assistance from the difference in belts’ speed and reduce energetic cost. Though we know what people should do to acquire this assistance, this strategy is not observed during typical adaptation studies. We hypothesized that extending the time allotted for adaptation would result in participants adopting asymmetric step lengths to increase the assistance they can acquire from the treadmill. Here, participants walked on a split-belt treadmill for 45 min while we measured spatiotemporal gait variables, metabolic cost, and mechanical work. We show that when people are given sufficient time to adapt, they naturally learn to step further forward on the fast belt, acquire positive mechanical work from the treadmill, and reduce the positive work performed by the legs. We also show that spatiotemporal adaptation and energy optimization operate over different timescales: people continue to reduce energetic cost even after spatiotemporal changes have plateaued. Our findings support the idea that walking with symmetric step lengths, which is traditionally thought of as the endpoint of adaptation, is only a point in the process by which people learn to take advantage of the assistance provided by the treadmill. These results provide further evidence that reducing energetic cost is central in shaping adaptive locomotion, but this process occurs over more extended timescales than those used in typical studies

Evidence of energy and momentum flux from swell to wind

Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 2143-2156, doi:10.1175/JPO-D-15-0213.1.Measurements of pressure near the surface in conditions of wind sea and swell are reported. Swell, or waves that overrun the wind, produces an upward flux of energy and momentum from waves to the wind and corresponding attenuation of the swell waves. The estimates of growth of wind sea are consistent with existing parameterizations. The attenuation of swell in the field is considerably smaller than existing measurements in the laboratory

Health Information Technology in the United States: The Information Base for Progress

Health information technology (HIT) has the potential to advance health care quality by helping patients with acute and chronic conditions receive recommended care, diminishing disparities in treatment and reducing medical errors. Nevertheless, HIT dissemination has not occurred rapidly, due in part to the high costs of electronic health record (EHR) systems for providers of care—including the upfront capital investment, ongoing maintenance and short-term productivity loss. Also, many observers are concerned that, if HIT follows patterns observed with other new medical technologies, HIT and EHRs may diffuse in ways that systematically disadvantage vulnerable patient populations, thus increasing or maintaining existing disparities in access to and quality of care. These and other concerns have led to public and private efforts that aim to increase the pace of and reduce disparities in HIT diffusion by formulating national plans for dissemination, catalyzing the development of standards to encourage interoperability and promoting public-private partnerships to develop HIT infrastructures at the local and regional levels

Observation of intermittency in wave turbulence

We report the observation of intermittency in gravity-capillary wave turbulence on the surface of mercury. We measure the temporal fluctuations of surface wave amplitude at a given location. We show that the shape of the probability density function of the local slope increments of the surface waves strongly changes across the time scales. The related structure functions and the flatness are found to be power laws of the time scale on more than one decade. The exponents of these power laws increase nonlinearly with the order of the structure function. All these observations show the intermittent nature of the increments of the local slope in wave turbulence. We discuss the possible origin of this intermittency.Comment: new version to Phys. Rev. Let