Wave power

About: Wave power is a research topic. Over the lifetime, 2671 publications have been published within this topic receiving 41439 citations. The topic is also known as: wind wave energy & sea wave energy.

Wave period ratios and the calculation of wave power

Abstract: An informed, and accurate, characterization of the wave energy resource is an essential aspect selection of suitable sites for the first commercial installations of wave energy converters. This paper describes a detailed study on the variability of wave climate and measured spectral shapes and how they differ from the standard formulations prescribed by theory. In particular dissonance between the ratio of the energy period (TE) to the average zero-crossing period (T02) is investigated at a range of open ocean locations. This relationship is important in the context of resource assessment as many previous works, lacking in detailed spectral data, have often assumed an incorrect ratio. This in turn has influenced the accuracy of the resulting estimates of wave energy. It is demonstrated that the earlier use of the frequently-employed wave period ratios is erroneous and more suitable relationships are presented for the Bretschneider and JONSWAP theoretical spectra. Furthermore, analysis of measured buoy data from real sea-states is used to illustrate that this relationship can in fact vary significantly in practice, depending on geographical location and the prevalent wave conditions. The variability that exists in spectral shape and bandwidth, and the effect this has on the relationship between TE and T02, is illustrated through the comparison of recorded spectra with the Bretschneider spectrum. Analysis of a fifteen year dataset measured by a buoy off the coast of Southern California is presented to illustrate how the wave period ratio fluctuates on a seasonal and interannual basis, while it is also shown that previous studies of the Irish wave energy resource may have underestimated the theoretical power available by as much as 18%.

Ground observations of high‐latitude Pc3‐4 ULF waves

Abstract: [1] A detailed study has been undertaken of Pc3-4 waves recorded on the ground with the IMAGE magnetometer array (56° 0.6) across the entire station array. Most of these had well-defined wave packet appearance in time series records and a clear peak in power spectra. Their occurrence and frequency suggest the waves are generated by the upstream ion-cyclotron resonance mechanism, with no evidence of generation by the Kelvin-Helmholtz instability. For each event the amplitude, phase, coherence, ellipticity, azimuth angle, and degree of polarization across the ground array were examined. The coherence length, azimuthal wave number, and hence the apparent wave propagation velocity were thus determined, with emphasis on the precision and significance of these measurements. It was found that these daytime Pc3-4 pulsations usually have maximum amplitude near the magnetopause projection, meridional coherence lengths of order 1.5–2.0 × 103 km, and low azimuthal wave numbers during morning hours, averaging around −4.0 (indicating westward propagation). Over 80% of events propagated poleward and westward, with average equivalent ground velocity of 41 km/s N43°W for the H component. About 24–30% of the events are higher harmonics of field line resonances. There is no evidence that the remaining events arise from cavity modes or localized modulated electron precipitation. The observations instead suggest a mechanism involving mode coupling and field-guided propagation. In this model, fast mode waves in the Pc3-4 range entering near the subsolar point propagate earthward and due to the inhomogeneity of the magnetosphere couple to the field-guided Alfven mode. At certain latitudes, standing oscillations are established at harmonics of the local resonant frequency, while at other latitudes traveling waves convey energy to low altitudes. The expected L dependence of wave power and travel time agree well with observed amplitude and phase profiles.

Off‐equatorial chorus occurrence and wave amplitude distributions as observed by the Polar Plasma Wave Instrument

Abstract: [1] Determining the global distribution of chorus wave power in the off-equatorial region (i.e., magnetic latitude λ > 15°) is a crucial component of understanding the contribution of chorus to radiation belt acceleration and loss. In this paper we use a database of chorus power spectral density observations from the Plasma Wave Instrument (PWI) Sweep Frequency Receiver (SFR) on the Polar spacecraft to generate separate distributions of wave occurrence rate and magnetic field amplitude as a function of space and geomagnetic activity. Previous studies focused on a band-integrated and time-averaged data product to characterize the global distribution of wave power. Using a slightly different technique, we first estimate the wave amplitude from the peak wave power spectral density for times when chorus is observed. The mean wave amplitude at a given location is then multiplied by the wave occurrence rate to yield the time-averaged amplitude. We present the spatial distributions of wave occurrence rate, mean amplitude, and time-averaged amplitude in the region of maximum statistics, λ > 15° and R = 4−8 RE. We find that waves of significant amplitude (>10 pT) can be observed in all local time sectors, but significant wave occurrence (>20%) is confined to the dawn and noon local time sectors. Wave mean and time-averaged amplitudes are also highest in the dawn and noon sectors. The spatial extent of regions with high time-averaged amplitude is primarily defined by regions of high occurrence rate. Time-averaged amplitudes exceeding ∼6 pT are observed up to a magnetic latitude of 40° at dawn and 50° at noon, while at midnight and dusk the time-averaged amplitude tends to be below that value. We also examine the geomagnetic and solar wind dependence of the spatial distribution of wave occurrence, mean amplitude, and time-averaged amplitude. In the off-equatorial region (λ > 15°), wave amplitude and occurrence on the nightside increase dramatically during disturbed geomagnetic and solar wind conditions. In contrast, waves on the dayside occur over a wider range of activity, and even during quiet conditions, mean and time-averaged amplitudes at noon significantly exceed amplitudes at midnight for disturbed times. In the dusk sector, observation of waves is mostly limited to quiet conditions, and during those times, mean amplitudes at dusk exceed those at midnight and approach amplitudes observed in the dawn sector. Parallel investigation of the independent variability of occurrence and amplitude provides a more complete picture of the chorus wave environment, particularly for application to modeling radiation belt dynamics on both short and long time scales.