Home About us Contact
|
Home About us Contact | ||
|
|
||
Solar Activity (solar + activity)
Selected AbstractsModulation of the sunspot cycleASTRONOMY & GEOPHYSICS, Issue 3 2010Nigel Weiss Solar activity has been abnormally high for the last half-century, but the extremely feeble start of the latest 11-year cycle suggests that this episode is probably coming to an end. This prospect raises some fascinating and important issues, involving an extremely wide range of timescales, writes Nigel Weiss. [source] Climatic change during the last 4000 years in the southern Tarim Basin, Xinjiang, northwest China,JOURNAL OF QUATERNARY SCIENCE, Issue 7 2007Wei Zhong Abstract In this study, a ca. 4000,cal. yr ancient lacustrine (or wetland) sediment record at the southern margin of Tarim Basin is used to reconstruct the history of climate change. Six radiocarbon dates on organic matter were obtained. ,18O and ,13C of carbonate, pollen and sediment particle size were analysed for climate proxies. The proxies indicate that a drier climate prevailed in the area before ca. 1010 BC and during period 1010 BC,AD 500 climate then changed rapidly and continuously from dry to moist, but after about AD 500 climate generally shows dry condition. Several centennial-scale climatic events were revealed, with the wettest spell during AD 450,550, and a relatively wetter interval between AD 930,1030. Pollen results show that regional climate may influence human agricultural activities. Spectral analysis of mean grain size (MGS) proxy reveals statistically pronounced cyclic signals, such as ca. 200,yr, ca. 120,yr, ca. 90,yr, ca. 45,yr and ca. 33 or 30,yr, which may be associated with solar activities, implying that solar variability plays an important role in the decadal- and centennial-scale climate variations in the study area. Copyright © 2007 John Wiley & Sons, Ltd. [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] A geochronological approach to understanding the role of solar activity on Holocene glacier length variability in the Swiss AlpsGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2006Anne Hormes ABSTRACT. We present a radiocarbon data set of 71 samples of wood and peat material that melted out or sheared out from underneath eight presentday mid-latitude glaciers in the Central Swiss Alps. Results indicated that in the past several glaciers have been repeatedly less extensive than they were in the 1990s. The periods when glaciers had a smaller volume and shorter length persisted between 320 and 2500 years. This data set provides greater insight into glacier variability than previously possible, especially for the early and middle Holocene. The radiocarbon-dated periods defined with less extensive glaciers coincide with periods of reduced radio-production, pointing to a connection between solar activity and glacier melting processes. Measured long-term series of glacier length variations show significant correlation with the total solar irradiance. Incoming solar irradiance and changing albedo can account for a direct forcing of the glacier mass balances. Long-term investigations of atmospheric processes that are in interaction with changing solar activity are needed in order to understand the feedback mechanisms with glacier mass balances. [source] Modeling tropical cyclone intensity with quantile regressionINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2009Thomas H. Jagger Abstract Wind speeds from tropical cyclones (TCs) occurring near the USA are modeled with climate variables (covariates) using quantile regression. The influences of Atlantic sea-surface temperature (SST), the Pacific El Nińo, and the North Atlantic oscillation (NAO) on near-coastal TC intensity are in the direction anticipated from previous studies using Poisson regression on cyclone counts and are, in general, strongest for higher intensity quantiles. The influence of solar activity, a new covariate, peaks near the median intensity level, but the relationship switches sign for the highest quantiles. An advantage of the quantile regression approach over a traditional parametric extreme value model is that it allows easier interpretation of model coefficients (parameters) with respect to changes to the covariates since coefficients vary as a function of quantile. It is proven mathematically that parameters of the Generalized Pareto Distribution (GPD) for extreme events can be used to estimate regression coefficients for the extreme quantiles. The mathematical relationship is demonstrated empirically using the subset of TC intensities exceeding 96 kt (49 m/s). Copyright © 2008 Royal Meteorological Society [source] Holocene vegetation and land-use changes in response to climatic changes in the forelands of the southwestern Alps, Italy,JOURNAL OF QUATERNARY SCIENCE, Issue 3 2006Walter Finsinger Abstract The Holocene sediment of Lago Piccolo di Avigliana (Piedmont, Italy, 356,m,a.s.l.) was dated by 14C and analysed for pollen to reconstruct the vegetation history of the area. The early- and mid-Holocene pollen record shows environmental responses to centennial-scale climatic changes as evidenced by independent palaeoclimatic proxies. When human impact was low or negligible, continental mixed-oak forests decreased at ca. 9300 BC in response to the early-Holocene Preboreal climatic oscillation. Abies alba expanded in two phases, probably in response to higher moisture availability at ca. 6000 and ca. 4000 BC, while Fagus expanded later, possibly in response to a climatic change at 3300 BC. During and after the Bronze Age five distinct phases of intensified land use were detected. The near synchroneity with the land-use phases detected in wetter regions in northern and southern Switzerland points to a common forcing factor in spite of cultural differences. Increasing minerogenic input to the lake since 1000 BC coincided with Late Bronze,Iron Age technical innovations and probably indicate soil erosion as a consequence of deforestation in the lake catchment. The highest values for cultural indicators occurred at 700,450 and at 300,50 BC, coinciding with periods of high solar activity (inferred from ,14C). This suggests that Iron Age land use was enhanced by high solar activity, while re-occupation of partly abandoned areas after crises in earlier periods match better with the GRIP stable isotope record. On the basis of our data and comparison with independent palaeoclimatic proxies we suggest that precipitation variation was much more important than temperature oscillations in driving vegetation and societal changes throughout the Holocene. Copyright © 2006 John Wiley & Sons, Ltd. [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] Search for solar cycle changes in the signature of rapid variation in BiSON dataMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2004G. A. Verner ABSTRACT The second helium ionization zone and the base of the convective envelope are regions of rapid variation of solar structure which introduce characteristic signatures into the frequencies of p-mode oscillations. These signals provide a direct seismological method to probe the acoustic properties of these regions. In this work we isolate these signatures in over 9 yr of low-degree BiSON data and extract information on the acoustic depth and local properties from each signal. Any temporal variations are investigated by fitting the signals extracted from 432, 864 and 1728-d spectra. The extracted parameters are found to be in agreement over the different length spectra and within one formal standard deviation of the values obtained for model ,S'. There is no evidence found for any systematic variation in the acoustic depth, width or magnitude of the second helium ionization zone, which suggests any activity-dependent disturbance to the near surface layers does not propagate down to this layer. The convection zone signal does show some temporal variation that may be correlated with solar activity, although further analysis with current data is required. The isolation of these signatures in low-degree data confirms that this method can be used to provide structural information on Sun-like stars once similar asteroseismic data become available. [source] Strong signature of the active Sun in 100 years of terrestrial insolation dataANNALEN DER PHYSIK, Issue 6 2010W. Weber Abstract Terrestrial solar irradiance data of the Smithsonian Astrophysical Observatory from 1905 to 1954 and of Mauna Loa Observatory from 1958 to 2008 are analyzed. The analysis shows that, with changing solar activity, the atmosphere modifies the solar irradiance on the percentage level, in all likelihood via cosmic ray intensity variations produced by the active sun. The analysis strongly suggests that cosmic rays cause a large part of the atmospheric aerosols. These aerosols show specific absorption and scattering properties due to an inner structure of hydrated ionic centers, most probably of O2 - and O2+ produced by the cosmic rays. [source] CLIMATE FORCINGS AND THEIR INFLUENCE ON ALPINE HISTORY AS RECONSTRUCTED THROUGH THE APPLICATION OF SYNCHROTRON-BASED X-RAY MICROFLUORESCENCE ON LAYERED STALAGMITES*ARCHAEOMETRY, Issue 2 2005S. FRISIA Solar variability and volcanic activity strongly interact with climate and the environment. Synchrotron radiation X-ray microfluorescence (micro-XRF) to an annually laminated Alpine stalagmite confirmed that annual laminae result from hydrological variability and changes in the duration of soil microbial degradation. The latter is modulated by solar variability. At the centennial timescale, growth rate and solar activity appear to be correlated with temperature change, with low temperatures at solar minima. By combining micro-XRF and absorption spectroscopy techniques (XANES), we also found that speleothems are a new archive of aerosol sulphate related to volcanic activity. Peaks in S-concentration from c. 5.2 to 5.0 ka bp in an Alpine stalagmite suggest that multiple volcanic sulphate aerosol emissions enhanced Mid-Holocene summer cooling, thus favouring the preservation of the Alpine Iceman mummy in a persistent ice casket. [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] 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] Background magnetic fields during last three cycles of solar activityASTRONOMISCHE NACHRICHTEN, Issue 6 2008O.A. Andryeyeva Abstract This paper describes our studies of evolution of the solar magnetic field with different sign and field strength in the range from ,100 G to 100 G. The structure and evolution of large-scale magnetic fields on the Sun during the last 3 cycles of solar activity is investigated using magnetograph data from the Kitt Peak Solar Observatory. This analysis reveals two groups of the large-scale magnetic fields evolving differently during the cycles. The first group is represented by relatively weak background fields, and is best observed in the range of 3,10 Gauss. The second group is represented by stronger fields of 75,100 Gauss. The spatial and temporal properties of these groups are described and compared with the total magnetic flux. It is shown that the anomalous behaviour of the total flux during the last cycle can be found only in the second group. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ir A.H. de Voogt: life and career of a radio pioneerASTRONOMISCHE NACHRICHTEN, Issue 5 2007R.G. Strom Abstract There are probably few radio astronomers who would be able to recall A.H. de Voogt, which is unfortunate, but at the same time unsurprising: for he published no original astronomical research, never carried out pioneering observations, nor is his name linked to either theoretical or instrumental breakthroughs. Yet he was described by the man who first observed the 21 cm hydrogen line from the Netherlands as a radio astronomy pioneer, at the very birth of the Dutch effort. He was, moreover, a trail blazer at the cutting edge of radio, not once but twice in his career. Without him it is unlikely that the 21 cm line would have been observed in the Netherlands in 1951, and arguably the H I mapping of the Milky Way under Jan Oort's leadership would have taken place much later, if at all. Radio astronomy observing itself might well have been compromised by interference had it not been for De Voogt's foresight. Anthonet Hugo de Voogt (1892,1969) built, while still a teenager, one of the very first amateur radio stations (call letters VO: · · · ,/, , ,) in Holland, earned the radio-telegrapher's diploma during his student days, and was intimately involved in the foundation of the Dutch Society for Radio-Telegraphy in 1916. Until the 1920s, he was very active in amateur radio and astronomy circles. Trained in electrical engineering at Delft, he joined the PTT (Post Office) as a telegraph engineer in 1919, worked his way through the ranks to become head of the telephone district of Breda in 1939, and was promoted to head the PTT Radio Service just days after the end of the war. As his department was responsible for overseas radio communication, he initiated a research effort to study radio propagation in the ionosphere and the effects of solar activity. To this end, he rescued a number of Würzburg-Riese 7.5-m radar antennas abandoned at the end of the war, made one available for Jan Oort's H I work, and launched a series of radio astronomical initiatives. His group also built a number of antennas, monitored solar emission, and participated in the International Geophysical Year (1957,1958). (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Helioseismology program for Solar Dynamics ObservatoryASTRONOMISCHE NACHRICHTEN, Issue 3-4 2007A. G. Kosovichev Abstract An overview of the science investigation program for the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO) space mission scheduled for launch in 2008 is presented. The HMI investigation encompasses three primary objectives of the Living With a Star Program:.rst, to determine how and why the Sun varies; second, to improve our understanding of how the Sun drives global change and space weather; and third, to determine to what extent predictions of space weather and global change can be made and to prototype predictive techniques. Helioseismology provides unique tools to study the basic mechanisms of the Sun's magnetic activity and variability. It plays a crucial role in all HMI investigations, which include convection-zone dynamics and the solar dynamo; origin and evolution of sunspots, active regions and complexes of activity; sources and drivers of solar activity and disturbances; links between the internal processes and dynamics of the corona and heliosphere; and precursors of solar disturbances for space-weather forecasts. We describe new unique opportunities for helioseismology studies with HMI data, in combination with data from the other SDO instruments, Atmospheric Imaging Assembly (AIA) and Extreme-ultraviolet Variability Experiment (EVE), and also from various space and ground-based observatories. The complete HMI science investigation and data analysis plan is available at http://hmi.stanford.edu. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The Sun's influence , and beyondASTRONOMY & GEOPHYSICS, Issue 1 2004Peter Bond Peter Bond reports on unusual solar activity, space weather forecasting and a momentous moment for Voyager 1 , or is it? [source] | |||||||||||||