Signatures of solar activity variability in meteorological parameters

Solar radiation (both total and in various wavelengths) varies at different time scales—from seconds to decades or centuries—as a consequence of solar activity. The energy received from the Sun is one of the natural driving forces of the Earth's atmosphere and since this energy is not constant, it has been argued that there must be some non-zero climate response to it. This response must be fully specified in order to improve our understanding of the climate system and the impact of anthropogenic activities on it. However, despite all the efforts, if and how subtle variations of solar radiation affect climate and weather still remains an unsolved puzzle. One key element that is very often taken as evidence of a response, is the similarity of periodicities between several solar activity indices and different meteorological parameters. The literature contains a long history of positive or negative correlations between weather and climate parameters like temperature, rainfall, droughts, etc. and solar activity cycles like the 27-day cycle, the prominent 11-year sunspot cycle, the 22-year Hale cycle and the Gleissberg cycle of 80–90 years. A review of these different cycles is provided as well as some of the correlative analyses between them and several stratospheric parameters (like stratospheric geopotential heights, temperature and ozone concentration) and tropospheric parameters (like temperature, rainfall, water level in lakes and river flooding, clouds) that point to a relationship of some kind. However, the suspicion on these relationships will remain as long as an indisputable physical mechanism, which might act to produce these correlations, is not available.     

The 11-year solar cycle,the sun’s rotation,and the middle stratosphere in winter: Part I: Response of zonal means

The effect of the 11-year solar cycle on the response of the stratospheric geopotential height and temperature fields at 10 and 30 hPa in winter to solar activity oscillations with periods related to the period of the Sun’s rotation (27.2 days) is discussed, applying methods of statistical spectral analysis to daily data for the period from 1965 to 1996. Atmospheric responses for three periodicities — 27.2 days (period of the Sun’s rotation), 25.3 days (periodicity caused by the modulation of the 27.2 days oscillation by annual atmospheric variation), and 54.4 days (doubled period of the solar rotation) — are studied. A significant effect of the 11-year solar cycle on the atmospheric response to the 27.2 days solar periodicity has not been found. We explain it by a frequency shift of the response from the 27.2 days to the 25.3 days periodicity via amplitude modulation. For the 25.3 days oscillation, prominent differences between the maximum and minimum of the 11-year solar cycle have been found in the coherence between the 10.7 cm solar radio flux and the height/temperature fields: the relationships are stronger at solar maximum than at the minimum of the 11-year cycle. The same differences, but to a greater extent, are revealed for the oscillation with a period of 54.4 days. Coherence and amplitude estimates for this doubled solar rotation periodicity exhibit strong differences between extrema of the 11-year solar cycle. Phase estimates also demonstrate a clear difference between high and low solar activity: on the average, the delay of the atmospheric response after the solar signal is smaller at solar maximum than at solar minimum. Thus, we conclude that the mechanism of the influence of the 11-year solar cycle on the winter middle stratosphere can include both a direct effect of the frequency corresponding to the doubled solar rotation periodicity and an indirect effect of modulation of the intensity of the interaction between the solar 27.2 days oscillation and seasonal atmospheric variations.     

Empirical model of the OI 630 nm emission variations. 3. Emitting layer height

The empirical model of variations in the emitting layer height and parameters has been developed based on an analysis of the rocket measurements of the vertical distributions in the 630 nm intensity. The dependences on the solar zenith angle during a day are most substantial. This dependence is responsible for the character of seasonal variations at different latitudes. The height of the emitting layer increases with increasing solar activity, reflecting a temperature rise in the upper atmosphere. The negative trend—0.35 km yr^?1 in the interval 1964–1990—has been revealed.     

On the 18-day quasi-periodic oscillation in the ionosphere

The presence and persistence of an 18-day quasi-periodic oscillation in the ionospheric electron density variations were studied. The data of lower ionosphere (radio-wave absorption at equivalent frequency near 1 MHz), middle and upper ionosphere (critical frequencies f₀E and f₀F2) for the period 1970–1990 have been used in the analysis. Also, solar and geomagnetic activity data (the sunspot numbers Rz and solar radio flux F10.7 cm, and a_N index respectively) were used to compare the time variations of the ionospheric with the solar and geomagnetic activity data. Periodogram, complex demodulation, auto- and cross-correlation analysis have been used. It was found that 18-day quasi-periodic oscillation exists and persists in the temporal variations of the ionospheric parameters under study with high level of correlation and mean period of 18–19 days. The time variation of the amplitude of the 18-day quasi-periodic oscillation in the ionosphere seems to be modulated by the long-term solar cycle variations. Such oscillations exist in some solar and geomagnetic parameters and in the planetary wave activity of the middle atmosphere. The high similarities in the amplitude modulation, long-term amplitude variation, period range between the oscillation of investigated parameters and the global activity of oscillation suggests a possible solar influence on the 18-day quasi-periodic oscillation in the ionosphere.     

Global magnetic field of the Sun and long-term variations of galactic cosmic rays

The paper deals with the relation of long-term variations of 10 GV galactic cosmic rays (GCR) to the global solar magnetic field and solar wind parameters. This study continues previous works, where the tilt of the heliospheric current sheet (HCS) and other solar-heliospheric parameters are successfully used to describe long-term variations of cosmic rays in the past two solar cycles. The novelty of the present work is the use of the HCS tilt and other parameters reconstructed from Hα observations of filaments for the period when direct global solar magnetic field observations were unavailable. Thus, we could extend the GCR simulation interval back to 1953. The analysis of data for 1953–1999 revealed a good correlation (the correlation coefficient >0.88) between the solar-heliospheric parameters and GCR in different cycles of solar activity. Moreover, the approach applied makes it possible to describe the behavior of cosmic rays in the epochs of solar maxima, which could not be done before. This indicates both the adequacy of the model and the reliability of the reconstructed global solar magnetic field parameters.     

Transition of solar cycle length in association with the occurrence of grand solar minima indicated by radiocarbon content in tree-rings

In this paper, we review the variation of the 11-year solar cycle since the 15th century revealed by the measurement of radiocarbon content in single-year tree-rings of Japanese cedar trees. Measurements of radiocarbon content in absolutely dated tree-rings provide a calibration curve for accurate dating of archaeological matters, but at the same time, enable us to examine the variations of solar magnetic activity in the pre-historical period. The Sun holds several long-term quasi-cyclic variations in addition to the fundamental 11-year sunspot activity cycle and the 22-year polarity reversal cycle, and it is speculated that the property of the 11-year and the 22-year solar cycle varies in association with such long-term quasi-cycles. It is essential to reveal the details of solar variations around the transition time of solar dynamo for illuminating the mechanisms of the long-term solar variations. We therefore have investigated the property of the 11-year and 22-year cycles around the two grand solar minima; the Maunder Minimum (1645–1715 AD) and the Spoerer Minimum (1415–1534 AD), the periods of prolonged sunspot minima. As a result, slight stretching of the “11-year” and the “22-year” solar cycles was found during these two grand solar activity minima; continuously during the Maunder Minimum and only intermittently during the Spoerer Minimum. On the contrary, normal or slightly shortened 11-year cycles were detected during the interval period of these two minima. It suggests the inverse correlation between the solar cycle length and solar magnetic activity level, and also the change of meridional flow during the grand solar activity minima. Further measurements for the beginning of the grand solar minima will provide a clue to the occurrence of such prolonged sunspot disappearance. We also discuss the effect of solar variations to radiocarbon dating.     

Anisotropy and symmetry of fluctuations in the solar wind magnetic field and velocity

The behavior of correlation tensors of fluctuations in the solar wind magnetic field and velocity is studied during different phases of a solar cycle on the basis of a 45-year measurement series of solar wind parameters. It is found that the orientation of fluctuations in the magnetic field and velocity is approximately axisymmetric relative to the direction of a local magnetic field during high solar activity. This symmetry is violated significantly during periods of low solar activity, and deviations from the symmetry are regular and oppositely directed during minima of even and odd 11-year cycles, which is probably connected with variations in the orientation of the Sun??s magnetic field. The dependence of the power of fluctuations on the local magnetic field direction reveals significant deviations from local symmetry during all phases of a solar cycle, especially for velocity fluctuations.     

Determination of the running quiet daily geomagnetic variation

A new automatic running method for derivation of the quiet daily geomagnetic variation—“quiet day curve” (QDC) is described. The method consists in the automatic distinction of the quietest periods using the geomagnetic variations parameterization, calculation of the proper quiet daily variation for certain days, reconstruction of QDC for each day of the elapsed period and extrapolation of QDC for the subsequent period. The method ensures statistically reliable QDCs during the epoch of the solar activity maximum if the time interval used for derivation of QDC is not less than 30 days. The method of the running QDC calculation implies the uninterrupted calculation of the QDC resulting from the continuous 1-day forward shift of the 30-day interval. The method makes it possible to derive automatically and on-line the quiet daily variation in the polar caps, where northward interplanetary magnetic field can generate large magnetic disturbances during periods of planetary magnetic quiescence. This is the main advantage of the running QDC method over other known methods. It is shown that along with the seasonal (from month to month) and the solar cycle (from year to year) changes, the QDC amplitude is modified on a time scale less then a month following solar activity flashes.     

The sunspot cycle, the QBO, and the total ozone over Northeastern Europe: a connection through the dynamics of stratospheric circulation

The interaction between the factors of the quasi-biennial oscillation (QBO) and the 11-year solar cycle is considered as an separate factor influencing the interannual January–March variations of total ozone over Northeastern Europe. Linear correlation analysis and the running correlation method are used to examine possible connections between ozone and solar activity at simultaneous moment the QBO phase. Statistically significant correlations between the variations of total ozone in February and, partially, in March, and the sunspot numbers during the different phases of QBO are found. The running correlation method between the ozone and the equatorial zonal wind demonstrates a clear modulation of 11-y solar signal for February and March. Modulation is clearer if the QBO phases are defined at the level of 50 hPa rather than at 30 hPa. The same statistical analyses are conducted also for possible connections between the index of stratospheric circulation C₁ and sunspot numbers considering the QBO phase. Statistically significant connections are found for February. The running correlations between the index C₁ and the equatorial zonal wind show the clear modulation of 11-y solar signal for February and March. Based on the obtained correlations between the interannual variations of ozone and index C₁, it may be concluded that a connection between solar cycle – QBO – ozone occurs through the dynamics of stratospheric circulation.     

Spectral composition of the cyclic aperiodic (quasibiennial) variations in solar activity and the Earth’s atmosphere

Based on the published analysis of the average monthly variations in solar activity and temperature of the upper atmosphere in the region of the mesopause and lower thermosphere (after elimination of the average long-term variations during different 11-year cycles), it was indicated that the periods and amplitudes of the observed quasibiennial variations monotonically decrease in the course of time. The regularity of these variations is described by the Airy function, which represents a wave train with decreasing amplitude and period and reflects cyclic hydrodynamic processes in the Sun’s interior. A spectral analysis of the quasibiennial variations modelly described by the Airy function has been performed. It has been revealed that the period amplitudes near the average value for 2.25 years (27 months) are distributed normally with a dispersion of ～0.5 years. According to several publications, similar periods are obtained by analyzing measurements of long-term variations in solar activity and parameters of the lower and middle atmosphere. This indicates that the values of the periods are obtained randomly. Therefore, a standard Fourier analysis does not make it possible to determine a real character of the quasibiennial variations since a real physical process is not revealed in the course of this analysis.     

Long-term variations of solar magnetic fields derived from geomagnetic data

There are limited homogeneous instrumental observations of the sunspot magnetic fields, but the Earth is a sort of a probe reacting to interplanetary disturbances which are manifestation of the solar magnetic fields. We find correlations between some parameters of geomagnetic activity (the geomagnetic activity “floor”—the minimum value under which the geomagnetic activity cannot fall in a sunspot cycle, and the rate of increase of the geomagnetic activity with increasing sunspot number), and sunspot magnetic fields (the sunspot magnetic field in the cycle minimum, and the rate of increase of the sunspot magnetic field from cycle minimum to cycle maximum). Based on these correlations we are able to reconstruct the sunspot magnetic fields in sunspot minima and maxima since sunspot cycle 9 (mid 19th century).     

Shortwave forcing of the Earth's climate: Modern and historical variations in the Sun's irradiance and the Earth's reflectance

Changes in the Earth's radiation budget are driven by changes in the balance between the thermal emission from the top of the atmosphere and the net sunlight absorbed. The shortwave radiation entering the climate system depends on the Sun's irradiance and the Earth's reflectance. Often, studies replace the net sunlight by proxy measures of solar irradiance, which is an oversimplification used in efforts to probe the Sun's role in past climate change. With new helioseismic data and new measures of the Earth's reflectance, we can usefully separate and constrain the relative roles of the net sunlight's two components, while probing the degree of their linkage. First, this is possible because helioseismic data provide the most precise measure ever of the solar cycle, which ultimately yields more profound physical limits on past irradiance variations. Since irradiance variations are apparently minimal, changes in the Earth's climate that seem to be associated with changes in the level of solar activity—the Maunder Minimum and the Little Ice age for example—would then seem to be due to terrestrial responses to more subtle changes in the Sun's spectrum of radiative output. This leads naturally to a linkage with terrestrial reflectance, the second component of the net sunlight, as the carrier of the terrestrial amplification of the Sun's varying output. Much progress has also been made in determining this difficult to measure, and not-so-well-known quantity. We review our understanding of these two closely linked, fundamental drivers of climate.     

ULF wave occurrence statistics in a high-latitude HF Doppler sounder

Ultra low frequency (ULF) wave activity in the high-latitude ionosphere has been observed by a high frequency (HF) Doppler sounder located at Tromsø, Norway (69.71°N, 19.2°E geographic coordinates). A statistical study of the occurrence of these waves has been undertaken from data collected between 1979 and 1984. The diurnal, seasonal, solar cycle and geomagnetic activity variations in occurrence have been investigated. The findings demonstrate that the ability of the sounder to detect ULF wave signatures maximises at the equinoxes and that there is a peak in occurrence in the morning sector. The occurrence rate is fairly insensitive to changes associated with the solar cycle but increases with the level of geomagnetic activity. As a result, it has been possible to characterise the way in which prevailing ionospheric and magnetospheric conditions affect such observations of ULF waves.     

Cosmic ray modulation during the solar activity growth phase of cycle 24

Recent years allowed us to study long-term variations in the cosmic ray (CR) intensity at an unusually deep solar activity (SA) minimum between cycles 23 and 24 and during the SA growth phase in cycle 24, which was the cycle when SA was the lowest for the epoch of regular ground-based CR observations since 1951. The intensity maximum, the value of which depends on the particle energy, was observed in CR variations during the period of an unusually prolonged SA minimum: the CR density during the aformentioned period (2009) is higher than this density at previous CR maxima in cycles 19–23 for low-energy particles (observed on spacecraft and in the stratosphere) and medium-energy particles (observed with neutron monitors). After 2009 CR modulation at the SA growth phase was much weaker over three years (2010–2012) than during the corresponding SA growth periods in the previous cycles. The possible causes of this anomaly in CR variations, which are related to the CR residual modulation value at a minimum between cycles 23 and 24 and to variations in SA characteristics during this period, were examined. The contribution of different solar magnetic field characteristics and indices, taking into account sporadic solar activity, has been estimated.     

Galactic Cosmic Ray Intensity in the Upcoming Minimum of the Solar Activity Cycle

During the prolonged and deep minimum of solar activity between cycles 23 and 24, an unusual behavior of the heliospheric characteristics and increased intensity of galactic cosmic rays (GCRs) near the Earth’s orbit were observed. The maximum of the current solar cycle 24 is lower than the previous one, and the decline in solar and, therefore, heliospheric activity is expected to continue in the next cycle. In these conditions, it is important for an understanding of the process of GCR modulation in the heliosphere, as well as for applied purposes (evaluation of the radiation safety of planned space flights, etc.), to estimate quantitatively the possible GCR characteristics near the Earth in the upcoming solar minimum (~2019–2020). Our estimation is based on the prediction of the heliospheric characteristics that are important for cosmic ray modulation, as well as on numeric calculations of GCR intensity. Additionally, we consider the distribution of the intensity and other GCR characteristics in the heliosphere and discuss the intercycle variations in the GCR characteristics that are integral for the whole heliosphere (total energy, mean energy, and charge).     

Search for tidal seismicity in Greece using different techniques: Part 3. Correlation with solar and lunar tidal waves

The last of a cycle of three papers aimed at searching for the influence of the gravitational tide on regional Greece seismicity using different techniques is presented. Twenty-five nonintersecting samplings of earthquakes in Greece compiled from events with different energy and time intervals were studied in the two previous papers (Desherevskii and Sidorin, 2012d, 2014). Stable diurnal and semidiurnal periodicities (24:00 and 12:00 h) were revealed in the seismicity spectra. Periodicities with a small amplitude with periods close to M₂ and O₁ tidal waves were also found in some samples. The correlation coefficients of all time series of earthquakes were calculated with the following theoretical tide parameters: volume deformation, strain rate, of strain rate modulus, and smoothed diurnal tidal amplitude. As the main result, stable significant correlation of seismicity was revealed with some tidal parameters. However, this could be the result of coincidence in periods of sub-harmonics of the diurnal seismicity rhythm with solar tidal waves. This means that the discovered correlation could simply be caused by the coincidence of two regular components in variations of the compared processes, but not with the gravitational tide. Correlations of seismic activity with solar and lunar tides are studied separately in this paper. This makes possible to separate the influence of gravitational and nongravitational factors. Strong correlation of seismicity was observed only with the solar tide. No stable correlation of seismicity with the lunar tide was revealed. The results can be considered evidence for the nongravitational origin of seismic activity variations that correlate with the tidal parameters. This means that tidal seismicity variations, if they are real, should have a much smaller amplitude in comparison with diurnal solar variations of nongravitational origin. Similar effects could cause wrong conclusions on the tidal influence on seismicity in some studies.     

Long-range forecasts of River Po discharges based on predictable solar activity and a fuzzy neural network model / Prévisions à long terme des débits du Fleuve Pô basées sur l’activité solaire prévisible et sur un modèle de réseau de neurones flou

Abstract

Abstract Is it possible to make seasonal and interannual forecasts of hydrological variables if one cannot predict next week’s rainfall? Contrary to common view, some scientists support the hypothesis that variations in mean global temperature and precipitation are controlled more by external forcing (solar variability and volcanic eruptions) than by increasing atmospheric concentration of greenhouse gases. Temperature and precipitation are connected with special phases of the 11-year sunspot cycle, which coincide with significant accumulation of energetic solar eruptions. Because of the possibility of identifying years with many solar eruptions, the attractive prospect emerges of the long-term hydrological forecasting based on cycles of solar activity. Starting from this assumption, an expert system was built based on a fuzzy neural network model for seasonal and interannual forecasting of the Po River discharge. It was found that indices of solar activity and of global circulation are sufficient to yield useful forecasts of hydrological variables.     

The role of solar activity in observed climate changes in the 20th century

The possible contribution of solar and geomagnetic activity to changes in the characteristics of the main components of the climatic system—the ocean and the atmosphere—is considered and discussed. The mechanisms and models of the solar activity impact on thermobaric and climatic characteristics of the troposphere are presented. Based on a complex analysis of hydrometeorological data, it has been shown that changes in the temperature of the troposphere and the World Ocean reflect a response both to individual helio-geophysical perturbations and to long-term changes (1854–2015) of solar and geomagnetic activity. It is established that the climatic response to the influence of solar and geomagnetic activity is characterized by considerable spatio-temporal heterogeneity, is of a regional nature, and depends on the general circulation of the atmosphere. The largest contribution of solar activity to the global climate changes was observed in the period 1910–1943.     

Fractal dimension of changes in the solar magnetic field energy and quasi-biennial solar activity variations

Using the data of 1960–1999 on solar magnetic fields on the source surface and the Higuchi method, the fractal dimension of changes in the solar magnetic field energy at various heliolatitudes and in different time intervals is analyzed. The fractal dimension obtained on a moving 1-year interval displays substantial time variations. The 11-year cycle, which dominates at high latitudes, and quasi-biennial variations (QBVs), which dominate at low latitudes and are similar to QBVs of solar activity indices, are traced in these variations. Thus, solar QBVs that appear in all heliomagnetic activity indices are also present in the fractal structure of the solar magnetic field variations.     

Obtaining of information about the IMF evolution from an analysis of the geomagnetic field data

A comparison of the time variations in the geomagnetic field characteristics (the u and aa indices of geomagnetic activity) with the variation in the solar magnetic dipole inclination shows close agreement between these variations. The linear correlation coefficients between the u and aa indices, the u index and solar magnetic dipole inclination, and the aa index and solar magnetic dipole inclination are 0.93, 0.45, and 0.49, respectively. This makes it possible to extend studying the IMF evolution in the 11-year cycle of solar activity to the 170-year period beginning from 1835. It has been indicated that the time variation in the heliospheric current sheet (HCS) surface deviation from the solar magnetic equator plane, calculated based on the actual HCS configuration, is in good agreement with the time variation in the amplitude of the Fourier series second harmonics in a harmonic analysis of the series of daily data on the IMF sign in the vicinity of the Earth. The linear correlation coefficient is 0.9 in this case.