Solar Transition Research Articles

High-resolution observations of the solar photosphere, chromosphere, and transition region

NASA’s Interface Region Imaging Spectrograph (IRIS) provides high-resolution observations of the solar atmosphere through ultraviolet spectroscopy and imaging. Since the launch of IRIS in June 2013, we have conducted systematic observation campaigns in coordination with the Swedish 1 m Solar Telescope (SST) on La Palma. The SST provides complementary high-resolution observations of the photosphere and chromosphere. The SST observations include spectropolarimetric imaging in photospheric Fe I lines and spectrally resolved imaging in the chromospheric Ca II 8542 Å, Hα, and Ca II K lines. We present a database of co-aligned IRIS and SST datasets that is open for analysis to the scientific community. The database covers a variety of targets including active regions, sunspots, plages, the quiet Sun, and coronal holes.

The case study of a photovoltaic plant located at the university of L’Aquila: An economic analysis

Solar energy has contributed significantly to the energy transition towards a low carbon society. Public offices – including universities – are being called to participate in the solar energy transition, as the availability of their rooftops represents an opportunity. The present study aimed at evaluating the economic feasibility of a photovoltaic (PV) plant at the University of L’Aquila, approximately 10 years after an earthquake devastated the region. The reconstruction process is ongoing, and a solar PV plant could potentially move the city in a sustainable direction. The development of sustainability models requires the economic verification of relevant projects and a complete list of indicators for decision-makers. The present work found that a 210 kW PV plant at the University of L’Aquila would reduce emissions by 184.9 t CO2eq/year and generate 1500 € profits for each kW installed; and a 115 kW PV plant would reduce emissions by 101.5 t CO2eq/year and generate profits of 1370 € for each kW installed. The analysis of alternative scenarios gave solidity to the results, confirming the pivotal role of the share of self-consumed energy. Level of insolation and plant size were also found to significantly influence economic performance. Finally, the adoption of a bonus to encourage the production and self-consumption of energy may increase investors’ attention towards environmental issues.

Effects of density on the oxygen ionization equilibrium in collisional plasmas

ABSTRACT The ion populations most frequently adopted for diagnostics in collisional plasmas are derived from the density independent coronal approximation. In higher density, lower temperature conditions, ionization rates are enhanced once metastable levels become populated, and recombination rates are suppressed if ions recombine into Rydberg levels. As a result, the formation temperatures of ions shift, altering the diagnostics of the plasma. To accurately model the effect of ionization from metastable levels, new electron impact ionization cross-sections have been calculated for oxygen, both for direct ionization and excitation–auto-ionization of the ground and metastable levels. The results have been incorporated into collisional radiative modelling to show how the ionization equilibrium of oxygen changes once metastable levels become populated. Suppression of dielectronic recombination has been estimated and also included in the modelling, demonstrating the shifts with density in comparison to the coronal approximation. The final results for the ionization equilibrium are used in differential emission measure modelling to predict line intensities for many lines emitted by O ii–O vi in the solar transition region. The predictions show improved agreement by 15–40 per cent for O ii, O vi, and the intercombination lines of O iii–O v, when compared to results from coronal approximation modelling. While there are still discrepancies with observations of these lines, this could, to a large part, be explained by variability in the observations.

On the Ratios of Si IV Lines (λ1394/λ1403) in an Emerging Flux Region

Abstract The resonance lines of Si iv formed at λ1394 and 1403 Å are the most critical for the diagnostics of the solar transition region in the observations of the Interface Region Imaging Spectrograph (IRIS). Studying the intensity ratios of these lines (1394 Å/1403 Å), which under optically thin conditions is predicted to be two, helps us to diagnose the optical thickness of the plasma being observed. Here we study the evolution of the distribution of intensity ratios in 31 IRIS rasters recorded for four days during the emergence of an active region. We found that during the early phase of the development, the majority of the pixels show intensity ratios smaller than two. However, as the active region evolves, more and more pixels show the ratios closer to two. Besides, there are a substantial number of pixels with ratio values larger than 2. At the evolved stage of the active region, the pixels with ratios smaller than two were located on the periphery, whereas those with values larger than 2 were in the core. However, for quiet Sun regions, the obtained intensity ratios were close to two irrespective of the location on the disk. Our findings suggest that the Si iv lines observed in active regions are affected by the opacity during the early phase of the flux emergence. The results obtained here could have important implications for the modeling of the solar atmosphere, including the initial stage of the emergence of an active region as well as the quiet Sun.

The evolution of inverted magnetic fields through the inner heliosphere

ABSTRACT Local inversions are often observed in the heliospheric magnetic field (HMF), but their origins and evolution are not yet fully understood. Parker Solar Probe has recently observed rapid, Alfvénic, HMF inversions in the inner heliosphere, known as ‘switchbacks’, which have been interpreted as the possible remnants of coronal jets. It has also been suggested that inverted HMF may be produced by near-Sun interchange reconnection; a key process in mechanisms proposed for slow solar wind release. These cases suggest that the source of inverted HMF is near the Sun, and it follows that these inversions would gradually decay and straighten as they propagate out through the heliosphere. Alternatively, HMF inversions could form during solar wind transit, through phenomena such velocity shears, draping over ejecta, or waves and turbulence. Such processes are expected to lead to a qualitatively radial evolution of inverted HMF structures. Using Helios measurements spanning 0.3–1 au, we examine the occurrence rate of inverted HMF, as well as other magnetic field morphologies, as a function of radial distance r, and find that it continually increases. This trend may be explained by inverted HMF observed between 0.3 and 1 au being primarily driven by one or more of the above in-transit processes, rather than created at the Sun. We make suggestions as to the relative importance of these different processes based on the evolution of the magnetic field properties associated with inverted HMF. We also explore alternative explanations outside of our suggested driving processes which may lead to the observed trend.

Statistical analysis of solar wind parameter variation with heliospheric distance: Ulysses observations in the ecliptic plane

The interplanetary magnetic field magnitude Bo, proton density Np and solar wind speed Vsw data from Ulysses spacecraft during its interplanetary cruise interval from Earth to Jupiter, from 18 November 1990 to 31 January 1992, are analyzed in this study. Statistical and wavelet techniques are employed to characterize some properties from the solar wind parameters near the ecliptic plane and their dependence with radial distance. The results from kurtosis analysis showed that the three solar wind parameters (Bo, Np and Vsw) presented a decrease of this statistical quantity with the increase of scales, indicating that these variables are intermittent in short time scales. Further, the kurtosis parameter presented an increase in all scales around 2–3 AU distance range that corresponds to a solar wind regime transition. It was noted that the interplanetary medium was dominated by solar transients (interplanetary coronal mass ejections) until the middle of 1991. Afterwards a more stable pattern of corotating interaction regions arose. Furthermore, the probability distribution functions presented a spreading shape due to the occurrence of intermittence. In order to study the temporal variability of the solar wind parameters, the wavelet approach was used. The following major periodicities were found for the three solar wind variables studied: ~13, ~26, and ~83–88 days. It was noted that the ~13 day periods presented strong spectral power in the 2 to 4 AU range, where the solar wind was dominated by ICME transients. On the other hand, the 26 day period shows higher spectral power for distances higher than 4 AU, where the interplanetary space is more dominated by CIRs. Thus, it was found in this paper a significant dependence of solar wind parameters on radial heliocentric distance which can be accounted by the dynamical evolution of solar wind structures with distance.

Modelling the solar transition region using an adaptive conduction method

Modelling the solar Transition Region with the use of an Adaptive Conduction (TRAC) method permits fast and accurate numerical solutions of the field-aligned hydrodynamic equations, capturing the enthalpy exchange between the corona and transition region, when the corona undergoes impulsive heating. The TRAC method eliminates the need for highly resolved numerical grids in the transition region and the commensurate very short time steps that are required for numerical stability. When employed with coarse spatial resolutions, typically achieved in multi-dimensional magnetohydrodynamic codes, the errors at peak density are less than 5% and the computation time is three orders of magnitude faster than fully resolved field-aligned models. This paper presents further examples that demonstrate the versatility and robustness of the method over a range of heating events, including impulsive and quasi-steady footpoint heating. A detailed analytical assessment of the TRAC method is also presented, showing that the approach works through all phases of an impulsive heating event because (i) the total radiative losses and (ii) the total heating when integrated over the transition region are both preserved at all temperatures under the broadening modifications of the method. The results from the numerical simulations complement this conclusion.

Perhitungan Waktu (Time Calculation) Fenomena Tanpa Bayangan di Kota Sambas Kalimantan Barat

The shadow less phenomenon in a city is actually already known by the people in Indonesia. In the City of Sambas, the shadow less phenomenon has not been as popular as in the City of Pontianak. The public perception in general is that phenomenon does not occur in this city, but only in certain cities. This research is a kind of qualitative library research by utilizing secondary data derived from five-year ephemeris data, which are 2019, 2020, 2021, 2022, and 2023. The data collection technique uses documentation techniques derived from ephemeris data which is taken from the Winhisab software. Based on this study, the shadow less phenomenon in the City of Sambas occurs twice a year, in March and September. In March, this phenomenon occurred on the 23rd to 24th or after the vernal equinox. Whereas in September, this phenomenon occurred on the 19th to 20th or before the autumnal equinox. In addition, based on the solar transit time calculation using the mid-WIB time, we get that in September, the time of the shadow less phenomenon in the City of Sambas occurred earlier than March.

The prospects of decentralised solar energy home systems in rural communities: User experience, determinants, and impact of free solar power on the energy poverty cycle

Distributed solar photovoltaic is a well-established technology to meet small-scale rural energy needs in an affordable, reliable, and carbon-neutral manner. Such socio-technical transitions offer substantive support to address energy poverty and act as a key tool to realise human well-being, economic prosperity, and environmental conservation envisioned under Sustainable development goals (SDGs). In this study, households using solar photovoltaic were surveyed to determine prospects of solar energy use in rural communities. The participants include rural households from Uttar Pradesh, India that had received i) a small scale and subsidised solar systems, ii) obtained paid connection from solar microgrids, and iii) those who purchased solar systems for power reliability. We report high satisfaction with distributed solar photovoltaic among rural households. The factors influencing a desire to procure additional solar power include income, level of education, duration of solar use, user satisfaction, time of day for the power supply and financial support for procurement. Our findings also suggest that freely given solar power offers limited incentives for procuring more solar power. We further analyse the policy of welfare using energy justice as a conceptual tool. This can explain paradoxical aspects of subsidies that are widely used as a socio-political tool to improve quality of life for those that are disadvantaged but fail to address fundamental structural aspects of the energy system that are underscored by procedural justice issues. We propose policies for distributed clean energy in emerging countries must address concurrent energy transitions and energy justice frameworks to support sustained decentralised solar transitions. Without these two foundations operating in tandem, carbon lock-in and the energy poverty cycle will be inexorably linked.

Some thoughts on emission-line spectroscopy

ABSTRACTThe interpretation of emission lines formed in large astrophysical plasmas such as the solar atmosphere faces many challenges. Relatively simple line-ratio estimates of physical parameters, while appealing, are heavily laden with assumptions. In practical cases, some critical assumptions are neither defensible from first principles, nor testable by experiment. Free parameters and functional forms must be defined, whose numbers of degrees of freedom exceed the number of independent data points. These issues are illustrated in the particular case of using lines of Si iv and O iv formed in the solar transition region, observed for decades, most recently using the IRIS mission. The problems highlighted are in addition to well-known problems of mathematical ill-posedness.

Spectroscopic diagnostics of electron density in a flare ribbon by oxygen IV lines using Non-Maxwellian distribution

By the line ratio of Oxygen IV 1399.776.50 Å and 1401.163 Å lines in a flare ribbon in the solar transition region, the principle of the electron density diagnostics using the collisional radiative model is discussed, and the relationship of the electron density with the line ratio is obtained, for both Maxwellian and Kappa distributions. By the observed line ratio, the diagnostic result of the electron density in the flare ribbon for the Maxwellian distribution are and at the temperature of K, 5.0 K and 5.17 K, respectively, which are slightly smaller than reported using the method of differential emission measure. The electron density for the Kappa distributions are and for κ = 2, 3 and 5, respectively. With increasing κ, the electron density for the Kappa distribution will be close to that for the Maxwellian distribution. This discussion is significant in the electron density diagnostics in the solar transition region, which will be also important for diagnostics for non-Maxwellian distribution.

Novel Open-Circuit Photovoltaic Bypass Diode Fault Detection Algorithm

In this article, a novel photovoltaic (PV) bypass diode fault detection algorithm is presented. The algorithm consists of three main steps. First, the threshold voltage of the current–voltage ( I–V ) curve is obtained using different failure bypass diode scenarios. Second, the theoretical prediction for the faulty regions of bypass diodes is calculated using the analysis of voltage drop in the I–V curve as well as the voltage at maximum power point. Finally, the actual I–V curve under any environmental condition is measured and compared with theoretical predictions. The proposed algorithm has been experimentally evaluated using a PV string that comprises three series-connected PV modules, and subtotal of nine bypass diodes. Various experiments have been conducted under diverse bypass diodes failure conditions. The achieved detection accuracy is always greater than 99.39% and 99.74% under slow and fast solar irradiance transition, respectively.

Detection of Hundreds of New Planet Candidates and Eclipsing Binaries in K2 Campaigns 0–8

Abstract We implement a search for exoplanets in campaigns zero through eight (C0–8) of the K2 extension of the Kepler spacecraft. We apply a modified version of the QATS planet search algorithm to K2 light curves produced by the EVEREST pipeline, carrying out the C0–8 search on 1.5 × 105 target stars with magnitudes in the range of Kp = 9−15. We detect 818 transiting planet candidates, of which 374 were undiscovered by prior searches, with {64, 15, 5, 2, 1} in {2, 3, 4, 5, 6}-planet multiplanet candidate systems, respectively. Of the new planets detected, 100 orbit M dwarfs, including one that is potentially rocky and in the habitable zone. A total of 154 of our candidates reciprocally transit with our solar system: they are geometrically aligned to see at least one solar system planet transit. We find candidates that display transit timing variations and dozens of candidates on both period extremes with single transits or ultrashort periods. We point to evidence that our candidates display similar patterns in frequency and size–period relation to confirmed planets, such as tentative evidence for the radius gap. Confirmation of these planet candidates with follow-up studies will increase the number of K2 planets by up to 50%, and characterization of their host stars will improve statistical studies of planet properties. Our sample includes many planets orbiting bright stars amenable for radial velocity follow-up and future characterization with JWST. We also list the 579 eclipsing binary systems detected as part of this search.

Solar lobby and energy transition in Japan

Due to significant cost advantages, wind energy penetrated the energy mix of most large countries much faster than solar PV did until the recent decade. However, Japan has been almost one-sidedly leaning toward the more expensive solar PV. For using solar PV electricity, the Japanese consumers are also paying sizably higher tariffs than those in other countries, especially after the Fukushima nuclear accident in 2011 that led to the sudden suspension of all nuclear power plants. Japan's energy transition towards renewables is accordingly largely single legged, rather than more balanced to take advantage of both wind turbines and solar PV. This article explains the puzzle on why renewable energy development in Japan has created such a wide distance from more economically optimal situations. We focus on the initiation, formation and impacts of the solar lobby that comprises bureaucracies, politicians, solar PV manufacturers, and independent power producers. Policy implications are drawn for Japan and other countries on the importance of controlling political lobby to achieve less costly energy transition.

Emerging Low-Carbon Energy Landscapes and Energy Innovation Dilemmas in the Kenyan Periphery

Interest in electrical grid access is high throughout Kenya and yet parastatals continually use location and proximity concepts to define the periphery as spaces ineligible for electrical grids due to dispersed and low electricity demand. Even the ongoing spatial expansion of electrical infrastructures to achieve universal electricity access (Vision 2020) and nation-wide economic transformation (Vision 2030) agenda favor peripheral locations only where electricity demand is considered adequate and residents live within the required 600-m radius from existing transformers. Uncertainties surrounding future grid extensions, unreliable electricity supply, and strong sociocultural attachments to homelands are the driving forces behind the uptake of decentralized solar photovoltaic (PV) systems in the periphery to gain energy autonomy by means of self-generating electricity in homes. Most households, at least based on the sample, frequently performed very important social practices according to energy services provided by decentralized systems and could perform energy-intensive practices only occasionally. Solar PV system uptake, however, grants users only a partial energy autonomy because it engenders rather precautionary energy practices, thereby obstructing certain social practices, not excluding home-based microbusiness activities. The solar PV transition potentially obstructs the state’s socioeconomic transformation visions, undermines the monopolistic agenda of parastatals, restricts practices in households and expectations placed on energy infrastructure, and fortuitously creates low-carbon energy solutions in specific spaces. The placemaking processes create low-carbon energy landscapes in the periphery but are inextricably bundled with tensions and conundrums in energy systems—henceforth called energy innovation dilemmas—subject to spatial (re-)organization of electrical grids and societal energy visions. In this article, I hypothesize geographical energy futures in Kenya and emphasize academic contributions realized by employing relational perspectives of energy, practices, and space in energy transition studies in settings characterized by structural uncertainties and constantly changing energy systems. Key Words: energy geographies, Kenya, social practices, solar PV systems, space production.

Observations of small-scale energetic events in the solar transition region: explosive events, UV bursts, and network jets

In this paper, we review observational aspects of three common small-scale energetic events in the solar transition region (TR), namely TR explosive events, ultraviolet bursts and jets. These events are defined in either (both) spectral or (and) imaging data. The development of multiple instruments capable of observing the TR has allowed researchers to gain numerous insights into these phenomena in recent years. These events have provided a proxy to study how mass and energy are transported between the solar chromosphere and the corona. As the physical mechanisms responsible for these small-scale events might be similar to the mechanisms responsible for large-scale phenomena, such as flares and coronal mass ejections, analysis of these events could also help our understanding of the solar atmosphere from small to large scales. The observations of these small-scale energetic events demonstrate that the TR is extremely dynamic and is a crucial layer in the solar atmosphere between the chromosphere and the corona.

Наблюдения мелкомасштабных энергетических событий в солнечной переходной области: взрывных событий, всплесков ультрафиолетового излучения и струйных явлений

In this paper, we review observational aspects of three common small-scale energetic events in the solar transition region (TR), namely TR explosive events, ultraviolet bursts and jets. These events are defined in either (both) spectral or (and) imaging data. The development of multiple instruments capable of observing the TR has allowed researchers to gain numerous insights into these phenomena in recent years. These events have provided a proxy to study how mass and energy are transported between the solar chromosphere and the corona. As the physical mechanisms responsible for these small-scale events might be similar to the mechanisms responsible for large-scale phenomena, such as flares and coronal mass ejections, analysis of these events could also help our understanding of the solar atmosphere from small to large scales. The observations of these small-scale energetic events demonstrate that the TR is extremely dynamic and is a crucial layer in the solar atmosphere between the chromosphere and the corona.

Incumbent resistance and the solar transition: Changing opportunity structures and framing strategies

Sustainability transitions often involve policy conflicts, especially when incumbents perceive threats to their business models, and conflicts involve framing of competing positions in the public sphere. Using the case of the growth of distributed solar energy in the U.S. electricity sector, this study shows how the concepts of industry and political opportunity structures can help to explain variation in discursive strategy. First, when incumbents perceive the growth of the challenger as a threat, the industry opportunity structure closes, the volume of framing activity in the public sphere increases as contention grows, and the differentiation in framing (the ratio of pro- to anti-transition frames) between incumbents and challengers increases. Second, with respect to the political opportunity structure, the selection of frame types (environmental versus economic-consumer) varies in relationship to control of the government by conservative or progressive parties. Theoretical implications for transitions studies are discussed.

Modelling ion populations in astrophysical plasmas: carbon in the solar transition region

The aim of this work is to improve the modelling of ion populations in higher density, lower temperature astrophysical plasmas, of the type commonly found in lower solar and stellar atmospheres. Ion population models for these regions frequently employ the coronal approximation, which assumes conditions more suitable to the upper solar atmosphere, where high temperatures and lower densities prevail. The assumed conditions include all ions being in the ground state and steady-state equilibrium, where there is sufficient time for ionisation and recombination to take place. Using the coronal approximation for modelling the solar transition region gives theoretical lines intensities for the Li-like and Na-like isoelectronic sequences which are often factors of two to five times lower than observed. The works of Burgess & Summers (1969, ApJ, 157, 1007) and Nussbaumer & Storey (1975, A&A, 44, 321) show the important part ions in excited levels play when included in the modelling. As density increases metastable levels become populated and ionisation rates increase, whereas dielectronic recombination through highly excited levels is suppressed. Photo-ionisation is also shown by Nussbaumer & Storey to have an effect on the charge-state distribution of carbon in these regions. Their models, however, use approximations for the atomic rates to determine the ion balance. Presented here is the first stage in updating these earlier models of carbon by using rates from up-to-date atomic calculations and more recent photo-ionising radiances. Where atomic rates were not readily available, in the case of electron impact direct ionisation and excitation–auto-ionisation, new calculations were made using the Flexible Atomic Code and Autostructure, and compared to theoretical and experimental studies. The effects each atomic process has on the ion populations as density changes is illustrated, and final results from the modelling are compared to the earlier works. Lastly, the new results for ion populations were used to predict line intensities for the solar transition region in the quiet Sun. In comparison to coronal approximation modelling the new results show significantly improved agreement with observations.

Development of a radio telescope for the observation of celestial bodies in the Ku Band

Solar events such as flares or explosions present intense radiation in the KU band (10-12) GHz, the range in which satellite television operates. Subsequently, the development of radio telescopes that make use of elements present in satellite television due to its low cost is evident around the world. The radio telescope in the study is, composed of a reflective mesh antenna, a mount that allows for remote operation, a Low Noise Block, and a satellite search engine. The system is installed in the Astronomical Observatory of the Technological University of Pereira and has a freedom of movement of 360° in azimuth and 180° in altitude, with a resolution of 0.2°. The set-up of the radio telescope was done by observing television satellites and registering the Solar transit. The developed radio telescope is easily scalable thanks to its modular architecture. Additionally, it is stable in adverse weather conditions because of its mesh antenna.