North-south asymmetries in the green corona brightness between 1947 and 1976

The north-south asymmetry has been studied using the green emission corona brightness in the period of 1947–1976. (N - S)/(N + S) values are constructed with the 5-deg opposite coronal belts brightnesses between ± 5 and ± 60 deg. Power spectra analyses were performed to study periodicities of these (N - S)/(N + S) values. Two noticeable periodicities (14.5 and 5 yr) have been found.     

On midrange periodicities in solar radio flux and sunspot areas

Using the Hilbert-Huang transform technique, we investigate the midrange periodicities in solar radio flux at 2800 MHz (F10.7) and sunspot areas (SAs) from February 1, 1947 to September 30, 2016. The following prominent results are found: (1) The quasi-periodic oscillations of both data sets are not identical, such as the rotational cycle, the midrange periodicities, and the Schwabe cycle. In particular, the midrange periodicities ranging from 37.9 days to 297.3 days are related to the magnetic Rossby-type waves; (2) The 1.3-year and 1.7-year fluctuations in solar activity indicators are surface manifestations (from photosphere to corona) of magnetic flux changes generated deep inside the Sun; (3) At the timescale of the Schwabe cycle, the complicated phase relationships in the three intervals (1947–1958, 1959–1988, and 1989–2016) agree with the produced periodicities of the magnetic Rossby-type waves. The findings indicate that the magnetic Rossby-type waves are the possible physical mechanism behind the midrange periodicities of solar activity indicators. Moreover, the significant change in the relationship between photospheric and coronal activity took place after the maximum of solar cycle 22 could be interpreted by the magnetic Rossby-type waves.     

Intermediate-term periodicities in the green corona brightness of the Sun

We have analysed intermediate-term periodicities in the green corona by dividing 10° latitudinal belts for the solar cycles 18, 19, and 20 (1947–1976). Discrete Fourier transform technique was used and three noticeable periodicities (3.48, 2.57, and 2.27 years) were found. The physical origin of these periods is not known, but evidence in our results exclude the possibility that the observed periods are a harmonic due to the method of analyse. The period of 3.48-year is the strongest one. 17.6-month periodicity was found only on around +40° belt while 155-day periodicity was not found in our analysis.     

Periodic variation and phase analysis of grouped solar flare with sunspot activity

Studies on the periodic variation and the phase relationship between different solar activity indicators are useful for understanding the long-term evolution of solar activity cycles.Here we report the statistical analysis of grouped solar flare(GSF) and sunspot number(SN) during the time interval from January 1965 to March 2009.We find that,(1) the significant periodicities of both GSF and SN are related to the differential rotation periodicity,the quasi-biennial oscillation(QBO),and the eleven-year Schwabe cycle(ESC),but the specific values are not absolutely identical;(2) the ESC signal of GSF lags behind that of SN with an average of 7.8 months during the considered time interval,which implies that the systematic phase delays between GSF and SN originate from the inter-solar-cycle signal.Our results may provide evidence about the storage of magnetic energy in the corona.     

On Mid-Term Periodicities in Sunspot Groups and Flare Index

In this work we study the mid-term periodicities (MTPs), between 1 and 2 years, of the sunspot groups and the flare index (FI), by separating the data into hemispheres and spectral bands (SBs) according to the most significant periodicities presented by these phenomena. We found that the MTP of sunspot groups has a diminished power during the Modern Minimum and an increased power during the Modern Maximum, with the exception of cycle 20. For flares, the MTP has a diminished power during the low activity cycle 20, and an increased power during cycles 21 and 22. Therefore, for both sunspot groups and FI, cycle 20 shows a very diminished power followed by the active and higher-power cycles 21 and 22; cycle 23 shows a weaker power than cycles 21 and 22. It is uncertain whether MTP can be a precursor of a long-term minimum of solar activity or not, as has been previously suggested. Also, there is no one-to-one correlation between the cycle intensity and the importance of MTP. Concerning the quasi-biennial periodicities and the theory of two kinds of dynamos, we notice the tendency that higher-power cycles mean weaker coupling in the model. Concerning the hemispheric north-south asymmetry, for sunspot groups the southern hemisphere dominates in most of the SBs, while for FI the northern hemisphere dominates for all the SBs. Additionally, the time lag found between the two hemispheres indicates that the degrees of coupling in the photosphere for sunspot groups and in the corona for flares are between moderate and strong. Finally, the modulation shown by the MTP time series suggests that these periodicities are the product of chaotic quasi-periodic processes and not of stochastic processes.     

Systematic investigation of mid-term periodicity of the solar full-disk magnetic fields

The Magnetic Plage Strength Index(MPSI) and the Mount Wilson Sunspot Index(MWSI), which have been measured at Mount Wilson Observatory(MWO) since the 1970 s and which indicate weak and strong magnetic field activity on the solar full disk, respectively, are used to systematically investigate midterm periodicities in the solar full-disk magnetic fields. Multitudinous mid-term periodicities are detected in MPSI and MWSI on timescales of 0.3 to 4.5 yr, and these periodicities are found to fluctuate around several typical periodicities within a small amplitude in different solar cycles or phases. The periodicity of 3.44 yr is found in MPSI, and the periodicities of 3.85 and 3.00 yr are detected in MWSI. Our analysis indicates that they reflect the true oscillating signals of solar magnetic field activity. The typical periodicities are 2.8,2.3 and 1.8 yr in MPSI and MWSI, and possible mechanisms for these periodicities are discussed. A 1.3 yr periodicity is only detected in MPSI, and should be related to meridional flows on the solar surface. The typical annual periodicity of MPSI and MWSI is 1.07 yr, which is not derived from the annual variation of Earth's heliolatitude. Several periodicities shorter than 1 yr found in MPSI and MWSI are considered to be Rieger-type periodicities.     

Periodic behavior of solar flare index during solar cycles 20 and 21

Short-term periodicities of solar activity were studied with the flare index by using Discrete Fourier Transform for the time interval 1966–1986. Two noticeable periodicities (18.5 and 5 months) have been found. The existence of these periodicities comparing with the early findings is discussed.     

Solar-planetary cycles in Jupiter's great red spot darkness

The change in the darkness of the Great Red Spot (GRS) of Jupiter (1894–1974) has been analysed with Fourier (FFT), Maximum Entropy and Power spectrum (Blackman-Tukey window) (PSA) methods of spectrum analysis. Significance, non-randomness and stationarity tests assigned high variance to periodicities of 33 ± 4, 13–15, about 11, 9 and 3 yrs. The highest correlation between solar activity and GRS darkness was found for the 14th and 16th solar cycle. The periodicities obtained are interpreted as the combined eftects of solar activity, planetary resonances and internal jovian mechanisms.     

The Extended Solar Cycle Tracked High into the Corona

We present observations of the extended solar cycle activity in white-light coronagraphs, and compare them with the more familiar features seen in the Fe?xiv green-line corona. We show that the coronal activity zones seen in the emission corona can be tracked high into the corona. The peak latitude of the activity, which occurs near solar maximum, is found to be very similar at all heights. But we find that the equatorward drift of the activity zones is faster at greater heights, and that during the declining phase of the solar cycle, the lower branch of activity (that associated with the current cycle) disappears at about 3R _??. This implies that during the declining phase of the cycle, the solar wind detected near Earth is likely to be dominated by the next cycle. The so-called ??rush to the poles?? is also seen in the higher corona. In the higher corona it is found to start at a similar time but at lower latitudes than in the green-line corona. The structure is found to be similar to that of the equatorward drift.     

Fluctuations of the Solar Dynamo Observed in the Solar Wind and Interplanetary Magnetic Field at 1 AU and in the Outer Heliosphere

Recent helioseismic observations have found strong fluctuations at a period of about 1.3 years in the rotation speed around the tachocline in the deep solar convection layer. Similar mid-term quasi-periodicities (MTQP; periods between 1–2 years) are known to occur in various solar atmospheric and heliospheric parameters for centuries. Since the deep convection layer is the expected location of the solar magnetic dynamo, its fluctuations could modulate magnetic flux generation and cause related MTQP fluctuations at the solar surface and beyond. Accordingly, it is likely that the heliospheric MTQP periodicities reflect similar changes in solar dynamo activity. Here we study the occurrence of the MTQP periodicities in the near and distant heliosphere in the solar wind speed and interplanetary magnetic field observed by several satellites at 1 AU and by four interplanetary probes (Pioneer 10 and 11 and Voyager 1 and 2) in the outer heliosphere. The overall structure of MTQP fluctuations in the different locations of the heliosphere is very consistent, verifying the solar (not heliospheric) origin of these periodicities. We find that the mid-term periodicities were particularly strong during solar cycle 22 and were observed at two different periods of 1.3 and 1.7 years simultaneously. These periodicities were latitudinally organized so that the 1.3-year periodicity was found in solar wind speed at low latitudes and the 1.7-year periodicity in IMF intensity at mid-latitudes. While all heliospheric results on the 1.3-year periodicity are in a good agreement with helioseismic observations, the 1.7-year periodicity has so far not been detected in helioseismic observations. This may be due to temporal changes or due to the helioseismic method where hemispherically antisymmetric fluctuations would so far have remained hidden. In fact, there is evidence that MTQP fluctuations may occur antisymmetrically in the northern and southern solar hemisphere. Moreover, we note that the MTQP pattern was quite different during solar cycles 21 and 22, implying fundamental differences in solar dynamo action between the two halves of the magnetic cycle.     

Periodicities in the Time Series of Solar Coronal Radio Emissions and Chromospheric uv Emission Lines

A spectral analysis of the time series of daily values of ten solar coronal radio emissions in the range 275–1755 MHz, the 2800 MHz radio flux, several UV emission lines in the chromosphere and in the transition region, and sunspot number, for six successive intervals of 132 days each, during June 1997–July 1999 (26 months) showed that the spectral characteristics were not the same for all intervals. Details are presented for Interval 1, where there was no 27-day oscillation, and Interval 2, where there was a strong 27-day oscillation. In every interval, periodicities were remarkably similar in most of these indices, indicating that the solar atmosphere (chromosphere and corona) rotated as one block, up to a height of 150000 km. Above this height, the periodicities became obscure. Near the solar surface, sunspots showed extra or different periodicities, some of which vanished at low altitudes. For the 27-day feature as also for the long-term rise during 1996–1998, the maximum percentage changes were for radio emissions near 1350–1620 MHz.     

Short periodicities in solar activity

Several indices of solar activity are subjected to a high pass filter and power spectral analysis to verify the existance of shorter periodicities in solar activity. Though all these indices show the presence of short periodicities, above 95% confidence level, the common indices like sunspot number, fail to show these periodicities when a stringest statistical test is applied based on a percentage of the ²/v distribution that is appropriately higher than the 95% point (Mitchell et al., 1966). The basic parameters given by Kopecký (1967), however, reveal the presence of 5.6- and 3.5-yr periodicities even when this stringent statistical test is applied.     

Short-Period Fluctuations in Coronal Mass Ejection Activity during Solar Cycle 23

We have constructed a time series of the number of coronal mass ejections (CMEs) observed by SOHO/LASCO during solar cycle 23. Using spectral analysis techniques (the maximum entropy method and wavelet analysis) we found short-period (< one year) semiperiodic activity. Among others, we found interesting periodicities at 193, 36, 28, and 25 days. We discuss the implications of such short-period activity in terms of the emergence and escape of magnetic flux from the convection zone, through the low solar atmosphere (where these periodicities have been found for numerous activity parameters), toward interplanetary space. This analysis shows that CMEs remove the magnetic flux in a quasiperiodic process in a way similar to that of magnetic flux emergence and other solar eruptive activity.     

A Search for Periodicities in F10.7 Solar Radio Flux Data

The radio frequency emission at 10.7 cm (or 2800 MHz) wavelength (considered as solar flux density) out of different possible wavelengths is usually selected to identify periodicities because of its high correlation with solar extreme ultraviolet radiation as well as its complete and long observational record other than sunspot related indices. The solar radio flux at 10.7 cm wavelength plays a very valuable role for forecasting the space weather because it is originated from lower corona and chromospheres region of the Sun. Also, solar radio flux is a magnificent indicator of major solar activity. Here in the present work the solar radio flux data from 1965 to 2014 observed at the Domimion Radio Astrophysical Observatory in Penticton, British Columbiahas been processed using Date Compensated Discrete Fourier Transform (DCDFT) to identify predominant periods within the data along with their confidence levels. Also, the multi-taper method (MTM) for periodicity analysis is used to validate the observed periods. Present investigation exhibits multiperiodicity of the time series F10.7 solar radio flux data around 27, 57, 78, 127, 157, 4096 days etc. The observed periods are also compared with the periods of MgII Index data using same algorithm as MgII Index data has 99.9% correlation with F10.7 Solar Radio Flux data. It can be observed that the MgII index data exhibits similar periodicities with very high confidence levels.Present investigation also clearly indicates that the computed results are very much confining with the results obtained in different communication for the similar data of 10.7 cm Solar Radio Flux as well as for the other solar activities.

     

Short time periodicities of the atmospheric activity of Jupiter

Short time periodicities of 3, 6, and 12 months have been found by analysis of the coefficient of atmospheric activity of Jupiter for the time period 1963–1967.These periodicities have been attributed to seasonal variations of the Jovian atmosphere, and could be related to similar periodicities observed in solar flares and in the high velocity solar wind streamers.     

Two types of differential rotation of the solar corona

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.     

On the stability of the 11-year solar cycle period (and a few others)

The existence of an 11.1-yr periodic variation in the sunspot number record has been recognized for many years; however, periodicities other than this remain questionable. Power spectral analysis of the International sunspot number is performed and the results are compared with those for the same period using values that were taken randomly inside the error bars. The findings are that only a few periodicities show noticeable peaks. These include periodicities of 8.49, 10.01, 10.58, 11.10, 12.50, 58.50, and 97.20 yr. On the basis of these seven periodicities, one can loosely simulate the observable sunspot record (r = 0.75). We find that discrepancies in number and value of periodicities with other authors appear to be related to the length of the sunspot record used in the analysis and to the occurrence of 0.3-yr windows around the inferred periodicities.     

Onset Time and Duration of Corona Activity on Venus: Stratigraphy and History from Photogeologic Study of Stereo Images

The details of stratigraphic units and structures making up six coronae and their regional surroundings on Venus were examined using full resolution Magellan images and stereoscopic coverage. Altimetry and stereoscopic coverage were essential in establishing the local stratigraphic relationships and the timing of corona-related topography. The degree of preservation of signatures of earlier corona-related activities and the scale of later corona-related activities vary significantly from corona to corona. We compared the geologic sequence in each corona to regional and global stratigraphic units, placing the coronae in the broader context of the geologic history of Venus. The results of this study were compared with earlier analyses bringing the total number of corona considered to about 15% of the total corona population. We found that corona started forming soon after tessera formation and largely spanned a significant part of the subsequent geologic history of Venus, over about 200–400 million years. Topographic annulae were initiated in early post-tessera time but were largely completely formed by the time of emplacement of regional plains with wrinkle ridges. Some coronae ceased activity by this time, while others continued until closer to the present, although showing evidence of waning activity. Coronae-associated volcanism dominated many coronae during this later stage. Convincing evidence of pre-regional plains corona- related volcanism was not found in the population examined here. We conclude that coronae formed in a two stage process; the first stage (tectonic phase) involved the annular warping of early extensive stratigraphic units of volcanic origin and the second (volcanic phase) involved coronae-related lava flow activity and local fracturing. For the vast majority of coronae, the first tectonic phase was largely complete prior to the emplacement of the regional plains (Pwr, plains with wrinkle ridges). The vast majority of corona-related volcanic activity (emplacement of Pl, lobate flows) occurred subsequent to the emplacement of regional plains. We found no evidence of coronae initiation in substantially later periods of the observed history of Venus. This revised version was published online in July 2006 with corrections to the Cover Date.     

Power-spectrum analysis of local geomagnetic disturbances and their relationship to cosmic-ray and aurora intensity

Power-spectrum analyses have been carried out on two data sets of the geomagnetic K-index from the Athens and Sofia magnetic Observatories. For the period between 1956–1984, periodicities of about 2.8 and 6 months have been obtained. Similar results were found by the auto-correlation technique. Both periods are significant to 0.05 and 0.01 level, respectively. In our attempt to explain transient geomagnetic disturbances caused by other parameters, the K-index was correlated to cosmic-ray and aurora intensity. The best correlation coefficient between K-variations and cosmic-ray data from Athens Neutron-Monitor Station was 0.58 and between K-index and Auroral, activity index was 0.47.An attempt to interpret these periodicities and relationships has been made.     

Brightness,polarization and electron density of the solar corona of 1980 february 16

During the eclipse of 1980 February 16 we photographed the solar corona at an effective wavelength of 6300 å. Using a quadruple camera we also obtained the coronal pictures in polarized light for four Polaroid orientations. We have used these observations to derive the coronal brightness and polarization and from these the electron densities in the corona out to a distance of about 2.5 R⊙ from the centre of the disc. The coronal brightness matches well with that of the corona of 1958 October 12.