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Artículos de revistas sobre el tema "Solar variations"

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Publicado: 6 de septiembre de 2023

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1

Solanki, S. K., M. Fligge y Y. C. Unruh. "Variations of the Solar Spectral Irradiance". Symposium - International Astronomical Union 203 (2001): 66–77. http://dx.doi.org/10.1017/s0074180900218809.

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The relative variation of the solar irradiance depends strongly on the wavelength band, with the shortest wavelengths exhibiting the largest variations over the solar cycle. This means that not only the total irradiance varies with solar activity but also the shape of the solar spectrum. These measured effects have been successfully modelled. The models indicate that more than 90% of the total and spectral irradiance variations over the solar cycle are due to the magnetic field at the solar surface. The solar spectral irradiance variations play an important part in constraining the models, since they can directly distinguish between changes in the solar effective temperature and changes produced by variations of solar surface magnetic flux. They also help to determine what fraction of the total solar radiative input to Earth is absorbed by the Earth's atmosphere.

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2

Willson, Richard C. y H. S. Hudson. "Solar luminosity variations in solar cycle 21". Nature 332, n.º 6167 (abril de 1988): 810–12. http://dx.doi.org/10.1038/332810a0.

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3

SIMON, Paul C. y W. Kent TOBISKA. "Solar EUV Irradiance Variations". Journal of geomagnetism and geoelectricity 43, Supplement2 (1991): 823–33. http://dx.doi.org/10.5636/jgg.43.supplement2_823.

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4

Bruls, J. H. M. J. y S. K. Solanki. "Apparent solar radius variations". Astronomy & Astrophysics 427, n.º 2 (28 de octubre de 2004): 735–43. http://dx.doi.org/10.1051/0004-6361:20041311.

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5

Kuhn, J. R. y K. G. Librecht. "Nonfacular solar luminosity variations". Astrophysical Journal 381 (noviembre de 1991): L35. http://dx.doi.org/10.1086/186190.

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6

GAVRYUSEV, V. y E. GAVRYUSEVA. "Solar Neutrino Flux Variations". Annals of the New York Academy of Sciences 647, n.º 1 Texas/ESO-Cer (diciembre de 1991): 483–94. http://dx.doi.org/10.1111/j.1749-6632.1991.tb32198.x.

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7

Pap, J. M. y C. Fröhlich. "Total solar irradiance variations". Journal of Atmospheric and Solar-Terrestrial Physics 61, n.º 1-2 (enero de 1999): 15–24. http://dx.doi.org/10.1016/s1364-6826(98)00112-6.

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8

Spruit, H. C. "Solar Irradiance Variations: Theory". Symposium - International Astronomical Union 185 (1998): 103–9. http://dx.doi.org/10.1017/s0074180900238369.

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The following is a somewhat condensed version of discussions previously given elsewhere (Spruit, 1991, 1992). Some new developments not discussed there are presented in sections 4 and 5.Since the observed irradiance variations are so clearly associated with manifestations of the solar magnetic field, I focus here on magnetic causes. Much of the physics of irradiance variations, however, is governed by the thermal response of the convective envelope and this response is similar for other possible causes of irradiance variations.

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9

Foukal, Peter V. "Solar radiative output variations". Eos, Transactions American Geophysical Union 69, n.º 47 (1988): 1598. http://dx.doi.org/10.1029/88eo01201.

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10

Reames, D. V. "Solar energetic particle variations". Advances in Space Research 34, n.º 2 (enero de 2004): 381–90. http://dx.doi.org/10.1016/j.asr.2003.02.046.

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11

El-Borie, M. A. "Galactic cosmic-ray modulation effect by solar-wind streams". Canadian Journal of Physics 73, n.º 9-10 (1 de septiembre de 1995): 642–46. http://dx.doi.org/10.1139/p95-094.

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Data, from the worldwide network of neutron monitors, recorded at Deep River, Hermanus, Rome, Tokyo, and Huancayo, over two solar cycles (Nos. 20 and 21) are analyzed to study the long-term variations of the solar diurnal variations as they relate to solar-wind speed. The median primary rigidities of response (Rm) for these detectors cover the range 16 GV ≤ Rm ≤ 33 GV. We discuss the solar diurnal variations (amplitude and phase) of cosmic rays as a function of solar activity. The behavior of solar diurnal phases is completely different for the two epochs of high-wind speed. Data of solar-wind speed from 1966–1986 are classified according to the state of the daily mean values. Variation in the amplitudes of the diurnal variations, as functions of the median primary rigidity of cosmic rays, for the two selected periods (1973–1975 and 1979–1981) of high and low solar-wind speeds were determined at the selected stations. The rigidity dependence of the averaged solar diurnal variations of cosmic rays related to the high solar-wind speed was studied. The most sensitive rigidity of modulation is around 20 and 30 GV during the 1973–1975 and 1979–1981 periods, respectively. Our results also show that there is a significant correlation in the solar diurnal amplitudes between the two divisions of high and low solar-wind speed days.

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12

Radick, R. R. "Stellar Irradiance Variations". Symposium - International Astronomical Union 203 (2001): 78–85. http://dx.doi.org/10.1017/s0074180900218810.

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The variability of several dozen stars similar to the Sun in mass, age, and average activity has been monitored regularly in chromospheric Ca II HK emission for over three decades, and photometrically for over fifteen years. Larger samples have been observed less comprehensively. Analogous solar time series exist. A comparison of solar variability with its stellar analogs indicates that the Sun's current behavior is not unusual among sunlike stars. Both solar models and stellar measurements suggest that a true luminosity variation underlies the cyclic total irradiance changes observed on the Sun.

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13

Mukasheva, Saule, Vitaliy Kapytin y Andrey Malimbaev. "VARIATIONS OF IONOSPHERIC PARAMETERS OVER ALMATY (KAZAKHSTAN) IN 1999–2013". Solar-Terrestrial Physics 5, n.º 4 (17 de diciembre de 2019): 91–96. http://dx.doi.org/10.12737/stp-54201912.

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The paper presents the results of a study of the behavior of ionospheric parameters of the total electron content, I(t), and electron density in the maximum F2 layer, Nm, over Almaty (Kazakhstan) [43.25° N; 76.92° E] in 1999–2013. The time interval under study covers different solar activity levels. We have shown that at F10.7>175 in summer and at F10.7>225 in winter there is a saturation effect, i.e. with increasing solar activity level values of I(t) do not increase. The observed nonlinear relationship between the total electron content of the ionosphere and the solar radiation flux F10.7 results from the nonlinear relationship between the solar ultraviolet radiation and the solar radiation flux. The study of the variability of the mid-latitude ionosphere parameters during different solar and geomagnetic activity levels has shown that the standard deviation ç(x) and average shift Xave of I(t) and Nm fluctuations relative to the quiet level weakly depend on solar activity, but greatly depend on geomagnetic activity when F10.7<100.

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14

DONNELLY, Richard F. "Solar UV Spectral Irradiance Variations". Journal of geomagnetism and geoelectricity 43, Supplement2 (1991): 835–42. http://dx.doi.org/10.5636/jgg.43.supplement2_835.

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15

Vilinga, J., S. Koutchmy, Fr Auchere, Fr Baudin, B. Filippov y J.-C. Noens. "Chromospheric Prolateness: Solar Cycle Variations". Proceedings of the International Astronomical Union 2, S233 (marzo de 2006): 240. http://dx.doi.org/10.1017/s1743921306001931.

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16

Ivanov-Kholodny, G. S. "Solar EUV quasi-biannual variations". Physics and Chemistry of the Earth, Part C: Solar, Terrestrial & Planetary Science 25, n.º 5-6 (enero de 2000): 433–35. http://dx.doi.org/10.1016/s1464-1917(00)00051-9.

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17

Solanki, S. K. y M. Fligge. "Solar irradiance variations and climate". Journal of Atmospheric and Solar-Terrestrial Physics 64, n.º 5-6 (marzo de 2002): 677–85. http://dx.doi.org/10.1016/s1364-6826(02)00029-9.

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18

Reid, George C. "Do solar variations change climate?" Eos, Transactions American Geophysical Union 74, n.º 2 (12 de enero de 1993): 23. http://dx.doi.org/10.1029/93eo00218.

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19

Altadill, D. "On the 18-day quasi-periodic oscillation in the ionosphere". Annales Geophysicae 14, n.º 7 (31 de julio de 1996): 716–24. http://dx.doi.org/10.1007/s00585-996-0716-0.

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Abstract. The presence and persistence of an 18-day quasi-periodic oscillation in the ionospheric electron density variations were studied. The data of lower ionosphere (radio-wave absorption at equivalent frequency near 1 MHz), middle and upper ionosphere (critical frequencies f0E and f0F2) for the period 1970–1990 have been used in the analysis. Also, solar and geomagnetic activity data (the sunspot numbers Rz and solar radio flux F10.7 cm, and aN index respectively) were used to compare the time variations of the ionospheric with the solar and geomagnetic activity data. Periodogram, complex demodulation, auto- and cross-correlation analysis have been used. It was found that 18-day quasi-periodic oscillation exists and persists in the temporal variations of the ionospheric parameters under study with high level of correlation and mean period of 18–19 days. The time variation of the amplitude of the 18-day quasi-periodic oscillation in the ionosphere seems to be modulated by the long-term solar cycle variations. Such oscillations exist in some solar and geomagnetic parameters and in the planetary wave activity of the middle atmosphere. The high similarities in the amplitude modulation, long-term amplitude variation, period range between the oscillation of investigated parameters and the global activity of oscillation suggests a possible solar influence on the 18-day quasi-periodic oscillation in the ionosphere.

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20

Trelles Arjona, J. C., M. J. Martínez González y B. Ruiz Cobo. "Solar-cycle and Latitude Variations in the Internetwork Magnetism". Astrophysical Journal 944, n.º 1 (1 de febrero de 2023): 95. http://dx.doi.org/10.3847/1538-4357/acb64d.

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Abstract The importance of the quiet-Sun magnetism is that it is always there to a greater or lesser extent, being a constant provider of energy, independently of the solar cycle phase. The open questions about the quiet-Sun magnetism include those related to its origin. Most people claim that the local dynamo action is the mechanism that causes it. This fact would imply that the quiet-Sun magnetism is nearly the same at any location over the solar surface and at any time. Many works claim that the quiet Sun does not have any variation at all, although a few of them raise doubt on this claim and find mild evidence of a cyclic variation in the the quiet-Sun magnetism. In this work, we detect clear variations in the internetwork magnetism both with latitude and solar cycle. In terms of latitude, we find an increase in the averaged magnetic fields toward the solar poles. We also find long-term variations in the averaged magnetic field at the disk center and solar poles, and both variations are almost anticorrelated. These findings do not support the idea that the local dynamo action is the unique factory of the quiet-Sun magnetism.

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21

Javaraiah, J. "22-Year Periodicity in the Solar Differential Rotation". International Astronomical Union Colloquium 179 (2000): 167–70. http://dx.doi.org/10.1017/s0252921100064423.

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AbstractUsing the data on sunspot groups compiled during 1879–1975, we determined variations in the differential rotation coefficientsAandBduring the solar cycle. The variation in the equatorial rotation rateAis found to be significant only in the odd numbered cycles, with an amplitude ∼ 0.01μrads−1. There exists a good anticorrelation between the variations of the differential rotation rateBderived from the odd and even numbered cycles, suggesting existence of a ‘22-year’ periodicity inB. The amplitude of the variation ofBis ∼ 0.05μrads−1.

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22

Gupta, J. K. y L. Singh. "Long term ionospheric electron content variations over Delhi". Annales Geophysicae 18, n.º 12 (31 de diciembre de 2000): 1635–44. http://dx.doi.org/10.1007/s00585-001-1635-8.

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Abstract. Ionospheric electron content (IEC) observed at Delhi (geographic co-ordinates: 28.63°N, 77.22°E; geomagnetic co-ordinates: 19.08°N, 148.91°E; dip Latitude 24.8°N), India, for the period 1975–80 and 1986–89 belonging to an ascending phase of solar activity during first halves of solar cycles 21 and 22 respectively have been used to study the diurnal, seasonal, solar and magnetic activity variations. The diurnal variation of seasonal mean of IEC on quiet days shows a secondary peak comparable to the daytime peak in equinox and winter in high solar activity. IECmax (daytime maximum value of IEC, one per day) shows winter anomaly only during high solar activity at Delhi. Further, IECmax shows positive correlation with F10.7 up to about 200 flux units at equinox and 240 units both in winter and summer; for greater F10.7 values, IECmax is substantially constant in all the seasons. IECmax and magnetic activity (Ap) are found to be positively correlated in summer in high solar activity. Winter IECmax shows positive correlation with Ap in low solar activity and negative correlation in high solar activity in both the solar cycles. In equinox IECmax is independent of Ap in both solar cycles in low solar activity. A study of day-to-day variations in IECmax shows single day and alternate day abnormalities, semi-annual and annual variations controlled by the equatorial electrojet strength, and 27-day periodicity attributable to the solar rotation.Key words: Ionosphere (equatorial ionosphere) · Magnetospheric physics (magnetosphere · ionosphere interactions) · Radio science (ionospheric physics)

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23

Penna, J. L., A. H. Andrei, S. C. Boscardin, E. Reis Neto y V. A. d'Ávila. "A solar cycle lengthwise series of solar diameter measurements". Proceedings of the International Astronomical Union 5, S264 (agosto de 2009): 49–54. http://dx.doi.org/10.1017/s174392130999233x.

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AbstractThe measurements of the solar photospheric diameter rank among the most difficult astronomic observations. Reasons for this are the fuzzy definition of the limb, the SNR excess, and the adverse daytime seeing condition. As a consequence there are very few lengthy and consistent time series of such measurements. Using modern techniques, just the series from the IAG/USP and from Calern/OCA span more than one solar cycle. The Rio de Janeiro Group observations started in 1997, and therefore in 2008 one complete solar cycle time span can be analyzed. The series shares common principles of observation and analysis with the ones afore mentioned, and it is complementary on time to them. The distinctive features are the larger number of individual points and the improved precision. The series contains about 25,000 single observations, evenly distributed on a day-by-day basis. The typical error of a single observation is half an arc-second, enabling us to investigate variations at the expected level of tens of arc-second on a weekly basis. These features prompted to develop a new methodology for the investigation of the heliophysical scenarios leading to the observed variations, both on time and on heliolatitude. The algorithms rely on running averages and time shifts to derive the correlation and statistical incertitude for the comparison of the long term and major episodes variations of the solar diameter against activity markers. The results bring support to the correlation between the diameter variation and the solar activity, but evidentiating two different regimens for the long term trend and the major solar events.

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24

Pittock, Barrie. "Can solar variations explain variations in the Earth’s climate?" Climatic Change 96, n.º 4 (28 de agosto de 2009): 483–87. http://dx.doi.org/10.1007/s10584-009-9645-8.

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25

RAYCHAUDHURI, PROBHAS. "TIME VARIATIONS IN KAMIOKANDE SOLAR NEUTRINO DATA". Modern Physics Letters A 06, n.º 22 (20 de julio de 1991): 2003–7. http://dx.doi.org/10.1142/s0217732391002165.

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Solar neutrino flux (Eν ≥ 7.5 MeV ) data from 1st January to April 1990 as measured in Kamiokande solar neutrino experiment have been analyzed statistically and have found that the solar neutrino data varies with the solar activity cycle with very high statistical significance (> 98% confidence level). Average solar neutrino flux data in the sunspot minimum range cannot be equal to twice the average solar neutrino flux data in the sunspot maximum range, which suggests that the neutrino flip through the magnetic field of the convection zone of the sun is not responsible for the solar neutrino flux variation. Thus the variation of solar neutrino flux with the solar activity cycle suggests that the solar activity cycle is due to the pulsating character of the nuclear energy generation inside the core of the sun.

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26

Fujiwara, Hitoshi, Yasunobu Miyoshi, Hidekatsu Jin, Hiroyuki Shinagawa, Yuichi Otsuka, Akinori Saito y Mamoru Ishii. "Thermospheric temperature and density variations". Proceedings of the International Astronomical Union 5, S264 (agosto de 2009): 310–19. http://dx.doi.org/10.1017/s1743921309992857.

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AbstractThe thermosphere is the transition region from the atmosphere to space. Both the solar ultraviolet radiation and the solar wind energy inputs have caused significant thermospheric variations from past to present. In order to understand thermospheric/ionospheric disturbances in association with changes in solar activity, observational and modelling efforts have been made by many researchers. Recent satellite observations, e.g., the satellite CHAMP, have revealed mass density variations in the upper thermosphere. The thermospheric temperature, wind, and composition variations have been also investigated with general/global circulation models (GCMs) which include forcings due to the solar wind energy inputs and the lower atmospheric effects. In particular, we have developed a GCM which covers all the atmospheric regions, troposphere, stratosphere, mesosphere, and thermosphere, to describe variations of the thermospheric temperature and density caused by both effects from the lower atmosphere and the magnetosphere. GCM simulations represent global and localized temperature and density structures, which vary from hour to hour, depending on forcings due to the lower atmosphere, solar and geomagnetic activities. This modelling attempt will enable us to describe the thermospheric weather influenced by solar activity in cooperation with ground-based and satellite observations.

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27

Takahashi, Y., Y. Okazaki, M. Sato, H. Miyahara, K. Sakanoi y P. K. Hong. "27-day variation in cloud amount and relationship to the solar cycle". Atmospheric Chemistry and Physics Discussions 9, n.º 4 (16 de julio de 2009): 15327–38. http://dx.doi.org/10.5194/acpd-9-15327-2009.

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Abstract. Linkages between solar activity and the earth's climate have been suggested in previous studies. The 11-year cycle in solar activity evident in sunspot numbers is the most examined example of periodicity, and it is clearly recognized in variations in the thermal structure and dynamical motion of the stratospheric atmosphere. Also the variations in the stratosphere related to the period of apparent solar rotation have also been suggested; however, for such a short period, no quantitative evidence indicating a relationship to the tropospheric phenomena. We clearly demonstrate a 27-day variation in the cloud amount in the region of the Western Pacific warm pool, which is only seen in the solar maximum years of the 11-year cycle. The average spectrum in solar maximum years also shows an enhancement in the range of MJO period. Long-term variations in the tropospheric phenomena, including the 11-year cycle, are generally investigated based on monthly or even yearly averaged data, but the present results may suggest an alternative possibility: short-period variations could modulate longer periodic phenomena.

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28

Rahoma, Usama Ali y Rabab Helal. "Influence of Solar Cycle Variations on Solar Spectral Radiation". Atmospheric and Climate Sciences 03, n.º 01 (2013): 47–54. http://dx.doi.org/10.4236/acs.2013.31007.

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29

Gosling, J. T., D. J. McComas, J. L. Phillips y S. J. Bame. "Counterstreaming solar wind halo electron events: Solar cycle variations". Journal of Geophysical Research 97, A5 (1992): 6531. http://dx.doi.org/10.1029/92ja00302.

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30

Chapman, G. A., A. M. Cookson y J. J. Dobias. "Variations in total solar irradiance during solar cycle 22". Journal of Geophysical Research: Space Physics 101, A6 (1 de junio de 1996): 13541–48. http://dx.doi.org/10.1029/96ja00683.

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31

Pap, Judit y Bojan Vrsnak. "Solar Irradiance Variations and their Relation with Solar Flares". International Astronomical Union Colloquium 104, n.º 2 (1989): 243–46. http://dx.doi.org/10.1017/s0252921100154260.

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32

Richardson, J. D. y J. C. Kasper. "Solar cycle variations of solar wind dynamics and structures". Journal of Atmospheric and Solar-Terrestrial Physics 70, n.º 2-4 (febrero de 2008): 219–25. http://dx.doi.org/10.1016/j.jastp.2007.08.039.

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33

Mahajan, Sushant S., Xudong Sun y Junwei Zhao. "Removal of Active Region Inflows Reveals a Weak Solar Cycle Scale Trend in the Near-surface Meridional Flow". Astrophysical Journal 950, n.º 1 (1 de junio de 2023): 63. http://dx.doi.org/10.3847/1538-4357/acc839.

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Abstract Using time–distance local helioseismology flow maps within 1 Mm of the solar photosphere, we detect inflows toward activity belts that contribute to solar-cycle scale variations in the near-surface meridional flow. These inflows stretch out as far as 30° away from the active region centroids. If active region neighborhoods are excluded, the solar-cycle-scale variation in the background meridional flow diminishes to below 2 m s−1, but still shows systematic variations in the absence of active regions between sunspot cycles 24 and 25. We therefore propose that the near-surface meridional flow is a three-component flow made up of a constant baseline flow profile that can be derived from quiet-Sun regions, variations due to inflows around active regions, and solar-cycle-scale variation of about 2 m s−1. Torsional oscillation, on the other hand, is found to be a global phenomenon, i.e., exclusion of active region neighborhoods does not significantly affect its magnitude or phase. This nonvariation in torsional oscillation with distance away from active regions and the three-component breakdown of the near-surface meridional flow serve as vital constraints for solar dynamo models and surface flux-transport simulations.

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34

Ouattara, F., C. Amory-Mazaudier, R. Fleury, P. Lassudrie Duchesne, P. Vila y M. Petitdidier. "West African equatorial ionospheric parameters climatology based on Ouagadougou ionosonde station data from June 1966 to February 1998". Annales Geophysicae 27, n.º 6 (23 de junio de 2009): 2503–14. http://dx.doi.org/10.5194/angeo-27-2503-2009.

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Abstract. This study is the first which gives the climatology of West African equatorial ionosphere by using Ouagadougou station through three solar cycles. It has permitted to show the complete morphology of ionosphere parameters by analyzing yearly variation, solar cycle and geomagnetic activity, seasonal evolution and diurnal development. This work shows that almost all ionospheric parameters have 11-year solar cycle evolution. Seasonal variation shows that only foF2 exhibits annual, winter and semiannual anomaly. foF2 seasonal variation has permitted us to identify and characterize solar events effects on F2 layer in this area. In fact (1) during quiet geomagnetic condition foF2 presents winter and semiannual anomalies asymmetric peaks in March/April and October. (2) The absence of winter anomaly and the presence of equinoctial peaks are the most visible effects of fluctuating activity in foF2 seasonal time profiles. (3) Solar wind shock activity does not modify the profile of foF2 but increases ionization. (4) The absence of asymmetry peaks, the location of the peaks in March and October and the increase of ionization characterize recurrent storm activity. F1 layers shows increasing trend from cycle 20 to cycle 21. Moreover, E layer parameters seasonal variations exhibit complex structure. It seems impossible to detect fluctuating activity effect in E layer parameters seasonal variations but shock activity and wind stream activity act to decrease E layer ionization. It can be seen from Es layer parameters seasonal variations that wind stream activity effect is fairly independent of solar cycle. E and Es layers critical frequencies and virtual heights diurnal variations let us see the effects of the greenhouse gases in these layers.

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35

Tripathy, S. C., Kiran Jain y A. Bhatnagar. "Helioseismic Solar Cycle Changes and Splitting Coefficients". International Astronomical Union Colloquium 179 (2000): 349–52. http://dx.doi.org/10.1017/s0252921100064800.

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AbstractUsing the GONG data for a period over four years, we have studied the variation of frequencies and splitting coefficients with solar cycle. Frequencies and even-order coefficients are found to change significantly with rising phase of the solar cycle. We also find temporal variations in the rotation rate near the solar surface.

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36

Witzke, V., A. I. Shapiro, S. K. Solanki, N. A. Krivova y W. Schmutz. "From solar to stellar brightness variations". Astronomy & Astrophysics 619 (noviembre de 2018): A146. http://dx.doi.org/10.1051/0004-6361/201833936.

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Context. Comparison studies of Sun-like stars with the Sun suggest an anomalously low photometric variability of the Sun compared to Sun-like stars with similar magnetic activity. Comprehensive understanding of stellar variability is needed to find a physical reason for this observation. Aims. We investigate the effect of metallicity and effective temperature on the photometric brightness change of Sun-like stars seen at different inclinations. The considered range of fundamental stellar parameters is sufficiently small so the stars investigated here still count as Sun-like or even as solar twins. Methods. To model the brightness change of stars with solar magnetic activity, we extended a well-established model of solar brightness variations based on solar spectra, Spectral And Total Irradiance REconstruction (SATIRE), to stars with different fundamental parameters. For this we calculated stellar spectra for different metallicities and effective temperature using the radiative transfer code ATLAS9. Results. We show that even a small change (e.g. within the observational error range) of metallicity or effective temperature significantly affects the photometric brightness change compared to the Sun. We find that for Sun-like stars, the amplitude of the brightness variations obtained for Strömgren (b + y)/2 reaches a local minimum for fundamental stellar parameters close to the solar metallicity and effective temperature. Moreover, our results show that the effect of inclination decreases for metallicity values greater than the solar metallicity. Overall, we find that an exact determination of fundamental stellar parameters is crucially important for understanding stellar brightness changes.

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37

Weng, Libin, Jiuhou Lei, Eelco Doornbos, Hanxian Fang y Xiankang Dou. "Seasonal variations of thermospheric mass density at dawn/dusk from GOCE observations". Annales Geophysicae 36, n.º 2 (22 de marzo de 2018): 489–96. http://dx.doi.org/10.5194/angeo-36-489-2018.

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Abstract. Thermospheric mass densities from the GOCE (Gravity field and steady-state Ocean Circulation Explorer) satellite for Sun-synchronous orbits between 83.5∘ S and 83.5∘ N, normalized to 270 km during 2009–2013, have been used to develop an empirical mass density model at dawn/dusk local solar time (LST) sectors based on the empirical orthogonal function (EOF) method. The main results of this study are that (1) the dawn densities peak in the polar regions, but the dusk densities maximize in the equatorial regions; (2) the relative seasonal variations to the annual mean have similar patterns across all latitudes regardless of solar activity conditions; (3) the seasonal density variations show obvious hemispheric asymmetry, with large amplitudes in the Southern Hemisphere; (4) both amplitude and phase of the seasonal variations have strong latitudinal and solar activity dependences, with high amplitude for the annual variation at higher latitudes and semiannual variation at lower latitudes; (5) the annual asymmetry and effect of the Sun–Earth distance vary with latitude and solar activity. Keywords. Atmospheric composition and structure (pressure, density, and temperature)

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38

Pintér, T., I. Dorotovič y M. Rybanský. "The heliosphere mass variations: 1996–2006". Proceedings of the International Astronomical Union 4, S257 (septiembre de 2008): 291–93. http://dx.doi.org/10.1017/s1743921309029433.

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AbstractThe variations of the global mass of heliosphere in the 23rd cycle of the solar activity are described. The results are derived from solar corona observations and from ‘in situ’ measurements made by the space probes SOHO, VOYAGER2, ACE, WIND, and ULYSSES. It has been revealed that though the total mass of corona fluctuates during the solar activity cycle approximately in a ratio of 1 : 3, the specific mass flow (q) in the solar wind does not change in the ecliptic plane. In the polar regions the q decreases during the minimum in a third of the original value and the velocity of expansion is roughly double. These findings are valid for the 23rd solar cycle.

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39

Owens, Mathew J., Mike Lockwood, Pete Riley y Luke Barnard. "Long-term variations in the heliosphere". Proceedings of the International Astronomical Union 13, S340 (febrero de 2018): 108–14. http://dx.doi.org/10.1017/s1743921318000972.

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AbstractReconstructions of long-term solar variability underpin our understanding of the solar dynamo, potential tropospheric climate implications and future space weather scenarios. Prior to direct spacecraft measurements of the heliospheric magnetic field (HMF) and solar wind, accurate annual reconstructions are possible using geomagnetic and sunspot records. On longer timescales, information about the HMF can be extracted from cosmogenic radionuclide records, particularly 14C in ancient trees and 10Be in ice sheets. These proxies, and what they reveal about the HMF and solar wind, are briefly reviewed here.

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40

Radick, Richard R. "Photometric Variations of Solar Type Stars". International Astronomical Union Colloquium 143 (1994): 109–16. http://dx.doi.org/10.1017/s0252921100024611.

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High precision measurements of photometric variability among solar type stars have now been made since 1980. These observations clearly show that year-to-year brightness variations connected with magnetic activity are a widespread phenomenon among such stars. They also suggest that the Sun’s potential for long-term white light variability may be significantly understated by measurements of solar total irradiance during the 1980s.

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41

Atia, Abdulhamid, Fatih Anayi y Min Gao. "Influence of Shading on Solar Cell Parameters and Modelling Accuracy Improvement of PV Modules with Reverse Biased Solar Cells". Energies 15, n.º 23 (30 de noviembre de 2022): 9067. http://dx.doi.org/10.3390/en15239067.

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This paper presents an experimental investigation on the influence of shading on mono-crystalline (mono-Si) solar cell parameters. The variations of equivalent circuit parameters with shading were determined and then used in modelling a mono-Si solar cell and a mono-Si photovoltaic (PV) module under partial shading. It was found that the simulation by considering the parameter variations with shading in the single cell model did not lead to a noticeable improvement in modelling accuracy. However, for the PV module, a significant improvement in modelling accuracy in the reverse bias region was achieved when considering all parameter variations in the model. A further investigation was performed to identify the key parameters that are responsible for the improvement. The results revealed that in addition to the photo-generated current, the shunt resistance also has a significant effect on the model accuracy. A modelling approach was thus proposed, which includes the variation of the shunt resistance with shading, in addition to the variation of the photo-generated current. This approach was experimentally validated using a mono-Si PV module. The results show that the proposed approach is more accurate, compared to the approach that considers only the variation of the photo-generated current, without the need to include an avalanche breakdown term.

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42

Pham Thi Thu, H., C. Amory-Mazaudier y M. Le Huy. "Time variations of the ionosphere at the northern tropical crest of ionization at Phu Thuy, Vietnam". Annales Geophysicae 29, n.º 1 (26 de enero de 2011): 197–207. http://dx.doi.org/10.5194/angeo-29-197-2011.

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Abstract. This study is the first which gives the climatology of the ionosphere at the northern tropical crest of ionization in the Asian sector. We use the data from Phu Thuy station, in Vietnam, through three solar cycles (20, 21 and 22), showing the complete morphology of ionosphere parameters by analyzing long term variation, solar cycle variation and geomagnetic activity effects, seasonal evolution and diurnal development. Ionospheric critical frequencies, foF2, foF1 and foE, evolve according to the 11-year sunspot cycle. Seasonal variations show that foF2 exhibits a semiannual pattern with maxima at equinox, and winter and equinoctial anomalies depending on the phases of the sunspot solar cycle. ΔfoF2 exhibits a semiannual variation during the minimum phase of the sunspot solar cycle 20 and the increasing and decreasing phases of solar cycle 20, 21 and 22. ΔfoF1 exhibits an annual variation during the maximum phase of solar cycles 20, 21 and 22. Δh'F2 shows a regular seasonal variation for the different solar cycles while Δh'F1 exhibits a large magnitude dispersion from one sunspot cycle to another. The long term variations consist in an increase of 1.0 MHz for foF2 and of 0.36 MHz for foF1. foE increases 0.53 MHz from solar cycle 20 to solar cycle 21 and then decreases −0.23 MHz during the decreasing phase of cycle 21. The diurnal variation of the critical frequency foF2 shows minima at 05:00 LT and maxima around 14:00 LT. foF1 and foE have a maximum around noon. The diurnal variation of h'F2 exhibits a maximum around noon. The main features of h'F1 are a minimum near noon and the maximum near midnight. Other minima and maxima occur in the morning, at about 04:00 or 05:00 LT and in the afternoon, at about 18:00 or 19:00 LT but they are markedly smaller. Only during the maximum phase of all sunspot solar cycles the maximum near 19:00 LT is more pronounced.

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43

Mikhalev, Aleksandr. "MANIFESTATION OF SOLAR ACTIVITY AND DYNAMICS OF THE ATMOSPHERE IN VARIATIONS OF 577.7 AND 630.0 nm ATMOSPHERIC EMISSIONS IN SOLAR CYCLE 24". Solar-Terrestrial Physics 6, n.º 3 (22 de septiembre de 2020): 81–85. http://dx.doi.org/10.12737/stp-63202011.

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In the paper, variations of the night emission intensities in the 557.7 and 630 nm atomic oxygen lines [OI] in 2011–2019 have been analyzed. The analysis is based on data from the ISTP SB RAS Geophysical Observatory. The emission intensities are compared with atmospheric, solar, and geophysical parameters. High correlation coefficients between monthly average and annual average 630.0 nm emission intensities and solar activity indices F10.7 have been obtained. This suggests a key role of solar activity in variations of this emission in the period of interest. Variations of the 557.7 nm emission demonstrate to a greater extent the correlations of the stratospheric zonal wind (QBO.U30 index) with quasi-biennial oscillations. The causes of the weak dependence of the 557.7 nm emission intensity on solar activity in solar cycle 24 are discussed.

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44

Kjeldseth-Moe, Olav y Sven Wedemeyer-Böhm. "Are there variations in Earth's global mean temperature related to the solar activity?" Proceedings of the International Astronomical Union 5, S264 (agosto de 2009): 320–25. http://dx.doi.org/10.1017/s1743921309992869.

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AbstractWe have analyzed the record of Earth's global temperature variations between 1850 and 2007 looking for signals of periodic variations and compared our results with solar activity variations in the same time period. Significant periods are found at 9.4, 10.6 and 20.9 years. These periodic variations may be caused by solar activity. However, and amazingly enough, we also find at least 17 other significant periodic variations in addition to expected variations with periods of 1 year and of half a year. The result is considered in terms of solar related forcing mechanisms. These may be variable solar heating associated with the small changes in solar irradiance over the solar cycle, or direct effects of interactions between variable magnetic fields carried by the solar wind and particles and fields in interplanetary space or in the Earth's ionosphere.

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45

Spruit, Henk C. "Theoretical Interpretation of Solar and Stellar Irradiance Variations". International Astronomical Union Colloquium 143 (1994): 270–79. http://dx.doi.org/10.1017/s0252921100024775.

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The main cause of variability of solar type stars are their varying magnetic fields. To compute irradiance variations one has to compute the magnetic field (the dynamo problem), and from this the irradiance effects. The second problem is considered here. The theoretical work of the past decade has shown that the dominant effect of magnetic fields is a surface effect: a change of effective emissivity of the magnetic parts of the surface while the nonmagnetic part of the surface contributes very little to the irradiance variation on almost all time scales. No other processes have yet been found that would cause variations exceeding (at the current level of magnetic activity) the observed 0.1% irradiance fluctuation of the Sun. This implies that a knowledge of the surface magnetic fields [separated into its bright small scale (faculae, network) and dark large scale (spots) components] is sufficient for pre- or postdicting the solar irradiance. It is hypothesized that the discrepancy remaining between the measured irradiance variations and values reconstructed from proxies is due to the difficulty of finding a proxy that accurately correlates with the continuum contrast of a dispersed small scale magnetic field. Stellar structure theory predicts that the variations in the solar radius associated with magnetic activity are quite small. For stars, color and brightness variations should primarily be interpreted in terms of variations in the fraction of the surface covered by magnetic patches. Their (long term) displacement from the main sequence is not very large.

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46

Fox, Peter A. y Sabatino Sofia. "Convection and Irradiance Variations". International Astronomical Union Colloquium 143 (1994): 280–90. http://dx.doi.org/10.1017/s0252921100024787.

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In the outer layers of the Sun (≈ 30% by radius), energy is transported by convection. The nature of the highly stratified and compressible convective flow is determined from the components of the energy flux (internal, kinetic, viscous, magnetic and radiative). Local suppressions or enhancements of any of these components may give rise to measurable changes in the emergent radiation.On the solar surface there is direct evidence for modulation of the emerging heat flux covering a large range in spatial and temporal scales, particularly associated with concentrated magnetic fields (e.g. sunspots, plages). Associated with these surface features is the observation that the characteristics of convective motions are also modified. In the deeper layers, the interaction of convection and magnetic fields will play an important role in readjusting the local emerging heat flux and thus should contribute to the modulation of the total solar irradiance.The task of calculating the response of the convection zone structure to developing active regions, and the solar activity cycle in general is difficult and complex due to the highly non-linear nature of the interaction of convection and magnetic fields. Theoretical work has ranged from empirical and global structure models, all the way to fine scale compressible convection simulations. This paper will highlight some recent theoretical advances that may have a direct bearing on the understanding of solar luminosity and irradiance variations and outline the important problems that must be addressed and what observational constraints may be used.

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47

Gelfreikh, G. B., T. B. Goldvarg, Yu G. Kopylova, Y. A. Nagovitsin, Y. T. Tsap y L. I. Tsvetkov. "Solar corona heating and microwave variations". Kosmìčna nauka ì tehnologìâ 8, n.º 2s (2002): 243–47. http://dx.doi.org/10.15407/knit2002.02s.243.

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48

Selhorst, C. L., A. V. R. Silva y J. E. R. Costa. "Radius variations over a solar cycle". Astronomy & Astrophysics 420, n.º 3 (junio de 2004): 1117–21. http://dx.doi.org/10.1051/0004-6361:20034382.

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49

Winch, D. E. "Solar and Lunar Daily Geomagnetic Variations". Exploration Geophysics 24, n.º 2 (junio de 1993): 147–50. http://dx.doi.org/10.1071/eg993147.

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50

Chapman, G. A. y J. E. Boyden. "Solar irradiance variations derived from magnetograms". Astrophysical Journal 302 (marzo de 1986): L71. http://dx.doi.org/10.1086/184640.

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