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Solar Cycle (solar + cycle)
Selected AbstractsA fast computation of the secondary ion production in the ionosphere of MarsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2009William P. Nicholson ABSTRACT We present an analytic method for the rapid computation of secondary ion and electron production due to electron impact as suprathermal electrons produced by primary photoproduction propagate through the neutral background Martian atmosphere. We use a one-dimensional kinetic model, Trans -Mars, that solves a stationary Boltzmann transport equation to describe the ionosphere of Mars with the neutral background atmosphere (temperatures, number densities and geopotential heights) provided by a three-dimensional global circulation model, MarTIM. Parameters are given to allow the rapid computation of secondary ion production for 11 ion species (CO+2, CO++2, CO+, C+, N+2, N++2, N+, O+2, O++2, O+, O++) as well as for the secondary electron production. We use the neutral global circulation model to show that while the efficiency (,) of ion and electron production (ratio of secondary to primary production) does vary with solar zenith angle it can be parametrized with a simple function, which is given. We also show that variations with solar cycle and solar longitude are negligible about the region of the primary and secondary production peaks. [source] Changes in convective properties over the solar cycle: effect on p-mode damping ratesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2001G. Houdek Measurements of both solar irradiance and p-mode oscillation frequencies indicate that the structure of the Sun changes with the solar cycle. Balmforth, Gough & Merryfield investigated the effect of symmetrical thermal disturbances on the solar structure and the resulting pulsation frequency changes. They concluded that thermal perturbations alone cannot account for the variations in both irradiance and p-mode frequencies, and that the presence of a magnetic field affecting acoustical propagation is the most likely explanation of the frequency change, in the manner suggested earlier by Gough & Thompson and by Goldreich et al. Numerical simulations of Boussinesq convection in a magnetic field have shown that at high Rayleigh number the magnetic field can modify the preferred horizontal length scale of the convective flow. Here, we investigate the effect of changing the horizontal length scale of convective eddies on the linewidths of the acoustic resonant mode peaks observed in helioseismic power spectra. The turbulent fluxes in these model computations are obtained from a time-dependent, non-local generalization of the mixing-length formalism. The modelled variations are compared with p-mode linewidth changes revealed by the analysis of helioseismic data collected by the Birmingham Solar-Oscillations Network (BiSON); these low-degree (low- l) observations cover the complete falling phase of solar activity cycle 22. The results are also discussed in the light of observations of solar-cycle variations of the horizontal size of granules and with results from 2D simulations by Steffen of convective granules. [source] Life cycle of the QBO-modulated 11-year solar cycle signals in the Northern Hemispheric winterTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 641 2009Hua Lu Abstract This paper provides some insights on the quasi-biennial oscillation (QBO) modulated 11-year solar cycle (11-yr SC) signals in Northern Hemisphere (NH) winter temperature and zonal wind. Daily ERA-40 Reanalysis and ECMWF Operational data for the period of 1958,2006 were used to examine the seasonal evolution of the QBO-solar cycle relationship at various pressure levels up to the stratopause. The results show that the solar signals in the NH winter extratropics are indeed QBO-phase dependent, moving poleward and downward as winter progresses with a faster descent rate under westerly QBO than under easterly QBO. In the stratosphere, the signals are highly significant in late January to early March and have a life span of ,30,50 days. Under westerly QBO, the stratospheric solar signals clearly lead and connect to those in the troposphere in late March and early April where they have a life span of ,10 days. As the structure changes considerably from the upper stratosphere to the lower troposphere, the exact month when the maximum solar signals occur depends largely on the altitude chosen. For the low-latitude stratosphere, our analysis supports a vertical double-peaked structure of positive signature of the 11-yr SC in temperature, and demonstrates that this structure is further modulated by the QBO. These solar signals have a longer life span (,3,4 months) in comparison to those in the extratropics. The solar signals in the lower stratosphere are stronger in early winter but weaker in late winter, while the reverse holds in the upper stratosphere. Copyright © 2009 Royal Meteorological Society [source] Secular variation of hemispheric phase differences in the solar cycleASTRONOMISCHE NACHRICHTEN, Issue 8 2010N.V. Zolotova Abstract We investigate the phase difference of the sunspot cycles in the two hemispheres and compare it with the latitudinal sunspot distribution. If the north-south phase difference exhibits a long-term tendency, it should not be regarded as a stochastic phenomenon. We use datasets of historical sunspot records and drawings made by Staudacher, Hamilton, Gimingham, Carrington, Spörer, and Greenwich observers, as well as the sunspot activity during the Maunder minimum reconstructed by Ribes and Nesme-Ribes. We employ cross-recurrence plots to analyse north-south phase differences. We show that during the last 300 years, the persistence of phase-leading in one of the hemispheres exhibits a secular variation. Changes from one hemisphere to the other leading in phase were registered near 1928 and 1968 as well as two historical ones near 1783 and 1875. A long-term anticorrelation between the hemispheric phase differences in the sunspot cycles and the latitudinal distribution of sunspots was traced since 1750 (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The Big Bear Solar Observatory Ca II K-line index for solar cycle 23ASTRONOMISCHE NACHRICHTEN, Issue 7 2010M.F. Naqvi Abstract We present an analysis of 2634 Ca II K-line full-disk filtergrams obtained with the 15-cm aperture photometric full-disk telescope at Big Bear Solar Observatory during the period from 1996 January 1 to 2005 October 24. Using limb darkening corrected and contrast enhanced filtergrams, solar activity indices were derived, which are sensitive to the 11-year solar activity cycle and 27-day rotational period of plages around active regions and the bright chromospheric network. The present work extends an earlier study (solar cycle 22), which was based on video data. The current digital data are of much improved quality with higher spatial resolution and a narrower passband ameliorating photometric accuracy. The time series of chromospheric activity indices cover most of solar cycle 23. One of the most conspicuous features of the Ca II K indices is the secondary maximum in late 2001/early 2002 after an initial decline of chromospheric activity during the first half of 2001. We conclude that a secular trend exists in the Ca II K indices, which has its origin in the bright chromospheric network and brightenings related to decaying active regions. Superposed on this secular trend are the signatures of recurring, long-lived active regions, which are clusters of persistent and continuously emerging magnetic flux. Such features are less visible, when the activity belts on both side of the equator are devoid of the brightenings related to decaying active regions as was the case in October/November 2003 at a time when a superactivity complex including several naked-eye sunspots emerged (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Relationship between group sunspot numbers and Wolf sunspot numbersASTRONOMISCHE NACHRICHTEN, Issue 7 2010K.J. Li Abstract Continuous wavelet transform and cross-wavelet transform have been used to investigate the phase periodicity and synchrony of the monthly mean Wolf (Rz) and group (Rg) sunspot numbers during the period of June 1795 to December 1995. The Schwabe cycle is the only one common period in Rg and Rz, but it is not well-defined in case of cycles 5,7 of Rg and in case of cycles 5 and 6 of Rz. In fact, the Schwabe period is slightly different in Rg and Rz before cycle 12, but from cycle 12 onwards it is almost the same for the two time series. Asynchrony of the two time series is more obviously seen in cycles 5 and 6 than in the following cycles, and usually more obviously seen around the maximum time of a cycle than during the rest of the cycle. Rg is found to fit Rz better in both amplitudes and peak epoch during the minimum time time of a solar cycle than during the maximum time of the cycle, which should be caused by their different definition, and around the maximum time of a cycle, Rg is usually less than Rz. Asynchrony of Rg and Rz should somewhat agree with different sunspot cycle characteristics exhibited by themselves (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dynamics of the solar magnetic field from SOHO/MDIASTRONOMISCHE NACHRICHTEN, Issue 1 2010E.E. Benevolenskaya Abstract The investigation of the dynamics of magnetic fields from small scales to the large scales is very important for the understanding of the nature of solar activity. It is also the base for producing adequate models of the solar cycle with the purpose to predict the level of solar activity. Since December 1995 the Michelson Doppler Imager (MDI) on board of the Solar and Heliospheric Observatory (SOHO) provides full disk magnetograms and synoptic maps which cover the period of solar cycle 23 and the current minimum. In this paper, I review the following important topics with a focus on the dynamics of the solar magnetic field. The synoptic structure of the solar cycle; the birth of the solar cycle (overlapping cycles 23 and 24); the relationship of the photospheric magnetic activity and the EUV solar corona, polar magnetic fields and dynamo theory (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The solar dynamo in the light of the distribution of various sunspot magnetic classes over butterfly diagramASTRONOMISCHE NACHRICHTEN, Issue 1 2010D. Sokoloff Abstract We present the data concerning the distribution of various sunspot magnetic classes over the solar butterfly diagram and discuss how this data can inform solar dynamo models. We use the statistics of sunspots that violate the Hale polarity law to estimate the ratio of the fluctuating and mean components of the toroidal magnetic field inside the solar convective zone. An analysis of the spatial distribution of bipolar, unipolar and complex sunspot groups in the context of simple dynamo models results in the conclusion that the mean toroidal field is relatively simple and maintains its shape during the course of the solar cycle (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] From Gauß to Biermann: Highlights from the first 117 years of publications in Astronomische Nachrichten/Astronomical NotesASTRONOMISCHE NACHRICHTEN, Issue 6 2009R. von Berlepsch Abstract We present facsimiles of some of the scientifically and historically most relevant papers published in Astronomische Nachrichten/Astronomical Notes (AN) between 1821 and 1938. Almost all of these papers were written and printed in German and it is sometimes not completely straightforward to find these original works and then to cite the historically correct version, e.g. in case of a series of articles or editorial letters. It was common during the early years that many contributions were made in form of letters to the editor. We present a summary for these original works with an English translation of their titles. Among the highlights are the originals of the discovery of stellar parallaxes by FriedrichWilhelm Bessel, the discovery of the solar cycle by Heinrich Schwabe, the discovery of the planet Neptune by Johann Gottfried Galle, the first ever measured stellar radial velocity by Hermann Vogel, the discovery of radio emission from the Sun by Wilsing and Scheiner, the first ever conducted photoelectric photometry of stars by Paul Guthnick and up to the pioneering work by Karl Schwarzschild, Ejnar Hertzsprung, Erwin Finlay Freundlich and others. As a particular gimmick we present the still world record holding shortest paper ever published; by Johannes Hartmann in AN 226, 63 (1926) on Nova Pictoris. Our focus is on contributions in the early years and published until 1938 near the verge of the second world war (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Intermediate-term variations in solar radius during solar cycle 23ASTRONOMISCHE NACHRICHTEN, Issue 4 2009H. Kiliç Abstract 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) [source] CLIMATIC VARIABILITY ALONG A NORTH,SOUTH TRANSECT OF FINLAND OVER THE LAST 500 YEARS: SIGNATURE OF SOLAR INFLUENCE OR INTERNAL CLIMATE OSCILLATIONS?GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 2 2008MAXIM G. OGURTSOV ABSTRACT. Statistical analysis of a multi-centennial dendrochronological proxy dataset of regional climate, constructed across the latitudinal gradient of 1000 km, was performed. It was shown that centennial (c. 100 year), tri-decadal (27-32 year), bi-decadal (17-23 year) and decadal (9-13 year) periodicities governed the climate variability in Finland over the last five centuries. Despite the fact that many of the climatic periodicities bore great resemblance to periodicities of solar cycles, little evidence of actual solar influence on Finnish climate was found when the climate proxy records were subjected to linear correlation analysis with sunspot numbers. Highly non-linear response of Northern Fennoscandian climate to solar forcing might be a cause of this result, as well as influence of terrestrial climatic processes (e.g. effect of other forcing factors and internal dynamics of regional climate). Our results show that the presence of internal climate variability at time-scales of solar activity might distort the solar signature in climatic data and complicate its detection. [source] Searching for mid-term variations in different aspects of solar activity , looking for probable common origins and studying temporal variations of magnetic polaritiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007E. Forgács-Dajka ABSTRACT Several studies have examined the temporal variability of the solar activity, and many variations are reported in the literature. We also (re)analyse the statistical properties of the following kinds of data series of solar activity phenomena: magnetic synoptic charts, hemispherical relative sunspot numbers, solar flare index, coronal index, solar radio flux, interplanetary magnetic field and proton speed in the solar wind, in order to find common mid-term periods during solar cycles 21,23. As a new approach, we focus on the magnetic polarity relations and we define new quantities (e.g. magnetic positive,negative polarity asymmetry) to explore the connections between several aspects of the solar activity from different points of view. According to our survey, the mid-term periodicities (1,2 yr) are manifest in almost all data with the exception of the coronal index and the 10.7-cm solar flux data. In the case of these latter two we note that these surveys produce global data on the solar corona, so the Sun is studied on these bandwidths as a star. Besides these, with the accumulation of helioseismic data over the last 10 yr, it has become possible to study the temporal variation in the rotational rate residuals in tachocline region. In addition, we examine possible common origins of different activity markers and/or possible connections to differential rotation. [source] Intermediate-term variations in solar radius during solar cycle 23ASTRONOMISCHE NACHRICHTEN, Issue 4 2009H. Kiliç Abstract 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) [source] Are solar cycles predictable?ASTRONOMISCHE NACHRICHTEN, Issue 10 2007M. Schüssler Abstract Various methods (or recipes) have been proposed to predict future solar activity levels , with mixed success. Among these, some precursor methods based upon quantities determined around or a few years before solar minimum have provided rather high correlations with the strength of the following cycles. Recently, data assimilation with an advection-dominated (flux-transport) dynamo model has been proposed as a predictive tool, yielding remarkably high correlation coefficients. After discussing the potential implications of these results and the criticism that has been raised, we study the possible physical origin(s) of the predictive skill provided by precursor and other methods. It is found that the combination of the overlap of solar cycles and their amplitude-dependent rise time (Waldmeier's rule) introduces correlations in the sunspot number (or area) record, which account for the predictive skill of many precursor methods. This explanation requires no direct physical relation between the precursor quantity and the dynamo mechanism (in the sense of the Babcock-Leighton scheme or otherwise). (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||