Wind Energy Flux Research Articles

How does the solar wind blow? Some basic aspects

Major properties of the solar atmosphere and wind are not understood. The energy distribution of the solar atmosphere perturbations, over nearly ten orders of magnitude in energy, is close (within one order of magnitude) to a power-law of index -2, even though there is no agreement on the detailed shape. There is no agreed explanation of the origin of the solar wind, either, nor of the fact that the total wind energy flux is independent of speed, latitude, and phase of solar cycle, with an average base flux of 70 W/m – a figure that is similar for a number of other cool stellar winds, and is close to the total observed energy flux of solar atmosphere perturbations. A major theoretical difficulty is that both coronal heating and wind production depend fundamentally on the heat flux, and the solar atmosphere is not collisional enough for classical transport theory to hold. Heat transport thus behaves non classically and the particle velocity distributions may have significant high energy tails, which should dramatically affect coronal heating and solar wind acceleration, in a way that is outside the scope of standard MHD.

Estimating the energy flux from the wind to ocean inertial motions: The sensitivity to surface wind fields

The energy flux from the wind to ocean inertial motions is estimated using three wind products in comparison to the benchmark NCEP winds: (1) corrected NCEP winds, based on scatterometer measurements (Large and Yeager, 2004), increase the energy flux by 50% globally and by 30% at mid‐latitudes, (2) blended QSCAT/NCEP winds double the energy flux at mid‐latitudes, and lead to much larger increases at high latitudes and near the equator, (3) enhanced NCEP winds in the North Atlantic Ocean, through a kinematic reanalysis procedure (Swail and Cox, 2000), increase the energy flux by 30%. We conclude that estimates of the energy fluxes are quite sensitive to wind errors and spatial resolution. NCEP winds provide a lower bound estimate of wind energy flux into ocean near‐inertial motions.

Momentum and energy exchange across an air–water interface. Partitioning (into waves and currents) and parameterization

Abstract Expressions have been derived to parameterize: (a) the total (time) mean wind momentum and energy fluxes across the air–sea interface, and (b) their partition into waves and a mean surface drift current, as expressed by the fractions γ M and γ E , in terms of the wave age, c p / u * , and the significant slope, § , of the wave field. Available laboratory and field observations support the parameterization predictions. The fraction of the wave-supported momentum, γ M , increases initially with the wave age (and/or the non-dimensional fetch, x ˜ ) but, as the wave field matures, it diminishes and attains rather constant small values (of about 0.05) at large wave ages (and/or x ˜ ). For a fixed wave-age (and/or x ˜ ), γ M , increases with § . The corresponding wave-supported energy fraction, γ E , shows a similar behavior for small and moderate wave ages (and/or x ˜ ), although γ E values remain greater than about 0.5 in the range 5 ⩽ c p / u * ⩽ 10 ; yet, at larger wave ages (and/or x ˜ ), although γ E values remain greater than about 0.5 in the range 5 ⩽ c p / u * ⩽ 10 ; yet, at larger wave ages (and/or x ˜ ) γ E appears to increase again, reaching values of about 0.8 when c p / u * ≈ 30 , features, all in accord with experimental observations. For waves generated locally by wind, where c p / u * is of O(1), a significant portion of the normalized total (time) mean wind-energy flux across the interface goes directly to the surface drift current, the remaining being transferred to the waves. For mature waves or waves generated in the presence of swell, where c p / u * is of O(10), this energy partition changes, the waves now supporting more energy than the surface drift current. The relative importance of the normalized wave-energy dissipation fraction, compared with the corresponding wave-energy fraction advected by the wave field and the energy fraction supported by the drift current, is also examined as the wave field develops.

On the relation between solar wind, pseudobreakups, and substorms

A statistical study of pseudobreakups and substorms is performed using Polar UV images from a 3‐month period in winter 1998–1999. Data from the ACE solar wind monitor are examined in order to determine the influence of solar wind parameters on the occurrence of different substorm and pseudobreakup types. The results confirm that the IMF clock angle and the amount of solar wind energy flux control the strength of a substorm. The majority of large substorms appear when the IMF is strongly southward and the solar wind energy flux is high. Most small substorms occur during weakly positive or zero IMF Bz and low solar wind energy flux values. Pseudobreakups are associated with even lower energy fluxes than small substorms and appear typically for weakly positive IMF Bz. These results are in agreement with the scenario that pseudobreakups essentially are very weak substorms. Pseudobreakups appear during quiet times and during the growth phase or the recovery phase of weak or medium strong substorms. Time periods of enhanced geomagnetic activity with recurrent substorms are devoid of pseudobreakups. A detailed analysis of the different pseudobreakup types reveals that quiet time pseudobreakups appear predominantly during northward IMF. At least 20 percent of these appear at the poleward oval boundary. Optically, they do not differ much from very weak substorms. Growth phase pseudobreakups develop typically at the end of a 1 to 2 hour long excursion from northward to weakly southward IMF and are followed by quite weak substorms. A large majority of recovery phase pseudobreakups occur at a strongly polewardly displaced oval boundary at the end of a very active recovery phase. A considerable decrease of the polar cap size during the preceding substorm is connected to a northward turning of the IMF.

Axially symmetric relativistic MHD simulations of Pulsar Wind Nebulae in Supernova Remnants

The structure and the evolution of Pulsar Wind Nebulae (PWNe) are studied by means of two-dimensional axisymmetric relativistic magnetohydrodynamic (RMHD) simulations. After the first imaging of the Crab Nebula with Chandra, a growing number of objects has been found to show in the X-rays spatial features such as rings and jets, that clearly cannot be accounted for within the standard framework of one-dimensional semi-analytical models. The most promising explanation suggested so far is based on the combined effects of the latitude dependence of the pulsar wind energy flux, shaping the wind termination shock and naturally providing a higher equatorial emission, and of the wind magnetization, likely responsible for the jet collimation by hoop stresses downstream of the shock. This scenario is investigated here by following the evolution of a PWN interacting with the confining Supernova Remnant (SNR), from the free expansion to the beginning of the reverberation phase. Our results confirm the oblate shape of the wind termination shock and the formation of a polar jet with supersonic velocities () for high enough values of the equatorial wind magnetization parameter ().

Assessment of wind-generation potentiality in Jordan using the site effectiveness approach

Wind data gathered over 3–10 years is used for a feasibility analysis of optimum future utilization of wind-generator potentiality in 22 sites covering all landscape types and regions in Jordan. The yearly mean wind speed and the yearly average available wind energy flux were computed for each site. Yearly mean wind speeds at a height of 24 m could reach as high as 7.6 m/s and available wind energy flux close to 3 MWh/m 2/year could be attained. Detailed technical assessment for the nine most promising potential wind sites was made using the site effectiveness approach. The maximum site effectiveness and its corresponding cut-in speed were indicated, both of which depended on the site. The investigation was performed assuming three models of small and medium size wind machines representing different ranges of characteristic speeds and rated power suitable for water pumping and electric supply. The results show that small and medium wind turbines could be installed in the highlands and desert regions and utilized for water supply and electrical power generation, provided the correct wind machine-site is selected.

The Effect of Transition Region Heating on the Solar Wind from Coronal Holes

Using a 16 moment solar wind model extending from the chromosphere to 1 AU, we study how the solar wind is affected by direct deposition of energy in the transition region, in both radially expanding geometries and rapidly expanding coronal holes. Energy is required in the transition region to lift the plasma up to the corona, where additional coronal heating takes place. The amount of energy deposited determines the transition region pressure and the number of particles reaching the corona and, hence, how the solar wind energy flux is divided between gravitational potential and kinetic energy. We find that when only protons are heated perpendicularly to the magnetic field in a rapidly expanding coronal hole, the protons quickly become collisionless and therefore conduct very little energy into the transition region, leading to a wind much faster than what is observed. Only by additional deposition of energy in the transition region can a reasonable mass flux and flow speed at 1 AU be obtained. Radiative loss in the transition region is negligible in these low-mass flux solutions. In a radially expanding geometry the same form of coronal heating results in a downward heat flux to the transition region substantially larger than what is needed to heat the upwelling plasma, resulting in a higher transition region pressure, a slow, massive solar wind, and radiative loss playing a dominant role in the transition region energy budget. No additional energy input is needed in the transition region in this case. In the coronal hole geometry the solar wind response to transition region heating is highly nonlinear, and even a tiny input of energy can have a very large influence on the asymptotic properties of the wind. By contrast, the radially expanding wind is quite insensitive to additional deposition of energy in the transition region.

Expected hysteresis of the 23-rd solar cycle in the heliosphere

Solar wind and interplanetary magnetic field parameters are investigated using the data obtained at the Earth's orbit for the 20–23 solar cycles. The time-epoch analysis and hysteresis curves of the heliospheric parameters show some general and specific properties of the cycles. We have found specific hysteresis behaviour when the solar wind energy flow and the induced electric field are plotted against the sunspot number during 20–22 solar cycles. Based on these finding and using measured heliospheric parameters during the rising phase of the current 23-rd solar cycle we are able to present some semi-quantitative estimations of the expected solar wind energy flux and the induced electric field for the time period after the solar maximum. The similarity between the rising phases of the 23-rd and 20-th solar cycles presents additional grounds for expectations of the lower maximum of the current solar cycle and the geomagnetic activity in the present solar cycle as compared with the 21-st and 22-nd solar cycles.

Magnetically-Driven Planetary Radio Emissions and Application to Extrasolar Planets

At least six intense nonthermal planetary radio emissions are known in our solar system: the auroral radio emissions from the Earth, Jupiter, Saturn, Uranus and Neptune, and the radio bursts from the Io-Jupiter flux tube. The former are thought to be driven by the solar wind flow pressure or energy flux on the magnetospheric cross-section, while the latter is a consequence of the Io-Jupiter electrodynamic interaction. Although in the solar wind, the flow ram pressure largely dominates the magnetic one, we suggest that the incident magnetic energy flux is the driving factor for all these six radio emissions, and that it can be estimated in the same way in all cases. Consequences for the possible radio emission from extrasolar planets are examined. ‘Hot Jupiters’, if they are magnetized, might possess a radio emission several orders of magnitude stronger than the Jovian one, detectable with large ground-based low-frequency arrays. On the other hand, ‘giants’ analogous to the Io-Jupiter interaction in the form of a pair star/hot-Jupiter are unlikely to produce intense radio emissions, unless the star is very strongly magnetized.

Modeling basin‐scale internal waves in a stratified lake

Basin—scale internal waves provide the driving forces for vertical and horizontal fluxes in a stratified lake below the wind‐mixed layer. Thus, correct modeling of lake mixing and transport requires accurate modeling of basin‐scale internal waves: examining this capability with a hydrostatic, z‐coordinate three‐dimensional (3D) numerical model at coarse grid resolutions is the focus of this paper. It is demonstrated that capturing the correct thermocline forcing with a 3D mixed‐layer model for surface dynamics results in a good representation of low‐frequency internal wave dynamics. The 3D estuary and lake computer model ELCOM is applied to modeling Lake Kinneret, Israel, and is compared with field data under summer stratification conditions to identify and illustrate the spatial structure of the lowest‐mode basin‐scale Kelvin and Poincaré waves that provide the largest two peaks in the internal wave energy spectra. The model solves the unsteady Reynolds‐averaged Navier‐Stokes equations using a semi‐implicit method similar to the momentum solution in the TRIM code with the addition of quadratic Euler‐Lagrange dis‐cretization, scalar (e.g., temperature) transport using a conservative flux‐limited approach, and elimination of vertical diffusion terms in the governing equations. A detailed description is provided of turbulence closure for the vertical Reynolds stress terms and vertical turbulent transport using a 3D mixed‐layer model parameterized on wind and shear energy fluxes instead of the convential eddy viscosity/diffusivity assumption. This approach gives a good representation of the depth of the mixed‐layer at coarse vertical grid resolutions that allows the internal waves to be energized correctly at the basin scale.

Lessons from the ring current injection during the September 24, 25, 1998 storm

Because the conditions in the solar wind that lead to the injection of energetic particles into the ring current simultaneously affect a variety of geomagnetic phenomena, it is often difficult to determine whether these magnetospheric processes are causally related or are simply contemporaneous. The sequence of interplanetary conditions leading up to the September 24–25, 1998 geomagnetic storm are particularly suited to illustrating what conditions lead to significant activity in the auroral zone as distinct from the injection into the ring current. This interval illustrates that the magnetosphere requires a period of strong, steady, not time‐varying, convection for the buildup of the ring current, and that the AE index cannot be used to forecast the ring current buildup. Furthermore, when the ring current reached its peak strength, it contained 6 PJ and was dissipating energy at a rate of about 0.4 TW. The northern auroral regions and southern added another 1.2 TW of dissipation. This rate of dissipation could be maintained readily by the mechanical energy flux of the solar wind of about 40 TW but would require coupling to much of the incident solar‐wind Poynting flux if that were the sole energy source.

Numerical evaluation of the wind energy resource of Liguria

Abstract The procedure applied and the results obtained to ascertain the wind resource of Liguria (Italy) are presented. Liguria is squeezed between the sea and the mountains, with few flat areas, short valleys, and often continuous housing close to the coast. In such a complex situation, the identification of areas suitable for installing wind turbines needs a complex procedure based on different disciplines, one of which is the numerical modelling of wind fields. The present study, based on the measurements performed in stations with long and continuous time series, has pointed out the high wind resource in areas near the shoreline and on tops and ridges of mountains and hills. Indeed the annual average wind energy flux was calculated and found to be quite high (in excess of 600 W/(m 2 yr) at 30 m) in these areas, which makes Liguria a likely candidate for wind power utilization.

Enhanced mixing in narrows: A case study at the Mainau sill (Lake Constance)

Previous work has identified bottom currents as a significant source of turbulence in stratified lakes. Sills may therefore be a major factor determining overall turbulent diapycnal (vertical) exchange in lakes with multi-basin hypolimnia.¶In order to investigate the contribution of the Mainau sill (separating Upper Lake Constance from Lake Uberlingen) to the overall diapycnal mixing in Lake Constance, a series of temperature microstructure profiles was taken at Mainau Island in October 1993. From these profiles, using Batchelor's method, the rate of dissipation of turbulent kinetic energy was determined and related in an energy balance to the turbulent kinetic energy input from the wind, the energy content of internal seiches and the energy dissipation of bottom currents at the sill. Further, the vertical diffusivities were calculated using the dissipation method.¶The analysis shows that ≈ 5.5% of the wind energy flux was found in to the water column (below 2 m depth) and that energy dissipation was 8 times higher in the shear zone of the thermocline (≈ 8.4 ˙ 10-3 W m-2) than in the bottom boundary layer (≈ 1.1 ˙ 10-3 W m-2). Dissipation above the Mainau sill (≈ 9.5 ˙ 10-3 W m-2) exceeded the basin-wide average dissipation of internal seiche energy (≈ 0.3 ˙ 10-3 W m-2) by a factor of 34. However, since the areal extent of the sill is small (≈ 1% of the lake area), the sill contributes only about 40% to the basin-wide dissipation. Also vertical diffusivities within the thermocline were consistently enhanced by approximately the same amount over the sill. The synthesis of the observations implies that the sill plays a disproportionately large, but not dominant, role for small-scale diapycnal mixing in the hypolimnion of Lake Constance.

The Role of Helium in the Outer Solar Atmosphere

We construct models of the outer solar atmosphere comprising the region from the mid-chromosphere and into the solar wind in order to study the force and energy balance in models with a significant helium abundance. The corona is created by dissipation of an energy flux from the Sun. The energy flux is lost as radiation from the top of the chromosphere and as gravitational and kinetic solar wind energy flux. We find that in models with significant ion heating of the extended corona most of the energy flux is lost in the solar wind. The ion temperatures are higher than the electron temperature in these models, and the α-particle temperature is much higher than the proton temperature, so there is energy transfer from the α-particle fluid to the protons and electrons, but this energy exchange between the different species is relatively small. To a fairly good approximation we can say that the energy flux deposited in the protons and α-particles is lost as kinetic and gravitational energy flux in the proton and α-particle flow. How this energy flux is divided between gravitational and kinetic energy flux (i.e., how large the particle fluxes and flow speeds are) depends upon details of the heating process. We also find that mixing processes in the chromosphere play an important role in determining the coronal helium abundance and the relative solar wind proton and α-particle fluxes. Roughly speaking, we find that the relative α-particle and proton fluxes are set by the degree of chromospheric mixing, while the speeds are set by the details of the coronal heating process.

A survey on the assessment of wind energy potential in Egypt

In this paper, wind data obtained from the Egyptian Meteorological Authority are used to assess monthly and annual wind power and wind energy. The study is based on data from 15 anemometer meteorological stations, distributed all over Egypt and covering a period ranging from 1973 to 1994. For these stations the wind data are summarized. The wind energy potential at the 25 m height was obtained by extrapolation of data at 10 m using a power-law expression. The result presents the mean wind energy density estimates and potential for application in Egypt. The analysis showed that along Red Sea coasts, the annual wind energy flux is found to be high, which indicates that these coastal stations are possible locations for wind energy utilization. On both the Mediterranean coast and in the interior parts of Egypt, some stations are of low available wind energy, while others are found to be rather high. Also, the two Weibull distribution parameters have been estimated from the wind speed data for some meteorological stations and the wind power density is calculated using the values of these parameters.

Statistical investigation of IMF Bz effects on energetic (0.1‐ to 16‐keV) magnetospheric O+ ions

More than 2 years of magnetospheric O+ data from the Plasma Composition Experiment on the ISEE 1 spacecraft are compared, in a statistical manner, with concurrent data on the interplanetary magnetic field (IMF) and the solar wind plasma in an attempt to clarify the geophysical responses to varying solar wind inputs, in particular to variations in the GSM Bz component of the IMF. It is found that the energy density of 0.1‐ to 16‐keV O+ ions in the plasma sheet, inside of 23 RE, is well correlated with the average solar wind energy flux during the preceding few hours, whether that flux is measured by its electromagnetic (Poynting) component P or by its far greater kinetic component K. Although P and K are well correlated with each other, the correlation of the O+ energy density is slightly better with K than with P during times of positive Bz, while the opposite holds for negative Bz. In either case the O+ energy density is more nearly proportional to K, and, given a typical value of K, there is at most a marginal (less than a factor of 2) increase in this density associated with a negative Bz. Except for this latter effect, which can perhaps be taken as evidence that a change in polarity of Bz from positive to negative may induce “unloading” of internal tail energy, there is no evidence in these O+ data, including data from the inner magnetosphere (L < 10), that a negative, or southward, Bz is inherently favorable to the transfer of solar wind power across the magnetopause. These findings, together with the results of correlating the hourly AE index with P and K, suggest that the strong dependence of the AE on the Bz polarity is substantially exaggerated by the lack of AE magnetometers above 71° magnetic latitude.

Ulysses solar wind plasma observations from pole to pole

We present Ulysses solar wind plasma data from the peak southerly latitude of −80.2° on 12 September 1994 through the corresponding northerly latitude on 31 July 1995. Ulysses encountered fast wind throughout this time except for a 43° band centered on the solar equator. Median mass flux was nearly constant with latitude, while speed and density had positive and negative poleward gradients, respectively. Solar wind momentum flux was highest at high latitudes, suggesting a latitudinal asymmetry in the heliopause cross section. Solar wind energy flux density was also highest at high latitudes.

Physical versus chemical processes of “whiting” formation in the Bahamas

Whitings are common yet problematic occurrences of highly turbid water parcels among the relatively clear waters of shallow, tropical and subtropical carbonate platforms, banks and seas (e.g. Bahamas, Belize, Gulf of Carpentaria, Persian Gulf). In this paper, existing data on Bahamian whitings are scrutinized in an attempt to identify processes which may account for whiting phenomena worldwide. An examination of the areal distribution of whitings on Great Bahama Bank shows that>90% are associated with either mud or pellet-mud sediment facies. In view of this non-random distribution, several prominent hypotheses of whiting origin are considered: a) resuspension of fine-grained sediment by bottom-feeding fish (fish-muds); b) largescale, instantaneous physicochemical precipitation events; c) large-scale carbonate precipitation incidental to planktonic algal blooms; d) bottom sediment resuspension as a result of turbulent tidal flow. Although none of the above hypotheses can be discounted completely, this paper proposes that the observed geographic and physical characteristics of whitings are consistent with predicted and observed characteristics of turbulent-flow systems; that whitings are the observable manifestation of the “bursting” cycle of turbulence production at flow boundaries. The bursting process is a primary source of turbulence emanating from flow boundaries and can generate velocity excursions which deviate from mean flow velocity by a factor of 4. Published data for mean tidal current velocities on Great Bahama Bank range from 8 to 50 cm s−1. Thus, maximum predictable velocities during the bursting process will range from 32 to 200 cm s−1, quite in excess of empirically determined threshold sand-transport velocities (<25 cm s−1). Four-fold velocity excursions during turbulent flow increase shear stress up to 4-fold and generate 16-fold increases in lift force at the sediment water interface, enhancing bottom-sediment destabilization, particle entrainment and suspension. The visible, roiling nature of whiting water parcels is believed to be the expression of the above turbulent flow processes on Great Bahama Bank. Organization of turbulent boundary-layer flow into alternating low- and high-velocity “streaks” gives rise to alternating zones of active sediment-resuspension and deposition and may account for the development of subparallel digitations frequently observed within whitings. An integrated, conceptual explanation of whiting distribution on Great Bahama Bank is proposed which considers the interaction of physical environmental energy and sediment textural characteristics across the bank-top. Despite high tidal-current, wind and wave energy flux (and sediment resuspension potential) near bank margins, whitings are rare because sediments are nearly devoid of mud-sized particles. Near Andros Island, carbonate-mud is plentiful but whitings are infrequent because deposition occurs in the tidal- and wind-energy shadow of the island. Only on the center of the bank-top is environmental energy (sediment resuspension potential) sufficiently high and carbonate-mud sufficiently abundant for whitings to originate. Evaluation of this proposed whiting generation concept requires an interdisciplinary understanding of chemical, physical, sedimentological and biological aspects of the Great Bahama Bank environment.

Universal multifractal indices for the ocean surface at far red wavelengths

For some time, ocean wave breaking has been conceptualized as a cascade process in which the large scale wind energy flux driving the system is dissipated by wave breaking at small scales, the two seperated by the “equilibrium” scaling range. Cascades are now known to generically lead to multifractals; with special “universal” multifractals theoretically predicted. In this paper we use far red (0.95 μm) radiances at 1m resolution obtained from aircraft to test the multifractal behavior of the ocean surface and estimate the corresponding universal multifractal parameters of the radiance field.

A survey on the assessment of wind energy potential in Greece

In the present paper a statistical study of the available wind data for Greece is carried out to assess its wind energy potential. It is essential to establish the available wind energy for any given region in order to assess the relative potential at different sites. The applicability of the Weibull distribution is examined and tables and plots of Weibull parameters are given. The analysis showed that in the interior lowland parts of Greece, low available annual wind power densities exist (less than 20 w·m−2). In the eastern parts, along the coasts, especially on the Aegean Sea islands, the annual average wind energy flux is found to be rather high (more than 600 w·m−2 may be gained) which makes these islands possible locations for wind power utilization. On the other hand, the annual wind energy on the western parts along the coast and on the lonian Sea islands, a wind power of over 200 w·m−2 may be extracted.