Effects Of Solar Flux Research Articles

Investigation of parabolic trough collector receiver with U-pipe exchanger using a numerical approach: Towards temperature non-uniformity optimization

In this work, a numerical study of the heat flux and temperature distribution for a parabolic trough collector absorber with an internal U-pipe tube exchanger is carried out using SolTrace and ANSYS Fluent software. The effect of solar flux and temperature non-uniformity on the system performance related to the focal distance is investigated. It was noticed that the highest circumferential temperature gap of about 105 °C occurs at the medium of the absorber (0.9 m). Moreover, for the focal distances of 0.18 m, 0.19 m, and 0.2 m, the outlet water temperatures are increased to 328.8, 329.01 and 328.89 K, respectively. For these distances, the highest thermal efficiencies of about 69, 70 and 71%, respectively, are reported. Furthermore, the promising proposed approach to investigate the receiver performance combines simulation results and correlations between variables. Indeed, a strong negative correlation of −0.65 between thermal efficiency and focal distance is noticed. Thus, thermal efficiency correlates positively with maximum temperature gap, inlet–outlet temperature gap, flow rate, and outlet temperature in decreasing order with correlation coefficients of 0.64, 0.59, 0.38, and 0.32, respectively. Additionally, the simulation study emphasizes the importance of relating optimum temperature uniformity and thermal efficiency for optimizing the system performance.

Solar Flux Effects on the Variations of Equatorial Electrojet (EEJ) and Counter-Electrojet (CEJ) Current across the Different Longitudinal Sectors during Low and High Solar Activity

This study examined the effect of solar flux (F10.7) and sunspots number (R) on the daily variation of equatorial electrojet (EEJ) and morning/afternoon counter electrojet (MCEJ/ACEJ) in the ionospheric E region across the eight longitudinal sectors during quiet days from January 2008 to December 2013. In particular, we focus on both minimum and maximum solar cycle of 24. For this purpose, we have collected a 6-year ground-based magnetic data from multiple stations to investigate EEJ/CEJ climatology in the Peruvian, Brazilian, West & East African, Indian, Southeast Asian, Philippine, and Pacific sectors with the corresponding F10.7 and R data from satellites simultaneously. Our results reveal that the variations of monthly mean EEJ intensities were consistent with the variations of solar flux and sunspot number patterns of a cycle, further indicating that there is a significant seasonal and longitudinal dependence. During the high solar cycle period, F10.7 and R have shown a strong peak around equinoctial months, consequently, the strong daytime EEJs occurred in the Peruvian and Southeast Asian sectors followed by the Philippine regions throughout the years investigated. In those sectors, the correlation between the day Maxima EEJ and F10.7 strengths have a positive value during periods of high solar activity, and they have relatively higher values than the other sectors. A predominance of MCEJ occurrences is observed in the Brazilian (TTB), East African (AAE), and Peruvian (HUA) sectors. We have also observed the CEJ dependence on solar flux with an anti-correlation between ACEJ events and F10.7 are observed especially during a high solar cycle period.

Effect of Environmental Exposure on the Cooling Rate of Asphalt Mixtures

Temperature is one of the major factors that affect the compactability and mechanical performance of asphalt pavement. Therefore, the cooling rate variability of asphalt due to various surrounding conditions and aggregate surface areas is crucial to achieving proper compaction. This study focused on the effect of environmental exposure on the cooling rate and available time for compaction of the asphalt mixtures (AC10 and AC14). Several factors, such as base and ambient temperatures, daytime and nighttime, solar flux, and wind speed, were considered in the evaluation of the cooling curve. A few loose samples were prepared and grouped as covered (with canvas) and uncovered during the monitoring process. The time and temperature of both samples were monitored during the day and night, starting after the mixing process and ending at 80 °C. Results reveal that the cooling rate of asphalt mixtures is undoubtedly affected by the surrounding factors. The use of canvas and coarse aggregate gradation could retain the heat and minimize the wind and solar flux effects, thus increasing the available time for compaction or lengthening the cooling time. In addition, the cooling rate tends to increase during nighttime compared with daytime exposure.

Some Differences in the Dynamics of the Intermediate Descending Layers Observed During Periods of Maximum and Minimum Solar Flux

AbstractIn this paper, ionograms from São Luís (SL, 2°S; 44°W, I: −3.8°) and Cachoeira Paulista (CP, 22.42°S; 45°W, I: −34.4°) are analyzed to examine the characteristics of the intermediate descending layers (ILs) over the Brazilian equatorial and low‐latitude regions under different solar flux conditions. The solar flux effects on the ILs are investigated in terms of the rate of occurrence of the IL; the seasonal behavior of some parameters such as the height, frequency, and velocity; and the duration and the number of ILs events observed per day. One of the main results of this work is that unlike over CP, the ILs over SL presented some peculiarities, such as a lower rate of occurrence during a period of solar maximum activity (2003) when compared with a period of solar minimum activity (2009). This apparent variation was likely caused by the magnetic equator moving away from SL during this period. The duration of the ILs was also investigated, and it was found that in 2009, the ILs presented higher life time than in 2003. The descending velocity of the ILs is compatible with the semidiurnal and quarter‐diurnal tides. Over SL, the larger descending rate in some cases (>10 km/hr) may reveal the additional influence of the gravity waves in the IL's dynamics.

Effect of solar flux versus compositional variations on the variability of daytime oxygen optical emission rates over low- and mid-latitudes

Daytime oxygen airglow emission rate variability provides us with a means of remote investigations of the upper atmospheric behavior. Dayglow emission rates typically show a diurnal pattern with a peak at around noon, especially during geomagnetic quiet conditions. The photochemical and empirical models show that the emission rates typically vary as a function of solar zenith angle (SZA) and solar flux. Thus, both, larger solar flux magnitudes and smaller solar zenith angles, contribute to larger dayglow emission rates as the yield of excited oxygen atoms is expected to be greater in those conditions. However, variability in the annual dayglow emission rates obtained from measurements at low-latitudes (Hyderabad, India; 170 N, 800 E; 8.70 N Mag. Lat.) and mid-latitudes (Boston, USA; 42.20 N, 710 W; 48.30 N Mag. Lat.) show different behavior with regard to solar flux variation. The variability in the low-latitude emission rate is primarily dependent on that of the solar flux. However, such primary dependence on the solar flux is not reflected on the emission rate variability seen over mid-latitudes. This discrepancy is understood to be due to the relative effects of solar flux and the globally changing compositional variability, characterized by the oxygen to molecular density ratios (O/N2), that show varying behavior from mid- to low-latitudes. Seasonal compositional variation due to transport processes is attributed to be the cause for the observed discrepancy which is also confirmed by independent satellite measurements. We also present an empirical model of O/N2 as a function of day of the year and latitude obtained using satellite based ultraviolet measurements to quantify the compositional variation.

Comparison of the QBO and F10.7 Solar Flux Effects on Total Mass Density

The comparison of the Quasi Biennial Oscillation (QBO) and F10.7 solar flux effects on Total Mass Density (TMD) obtained from NRLMSIS-00 model for 90 km altitude of ionosphere known as Mesosphere-Lower Thermosphere (MLT) region was made statistically. In the results of calculations, it was observed that QBO and F10.7 solar flux have an effect on TMD. It was determined that about 69% of the variations in TMD could be explained by F10.7 and QBO. Also, it was seen that an increase/a decrease of 1 meter per second occurred in QBO gave rise to an increase/a decrease of 2.36 × 10–9 kg/m3 in TMD while an increase/a decrease of 1 s.f.u. in F10.7 gave rise to a decrease/increase of 1.02 × 10–9 kg/m3 in TMD. Based on these results, it was observed that the effects of stratospheric QBO, which is one of the meteorological processes, and F10.7, which is one of the indicators of the solar processes, were nearly at the same rate on TMD of MLT region. Furthermore, the results show that the stratospheric QBO may be a suitable candidate for increasing the anomalous density reductions observed in TMD.

Quiet and Disturbed Time Characteristics of Blanketing Es (Esb) During Solar Cycle 23

AbstractA sporadic E layer with dense ionization blocks the upper ionospheric layers in ionosonde observations and it is called, blanketing sporadic E (Esb). Although earlier studies have demonstrated that Esb occurrence is dependent on solar activity, seasons, local time, and equatorial electrojet/counter equatorial electrojet (EEJ/CEEJ) strength, the physics behind this dependence is not well established particularly at the dip equatorial stations. Moreover, fewer comprehensive studies are available on Esb. Present work is a detailed statistical study of Esb occurrence and its characteristics during solar cycle 23 (1996–2006) at Indian dip equatorial station Trivandrum (dip latitude 0.5°N). In present study, solar flux dependence of Esb occurrence is clearly evident not only for magnetically quiet but also for the disturbed periods with maximum during low solar activity. Known seasonal peak Esb occurrence during summer (May–August) is found to be dominated by larger percentage of total blanketing events (fbEs ≥ 8 MHz) on magnetically disturbed days as compared to quiet days. We noticed prevalent Esb occurrence in the postmidnight (00–06 India Standard Time) periods during low solar activity. Besides Esb characteristics, the present study aims to investigate effect of solar flux on association of Esb and CEEJ. Coexistence of Esb and CEEJ is emphasized in earlier observational studies. However, any dependence of their association on solar flux is not yet examined. We find that their association is weaker during low solar activity as compared to high solar activity in summer, indicating that Esb occurrence is highly likely on CEEJ days during high solar activity periods.

Hyperion image analysis and linear spectral unmixing to evaluate the grades of iron ores in parts of Noamundi, Eastern India

This paper reports the results of a study to differentiate iron ores in terms of their grades, using the hyperspectral (EO-1 Hyperion) image data, covering a mineralized belt in the Noamundi area, eastern India. The study involves hyperspectral data collection, pre-processing (reduction of atmospheric and solar flux effects), generation of spectral curves from the image for the iron ore deposits, extraction of key spectral parameters and linear spectral unmixing for mapping iron ore abundance. Spectral curves for iron ore deposits extracted from the Hyperion image pixels exhibit strong absorption at 850–900nm and 2150–2250nm wavelengths, which is typical of iron ores. The strength of the absorption features in the continuum removed spectra varies spatially in the image around the mining areas, indicating differences in composition/grade of the iron ores. Spectral parameters such as the depth, width, area and wavelength position of the absorption features, derived from image spectra in the 850–900nm and 2150–2250nm regions, correlate well with the concentration of iron-oxide and alumina (gangue) in the ore samples obtained from the mine face. Well defined correlations are evident between the concentration of iron oxide and (i) the depth of NIR absorption feature (R2=0.883); (ii) the width of NIR absorption feature (R2=0.912); and (iii) the area of the NIR absorption feature and (R2=0.882). Further, the linear spectral unmixing resulted in an iron ore abundance map which, in conjunction with the image- and laboratory-spectra, helped in assessing the grades of iron ores in the study area. Thus, this study demonstrates the feasibility of discriminating grades of iron ores based on spectral information derived from spaceborne hyperspectral imagery.

Evaluation of photocatalytic activity of carbon-doped TiO2 films under solar irradiation

We proposed a method to obtain carbon-doped TiO2 (C-TiO2) with a higher photocatalytic activity for degradation of toluene. Solar radiation was used as a visible light source for photocatalytic oxidation. An optical fiber reactor (OFR) was used to investigate the photocatalytic oxidation of toluene in air. All C-TiO2 films used as catalysts were synthesized by a modified sol-gel and combustion method using carbon nanoparticles. The performance of the OFR using C-TiO2 was evaluated under various experimental conditions. The effects of solar flux, surface sensitization, inlet concentration of toluene and concentration of carbon nanopowder in C-TiO2 were examined.

Solar flux effects on the equatorial evening vertical drift and meridional winds over Brazil: A comparison between observational data and the IRI model and the HWM representations

We present the results of a study of the equatorial evening F region prereversal vertical drift enhancement over Brazil as a function of solar flux (F10.7). The vertical drift is measured from true heights obtained from digisondes operated at an equatorial site, Sao Luis, and at an off equatorial site, Fortaleza. The different magnetic inclinations of the two sites cause different degree of dependence of the vertical drift on magnetic meridional winds permitting an evaluation of the solar flux control on both the evening vertical drift (zonal electric field) and meridional winds. The analysis period covers the year 2001 and 2004 during which the monthly mean F10.7 varied from 245 to 80. The solar flux dependence of the vertical drift of the evening F layer as obtained from the data are compared with the representation of such dependence in the IRI model. While the IRI description of such dependence appears comparable to that is determined from observational data there is significant difference between the drift values in the two cases, the IRI representation being an under-estimation of the observed drift for all flux values. The results are discussed from the perspective of validating the IRI model representations of the vertical drift. The results of the study also shows that the HWM description of the evening thermospheric meridional wind in the Brazilian sector, shows agreement with observation for lower F10.7 values, while it significantly deviates from the observed/calculated meridional wind for higher solar flux values.

Electrojet control of ambient ionization near the crest of the equatorial anomaly in the Indian zone

Abstract. A long-term (1978–1990) database of total electron content (TEC) from a location (Calcutta: 22.58° N, 88.38° E geographic, dip: 32° N) near the northern crest of the equatorial ionization anomaly has extensively been studied to characterize the contribution of fountain effect in the maintenance of ambient ionization. The equatorial electrojet (EEJ) data obtained from ground magnetometer recording are used to assess the contribution of equatorial fountain. Analysis made with instantaneous values, day's maximum values and time-integrated values of EEJ strength exhibit more or less similar features. When instantaneous values of EEJ are considered TEC variations exhibit two maxima in correlation, one around 10:00–12:00 IST and the other around 18:00–20:00 IST. The later maximum in correlation coefficient is conspicuously absent when integrated values of EEJ are considered. An impulse-like feature is reflected in the diurnal TEC variation during the time intervals (09:00–10:00 IST) and (18:00–19:00 IST). The statistical analysis reveals greater correspondence with high level of significance between diurnal TEC and EEJ in the descending epoch of solar cycle than in the ascending one. On the seasonal basis, TEC in the summer solstitial months are observed to be more sensitive to the changes in EEJ strength than in the equinoctial and winter solstitial months. Combining the effects of solar flux, season, local time and EEJ an empirical formula for monthly mean diurnal TEC has been developed and validated using observed TEC data. An estimation of the relative contributions of the several terms appearing in the formula reveals much more solar flux contribution (~50–70%) in the maintenance of ambient ionization around the present location than the EEJ effects (maximum~20%).

Thermospheric density oscillations due to periodic solar wind high‐speed streams

We report on periodic oscillations in thermosphere density, measured by the accelerometer on the CHAMP satellite during 2006, and relate these periodicities to oscillations observed in solar wind speed and Kp index. Common periodic oscillations at 4–5, 6–7, and 9–11 day periods are observed in the neutral density at 400 km in the 2006 data set, with the 7 day period being the predominant oscillation. Spectral analysis reveals that similar periodicities are present in both the solar wind and the planetary magnetic index Kp but not in the EUV solar flux proxy F10.7. We suggest that the periodic oscillations observed in thermosphere density are a direct response to recurrent geomagnetic activity and associated high‐speed streams in the solar wind. The lack of response in F10.7 at the 7 day period enables storm effects on the thermosphere density to be isolated from solar flux effects. The Kp index for these events correspond to moderate levels of geomagnetic activity, and the resultant perturbations in thermosphere density are ±20–30% of background levels. Although these levels of perturbation are small compared to major magnetic storms, their much higher occurrence frequency and characteristic long recovery time may lead to a cumulative effect on the state of the thermosphere and ionosphere.

Solar flux effects on equatorial ionization anomaly and total electron content over Brazil: Observational results versus IRI representations

The F layer critical frequency (foF2) as measured by Digisondes in the equatorial and low latitude locations in Brazil is analyzed to investigate the seasonal and solar flux controls of the intensity of the equatorial ionization anomaly (EIA) in the equinoctial month of March. The analysis also included the total electron content (TEC) as measured by a GPS receiver operated at the EIA crest location. The foF2 data set covered a period of large solar flux variation from 1996 to 2003, while the GPS TEC data was for a period in 2002–2003 when the solar flux parameter F10.7 underwent large variations, permitting in both cases an examination of the solar flux effects on these parameters. The seasonal variation pattern in TEC shows a maximum in equinoctial months and a minimum in June solstice, with similar variations for foF2. The solar flux dependence of the TEC is a maximum during equinoxes, especially for post-sunset TEC values at times when the latitudinal distribution is controlled by the equatorial evening plasma fountain processes. Significant variations with local time are found in the degree of solar flux dependence for both the TEC and EIA. The EIA intensity shows large dependence on F10.7 during post-sunset to midnight hours. These results are discussed in comparison with their corresponding IRI representations.

A simplified analytical method to evaluate the effects of roof spray evaporative cooling

A simplified mathematical technique is presented with which preliminary evaluation of the effects of roof spray evaporative cooling can be made. This method incorporates the effects of solar flux, ambient temperature and the humidity of the environment and is much simpler to implement than previously suggested models. The use of the model is illustrated via the use of TMY weather data for Washington, D.C., and the trends predicted are found to be consistent with that in the literature.

Ionospheric effects on C3I satellite communications systems in Greenland

For the past 25 years the effects of the polar ionosphere on satellite communications has been under evaluation in Greenland. As a result of the testing, models have been developed which quantify the effects of solar flux, magnetic index, time of day, season, elevation angle, and frequency on ionospheric scintillation fading. For the past 10 years, operational type of satellite communications testing has been conducted in Greenland to evaluate the feasibility of replacing the traditional HF radio links with satellite communications links. This paper reviews the effects of polar ionospheric scintillation fading, describes the operational testing, and identifies plans for operational use of satellite communications in Greenland.

Lower thermospheric structure from Millstone Hill Incoherent Scatter Radar Measurements: 2. Semidiurnal temperature component

Daytime temperature determinations from 151 days of incoherent scatter radar measurements at Millstone Hill (42°N) from 1970 to 1975 were analyzed to characterize the semidiurnal temperature oscillation in the lower thermosphere (105–125 km). An analytical model fitted to the measured temperatures contained terms to specify the dependencies of the semidiurnal term on day of year (annual and semiannual terms), solar activity, and geomagnetic activity. The model representation, whose coefficients are tabulated, showed that seasonal effects were larger than effects associated with the other parameters. The annual mean semidiurnal oscillation had a maximum amplitude of 28 K at 115 km and a vertical wavelength of 43 km. Variations associated with season were large, for example, ±17 K in amplitude and ± 1.2 hours in phase at 115 km when referred to the annual mean semidiurnal vector. Generally, the altitude of maximum was lowest at the solstices, and the longest vertical wavelength occurred in winter. Semidiurnal temperature measurements from Saint Santin showed good agreement with the Millstone Hill model results in winter, but some significant amplitude and phase differences were apparent in other seasons. Theoretical predictions indicated that the observed semidiurnal oscillation at Millstone Hill is primarily the upward propagating tide rather than an in situ tide. Comparisons with thermospheric Hough mode extensions indicated a temperature structure best matched by the S2,4 mode, whereas previously reported wind measurements were found to be best matched by the S2,2 mode. Because of their different vertical structures it was postulated that it might be possible to reproduce both the observed temperature and wind measurements by a suitable synthesis of the S2,2 and S2,4 modes. The observed solar flux effects could be reasonably attributed to changes in tidal dissipation in the lower temperature produced by changes in mean density and temperature with solar cycle.

CORRELATIONS BETWEEN PERIODICITIES IN GERMINATION OF CHENOPODIUM BOTRYS AND VARIATIONS IN SOLAR RADIO FLUX

There were pronounced fluctuations in the percentage germination of seeds of Chenopodium botrys that were kept stored in darkness under carefully controlled conditions of temperature, humidity, and barometric pressure. Germination tests were conducted over a period of more than 2 years in controlled environment cabinets at 30 °C with different photoperiods supplied by fluorescent light. The fluctuations in percentage germination showed no evident correlation with the following factors: relative humidity, barometric pressure, lunar cycle, magnetic intensity.There were highly significant correlations between the fluctuations in germination and solar radio flux (10.7 cm wavelength, indicative of sunspot activity). The best positive correlation between values for solar radio flux and percentage germination suggested that the effect of solar flux on germination (whether direct or indirect) was greatest during the week immediately preceding the wetting of seeds. Periodogram analyses of the periodicity of percentage germination and solar flux has provided two periodograms which have corresponding peaks, showing that the component periods for solar flux are practically the same as those for germination. It cannot yet be stated whether these correlations were indicative of a direct effect of solar radio flux on germination. The present evidence affirms the contention that largely unexamined exogenous factors may influence rhythmic biological processes.