Short-time variations of solar neutrinos and solar activity cycle

It is shown from the statistical analysis of the sunspot data and solar neutrino data that both the data exhibits 5, 10, 15, 20, 25, and 30 months period and these periods may be g-mode oscillation of the core associated with the solar activity.     

Possible solar cycle variations in the convection zone

Using data from the Global Oscillations Network Group (GONG) that covers the period from 1995 to 1998 we study the change in frequencies of solar oscillations with solar activity. From these frequencies we attempt to determine any possible variation in solar structure with solar activity. We do not find any evidence of a change in the convection zone depth or extent of overshoot below the convection zone during the solar cycle.     

On the short term variations of solar activity during solar cycle 21

Short-term variations of the last solar activity cycle were studied by the flare and coronal indices using Gleissberg method. Systematic short-term variations are found from their course during the 21st solar activity cycle. Comparison of their autocorrelograms constructed by the new set of data obtained from the magnitude of the fluctuations showed us the existence of the phase shift between the temporal variations of the two indices.     

160 minute solar variations and the 22 year cycle

Systematic measurements of the differential Doppler velocity of the Sun have been performed in Crimea from 1974 through 1988 (total 987 days, 6197 hours of observations). They confirm the presence of a long-term phase-coherent solar pulsation with a period of 160.010 min. On the other hand, the analysis of new data suggests that solar 160 min pulsation might, in frequency, have a multiplet fine structure. In particular, large changes of amplitude and phase of the pulsation over the years 1982–1986 may indicate that during the last few years we have been observing the solar 160 min oscillation of the second portion of the 22 year solar cycle.It is further noted that the beat period of the two closely spaced frequencies (periods are 160.0101 and 160.0126 min) equals 19.5 ± 1.1 year, which is in good agreement with the average length of the solar magnetic activity cycle, 20–22 years. Being verified, this unpredicted property of the pulsation can offer a novel possibility for probing the Sun's interior and perhaps for the study of the internal rotation and 11(22) year cycle of a star.     

Coronal rotation dependence on the solar cycle phase

A study of the green corona rotation rate, during the period 1970–1974, confirms that the differential rotation degree varies systematically through a solar cycle and that the corona rotates in an almost rigid manner before sunspot minimum. During the first two years, 1970–1971, the differential rotation degree, characteristic of high solar activity periods is detected. While during the years of declining activity, 1972–1974, a drastic decrease of the differential rotation degree occurs and the green corona rotates almost rigidly, as the coronal holes observed in the same period. These conclusions are valid only for the rotation of coronal features with lifetime of at least one solar rotation.     

Frequencies of low-degree solar acoustic oscillations and the phase of the solar cycle

A study of the solar total irradiance data of the Active Cavity Radiometer Irradiance Monitor (ACRIM) on the Solar Maximum Mission (SMM) satellite shows a small but formally significant shift in the frequencies of solar acoustic (p-mode) oscillations between the epochs of maximum and minimum solar activity. Specifically, the mean frequency of the strongest p-mode resonances of low spherical-harmonic degree (l = 0–2) is approximately 1.3 parts in 10⁴ higher in 1980, near the time of sunspot maximum, than in 1985, near sunspot minimum. The observed frequency shift may be an 11-yr effect but the precise mechanism is not clear.     

Observations of hysteresis in solar cycle variations among seven solar activity indicators

We show that smoothed time series of 7 indices of solar activity exhibit significant solar cycle dependent differences in their relative variations during the past 20 years. In some cases these observed hysteresis patterns start to repeat over more than one solar cycle, giving evidence that this is a normal feature of solar variability. Among the indices we study, we find that the hysteresis effects are approximately simple phase shifts, and we quantify these phase shifts in terms of lag times behind the leading index, the International Sunspot Number. Our measured lag times range from less than one month to greater than four months and can be much larger than lag times estimated from short-term variations of these same activity indices during the emergence and decay of major active regions. We argue that hysteresis represents a real delay in the onset and decline of solar activity and is an important clue in the search for physical processes responsible for changing solar emission at various wavelengths. The High Altitude Observatory is sponsored by the National Science Foundation.     

Asymmetries during the maximum phase of solar cycle 22

This paper presents the results of studies of the asymmetries (N-S and E-W) for different manifestations of solar activity events (sunspot groups, H flares and active prominences/filaments) during the maximum-phase (1989–1991) of solar cycle 22. During the period considered, the results obtained show the existence of a real N-S asymmetry, whereas the E-W asymmetry may exist only for H flares. There is no definite relationship between the asymmetries and the occurrence of events; however, around low activity sometimes we find enhanced asymmetry, and low asymmetry around high activity. Our study suggests a good agreement with similar studies made by others.     

Intermediate‐term variations in solar radius during solar cycle 23

In this study, we look for the mid‐term variations in the daily average data of solar radius measurements made at the Solar Astrolabe Station of TUBITAK National Observatory (TUG) during solar cycle 23 for a time interval from 2000 February 26 to 2006 November 15. Due to the weather conditions and seasonal effect dependent on the latitude, the data series has the temporal gaps. For spectral analysis of the data series, thus, we use the Date Compensated Discrete Fourier Transform (DCDFT) and the CLEANest algorithm, which are powerful methods for irregularly spaced data. The CLEANest spectra of the solar radius data exhibit several significant mid‐term periodicities at 393.2, 338.9, 206.5, 195.2, 172.3 and 125.4 days which are consistent with periods detected in several solar time series by several authors during different solar cycles. The knowledge relating to the origin of solar radius variations is not yet present. To see whether these variations will repeat in next cycles and to understand how the amplitudes of such variations change with different phases of the solar cycles, we need more systematic efforts and the long‐term homogeneous data. Since most of the periodicities detected in the present study are frequently seen in solar activity indicators, it is thought that the physical mechanisms driving the periodicities of solar activity may also be effective in solar radius variations (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Atmospheric temperature response to solar cycle UV flux variations

A radiative-convective climate model was used to explore the response of the mean global vertical temperature structure to a variation in the solar UV flux over the solar cycle. The model predicted a cooling of the troposphere and a warming of the stratosphere from solar minimum to solar maximum. The response of the atmospheric temperature to solar UV variations was found to be moderated by a concomitant change in the mean global stratospheric ozone content.     

High energetic solar proton flares on the declining phase of solar cycle 22

The year 1991 is a part of the declining phase of the solar cycle 22, during which high energetic flares have been produced by active regions NOAA/USAF 6659 in June. The associated solar proton events have affected the Earth environment and their proton fluxes have been measured by GOES space craft. The evaluation of solar activity during the first half of June 1991, have been carried out by applying a method for high energetic solar flares prediction on the flares of June 1991. The method depends on cumulative summation curves according to observed H-alpha flares, X-ray bursts, in the active region 6659 during one rotation when the energetic solar flares of June 1991 have occurred. It has been found that the steep trend of increased activity sets on several tens of hours prior to the occurrence of the energetic flare, which can be used, together with other methods, for forecasts of major flares. All the used data at the present work are received from NOAA, Boulder, Colorado, USA.     

Prominence activity during the ascending phase of solar cycle 22

Longitude-latitude and time-latitude distributions of the number and area of prominences observed at Lomnický Stit coronal station in the years 1986–1990 are studied using the method of contour maps construction with different degree of smoothing. Special attention is paid to the bifurcation in the prominence distribution. Comparison with the ascending phase of solar cycle 21 is made.     

Diurnal variations of cosmic rays during a solar magnetic cycle

We have used data from five neutron monitor stations with primary rigidity (Rm) ranging from 16 GeV to 33 GeV to study the diurnal variations of cosmic rays over the period: 1965–1986 covering one 22-year solar magnetic cycle. The heliosphere interplanetary magnetic field (IMF) and plasma hourly measurements taken near Earth orbit, by a variety of spacecraft, are also used to compare with the results of solar diurnal variation. The local time of maximum of solar diurnal diurnal variations displays a 22-year cycle due to the solar polar magnetic field polarities. In general, the annual mean of solar diurnal amplitudes, magnitude of IMF and plasma parameters are found to show separte solar cycle variations. Moreover, during the declining period of the twenty and twenty-ne solar cycles, large solar diurnal amplitudes are observed which associated with high values of solar wind speed, plasma temperature and interplanetary magnetic field magnitude B3.     

On the variations in the parameters of high-degree acoustic modes with solar cycle

We analyze the pattern of behavior of p-mode wave packets with solar cycle using TON one-day helioseismic data with a high spatial resolution. The time—distance method is used to perform this task. We make an attempt to determine the variations in the travel time of acoustic waves at maximum and minimum solar activity; at maximum activity, this time decreases by 2 s compared to that at minimum activity to a depth of 0.8R_⊙. In addition, the correlation amplitudes of acoustic wave packets from minimum to maximum solar activity were found to decrease by 10–20% for all angular distances.     

Stability of the photometric observations of the solar corona and variations of its intensity in the solar cycle 21

A comparison of the measurements of the intensity of the coronal line 5303 Å at the observations at Norikura, Kislovodsk and Lomnický tít is used to determine the stability of photometric systems and cancel the effect of its variations. The intensity variations of the solar corona during the 21st solar cycle are plotted. It is confirmed that the 11-year solar cycle consists of two maxima of activity; the first one is characterized by a simultaneous enhancement of activity at all latitudes and the second one shows up only in the equatorial zone.     

The solar differential rotation from the eightteenth solar cycle

The sidereal daily rotation of the Sun, (), depends on the data used. From an appropriate selection of the data — sunspots with regular motion — it is found that ()=14.31–2.70 sin² , where denotes the heliographic latitude. Moreover, it seems that there is a variation, of the order of 3%, with the solar activity.     

Evolution of coronal helmets during the ascending phase of solar cycle 20

The principal polar-crown coronal helmet structures were selected from nearly three years (May, 1965–January, 1968) of K-coronameter observations made at Haleakala and Mauna Loa, Hawaii. Six isolated and long-lived helmet systems were found at latitudes of 45° and above. Their developments are compared with underlying chromospheric and photospheric activity and a simple phenomenological model is presented showing that a coronal system is formed over an active region. Thereafter the center of gravity of the system gradually drifts poleward with the trailing unipolar magnetic region (UMR), and it becomes a high latitude coronal helmet, arched over a polar crown filament.By comparison of these coronal helmets with observations of the outer corona (to circa 4 R ) made at solar eclipse, lunar sunset, and with balloon and rocket-borne externally occulted corona-graphs, it appears that ground-based K-coronameter measurements to a distance of 1.5–2.0 R are sufficient to detect the coronal streamers.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Thermospheric no profiles observed at the diminishing phase of solar cycle 21

Two density profiles of the thermospheric nitric oxide were obtained by means of the γ(1,0) band airglow measured with rocket-home radiometers flown from Uchinoura, Japan (31°N) at around autumnal equinoxes in 1982 and 1983. The peak densities were found at altitudes of 105–110 km and are 9 × 10⁷ and 7 × 10⁷ cm⁻³, respectively. They are well reproduced by the variation of solar activity in terms of a one-dimensional photochemical-diffusive model, but the densities above 140 km under moderate solar activity differ considerably from the model prediction. A similar discrepancy has already been found in the NO density profile obtained by our previous experiment at solar maximum. These discrepancies infer a possibility either that our understanding of thermospheric nitrogen chemisty includes a serious error, or that the meridional circulation affects considerably the NO density profile even at altitudes above 140 km and at low latitudes.     

Effects of solar XUV variations on the thermosphere and the variability of the photoionization efficiency parameter during the solar cycle 21

Making use of the latest available semi-empirical atmospheric models, solar XUV radiations rates of photoionization and absorbed energy profiles have been graphically presented showing the latitudinal, seasonal and solar cycle variations. The photoionization limits of the major neutral constitutents of the terrestrial atmosphere O₂, O, and N₂ that occur at wavelengths 102.7, 91.2, and 79.6 nm, respectively have been quantified by showing the photoionization rates of O ₂ ⁺ , O⁺, and N ₂ ⁺ for different spectral groups both under quiet and different solar flare conditions. The variability of the photoionization efficiency parameter which is height-dependent, from winter to summer, for solar minimum to solar maximum for four significantly different latitudes under local noon conditions have been investigated during the solar cycle 21. More energy is required to produce an electron-ion pair in a denser atmosphere than in a thinner atmosphere and hence more energy is being deposited in the height range between 100–120 km which itself manifests in raising the electron gas temperatures higher than the neutral gas temperatures.