Solar Spectra Research Articles

GLE events in 24th solar cycle

Started in 2009, the 24th solar cycle is going to end. In 2015, the solar activity was at its maximum, turning down. According to many indices, this cycle turned out to be abnormal. For instance, in the previous, the 23rd cycle, the index such as the number of solar spots was as high as 175, compared with that of the 24th cycle, not exceeding 100. According to the number of GLE-events (ground level enhancement of solar cosmic rays, observed on neutron monitors), the current cycle also differs greatly from the previous ones. In the 23rd cycle, the number of great GLE-events was as high as four, and that of small and moderate being five. In the 24th cycle, only two GLE-events were recorded: GLE 71 (17.05.2012) и GLE 72 (10.09.2017), with the last event being of small amplitude (5%). The presence of the neutron monitors network data enables calculation of the energy spectrum and other parameters of solar cosmic rays. The GLEevents are processed by special technique developed at PGI. It is aimed at solving the inverse problem: based on the data from the world neutron monitors network, to obtain the parameters of solar cosmic rays energy spectra. Like the previous ones, GLE-events 71 and 72 were processed by this technique. The energetic spectra obtained were compared with those in other events of the previous cycles

Fabrication and photocatalytic property of magnetic SrTiO3/NiFe2O4 heterojunction nanocomposites.

Novel multifunctional SrTiO3/NiFe2O4 nanocomposites were successfully fabricated via a two-step route. The as-prepared samples were characterized by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), field-emission transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy and vibrating sample magnetometry (VSM). The results indicate that the SrTiO3/NiFe2O4 heterostructures are composed of SrTiO3 spheroidal nanoparticles adhered to NiFe2O4 polyhedra. The heterojunction established in the composite material accelerates the process of electron–hole pair separation and boosts the photo-Fenton reaction. Among the samples, 15 wt% SrTiO3/NiFe2O4 nanocomposites exhibit a powerful light response and excellent room temperature ferromagnetism. Subsequently, the photocatalytic degradation of RhB over the as-prepared samples was investigated and optimized, revealing that the 15 wt% SrTiO3/NiFe2O4 nanocomposites exhibit the best photocatalytic activity and stability under simulated solar light irradiation. Furthermore, according to experimental results, the possible mechanism of improved photocatalytic activity was also proposed.

A Generalized Approach to Model the Spectra and Radiation Dose Rate of Solar Particle Events on the Surface of Mars

Abstract For future human missions to Mars, it is important to study the surface radiation environment during extreme and elevated conditions. In the long term, it is mainly galactic cosmic rays (GCRs) modulated by solar activity that contribute to the radiation on the surface of Mars, but intense solar energetic particle (SEP) events may induce acute health effects. Such events may enhance the radiation level significantly and should be detected as immediately as possible to prevent severe damage to humans and equipment. However, the energetic particle environment on the Martian surface is significantly different from that in deep space due to the influence of the Martian atmosphere. Depending on the intensity and shape of the original solar particle spectra, as well as particle types, the surface spectra may induce entirely different radiation effects. In order to give immediate and accurate alerts while avoiding unnecessary ones, it is important to model and well understand the atmospheric effect on the incoming SEPs, including both protons and helium ions. In this paper, we have developed a generalized approach to quickly model the surface response of any given incoming proton/helium ion spectra and have applied it to a set of historical large solar events, thus providing insights into the possible variety of surface radiation environments that may be induced during SEP events. Based on the statistical study of more than 30 significant solar events, we have obtained an empirical model for estimating the surface dose rate directly from the intensities of a power-law SEP spectra.

Neutron monitor count rate increase as a proxy for dose rate assessment at aviation altitudes during GLEs

Radiation exposure due to cosmic rays, specifically at cruising aviation altitudes, is an important topic in the field of space weather. While the effect of galactic cosmic rays can be easily assessed on the basis of recent models, estimate of the dose rate during strong solar particle events is rather complicated and time consuming. Here we compute the maximum effective dose rates at a typical commercial flight altitude of 35 kft (≈11 000 m above sea level) during ground level enhancement events, where the necessary information, namely derived energy/rigidity spectra of solar energetic particles, is available. The computations are carried out using different reconstructions of the solar proton spectra, available in bibliographic sources, leading to multiple results for some events. The computations were performed employing a recent model for effective dose and/or ambient dose equivalent due to cosmic ray particles. A conservative approach for the computation was assumed. A highly significant correlation between the maximum effective dose rate and peak NM count rate increase during ground level enhancement events is derived. Hence, we propose to use the peak NM count rate increase as a proxy in order to assess the peak effective dose rate at flight altitude during strong solar particle events using the real time records of the worldwide global neutron monitor network.

In-=SUB=-0.8-=/SUB=-Ga-=SUB=-0.2-=/SUB=-As квантовые точки для GaAs-фотопреобразователей: особенности роста, исследование методом металлорганической газофазной эпитаксии, и свойства

AbstractThe growth peculiarities of In_0.8Ga_0.2As quantum dots and their arrays on GaAs surface by metalorganic vapor-phase epitaxy are investigated. The bimodal size distribution of In_0.8Ga_0.2As quantum dots is established from the photoluminescence spectra recorded at different temperatures. The growth parameters were determined at which the stacking of 20 In_0.8Ga_0.2As quantum-dot layers in the active area of a GaAs solar cell makes it possible to enhance the photogenerated current by 0.97 and 0.77 mA/cm^2 for space and terrestrial solar spectra, respectively, with the high quality of the p–n junction retained. The photogenerated current in a solar cell with quantum dots is higher than in the reference GaAs structure by ~1% with regard to nonradiative-recombination loss originating from stresses induced by the quantum-dot array.

Enhanced solar thermal conversion and thermal conduction of MWCNT-SiO2/Ag binary nanofluids

The features of working fluids which enable synchronously high solar thermal conversion within broadband wavelength ranges and high heat transport are extremely vital for direct volumetric solar receivers. By making use of unique different spectral absorption behaviors of unitary nanofluids, in this paper, we study feasibility of binary nanofluids with enhanced solar thermal conversion and thermal conduction. The binary nanofluid contains multi-wall carbon nanotubes (MWCNTs) and silica/silver (SiO2/Ag) plamonic nanoparticles. Instead of the limited absorption property of unitary nanofluids, by mixing different types of nanofluids with different spectrally absorptive features in proper manners, the spectral absorptance of binary nanofluids can be adjusted by controlling the ratio of two components. Since MWCNTs have high absorption in infrared spectra while SiO2/Ag nanoparticles have strong absorption peaks within visible spectra, the mixed nanofluid get higher absorption within wider solar spectra. Meanwhile, the existence of MWCNTs in the working fluid remarkably improves energy transport of the binary nanofluid. Specifically, MWCNT with the volume fraction of 0.1% can enhance the thermal conductivity of about 7%. The favorable light absorption and heat transfer performance can lead to the higher light absorption efficiency. This work provides a new strategy to improve the solar energy harvesting efficiency of nanofluids being used for volumetric solar collectors.

Automated design of multi junction solar cells by genetic approach: Reaching the [formula omitted] efficiency target

The proper design of the multi-junction solar cell (MJSC) requires the optimisation search through the vast parameter space, with parameters for the proper operation quite often being constrained, like the current matching throughout the cell. Due to high complexity number of MJSC device parameters might be huge, which makes it a demanding task for the most of the optimising strategies based on gradient algorithm. One way to overcome those difficulties is to employ the global optimisation algorithms based on the stochastic search. We present the procedure for the design of MJSC based on the heuristic method, the genetic algorithm, taking into account physical parameters of the solar cell as well as various relevant radiative and non-radiative losses. In the presented model, the number of optimising parameters is 5M+1 for a series constrained M-junctions solar cell. Diffusion dark current, radiative and Auger recombinations are taken into account with actual ASTM G173-03 Global tilted solar spectra, while the absorption properties of individual SCs were calculated using the multi band k·p Hamiltonian. We predicted the efficiencies in case of M=4 to be 50.8% and 55.2% when all losses are taken into account and with only radiative recombination, respectively.

Image restoration of solar spectra

When recording spectra from the ground, atmospheric turbulence causes degradation of the spatial resolution. We present a data reduction method that restores the spatial resolution of the spectra to their undegraded state. By assuming that the point spread function (PSF) estimated from a strictly synchronized, broadband slit-jaw camera is the same as the PSF that spatially degraded the spectra, we can quantify what linear combination of undegraded spectra is present in each degraded data point. The set of equations obtained in this way is found to be generally well-conditioned and sufficiently diagonal to be solved using an iterative linear solver. The resulting solution has regained a spatial resolution comparable to that of the restored slit-jaw images.

Spectral Performance and Calibration of the Suomi NPP OMPS Nadir Profiler Sensor

AbstractThe Ozone Mapping and Profiler Suite (OMPS) is one of five instruments on board the Suomi National Polar‐orbiting Partnership (Suomi NPP) satellite. As part of OMPS, the Nadir Profiler (NP) spectrometer measures Earth's albedo in ultraviolet wavelengths from 250 to 310 nm to profile Earth atmospheric ozone concentration. Since launch in 2011, many changes in the NP radiometric and spectrometric calibration have been made to improve sensor data quality. The most challenging issue is to characterize instrument on‐orbit spectral calibration and to maintain a stable spectral performance to meet sensor design criteria. Validation of the NP sensor data found an average of 3–5% error in the sensor albedo measurements that exceeded 2% requirement, creating 1–2% uncertainty in ozone profile. Data analysis attributes the error to prelaunch calibration uncertainty, ground‐to‐orbit dichroic changes, and on‐orbit detector wavelength registration drifts. A recent update of calibration significantly improved spectral wavelength knowledge as well as the accuracy of the measured solar spectra. As a result, the wavelength‐dependent albedo error is significantly reduced and generally meets the radiometric uncertainty requirement of 2%.

Astro-comb calibrator and spectrograph characterization using a turn-key laser frequency comb

Using a turn-key Ti:sapphire femtosecond laser frequency comb, an off-the-shelf supercontinuum device, and Fabry-Perot mode filters, we report the generation of a 16 GHz frequency comb spanning a 90 nm band about a center wavelength of 566 nm. The light from this astro-comb is used to calibrate the HARPS-N astrophysical spectrograph for precision radial velocity measurements. The comb-calibrated spectrograph achieves a stability of $\sim$ 1 cm/s within half an hour of averaging time. We also use the astro-comb as a reference for measurements of solar spectra obtained with a compact telescope, and as a tool to study intrapixel sensitivity variations on the CCD of the spectrograph.

Polarization independent triple-band (5,4) semiconducting carbon nanotube metamaterial absorber design for visible and ultraviolet regions

Various metamaterial absorber designs operating in the microwave, infrared, visible, and ultraviolet frequency regions have been proposed in the literature. However, only a few studies have been done on the metamaterials that absorb in both visible and ultraviolet solar spectra. A triple-band polarization-insensitive metamaterial absorber structure with semiconducting single-walled carbon nanotube as the dielectric layer is proposed to efficiently absorb the incident electromagnetic radiations in visible and ultraviolet frequency regions. A unit cell of this design comprises three basic components in the form of metal–semiconductor–metal layers. The metallic part of the structure is aluminum, and the (5,4) single-walled carbon nanotube is used as the semiconducting material. The electromagnetic response of the proposed design is numerically simulated in the visible and ultraviolet regions with the maximum absorption rates of 99.75% at 479.4 THz, 99.94% at 766.9 THz, and 97.33% at 938.8 THz with corresponding skin depths of 13.0, 12.8, and 12.9 nm, respectively. Thus, solar cells based on this metamaterial absorber can offer nearly perfect absorption in the suggested frequency regions. The simple configuration of the design provides flexibility to control geometric parameters to be used in the solar cell and possesses the capability to be rescaled for other solar spectrum.

Characterisation of methane variability and trends from near-infrared solar spectra over Hefei, China

This study presents the characterization of XCH4 (averaged-column dry air mole fraction) variability and trends using the near-infrared (NIR) solar spectra recorded by the ground-based high-resolution Fourier transform spectrometer (FTS) over Hefei, China. An annual increase of 10.55 ± 2.87 ppb yr−1 (0.56 ± 0.15% yr−1) in CH4 concentrations was deduced from the three years’ worth of FTS measurements. Seasonal cycles and three typical diurnal variation modes were captured. The maximum CH4 concentration occurred in late summer or early autumn, while the minimum CH4 concentration occurred in winter. CH4 concentrations in August were 30–55 ppb higher than those in January. In most cases, the diurnal variability exhibited an increasing trend in summer or early autumn, while it exhibited a decreasing trend or remained relatively constant in other seasons. We compared the FTS data with the GOSAT data and the GEOS-Chem model data. The average difference between the GOSAT and FTS data (GOSAT minus FTS) was 1.60 ppb (0.09%) ±13.0 ppb (0.70%), and between the smoothed GEOS-Chem model data and FTS data (GEOS-Chem minus FTS) was −8.09 ppb (0.45%) ±17.83 ppb (0.95%). The differences between GOSAT and FTS were season-independent; however, obvious season-dependent differences were observed between GEOS-Chem and FTS. The GOSAT and GEOS-Chem models could reproduce the seasonal cycle observed by FTS with correlation coefficients (r) of 0.77 and 0.86, respectively.

4D Data Cubes from Radio-Interferometric Spectroscopic Snapshot Imaging

The new generation of low radio-frequency interferometric arrays have enabled the imaging of the solar corona at high spectro-temporal resolutions and sensitivity. In this article we introduce and implement a formalism to generate flux density and brightness temperature ($T_{\mathrm B}$) maps from such images, using independently obtained disc-integrated solar flux density dynamic spectra. These images collectively generate a 4D data cube, with axes spanning angular coordinates ($\theta,\phi$), frequency ($\nu$) and time ($t$). This 4D data cube is the most informative data product which can be generated from interferometric radio data. It will allow us to track solar emission simultaneously in these four dimensions. We also introduce SPatially REsolved Dynamic Spectra (SPREDS), named in analogy to the usual dynamic spectra. For any arbitrary region, ($\theta_i,\phi_j$), in the maps, these 2D projections of the 4D data cube correspond to the dynamic spectrum of emission arising from there. We show examples of these data products using observations from the Murchison Widefield Array (MWA). These are also the first calibrated solar maps from the MWA.

Microwave assisted construction of Ag-AgBr/reduced TiO2 nano-tube arrays photoelectrode and its enhanced visible light photocatalytic performance for degradation of 4-chlorphenol

Abstract There is an increasingly significant issue on decomposition of contaminants in modern chemical industry and environmental protection. Hence, in the study, to improve the catalytic of semiconductor materials, the silver-silver bromide nanoparticles decorated reduced TiO2 nano-tube arrays photoelectrode (Ag-AgBr/r-TiO2 NTAs), which exhibits better photocatalytic (PC) performance in the wide range of solar spectra, was successfully fabricated by anodization process, followed by microwave reduction strategy. The partly reduced AgBr nanoparticles are decorated and both Ti3+and Ov states are simultaneously introduced in the TiO2 NTAs photoelectrode inducing the formation of impurity energy level to form Ag-AgBr/r-TiO2 NTAs photoelectrode. Moreover, PC activity of Ag-AgBr/r-TiO2 NTAs photoelelctrode was measured by degradation of 4-chlorphenol (4-CP). Results suggest that Ag-AgBr/r-TiO2 NTAs photoelectrode exhibits higher PC activity (99.9%) than that of other samples within 120 min illumination. The well combination of surface plasmons Ag-AgBr nanoparticles and r-TiO2 NTAs was responsible for the enhancing of PC, and the recombination of photo-generated electrons and holes can simultaneously be inhibited. Thus, Ag-AgBr nanoparticles and Ti3+ exert huge influence on the PC and photoelectrochemical properties of Ag-AgBr/r-TiO2 NTAs photoelectrode.

BiVO3 : A Bi-based material with promising uv-visible light absorption properties

Spin polarized density functional theory calculations on a predicted ${\mathrm{BiVO}}_{3}$ crystal structure is presented. An orthorhombic phase with space group $Pnma$ is observed to be highly stable compared to the aristotype cubic structure. An optical band gap of 1.92 eV and a strong optical absorption at 2.25 eV---which lie in the visible region of the solar spectra---are estimated at the coupled-perturbed hybrid density-functional theory level. In addition, the band-structure analysis somewhat shows dispersion at the valence and conduction bands, and the binding energy of the excitons is calculated to be quite low, which can be possibly dissociated at room temperature. ${\mathrm{BiVO}}_{3}$ is, therefore, expected to be a promising candidate worth being investigated for visible light driven photocatalytic applications. Simulated infrared and Raman spectra are reported, which could represent a guideline for future experiments, along with a full characterization of structural, electronic, and dynamic properties.

Can Measurements of the Near‐Infrared Solar Spectral Irradiance be Reconciled? A New Ground‐Based Assessment Between 4,000 and 10,000 cm−1

AbstractThe near‐infrared solar spectral irradiance (SSI) is of vital importance for understanding the Earth's radiation budget, and in Earth observation applications. Differences between previously published solar spectra (including the commonly used ATLAS3 spectrum) reach up to 10% at the low wavenumber end of the 4,000–10,000 cm−1 (2.5–1 μm) spectral region. The implications for the atmospheric sciences are significant, since this spectral region contains 25% of the incoming total solar irradiance. This work details an updated analysis of the CAVIAR SSI, featuring additional analysis techniques and an updated uncertainty budget using a Monte Carlo method. We report good consistency with ATLAS3 in the 7,000–10,000 cm−1 region where there is confidence in these results due to agreement with other spectra, but ~7% lower in the 4,000–7,000 cm−1 region, in general agreement with several other analyses.

Investigation of sensing properties of sol–gel processed 4 at%Sb:SnO2/TiO2 thin films

In this work we investigate the gas and photo sensing properties of the antimony doped tin oxide and titanium oxide (4 at%Sb:SnO2/TiO2) nanocrystalline thin films deposited by sol–gel dip-coating. Photoconductivity measurements are carried out under solar light spectra irradiation at different powers. These results show a photo sensitivity of the films in a lateral junction due to interfacial defects. Gas sensitivity was studied at different pressures, and higher conductivity is presented at lower pressure compared to oxygen-rich atmosphere. It occurs due to absence of oxygen adsorption on the semiconductors surface. TiO2 films are also investigated concerning its properties to gas sensing under photo-excitation with InGaN LED light source with wavelength centered in 450 nm. The decay of photo-induced current evaluated under O2 and vacuum atmospheres shows that the sample illumination may contribute to higher gas-sensitivity. This measurement allows determining the charge carrier capture energy, that is related to trapping dominated by distinct defects in each atmosphere.

The Magnetic Future of the Sun

Abstract We analyze space- and ground-based data for the old (7.0 ± 0.3 Gyr) solar analogs 16 Cyg A and B. The stars were observed with the Cosmic Origins UV Spectrographs on the Hubble Space Telescope (HST) on 2015 October 23 and 2016 February 3, respectively, and with the Chandra X-ray Observatory on 2016 February 7. Time-series data in Ca ii data are used to place the UV data in context. The UV spectra of 18 Sco (3.7 ± 0.5 Gyr), the Sun (4.6 ± 0.04 Gyr), and α Cen A ( ) appear remarkably similar, pointing to a convergence of magnetic heating rates for G2 main-sequence stars older than ≈2–4 Gyr. But the B component’s X-ray (0.3–2.5 keV) flux lies 20× below a well-known minimum level reported by Schmitt. As reported for α Cen A, the coronal temperature probably lies below that detectable in soft X-rays. No solar UV flux spectra of comparable resolution to those of stellar data exist, but they are badly needed for comparison with stellar data. Center-to-limb variations are reevaluated for lines such as Ca ii through X-rays, with important consequences for observing activity cycles in such features. We also call into question work that has mixed solar intensity–intensity statistics with flux–flux relations of stars.

Low-Temperature Growth of Hydrogenated Amorphous Silicon Carbide Solar Cell by Inductively Coupled Plasma Deposition Toward High Conversion Efficiency in Indoor Lighting

A p-a-SiC:H window layer was used in amorphous Si thin film solar cells to boost the conversion efficiency in an indoor lighting of 500 lx. The p-a-SiC:H window layer/p-a-Si:H buffer layer scheme moderates the abrupt band bending across the p/i interface for the enhancement of VOC, JSC and FF in the solar spectra of short wavelengths. The optimized thickness of i-a-Si:H absorber layer is 400 nm to achieve the conversion efficiency of ~9.58% in an AM1.5 G solar spectrum. However, the optimized thickness of the absorber layer can be changed from 400 to 600 nm in the indoor lighting of 500 lx, exhibiting the maximum output power of 25.56 μW/cm2. Furthermore, various durability tests with excellent performance were investigated, which are significantly beneficial to harvest the indoor lights for applications in the self-powered internet of thing (IoT).

The high-resolution extraterrestrial solar spectrum (QASUMEFTS) determined from ground-based solar irradiance measurements

Abstract. A high-resolution extraterrestrial solar spectrum has been determined from ground-based measurements of direct solar spectral irradiance (SSI) over the wavelength range from 300 to 500 nm using the Langley-plot technique. The measurements were obtained at the Izaña Atmospheric Research Centre from the Agencia Estatal de Meteorología, Tenerife, Spain, during the period 12 to 24 September 2016. This solar spectrum (QASUMEFTS) was combined from medium-resolution (bandpass of 0.86 nm) measurements of the QASUME (Quality Assurance of Spectral Ultraviolet Measurements in Europe) spectroradiometer in the wavelength range from 300 to 500 nm and high-resolution measurements (0.025 nm) from a Fourier transform spectroradiometer (FTS) over the wavelength range from 305 to 380 nm. The Kitt Peak solar flux atlas was used to extend this high-resolution solar spectrum to 500 nm. The expanded uncertainties of this solar spectrum are 2 % between 310 and 500 nm and 4 % at 300 nm. The comparison of this solar spectrum with solar spectra measured in space (top of the atmosphere) gave very good agreements in some cases, while in some other cases discrepancies of up to 5 % were observed. The QASUMEFTS solar spectrum represents a benchmark dataset with uncertainties lower than anything previously published. The metrological traceability of the measurements to the International System of Units (SI) is assured by an unbroken chain of calibrations leading to the primary spectral irradiance standard of the Physikalisch-Technische Bundesanstalt in Germany.