Solar Spectra Research Articles

Low-frequency oscillations while magnetic storms as a tool to determine the types of solar plasma flows

Comparison of wavelet spectrum (skeletons) local maxima for disturbed components of solar plasma flow parameters and geomagnetic field disturbances recorded along the meridional station chain during geomagnetic storm intervals is performed in the range of magnetohydrodynamic (MHD) waves. An algorithm for quantitative evaluation of analyzed skeletons consistency has been developed. It has been used to demonstrate the possibility of the type of solar wind plasma flow elaboration on unique spectral signs of Solar wind speed disturbances, density and interplanetary magnetic field. It is shown that the energy spectrum of oscillations for these parameters reflects the internal structure of the corresponding plasma formation. The skeletons application to the analysis of the interplanetary space main parameters made it possible to estimate the magnetosphere reaction time in geomagnetic field horizontal component oscillations at different latitudes on the disturbance. As a result, the distributed magnetosphere reaction over latitude was determined in the form of geomagnetic field oscillations on the disturbed solar flow parameters. It is shown that the dynamics of the components of the solar wind parameters disturbance spectra corresponding to plasma flows manifest themselves in the MHD spectra of high-latitude stations magnetograms and can be used as a diagnostic tool.

The first comprehensive experiment for determining parameters of the vertical distribution of methane in the troposphere over Western Siberia from solar spectra recorded with an IFS-125M FTIR spectrometer and in situ aircraft measurements

The first comprehensive experiment for determining parameters of the vertical distribution of methane in the troposphere over Western Siberia from solar spectra recorded with an IFS-125M FTIR spectrometer and in situ aircraft measurements

Density functional theory analysis of electronic and optical properties of orthorhombic perovskite CH3NH3SnX3 (X = Br, I)

The electronic and optical properties of hybrid perovskites CH3NH3SnX3 (X = Br, I) are investigated by first-principles calculations. Our results show that consideration of the weak van der Waals interactions is important for theoretical investigations of Sn-based hybrid materials. During light harvesting, the electron transition will occur between the p states of halogen at the valence band maximum (VBM) and the Sn 5p states at the conduction band minimum (CBM). Comparing with the energy distribution of solar spectra, CH3NH3SnI3 has better absorption characteristics in the visible region than CH3NH3PbI3, which shows promising prospects in realizing lead-free, highly efficient solar cells.

Analysis of Quiescent Corona X-ray Spectra from SphinX During the 2009 Solar Minimum

The SphinX X-ray spectrophotometer on the {\em CORONAS-PHOTON}\/ mission observed the 1~--~15\,keV X-ray spectrum of the spatially integrated solar corona during the deep minimum of 2009, when solar activity was exceptionally low. Its sensitivity for energies $> 1.2$\,keV was higher than that of any other solar X-ray spectrometer in orbit at the time, including the detectors on GOES. Using much improved instrumental data than was used previously, we analyzed SphinX spectra in 576 intervals for which there was no discernible activity (NA), 40 intervals when there were X-ray brightenings (B), and sixteen intervals when there were micro-flares with peak emission less than GOES A1 (F). An instrumental background spectrum, formed over 34 hours of spacecraft night-time periods and including electronic noise and particle radiation, was subtracted from the solar spectra. Theoretical spectra were used to deduce temperatures on an isothermal assumption for the NA, B, and F intervals (1.69, 1.81, and 1.86\,MK respectively). Differential emission measure (DEM) analysis for the same spectra revealed a "cooler" component (log\,$T = 6.2$ or $T \approx 1.6$\,MK) in each case, but with a second hotter component having a less well-defined peak temperature varying from $\approx 2.5$ to $\approx 3.5$\,MK (log\,$T = 6.4$ and 6.55) and an emission measure between two and three orders smaller than that of the cooler component. These results are similar to those obtained at times just after solar minimum with the EVE instrument. A very hot component that might indicate the signature of nano-flare heating of the corona is not evident in SphinX data.

SOLPEX Complex for Studies of Solar Radiation in the Soft X-Ray Range

The SOLPEX complex consists of two instruments for recording soft X-ray radiation from the Sun and is a part of the KORTES equipment, which will be installed on board the International Space Station. The first instrument is a fast-rotating multi-crystalagg spectrometer designed to record solar spectra in the range of 0.4–23 A with a time resolution of no less than 0.1 s. The second instrument is a pinhole camera with a focal length of 58 cm. The camera has a field of viewof 2° × 2°, angular resolution of 2 arcmin, and time resolution up to 0.2 s. The energy range is determined by the input filter and is 1–10 keV; the energy resolution is 0.5 keV. The combination of these two instruments makes it possible to locate hot solar sources in the corona, determine their speed, and conduct spectral diagnostics.

8B and hep solar neutrino detection by terrestrial experiments

Solar neutrino spectra of 8B and hep neutrinos produced by pp-chain reactions are analysed for various nuclear detectors in current terrestrial experiments. The well known folding method is applied by employing appropriately simulated solar neutrino distributions and using recently calculated total cross section of neutrino- nucleus processes. We focus on the nuclear target of current experiments like MOON and ICARUS as well to other promising nuclear isotopes.

Synergic effect of Zinc (Zn) precursors on the microstructural, optical and electrical properties of Zinc oxide thin films for solar cell applications

Zinc oxide (ZnO) nanoparticles, with their inimitable characteristics such as easy synthesis, high selectivity and enhanced cytotoxicity are becoming progressively important candidate in modern applications. In this study, we have systematically investigated the effect of fabrication conditions on the morphological, structural, optical and electrical properties of zinc oxide (ZnO) thin films. It was observed that the change in Zn-precursor leads to the growth of grains structure at the surface of ZnO thin films. Broadly mentioned, two different regions of growth were observed with the change in the Zn precursor medium. The presence of ZnO hexagonal structure wurtzite was confirmed with the help of non-destructive X-ray Diffraction (XRD) analysis. Scanning Electron Microscopy (SEM) showed that the islands of nano-grains started to nucleate into highly stressed, uniform and roughly compact morphology of the ZnO grains structures of the crack-free thin films. The as-fabricated ZnO thin films comprised of micro and nanoparticles grains structures. The electrical properties measurement revealed the decrease in the average resistivity with the change in Zn-precursor solution of the as-fabricated ZnO thin films. The UV–Vis. Spectroscopy showed the optical absorption spectra of the ZnO thin films have maximum transmittance in the visible region i.e. 80 %. Such kind of films characteristics are very important for solar spectra. It was observed that the change in Zn precursor solution has impact on the transmittance properties of the ZnO thin films. This study highlights an environment friendly, low cost and facile roots for the fabrication of ZnO thin films for probable use in solar cells applications.

Evaluation of the Recent Atomic Data for Fe i Lines Based on Solar and Stellar Spectra

We performed an extensive comparative analysis of the recent experimental data on Fe i transition probabilities (TP) based on the observed solar and stellar spectra. This work is part of the Vienna Atomic Line database (VALD) activities. Our motivation is to keep the VALD line list as complete as possible and provide VALD users with substantiated recommendations for the most accurate atomic data. For assessment of data quality we choose the “normal” (as opposed to peculiar and/or magnetic) Main Sequence sharp-line stars of different effective temperatures with accurately known atmospheric parameters: Sun, Procyon, HD 32115, and 21 Peg. Theoretical spectra of these stars were synthesized for 1D plane-parallel model atmospheres accounting for non-local thermodynamic equilibrium (NLTE) effects, and then they were compared with the observations. For all of the stars we derived atmospheric abundances based on the new and previous experimental TP. When using the new TPs the best agreement for iron is achieved with the TP of the Hannover group (Bard, Kock, and Kock, Astron. Astrophys.248, 315, 1991; Bard and Kock, Astron. Astrophys.282, 1014, 1994). The Hannover set is recommended as the primary source of transition probabilities in stellar abundance analysis. The new TP data significantly increase the number of spectral lines of Fe i in the optical and red spectral regions available for accurate abundance analysis of stars in a wide range of temperatures and metallicities. Comparison with the observed stellar spectra invalidates some new experimental data despite the small given uncertainty of the laboratory measurements. Finally, we note the importance of accurate line-broadening data.

Solar Eclipse Observations from the Ground and Air from 0.31 to 5.5 Microns

We present spectra and broad-band polarized light data from a novel suite of instruments deployed during the 21st August 2017 total solar eclipse. Our goals were to survey solar spectra at thermal infrared wavelengths during eclipse, and to test new technology for measuring polarized coronal light. An infrared coronal imaging spectrometer, flown at 14.3 km altitude above Kentucky, was supported on the ground by observations from Madras, Oregon (elevation 683 m) and Camp Wyoba on Casper Mountain, Wyoming (2402 m). In Wyoming we deployed a new infrared Fourier Transform Spectrometer (FTS), three low-dispersion spectrometers loaned to us by Avantes, a novel visible-light camera PolarCam, sensitive to linear polarization, and one of two infrared cameras from FLIR Systems, the other operated at Madras. Circumstances of eclipse demanded that the observations spanned 17:19 to 18:26 UT. We analyze spectra of the limb photosphere, the chromosphere, prominences, and coronal lines from 310 nm to 5.5 μm. We calibrated data photometrically using the solar disk as a source. Between different spectrometers, the calibrations were consistent to better than 13%. But the sensitivities achieved were insufficient to detect coronal lines from the ground. The PolarCam data are in remarkable agreement with polarization data from the K-Cor synoptic instrument on Mauna Loa, and with FLIR intensity data acquired in Madras. We discuss new results, including a detection of the He i 1083 nm multiplet in emission during the whole of totality. The combination of the FTS and AIR-Spec spectra reveals for the first time the effects of the telluric extinction on the infrared coronal emission lines, to be observed with upcoming Daniel K. Inouye Solar Telescope.

Highly robust La1-xTixFeO3 dual catalyst with combined photocatalytic and photo-CWPO activity under visible light for 4-chlorophenol removal in water

A highly robust Ti-substituted LaFeO3 dual catalyst was synthesized via a facile Pechini sol-gel route using a dried amorphous sol-gel titania as titanium source and a final calcination at 800 °C that enabled solid-solid diffusion of titanium atoms within the perovskite network. Using an amorphous precursor instead of crystallized titania nanocrystals increased the Ti → La atomic substitution degree in the crystalline network from 5 at% to 11 at%, together with a strong increase in the catalytic activity. The partially substituted La1-xTixFeO3 catalyst with a 11 at% substitution degree allowed pure heterogeneous surface reactions to take place under pure visible light (λ > 420 nm), with an increase in the catalyst robustness by more than two orders of magnitude compared to the unmodified LaFeO3 counterpart, evidenced by the absence of any Fe release, the structural stability of the substituted catalyst and the absence of any loss of catalytic activity with test cycles. Further, the strategy of combining both photocatalysis and H2O2-mediated heterogeneous photo-Fenton advanced oxidation processes within one single heterogeneous catalyst allowed the dual La1-xTixFeO3 catalyst to simultaneously take advantage from the higher reaction rate of photo-Fenton and from the higher mineralization yield of photocatalysis in water treatment. As a result, the dual 11 at% Ti-substituted La1-xTixFeO3 catalyst clearly outperformed its unmodified LaFeO3 counterpart and led to a complete mineralization of the 4-chlorophenol substrate under pure visible light, with strongly enhanced H2O2 decomposition, 4-chlorophenol and TOC conversion rates. Finally, the activity of the La1-xTixFeO3 catalyst under visible light contributed significantly to its overall activity obtained using the full solar spectra.

Improved FTIR retrieval strategy for HCFC-22 (CHClF<sub>2</sub>), comparisons with in situ and satellite datasets with the support of models, and determination of its long-term trend above Jungfraujoch

Abstract. Hydrochlorofluorocarbons (HCFCs) are the first, but temporary, substitution products for the strong ozone-depleting chlorofluorocarbons (CFCs). HCFC consumption and production are currently regulated under the Montreal Protocol on Substances that Deplete the Ozone Layer and their emissions have started to stabilize or even decrease. As HCFC-22 (CHClF2) is by far the most abundant HCFC in today's atmosphere, it is crucial to continue to monitor the evolution of its atmospheric concentration. In this study, we describe an improved HCFC-22 retrieval strategy from ground-based high-resolution Fourier transform infrared (FTIR) solar spectra recorded at the high-altitude scientific station of Jungfraujoch, the Swiss Alps, 3580 m a.m.s.l. (above mean sea level). This new strategy distinguishes tropospheric and lower-stratospheric partial columns. Comparisons with independent datasets, such as the Advanced Global Atmospheric Gases Experiment (AGAGE) and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), supported by models, such as the Belgian Assimilation System for Chemical ObErvation (BASCOE) and the Whole Atmosphere Community Climate Model (WACCM), demonstrate the validity of our tropospheric and lower-stratospheric long-term time series. A trend analysis on the datasets used here, now spanning 30 years, confirms the last decade's decline in the HCFC-22 growth rate. This updated retrieval strategy can be adapted for other ozone-depleting substances (ODSs), such as CFC-12. Measuring or retrieving ODS atmospheric concentrations is essential for scrutinizing the fulfilment of the globally ratified Montreal Protocol.

Electronic and Optical Response of Chalcopyrites Cu2InMSe4 (M = Al, Ga): First Principles Investigation for Use in Solar Cells

We report systematic investigations of opto-electronic behavior of promising semiconducting chalcopyrite compounds Cu2In(Al,Ga)Se4 within the framework of density functional theory. In view to explore their possible utilization in opto-electronic devices, we have firstly performed calculations using one of the most accurate prescriptions, namely full-potential linearized augmented plane wave method. For a better accuracy, computations have been carried out using different exchange–correlation potentials including the most accurate modified Becke–Johnson potential with hybrid functional features. Computations have been performed for various electronic and optical properties such as energy bands, total and partial density of states, real and imaginary parts of dielectric tensors, absorption spectra, reflection, refraction and energy loss spectra for both chalcopyrite compounds. We have compared our data with the existing experimental and theoretical calculations for both compounds, which validates the accuracy of present computations. Both chalcopyrites are observed to have a direct band gap nature (Cu2InAlSe4: 1.14 eV and Cu2InGaSe4: 0.96 eV). Energy peaks recorded in the imaginary part of dielectric tensors are well interpreted by means of inter-band transitions. Significant intensities observed in absorption spectra within the energy range of solar spectra unambiguously depict feasibility of these compounds in optoelectronic devices.

Shortwave Spectral Radiative Signatures and Their Physical Controls

AbstractThe spectrum of reflected solar radiation emerging at the top of the atmosphere is rich with Earth system information. To identify spectral signatures in the reflected solar radiation and directly relate them to the underlying physical properties controlling their structure, over 90 000 solar reflectance spectra are computed over West Africa in 2010 using a fast radiation code employing the spectral characteristics of the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). Cluster analysis applied to the computed spectra reveals spectral signatures related to distinct surface properties, and cloud regimes distinguished by their spectral shortwave cloud radiative effect (SWCRE). The cloud regimes exhibit a diverse variety of mean broadband SWCREs, and offer an alternative approach to define cloud type for SWCRE applications that does not require any prior assumptions. The direct link between spectral signatures and distinct physical properties extracted from clustering remains robust between spatial scales of 1, 20, and 240 km, and presents an excellent opportunity to understand the underlying properties controlling real spectral reflectance observations. Observed SCIAMACHY spectra are assigned to the calculated spectral clusters, showing that cloud regimes are most frequent during the active West African monsoon season of June–October in 2010, and all cloud regimes have a higher frequency of occurrence during the active monsoon season of 2003 compared with the inactive monsoon season of 2004. Overall, the distinct underlying physical properties controlling spectral signatures show great promise for monitoring evolution of the Earth system directly from solar spectral reflectance observations.

The low-frequency break observed in the slow solar wind magnetic spectra

Fluctuations of solar wind magnetic field and plasma parameters exhibit a typical turbulence power spectrum with a spectral index ranging between ∼5/3 and ∼3/2. In particular, at 1 AU, the magnetic field spectrum, observed within fast corotating streams, also shows a clear steepening for frequencies higher than the typical proton scales, of the order of ∼3 × 10−1 Hz, and a flattening towards 1/f at frequencies lower than ∼10−3 Hz. However, the current literature reports observations of the low-frequency break only for fast streams. Slow streams, as observed to date, have not shown a clear break, and this has commonly been attributed to slow wind intervals not being long enough. Actually, because of the longer transit time from the Sun, slow wind turbulence would be older and the frequency break would be shifted to lower frequencies with respect to fast wind. Based on this hypothesis, we performed a careful search for long-lasting slow wind intervals throughout 12 years of Wind satellite measurements. Our search, based on stringent requirements not only on wind speed but also on the level of magnetic compressibility and Alfvénicity of the turbulent fluctuations, yielded 48 slow wind streams lasting longer than 7 days. This result allowed us to extend our study to frequencies sufficiently low and, for the first time in the literature, we are able to show that the 1/f magnetic spectral scaling is also present in the slow solar wind, provided the interval is long enough. However, this is not the case for the slow wind velocity spectrum, which keeps the typical Kolmogorov scaling throughout the analysed frequency range. After ruling out the possible role of compressibility and Alfvénicity for the 1/f scaling, a possible explanation in terms of magnetic amplitude saturation, as recently proposed in the literature, is suggested.

Retrieval of Carbon Monoxide Total Column in the Atmosphere from High Resolution Atmospheric Spectra

Carbon monoxide (CO) is a marker of the atmospheric pollution caused by fires and combustion engine emissions. The regular monitoring of the CO content in the atmosphere is needed to control air quality. In this work, the results of CO atmospheric total column retrievals from the solar spectra recorded by Fourier -transform spectrometers at the St. Petersburg (59.88° N, 29.83° E) and Kourovka (57.038° N, 59.545° E) stations are presented. The impact of differences in CO absorption line parameters in modern spectroscopic databases on the accuracy of the CO atmospheric total column retrieved from high resolution spectra is estimated.

MARVEL analysis of the measured high-resolution spectra of [formula omitted]NH

Rovibronic energy levels are determined for four low-lying electronic states (X3Σ-, A3Π, a1Δ, and c1Π) of the imidogen free radical (14NH) using the Marvel (Measured Active Rotational-Vibrational Energy Levels) technique. Compilation of transitions from both laboratory measurements and solar spectra, found in 18 publications, yields a dataset of 3002 rovibronic transitions forming elements of a measured spectroscopic network (SN). At the end of the MARVEL procedure, the majority of the transitions form a single, self-consistent SN component of 2954 rovibronic transitions and 1058 energy levels, 542, 403, and 58 for the X3Σ-, A3Π, and c1Π electronic states, respectively. The a1Δ electronic state is characterized by 55 Λ-doublet levels, counting each level only once. Electronic structure computations show that unusually the CCSD(T) method does not accurately predict the a1Δ excitation energy even at the complete basis set limit.

Sun-as-a-star observations of the 2017 August 21 solar eclipse

AbstractThe Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) is a state-of-the-art, thermally stabilized, fiber-fed, high-resolution spectrograph for the Large Binocular Telescope (LBT) at Mt. Graham, Arizona. During daytime the instrument is fed with sunlight from the 10-millimeter aperture, fully automated, binocular Solar Disk-Integrated (SDI) telescope. The observed Sun-as-a-star spectra contain a multitude of photospheric and chromospheric spectral lines in the wavelength ranges 4200–4800 Å and 5300–6300 Å. One of the advantages of PEPSI is that solar spectra are recorded in the exactly same manner as nighttime targets. Thus, solar and stellar spectra can be directly compared. PEPSI/SDI recorded 116 Sun-as-a-star spectra during the 2017 August 21 solar eclipse. The observed maximum obscuration was 61.6%. The spectra were taken with a spectral resolution of ≈ 250000 and an exposure time of 0.3 s. The high-spectral resolution facilitates detecting subtle changes in the spectra while the Moon passes the solar disk. Sun-as-a-star spectra are affected by changing contributions due to limb darkening and solar differential rotation, and to a lesser extend by supergranular velocity pattern and the presence of active regions on the solar surface. The goal of this study is to investigate the temporal evolution of the chromospheric Na D doublet during the eclipse and to compare observations with synthetic line profiles computed with the state-of-the-art Bifrost code.

Diagnostics of non-thermal-distributions from solar flare EUV line spectra

AbstractSpectral line intensities observed by the Extreme Ultraviolet Variability Experiment (EVE) on board the Solar Dynamics Observatory (SDO) during 2012 March 9 M6.3 flare were used to diagnose a presence of a non-thermal electron distribution represented by a κ-distribution. The diagnosed electron densities ($\approx 2 \times {10^{11}}{\rm{c}}{{\rm{m}}^{ - 3}}$) are affected only a little by the presence of the non-thermal distribution, and are within the uncertainties of observation. On the other hand, the temperature diagnostics based on the line ratios involving different ionization degrees is strongly affected by the type of the electron distribution. The distribution functions diagnosed from relative Fe line intensities demonstrate the presence of strongly non-thermal distributions during the impulsive phase of the flare and later their gradual thermalization.

Direct Observations of Traveling Ionospheric Disturbances as Focusers of Solar Radiation: Spectral Caustics

Abstract The solar radiation focusing effect is related to the specific phenomenon of propagation of the Sun-emitted HF and VHF waves through terrestrial ionosphere. This natural effect is observed with ground-based radio instruments running within the 10–200 MHz range as distinctive patterns—the spectral caustics (SCs)—on the solar dynamic spectra. It has been suggested that SCs are associated with medium-scale traveling ionospheric disturbances (MSTIDs). In this paper, we present the first direct observations of SCs induced by MSTIDs, using solar dynamic spectra with SCs obtained by different European radio telescopes on 2014 January 8 and simultaneous two-dimensional detrended total electron content (dTEC) maps over Europe. Spatial examination of dTEC maps as well as precise timing analysis of the maps and the dynamic spectra have been performed. First, we found several pairs of one-to-one (TID-SC) correspondences. The study provides strong observational evidence supporting the suggestion that MSTIDs are the cause of SCs.

Thermochromic glazing performance: From component experimental characterisation to whole building performance evaluation

Thermochromic switchable glazing have been gaining increasing popularity among dynamic building envelope solutions aimed at reducing energy demand in tertiary buildings, due to their capability of varying optical properties according to the material temperature. This enables the management of entering solar loads without any need for an active control, hence thermochromic glazing performance relies on effective material design. Nevertheless, to date the development of thermochromic glazing materials has relied on limited building performance evaluations, considering the effect of managing solar radiation on energy use for heating and cooling alone, and without representing in a comprehensive way the variations of the thermochromic optical properties to include hysteresis phenomena. The present paper aims to evaluate the building performance of a ligand exchange thermochromic glazing (LETC), characterised by a wide variation of optical properties in the visible and solar spectra and hysteresis between heating and cooling cycles. To this aim an ad-hoc developed building performance simulation strategy is presented, enabling data integration between dynamic thermal simulation and climate based daylight analysis, including a thermochromic parametrical model describing the hysteretical variation of optical properties as a function of material temperature, derived from experimental measurements. The simulation method is adopted to evaluate the energy uses for heating, cooling and lighting and the visual comfort in an office space integrating the LETC glazing in different climatic contexts. The results show that the LETC glazing is able to optimise multiple building performance aspects simultaneously. Compared to static glazing benchmarks with comparable selectiveness, for the considered locations, the LETC glazing achieves a total energy use reduction from 3% to 10% and daylight availability improvements from 5% to nearly 20%. Increasing the thermochromic hysteresis has shown a positive effect on improving daylight availability (from 5% to 15%) and on reducing probable glare due to direct solar radiation (from 12% to 25%), with negligible effect on total energy use. Finally, the simulation framework presented represents a general method that can be adopted to evaluate the performance of other switchable glazing technologies as well.