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The presence of coronal holes in solar disk plays an important role in influencing the space weather and generation of the solar wind. As such there lies a requirement in proper study and prediction of coronal holes occurs in the solar disk. This, in turn, arises the necessity of detection of coronal holes present in the solar disk. In this work, a Hough transformed inspired fuzzy-energy simulated dual contours-based segmentation technique has been proposed for the detection and extraction of holes in solar disk. In the proposed method Hough transform has been induced to initialize the contour for the contour-based method of segmentation. In the algorithm, two contours (active and static) have been initiated and made to evolve based on the energy function by incorporating the gray-scale intensity. Here in the work one contour is made to deform its shape while the other contour is kept static for the coronal holes detection purpose. The experiment has been carried out on few benchmark datasets and the corresponding outcomes have been compared with the results of other existing algorithms. The comparison results highlight the performance of the proposed technique in detection of coronal holes in solar disk.

Understanding the deflection of coronal mass ejections (CMEs) is of great interest to the space weather community because of their implications for improving the prediction of CME. This paper aims to shed light into the effects of the coronal magnetic field environment on CME trajectories. We analyze the influence of the magnetic environment on the early development of a particular CME event. On 2011 January 24 an eruptive filament was ejected in association with a CME that suffered a large deflection from its source region and expected trajectory. We characterize the 3D evolution of the prominence material using the tie-pointing/triangulation reconstruction technique on EUV and white-light images. To estimate the coordinates in 3D space of the apex of the CME we use a forward-modeling technique that reproduces the large-scale structure of the flux rope-like CME, the Graduated Cylindrical Shell model. We found that the deflection amounts to 42 ° in latitude and 20 ° in longitude and that most of it occurs at altitudes below 4 R ⊙ . Moreover, we found a non-negligible deflection at higher altitudes. Combining images of different wavelengths with the extrapolated magnetic field obtained from a potential field source surface model we confirm the presence of two magnetic structures near the erupting event. The magnetic field environment suggests that field lines from the southern coronal hole act as a magnetic wall that produces the large latitudinal deflection; while a nearby pseudostreamer and a northward extension of the southern coronal hole may be responsible for the eastward deflection of the CME.

We discuss elemental abundances of noble gases in targets exposed to the solar wind (SW) onboard the “Genesis” mission during the three different SW “regimes”: “Slow” (interstream, IS) wind, “Fast” (coronal hole, CH) wind and solar wind related to coronal mass ejections (CME). To this end we first present new Ar, Kr, and Xe elemental abundance data in Si targets sampling the different regimes. We also discuss He, Ne, and Ar elemental and isotopic abundances obtained on Genesis regime targets partly published previously. Average Kr/Ar ratios for all three regimes are identical to each other within their uncertainties of about 1% with one exception: the Fast SW has a 12% lower Xe/Ar ratio than do the other two regimes. In contrast, the He/Ar and Ne/Ar ratios in the CME targets are higher by more than 20% and 10%, respectively, than the corresponding Fast and Slow SW values, which among themselves vary by no more than 2–4%. Earlier observations on lunar samples and Genesis targets sampling bulk SW wind had shown that Xe, with a first ionisation potential (FIP) of ∼12 eV, is enriched by about a factor of two in the bulk solar wind over Ar and Kr compared to photospheric abundances, similar to many “low FIP” elements with a FIP less than ∼10 eV. This behaviour of the “high FIP” element Xe was not easily explained, also because it has a Coulomb drag factor suggesting a relatively inefficient feeding into the SW acceleration region and hence a depletion relative to other high FIP elements such as Kr and Ar. The about 12% lower enrichment of Xe in Genesis’ Fast SW regime observed here is, however, in line with the hypothesis that the depletion of Xe in the SW due to the Coulomb drag effect is overcompensated as a result of the relatively short ionisation time of Xe in the ion-neutral separation region in the solar chromosphere. We will also discuss the rather surprising fact that He and Ne in CME targets are quite substantially enriched (by 20% and 10%, respectively) relative to the other solar wind regimes, but that this enrichment is not accompanied by an isotopic fractionation. The Ne isotopic data in CMEs are consistent with a previous hypothesis that isotopic fractionation in the solar wind is mass-dependent.

We studied the limb brightening of SOHO EIT daily images of the solar corona taken in 195 A wavelength line from 1996 to 2018. Using special software, we studied the distribution of the background intensity of the entire disk in the direction of rotation (horizontally) and perpendicular to the direction of rotation (vertical). The study shows that the intensity distribution from the center to the limb of the solar disk is not polar-symmetric. A data-derived study showed that the coronal limb brightening has rather elliptical than circular isophotes. The pattern of the limb brightening correlates with the cycle of solar activity. The moving average patterns with the window of the year give good results for removing the limb brightening when preparing coronal images for further study.

Rapid intensification of tropical storms is examined in the context of solar wind coupling to the magnetosphere-ionosphere-atmosphere system. Tropical cyclone “best tracks” in the southern and northern hemispheres are used in the superposed epoch analysis of time series of solar wind parameters. The results indicate that rapid intensification of tropical storms tends to follow arrivals of high-speed streams from coronal holes or interplanetary coronal mass ejections, which can trigger geomagnetic storms. The ensuing auroral and polar cap activity including ionospheric currents and ionospheric convection generates atmospheric gravity waves that propagate from the high-latitude lower thermosphere both upward and downward. If ducted in the lower atmosphere, they can reach tropical troposphere. Despite significantly reduced wave amplitudes, but subject to amplification upon reflection in the upper troposphere, these gravity waves can trigger/release moist instabilities to initiate convective bursts, with the latent heat release leading to intensification of storms. Convective bursts have been linked to rapid intensification of tropical cyclones. Cases of tropical cyclone intensification closely correlated with the solar wind structure are found to be preceded by atmospheric gravity waves generated by the solar wind magnetosphere-ionosphere-atmosphere coupling process. The gravity waves are observed in the ionosphere as traveling ionospheric disturbances. Their propagation in the lower atmosphere is examined by ray tracing in a model atmosphere to show that they can reach tropical cyclones. It is suggested that the interaction of aurorally-generated gravity waves with the tropical cyclone vortex and the inner primary eyewall could play a role in the intensification process. Assuming that quasi-periodic convective bursts lead to vortex waves, a two-dimensional barotropic approximation is used to obtain asymptotic solutions representing propagation of vortex waves and their absorption by the mean flow in the critical layer.

In this paper, we compare Forbush decreases associated with solar wind disturbances from two types of solar sources: coronal mass ejections (sporadic Forbush decreases) and coronal holes (recurrent Forbush decreases). We used Forbush Effects and Interplanetary Disturbances database created and maintained by IZMIRAN and associated a certain amount of Forbush decreases in this database with interplanetary disturbances from coronal mass ejections (207 cases) as well as high speed streams from coronal holes (350 cases). Large number of events allows to apply statistical methods (distribution analysis, correlation analysis, multiple linear regression analysis) to compare those two groups of events. The results reveal that Forbush decreases associated with solar wind disturbances from the two types of solar sources differ significantly in their statistical characteristics: distributions, descriptive statistics, correlation and multiple regression coefficients.

We statistically study the geoeffectiveness of two types of compression regions: corotating interaction regions (CIRs) before the solar wind high-speed streams (HSSs) from the coronal holes and Sheaths before the fast interplanetary CMEs (ICMEs) including flux-rope magnetic clouds (MCs) and non-MC Ejecta using the OMNI dataset ( http://omniweb.gsfc.nasa.gov (King and Papitashvili, 2004)) and our Catalog of large-scale solar wind phenomena for 1976–2000 ( ftp://ftp.iki.rssi.ru/pub/omni/ (Yermolaev et al., 2009)). Our analysis shows that the magnitude of the interplanetary magnetic field B in CIRs and Sheaths increases with increasing speed of both types of pistons: HSS and ICME; the increase of the piston speed results in the increase of geoeffectiveness of both compression regions. The value B in Sheaths before Ejecta is higher than B in Ejecta. The value B in Sheaths before MCs in the beginning of phenomena interval is lower than in MCs but in the end of interval it is close to B in MCs. The contribution of Sheath in storm generation can be significant for so-called "CME-induced" storms and Sheath-induced storms should be identified and analyzed separately.

Correlations of solar and ionospheric activity are investigated during the long-lived coronal mega-hole (CMH) for 24 solar rotations at the decline phase of SC24 from June, 2015, to March, 2017. Pch index (Luo et al., 2008) which is a function of the intensity in the central area developed for forecasting of daily solar wind speed (Vsw) is used as characteristic of efficiency of CMH. The solar activity indices Pch, SSN2, F10.7, Lyman-α, MgII, Vsw, and the ionospheric indices – global electron content GEC and global noon TECgn index averaged from data of 288 IGS observatories are analyzed. Sporadic disturbances in solar and ionospheric data are smoothed by the time-weighted exponential accumulation of their history with the persistence factor τ (0 ≤τ

We study relative geoeffectiveness of the high-speed streams (HSS) coming from different sources on the Sun, identified from 16 years (1996–2011) of continuous plasma and field data. These HSS could be associated to a single coronal hole, multiple coronal holes, single coronal mass ejection, multiple coronal mass ejections, or both the coronal holes and the coronal mass ejections. We analyze the solar wind plasma and field data during the passage of the HSS, and study the relative importance of different parameters in influencing the geomagnetic activity. We apply the method of superposed epoch analysis on the geomagnetic as well as solar plasma and field data. Based on our analysis, we found that the average (Dst)min is lowest (∼20 nT) due to streams from single coronal hole and multiple coronal holes, and it is comparatively higher (∼25 nT) due to compound streams. However, as compared to single coronal hole, the (Dst)min is nearly twice (∼40 nT) and thrice (∼65 nT) due to single coronal mass ejection and multiple coronal mass ejections, respectively. We found differences in not only the magnitudes but also the time profiles and recovery characteristics of geomagnetic disturbances due to the HSS from different solar sources. We performed correlation analysis between (Dst)min and the amplitudes of various plasma/field parameters, separately, due to the HSS associated with different solar sources. We found that, during the passage of all five group of streams, the (−Bz) and/or Ey is best correlated with the Dst amplitude. However, comparatively, the relationship between the amplitudes of (−Bz) and (−Dst) is weakest (cc = 0.71) during the passage of multiple coronal holes associated stream, and the relation is strongest (cc = 0.89) during the passage of single CMEs. As regards the relationship between (Ey) and (−Dst) amplitudes, it is weakest (cc = −0.71) during multiple coronal associated streams and strongest (cc = −0.91) during streams due to multiple coronal mass ejections.

We have studied the characteristics of large kinetic energy coronal mass ejections (LE-CMEs) (kinetic energy ≥1E + 31 ergs) observed between the time period years 1996–2015. During the study period, total 1250 CMEs occurred, which have their kinetic energy ≥1E + 31 ergs. Out of these 1250 events; only 314 events have proper acceleration, mass, kinetic energy and velocity, so other events are left out due to uncertainty or non availability of data. Out of 314 LE-CMEs there are 207 LE-CMEs those are not associated with solar flare events. Only 107 LE-CME events are associated with flares on solar disc. Our study shows that the average and the median linear speed of 314 LE-CMEs events are 835 km/s and 817 km/s, respectively. There are 197 LE-CMEs those are halo but we left out them from our study because of uncertainty in mass and energy. The angular widths of LE-CMEs for selected data set are less than ≤120° with a mean value of angular width as 84°. The mean value of mass and kinetic energy of LE-CMEs is 8.96E + 15 g and 2.38E + 31 ergs, respectively. The mean value of acceleration of large kinetic energy CMEs is 0.84 m/s2. It is also found that most of the events are biased towards acceleration that shows that large kinetic energy CMEs accelerate in general. The study also shows that 107 large kinetic energy CMEs associated with flares occurred when there is coronal holes (CH) in the nearby area and the mean distance between CMEs/ flares and the boundary of a coronal hole (CH) is 24°. We also find that mass and kinetic energy of CMEs do not depend on the location of CME and associated flare on the solar disc. It is also found that it is not necessary that energetic flares should associate with LE-CMEs.

This article reports on an investigation of the effect of interplanetary coronal mass ejections (ICMEs) on the transport and delivery of nano-dust to 1 AU. Charged nanometer-sized dust particles are expected to be generated close to the Sun and interact strongly with the solar wind as well as solar transient events. Nano-dust generated outside of ∼0.2 AU are picked up and transported away from the Sun due to the electromagnetic forces exerted by the solar wind. A numerical model has been developed to calculate the trajectories of nano-dust through their interaction with the solar wind and explore the potential for their detection near Earth's orbit (Juhasz and Horanyi, 2013). Here, we extend the model to include the interaction with interplanetary coronal mass ejections. We report that ICMEs can greatly alter nano-dust trajectories, their transport to 1 AU, and their distribution near Earth's orbit. The smallest nano-dust (

Rotation of coronal holes is studied using data from SDO/AIA for 2014 and 2015. A new approach to the treatment of data is applied. Instead of calculated average angular velocities of each coronal hole centroid and then grouping them in latitudinal bins for calculating average rotation rates of corresponding latitudes, we compiled instant rotation rates of centroids and their corresponding heliographic coordinates in one matrix for further processing. Even unfiltered data showed clear differential nature of rotation of coronal holes. We studied possible reasons for distortion of data by the limb effects to eliminate some discrepancies at high latitudes caused by the high order of scattering of data in that region. A study of the longitudinal distribution of angular velocities revealed the optimal longitudinal interval for the best result. We examined different methods of data filtering and realized that filtration using targeting on the local medians of data with a constant threshold is a more acceptable approach that is not biased towards a predefined notion of an expected result. The results showed a differential pattern of rotation of coronal holes.

The long term solar activity dependencies of ionospheric F1 and F2 regions’ critical frequencies ( f 0 F 1 and f 0 F 2 ) are analyzed for the last four solar cycles (1976–2015). We show that the ionospheric F1 and F2 regions have different solar activity dependencies in terms of the sunspot group (SG) numbers: F1 region critical frequency ( f 0 F 1 ) peaks at the same time with the small SG numbers, while the f 0 F 2 reaches its maximum at the same time with the large SG numbers, especially during the solar cycle 23. The observed differences in the sensitivity of ionospheric critical frequencies to sunspot group (SG) numbers provide a new insight into the solar activity effects on the ionosphere and space weather. While the F1 layer is influenced by the slow solar wind, which is largely associated with small SGs, the ionospheric F2 layer is more sensitive to Coronal Mass Ejections (CMEs) and fast solar winds, which are mainly produced by large SGs and coronal holes. The SG numbers maximize during of peak of the solar cycle and the number of coronal holes peaks during the sunspot declining phase. During solar minimum there are relatively less large SGs, hence reduced CME and flare activity. These results provide a new perspective for assessing how the different regions of the ionosphere respond to space weather effects.

We investigate the conditions under which the fluting ($m = 2$), $m = 3$, and $m = 12$ magnetohydrodynamic (MHD) modes in a uniformly twisted flux tube moving along its axis become unstable in order to model the Kelvin--Helmholtz (KH) instability in a twisting solar coronal hole jet near the northern pole of the Sun. Using a twisting jet of 2010 August 21 by \emph{SDO}/AIA and other observations of coronal jets we set the parameters of our theoretical model and have obtained that in a twisted magnetic flux tube of radius of $9.8$~Mm, at a density contrast of $0.474$ and fixed Alfv\'en Mach number of ${\cong}0.76$, for three MHD modes there exist instability windows whose width crucially depends upon the internal magnetic field twist. It is found that for the considered modes an azimuthal magnetic field of $1.3$--$1.4$~G (computed at the tube boundary) makes the width of the instability windows equal to zero, that is, it suppress the KH instability onset. On the other hand, the times for developing KH instability of the $m = 12$ MHD mode at instability wavelengths between $15$ and $12$~Mm turn out to be in the range of $1.9$ to $4.7$~minutes that is in agreement with the growth rates estimated from the temporal evolution of the observed unstable jet's blobs in their initial stage., Comment: 23 pages, 6 figures, 1 movie

In the present study we have investigated 426 DH Type II radio burst and associated CMEs events observed during the time period of 1997–2014. The starting frequency of most of associated DH type-II bursts (85%) lies in the range of 1–14 MHz (364 out of 426) with mean value of starting frequency is ∼11 MHz. The study of starting frequency (1–16 MHz) of DH type II bursts and heliocentric distance in solar radii indicate that DH type II radio bursts originate from 2.2–4.5 (RS) heliocentric distance in solar radii. We also found that the ∼ 48% DH Type II radio bursts associated CMEs are located between ± 40° of solar central disc and we also found that duration of DH type II radio bursts located at solar disc center are more than the duration of DH type II radio bursts located at solar limb. It is found that mean value for linear and initial speed of DH Type II associated CMEs are 1157 km/s and 1200 km/s, respectively. The CMEs speed are not correlated with duration of DH Type II radio bursts indicate that the durations of DH Type II radio bursts does not depend on speed of CMEs. The study also show that 426 DH type II radio bursts associated CMEs/flares occurred when there is coronal holes(CH) in nearby area and the mean distance between DH type II burst associated CMEs/ flares and boundary of coronal hole (CH) is 26°. The study also shows that there is no relation between drift velocity of DH type II radio bursts and speed of CMEs. The study also indicate that about 45% flares those associated DH Type II radio bursts have duration about 60 minutes and long duration DH Type II radio bursts are associated with X-class flares. We have also discussed that the results obtained in the present investigation in view of latest heliophysics interpretations.

A link between solar wind magnetic sector boundary (heliospheric current sheet) crossings by the Earth and the upper-level tropospheric vorticity was discovered in the 1970s. These results have been later confirmed but the proposed mechanisms remain controversial. Extratropical-cyclone tracks obtained from two meteorological reanalysis datasets are used in superposed epoch analysis of time series of solar wind plasma parameters and green coronal emission line intensity. The time series are keyed to times of maximum growth of explosively developing extratropical cyclones in the winter season. The new statistical evidence corroborates the previously published results (Prikryl et al., 2009). This evidence shows that explosive extratropical cyclones tend to occur after arrivals of solar wind disturbances such as high-speed solar wind streams from coronal holes when large amplitude magneto-hydrodynamic waves couple to the magnetosphere-ionosphere system. These MHD waves modulate Joule heating and/or Lorentz forcing of the high-latitude thermosphere generating medium-scale atmospheric gravity waves that propagate energy upward and downward from auroral zone through the atmosphere. At the tropospheric level, in spite of significantly reduced amplitudes, these gravity waves can provide a lift of unstable air to release the moist symmetric instability thus initiating slantwise convection and forming cloud/precipitation bands. The release of latent heat is known to provide energy for rapid development and intensification of extratropical cyclones.

Here we present study of Geomagnetic storms (GMS) and its relation with solar flares, coronal mass ejections (CMEs) and coronal holes (CHs). The arrival of CMEs in the vicinity of the Earth plays an important role and affects solar terrestrial environment. The space weather prediction about GMS can be only possible if we know the CMEs arrival time at 1 AU. In the present study we have investigated 153 CMEs observed during the time period of 1996–2009 to know the arrival times of CMEs associated with the GMS. In study we found that the strength of GMS didn׳t depend on the speed and accelerations of CMEs but strength of GMS depend on the importance of solar flares. We also found that the strength of GMS are excellently correlated with southward magnetic field near Earth at 1 AU and support earlier result of investigators. The arrival time of CMEs near Earth at 1 AU, can be calculated using equations for linear and initial speed of CMEs with error ±5 h. We have also discussed the various results obtained in present investigation in view recent scenario of solar helio-physics.

The monthly solar wind speed and density observed near 1 AU in IMF sectors of opposite magnetic polarity are studied during the minimum of sunspot cycles 23 and 24. During sunspot minima, the IMF is pointing away from the sun (Away sector) in the north of the Heliospheric Current Sheet (HCS) and pointing towards the sun (Toward sector) in the south of HCS during odd sunspot cycles and the same process is reversed during the even cycles. During this period, the solar wind plasma parameters (number density and speed) show a systematic month to month variation with solar wind number density decreases and velocity increases from equator to poles (heliomagnetic latitudinal organization) only in ‘Away’ IMF sectors compared to ‘Toward’ IMF sectors. This feature is particularly more evident for low speed solar wind and happens in a helio-hemisphere with a larger polar coronal hole. The association of the above phenomena with north–south asymmetry in coronal and solar wind flow characteristics will be discussed.

Results of analysis of the proxy of Coronal Hole (CH) Power index, Pch, combined with the high speed streams HSS of solar wind for a period from 2011 to 2019 are presented. It is found that the long-term variation of Pch index shows a trend of growing Pch towards the minimum of solar cycle while most of other identities of solar activity tend to diminish. Superposition of fast solar wind of CH origin with slow SW of CME's origin synchronized with SC explains increasing/decreasing solar wind speed Vsw at L1 point. Total 136 geo-effective Pch/HSS storms are selected with 4 criteria: (1) 3-day increment ΔPch ≥ 90 i.u. where ΔPch = Pch(1d_dmax) – Pch(-3d_dmin); (2) the Pch event is consistent with data of VizieR catalogue of CHs; (3) during 1–4 days after Pch(1d_dmax) the jump of HSS solar wind speed ΔVsw exceeds 50 km/s where ΔVsw = Vswmax(t0 + Δt) - Vswmin(t0) for running time window Δt ≤ 24 h; (4) index kp ≥ 3 occurs during 48 h after zero time t0. Example of moderate storm on 27–28 September 2019, is provided to illustrate Pch/HSS related storm. The superposed epoch analysis is applied to the solar wind speed Vsw, geomagnetic AE, AU, AL, aa, ap, kp, Dst indices and planetary ionosphere TEC-based Wp index during time t0-24 h ≤ t

The paper deals with the dynamics of the young Sun, physical conditions in the early Solar System and on the Earth. An extended interpretation of the faint young Sun paradox and its possible solutions are proposed. Various hypotheses are discussed including their advantages and disadvantages. The faint young Sun paradox follows from the Standard Solar Model with the conservation of mass condition. However, the mass of the Sun did not remain constant during its evolution. It was steadily decreasing, mainly in the first 2–2.5 billion years. But even with the most optimistic estimates, the uneven loss of mass during the evolution of our star is unable to fully compensate for the lack of luminosity reaching the surface of the early Earth. The primary biosphere had to search for alternative — e.g., radiation, chemical or geothermal — sources of energy. The prevalent configurations of solar magnetic fields also changed in the course of evolution, the strong quadrupole fields dominating at the early stages. At the age of about 2–2.5 billion years and the rotation period of about 15 days, the dipole magnetic field with large mass outflow from coronal holes begins to dominate, and the steady solar wind becomes the main mechanism of mass loss in the Sun in the following two billion years. The activity of the early Sun was much higher than it is today. The high-frequency (gamma-, X-ray, and UV) radiation, radio emission, coronal mass ejections, and solar cosmic rays exceeded the present-day values by 2–3 orders of magnitude. The article emphasizes the role of the dynamics of the young Sun, cosmic rays, magnetic field and other protective shells of the Earth as factors determining the occurrence, selection, and development of the first living systems.

Long-term variations in annual frequencies of occurrence of magnetic storms with sudden and gradual commencements were studied on the base of the data from IZMIRAN and Slutsk (Pavlovsk) magnetic observatories for the period 1878–2015. It was found that occurrences of strong and moderate magnetic storms with gradual commencements are characterized by a pronounced variability on the multidecadal time scale. Their wavelet spectra reveal strong periodicities of ~36 years (close to the climatic Bruckner cycle), as well as less pronounced ~60-year and ~90-year ones throughout the entire time interval under study. The occurrences of strong, moderate and weak magnetic storms with sudden commencements are characterized by dominating ~11-year periodicities, whereas long-term variations are substantially weaker. The obtained results provide evidence for a different temporal evolution of local and global solar magnetic fields responsible for solar agents (CMEs and high-speed solar wind streams from coronal holes) contributing to the development of these types of magnetic storms. The obtained results allow suggesting a possible contribution of solar/geomagnetic activity to the formation of climatic oscillations on the multidecadal time scale.

Images of the corona contain information over a wide range of spatial scales and various structures such as coronal holes, coronal loops, coronal mass ejections (CMEs), and helmet streamers with differences in brightness. Therefore, processing these images is important for determining various types of information. However, it is very difficult to elucidate the intricate structure of the corona because of the steep radial gradient in terms of brightness and the large differences in brightness within local areas of coronal images. In this study, we present a filter inspired by the normalizing-radial-graded filter, which we call the radial local multi-scale filter (RLMF). The RLMF method extracts radial vectors and performs local multi-scale filtering based on each vector, before normalizing the vector in order to enhance coronal images. This method facilitates the enhancement of large-scale structural characteristics and fine details in low contrast regions. To demonstrate the power of the RLMF, we applied the proposed method to Large Angle and Spectrometric Coronagraph C2 and K-Coronagraph observations. The RLMF method more clearly revealed the fine details of the corona and CMEs compared with the original observations.

A continuous experiment was carried out at the Ekaterinburg (EKB) stereoradar of the Russian segment of SuperDARN in order to examine the spatio-temporal characteristics of radar-detected magnetospheric ULF waves. The study of magnetospheric oscillations is based on analysis of scattering from field-aligned F-layer irregularities. Their E × B drift Doppler velocity at F-layer heights is associated with the background electric field in the ionosphere. During the experiment one of the radar channels operates in 0–2 beam scanning, with an integration time of 6 s, which corresponds to the total 18-s time resolution at each beam. This allows detecting magnetospheric ULF waves with periods of 40 s and up. Beam 0 is along the 132 magnetic meridian, so the registered velocity oscillations correspond to the wave electric field azimuthal component. Operation of the radar in this mode was started in December 2013. The first ULF wave events observed in the experiment and presented here occurred on 14 December 2013 and 2 January 2014 in the nightside magnetosphere during two geomagnetic disturbances classified as small magnetic storms and associated with high speed streams from coronal holes. Both the ULF events occurred after substorm-like auroral disturbances. The ULF waves observed during these events are classified as Pc5 geomagnetic pulsations. Two oscillation branches were observed, the higher and the lower frequency ones. As the azimuthal wave numbers m increase, the branches converge and merge into a single oscillation branch at some critical azimuthal wave number value m ⋆ . This ω ( m ) dependence is characteristic of the coupled Alfven and drift-compressional waves which according to theory merge if the azimuthal wave number exceeds some critical value. This merged single oscillation branch represents an unstable drift ballooning coupling mode. Thus, the following interpretation of the observed events can be suggested; at m m ⋆ the higher and lower frequency branches can be identified with the Alfven and drift-compressional modes, respectively, and at m > m ⋆ the single branch can be identified with the drift ballooning coupling mode.

There is strong statistical evidence that solar activity influences the Indian summer monsoon rainfall. To search for a physical link between the two, we consider the coupled cloud hydrodynamic equations, and derive an equation for the rate of precipitation that is similar to the equation of a forced harmonic oscillator, with cloud and rain water mixing ratios as forcing variables. Those internal forcing variables are parameterized in terms of the combined effect of external forcing as measured by sunspot and coronal hole activities with several well known solar periods (9, 13 and 27 days; 1.3, 5, 11 and 22 years). The equation is then numerically solved and the results show that the variability of the simulated rate of precipitation captures very well the actual variability of the Indian monsoon rainfall, yielding vital clues for a physical understanding that has so far eluded analyses based on statistical correlations alone. We also solved the precipitation equation by allowing for the effects of long-term variation of aerosols. We tentatively conclude that the net effects of aerosols variation are small, when compared to the solar factors, in terms of explaining the observed rainfall variability covering the full Indian monsoonal geographical domains.

The stability of a thin magnetic tube located at different depths of the convective zone has been studied numerically and analytically. Three spectral regions are shown to be responsible for different processes related to solar activity. Numerical simulation shows that Parker instability in the high frequency domain (wave number m > 20) may accelerate magnetic fibrils to emerge into the solar atmosphere at supersonic speed. Such a physical process may be responsible for impulsive CME generation.

With the advent and successful operation of the 1.6 m aperture New Solar Telescope of Big Bear Solar Observatory (BBSO/NST), solar observation has entered the era of high resolution better than 0.1”. This permits us to carry out the case studies of single coronal heating events, to provide the original high-resolution observational evidence for finally solving the problem of coronal heating. By combining the high-resolution Helium I 10830 A, TiO 7057 A, and Ha blue-wing (-0.7 A) imaging data from the NST with the imaging data of extreme ultraviolet and longitudinal magnetic field observed simultaneously by the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) on board of the Solar Dynamics Observatory (SDO), we have analyzed the evolution of magnetic field in two tiny dynamical events of coronal heating (brightening of magnetic loops) that originate from the solar intergranular lanes. It is found that the footpoints of both brightening magnetic loops were all located in the one side of nearby neutral line of magnetic fields, the footpoints of one magnetic loop were accompanied by the disappearance of a small longitudinal magnetic element and the newly formed connection between two granulations, while the footpoints of another magnetic loop were accompanied by a weak variation of longitudinal magnetic field and the breakdown of a granulation. The observed result tends to suggest that the low-temperature and high-temperature outflows were produced simultaneously by the magnetic reconnection occurred among the solar granulations in the low-layer atmosphere. Meanwhile, it is noted that the high-resolution and high-accuracy polarization measurement of photospheric magnetic field is crucial for finally solving the problem of coronal heating.

Recurrent high speed solar wind streams from coronal holes on the Sun are more frequent and Geoeffective during the declining phase of solar cycle which interact with the ambient solar wind leading the formation of Corotating Interaction Regions (CIRs) in the interplanetary medium. These CIR-High Speed Stream (HSS) structures of enhanced density and magnetic fields, when they impinge up on the Earth’s magnetosphere, can cause recurrent geomagnetic storms in the Geospace environment. In this study, we investigate the influence of two CIR-driven recurrent geomagnetic storms on the equatorial and low-latitude ionosphere in the context of the development of equatorial plasma bubbles over Indian and Asian longitudes. The results consistently indicate that prompt penetration of eastward electric fields into equatorial and low-latitudes under southward IMF Bz can occur even during the CIR-driven storms. Further, the penetration of eastward electric fields augments the evening pre-reversal enhancement and triggers the development of EPBs over wide longitudinal sectors where the local post-sunset hours coincide with the main phase of the storm. Similar results that are consistently observed during both the CIR-driven geomagnetic storms are reported and discussed in this paper.

We use high-cadence observations in the He ii 304 A line and a simple one-dimensional hydrodynamic model to reconstruct the evolution of the velocity field of 18 macrospicules. Besides, we study motions of their apparent summits and find them to follow parabolic trajectories, which correspond closely to the obtained velocity field. The trajectory decelerations typically range from 140 to 240 m/s2, and initial velocities from 80 to 145 km/s. Moreover, we find a clear linear dependence between these two values. We estimate that typically from 10 to 30% of the macrospicule's observed mass fade out of the spectral line.

We have studied conditions in interplanetary space, which can have an influence on galactic cosmic ray (CR) and climate change. In this connection the solar wind and interplanetary magnetic field parameters and cosmic ray variations have been compared with geomagnetic activity represented by the equatorial Dst index from the beginning 1965 to the end of 2012. Dst index is commonly used as the solar wind–magnetosphere–ionosphere interaction characteristic. The important drivers in interplanetary medium which have effect on cosmic rays as CMEs (coronal mass ejections) and CIRs (corotating interaction regions) undergo very strong changes during their propagation to the Earth. Because of this CMEs, coronal holes and the solar spot numbers (SSN) do not adequately reflect peculiarities concerned with the solar wind arrival to 1 AU. Therefore, the geomagnetic indices have some inestimable advantage as continuous series other the irregular solar wind measurements. We have compared the yearly average variations of Dst index and the solar wind parameters with cosmic ray data from Moscow, Climax, and Haleakala neutron monitors during the solar cycles 20–23. The descending phases of these solar cycles (CSs) had the long-lasting solar wind high speed streams occurred frequently and were the primary contributors to the recurrent Dst variations. They also had effects on cosmic rays variations. We show that long-term Dst variations in these solar cycles were correlated with the cosmic ray count rate and can be used for study of CR variations. Global temperature variations in connection with evolution of Dst index and CR variations is discussed.

In this paper we research the relationship between solar activity and the weather on Earth. This research is based on the assumption that every ejection of magnetic field energy and particles from the Sun (also known as Solar wind) has direct effects on the Earth’s weather. The impact of coronal holes and active regions on cold air advection (cold fronts, precipitation, and temperature decrease on the surface and higher layers) in the Belgrade region (Serbia) was analyzed. Some active regions and coronal holes appear to be in a geo-effective position nearly every 27 days, which is the duration of a solar rotation. A similar period of repetitiveness (27–29 days) of the passage of the cold front, and maximum and minimum temperatures measured at surface and at levels of 850 and 500 hPa were detected. We found that 10–12 days after Solar wind velocity starts significantly increasing, we could expect the passage of a cold front. After eight days, the maximum temperatures in the Belgrade region are measured, and it was found that their minimum values appear after 12–16 days. The maximum amount of precipitation occurs 14 days after Solar wind is observed. A recurring period of nearly 27 days of different phases of development for hurricanes Katrina, Rita and Wilma was found. This analysis confirmed that the intervals of time between two occurrences of some particular meteorological parameter correlate well with Solar wind and A index.

We studied coronal white-light jets in the polar regions of solar corona in 2009–2014. Jets were tracked on data producing by coronographs COR2/STEREO with the 2.5–16 solar radii field of view. We also considered their characteristics on solar cycle progress: jet occurrence rate of jets per year above the northern and southern poles, angular distributions and measured apparent velocities. The jet mean occurrence rate per year is 234 registered events. It is defined that both occurrence rate per year and the mean apparent velocities are increased to solar cycle maximum. This changes were shown to be different for the north and south polar regions and to depend on polar magnetic fields. The mean apparent velocities are increased by 1.7 times for north pole (from 134 ± 66 km/s to 229 ± 59 km/s) and by 2.4 times for south pole (from 101 ± 37 km/s to 243 ± 79 km/s). Most of the jets with velocities > 450 km/s was registered at the solar cycle maximum.

The area of coronal holes, located at solar latitudes of more than 60°, is compared with the evolution of the large-scale magnetic fields on the Sun’s surface. We found a decrease in the area of the coronal holes as well as growth of their low-latitude boundaries in connection with a reversal of the polar magnetic field.

Signs were looked for that would indicate a possible connection between plasma velocity oscillations observed in the region of solar coronal holes and magnetic field oscillations as recorded in the interplanetary medium. The problem appears to be quite important since the presence of large-scale ULF waves in the solar wind can increase geoeffectiveness of high speed streams in the interplanetary plasma. Observations of solar oscillations in the FeI 6569 A spectral line in a coronal hole were taken as a basis. The measurements were carried out at the Horizontal Automated Solar Telescope of the Sayan Solar Observatory. High speed solar wind stream ejected from the coronal hole reached the Earth's orbit after approximately 60 h. The spectra of solar oscillations were compared with those of ultra low frequency (ULF) oscillations of the interplanetary magnetic field (IMF) at libration point L1. The oscillations were recorded with the ACE magnetometer when the leading edge of the high speed stream, bringing increased ULF wave activity, reached the Earth. The spectra of solar oscillations had a sharp peak at about 3.4–3.6 mHz. The spectrum of the solar wind ULF oscillations is much more complex, being formed by different sources. Nevertheless, ULF oscillations of the IMF often had peaks that were close in frequency to those of the solar oscillations. Analysis of the ULF wave spectra observed in the 92 high speed streams confirmed the presence of 3- and 5-min oscillations in the total wave spectrum. It is emphasized that the results cannot be regarded as proving a direct connection between solar oscillations and ULF waves at the Earth's orbit even though they do support such a possibility. Additional research is needed involving IMF wave trajectory calculations.

We present results from the Chandra X-ray Observatory’s characterization of the X-ray emission from Comet 103P/Hartley 2, in support of NASA’s Deep Impact Extended close flyby of the comet on 04 November 2010. The comet was observed 4 times for a total on target time of ∼60 ks between the 17th of October and 16th of November 2010, with two of the visits occurring during the EPOXI close approach on 04 November and 05 November 2010. X-ray emission from 103P was qualitatively similar to that observed for collisionally thin Comets 2P/Encke (Lisse, C.M. et al. [2005]. Astrophys. J. 635, 1329–1347) and 9P/Tempel 1 (Lisse, C.M. et al. [2007]. Icarus 190, 391–405). Emission morphology offset sunward but asymmetrical from the nucleus and emission lines produced by charge exchange between highly stripped C, N, and O solar wind minor ions and coma neutral gas species were found. The comet was very under-luminous in the X-ray at all times, representing the 3rd faintest comet ever detected (LX = 1.1 ± 0.3 × 1014 erg s−1). The coma was collisionally thin to the solar wind at all times, allowing solar wind ions to flow into the inner coma and interact with the densest neutral coma gas. Localization of the X-ray emission in the regions of the major rotating gas jets was observed, consistent with the major source of cometary neutral gas species being icy coma dust particles. Variable spectral features due to changing solar wind flux densities and charge states were also seen. Modeling of the Chandra observations from the first three visits using observed gas production rates and ACE solar wind ion fluxes with a charge exchange mechanism for the emission is consistent with the temporal and spectral behavior expected for a slow, hot wind typical of low latitude emission from the solar corona interacting with the comet’s neutral coma. The X-ray emission during the 4th visit on 16 November 2010 is similar to the unusual behavior seen for Comet 17P/Holmes in 2007 (Christian, D.J. et al. [2010]. Astrophys. J. Suppl. 187, 447–459) as the solar wind became dominated by a less ionized and faster plasma, more typical of outflow from polar coronal hole regions. We postulate that the overall faintness of the comet seen during all visits is due to the unusually well mixed dust and gas content of this hyperactive comet’s coma producing Auger electrons rather than X-rays via charge exchange with the solar wind. An alternative possible explanation for the faintness of the comet’s X-ray emission, and its unusual high CV and unusually low CVI emission, is that the impinging solar wind was drastically slowed in the inner coma, below 150 km s−1, before charge exchanging with cometary neutrals.

The SOHO/MDI data provide the uniform time series of the synoptic magnetic maps which cover the period of the cycle 23 and the beginning of the cycle 24. It is very interesting period because of the long and deep solar minimum between the cycles 23 and 24. Synoptic structure of the solar magnetic field shows variability during solar cycles. It is known that the magnetic activity contributes to the solar irradiance. The axisymmetrical distribution of the magnetic flux ( Fig. 3 c) is closely associated with the ‘butterfly’ diagram in the EUV emission ( Benevolenskaya et al., 2001 ). And, also, the magnetic field ( B ∥ ) shows the non-uniform distributions of the solar activity with longitude, so-called ‘active zones’, and ‘coronal holes’ in the mid-latitude. Polar coronal holes are forming after the solar maxima and they persist during the solar minima. SOHO/EIT data in the emission of Fe XII (195 A) could be a proxy for the coronal holes tracking. The active longitudinal zones or active longitude exist due to the reappearance of the activity and it is clearly seen in the synoptic structure of the solar cycle. On the descending branch of the solar cycle 23 active zones are less pronounced comparing with previous cycles 20, 21 and 22. Moreover, the weak polar magnetic field precedes the long and deep solar minimum. In this paper we have discussed the development of solar cycles 23 and 24 in details.

While it is widely known that coronal mass ejections and their related solar wind features are significant drivers of activity with geospace it is less known that corotating interaction regions (CIRs) and the high speed stream (HSS) periods that precede them are also drivers of activity within geospace. The most recent extended and weak solar minimum interval has brought renewed attention to the space weather impacts of CIR+HSS periods since the highly structured and relatively stable coronal hole features on the Sun resulted in numerous CIR+HSS periods. In this paper we examine two Carrington Rotations (CRs) using the Coupled Magnetosphere Ionosphere Thermosphere (CMIT) model. CR2060 lasted from August 14, 2007 to September 11, 2007 and contained three CIR+HSS periods. CR2068, also known as the Whole Heliosphere Interval (WHI), began on March 20, 2008 and lasted until April 16, 2008 and contained two CIR+HSS periods. For each CR simulations driven by both L1 solar wind observations from the OMNI data set and L1 conditions extracted from CORHEL heliospheric simulations were conducted. The heliospheric simulation results capture the velocity and density structures seen in the solar wind well for CR2060 and only get one of the CIR+HSS periods in CR2068. In each CR the heliospheric simulations produce a much weaker IMF and have less temporal variability in all parameters. We compare the results of the CMIT simulations for each CR to observations of the cross polar cap potential (CPCP), hemispheric power (HP), and SYM H index including the computation of RMS and cross correlation error metrics. We examine the response of the thermospheric density during these intervals by utilizing data from the CHAMP satellite. In the magnetosphere we use magnetic field data from the GOES spacecraft to asses the different simulations ability to describe the distribution and intensity the ULF wave power. Our results show that the L1 driven simulations under-estimates the SYM H index and HP and over-estimates the CPCP. We believe that over estimation of the CPCP is directly linked to the low HP highlighting the need for an improved precipitation model within CMIT. The ULF power in the L1 simulations compares well with the observations, especially for the compressional component important in radiation belt energization processes. In all cases, the CMIT simulations driven by the heliospheric simulation results produce dramatically inferior predictions highlighting the importance of having good IMF predictions in heliospheric model results and possibly indicating the importance of having fluctuations in the solar wind.

In this paper, we have developed an improved model to build a self-consistent global structure on the source surface of 2.5 Rs covering four different phases of solar activity. This model involves the topological effect of the magnetic field expansion factor f(s) and the minimum angular distance theta(b) (at the photosphere) between an open field foot point and its nearest coronal hole boundary. The purpose of this effect is to separate the open field area and the close field area more effectively. The model uses as input for 136 Carrington Rotations (CRs) covering four different phases of solar activity: (1) an empirical model of the magnetic field topology on the source surface using Line-of-sight (los) photospheric field (B-los) measurements by Wilcox Solar Observatory (WSO): and (2) an empirically derived global coronal density distribution using K coronal polarized brightness (pB) by MKIII in High Altitude Observator (HAO). The solar wind speed on the source surface is specified by the function of both f(s) and theta(b), which are obtained by the magnetic field data. Then the coronal mass outputs are analyzed and the self-consistent global distribution on the source surface is numerically studied for the four different phases. Finally, the model estimates the solar wind speed at 1 AU as a simple function of the speed on the source surface. Our numerical results indicate reasonable semi-quantitative agreement with observations at different phases of solar activity. (C) 2011 Elsevier Ltd. All rights reserved.

Coronal hole jets are fast ejections of plasma occurring within coronal holes, observed at Extreme-UltraViolet (EUV) and X-ray wavelengths. Recent observations of jets by the STEREO and Hinode missions show that they are transient phenomena which occur at much higher rates than large-scale impulsive phenomena like flares and Coronal Mass Ejections (CMEs). In this paper we describe some typical characteristics of coronal jets observed by the SECCHI instruments of STEREO spacecraft. We show an example of 3D reconstruction of the helical structure for a south pole jet, and present how the angular distribution of the jet position angles changes from the Extreme-UltraViolet-Imager (EUVI) field of view to the CORonagraph1 (COR1) (height similar to 2.0 R(circle dot) heliocentric distance) field of view. Then we discuss a preliminary temperature determination for the jet plasma by using the filter ratio method at 171 and 195 angstrom and applying a technique for subtracting the EUV background radiation. The results show that jets are characterized by electron temperatures ranging between 0.8 and 1.3 MK. We present the thermal structure of the jet as temperature maps and we describe its thermal evolution. (C) 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. Advances in Space Research

We report on the development and current status of the Brazilian Decimetric Array (BDA), which will play a vital role in filling the existing gaps in imaging the Sun at decimetric wavelengths. The BDA will operate in the following radio bands: 1.2–1.7, 2.8, and 5.6 GHz with high spatial and temporal resolutions. BDA can observe flares and coronal mass ejections (CMEs) in a spectral range poorly covered in the past, thus providing important information to space weather science. The smallest baseline of 9 m employed by the BDA combined with high sensitivity will readily identify large-scale structures such as coronal holes and provide information on wave flows from them. New methods are being developed to analyze the solar-disk data with high time resolution by using tomographic and spatial PWF techniques that can readily identify coronal holes in their initial stage. Efforts are also being made to analyze the BDA data in real time in conjunction with SOHO data for a better understanding of CMEs and coronal holes. This paper provides a brief description of the BDA, and the new techniques of data analysis.

We analyze the large-scale dynamical forms of three erupting prominences (filaments) observed by at least one of the two STEREO spacecraft and which reveal evidence of sideways rolling motion beginning at the crest of the erupting filament. We find that all three events were also highly non-radial and occurred adjacent to large coronal holes. For each event, the rolling motion and the average non-radial outward motion of the erupting filament and associated CME were away from a neighboring coronal hole. The location of each coronal hole was adjacent to the outer boundary of the arcade of loops overlying the filaments. The erupting filaments were all more non-radial than the CMEs but in the same general direction. From these associations, we make the hypothesis that the degree of the roll effect depends on the level of force imbalances inside the filament arcade related to the coronal hole and the relative amount of magnetic flux on each side of the filament, while the non-radial motion of the CME is related to global magnetic configuration force imbalances. Our analyses of the prominence eruption best observed from both STEREO-A and STEREO-B shows that its spine retained the thin ribbon-like topology that it had prior to the eruption. This topology allows bending, rolling, and twisting during the early phase of the eruption.

Long-term forecast of space weather allows in achieving a longer lead time for taking the necessary precautions against disturbances. Hence, there is a need for long-term forecasting of space weather. We studied the possibility for a long-term forecast of recurrent geomagnetic storms. Geomagnetic storms recur with an approximate 27-day period during the declining phase of a solar cycle. These disturbances are caused by the passage of corotating interaction regions, which are formed by interactions between the background slow-speed solar wind and high-speed solar wind streams from a coronal hole. In this study, we report on the performance of 27-day-ahead forecasts of the recurrent geomagnetic disturbances using Kp index. The methods of the forecasts are on the basis of persistence, autoregressive model, and categorical forecast using occurrence probability. The forecasts show better performance during the declining phase of a solar cycle than other phases. The categorical forecast shows the probability of detection (POD) more than 0.5 during the declining phase. Transition of the performance occurs sharply among the declining phases and other phases.

In the absence of solar activity, Co-rotating Interaction Regions (CIRs) are a prevailing source of energetic ions observed near 1 AU. The combination of observations by near-Earth space observatories and the twin STEREO spacecraft offers an excellent platform for multi-point studies of CIRs. The analysis of CIR events during Carrington rotations 2067–2082 provides evidence that CIR-associated energetic ions frequently show significant differences, particularly at sub-MeV energies. We found discrepancies in the structures observed by different spacecraft which cannot always be attributed to the latitudinal separation or to changes in the coronal hole which generates the high-speed stream. We present several cases where these differences are linked to the presence of Interplanetary Coronal Mass Ejections (ICMEs) or small-scale interplanetary transients in the vicinity of or embedded within the CIR. Evidence of the possible role of ICME-CIR interactions as sources of temporal variations in the CIR-associated ion increases are presented and discussed.

The outer radiation belt shows solar cycle variation: the L-shell of the electron flux peak in the outer belt shifts inward during the period between the rising phase and the solar maximum, while it shifts outward between the beginning of the declining phase and the solar minimum. We show a possible mechanism which considers two typical types of magnetic storms categorized in accordance with solar wind drivers, namely coronal mass ejections (CMEs) and corotating interaction regions (CIRs). Large flux enhancements at the inner portion of the outer belt tend to occur during the recovery phase of great storms driven by CMEs, while large flux enhancements at the outer portion and at geosynchronous orbit tend to occur during the recovery phase of relatively moderate storms driven by CIRs. High-speed coronal hole streams which do not always cause large magnetic storms also effectively enhance the electron flux enhancement at the outer portion and in geosynchronous orbit. In this framework, the plasmapause always plays an important role in both flux enhancement and flux loss in the outer belt. The average plasmapause position depends on the storm amplitude, and the plasmapause reaches closest to the Earth during great storms driven by CMEs. CMEs themselves and CME-driven storms occur during maximum periods of solar activity, while CIRs themselves and CIR-driven storms occur during the solar declining phase. The observed long-term variations of the outer belt can therefore be understood in terms of their dependence on the large-scale interplanetary structures, varying depending on the phase of the solar cycle.

In order to learn the nature of coronal holes for a long period, magnetic disturbances represented by the geomagnetic index C9 (though proxy for coronal holes) for the period from 1884 to 2002 are examined, selecting only those that recur every 27 days during at least six solar rotation periods and separating the rising and declining phases, and also distinguishing one and two coronal holes in one solar rotation. It was found that the occurrence of coronal holes per year (N) during both the rising and the declining phases tends to be more frequent for greater numbers of the peak value of sunspots (R) in each sunspot cycle. The frequency per year is about twice as large for the declining phase as for the rising phase. The N–R relationship is 0.0080R+0.302 for the rising phase and 0.0152R+0.203 for the declining phase.

Coronal hole (CH) and the quiet Sun (QS) are considered to account for sources of fast and slow solar wind streams, respectively. The differences between the solar wind streams flowing out from the CH and the QS are thought to be related with different plasma generation and acceleration mechanisms in the respective source regions. Here we review recent studies on the solar wind origin in the CH and the QS, compare the possible flow geometries and magnetic structures in these two kinds of solar regions, and summarize the physics associated with two different origin scenarios.

The differential rotation of the solar corona has been analyzed using as the input data the brightness of the coronal green line Fe xiv 530.3 nm for more than five activity cycles. It is found that the character of rotation of the solar corona changes during the activity cycle. Approximately at the middle of the descending branch the differential rotation is weakly pronounced, while the greatest differential gradient is observed at the ascending branch and, occasionally, at the maximum of the cycle. An explanation of this difference has been suggested. The total rotation rate of the corona can be represented as a superposition of two rotation modes (components) – the fast and slow ones. The synodic period of the fast mode near the equator is about 27 days, increasing slightly with latitude. The synodic period of the slow mode exceeds 30 days. The changing relative fraction of these two modes results in variation of the latitude dependence of the observed rotation rate during the activity cycle. The characteristics of two principal types of differential rotation of the solar corona have been determined. The first type consists of the fast mode alone and is established approximately at the middle of the descending branch of the cycle. The second type is the sum of both modes with the fast mode dominating at low latitudes and the slow mode at high latitudes. The results obtained can be used for in-depth study of interaction of the velocity field and dynamo mechanism in the Sun and stars.

We assess the contributions of various types of solar wind structures (transients, coronal hole high-speed streams (HSS), and slow-speed wind) to hourly average auroral electron power ( P e ). The time variation of the solar wind velocity ( V sw ) and P e are determined by HSS, which contribute ∼47% to P e and V sw . Transients contribute ∼42% of P e in solar maxima, and ∼6% in solar minimum. Cross-correlations of P e with V sw |B| for negative B z are significant. P e exhibits solar rotational periodicities similar to those for V sw , with strong 7- and 9-day periodicities in 2005–2008 and equinox semiannual periodicities in 1995–1999.

Coronal holes produce high speed solar wind streams (HSS) that subsequently interact with the slower downstream solar wind forming co-rotating interaction regions (CIRs). The CIR/HSS combination drives geomagnetic storms that have a weak to moderate signature in D st . We simulate the behavior of relativistic (976 keV) electrons in the outer radiation belt and the slot region ( 2 ⩽ L ⩽ 7 ) during three CIR-driven storms associated with three consecutive rotations of a coronal hole that occurred just after solar maximum during June–August 1991. We use a 1d radial diffusion model (RADICAL) with losses due to pitch-angle scattering by plasmaspheric hiss. The losses are expressed through the electron lifetime calculated using the PADIE code driven by a global K p -dependent model of plasmaspheric hiss intensity and f pe / f ce . The outer boundary condition is time and energy-dependent and derived from observations. The model reproduces the observed flux at L = 5 to within about a factor of 3 suggesting that flux levels are well-described by radial diffusion to and from the outer boundary. At L = 3.5 and 4, the model overestimates the flux decay rates. This results in the observed flux exceeding the model flux, by up to a factor of 5 at L = 4 and by up to a factor of 8 at L = 3.5 , by the end of the recovery phase. Comparison with model results from a geomagnetically quieter interval suggest that the underestimation in flux may be due to the lack of representation of local wave acceleration in the model.

Solar corona is the outermost part of the solar atmosphere. Coronal activities influence space environment between the Sun and the Earth, space weather and the Earth itself. The total solar eclipse (TSE) is the best opportunity to observe the solar corona on ground. During the TSE 2008, a series of images of the corona and partial eclipse of solar disk were obtained using telescope and CCD camera. After image processing, preliminary results of coronal structure are given, and radial brightness profiles of the corona in directions of pole and equator of the Sun are measured. Though in solar activity minimum, the shape and structure of the corona are not symmetry. The equatorial regions are more extent than the polar one, and there are also larger differences between the east and west equatorial regions and between the south and north polar regions. Coronal streamers on east side of the equator, particularly the largest one in east-south direction, are very obvious. The coronal plume in south polar region consists of more polar rays than that in north polar region. These structures are also shown in other observations and data of SOHO. The radial brightness profiles in directions of pole and equator are similar to those of the Van de Hulst model in solar minimum, but there are a few differences due to coronal activity, which is shown in the isophote map of the corona.

In the present study the occurrence of an unusual class of low amplitude anisotropic wave trains in the cosmic ray neutron intensity, which is distinctly different from the average diurnal variation as well as from other recognized types of low amplitude anisotropic wave trains are noted and the directional distribution in the interplanetary space determined. The major objective of this paper is to study the first three harmonics of low amplitude anisotropic wave trains of cosmic ray intensity over the period 1981–1994 for Deep River neutron monitoring station. The significant characteristic of these events is that the low amplitude wave trains shows a maximum intensity of diurnal component in a direction earlier than 18:00 h/co-rotational direction. It is noticed that these events are not caused either by the high-speed solar wind streams or by the sources on the Sun responsible for producing these streams such as polar coronal holes. However the possibility of occurrence of these events during high-speed solar wind streams cannot be denied. The occurrence of low amplitude events is dominant for positive polarity of Bz. The disturbance storm time index i.e. Dst, remains consistently negative only for majority of the low amplitude wave train events, which is never been reported earlier. The amplitude as well as direction of first two harmonics seems to remain unaffected with the variation in the Dst and Ap-index. However, the amplitude as well as direction of third harmonic found to deviates with the increase of Dst and Ap-index. The corotating streams produce significant deviations in cosmic ray intensity as well as in solar wind speed during low amplitude anisotropic wave train events.