An ongoing compilation of new peer-reviewed, published papers demonstrating solar influences upon climate is maintained by Club du Soleil and Dr. Maarten Blaauw, PhD paleo-ecologist and lecturer at the School of Geography, Archaeology and Palaeoecology, Queen's University of Belfast, Northern Ireland.
The abstracts of papers published from 2013-2015 are excerpted below. Visit Club du Soleil for the remainder of their compilation extending back to 2010. Hundreds of other papers finding evidence of solar influence of climate published prior to 2010 may be found in the citations for these more recent papers.
This citation list is incomplete even for the last few years, as many posts at the Hockey Schtick and elsewhere have highlighted numerous additional published papers finding solar influence upon climate and solar amplification mechanisms that do not appear in the Club du Soleil compilation of citations below.
It's the Sun
The real hockey stick
Papers reported in 2015
Solar Irradiance Variability and Climate
Solanki et al. 2013 Annu. Rev. Astron. Astrophys. 51, 311-351
The brightness of the Sun varies on all time scales on which it has been observed, and there is increasing evidence that it has an influence on climate. The amplitudes of such variations depend on the wavelength and possibly on the time scale. Although many aspects of this variability are well established, the exact magnitude of secular variations (going beyond a solar cycle) and the spectral dependence of variations are under discussion. The main drivers of solar variability are thought to be magnetic features at the solar surface. The climate reponse can be, on a global scale, largely accounted for by simple energetic considerations, but understanding the regional climate effects is more difficult. Promising mechanisms for such a driving have been identified, including through the influence of UV irradiance on the stratosphere and dynamical coupling to the surface. Here we provide an overview of the current state of our knowledge, as well as of the main open questions.
Robust Response of the East Asian Monsoon Rainband to Solar Variability
Zhao and Wang 2014 Journal of Climaten 27, 3043-3051
This study provides evidence of the robust response of the East Asian monsoon rainband to the 11-yr solar cycle and first identify the exact time period within the summer half-year (1958-2012) with the strongest correlation between the mean latitude of the rainband (MLRB) over China and the sunspot number (SSN). This period just corresponds to the climatological-mean East Asian mei-yu season, characterized by a large-scale quasi-zonal monsoon rainband (i.e., 22 May-13 July). Both the statistically significant correlation and the temporal coincidence indicate a robust response of the mei-yu rainband to solar variability during the last five solar cycles. During the high SSN years, the mei-yu MLRB lies 1.2 ° farther north, and the amplitude of its interannual variations increases when compared with low SSN years. The robust response of monsoon rainband to solar forcing is related to an anomalous general atmospheric pattern with an up-down seesaw and a north-south seesaw over East Asia.
Cosmic ray event of A.D. 774-775 shown in quasi-annual 10Be data from the Antarctic Dome Fuji ice core
Miyake et al. 2015 Geophysical Research Letters
14C content in tree rings and 10Be concentration records in polar ice core provide information about past cosmic ray intensities. The A.D. 774-775 cosmic ray event has been identified by 14C measurement in several tree rings from all over the world. Although the quasi-decadal 10Be Dome Fuji data in the Antarctic ice core also shows a sharp peak around A.D. 775, annual 10Be variations in the Dome Fuji core or in other cores have not been revealed. We have measured quasi-annual 10Be concentrations from approximately A.D. 763-794 in the Dome Fuji ice core, and detected a clear increase (c. 80% above the baseline) in 10Be concentration around A.D. 775. However, an accurate height of this increase is not straightforwardly estimated due to the background variation in 10Be concentration. The 10Be increase can be due to the same cosmic ray event as shown in the 14C content in A.D. 774-775.
Abrupt Holocene Indian Summer Monsoon failures: A primary response to solar activity?
Xu et al. 2015 The Holocene
Knowledge of the millennial abrupt monsoon failures is critical to understanding the related causes. Here, we extracted proxy indices of Indian Summer Monsoon (ISM) intensity during the early to mid-Holocene, from peat deposits at Lake Xihu, in southwestern China. There are a series of abrupt, millennial-scale episodes of ISM weakening inferred from the Lake Xihu records, which are generally synchronous with those inferred from other archives over ISM areas. An important feature is that the ISM failures inferred from the Lake Xihu proxy indices synchronize well with abrupt changes in solar activity. We argue that changes in solar activity play a primary role in producing most of these millennial ISM failures, while some other causes, including freshwater outbursts into the North Atlantic Ocean and changes in sea surface temperatures of the eastern tropical Pacific Ocean, may have also exerted influences on parts of the millennial ISM failures.
Solar forcing of Earth's surface temperature in PMIP3 simulations of the last millennium
Le 2014 Atmospheric Science Letters
This study quantitatively diagnose the linkage between Total Solar Irradiance (TSI) and Earth's near-surface air temperature (TAS) of past 1000-year as simulated by Paleoclimate Modeling Intercomparison Project 3 (PMIP3) models. The results demonstrate that there is causal feedback of TAS from TSI variations, especially in the tropical and subtropical regions. The consistency between models in simulating solar signal in TAS responses is significant in these regions with more than 70% selected models showing agreement. There is no agreement between models in simulating TSI-TAS relationship in mid and high latitude regions.
papers reported in 2014
Evidence for the Gleissberg solar cycle at the high-latitudes of the Northern Hemisphere
Ogurtsov et al. 2014 Advances in Space Research
Time evolution of growing season temperatures in the Northern Hemisphere was analysed using both wavelet and Fourier approaches. A century-scale (60-140 year) cyclicity was found in the summer temperature reconstruction from the Taymir peninsula (72 N, 105 E) and other high-latitude (60-70 N) regions during the time interval AD 1576-1970. This periodicity is significant and consists of two oscillation modes, 60-70 year and 120-140 year variations. In the summer temperatures from the Yamal peninsula (70 N, 67 E) only a shorter-term (60-70 year) variation is present. A comparison of the secular variation in the Northern Hemisphere temperature proxies with the corresponding variations in sunspot numbers and the fluxes of cosmogenic 10Be in Greenland ice shows that a probable cause of this variability is the modulation of temperature by the century-scale solar cycle of Gleissberg. This is consistent with the results obtained previously for Northern Fennoscandia (67-70 N, 19-33 E). Thus, evidence for a connection between century-long variations in solar activity and climate was obtained for the entire boreal zone of the Northern Hemisphere.
Ultraviolet radiation exposure of a high arctic lake in Svalbard during the Holocene
Nevalainen et al. 2014 Boreas
Long-term fluctuations in lake-water optical properties were examined using a Holocene sediment sequence and multi-proxy palaeolimnological approach in Lake Einstaken, Nordaustlandet, Svalbard. UV-absorbance of sedimentary cladoceran remains provided information on underwater UV exposure and changes in lake-catchment coupling processes were inferred from sediment geochemistry. In addition, aquatic community succession was used as an indicator for lake-water bio-optical properties and a Holocene record of sun activity (sunspots) was utilized to evaluate long-term solar forcing. The results indicated that the UV-absorbance of cladoceran remains was highest (i.e. maximum UV-induced pigmentation) for a short period during the early Holocene and for several millennia during the mid-Holocene. Sun activity was high during these time intervals, probably impacting the UV intensities, but it is probable that the amount of UV-attenuating compounds (e.g. dissolved organic carbon (DOC)) also significantly affected the underwater UV environment and were low during high UV exposure. Benthic autotrophic communities also responded to the millennial changes in lake-water optical properties. UV-resistant Nostoc cyanobacterial colonies were established during the mid-Holocene, indicative of high underwater UV intensities, and Fontinalis mosses thrived during the early Holocene, indicating a highly transparent water column. The results further suggested that underwater UV exposure decreased during the late Holocene, which is probably attributable to increased DOC and decreased solar forcing. Owing to the location of Lake Einstaken and its catchment in the periglacial barren landscape of the polar desert, the fluctuations of bio-optical lake-water properties were apparently forced by postglacial environmental processes and Holocene climate development. These factors controlled sea shoreline proximity, water discharge, ice-cover duration and littoral-benthic primary production and further affected the underwater UV environment. Although the role of solar forcing cannot be underestimated, the current record emphasizes the role of climate-mediated lake-catchment interactions in impacting bio-optical properties and UV exposure of high arctic aquatic systems.
Origin and palaeoenvironmental significance of C25 and C27n-alk-1-enes in a 25,000-year lake-sedimentary record from equatorial East Africa
van Bree et al. 2014 Geochimica et Cosmochimica Acta
We studied the distribution of long-chain alkenes (n-C23 to n-C31) in well-dated sediments from Lake Challa, a deep crater lake near Mt. Kilimanjaro in equatorial East Africa, to reveal signatures of palaeo-environmental and palaeo-climatic changes affecting the production of these compounds during the last 25 kyr. The apolar fractions of organic sediment extracts dated to the last 16 kyr showed an unusual dominance of d13C-depleted n-C25:1 and n-C27:1 alk-1-enes. These alkenes were not detected in soil and litter from near the shoreline and from the inner rim of the crater, pointing to an autochthonous, aquatic source. Analysis of suspended particulate matter indicated that the n-alk-1-enes are produced in the well-oxygenated upper 30 m of the water column, indicating a phytoplanktonic origin. Sedimenting particles collected monthly from December 2006 to November 2007 showed increased fluxes of n-alk-1-enes following the locally prominent short rain season in November-December. Green algae and/or cyanobacteria were identified as candidate sources of these alkenes. Production of the n-C25:1 and n-C27:1 alkenes in Lake Challa was much reduced during the Last Glacial Maximum and early late-glacial period, suggesting a temperature or CO2 effect on habitat suitability. We explored the potential of n-alk-1-ene accumulation rates, and of a derived Alkene Index [n-C27:1]/([n-C25:1] + [n-C27:1]), to record longer-term climatic changes. The Alkene Index record of Lake Challa over the past 25 kyr shows clear periodicity with a dominant frequency of c. 2.3 kyr, potentially indicative of monsoon variability directly or indirectly forced by variation in solar radiation.
Influence of Solar Activity on the Climate Change
Kovalenko and Zherebtsov 2014 Atmospheric and Oceanic Optics 27, 506-510
We discuss problems which are of main importance for understanding the nature of climate changes in the 20th century and basic physical processes responsible for these changes. A possible role of solar activity in the Earth's climate changes in the past and future is considered. As shown, physical mechanisms which can provide for the solar variability effect on the weather and climate are reduced to the control of the energy flux from the Earth to space. A special emphasis is given on the solar activity effect on climatic characteristics of the troposphere through the atmospheric electricity. We consider peculiarities of the response of thermal and dynamic regimes of the World Ocean and atmosphere to solar activity changes and processes in the atmosphere, ocean, and cryosphere. We also show and discuss results of the analysis of regularities and peculiarities of troposphere and the ocean surface temperature response to both isolated heliogeophysical disturbances and long term changes in solar and geomagnetic activity.
Modulation of UK lightning by heliospheric magnetic field polarity
Owens et al. 2014 Environmental Research Letters 9 115009
Observational studies have reported solar magnetic modulation of terrestrial lightning on a range of time scales, from days to decades. The proposed mechanism is two-step: lightning rates vary with galactic cosmic ray (GCR) flux incident on Earth, either via changes in atmospheric conductivity and/or direct triggering of lightning. GCR flux is, in turn, primarily controlled by the heliospheric magnetic field (HMF) intensity. Consequently, global changes in lightning rates are expected. This study instead considers HMF polarity, which doesn't greatly affect total GCR flux. Opposing HMF polarities are, however, associated with a 40-60% difference in observed UK lightning and thunder rates. As HMF polarity skews the terrestrial magnetosphere from its nominal position, this perturbs local ionospheric potential at high latitudes and local exposure to energetic charged particles from the magnetosphere. We speculate as to the mechanism(s) by which this may, in turn, redistribute the global location and/or intensity of thunderstorm activity.
Frequency Characteristic of Response of Surface Air Pressure to Changes in Flux of Cosmic Rays
Bogdanov 2014 Geomagnetism and Aeronomy 54, 813-818
We compare the series of daily-average values of the surface air pressure for De Bilt and Lugano meteorological stations with subtracted linear trends and seasonal harmonics, as well as the series of the flux of galactic cosmic rays (GCRs) at Jungfraujoch station with subtracted moving average over 200 days. Using the method of superposed epochs, we show that the Forbush decreases at both stations are accompanied by increased pressure. Spectral analysis allows us to conclude that the analyzed series are characterized by nonzero coherence in almost the entire frequency range: from 0.02 day-1 up to the Nyquist frequency of 0.5 day-1. Using changes in the GCR flux as a probing signal, we obtain amplitude-frequency characteristics of the pressure reaction. For both stations, these characteristics are in qualitative agreement with each other and indicate that the atmospheric response can be described by a second-order linear dynamic system that has wide resonance with a maximum at a frequency of 0.15 day-1.
Do sunspot numbers cause global temperatures? Evidence from a frequency domain causality test
Gupta et al. 2014 Applied Economics
This article applies the causality test in the frequency domain, developed by Breitung and Candelon (2006), to analyse whether sunspot numbers (used as a partial approximation to solar irradiance) cause global temperatures, using monthly data covering the time period 1880:1-2013:9. While standard time domain Granger causality test fails to reject the null hypothesis that sunspot numbers do not cause global temperatures for both full and sub-samples (identified based on tests of structural breaks), the frequency domain causality test detects predictability for both the full-sample and the last sub-sample at short (2-2.6 months) and long (10.3 months and above) cycle lengths, respectively. Our results highlight the importance of analysing causality using the frequency domain test, which, unlike the time domain Granger causality test, allows us to decompose causality by different time horizons, and hence, could detect predictability at certain cycle lengths even when the time domain causality test might fail to pick up any causality. Further, given the widespread discussion in the literature, those results for the full-sample causality, irrespective of whether it is in time or frequency domains, cannot be relied upon when there are structural breaks present, and one needs to draw inference regarding causality from the sub-samples, we can conclude that there has been an emergence of causality running from sunspot numbers to global temperatures only recently at cycle length of 10.3 months and above.
A 2700 cal yr BP extreme flood event revealed by sediment accumulation in Amazon floodplains
Moreira-Turcq et al. 2014 Palaeogeography, Palaeoclimatology, Palaeoecology 415, 175-182
Climatic conditions are one of the most important factors affecting hydrological processes in fluvial systems. Higher discharges are responsible for higher erosion, greater transport, and also higher deposition. Consequently, sediment accumulation in Amazonia floodplain river-connected lakes can be directly related to hydrological patterns of the Amazon River mainstream. In this context, we analyzed five sediment cores taken in two floodplain systems situated in the lower Amazon River, to investigate sediment accumulation patterns during the Holocene. Our records show abrupt fluctuations in sedimentation rates in lakes that can reach more than 2 cm/yr during some periods. We find that in all cores, sediment stratigraphy is characterized by packages of sediments of uniform age, which are typically 10-80 cm thick and present a variegated color. The 14C age of the upper package is about 2700 cal yr BP. During this abrupt event, sediment accumulation rates in floodplain lakes can be at least 200 times higher than those of "normal" periods. This sedimentation event is interpreted as being the consequence of one or several successive extreme floods. The 2700 cal yr BP event has been also observed in other sites in South America and other regions in the world, although different impacts can be observed in each system. This event probably corresponds to a conjunction of favorable conditions for extreme Amazon discharge associated with the Middle to Late Holocene increase of austral summer insolation and shifts of the Intertropical Convergence Zone (ITCZ) from northern to southern positions. In this context, a marked negative peak in solar irradiance at 2700 cal yrs BP seems to have provoked cooling on the continents and a southward shift of the ITCZ associated with a probable reduction in the Atlantic Meridian Overturning Circulation.
Ultra-high-resolution paleoenvironmental records via direct laser-based analysis of lipid biomarkers in sediment core samples
Wörmer et al. 2014 PNAS
Lipid biomarkers in geological samples are important informants regarding past environments and ecosystems. Conventional biomarker analysis is labor intensive and requires relatively large sediment or rock samples; temporal resolution is consequently low. Here, we present an approach that has the potential to revolutionize paleoenvironmental biomarker research; it avoids wet-chemical sample preparation and enables analysis of biomarkers directly on sediment cores at submillimeter spatial resolution. Our initial application to a sediment core deposited during the Holocene climate optimum in the Mediterranean Sea reveals a new view of how small-scale variations in lipid distribution are integrated into commonly reported signals obtained by conventional analysis and demonstrates a strong influence of the c.200-y de Vries solar cycle on sea-surface temperatures and planktonic archaeal ecology.
A 449 year warm season temperature reconstruction in the southeastern Tibetan Plateau and its relation to solar activity
Duan & Zhang 2014 Journal of Geophysical Research: Atmospheres
There is a close relationship between solar activity and the Earth's surface temperature, but this relationship has weakened with recent global warming. To better understand this puzzle, temperature records need to be extended, and the relationship between long-term variation in temperature and solar activity needs to be examined. In this study, we reconstruct April-September temperature variation back to 1563 using tree ring maximum late wood density (MXD) data from Balfour spruce in the southeastern Tibetan Plateau (TP). Spatial correlation analysis indicates that our reconstruction is representative of temperature variability over the large-scale TP. On the 22 year time scale, the reconstructed April-September temperature corresponds generally to solar activity over the past three centuries. Spectral analyses also indicate that the significant periodicities of c. 11 years, 54 years, and 204 years observed in the MXD chronology correspond to the Schwabe cycle, the fourth harmonic of the Suess cycle, and the Suess solar cycle, respectively. However, disparities between temperature change and solar activity are identified in two periods, the 1880s-1900s and the 1980s-present. These results suggest that solar forcing is the critical driver for long-term temperature variability in the TP, but other factors may uncouple surface temperature and solar activity in some periods. One possible cause of the weak effect of solar activity on temperature during the 1880s-1900s is internal climate variability, while human-activity-induced greenhouse gas emissions have likely superseded solar forcing as the major driver of the rapid warming observed since the 1980s.
Mount Logan ice core record of tropical and solar influences on Aleutian Low variability: 500-1998 A.D.
Osterberg et al. 2014 Journal of Geophysical Research: Atmospheres
Continuous, high-resolution paleoclimate records from the North Pacific region spanning the past 1500 years are rare; and the behavior of the Aleutian Low (ALow) pressure center, the dominant climatological feature in the Gulf of Alaska, remains poorly constrained. Here we present a continuous, 1500 year long, calibrated proxy record for the strength of the wintertime (December-March) ALow from the Mount Logan summit (PR Col; 5200 m asl) ice core soluble sodium time series. We show that ice core sodium concentrations are statistically correlated with North Pacific sea level pressure and zonal wind speed. Our ALow proxy record reveals a weak ALow from circa 900-1300 A.D. and 1575-1675 A.D., and a comparatively stronger ALow from circa 500-900 A.D., 1300-1575 A.D., and 1675 A.D. to present. The Mount Logan ALow proxy record shows strong similarities with tropical paleoclimate proxy records sensitive to the El Niño-Southern Oscillation and is consistent with the hypothesis that the Medieval Climate Anomaly was characterized by more persistent La Niña-like conditions while the Little Ice Age was characterized by at least two intervals of more persistent El Niño-like conditions. The Mount Logan ALow proxy record is significantly (p < 0.05) correlated and coherent with solar irradiance proxy records over various time scales, with stronger solar irradiance generally associated with a weaker ALow and La Niña-like tropical conditions. However, a step-like increase in ALow strength during the Dalton solar minimum circa 1820 is associated with enhanced Walker circulation. Furthermore, rising CO2 forcing or internal variability may be masking the twentieth century rise in solar irradiance.
The cause of solar dimming and brightening at the Earth's surface during the last half century: Evidence from measurements of sunshine duration
Stanhill et al. 2014 Journal of Geophysical Research: Atmospheres
Analysis of the Angstrom-Prescott relationship between normalized values of global radiation and sunshine duration measured during the last 50 years made at five sites with a wide range of climate and aerosol emissions showed few significant differences in atmospheric transmissivity under clear or cloud-covered skies between years when global dimming occurred and years when global brightening was measured, nor in most cases were there any significant changes in the parameters or in their relationships to annual rates of fossil fuel combustion in the surrounding 1° cells. It is concluded that at the sites studied changes in cloud cover rather than anthropogenic aerosols emissions played the major role in determining solar dimming and brightening during the last half century and that there are reasons to suppose that these findings may have wider relevance.
Holocene cyclic climatic variations and the role of the Pacific Ocean as recorded in varved sediments from northeastern China
Chu et al. 2014 Quaternary Science Reviews 102, 85-95
We present an n-alkane and compound-specific carbon isotope record of the past 9 ka from the annually laminated sedimentary sequence of Lake Xiaolongwan, northeastern China. The n-alkane distribution suggests that Lake Xiaolongwan has undergone a shift from an oligotrophic state with low algal production and little emergent/submerged macrophytes in the early Holocene, to a eutrophic state with high algal production and abundant emergent/submerged macrophytes since the middle Holocene. The pattern of variation observed in the biomarker proxies ACL (the n-alkane average chain length), Paq (aquatic macrophyte versus aquatic macrophyte and terrestrial plant ratio), and LPTP (lake productivity/terrigenous organic production) is throughout the record similar to that of the total organic carbon. The variation of compound-specific carbon isotopic values in the middle- and short-chain alkanes was mainly regulated by lake productivity and the accumulating organic pool through time. In this forested region, where the vegetation is dominated by C3 plants, the long-chain n-alkanes (C27-C31) are predominantly derived from leaf wax lipids. The compound-specific δ13C27-31 value is sensitive to effective precipitation, and therefore represents a useful indicator of regional monsoonal precipitation. Spectral analysis on the δ13C27-31 time series reveals significant periodicities of 87-89, 205-212, 1020-1050 and 1750-2041 years. On the centennial timescale, the quasi-periodicities around 88 and 210 years suggest a strong link between solar activity and monsoon rainfall. The millennial monsoon cycle in northeastern China is associated with sea surface temperature (SST) variations in two active centers of the summer monsoon, the western Pacific Subtropical High (WPSH) and the Okhotsk High. Increasing SST in the subtropical sea may cause a northwards shift of the WPSH, which extends the monsoon rain band (Meiyu) to northeastern China, and thus increasing rainfall in that region. Meanwhile, decreasing SST in the Okhotsk Sea may strengthen the Okhotsk high, bringing more moisture into northeastern China. We suggest that the Pacific Ocean is a main regulator for summer monsoon rainfall in northeastern China at present and at different time scales during the Holocene.
Quasi-biennial oscillation and solar cycle influences on winter Arctic total ozone
Li and Tung 2014 Journal of Geophysical Research: Atmospheres 119, 5823-5835
The total column ozone (TCO) observed from satellites and assimilated in the European Centre for Medium-Range Weather Forecasts since 1979 is used as an atmospheric tracer to study the modulations of the winter Arctic stratosphere by the quasi-biennial oscillation (QBO) and the solar cycle. It is found that both the QBO and solar forcings in low latitudes can perturb the late winter polar vortex, likely via planetary wave divergence, causing an early breakdown of the vortex in the form of sudden stratospheric warming. As a result, TCO within the vortex in late winter can increase by ˜60 Dobson unit during either a solar maximum or an easterly phase of the QBO, or both, relative to the least perturbed state when the solar cycle is minimum and the QBO is in the westerly phase. In addition, from the solar maximum to the solar minimum during the QBO easterly phase, the change in TCO is found to be statistically insignificant. Therefore, the "reversal" of the Holton-Tan effect, reported in some previous studies using lower stratospheric temperature, is not evident in the TCO behavior of both observation and assimilation.
Solar forcing of Nile discharge and sapropel S1 formation in the early to middle Holocene eastern Mediterranean
Hennekam et al. 2014 Paleoceanography 29, 343-356
We present high-resolution records for oxygen isotopes of the planktic foraminifer Globigerinoides ruber (d18Oruber) and bulk sediment inorganic geochemistry for Holocene-age sediments from the southeast Mediterranean. Our d18Oruber record appears to be dominated by Nile discharge rather than basin-scale salinity/temperature changes. Nile discharge was enhanced in the early to middle Holocene relative to today. The timing of the long-term maximum in Nile discharge during the early Holocene corresponds to the timing of maximum intensity of the Indian Ocean-influenced Southwest Indian summer monsoon (SIM). This coincidence suggests a major influence of an Indian Ocean moisture source on Nile discharge in the early to middle Holocene, while, presently, the Atlantic Ocean is the main moisture source. Nile discharge was highly variable on multicentennial time scale during the early to middle Holocene, being strongly influenced by variable solar activity. This solar-driven variability is also recorded in contemporaneous SIM records, however, not observed in an Atlantic Ocean-derived West African summer monsoon record from the Holocene. This supports the hypothesis that the Indian Ocean moisture source predominantly controlled Nile discharge at that time. Solar-driven variability in Nile discharge also influenced paleoenvironmental conditions in the eastern Mediterranean. Bulk sediment Ba/Al and V/Al, used as indicators for (export) productivity and redox conditions, respectively, varied both in response to solar forcing on multicentennial time scales. We suggest that changes in Nile discharge on these time scales have been concordant with nutrient inputs to, and shallow ventilation of, the eastern Mediterranean.
Solar-wind-driven geopotential height anomalies originate in the Antarctic lower troposphere
Lam et al. 2014 Geophysical Research Letters
We use NCEP/NCAR reanalysis data to estimate the altitude and timelag dependence of the correlation between the interplanetary magnetic field component, By, and the geopotential height anomaly above Antarctica. The correlation is most statistically significant within the troposphere. The peak in the correlation occurs at greater timelags at the tropopause (c. 6-8 days) and in the mid-troposphere (c. 4 days), than in the lower troposphere (c. 1 day). This supports a mechanism involving the action of the global atmospheric electric circuit, modified by variations in the solar wind, on lower tropospheric clouds. The increase in timelag with increasing altitude is consistent with the upward propagation by conventional atmospheric processes of the solar-wind-induced variability in the lower troposphere. This is in contrast to the downward propagation of atmospheric effects to the lower troposphere from the stratosphere due to solar-variability-driven mechanisms involving ultra-violet radiation or energetic particle precipitation.
Is a sudden increase of irregularity of sunspot numbers a precursor of a return to low solar activity?
Shapoval et al. 2014 Journal of Geophysical Research - Space Physics
We have recently introduced an irregularity index λ for daily sunspot numbers International Sunspot Number (ISSN), derived from the well-known Lyapunov exponent, that attempts to reflect irregularities in the chaotic process of solar activity. Like the Lyapunov exponent, the irregularity index is computed from the data for different embedding dimensions m (2-32). When m = 2, λ maxima match ISSN maxima of the Schwabe cycle, whereas when m = 3, λ maxima occur at ISSN minima. The patterns of λ as a function of time remain similar from m = 4 to 16: the dynamics of λ change between 1915 and 1935, separating two regimes, one from 1850 to 1915 and the other from 1935 to 2005, in which λ retains a similar structure. A sharp peak occurs at the time of the ISSN minimum between cycles 23 and 24, possibly a precursor of unusual cycle 24 and maybe a new regime change; λ is significantly smaller during the ascending and descending phases of solar cycles. Differences in values of the irregularity index observed for different cycles reflect differences in correlations in sunspot series at a scale much less than the 4 year sliding window used in computing them; the lifetime of sunspots provides a source of correlation at that time scale. The burst of short-term irregularity evidenced by the strong λ peak at the minimum of cycles 23 and 24 would reflect a decrease in correlation at the time scale of several days rather than a change in the shape of the cycle.
Natural variability, radiative forcing and climate response in the recent hiatus reconciled
Huber and Knutti 2014 Nature Geoscience 7, 651-656
Global mean surface warming over the past 15 years or so has been less than in earlier decades and than simulated by most climate models. Natural variability, a reduced radiative forcing, a smaller warming response to atmospheric carbon dioxide concentrations8, 9 and coverage bias in the observations10 have been identified as potential causes. However, the explanations of the so-called 'warming hiatus' remain fragmented and the implications for long-term temperature projections are unclear. Here we estimate the contribution of internal variability associated with the El Niño/Southern Oscillation (ENSO) using segments of unforced climate model control simulations that match the observed climate variability. We find that ENSO variability analogous to that between 1997 or 1998 and 2012 leads to a cooling trend of about -0.06 °C. In addition, updated solar and stratospheric aerosol forcings from observations explain a cooling trend of similar magnitude (-0.07 °C). Accounting for these adjusted trends we show that a climate model of reduced complexity with a transient climate response of about 1.8 °C is consistent with the temperature record of the past 15 years, as is the ensemble mean of the models in the Coupled Model Intercomparison Project Phase 5 (CMIP5). We conclude that there is little evidence for a systematic overestimation of the temperature response to increasing atmospheric CO2 concentrations in the CMIP5 ensemble.
Indian summer monsoon rainfall: Dancing with the tunes of the sun
Hiremath et al. 2014 New Astronomy
There is strong statistical evidence that solar activity influences the Indian summer monsoon rainfall. To search for a physical link between the two, we consider the coupled cloud hydrodynamic equations, and derive an equation for the rate of precipitation that is similar to the equation of a forced harmonic oscillator, with cloud and rain water mixing ratios as forcing variables. Those internal forcing variables are parameterized in terms of the combined effect of external forcing as measured by sunspot and coronal hole activities with several well known solar periods (9, 13 and 27 days; 1.3, 5, 11 and 22 years). The equation is then numerically solved and the results show that the variability of the simulated rate of precipitation captures very well the actual variability of the Indian monsoon rainfall, yielding vital clues for a physical understanding that has so far eluded analyses based on statistical correlations alone. We also solved the precipitation equation by allowing for the effects of long-term variation of aerosols. We tentatively conclude that the net effects of aerosols variation are small, when compared to the solar factors, in terms of explaining the observed rainfall variability covering the full Indian monsoonal geographical domains.
Persistent link between solar activity and Greenland climate during the Last Glacial Maximum
Adolphi et al. 2014 Nature Geoscience
Changes in solar activity have previously been proposed to cause decadal- to millennial-scale fluctuations in both the modern and Holocene climates1. Direct observational records of solar activity, such as sunspot numbers, exist for only the past few hundred years, so solar variability for earlier periods is typically reconstructed from measurements of cosmogenic radionuclides such as 10Be and 14C from ice cores and tree rings. Here we present a high-resolution 10Be record from the ice core collected from central Greenland by the Greenland Ice Core Project (GRIP). The record spans from 22,500 to 10,000 years ago, and is based on new and compiled data. Using 14C records to control for climate-related influences on 10Be deposition, we reconstruct centennial changes in solar activity. We find that during the Last Glacial Maximum, solar minima correlate with more negative d18O values of ice and are accompanied by increased snow accumulation and sea-salt input over central Greenland. We suggest that solar minima could have induced changes in the stratosphere that favour the development of high-pressure blocking systems located to the south of Greenland, as has been found in observations and model simulations for recent climate. We conclude that the mechanism behind solar forcing of regional climate change may have been similar under both modern and Last Glacial Maximum climate conditions.
Rotation of the Earth, solar activity and cosmic ray intensity
Barlyaeva et al. 2014 Ann. Geophys. 32, 761-771
We analyse phase lags between the 11-year variations of three records: the semi-annual oscillation of the length of day (LOD), the solar activity (SA) and the cosmic ray intensity (CRI). The analysis was done for solar cycles 20-23. Observed relationships between LOD, CRI and SA are discussed separately for even and odd solar cycles. Phase lags were calculated using different methods (comparison of maximal points of cycles, maximal correlation coefficient, line of synchronization of cross-recurrence plots). We have found different phase lags between SA and CRI for even and odd solar cycles, confirming previous studies. The evolution of phase lags between SA and LOD as well as between CRI and LOD shows a positive trend with additional variations of phase lag values. For solar cycle 20, phase lags between SA and CRI, between SA and LOD, and between CRI and LOD were found to be negative. Overall, our study suggests that, if anything, the length of day could be influenced by solar irradiance rather than by cosmic rays.
On the detection of the solar signal in the tropical stratosphere
Chiodo et al. 2014 Atmos. Chem. Phys. 14, 5251-5269
We investigate the relative role of volcanic eruptions, El Niño-Southern Oscillation (ENSO), and the quasi-biennial oscillation (QBO) in the quasi-decadal signal in the tropical stratosphere with regard to temperature and ozone commonly attributed to the 11 yr solar cycle. For this purpose, we perform transient simulations with the Whole Atmosphere Community Climate Model forced from 1960 to 2004 with an 11 yr solar cycle in irradiance and different combinations of other forcings. An improved multiple linear regression technique is used to diagnose the 11 yr solar signal in the simulations. One set of simulations includes all observed forcings, and is thereby aimed at closely reproducing observations. Three idealized sets exclude ENSO variability, volcanic aerosol forcing, and QBO in tropical stratospheric winds, respectively. Differences in the derived solar response in the tropical stratosphere in the four sets quantify the impact of ENSO, volcanic events and the QBO in attributing quasi-decadal changes to the solar cycle in the model simulations. The novel regression approach shows that most of the apparent solar-induced lower-stratospheric temperature and ozone increase diagnosed in the simulations with all observed forcings is due to two major volcanic eruptions (i.e., El Chichon in 1982 and Mt. Pinatubo in 1991). This is caused by the alignment of these eruptions with periods of high solar activity. While it is feasible to detect a robust solar signal in the middle and upper tropical stratosphere, this is not the case in the tropical lower stratosphere, at least in a 45 yr simulation. The present results suggest that in the tropical lower stratosphere, the portion of decadal variability that can be unambiguously linked to the solar cycle may be smaller than previously thought.
Study of the influence of solar variability on a regional (Indian) climate: 1901-2007
Aslam and Badruddin 2014 Advances in Space Research
We use Indian temperature data of more than 100 years to study the influence of solar activity on climate. We study the Sun-climate relationship by averaging solar and climate data at various time scales; decadal, solar activity and solar magnetic cycles. We also consider the minimum and maximum values of sunspot number (SSN) during each solar cycle. This parameter SSN is correlated better with Indian temperature when these data are averaged over solar magnetic polarity epochs (SSN maximum to maximum). Our results indicate that the solar variability may still be contributing to ongoing climate change and suggest for more investigations.
Solar control on the cloud liquid water content and integrated water vapor associated with monsoon rainfall over India
Maitra et al. 2014 Journal of Atmospheric and Solar-Terrestrial Physics
A long-term observation over three solar cycles indicates a perceptible influence of solar activity on rainfall and associated parameters in the Indian region. This paper attempts to reveal the solar control on the cloud liquid water content (LWC) and integrated water vapor (IWV) along with Indian Summer Monsoon (ISM) rainfall during the period of 1977-2012 over nine different Indian stations. Cloud LWC and IWV are positively correlated with each other. An anti-correlation is observed between the Sunspot Number (SSN) and ISM rainfall for a majority of the stations and a poor positive correlation obtained for other locations. Cloud LWC and IWV possess positive correlations with Galactic Cosmic Rays (GCR) and SSN respectively for most of the stations. The wavelet analyses of SSN, ISM rainfall, cloud LWC and IWV have been performed to investigate the periodic characteristics of climatic parameters and also to indicate the varying relationship of solar activity with ISM rainfall, cloud LWC and IWV. SSN, ISM rainfall and IWV are found to have a peak at around 10.3 years whereas a dip is observed at that particular period for cloud LWC.
Reconstruction and prediction of the total solar irradiance: From the Medieval Warm Period to the 21st century
Herrera et al. 2014 New Astronomy 34, 221-233
Total solar irradiance is the primary energy source of the Earth's climate system and therefore its variations can contribute to natural climate change. This variability is characterized by, among other manifestations, decadal and secular oscillations, which has led to several attempts to estimate future solar activity. Of particular interest now is the fact that the behavior of the solar cycle 23 minimum has shown an activity decline not previously seen in past cycles for which spatial observations exist: this could be signaling the start of a new grand solar minimum. The estimation of solar activity for the next hundred years is one of the current problems in solar physics because the possible occurrence of a future grand solar minimum will probably have an impact on the Earth's climate. In this study, using the PMOD and ACRIM TSI composites, we have attempted to estimate the TSI index from year 1000 AD to 2100 AD based on the Least Squares Support Vector Machines, which is applied here for the first time to estimate a solar index. Using the wavelet transform, we analyzed the behavior of the total solar irradiance time series before and after the solar grand minima. Depending on the composite used, PMOD (or ACRIM), we found a grand minimum for the 21st century, starting in c. 2004c. 2004 (or 2002) and ending in c. 2075c. 2075 (or 2063), with an average irradiance of 1365.5 (or 1360.5) Wm-2+-1sd=0.3Wm-2+-1sd=0.3 (or 0.9) Wm-2Wm-2. Moreover, we calculated an average radiative forcing between the present and the 21st century minima of c. -0.1c. -0.1 (or -0.2) Wm-2Wm-2, with an uncertainty range of -0.04-0.04 to -0.14-0.14 (or -0.12-0.12 to -0.33-0.33) Wm-2Wm-2. As an indicator of the TSI level, we calculated its annual power anomalies; in particular, future solar cycles from 24 to 29 have lower power anomalies compared to the present, for both models. We also found that the solar activity grand minima periodicity is of 120 years; this periodicity could possibly be one of the principal periodicities of the magnetic solar activity not so previously well recognized. The negative (positive) 120-year phase coincides with the grand minima (maxima) of the 11-year periodicity.
Solar cycle effects on Indian summer monsoon dynamics
Ratnam et al. 2014 Journal of Atmospheric and Solar-Terrestrial Physics
Solar activity associated with sunspot number influences the atmospheric circulation on various time scales. As Indian summer monsoon (ISM) is the manifestation between warmer Asian continent and the cooler Indian Ocean, changes in the solar cycle are expected to influence the ISM characteristics. Among several elements of ISM, Tropical Easterly Jet (TEJ), Low Level Jet (LLJ), and rainfall are important features. As a part of CAWSES India Phase II theme 1 (solar influence on climate (0-100 km)) programme, we made an attempt to investigate the role of solar cycle variability on these ISM features using long-term data available from NECP/NCAR (1948-2010) and ERA-Interim (1979-2010) re-analysis products. To check the suitability of these data sets, ground based observations available over the Indian region are also considered. ISM characteristics are studied separately for the maximum and minimum as well as increasing and decreasing solar cycle conditions. Amplitudes corresponding to the solar cycle observed in TEJ, LLJ and rainfall are extracted using advanced statistical tool known as intrinsic mode function. Long-term trends i