A numerical response of the middle atmosphere to the 11-year solar cycle

A two-dimensional numerical model with coupled photochemistry and dynamics has been used to investigate the response of the middle atmosphere (16–116 km) to changes in solar activity over the 11-year solar cycle. Model inputs that vary with solar cycle include solar radiation, cosmic ray and auroral ionization rates and the flux of NO_x at the model's upper boundary.In this study, the results of model runs for solar cycle minimum and maximum conditions are compared. In the stratosphere, using currently accepted estimates of changes in solar radiation at wavelengths longer than 180 nm, only small responses in ozone, temperature and zonal winds are obtained. On the other hand, changes at shorter wavelengths, and the effects of particle precipitation, lead to large variations in the abundances of trace species in the thermosphere and upper mesosphere. In particular, very large abundances of NO_x are produced above 90 km by auroral particle precipitation. Considerable amounts of NO_x are transported subsequently to the stratosphere by the global mean meridional circulation. It is shown that this excess NO_x can lead to significant decreases in ozone concentrations at high latitudes and that it may explain observations of nitrate deposition in Antarctic snow.     

Transport of thermospheric NO to the upper stratosphere?

The rate of production of NO in the thermosphere is expected to vary greatly over the course of an 11-year solar cycle because the fluxes of both extreme ultraviolet radiation and auroral particles are known to increase substantially from solar minimum to solar maximum. In the stratosphere, NO participates in a catalytic cycle which constitutes the dominant photochemical destruction mechanism for stratospheric ozone. If appreciable long range transport of NO from the thermosphere to the upper stratosphere occurs, its effects should therefore be manifested in upper atmospheric ozone density variations over the 11-year solar cycle. In this paper, model predictions of the seasonal and latitudinal variations in upper stratospheric O₃ associated with NO transport for different levels of solar activity are compared to satellite observations of upper stratospheric ozone abundances.     

Solar irradiance between 120 and 400nm and its variations

The solar ultraviolet irradiance measurements in the 120–400 nm wavelength range are reviewed and compared showing still important discrepancies between the irradiance values deduced from the most recent observations.The possible variations of the solar ultraviolet irradiances with the 27-day rotation period of the Sun and with the 11-year activity cycle are presented and discussed on the basis of the available irradiation fluxes obtained during the rising phase of solar cycle 21.The spectral features of both kinds of variation are clearly related to the solar atmospheric layer from which the corresponding radiation is emitted.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

A dynamical mechanism through which variations in solar ultraviolet radiation can influence tropospheric climate

Variations in solar UV radiation can lead to changes in the mean temperature and wind distributions in the stratosphere and, through modification of the ozone photochemistry, to changes in the damping rate of temperature perturbations about the mean. Such changes can influence the stratospheric propagation characteristics of planetary waves generated in the troposphere, leading to changes in the steady state interference pattern of these waves at all levels. In particular, the poleward heat transfer by the planetary waves in the troposphere can be strongly modified, thus providing a mechanism whereby solar cycle variations in ultraviolet radiation can influence climate.The dynamics of the mechanism are presented in a simple form and the literature on the subject is reviewed.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Gome Solar UV/VIS Irradiance Measurements between 1995 and 1997 – First Results on Proxy Solar Activity Studies

The Global Ozone Monitoring Experiment (GOME) is the first of a series of European satellite instruments monitoring global ozone and other relevant trace constituents in the UV/visible spectral range. On 20 April 1995, the European Space Agency (ESA) launched the GOME from Kourou, French Guyana, aboard the second European Remote Sensing satellite (ERS-2). In order to obtain the geometric albedo from the backscattered terrestrial radiance measurements, a solar irradiance measurement sequence in the spectral range between 240 nm and 790 nm is carried out once every day. The GOME solar irradiance is recorded at a moderate spectral resolution (0.2–0.4 nm), thus providing an excellent opportunity to contribute to the long-term investigation of solar flux variation associated with the 11-year solar activity cycle from space, which started in 1978 with SBUV (Solar Backscatter UV Experiment) observations on Nimbus-7 and covers solar cycles 21 and 22. This paper briefly describes the GOME spectrometer and measurement mode which are relevant to the solar viewing. Preliminary results from the solar irradiance measurements between 1995 and 1997 and comparisons to SSBUV-8 (Shuttle SBUV) in January 1996 are presented. Solar activity indices used as proxies for solar flux variation are often used to find a correlation with observed variation in atmospheric quantities, for instance, total ozone. Initial results from the GOME Mgii (280 nm) and Caii K (393 nm) solar activity index calculation are presented and discussed. The coupling of solar irradiance variability to global change is a current source of scientific and public concern. This study shows that GOME/ERS-2 (1995–2001) and the next generation of European remote sensing instruments, SCIAMACHY and GOME/METOP, have the potential to provide continuity in the measurements of solar irradiance from space well into the next century.     

Pioneer-10 observation of the solar wind proton temperature heliocentric gradient

Solar wind isotropic proton temperatures as measured out to 12.2 AU heliocentric distance by the Ames plasma analyzer aboard Pioneer-10 are presented as consecutive averages over three Carrington solar rotations and discussed. The weighted least-squares fit of average temperature to heliocentric radial distance, R, yields the power law R ^-0.52. These average proton temperatures are not correlated as well with Pioneer-10's heliocentric radial distance (-0.85) as are the corresponding average Zürich sunspot numbers R _z (-0.95). Consequently, it is difficult to isolate the spatial gradient in the Pioneer-10 solar wind proton temperatures using that data alone.     

Can the Solar Cycle Amplitude Be Predicted Using the Preceding Solar Cycle Length?

In this work, the evolution of the relationship between Solar Cycle Length of solar cycle n (SCL _n ) and Solar Cycle Amplitude of the solar cycle n+1 (SCA _n+1) is studied by using the R _Z and R _G sunspot numbers. We conclude that this relationship is only strongly significant in a statistical sense during the first half of the historical record of R _Z sunspot number whereas it is considerably less significant for the R _G sunspot number. In this sense we assert that these simple lagged relationships should be avoided as a valid method to predict the following solar activity amplitude.     

The role of solar-wind velocity-waves in comet outburst activity

Comet outburst activity and the structure of solar wind streams were compared on the basis of Pioneer 10, 11, Vela 3 and IMP 7, 8 measurements at the heliocentric distance r ≈ 1–6 AU. It is shown that the solar wind velocity waves which are evolving into corotating shock waves beyond the Earth orbit may be responsible for comet outburst activity. The correlation between variations of comet outburst activity with heliocentric distance and the behavior of the solar wind velocity waves is established. The closeness of the characteristic times for the velocity waves and comet outburst activity (7–8 days at r = 1 AU) as well as the simultaneous growth of both the characteristic times with r are noted. The observed distribution of the comet outburst activity parameters during the 11-year cycle is also in good agreement with the phase distributions during the 11-year cycle of variations of the coronal hole areas and the rate of change of the sunspot area δS _p.     

Wavelet Analysis on Solar Wind Parameters and Geomagnetic Indices

The geomagnetic activity is the result of the solar wind–magnetosphere interaction. It varies following the basic 11-year solar cycle; yet shorter time-scale variations appear intermittently. We study the quasi-periodic behavior of the characteristics of solar wind (speed, temperature, pressure, density) and the interplanetary magnetic field (B _x , B _y , B _z , β, Alfvén Mach number) and the variations of the geomagnetic activity indices (D _ST, AE, A _p and K _p). In the analysis of the corresponding 14 time series, which span four solar cycles (1966?–?2010), we use both a wavelet expansion and the Lomb/Scargle periodograms. Our results verify intermittent periodicities in our time-series data, which correspond to already known solar activity variations on timescales shorter than the sunspot cycle; some of these are shared between the solar wind parameters and geomagnetic indices.     

Variability of Solar Five-Minute Oscillations in the Corona as Observed by the Extreme Ultraviolet Spectrophotometer (ESP) on the Solar Dynamics Observatory/Extreme Ultraviolet Variability Experiment (SDO/EVE)

Solar five-minute oscillations have been detected in the power spectra of two six-day time intervals from soft X-ray measurements of the Sun observed as a star using the Extreme Ultraviolet Spectrophotometer (ESP) onboard the Solar Dynamics Observatory (SDO)/Extreme Ultraviolet Variability Experiment (EVE). The frequencies of the largest amplitude peaks were found to match the known low-degree (?=0?–?3) modes of global acoustic oscillations within 3.7 μHz and can be explained by a leakage of the global modes into the corona. Due to the strong variability of the solar atmosphere between the photosphere and the corona, the frequencies and amplitudes of the coronal oscillations are likely to vary with time. We investigated the variations in the power spectra for individual days and their association with changes of solar activity, e.g. with the mean level of the EUV irradiance, and its short-term variations caused by evolving active regions. Our analysis of samples of one-day oscillation power spectra for a 49-day period of low and intermediate solar activity showed little correlation with the mean EUV irradiance and the short-term variability of the irradiance. We suggest that some other changes in the solar atmosphere, e.g., magnetic fields and/or inter-network configuration may affect the mode leakage to the corona.     

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.     

Periodicities in Global Mean TEC from GNSS Observations

As an important measurement parameter, global total electron content (TEC) is appropriate for the study of the Sun–Earth connection. In this paper, the wavelet technique is employed to investigate the periodicities in global mean TEC during 1995–2008. Analysis results show several remarkable components (including 27-day, semiannual and annual cycles) existing in global mean TEC with obvious time-variable characteristics, besides 11-year cycle. After analyzing sunspot numbers and solar extreme ultra-violet (EUV) radiation variations during this time period, except for semiannual variations, close correlation between global mean TEC and solar variations is found, especially, a strong resemblance of the 27-day fluctuation exists in global mean TEC, sunspot and solar EUV radiation variations.     

Clustering of Emerging Magnetic Flux

We report observations of the large-scale spatial dependence of the Sun's luminosity variations over the period 1993–1995. The measurements were made using a new scanning disk solar photometer at Big Bear Solar Observatory, specially designed to measure large-scale brightness variations at the 10^–4 level. Since the level of solar activity was very low for the entire observation period, the data show little solar cycle variation. However, the residual brightness signal I/I (after subtracting the mean, first, and second harmonics) does show a strong dependence on heliocentric angle, peaking near the limb. This is as one would expect if the residual brightness signal (including the excess brightness coming from the active latitudes) were primarily facular in origin. Additional data over the next few years, covering the period from solar minimum to maximum, should unambiguously reveal the large-scale spatial structure of the solar cycle luminosity variations.     

Nitrate Concentration in Greenland Ice: an Indicator of Changes in Fluxes of Solar and Galactic High-Energy Particles

Two sets of nitrate (NO₃ ^–) concentration data in Central Greenland ice, obtained through the GISP2 collaboration and by the University of Kansas, were analyzed statistically. The two records correlate well over time scales from a few years up to a century. They both contain quasi five-year, decadal and century-type time variations. A quasi five-year periodicity resulting from increases in the mean nitrate concentration before and after maximum sunspot number was confirmed. A tendency of solar proton events to occur more frequently during the rise/decline phases of the solar cycle may cause a quasi five-year variation. Century-type (60–110 yr) variability in nitrate outstrips the corresponding Gleissberg cycle in sunspots by 12–17 years and changes synchronously (correlates with zero phase shift) with the smoothed length of the solar Schwabe cycle. A significant correlation between century-type periodicities for nitrates in Greenland ice and northern Fennoscandian temperatures was established. The results show that despite a strong dependence on local meteorology, nitrate concentration in ice contains valuable information about global geophysical phenomena in the past.     

Two Unusual Episodes of ≈13-Day Variations II. Implications for the Solar Radio Flux Density, <Emphasis Type="Italic">F</Emphasis><Subscript>10.7 cm</Subscript>

Additional analysis of the behavior of the international sunspot number (R) series and the solar radio flux density (F_{10.7 cm}) series during two long (250–500 days) and distinct episodes of persistent ≈13-day variations (Crane, Solar Phys. 1998, 253, 177) is reported. The conclusion is that while the center-to-limb behavior of R does not change between solar minimum and solar maximum, F_{10.7 cm} exhibits significantly less limb brightening at solar maximum than at solar minimum.     

A New Method for Prediction of Peak Sunspot Number and Ascent Time of the Solar Cycle

The purpose of the present study is to develop an empirical model based on precursors in the preceding solar cycle that can be used to forecast the peak sunspot number and ascent time of the next solar cycle. Statistical parameters are derived for each solar cycle using “Monthly” and “Monthly smoothed” (SSN) data of international sunspot number (R _i). Primarily the variability in monthly sunspot number during different phases of the solar cycle is considered along with other statistical parameters that are computed using solar cycle characteristics, like ascent time, peak sunspot number and the length of the solar cycle. Using these statistical parameters, two mathematical formulae are developed to compute the quantities [Q _C] _n and [L] _n for each nth solar cycle. It is found that the peak sunspot number and ascent time of the n+1th solar cycle correlates well with the parameters [Q _C] _n and [L] _n /[S _Max] _n+1 and gives a correlation coefficient of 0.97 and 0.92, respectively. Empirical relations are obtained using least square fitting, which relates [S _Max] _n+1 with [Q _C] _n and [T _a] _n+1 with [L] _n /[S _Max] _n+1. These relations predict a peak of 74±10 in monthly smoothed sunspot number and an ascent time of 4.9±0.4 years for Solar Cycle 24, when November 2008 is considered as the start time for this cycle. Three different methods, which are commonly used to define solar cycle characteristics are used and mathematical relations developed for forecasting peak sunspot number and ascent time of the upcoming solar cycle, are examined separately.     

Comparative Analyses of the CSSS Calculation in the UCSD Tomographic Solar Observations

We describe a new method to derive the interplanetary magnetic field (IMF) out to 1 AU from photospheric magnetic field measurements. The method uses photospheric magnetograms to calculate a source surface magnetic field at 15R_⊙. Specifically, we use Wilcox Solar Observatory (WSO) magnetograms as input for the Stanford Current-Sheet Source-Surface (CSSS) model. Beyond the source surface the magnetic field is convected along velocity flow lines derived by a tomographic technique developed at UCSD and applied to interplanetary scintillation (IPS) observations. We compare the results with in situ data smoothed by an 18-h running mean. Radial and tangential magnetic field amplitudes fit well for the 20 Carrington rotations studied, which are largely from the active phase of the solar cycle. We show exemplary results for Carrington rotation 1965, which includes the Bastille Day event.     

Magnetic Flux Imbalance of the Solar and Heliospheric Magnetic Fields

A comparative analysis of solar and heliospheric magnetic fields in terms of their cumulative sums reveals cyclic and long-term changes that appear as a magnetic flux imbalance and alternations of dominant magnetic polarities. The global magnetic flux imbalance of the Sun manifests itself in the solar mean magnetic field (SMMF) signal. The north – south asymmetry of solar activity and the quadrupole mode of the solar magnetic field contribute the most to the observed magnetic flux imbalance. The polarity asymmetry exhibits the Hale magnetic cycle in both the radial and azimuthal components of the interplanetary magnetic field (IMF). Analysis of the cumulative sums of the IMF components clearly reveals cyclic changes in the IMF geometry. The accumulated deviations in the IMF spiral angle from its nominal value also demonstrate long-term changes resulting from a slow increase of the solar wind speed over 1965 – 2006. A predominance of the positive IMF B _z with a significant linear trend in its cumulative signal is interpreted as a manifestation of the relic magnetic field of the Sun. Long-term changes in the IMF B _z are revealed. They demonstrate decadal changes owing to the 11/22-year solar cycle. Long-duration time intervals with a dominant negative B _z component were found in temporal patterns of the cumulative sum of the IMF B _z .     

Solar indices and solar u.v.-irradiances

Solar radio fluxes, Zurich relative sunspot number R_z, and Solar Call plage indexes daily values for the period 1957–1980 are analyzed in order to test the stability of the series with respect to time and solar activity. It is found that between the series of the 3,8 and 10 cm radio fluxes and the series of R_z no significant trend with time, solar activity or solar cycle exists when mean values for periods of the order of one year are considered.Then, the daily solar u.v.-irradiances measured since 1969 for H-Lyman-alpha and-beta, the Hel-resonance line and HeII-Lyman-alpha are compared with the 10.7 cm radio fluxes and adjusted. After adjustment, the behaviour of the four series of irradiances with respect to the 10.7 cm flux shows a similar structure as the behaviour typical for the series of the 3 cm or the 8 cm fluxes.This adjustment allows the determination of the slope of the mean variation of the u.v.-irradiances with solar activity. The increases from solar minimum to solar maximum related to the minimum values are respectively : 60% for H-Lyman-alpha, 80% for H-Lyman-beta and 90% for Hel and Hell.     

The 156-day quasi-periodicity in solar indices

This paper investigates a series of daily solar indices: the sunspot number W (1900–2008), solar flux at 2800 MHz F _10.7 (1947–2008), and a number of X-ray flares N _x (1981–2008). The methods of Fourier and wavelet analysis are used to reveal the so-called 156-day Rieger-type periodicity (RTP). The W index is observed to have a statistically significant RTP amplitude in the neighborhood of the solar maxima in most of the solar cycles under study, except for cycles 14, 15, and 23. The 156-day peak is observed to have its largest power during the declining phase of cycle 16, at the maximum of cycle 21, and during the increasing phase of cycles 20 and 23. Statistically significant RTPs are also observed at the minima of cycles 17, 18 and 19. We conclude that there is no stable dependence between RTP and the solar cycle. The wavelet analysis shows that the pattern of the RTP time dependence for the F _10.7 index is almost identical to that of the W index. The correlation coefficient between the RTP curves is 0.95. The correlation coefficients for the pairs of indices W-N _x and F _10.7-N _x are 0.36 and 0.32, respectively. No time lags are found between the RTP starting points for different indices. Thus, the 156-day quasi-periodicity involves, almost simultaneously, events that occur in active regions of the solar atmosphere at different heights. This paper discusses the possible nature of RTP.