Solar Luminosity Research Articles

How faculae and network relate to sunspots, and the implications for solar and stellar brightness variations(Corrigendum)

How faculae and network relate to sunspots, and the implications for solar and stellar brightness variations(<i>Corrigendum</i>)

The feasibility of using solar powered submersible pumps in the State of Kuwait

The research aims to study the extent of the possible benefit from the solar fall falling in the state of Kuwait to operate submersible type pumps and to show the rate of flow of these pumps according to the change of solar radiation taking into account the spatial and temporal factor. The abundance of the area in southern Kuwait was chosen because there is good brightness for this area underground at different depths. As for the temporal factor, the timing of the transition was chosen between two important seasons that start from mid-January to mid-March, which is the period during which the brightness of the sun moves from the intermediate stage to the full brightness stage. The experimental study showed that the pump passes through two stages, the first of which is not operating and responding For the process of drawing if the solar radiation falling on the panels is less than 225 W/ m2, and the second stage occurs a response and operation of the pump gradually if the falling solar radiation is higher than the previous value, as the study showed that there is a large amount of external energy that is not exploited at some times of the day, especially in Sunny days, where the proportions decreased from 4.8 l/ 1000 watt to 1.5 l/ 1000 watt with an increase in the amount of energy from 430 w/ m 2 to 1005 w T/ m 2 The amount of flow fluctuated during the days of the study due to the differences in the sun's brightness and climate change, and the study was conducted using a method of taking periodic, daily and instant measurements, to determine the amount of energy and flow by using a solar radiation measuring device with a storage memory, which is a device for one of the companies that install solar energy panels And easily traded and other devices such as digital voltmeter and clip meter and water meter, the study concluded that the use of submersible pumps powered by solar energy with the presence of special characteristics such as the pump capacity, water depth and degree of brightness.

Growth of Jupiter: Formation in disks of gas and solids and evolution to the present epoch

The formation of Jupiter is modeled via core-nucleated accretion, and the planet's evolution is simulated up to the present epoch. Throughout the phases when the planet acquires most of its heavy-element content, the calculation of solids' accretion accounts for interactions with an evolving disk of planetesimals. The phase of growth from an embryo of a few hundred kilometers in radius until the time when the accretion of gas overtakes solids' accretion was presented by D'Angelo et al. (2014), and the same numerical methods are applied here. Those calculations followed the formation for about 4 × 105 years, until the epoch when the heavy-element and hydrogen/helium masses wereMZ ≈ 7.3 andMXY ≈ 0.15 Earth's masses (M⊕), respectively, and ṀXY≈ṀZ. Herein, the calculation is continued through the phase when MXYgrows to equalMZ, at which age, about 2.4 × 106 years, the total mass of the planet isMp ≈ 20M⊕. About 9 × 105 years later,Mpis approximately 60M⊕and MZ ≈ 16M⊕, three-quarters of which are delivered by planetesimals larger than 10km in radius. Around this epoch, the contraction of the envelope dictates gas accretion rates a few times 10−3M⊕per year, initiating the regime of disk-limited accretion, whereby the planet can accrete all the gas provided by the disk, and its evolution is therefore tied to disk's evolution. Growth is continued by constructing simplified models of protosolar accretion disks that evolve through viscous diffusion, winds, and accretion on the planet. Jupiter's formation ends after ≈ 3.4–4.2Myr, depending on the applied disk viscosity parameter, when nebula gas disperses. The young Jupiter is 4.5–5.5 times as voluminous as it is presently and thousands of times as luminous, ~10−5L⊙. The heavy-element mass is ≈ 20M⊕. The evolution proceeds through the cooling and contraction phase, in isolation except for solar irradiation. After 4570Myr, the age of the solar system, radius and luminosity of the planet are within 10% of current values, accounting also for uncertainties in the power absorbed from the Sun. During formation, and soon thereafter, the planet exhibits features, e.g., luminosity and effective temperature, that may probe aspects of the latter stages of formation, if observable. These possibly distinctive features, however, seem to disappear within a few tens of Myr

Exploring the Mass-loss Histories of the Red Supergiants*

Abstract We report mid- to far-infrared imaging and photometry from 7 to 37 μm with SOFIA/FORCAST and 2 μm adaptive optics imaging with LBTI/LMIRCam of a large sample of red supergiants (RSGs) in four Galactic clusters: RSGC1, RSGC2 = Stephenson 2, RSGC3, and NGC 7419. The RSGs in these clusters cover their expected range in luminosity and initial mass from ≈9 to more than 25 M ⊙. The population includes examples of very late-type RSGs such as MY Cep, which may be near the end of the RSG stage, high-mass-losing maser sources, yellow hypergiants, and post-RSG candidates. Many of the stars and almost all of the most luminous have spectral energy distributions (SEDs) with extended infrared excess radiation at the longest wavelengths. To best model their SEDs, we use the DUSTY code with a variable radial density distribution function to estimate their mass-loss rates. Our –luminosity relation for 42 RSGs basically follows the classical de Jager curve, but at luminosities below 105 , we find a significant population of RSGs with below the de Jager relation. At luminosities above 105 L ⊙, there is a rapid transition to higher mass-loss rates that approximates and overlaps the de Jager curve. We recommend that instead of using a linear relation or single curve, the empirical –luminosity relation is better represented by a broad band. Interestingly, the transition to much higher at about 105 L ⊙ corresponds approximately to an initial mass of 18–20 M ⊙, which is close to the upper limit for RSGs becoming Type II supernovae.

Active Region Irradiance during Quiescent Periods: New Insights from Sun-as-a-star Spectra

Abstract How much energy do solar active regions (ARs) typically radiate during quiescent periods? This is a fundamental question for storage and release models of flares and ARs, yet it is presently poorly answered by observations. Here we use the “Sun-as-a-point-source” spectra from the EUV Variability Experiment (EVE) on the Solar Dynamics Observatory to provide a novel estimate of radiative energy losses of an evolving AR. Although EVE provides excellent spectral (5–105 nm) and temperature (2–25 MK) coverage for AR analysis, to our knowledge, these data have not been used for this purpose due to the lack of spatial resolution and the likelihood of source confusion. Here we present a way around this problem. We analyze EVE data time series, when only one large AR 11520 was present on the disk. By subtracting the quiet-Sun background, we estimate the radiative contribution in EUV from the AR alone. We estimate the mean AR irradiance and cumulative AR radiative energy losses in the 1–300 Å and astronomical standard ROSAT-PSPC, 3–124 Å, passbands and compare these to the magnetic energy injection rate through the photosphere, and to variations of the solar cycle luminosity. We find that while AR radiative energy losses are ∼100 times smaller than typical magnetic energy injection rates at the photosphere, they are an order of magnitude larger or similar to the bolometric radiated energies associated with large flares. This study is the first detailed analysis of AR thermal properties using EVE Sun-as-a-star observations, opening doors to AR studies on other stars.

The Impact of Life on Climate Stabilization Over Different Timescales

AbstractSurface life has been argued to be crucial in keeping a planet habitable in the long term. Biologically enhanced weathering compensates for increasing solar luminosity, and temperature‐dependent plant productivity weakens climate perturbations. Furthermore, a reduced calcification rate of marine organisms provides a negative feedback to rising atmospheric CO2. Here, I present a model of the long‐term carbon cycle including biological enhancement of weathering and marine calcification. Climate oscillations of periods from thousands to millions of years arise from a simple model of mountain uplift and erosion. I systematically study the influence of the biologically driven feedbacks on damping these oscillations. For oscillations of periods &lt;2 Myr, the marine calcification feedback yields surface temperature amplitudes that are approximately 1/3 lower compared to a model that ignores this feedback. Abiotic oceans, however, would not necessarily imply a less stable climate on short timescales, due to a higher pH and thereby a higher buffer capacity. On longer timescales, the higher ocean pH would reduce climate stability, since the seafloor weathering feedback would work less efficiently. Biological enhancement of weathering helps stabilizing the climate against oscillations of periods &gt;0.5 Myr. These findings are sensitive to the ratio of land to oceans, however. Furthermore, the mantle carbon degassing rate plays a role, since the temperature dependence of biological primary productivity may be smaller at higher temperatures. Altogether, life can be argued to stabilize the climate on timescales longer than some 100 kyr, while details depend on the geological state of the planet.

Is the Faint Young Sun Problem for Earth Solved?

Stellar evolution models predict that the solar luminosity was lower in the past, typically 20-25% lower during the Archean (3.8-2.5 Ga). Despite the fainter Sun, there is strong evidence for the presence of liquid water on Earth’s surface at that time. This “faint young Sun problem” is a fundamental question in paleoclimatology, with important implications for the habitability of the early Earth, early Mars and exoplanets. Many solutions have been proposed based on the effects of greenhouse gases, atmospheric pressure, clouds, land distribution and Earth’s rotation rate. Here we review the faint young Sun problem for Earth, highlighting the latest geological and geochemical constraints on the early Earth’s atmosphere, and recent results from 3D global climate models and carbon cycle models. Based on these works, we argue that the faint young Sun problem for Earth has essentially been solved. Unfrozen Archean oceans were likely maintained by higher concentrations of CO2, consistent with the latest geological proxies, potentially helped by additional warming processes. This reinforces the expected key role of the carbon cycle for maintaining the habitability of terrestrial planets. Additional constraints on the Archean atmosphere and 3D fully coupled atmosphere-ocean models are required to validate this conclusion.

How faculae and network relate to sunspots, and the implications for solar and stellar brightness variations

Context. How global faculae and network coverage relates to that of sunspots is relevant to the brightness variations of the Sun and Sun-like stars. Aims. We aim to extend and improve on earlier studies that established that the facular-to-sunspot-area ratio diminishes with total sunspot coverage. Methods. Chromospheric indices and the total magnetic flux enclosed in network and faculae, referred to here as “facular indices”, are modulated by the amount of facular and network present. We probed the relationship between various facular and sunspot indices through an empirical model, taking into account how active regions evolve and the possible non-linear relationship between plage emission, facular magnetic flux, and sunspot area. This model was incorporated into a model of total solar irradiance (TSI) to elucidate the implications for solar and stellar brightness variations. Results. The reconstruction of the facular indices from the sunspot indices with the model presented here replicates most of the observed variability, and is better at doing so than earlier models. Contrary to recent studies, we found the relationship between the facular and sunspot indices to be stable over the past four decades. The model indicates that, like the facular-to-sunspot-area ratio, the ratio of the variation in chromospheric emission and total network and facular magnetic flux to sunspot area decreases with the latter. The TSI model indicates the ratio of the TSI excess from faculae and network to the deficit from sunspots also declines with sunspot area, with the consequence being that TSI rises with sunspot area more slowly than if the two quantities were linearly proportional to one another. This explains why even though solar cycle 23 is significantly weaker than cycle 22, TSI rose to comparable levels over both cycles. The extrapolation of the TSI model to higher activity levels indicates that in the activity range where Sun-like stars are observed to switch from growing brighter with increasing activity to becoming dimmer instead, the activity-dependence of TSI exhibits a similar transition. This happens as sunspot darkening starts to rise more rapidly with activity than facular and network brightening. This bolsters the interpretation of this behaviour of Sun-like stars as the transition from a faculae-dominated to a spot-dominated regime.

Solar luminosity bounds on mirror matter

We present bounds on mirror dark matter scenario derived by using the effect of mirror matter on the luminosity of the Sun. In the perturbative regime where the mirror matter concentration is small relative to the ordinary matter we estimate the heat transfer from ordinary matter to the mirror sector by simple analytic consideration. That amount of heat transfer is radiated via mirror photons and increases the required energy production in order to maintain the observed luminosity. We then present more detailed numerical calculations of the total amount of this energy transfer.

Connecting measurements of solar and stellar brightness variations

Context. A comparison of solar and stellar brightness variations is hampered by the difference in spectral passbands that are used in observations, and also by the possible difference in the inclination of the solar and stellar rotation axes from the line of sight. Aims. We calculate the rotational variability of the Sun as it would be measured in passbands used for stellar observations. In particular, we consider the filter systems used by the CoRoT, Kepler, TESS, and Gaia space missions. We also quantify the effect of the inclination of the rotation axis on the solar rotational variability. Methods. We employed the spectral and total irradiance reconstruction (SATIRE) model to calculate solar brightness variations in different filter systems as observed from the ecliptic plane. We then combined the simulations of the surface distribution of the magnetic features at different inclinations using a surface flux transport model with the SATIRE calculations to compute the dependence of the variability on the inclination. Results. For an ecliptic-bound observer, the amplitude of the solar rotational variability, as observed in the total solar irradiance (TSI), is 0.68 mmag (averaged over solar cycles 21–24). We obtained corresponding amplitudes in the Kepler (0.74 mmag), CoRoT (0.73 mmag), TESS (0.62 mmag), Gaia G (0.74 mmag), Gaia GRP (0.62 mmag), and Gaia GBP (0.86 mmag) passbands. Decreasing the inclination of the rotation axis decreases the rotational variability. For a sample of randomly inclined stars, the variability is on average 15% lower in all filter systems we considered. This almost compensates for the difference in amplitudes of the variability in TSI and Kepler passbands, making the amplitudes derived from the TSI records an ideal representation of the solar rotational variability for comparison to Kepler stars with unknown inclinations. Conclusions. The TSI appears to be a relatively good measure of solar variability for comparisons with stellar measurements in the CoRoT, Kepler, TESS Gaia G, and Gaia GRP filters. Whereas the correction factors can be used to convert the variability amplitude from solar measurements into the values expected for stellar missions, the inclination affects the shapes of the light curves so that a much more sophisticated correction than simple scaling is needed to obtain light curves out of the ecliptic for the Sun.

A Spectral Data Compression (SDCOMP) Radiative Transfer Model for High-Spectral-Resolution Radiation Simulations

Abstract With the increasing use of satellite and ground-based high-spectral-resolution (HSR) measurements for weather and climate applications, accurate and efficient radiative transfer (RT) models have become essential for accurate atmospheric retrievals, for instrument calibration, and to provide benchmark RT solutions. This study develops a spectral data compression (SDCOMP) RT model to simulate HSR radiances in both solar and infrared spectral regions. The SDCOMP approach “compresses” the spectral data in the optical property and radiance domains, utilizing principal component analysis (PCA) twice to alleviate the computational burden. First, an optical-property-based PCA is performed for a given atmospheric scenario (atmospheric, trace gas, and aerosol profiles) to simulate relatively low-spectral-resolution radiances at a small number of representative wavelengths. Second, by using precalculated principal components from an accurate radiance dataset computed for a large number of atmospheric scenarios, a radiance-based PCA is carried out to extend the low-spectral-resolution results to desired HSR results at all wavelengths. This procedure ensures both that individual monochromatic RT calculations are efficiently performed and that the number of such computations is optimized. SDCOMP is approximately three orders of magnitude faster than numerically exact RT calculations. The resulting monochromatic radiance has relative errors less than 0.2% in the solar region and brightness temperature differences less than 0.1 K for over 95% of the cases in the infrared region. The efficiency and accuracy of SDCOMP not only make it useful for analysis of HSR measurements, but also hint at the potential for utilizing this model to perform RT simulations in mesoscale numerical weather and general circulation models.

CO2 drawdown and cooling at the onset of the Great Oxidation Event recorded in 2.45 Ga paleoweathering crust

The Archean atmosphere is thought to have been devoid of oxygen but, instead, containing high concentrations of greenhouse gases, such as CO2 and possibly CH4, that were required to keep the Earth surface environments warm enough for maintenance of liquid water under faint-young-Sun conditions. Earlier studies have suggested that the CO2 concentrations must have been as high as over 1000 times present atmospheric levels (PAL) to overcome the effects of weaker solar luminosity. However, more recent studies of Precambrian paleosols imply existence of at least tenfold-lower, but still high pCO2 levels. The appearance of minute amounts of atmospheric O2 at the transition of Archean and Proterozoic is well documented, however, the bulk composition of the atmosphere and its dynamics at this crucial time is still widely debated. Different paleoclimate proxies of the ~2.45 Ga Kuksha paleoweathering crust suggest its formation in a cool, temperate climate. Paleoatmospheric pCO2 estimates by geochemical and isotopic mass-balance models suggest remarkably low paleoatmospheric CO2 levels, with the best guess estimates of atmospheric CO2 between 1 and 10 PAL. We speculate that the Kuksha paleoweathering crust either predates, or partly overlaps with, the onset of Huronian glaciation and corresponds to a time interval of low CO2 level during the first recorded large glaciation in Earth history.

Power spectra of solar brightness variations at various inclinations

Context. Magnetic features on the surfaces of cool stars lead to variations in their brightness. Such variations on the surface of the Sun have been studied extensively. Recent planet-hunting space telescopes have made it possible to measure brightness variations in hundred thousands of other stars. The new data may undermine the validity of setting the sun as a typical example of a variable star. Putting solar variability into the stellar context suffers, however, from a bias resulting from solar observations being carried out from its near-equatorial plane, whereas stars are generally observed at all possible inclinations. Aims. We model solar brightness variations at timescales from days to years as they would be observed at different inclinations. In particular, we consider the effect of the inclination on the power spectrum of solar brightness variations. The variations are calculated in several passbands that are routinely used for stellar measurements. Methods. We employ the surface flux transport model to simulate the time-dependent spatial distribution of magnetic features on both the near and far sides of the Sun. This distribution is then used to calculate solar brightness variations following the Spectral And Total Irradiance REconstruction approach. Results. We have quantified the effect of the inclination on solar brightness variability at timescales down to a single day. Thus, our results allow for solar brightness records to be made directly comparable to those obtained by planet-hunting space telescopes. Furthermore, we decompose solar brightness variations into components originating from the solar rotation and from the evolution of magnetic features.

On Stellar Evolution in a Neutrino Hertzsprung–Russell Diagram

Abstract We explore the evolution of a select grid of solar metallicity stellar models from their pre-main-sequence phase to near their final fates in a neutrino Hertzsprung–Russell diagram, where the neutrino luminosity replaces the traditional photon luminosity. Using a calibrated MESA solar model for the solar neutrino luminosity ( · × 1031 erg s−1) as a normalization, we identify ≃0.3 MeV electron neutrino emission from helium burning during the helium flash (peak , flux (10 pc/d)2 cm−2 s−1 for a star located at a distance of d parsec, timescale ≃3 days) and the thermal pulse (peak , flux × 107 (10 pc/d)2 cm−2 s−1, timescale ≃0.1 yr) phases of evolution in low-mass stars as potential probes for stellar neutrino astronomy. We also delineate the contribution of neutrinos from nuclear reactions and thermal processes to the total neutrino loss along the stellar tracks in a neutrino Hertzsprung–Russell diagram. We find, broadly but with exceptions, that neutrinos from nuclear reactions dominate whenever hydrogen and helium burn, and that neutrinos from thermal processes dominate otherwise.

Using Solar Energy for Irrigation in Kirkuk City and Outskirt

In this study, the possibility of using the produced energy from solar energy system for irrigation in Kirkuk city and outskirt is studied. The power from the photovoltaic PV panel is (300 W). Three values for the well depth (h) which are (60,70, and 80 m) are used respectively. Depending on the data from Iraqi Meteorological Organization and Seismology, the relations between the angle of solar radiation along the year, the solar radiation, and the actual and theoretical solar brightness in each month showed in graphical diagrams. The volume flow rate was represented graphically for each value of well depth. It was found that the volume flow rate increase with increasing PV panel power and the solar system is more efficient in mid-day and at mid-year (summer season). However, flow rate was inversely proportional and affected by the well depth. The solar power from the PV panel can be used in irrigation since the volume flow rate from the system fulfil water requirements for most crops that cultivated in Kirkuk city.

Análise da exposição ao ofuscamento e à insolação em ambiente de uso prolongado

Ocupantes expostos à radiação solar indesejada e a brilhos e contrastes excessivos, quando em ambiente de uso prolongado, vivenciam desconforto térmico ou visual e consequentemente reagem alterando as características de sua ocupação ou do sistema de iluminação natural mais comum: a janela. Neste contexto, essa pesquisa se objetivou em identificar e relacionar os níveis de probabilidade de ofuscamento e de radiação solar incidente para um ocupante em uma sala de permanência prolongada. A partir da modelagem e simulação computacional da irradiação solar, os valores horários dos indicadores de ofuscamento e insolação foram transformados em frequências e perfis anuais. Dentre as frequências anuais de ofuscamento, se atingiram diferenças de até 74%, advindas da mudança de 90º na direção de visão. As frequências de radiação solar direta maior que 50 W/m² apontaram vulnerabilidade, em cerca de 1/5 do tempo de uso, para ocupantes a 1,5 m da abertura, nas orientações Norte, Leste e Oeste. Os perfis anuais de probabilidade de ofuscamento e de radiação solar incidente permitiram identificar as horas do dia e os meses do ano em que há necessidade de controle solar. Correlações lineares realizadas entre valores horários de DGP (Daylight Glare Probability) e de radiação solar resultaram em grau (R²) abaixo do significativo, porém permitiram demonstrar a influência de cada componente no desconforto visual apurado. As 60 combinações investigadas de posições (03), direções de visão (05) e orientações solares (04) foram discriminadas com relação à exposição excessiva e assim agregaram recomendações de projeto que previnem os ocupantes do ofuscamento e da insolação.

Is the Solar System expanding?

It is argued in this article that observations undermine the no-expansion hypothesis of standard physics, where gravitationally bound systems do not expand along with the expansion of space, and support the contrary expansion hypothesis where the Solar System expands proportionally to the expansion of space. First, the no-expansion hypothesis yields the Faint Young Sun Paradox–the dilemma of explaining why there have been oceans on Mars and why the Earth has been warm 3.5 billion year ago, when luminosity of the Sun was 25% smaller than today–whereas the expansion hypothesis resolves the paradox. Second, the number of days in a year in the past cannot be explained with tidal friction alone, whereas the fusion of the tidal friction and the expansion hypothesis functions as a natural explanation. Third, the no-expansion hypothesis does not match the historical increase of the Earth-Moon distance, whereas the expansion hypothesis matches it perfectly. These three examples strongly indicate that the Solar System is expanding along with the expansion of space.

Evolution of the Global Carbon Cycle and Climate Regulation on Earth

AbstractThe existence of stabilizing feedbacks within Earth's climate system is generally thought to be necessary for the persistence of liquid water and life. Over the course of Earth's history, Earth's atmospheric composition appears to have adjusted to the gradual increase in solar luminosity, resulting in persistently habitable surface temperatures. With limited exceptions, the Earth system has been observed to recover rapidly from pulsed climatic perturbations. Carbon dioxide (CO2) regulation via negative feedbacks within the coupled global carbon‐silica cycles are classically viewed as the main processes giving rise to climate stability on Earth. Here we review the long‐term global carbon cycle budget, and how the processes modulating Earth's climate system have evolved over time. Specifically, we focus on the relative roles that shifts in carbon sources and sinks have played in driving long‐term changes in atmospheric pCO2. We make the case that marine processes are an important component of the canonical silicate weathering feedback, and have played a much more important role in pCO2 regulation than traditionally imagined. Notably, geochemical evidence indicate that the weathering of marine sediments and off‐axis basalt alteration act as major carbon sinks. However, this sink was potentially dampened during Earth's early history when oceans had higher levels of dissolved silicon (Si), iron (Fe), and magnesium (Mg), and instead likely fostered more extensive carbon recycling within the ocean‐atmosphere system via reverse weathering—that in turn acted to elevate ocean‐atmosphere CO2 levels.

Simulation of solar radiation brightness fields in the presence of optically anisotropic crystal clouds: algorithm and test results

Simulation of solar radiation brightness fields in the presence of optically anisotropic crystal clouds: algorithm and test results

Communication Pedagogy: The Coronavirus Pandemic

In this historical moment defined by the coronavirus, the global community struggles with and against a seemingly invisible foe. Students, faculty, and administrators open the blinds on windows in the morning, witnessing the brightness of the sun and seemingly the clarity of a morning welcome. Yet, there lurks, not in the shadows, but in the brightness of the everyday sunshine, the possibility of sickness and death. This responsive essay weaves together my communicative rejoinders to the coronavirus and its implications for this challenging time in human history. I turn to the autoethnographic insights of Art Bochner and Carolyn Ellis (2016) to frame the theoretical rationale for a conversation that rests within the dialectic of fear and tenacious hope.