arXiv subjects

E. A. Bruevich

Publications and source records attributed to E. A. Bruevich.

At least 19 recordsLinked to original sources

arXiv2019

Flux Variations in Lines of Solar EUV Radiation Beyond Flares in Cycle 24

Studies in the extreme ultraviolet (EUV) and X-ray ranges of the solar spectrum are important due to the active role of radiation of these ranges in the formation of the Earth's ionosphere. Photons of the EUV range are completely absorbed in the upper layers of the Earth's atmosphere and induce the excitation, dissociation, and ionization of its different components and, finally, the atmospheric heating. From the archive data of the EUV Variability Experiment of the Solar Dynamics Observatory (SDO/EVE), we formed series of diurnal values of the background fluxes radiated beyond flares in the EUV lines HeII (30.4 nm), HeI (58.4 nm), CIII (97.7 nm), and FeXVIII (9.4 nm) in cycle 24 (from 2010 to 2017). These fluxes are compared to the corresponding values of the radio flux F10.7 at a wavelength of 10.7 cm and the background radiation flux F0.1-0.8 in the X-ray range between 0.1 and 0.8 nm measured onboard the GOES-15 satellite of the Geostationary Operational Environmental Satellite system. Comparative analysis has shown that the solar radiation in individual lines of the EUV range and the fluxes F10.7 and F0.1-0.8 are closely interrelated.

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arXiv2018

Long-term trends in the solar activity. Variations of solar indices in last 40 years

The analysis of long-term variations of several solar activity indices (AI) since in last 40 years has been performed. We studied the AI which characterize the fluxes from different areas in solar atmosphere. Our consideration of mutual correlations between the solar indices is based on the study of relationships between them in the period from 1950 to 1990. This period of time, covering activity cycles 19 -- 22, is characterized by relatively stable relations between the indices. We have studied the normalized variations of these indices in the recent time in relation to their values which have been calculated with help of the radiation of the sun in the radio range at a wavelength of 10.7 cm (F10.7) in 1950 -- 1990. The analysis of time series of variations of the normalized AI (AIFF) in solar cycles 23 -- 24 shows an existence of different trends for different indices in their long-term variations. We assume that variations of normalized SSN, F530.3 and Flare Index, which have shown a sharp decrease in last 40 years is possibly associated with a decrease in the intensity of large-scale magnetic fields in the photosphere (SSN) and in the corona (the coronal index and the Flare Index)

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arXiv2018

Levels of chromospheric and coronal activity in Sun-like stars and various types of dynamo waves

We analyze the X-ray emission and chromospheric activity of Sun-like stars of F, G and K spectral classes (late-type stars) studied in the framework of the HK project. More powerful coronas are possessed by stars displaying irregular variations of their chromospheric emission, while stars with regular cyclic activity are characterized by comparatively modest X-ray luminosities and ratios of the X-ray to bolometric luminosity. This indicates that the nature of processes associated with magnetic-field amplification on the convective envelope changes appreciably in the transition from small to large dynamo numbers, directly affecting the character of the alpha-Omega dynamo. Due to the strong dependence of both the dynamo number and the Rossby number on the speed of axial rotation, earlier correlations found between various activity parameters and the Rossby number are consistent with our conclusion. Our analysis makes it possible to draw the first firm conclusions about the place of solar activity among analogous processes developing in active late-type stars.

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arXiv2018

Powerful solar flares in September 2017. Comparison with the largest flares in cycle 24

Solar flare activity in cycle 24 is studied. Satellite observations of x-ray fluxes from GOES-15 and UV emission lines from the SDO/EVE experiment are used. The most powerful flares of cycle 24 in classes X9.3 and X8.2 in September 2017 are compared with powerful flares in classes M5-X6.9. The times at which the fluxes in the 30.4 and 9.4 nm lines and in the 0.1-0.8 nm x-ray range begin to increase are compared for 21 of the large flares. The total energies arriving at the earth from flares in the 30.4 and 9.4 nm lines and in the 0.1-0.9 nm x-ray range, $E_{30.4}$, $E_{9.4}$, and $E_{0.1-0.8}$, from 25 flares during 2011 and 2012 are calculated. It is shown that the calculated energies of the flares in the analyzed lines from SDO/EVE and in the x-ray range from GOES-15 are closely interrelated.

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arXiv2018

Cyclic Variations in the Solar Radiation Fluxes at the Beginning of the 21st Century

The solar activity in the current, that is, the 24-th, sunspot cycle is analyzed. Cyclic variations in the sunspot number (SSN) and radiation fluxes in various spectral ranges have been estimated in comparison with the general level of the solar radiation, which is traditionally determined by the radio emission flux $F_ {10.7} $ at a wavelength of 10.7 cm (2.8 GHz). The comparative analysis of the variations in the solar constant and solar indices in the UV range, which are important for modeling the state of the Earth's atmosphere, in the weak 24th cycle and strong 22nd and 23rd cycles showed relative differences in the amplitudes of variations from the minimum to the maximum of the cycle. The influence of the hysteresis effect between the activity indices and $F_ {10.7} $ in the 24-th cycle, which is considered here, makes it possible to refine the forecast of the UV indices and solar constant depending on the quadratic regression coefficients that associate the solar indices with $F_ {10.7} $ depending on the phase of the cycle.

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arXiv2017

Flare activity of the Sun and variations in its UV emission during cyrcle 24

The flare activity and the ultraviolet emission of the sun during its 24-th cycle are analysed. As compared to cycles 21-23, where the most powerful flares were observed during the decay phase, in cycle 24 the greatest number of powerful flares (>X2.7) occurred in the rising phase and at the maximum with the exception of the two largest flares of cycle 24 X9.3 and X8.2 in September 2017. We showed that regression fits of solar UV indices to the overall radiation level from the sun are substantially different for cycle 24 compared to cycles 21-23. It is found that for the flare of August 9, 2011 (SDO and GOES-15 observations), the flare propagates in a direction from the upper corona to the transition region and to the chromosphere. A study of the N-S asymmetry in the distribution of the flares in cycle 24 reveals a strong predominance of flares in the N-hemisphere in 2011 and in the S-hemisphere in 2014. It is also found that during cycles 23 and 24, the delays in the onset of proton events relative to the onset of the flares that cause them have a distribution with a distinct maximum corresponding to a delay of 2 hours for protons with energies >10 MeV, as well as for those with energies >100 MeV.

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arXiv2017

Large flares (M1 - X7) in solar cycle 24

The large (X-ray class > M1) and very large (X-ray class >X1) flares (according to the observations of GOES-15 and Preliminary data from Current Catalog of Flare Events) in solar activity cycle 24 were analyzed. The monthly average values of optical Flare Index for 2010 - 2016 were calculated. The values of the total energy of the flare E (J m-2) in the 0.1 -- 0.8 nm range at the level of the earth's atmosphere were estimated. The energy spectrum (the dependence of the number of flares with the full energy E from the value of this full energy) for 115 flares of M5 - X7 classes was built. The comparative study of monthly averaged values of several indices of solar activity in current cycle 24: the relative sunspot numbers (SSN), the 10.7 cm radio flux, the radiation flux in the Lyman-alpha line, the solar constant (TSI) and the Flare Index (FI) was made.

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arXiv2016

Evolution of the cycles of magnetic activity of the Sun and Sun-like stars in time

We applied the method of continuous wavelet-transform to the time-frequency analysis to the sets of observations of relative sunspot numbers, sunspot areas and to 6 Mount Wilson HK-project stars with well-defined magnetic cycles. Wavelet analysis of these data reveals the following pattern: at the same time there are several activity cycles whose periods vary widely from the quasi-biennial up to the centennial period for the Sun and vary significant during observations time of the HK-project stars. These relatively low-frequency periodic variations of the solar and stellar activity gradually change the values of periods of different cycles in time. This phenomenon can be observed in every cycles of activity

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arXiv2016

The histeresis of the indices of solar activity and of the ionospheric indices in 11-yr cycles. The histeresis of the stellar activity indices in the cyclic activity similar to the Sun

The analysis of the effect of the hysteresis, which manifests itself in an ambiguous relationship of radiation from the photosphere, chromosphere and corona on the rise and decline phases of the solar and stellar activity cycles have done. Some indices of solar activity: the flux of the hydrogen Lyman-alpha emission, the 10.7 cm flux, the sunspot number SSN, the flux in the coronal green line 530.3 nm, the solar constant TSI and the 280 nm Mg II flux were studied. The stars with the well-determined cycles were examined to detect the effect of hysteresis between the chromosphere's S-index CaII fluxes versus the photosphere's fluxes Fphotosphere.

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arXiv2016

Magnetic cycles of Sun-like stars with different levels of coronal and chromospheric activity -- comparison with the Sun

The atmospheric activity of the Sun and Sun-like stars is analyzed involving observations from HK-project at the Mount Wilson Observatory, the California and Carnegie Planet Search Program at the Keck and Lick Observatories and the Magellan Planet Search Program at the Las Campanas Observatory. We show that for stars of F, G and K spectral classes, the cyclic activity, similar to the 11-yr solar cycles, is different: it becomes more prominent in K-stars. Comparative study of Sun-like stars with different levels of the chromospheric and coronal activity confirms that the Sun belongs to stars with the low level of the chromospheric activity and stands apart among these stars by the minimum level of its coronal radiation and the minimum level of its variations of the photospheric flux.

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arXiv2015

Wavelet-analysis of series of observations of relative sunspot numbers. The dependence of the periods of cyclic activity on the time at different time scales

We applied the method of continuous wavelet-transform to high-quality time-frequency analysis to the sets of observations of relative sunspot numbers. Wavelet analysis of these data reveals the following pattern: at the same time there are several activity cycles whose periods vary widely from the quasi biennial up to the centennial period. These relatively low-frequency periodic variations of the solar activity gradually change the values of periods of different cycles in time. This phenomenon can be observed in every cycle of activity.

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arXiv2015

On the global magnetic activity and dynamo of the Sun and solar-type stars

The activity of the Sun as a result of cyclic changes of the global magnetic field is studied. As a consequence of the analysis of magnetic activity of solar-type stars the following power dependencies were found: the dependence between the rotation periods and the effective temperatures, the dependence between the duration of the "11-year" cycles of activity and the effective temperatures, and the dependence between the duration of quasi-biennial cycles and the effective temperatures. It is shown that the physical nature of these dependencies associated with the observed properties of solar-type stars and can be explained by the existence of internal Rossby waves around the base of convective shells of these stars.

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arXiv2015

General trends in the changes of indices of solar activity in the late XX - early XXI century

The analysis of the observations of solar activity indexes SSN (NOAA Sunspot Numbers), the radio flux at a wavelength of 10.7 cm (F10.7) and the solar constant (TSI) during the cycles 22 - 24 is presented. We found a decrease of the observed values of the SSNobs which was calculated with SSNsyn (using regression relationships between SSN and F10.7) after 1990 year on 20 - 25% instead of 35%, as was previously assumed. The changes in characteristics of the most popular index, SSN, such as decrease in the number of sunspots, the reduction of the magnetic field in small and medium-sized spots are not in full compliance with the proposed scenario of solar activity predicted by radio flux F10.7 in the cycles 23 and 24, and cannot be fully explained by the influence on the SSN values of additional minimum of 50 - 70 year cycle. We have also showed that the observed changes of SSN lead to a slight increase of the solar constant TSI during the cycles 23 - 24 compared to the cycle 22.

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arXiv2015

Correlation study of some solar activity indices in the cycles 21 - 23

The correlation coefficients of the linear regression of six solar indices versus F10,7 were analyzed in solar cycles 21, 22 and 23. We also analyzed the interconnection between these indices and F10,7 with help of the approximation by the polynomials of second order. The indices we've studied in this paper are: Wolf numbers - W, 530,3 nm coronal line flux - F530, the total solar irradiance - TSI, Mg II UV-index 280 nm core-to-wing ratio, Flare Index - FI and Counts of flares. In the most cases the regressions of these solar indices versus F10,7 are close to linear except the moments of time near to the minimums and maximums of 11-year activity. For the linear regressions we found that the values of correlation coefficients Kcorr(t) for the indices versus F10,7 and W show the cyclic variations with periods approximately equal to the to half length of 11-year cycle - 5,5 years approximately.

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arXiv2015

Changed Relation Between Radio Flux F10,7 And Some Solar Activity Indices During Cycles 21 - 23

A stable cyclicity of correlation coefficients Kcorr for some solar activity indices versus F10,7 was found after monthly averages values analysis. These indices are: Wolf numbers, 10,7 cm radio flux F10,7, 0,1-0,8 nm background, the total solar irradiance, Mg II UV-index (280 nm core to wing ratio) and counts of flares. The correlation coefficients of the linear regression of these solar activity indices versus F10,7 were analyzed for every year in solar cycles 21 - 23. We found out that the values of yearly determined correlation coefficients Kcorr for solar activity indices versus F10,7 show the cyclic variations with stable period closed to half length of 11-year cycle (5,5 years approximately)

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arXiv2015

Cycles of magnetic activity in solar-type stars. The place of the Sun among the stars with different levels of coronal and chromospheric activity

The atmospheric activity of the Sun and solar-type stars is analysed involving observations from HK-project at the Mount Wilson Observatory, the California and Carnegie Planet Search Program at the Keck and Lick Observatories, and the Magellan Planet Search Program at the Las Campanas Observatory. We show that for stars of F, G and K spectral classes, the cyclic activity, similar to the 11-yr Solar cycles, is different: it becomes more prominent in K-stars. Comparative study of solar-type stars with different levels of the chromospheric and coronal activity confirms that the Sun belongs to stars with the low level of the chromospheric activity and stands apart among these stars by the minimum level of the coronal radiation and minimum flux variations of the photospheric radiation.

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arXiv2014

The study of time series of monthly averaged values of F10.7 from 1950 to 2010

Prior to 1947, the activity of the Sun was assessed by the relative numbers of sunspots (W). The 10.7 cm radio emission (frequency of 2.8 GHz) for observations of the variability of radiation of chromosphere and the lower corona (F10.7) became used from 1947. For the F10,7 are available more detailed observational archive data, so this activity index more often than the other indices is used in the prediction and monitoring of the solar activity. We have made the analysis of time series of F10.7 with the use of different mother wavelets: Daubechies 10, Symlet 8, Meyer, Gauss 8 and Morlet. Wavelet spectrum allows us not only to identify cycles, but analyze their change in time. Each wavelet has its own characteristic features, so sometimes with the help of different wavelets it can be better identify and highlight the different properties of the analyzed signal. We intended to choose the mother wavelet, which is more fully gives information about the analyzed index F10.7. We have received, that all these wavelets show similar values to the maximums of the cyclic activity. However, we can see the difference when using different wavelets. There are also a number of periods, which, perhaps, are the harmonics of main period. The mean value of 11-year cycle is about 10.2 years. All the above examples show that the best results we get when using wavelets Morley, Gauss (real-valued) and multiparameter family of wavelets Morley and Gauss (complex-valued).

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arXiv2013

Can Rossby waves explain the cyclic magnetic activity of the Sun and solar-type stars?

Magnetic activity is a global property of the Sun; the complex processes of solar activity are connected with the solar magnetic fields. For solar-type stars and the Sun magnetic activity depends on the physical parameters of the star. In this article we study the relationships between the duration of activity cycle and effective temperature for solar-type stars and the Sun. We've tried to explain these relationships due to the existence of layer of laminar convection near the bottom of the convective zone of the star. In this layer the Rossby waves are formed. They generate the primary poloidal magnetic field, which is the source of energy of the complex phenomena of magnetic activity.

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