Showing papers on "Solar constant published in 2016"

Differences in water vapor radiative transfer among 1d models can significantly affect the inner edge of the habitable zone

Abstract: An accurate estimate of the inner edge of the habitable zone is critical for determining which exoplanets are potentially habitable and for designing future telescopes to observe them. Here, we explore differences in estimating the inner edge among seven one-dimensional radiative transfer models: two line-by-line codes (SMART and LBLRTM) as well as five band codes (CAM3, CAM4_Wolf, LMDG, SBDART, and AM2) that are currently being used in global climate models. We compare radiative fluxes and spectra in clear-sky conditions around G and M stars, with fixed moist adiabatic profiles for surface temperatures from 250 to 360 K. We find that divergences among the models arise mainly from large uncertainties in water vapor absorption in the window region (10 μm) and in the region between 0.2 and 1.5 μm. Differences in outgoing longwave radiation increase with surface temperature and reach 10–20 W m^(−2); differences in shortwave reach up to 60 W m^(−2), especially at the surface and in the troposphere, and are larger for an M-dwarf spectrum than a solar spectrum. Differences between the two line-by-line models are significant, although smaller than among the band models. Our results imply that the uncertainty in estimating the insolation threshold of the inner edge (the runaway greenhouse limit) due only to clear-sky radiative transfer is ≈10% of modern Earth's solar constant (i.e., ≈34 W m^(−2) in global mean) among band models and ≈3% between the two line-by-line models. These comparisons show that future work is needed that focuses on improving water vapor absorption coefficients in both shortwave and longwave, as well as on increasing the resolution of stellar spectra in broadband models.

Mathematical modelling of solar radiation incident on tilted surface for photovoltaic application at Bhopal, M.P., India

Abstract: In general, solar radiations are the combination of beam plus diffuse and ground-reflected radiation. The availability of recorded data on a tilted surface is very rare due to lack of measuring equipment and techniques involved. In this study, a standard procedure is adopted for estimation of solar radiation on a tilted surface for a location in Central region of India. Solar radiation is estimated for three tilted positions: First, solar collector tilt equal to latitude angle, second, solar collector tilt equal to latitude angle +15° and third, solar collector tilt at latitude −15°. Total global solar radiation estimated on the inclined surface for various photovoltaic (PV) modules was used to obtain the annual energy yield based on the estimated value. It was found that on an average, 14 kWh/m2 of annual energy output can be obtained for monocrystalline solar PV module corresponding to the inclination of 23.26° latitude at Bhopal.

Mirror mode waves in Venus's magnetosheath: solar minimum vs. solar maximum

Abstract: The observational rate of mirror mode waves in Venus's magnetosheath for solar maximum conditions is studied and compared with previous results for solar minimum conditions. It is found that the number of mirror mode events is approximately 14 % higher for solar maximum than for solar minimum. A possible cause is the increase in solar UV radiation, ionizing more neutrals from Venus's exosphere and the outward displacement of the bow shock during solar maximum. Also, the solar wind properties (speed, density) differ for solar minimum and maximum. The maximum observational rate, however, over Venus's magnetosheath remains almost the same, with only differences in the distribution along the flow line. This may be caused by the interplay of a decreasing solar wind density and a slightly higher solar wind velocity for this solar maximum. The distribution of strengths of the mirror mode waves is shown to be exponentially falling off, with (almost) the same coefficient for solar maximum and minimum. The plasma conditions in Venus's magnetosheath are different for solar minimum as compared to solar maximum. For solar minimum, mirror mode waves are created directly behind where the bow shock will decay, whereas for solar maximum all created mirror modes can grow.

Possible Estimation of the Solar Cycle Characteristic Parameters by the 10.7 cm Solar Radio Flux

Abstract: Two independent methods for estimating basic parameters of the solar cycle are presented. The first of them, the ascending-descending triangle method, is based on a previous work by Tritakis (Astrophys. Space Sci. 82, 463, 1982), which described how the fundamental parameters of a certain solar cycle could be predicted from the shape of the previous one. The relation between the two cycles before and after a specific 11-year solar cycle is tighter than between the two cycles belonging to the same 22-year solar cycle (even-odd cycle). The second is the MinimaxX method, which uses a significant relation in the international sunspot number between the maximum value of a solar cycle and its value 2.5 or 3 years (depending on the enumeration of the even or odd cycle) before the preceding minimum. The tests applied to Cycles 12 to 24 indicate that both methods can estimate the peak of the 11-year solar radio flux at a high confidence level. The data used in this study are the 10.7 cm solar radio flux since 1947, which have been extrapolated back to 1848 from the strong correlation between the monthly international sunspot numbers and the adjusted values of the 10.7 cm radio flux.

Coordinated weather balloon solar radiation measurements during a solar eclipse.

Abstract: Solar eclipses provide a rapidly changing solar radiation environment. These changes can be studied using simple photodiode sensors, if the radiation reaching the sensors is unaffected by cloud.Transporting the sensors aloft using standard meteorological instrument packages modified to carry extra sensors, provides one promising but hitherto unexploited possibility for making solar eclipse radiation measurements. For the 20th March 2015 solar eclipse, a coordinated campaign of balloon-carried solar radiation measurements was undertaken from Reading (51.44N, 0.94W), Lerwick (60.15N, 1.13W) and Reykjavik (64.13N, 21.90W), straddling the path of the eclipse.The balloons reached sufficient altitude at the eclipse time for eclipse-induced variations in solar radiation and solar limb darkening to be measured above cloud. Because the sensor platforms were free to swing, techniques have been evaluated to correct the measurements for their changing orientation. In the swing-averaged technique, the mean value across a set of swings was used to approximate the radiation falling on a horizontal surface; in the swing-maximum technique, the direct beam was estimated by assuming the sensing surface becomes normal to the solar beam direction at a maximum swing. Both approaches, essentially independent,give values that agree with theoretical expectations for the eclipse-induced radiation changes.

Seasonal and spatial variation of solar radiation in Nepal Himalayas

Abstract: Solar radiation data (two-hourly data from 1987 to 1999) observed at high altitude meteorological stations in Nepal Himalayas were analyzed to study seasonal and spatial variation of solar radiation and shed some light on solar energy potential and prospect of vegetation development in the mountainous region of Nepal. Results showed significant similarities and differences on solar radiation with respect to seasons and locations (altitudes). Mean seasonal amount of solar radiation was generally higher in spring than in summer. The significant amount of monsoonal clouds in the summer hindered incoming solar radiation during summer, while less or no clouds during spring allowed more solar radiation to reach the earth’s surface. Absolute extreme values of solar radiation in the mountainous regions during fine weather conditions were close to the solar constant (1367 Wm -2 ) due to negligible depletion of radiation within the atmosphere. Amount of solar radiation increased with altitude due to smaller optical depth of the atmosphere at higher altitudes. The increasing rate of annual mean solar radiation with altitude is found to be 90 Wm -2 km -1 in the mountainous region of Nepal. Journal of Hydrology and Meteorology, Vol. 8(1) p.1-9

Theoretical calculation of the interannual variability of the Earth`s insolation with daily resolution

Abstract: Based on the astronomical ephemerides DE-406, theoretical calculations have been performed of the interannual variability of the Earth’s insolation related to celestial-mechanical processes for 365 points of a tropical year in the time period from 1900 to 2050. It has been determined that the average amplitude of variations of the interannual insolation is 0.310 W/m2 (0.023% of the solar constant). The calculated variations are characterized by strict periodicity that corresponds with the length of a synodic month. Connection between the extreme values of the calculated insolation variability and syzygies has been defined. The average amplitude of the calculated variability exceeds by 1.7 times (0.01% of the solar constant) the amplitude of the interannual variability in the 11-year variation of the total Earth’s insolation.

Total solar irradiance as measured by the SOVAP radiometer onboard PICARD

Abstract: From the SOlar VAriability PICARD (SOVAP) space-based radiometer, we obtained a new time series of the total solar irradiance (TSI) during Solar Cycle 24. Based on SOVAP data, we obtained that the TSI input at the top of the Earth’s atmosphere at a distance of one astronomical unit from the Sun is 1361.8 ± 2.4 W m -2 (1σ) representative of the 2008 solar minimum period. From 2010 to 2014, the amplitude of the changes has been of the order of ± 0.1%, corresponding to a range of about 2.7 W m -2 . To determine the TSI from SOVAP, we present here an improved instrument equation. A parameter was integrated from a theoretical analysis that highlighted the thermo-electrical non-equivalence of the radiometric cavity. From this approach, we obtained values that are lower than those previously provided with the same type of instrument. The results in this paper supersede the previous SOVAP analysis and provide the best SOVAP-based TSI-value estimate and its temporal variation.

Hysteresis Effect in the Activity Indices of the Atmospheres of the Sun and Solar-Type Stars During the Rising and Falling Phases of Cycles

Abstract: The hysteresis effect that shows up as a nonunique relationship among the emissions from the photosphere, chromosphere, and corona during the rising and falling phases of solar and stellar activity is analyzed. The following solar indices are analyzed and compared in different phases of the cycle: the radiative flux in the hydrogen Lyman alpha line FLα, radio emission at 10.7 cm F10.7, the sunspot number SSN, the radiative flux in the 530.0 nm green coronal line F530.3, the solar constant TSI, and the relative flux ratio c/w (ratio of the fluxes in the center and in the wings) for the 280 nm Mg II line. In stars with cycles, a hysteresis effect is observed between the CaII chromospheric S-activity index for stars in the Mount Wilson HK project and the photospheric flux Fph for these stars.

Properties of solar activity and ionosphere for solar cycle 25

Abstract: Based on the known forecast of solar cycle 25 amplitude (Rz max ≈ 50), the first assessments of the shape and amplitude of this cycle in the index of solar activity F10.7 (the magnitude of solar radio flux at the 10.7 cm wavelength) are given. It has been found that (F10.7)max ≈ 115, which means that it is the lowest solar cycle ever encountered in the history of regular ionospheric measurements. For this reason, many ionospheric parameters for cycle 25, including the F2-layer peak height and critical frequency (hmF2 and foF2), will be extremely low. For example, at middle latitudes, typical foF2 values will not exceed 8–10 MHz, which makes ionospheric heating ineffective in the area of upper hybrid resonance at frequencies higher than 10 MHz. The density of the atmosphere will also be extremely low, which significantly extends the lifetime of low-orbit satellites. The probability of F-spread will be increased, especially during night hours.

The Optimization of Flat Plate Solar Collectors

Abstract: Due to shortages in renewable energy resources, solar photovoltaic panels and solar thermal collectors have been widely researched and continue to be installed on commercial and residential buildings in order to reduce greenhouse gas emissions. Improvements in the efficiencies of photovoltaic panels are on the rise, making their use more feasible in more geographic locations. However, the angle at which the panels are mounted (angle of inclination or slope angle) can also significantly affect the solar irradiation they receive. The theoretical optimal angle of inclination of these panels has been determined based on the extraterrestrial solar constant, the effect of air mass, and assumption of clear skies. However, the assumption of clear skies may lead to significant discrepancies between theoretical model predictions and otherwise available meteorological data. Therefore, this paper aims to determine whether the optimal angle of inclination of solar photovoltaic panels will differ when the meteorologically accurate irradiation values are used. In this paper, 20 years of solar irradiation data was examined at three different geographic locations of the continental United States to determine if the optimal mounting angle of solar photovoltaic panels was different when comparing theoretical clear sky data to meteorologically accurate data. The data analyzed was from the National Solar Radiation Database from years 1990-2010. This irradiation data is a combination of meteorological statistical models, actual solar irradiation values measured by pyranometers from over 1400 locations in the United States, and cloud data using satellite imagery and a ceilometer. This data set is called METSTAT and is one of the two data sets provided by the National Solar Radiation Database. However, it is the only data set which provided consistent data over all of the twenty years analyzed at all three locations. The locations at which the clear sky and meteorologically accurate data were analyzed were dispersed in latitude and longitude across the United States and included: San Antonio, TX, San Francisco, CA, and Grand Rapids, MI. Using the generally accepted rule of thumb that the optimal angle of inclination is between -15˚ and 15˚ of the latitude of the location, both the clear sky and meteorologically accurate data were analyzed at each of the angles of inclination in this range to determine the optimal angle. From this analysis, it was determined that the optimal angle of inclination did vary between the two datasets. The results of this study show that the optimal angle of inclination of solar photovoltaic/solar thermal panels decreases as the cloudiness of the geographic location at which they are mounted increases. These results will be presented and discussed in detail in this paper.