Renewable energy is accepted as a key source for the future, not only for Saudi Arabia, but also for the world. Saudi Arabia has abundant potential for exploiting solar energy, which is renewable, ...clean, and freely available. The average annual solar radiation falling on the Arabian Peninsula is about 2200kWh/m2. Applications of solar energy in Saudi Arabia have been growing since 1960. Solar hydrogen production plant situated at the Solar Village, Riyadh, Saudi Arabia, could have been considered as the world's first 350kW solar-powered hydrogen-generation plant at the time of its inception. The development of solar energy, however, has been relatively low due to several obstacles although utilization of solar energy in its various aspects is very attractive for the country. The main objectives of this study are to address current applications and future aspects of solar energy along with studies conducted in this field and to assess them in the light of available sustainable energy technologies towards establishing energy policies. The solar energy-related topics reviewed include various types of solar radiation correlations, exergetic solar radiation, solar collectors, solar photovoltaic (PV) systems, solar stills, solar-powered irrigation, solar energy-related greenhouses, solar hydrogen, solar water desalination and solar energy education. Some barriers, scenarios and constraints are also covered. The utilization of solar energy could cover a significant part of the energy demand in the country. If a major breakthrough is achieved in the field of solar-energy conversion, Saudi Arabia can be a leading producer and exporter of solar energy in the form of electricity. The geographical location of the country, its widespread unused desert land, and year-round clear skies, all make it an excellent candidate for this.
Nine Outstanding Questions of Solar Wind Physics Viall, Nicholeen M.; Borovsky, Joseph E.
Journal of geophysical research. Space physics,
July 2020, 2020-Jul, 2020-07-00, 20200701, Letnik:
125, Številka:
7
Journal Article
Recenzirano
Odprti dostop
In situ measurements of the solar wind have been available for almost 60 years, and in that time plasma physics simulation capabilities have commenced and ground‐based solar observations have ...expanded into space‐based solar observations. These observations and simulations have yielded an increasingly improved knowledge of fundamental physics and have delivered a remarkable understanding of the solar wind and its complexity. Yet there are longstanding major unsolved questions. Synthesizing inputs from the solar wind research community, nine outstanding questions of solar wind physics are developed and discussed in this commentary. These involve questions about the formation of the solar wind, about the inherent properties of the solar wind (and what the properties say about its formation), and about the evolution of the solar wind. The questions focus on (1) origin locations on the Sun, (2) plasma release, (3) acceleration, (4) heavy‐ion abundances and charge states, (5) magnetic structure, (6) Alfven waves, (7) turbulence, (8) distribution‐function evolution, and (9) energetic‐particle transport. On these nine questions we offer suggestions for future progress, forward looking on what is likely to be accomplished in near future with data from Parker Solar Probe, from Solar Orbiter, from the Daniel K. Inouye Solar Telescope (DKIST), and from Polarimeter to Unify the Corona and Heliosphere (PUNCH). Calls are made for improved measurements, for higher‐resolution simulations, and for advances in plasma physics theory.
Plain Language Summary
The Sun's atmosphere, called the solar corona, is a very hot plasma (ions and electrons) that reaches temperatures of 1000000 K or more. The coronal plasma continually expands away from the Sun, carrying solar magnetic field with it. This is the solar wind. It reaches speeds of hundreds of kilometers per second and fills the solar system. The space carved out by the solar wind flow defines the heliosphere. The formation of the solar wind and its evolution as it flows away from the Sun is fundamental to how the Sun and stars get rid of stressed magnetic fields and involves physical processes that operate throughout the universe. Additionally, the solar wind constantly bombards Earth's magnetic field and plasma environment, driving dynamics called space weather. The solar wind is the medium through which larger space weather events from solar storms propagate. Understanding the solar wind is therefore key for understanding the space environment around Earth. In this paper, we synthesize input from the heliophysics community on the outstanding questions of solar wind physics. We describe the current state of research, an updated framework for understanding solar wind formation, and future needs and opportunities for progress, including what is likely to be accomplished in near future with data from Parker Solar Probe, from Solar Orbiter, from the Daniel K. Inouye Solar Telescope (DKIST), and from Polarimeter to Unify the Corona and Heliosphere (PUNCH).
Key Points
Nine outstanding questions of solar wind physics are synthesized from inputs from the heliospheric research community
New ways of viewing these questions are put forth, and suggestions for future progress are offered
Calls are made for improved measurements, simulations, and plasma physics theory
Extreme-ultraviolet images from the Solar Dynamics Observatory often show loop-like fine structure to be present where no minority-polarity flux is visible in magnetograms, suggesting that the rate ...of ephemeral region (ER) emergence inside "unipolar" regions has been underestimated. Assuming that this rate is the same inside coronal holes as in the quiet Sun, we show that interchange reconnection between ERs and open field lines gives rise to a solar wind energy flux that exceeds 105 erg cm−2 s−1 and that scales as the field strength at the coronal base, consistent with observations. In addition to providing ohmic heating in the low corona, these reconnection events may be a source of Alfvén waves with periods ranging from the granular timescale of ∼10 minutes to the supergranular/plume timescale of many hours, with some of the longer-period waves being reflected and dissipated in the outer corona. The asymptotic wind speed depends on the radial distribution of the heating, which is largely controlled by the rate of flux-tube expansion. Along the rapidly diverging flux tubes associated with slow wind, heating is concentrated well inside the sonic point (1) because the outward conductive heat-flux density and thus the outer coronal temperatures are reduced, and (2) because the net wave energy flux is dissipated at a rate proportional to the local Alfvén speed. In this "hybrid" solar wind model, reconnection heats the lower corona and drives the mass flux, whereas waves impart energy and momentum to the outflow at greater distances.
Solar coronal plumes long seemed to possess a simple geometry supporting spatially coherent, stable outflow without significant fine structure. Recent high-resolution observations have challenged ...this picture by revealing numerous transient, small-scale, collimated out-flows (“jetlets”) at the base of plumes. The dynamic filamentary structure of solar plumes above these outflows, and its relationship with the overall plume structure, have remained largely unexplored. We analyzed the statistics of continuously observed fine structure in-side a single representative bright plume within a mid-latitude coronal hole during 2016 July2-3. By applying advanced edge-enhancement and spatiotemporal analysis techniques to ex-tended series of high-resolution images from the Solar Dynamics Observatory’s Atmospheric Imaging Assembly, we determined that the plume was composed of numerous time-evolving filamentary substructures, referred to as “plumelets” in this paper, that accounted for most of the plume emission. The number of simultaneously identifiable plumelets was positively correlated with plume brightness, peaked in the fully formed plume, and remained saturated thereafter. The plumelets had transverse widths of 10 Mm and intermittently supported upwardly propagating periodic disturbances with phase speeds of 190-260 km s−1and longitudinal wavelengths of 55-65 Mm. The characteristic frequency (3.5 mHz) is commensurate with that of solar p-modes. Oscillations in neighboring plumelets are uncorrelated, indicating that the waves could be driven by p-mode flows at spatial scales smaller than the plumelet separation. Multiple independent sources of outflow within a single coronal plume should impart significant fine structure to the solar wind that may be detectable by Parker Solar Probe and Solar Orbiter.
The magnetic field measurements of the FIELDS instrument on the Parker Solar Probe (PSP) have shown intensities, throughout its first solar encounter, that require a very low source surface (SS) ...height ( ) to be reconciled with magnetic field measurements at the Sun via potential field extrapolation (PFSS). However, during PSP's second encounter, the situation went back to a more classic SS height ( ). Here we use high-resolution observations of the photospheric magnetic field (Solar Dynamics Observatory/Helioseismic and Magnetic Imager) to calculate neutral lines and boundaries of the open field regions for SS heights from 1.2 to 2.5 R using an evolving PFSS model and the measured solar wind speed to trace the source of the wind observed by PSP to the low corona and photosphere. We adjust RSS to get the best match for the field polarity over the period 2018 October-November and 2019 March-April, finding that the best fit for the observed magnetic field polarity inversions requires a nonspherical SS. The geometry of the coronal hole boundaries for different RSS is tested using the PSP perihelion passes, 3D PFSS models, and LASCO/C2 observations. We investigate the sources of stronger-than-average magnetic fields and times of Alfvénic fast and slow wind. Only some of the strongly Alfvénic slow wind streams seen by PSP survive and are observed at 1 au: the origins and peculiar topology of the background in which they propagate is discussed.
Abstract
We provide a simple geometric explanation for the source of switchbacks and associated large and one-sided transverse flows in the solar wind observed by the Parker Solar Probe (PSP). The ...more radial, sub-Parker spiral structure of the heliospheric magnetic field observed previously by Ulysses, ACE, and STEREO is created within rarefaction regions where footpoint motion from the source of fast into slow wind at the Sun creates a magnetic fieldline connection across solar wind speed shear. Conversely, when footpoints move from the source of slow wind into faster wind, a super-Parker spiral field structure is formed: below the Alfvén critical point, one-sided transverse field-aligned flows develop; above the Alfvén critical point, the field structure contracts between adjacent solar wind flows, and the radial field component decreases in magnitude with distance from the Sun, eventually reversing into a switchback. The sub-Parker and super-Parker spirals behave functionally as opposites. Observations from PSP confirm the paucity of switchbacks within rarefaction regions and immediately outside these rarefaction regions, we observe numerous switchbacks in the magnetic field that are directly associated with abrupt transients in solar wind speed. The magnetic field strength, the radial component of the magnetic field, the speed gradients, radial Alfvén speed, and the ratio of the sound speed to the radial Alfvén speed all conform to predictions based on the sub-Parker and super-Parker spirals within rarefaction regions and solar wind speed enhancements (spikes or jets), respectively. Critically, the predictions associated with the super-Parker spiral naturally explain the observations of switchbacks being associated with unexpectedly large and one-sided tangential flows.
Measuring the global magnetic field of the solar corona remains exceptionally challenging. The fine-scale density structures observed in white-light images taken during total solar eclipses are ...currently the best proxies for inferring the magnetic field direction in the corona from the solar limb out to several solar radii (R ). We present, for the first time, the topology of the coronal magnetic field continuously between 1 and 6 R , as quantitatively inferred with the rolling Hough transform for 14 unique eclipse coronae that span almost two complete solar cycles. We find that the direction of the coronal magnetic field does not become radial until at least 3 R , with a high variance between 1.5 and 3 R at different latitudes and phases of the solar cycle. We find that the most nonradial coronal field topologies occur above regions with weaker magnetic field strengths in the photosphere, while stronger photospheric fields are associated with highly radial field lines in the corona. In addition, we find an abundance of field lines that extend continuously from the solar surface out to several solar radii at all latitudes, regardless of the presence of coronal holes. These results have implications for testing and constraining coronal magnetic field models, and for linking in situ solar wind measurements to their sources at the Sun.
The Earth's climate system depends entirely on the Sun for its energy. Solar radiation warms the atmosphere and is fundamental to atmospheric composition, while the distribution of solar heating ...across the planet produces global wind patterns and contributes to the formation of clouds, storms, and rainfall.The Sun's Influence on Climateprovides an unparalleled introduction to this vitally important relationship.
This accessible primer covers the basic properties of the Earth's climate system, the structure and behavior of the Sun, and the absorption of solar radiation in the atmosphere. It explains how solar activity varies and how these variations affect the Earth's environment, from long-term paleoclimate effects to century timescales in the context of human-induced climate change, and from signals of the 11-year sunspot cycle to the impacts of solar emissions on space weather in our planet's upper atmosphere.
Written by two of the leading authorities on the subject,The Sun's Influence on Climateis an essential primer for students and nonspecialists alike.
Abstract
We report the result of the first search for multipoint in situ and imaging observations of interplanetary coronal mass ejections (ICMEs) starting with the first Solar Orbiter (SolO) data in ...2020 April–2021 April. A data exploration analysis is performed including visualizations of the magnetic-field and plasma observations made by the five spacecraft SolO, BepiColombo, Parker Solar Probe (PSP), Wind, and STEREO-A, in connection with coronagraph and heliospheric imaging observations from STEREO-A/SECCHI and SOHO/LASCO. We identify ICME events that could be unambiguously followed with the STEREO-A heliospheric imagers during their interplanetary propagation to their impact at the aforementioned spacecraft and look for events where the same ICME is seen in situ by widely separated spacecraft. We highlight two events: (1) a small streamer blowout CME on 2020 June 23 observed with a triple lineup by PSP, BepiColombo and Wind, guided by imaging with STEREO-A, and (2) the first fast CME of solar cycle 25 (≈1600 km s
−1
) on 2020 November 29 observed in situ by PSP and STEREO-A. These results are useful for modeling the magnetic structure of ICMEs and the interplanetary evolution and global shape of their flux ropes and shocks, and for studying the propagation of solar energetic particles. The combined data from these missions are already turning out to be a treasure trove for space-weather research and are expected to become even more valuable with an increasing number of ICME events expected during the rise and maximum of solar cycle 25.
Solar filament eruptions are often associated with solar flares and coronal mass ejections, which have the greatest impact on space weather. However, the fine structures and the trigger mechanisms of ...solar filaments are still unclear. To address these issues, we studied a failed solar active-region filament eruption associated with a C-class flare by using high-resolution H images from the New Vacuum Solar Telescope, supplemented by EUV observations from the Solar Dynamics Observatory. Before the filament eruption, a small bipolar magnetic field emerged below the filament. Then magnetic reconnection between the filament and the emerging bipolar magnetic field triggered the filament eruption. During the filament eruption, the untwisting motion of the filament can be clearly traced by the eruptive threads. Moreover, the footpoints of the eruptive threads are determined by tracing the descending filament material. Note that the twisted structure of the filament and the right part of the eruptive filament threads cannot be seen before the filament eruption. These eruptive threads in the right part of the filament are found to be rooting in the weak negative polarities near the main negative sunspot. Moreover, a new filament formed in the filament channel due to material injection from the eruptive filament. The above observations and the potential field extrapolations are inclined to support the idea that the filament materials were transferred into the overlying magnetic loops and the nearby filament channel by magnetic reconnection. These observations improve our understanding of the complexity of filament eruptions.
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