Period Of Solar Cycle Research Articles

Electron Bulk Surface Density Variability in Ionosphere during Quiet Days at Low Latitudes

This work deals with electron surface density time variation in ionosphere region. The study uses international reference ionosphere (IRI) model for investigation. Total Electron Content (TEC) parameter is carried out at different levels in the F2-layer of ionosphere. The study takes place at Ouagadougou station (12,4°N and 358,5°E), in West Africa. Quiet time periods of solar cycle 22 are considered. This study considers only the maximum and minimum phases of solar cycle 22. The five quietest days of the characteristic months in each season are used in the study. Seasonal time profiles of ionosphere parameters highlight relation between Total Electron Content (TEC) and Height of F2-layer (hmF2) in ionosphere region. The results found in this study correlate closely with parameters behavior previously found in other works.

Evaluation of ionospheric models for Central and South Americas

This work shows a 20-month statistical evaluation of different Total Electron Content (TEC) estimators for the Central and South America regions. The TEC provided by the International GNSS Service (IGS) in the area covered around the monitoring GNSS stations are used as reference values, and they are compared to TEC estimates from the physics-based (Sheffield University Plasmasphere Ionosphere Model—PIM) and the empirical (Neustrelitz TEC Model-Global—NTCM-GL) models. The mean TEC values show strong dependence on both solar activity and seasonal variation. A clear response was noticed for a period close to 27 days due to the mean solar rotation, as seen in the solar flux measurements. Consistently, the mean TEC values present an annual variation with maxima during December solstices for southern stations with geographic latitudes greater than 25° S. Semi-annual dependence has been observed in TEC for the sector between ±25° of geographical latitude but with modulations caused by fluctuation in the solar radiation. We observed a high correlation between solar radio flux F10.7 and NTCM-GL outputs. The fast increases in F10.7 index have caused significant differences between IGS data and NTCM-GL results mainly for equatorial and low latitudes. For the initial months of the evaluated period (January–April, 2016), the errors of the physics-based model were considerably larger, mainly near the equatorial ionization anomaly. The discrepancies observed in SUPIM results are mainly due to inputs of solar EUV flux. The EUVAC model has underestimated EUV flux between January and April, 2016, when the solar activity was moderated and Solar2000 model has overestimated such flux during low solar cycle period between May and August, 2017. In relation to IGS data, the two assessed models presented smaller differences during the June solstice season of 2016.

Variations of Energetic Electron Fluxes in the Ionosphere during Periods of Solar Cycles

Energetic electrons (with energies of 10 to 1000 keV) from the Earth’s radiation belt (ERB) play an important role in the processes associated with the ionization of the upper atmosphere and ionosphere from the equator to high latitudes. The main sources and properties of energetic electrons at the altitudes of the ionosphere of up to 1000 km are considered. At high latitudes (more than 50°), precipitations from the outer belt are the sources of such electrons. At low latitudes, intensive fluxes of electrons appear as a result of their injection from the inner ERB. The analysis of the solar-cyclic variation of energetic electron fluxes during two solar cycles in the period from 1998 to 2018 is performed. It is shown that the maximum electron fluxes are most often observed at the declining phases of solar activity (SA), which is associated with the contribution from the recurrent geomagnetic activity. The lowest fluxes are found in the deep minimum of the SA of 2009. As a result, the energetic electron fluxes during the current, 24th, solar cycle are found to be weaker than those in the previous cycle. In addition, an anomalous shift of the position of the maximum of the outer ERB to the equator by 4° (which is equivalent to a distance of 400 km) which is not predicted by the standard model is observed over Siberia. Apparently, this is associated with an acceleration of the change in the geomagnetic field in this region.

A solar electron event model in near-Earth space

A new solar electron event model is developed based on Virtual Timeline Method (VTM). We study events individually by analyzing the 17-year data of 3DP instrument on WIND spacecraft. This model is established in different solar cycle phases and is based on statistics of duration, fluence, and waiting time of solar electron events. The fluences follow a log-normal distribution and logarithmic durations fit well with logarithmic fluences linearly. We prove that waiting times of events significantly deviates from the Poisson process by investigating the stationary and event independence property of Poisson distribution. After a comparison study on waiting times, we choose the Lévy distribution in solar minimum and maximum years. During solar minimum, the event frequency is much lower than that of solar maximum, but the event magnitude is independent of solar cycle period. Large events also happen in solar minimum years. In different solar cycle phases, this model can output a spectrum with confidence level and mission duration by generating many series of virtual timelines composed of many pseudo-events based on Monte Carlo method. On the other hand, spectra in solar minimum years are softer than that in solar maximum years. The fluences in solar maximum years are about one order of magnitude higher than that in solar minimum years in a given mission period. We also compare this model with Interplanetary Electron Model (IEM) quantitatively and prove that this model is advanced.

Variation of ionospheric range errors for L1 frequency GPS users during the 23rd solar cycle over BAHR IGS station

Errors induced by the ionosphere on global navigation satellite systems (GNSS) signal propagation significantly affect the positioning calculation done by ground receivers. These ionospheric errors may end up reaching tens of meters in the final positioning calculation. In this study, the ionospheric range error (IRE) was monitored over the local ionosphere of BAHR, Bahrain (26.209N, 50.608E) during the period of the 23rd solar cycle. IRE values were obtained through observation data derived from RINEX files and compared with NeQuick 2 (NQ2) model calculations. It was found that, for the region of study, NQ2 overestimated the total electron content (TEC) values as compared to observation data, resulting in higher IRE values of up to 12 m. However, IRE derived using GNSS observations and NQ2 follow similar trends over the course of the solar cycle. IRE values were also compared to the smoothed sunspot number (SSN) and F10.7 indexes which resulted in significant correlation between the seasonal calculation of IRE and solar activity. Throughout the 23rd solar cycle, the highest IRE values were found during the equinoxes and the lowest during solstices. The largest IRE value was observed in the vernal equinox of 2000 (19.13 m), while the lowest IRE value was observed in the winter solstice of 1998 (0.276 m).

Equatorial and low-latitude positive ionospheric phases due to moderate geomagnetic storm during high solar activity in January 2013

The day-to-day variability of the equatorial and low-latitude ionosphere during quiet and disturbed periods is one of the ionospheric highlighted Space Weather research topics, particularly the ionospheric electrodynamics during geomagnetic storms. This study investigates the response of ionospheric F-region from the equatorial region to beyond the Equatorial Ionization Anomaly (EIA) crest during moderate geomagnetic storm (minimum Dst = −53 nT) that took place on January 17 to 18, 2013, during the high solar activity period of solar cycle 24. The Total Electron Content (TEC) obtained through a network of 82 dual frequency GPS receivers, spanning over an area of 30° × 30° in latitude and longitude are used. Also the F-layer virtual height (h’F) and critical frequency (foF2) observations from 3 ionosondes, in the South American sector are used. Specifically, these GPS-TEC receivers and ionosondes are used to investigate how the F-layer was disturbed by two positive ionospheric phases occurred during the aforementioned disturbed period. The first positive ionospheric phase was probably due to a travelling ionospheric disturbance (TID). When this TID reached the Brazilian coast at low-latitude, the EIA crest was in the growth phase and makes it challenging to separate the spatial-temporal evolution of both phenomena. The second positive ionospheric phase was caused by an anomalous nighttime equatorial positive ionospheric cloud travelling from the east sector towards the west sector. In addition, how the EIA was disturbed by these two positive ionospheric phases in the eastern and western Brazilian sectors is also investigated.

Analysis of pre-telescopic sunspots and auroras from 8th to 16th century

In this paper, we use non-parametric kernel approach to estimate the probability density function (pdf) of auroral-night and naked-eye-sunspot series over multi-century timescale. We selected the events observed in medieval epoch, and auroral records from low geographical latitude (<45°). These astronomical phenomena are recorded mainly in the Oriental historical sources and much less in Occidental sources. The collected events are published in many recent catalogues. The density function are calculated using the Gaussian kernel, including 95% CI obtained by bootstrapping.Results confirm the existence of strong connection between auroras and sunspot activity, especially from 11th to 16th century. Indeed, a high correlation degree r = 0.72 is obtained for the period AD 800–1500 between the two pdf of sunspots (pdfS) and auroras (pdfA) for bandwidth h = 10 years, and exceed 0.8 for h > 43 years. However, we notice a time-shift between the two density functions. To calculate it, we use the cross-correlation technique, and we find τ = −5.9 years, that is strangely close to the half of solar cycle period. It is very important to note that our results revealed that the high frequency of low latitude auroras occurs before the maximum of naked-eye sunspots activity, and not afterward, on contrary to what is expected.The pdf curves show multiple peaks occurring at quasi-periodic times and show clearly the three grand minima of solar activity: Oort, Wolf and Spörer. In auroral-night data, the mean period at 95% CI obtained is:T‾=61±7years. Using power spectrum analysis, we observe clearly a strong signal of 60 years period that is a new evidence of the existence of such cycle. More importantly, we identified a cycle of 262 years period in the sunspot data, and a new oscillation of 310 years in auroral-night data. These two cycles appear clearly in the pdf curves using optimized bandwidth obtained by the direct plug-in approach of Sheather and Jones.

The First Solar Flare Effect Observation at UiTM-SID Station during Solar Cycle 23-24

International Heliophysical Year (IHY; 2007-2009) has a remarkable impact on space and earth electromagnetism research and society. For Malaysian perspectives, it acts as a spiral point to the expanding of space weather-related research. The research activities involve installation of real-time Magnetic Data Acquisition System of Circum-pan Pacific Magnetometer Network, i.e. MAGDAS/CPMN for space weather study and application, which was deployed for the IHY; 2007-2009. In addition to MAGDAS system, to understand the characteristics of the lower ionospheric layer (60-150km) during space weather events, a Very Low Frequency (VLF) monitoring system has been developed. The MAGDAS and VLF monitoring system called UiTM-SID are located at Universiti Pendidikan Sultan Idris, UPSI (3.71’, 101.53’), Malaysia. The first observation effects of solar flare during November 2016 to March 2017, for the period of a minimum solar cycle 23-24 have been examined on sub-ionospheric VLF signals from VTX4 (19.2 kHz) and NWC (19.8 kHz) transmitter monitored at UPSI. In general, the level of amplitude reading for VTX4 signals is higher than NWC signals for quite diurnal variations. The effects of the solar flare class C7.5 on 29th November 2016 shows an enhancement of amplitude due to increase in the lower region electron density by the radiation of solar flare. The average daily amplitude reading was compared to the average value of solar flare event, the result shows the percentage difference is 12% increased in VTX4 and NWC signals.

Variability of VTEC Gradient and TEC Rate Index Over Kisumu, Kenya During Selected Quiet and Storm Days of 2013 and 2014

Vertical Total electron content (VTEC) gradient or rate of change of TEC (ROT) and total electron content (TEC) rate index or rate of change of TEC index (ROTI) can directly be estimated from receiver independent exchange (RINEX) data and can be used to estimate presence and intensity of ionospheric irregularities. In this paper we present results of the variation of ROT and ROTI over Kisumu, Kenya (Geomagnetic coordinates: 9.64°S, 108.59°E; Geographic coordinates: 0.02°S, 34.6°E) for both selected quiet and disturbed conditions between 1^st January 2013 and 31^st December 2014 using data derived from NovAtel GSV4004B SCINDA-GPS receiver at Kisumu as a step in establishing ionospheric irregularities over Kisumu, Kenya during a high solar activity period of solar cycle 24. ROT was calculated from filtered average daily VTEC data within intervals of 120 seconds while ROTI was computed over 4 minutes window from ROT. ROT and corresponding ROTI for the selected quiet and storm days were plotted against universal time (UT). The presence and intensity of irregularities on the selected quiet and storm days of the years 2013 and 2014 were determined by checking ROT fluctuations and the corresponding ROTI values from the plots. The obtained results showed increased fluctuation of ROT corresponding with large ROTI values after sunset. The selected storm days of the years 2013 and 2014 had higher ROTI values than the selected quiet days of the years 2013 and 2014. The higher ROTI values during the selected storm days may be attributed to the impact of geomagnetic storms brought about by several competing dynamics including Prompt penetration electric field (PPEF), disturbance dynamo electric field (DDEF) and reduction in electron density due to increased recombination rates. The high ROTI values after sunset were a manifestation of post-sunset plasma irregularities. The obtained results also showed a diurnal trend for ROT and ROTI where ROT increased steadily from 0.00UT to around 12:00UT before falling and having an increased fluctuation between 18:00UT and 20:00UT. This corresponded well with low ROTI values between 0:00UT and 16:00UT followed by high ROTI values between 18:00UT and 20:00UT. The diurnal variability of ROT might have resulted from variation of TEC and which was attributed to changes in the intensity of incoming solar radiation.

Long‐Term Distribution of Meteors in a Solar Cycle Period Observed by VHF Meteor Radars at Near‐Equatorial Latitudes

AbstractWe investigated meteor height and number of meteor echoes over a 13‐year observation period, with the data recorded by the meteor wind radar systems in Kototabang (0.20°S, 100.32°E) and Biak (1.17°S, 136.10°E), Indonesia. We aimed to investigate the changes in meteor peak height according to solar activity, represented by the solar radio index F10.7, and the number of solar sunspots, R, compared with the empirical results of the Mass Spectrometer Incoherent Scatter Extending (MSISE) and Committee on Space Research International Reference Atmosphere models. We found that (i) the daily meteor count rates at both sites in the period from 2003 to 2016 could be used to determine the dynamics in the upper atmosphere, where peak conditions occurred in the middle of the year; (ii) through a statistical approach using the normal distribution function, the variation in meteor peak height showed a positive correlation with the trend in solar activity; and (iii) comparison between the two empirical models and our observations showed two points where annual air density seemed to have a clear relationship with peak meteor height. In addition, the annual neutral density pattern of the model was related to the daily meteor count every year, although it showed a pattern opposite to the solar activity trends.

Исследование солнечной активности радиотелескопами Службы Солнца KRIM

Radio astronomy diagnostic complex based on the RT-22 radio telescope and three small radio telescopes combined into the KRIM Sun Service is located at 330 59 '30'' E longitude and 440 23 '52'' N latitude. The KRIM Sun Service conducts observations of the Sun in monitoring mode and alerts. The complex is integrated into the World Service for Solar Activity Research, and the daily data is stored in real time in digital form and posted on the sites of the World Sun Service, which includes 14 ground stations in cooperation with orbital observatories. During the minimum period of the 11-year solar activity cycle from September 6 to 10, 2017, KRIM Sun Service radio telescopes recorded a number of strong solar radio bursts in the active region NOAA 12673. The information obtained correlates well with data from other ground-based and satellite observatories, such as RSTN (Network Solar Radio Telescopes) and GOES (Geostationary Operational Satellite for Surrounding Space). This confirms the high quality and accuracy of the KRIM Solar Service radio telescopes.

The influence of several atmospheric variables on cosmic ray muons observed by KACST detector

In this study, the effects of atmospheric pressure and temperature on cosmic ray muons have been investigated using data recorded by the KACST detector (Riyadh, Saudi Arabia; Rc = 14.4 GV) for the beginning of the quiet periods of the 24th solar cycle. The muon data were, initially, correlated with the atmospheric pressure, and the desired coefficient was obtained and used to eliminate the pressure effect from the muon measurements. The pressure-corrected data are then analysed to study the effect of the atmospheric temperature on cosmic ray muons, using five methods. Four methods investigate the effect of the ground temperature, the atmospheric temperatures and atmospheric heights at several atmospheric levels, on the measured muon rate. In the fifth method, the muon data were correlated with the atmospheric weighted temperatures integrated up to different atmospheric heights. For all cases, the desired correction coefficients were obtained, and their variations at several atmospheric levels were studied. The obtained coefficients were then used to correct the cosmic ray data. We found that the atmospheric pressure effect shows the greatest differences between the corrected and uncorrected rate (up to 1%). Instead, corrections made to the muon data using the remainder of the considered parameters modify the muon rate by a small amount (less than 0.5%) compared to the uncorrected rate.

Modeling of local ionospheric time varying characteristics based on singular value decomposition over low-latitude GPS stations

Singular Value Decomposition (SVD) model is implemented to recognize the Total Electron Content (TEC) time series of daily, temporal as well as seasonal characteristics throughout the 24th solar cycle period of the year 2015 in the study. The Vertical (vTEC) analysis has been carried out with Global Positioning System (GPS) data sets collected from five stations from India namely GNT, Guntur (16.44∘ N, 80.62∘ E), and IISC, Bangalore (12.97∘ N, 77.59∘ E), LCK2, Lucknow (26.76∘ N, 80.88∘ E), one station from Thailand namely AITB, Bangkok (14.07∘ N, 100.61∘ E), and one station from South Andaman Island namely PBR, Port Blair (11.43∘ N, 92.43∘ E), located in low latitude region. The first five singular value modes constitute about 98% of the total variance, which are linearly transformed from the observed TEC data sets. So it is viable to decrease the number of modeling parameters. The Fourier Series Analysis (FSA) is carried out to characterize the solar-cycle, annual and semi-annual dependences through modulating the first three singular values by the solar (F10.7) and geomagnetic (Ap) indices. The positive correlation coefficient (0.75) of daily averaged GPS–TEC with daily averaged F10.7 strongly supports the temporal variations of the ionospheric features depends on the solar activity. Further, the significance and reliability of the SVD model is evaluated by comparing it with GPS–TEC data and the standard global model (Standard Plasma-Spherical Ionospheric Model, SPIM and International Reference Ionosphere, IRI 2016).

How Different Are the Solar Wind‐Interplanetary Conditions and the Consequent Geomagnetic Activity During the Ascending and Early Descending Phases of the Solar Cycles 23 and 24?

AbstractThe current work investigates the possible solar wind‐interplanetary (SW‐IP) drivers of geomagnetic storms during the longest period (ascending to early descending phases) of the ongoing solar cycle (24). We present a comparative analysis between the two consecutive solar cycles (SCs) 23 and 24. Both the cycles exhibited dual peak feature as observed in the smoothed sunspot numbers SSNsmoothed. For both the cycles, second peak in the SSNsmoothed is higher than the first one as exhibited in the revised SSNsmoothed version. During the entire interval between the ascending to early descending phases (December 2008 to December 2016) of SC‐24, the southward directed Bz and the dawn‐dusk electric field (Ey) were consistently weaker as compared to that during similar interval of SC‐23 (May 1996 to July 2004). The geomagnetic field response represented by Dst index concurrently exhibited similar variation patterns during both the periods. A striking reduction in the intense storm occurrence rate by ∼75% was observed during the considered period of the current solar cycle in comparison to the previous cycle. However, moderate storm occurrence was reduced only by 32% in SC‐24 as compared to SC‐23, which could be attributed to the dominance of corotating interaction regions during SC‐24. No significant difference is found between the intense storm rates around the vernal and autumnal equinoxes in cycle 24, whereas distinct autumnal equinoctial dominance is evident for cycle 23. Further, within each cycle, there is no significant difference in the moderate storm rates around vernal and autumnal equinoxes.

Study of cosmic ray intensity in relation to the interplanetary magnetic field and geomagnetic storms for solar cycle 24

In the present study, we investigate the association of cosmic ray intensity (CRI) with various solar wind parameters (i.e. solar wind speed V, plasma proton temperature, plasma proton density), interplanetary magnetic field (IMF B), geomagnetic storms (GSs), averaged planetary A-index (Ap index) and sun spot number (SSN) for the period 2009–2016 (solar cycle 24) by using their daily mean average. To find the association of CRI with various solar wind parameters, GSs, IMF B, Ap index and SSN, we incorporate the analysis technique by superposed-epoch method. We have observed that CRI decreases with the increase in IMF B. Moreover the time-lag analysis has been performed by the method of correlation coefficient and observed a time lag of 0 to 2 day between the decrease in CRI and increase in IMF B. In addition, we show that the CRI is found to decrease in a similar pattern to disturbance storm time (Dst index) for most of the period of solar cycle 24. The high and positive correlation is found between CRI and Dst index. The CRI and Ap index are better anti-correlated to each other than CRI and IMF. CRI and SSN are positively correlated with each other. Solar wind parameters such as solar wind speed V is a CR-effective parameter while plasma proton temperature and plasma proton density are not CR-effective parameters. The indicated parameters such as Dst index, Ap index, IMF B and solar wind parameters such as solar wind speed V, plasma proton temperature, plasma proton density shows a kind of irregular variations for solar cycle 23 and 24 while CRI and SSN shows distinct behaviour for the two cycle.

Galactic Cosmic-Ray Anisotropy in the Northern Hemisphere from the ARGO-YBJ Experiment during 2008–2012

Abstract This paper reports on the observation of the sidereal large-scale anisotropy of cosmic rays using data collected by the ARGO-YBJ experiment over 5 years (2008–2012). This analysis extends previous work limited to the period from 2008 January to 2009 December, near the minimum of solar activity between cycles 23 and 24. With the new data sample, the period of solar cycle 24 from near minimum to maximum is investigated. A new method is used to improve the energy reconstruction, allowing us to cover a much wider energy range, from 4 to 520 TeV. Below 100 TeV, the anisotropy is dominated by two wide regions, the so-called “tail-in” and “loss-cone” features. At higher energies, a dramatic change of the morphology is confirmed. The yearly time dependence of the anisotropy is investigated. Finally, no noticeable variation of cosmic-ray anisotropy with solar activity is observed for a median energy of 7 TeV.

Rayleigh–Taylor instability of a magnetic tangential discontinuity in the presence of oscillating gravitational acceleration

We study the magnetic Rayleigh–Taylor (MRT) instability of a magnetohydrodynamic interface in an infinitely conducting incompressible plasma in the presence of oscillating gravity acceleration. We show that the evolution of the interface shape is described by the Mathieu equation. Written in the dimensionless form this equation contains two parameters, a and q. The parameter q can be considered as the dimensionless wavenumber. The two parameters are related by a = Kq2, where K, in turn, depends on the ratio of densities at the two sides of the interface, ζ, the parameter s determining the relative magnitude of the gravity acceleration, the magnetic shear angle α, and the angle ϕ determining the direction of the perturbation wave vector. We calculate the dependence of the instability increment on q at fixed K, and the dependence on K of the maximum value of the increment with respect to q. We apply the theoretical results to the stability of a part of the heliopause near its apex point. Using the typical values of plasma and magnetic field parameters near the heliopause we obtain that the instability growth time is comparable with the solar cycle period.

Modelling variability of solar activity cycles

Context. Solar activity cycles vary in amplitude and duration. The variations can be at least partly explained by fluctuations in dynamo parameters. Aims. We want to restrict uncertainty in fluctuating dynamo parameters and find out which properties of the fluctuations control the amplitudes of the magnetic field and energy in variable dynamo cycles. Methods. A flux-transport model for the solar dynamo with fluctuations of the Babcock–Leighton type α-effect was applied to generate statistics of magnetic cycles for our purposes. The statistics were compared with data on solar cycle periods to restrict the correlation time of dynamo fluctuations. Results. A characteristic time of fluctuations in the α-effect is estimated to be close to the solar rotation period. The fluctuations produce asymmetry between the times of rise and descent of dynamo cycles, the rise time being on average shorter. The affect of the fluctuations on cycle amplitudes depends on the phase of the cycle in which the fluctuations occur. Negative fluctuations (decrease in α) in the rise phase delay decay of poloidal field and increase the cycle amplitude in toroidal field and magnetic energy. Negative fluctuation in the decline phase reduces the polar field at the end of a cycle and the amplitude of the next cycle. The low amplitude of the 24th solar cycle compared to the preceding 23rd cycle can be explained by this effect. Positive fluctuations in the descent phase enhance the magnetic energy of the next cycle by increasing the seed poloidal field for the next cycle. The statistics of the computed energies of the cycles suggest that superflares of ≥1034 erg are not possible on the Sun.

English

It has been established that Coronal Mass Ejections (CMEs) follow the phase of solar activity cycle. CMEs are known to be the major cause of geomagnetic storms which have devastating effects on earth atmosphere. Predicting their arrival times has been a major issue in space weather forecast. Influence of the phases solar activity cycle 23 on CMEs transit time were investigated using fast CMEs data with initial speed &ge; 900 kms-1 that were associated with intense geomagnetic storm obtained from Large Angle Spectrometric Coronagraph (LASCO) aboard the Solar and Heliospheric Observatory (SOHO) for solar cycle 23. Empirical Coronal Mass Ejections Arrival (ECA) model equations of Ojih-Okeke modified model, Gopalswamy 2000 model (G2000), Gopalswamy 2001 model (G2001), and Vrsnak and Gopalswamy 2002 model (VG2002) were applied to the data points. Scatter plots of CMEs transit time as function of CMEs initial speed and solar wind speed were generated. Linear correlation coefficients were obtained. The significance of the correlation was tested at 0.05 level of significant. Linear correlation coefficients obtained for solar maximum period of solar cycle 23 for Ojih-Okeke model, VG2002 model, G2001 model and G2000 model were -0.63, -0.82, -0.78 and -0.79 respectively and those obtained for declining phase of solar cycle 23 were -0.93, -0.80, -0.80 and -0.86 respectively. There is no significant difference between the correlations obtained for solar maximum phase and the declining phase of solar cycle 23. The findings depict that phases of solar activity cycle has no significant influence on CMEs transit time. Key words: Coronal mass ejections, solar activity cycle, transit time, phase, geomagnetic storm. &nbsp

A study on the variations in long-range dependence of solar energetic particles during different solar cycles

AbstractSolar Energetic Particles (SEPs) are high-energy particles ejected by the Sun which consist of protons, electrons and heavy ions having energies in the range of a few tens of keVs to several GeVs. The statistical features of the solar energetic particles (SEPs) during different periods of solar cycles are highly variable. In the present study we try to quantify the long-range dependence (or long-memory) of the solar energetic particles during different periods of solar cycle (SC) 23 and 24. For stochastic processes, long-range dependence or self-similarity is usually quantified by the Hurst exponent. We compare the Hurst exponent of SEP proton fluxes having energies (&gt;1MeV to &gt;100 MeV) for different periods, which include both solar maximum and minimum years, in order to find whether SC-dependent self-similarity exist for SEP flux.