Neues vom Svensmark-Wolken-Solarverstärker

Vor einigen Jahren beschrieb Henrik Svensmark einen Mechanismus, bei dem solare Aktivitätsschwankungen die Wolkenbedeckung verändern. War dies der gesuchte Solarverstärker? Der vorgeschlagene Prozess enthält eine Reihe von Zwischenschritten, wobei das Sonnenmagnetfeld die kosmische Strahlung mal mehr und mal weniger stark abschirmt, also moduliert. Die kleinen galaktischen Teilchen sollen dann als Kondensationskeime für Wolken dienen. Der Mechanismus leuchtet im Großen und Ganzen ein, und Svensmark konnte zunächst eine schöne Korrelation der Sonnenaktivität mit den Wolken liefern. Dann allerdings liefen die Kurven auseinander. Es war wohl doch etwas komplizierter. Der IPCC freute sich und verwarf das Modell kurzerhand. Vermutlich vorschnell, denn Stück für Stück wird nun allmählich klarer, dass man stärker differenzieren muss: Zwischen verschiedenen Breitengraden, Wolkenstockwerken, Jahreszeiten. Im Folgenden wollen wir für Sie das Neueste zum Wolken-Solarverstärker zusammenfassen.

Im November 2014 berichteten M. Kancirova und K. Kudela in Atmospheric Research über eine Studie zur Entwicklung der Wolkenbedeckung und der kosmischen Strahlen auf einem 2634 m hohen Berg in der Slovakei für den Zeitraum 1982–2010. Die Autoren fanden dabei eine stabile Korrelation zwischen Wolken und kosmischer Strahlung, wenn auch schwach ausgeprägt. Hier der Abstract:

Cloud cover and cosmic ray variations at Lomnický štít high altitude observing site
We studied the relation of cloud cover and cosmic rays during the period 1982–2010 measured at Lomnický štít (2634 m above sea level, in the direction of 49.40°N, 20.22°E, geomagnetic vertical cut-off rigidity for cosmic ray ~ 3.85 GV). Daily means are used. It is seen that the correlations are insignificant for averaging shorter than about one year. We have found weak positive correlation for longer averaging times. Difference in distributions of cosmic ray intensity between the days with cloudless and overcast sky level at α = 0.05 is found in the data. In addition to the experiments and clarification of physical mechanisms behind the relations studied here, longer time intervals and analysis at different sites with respect to cut-off rigidity and sea/continents along with the satellite data are important for progress in understanding the cosmic ray–cloud relation questions, at least from the point of view of empirical description of the dependencies.

Im Januar 2015 legten Badruddin & Aslam dann im Journal of Atmospheric and Solar-Terrestrial Physics nach. Sie studierten den Einfluss der kosmischen Strahlung auf den Indischen Sommermonsun. Und sie wurde fündig: Dürrephasen ereigneten sich überwiegend wenn die kosmische Strahlung abnahm, während feuchte Phasen mit zunehmender kosmischer Strahlung gepaart waren. Zudem fanden sie einen Zusammenhang mit der Temperatur. Hier die Kurzfassung:

Influence of cosmic-ray variability on the monsoon rainfall and temperature
We study the role of galactic cosmic ray (GCR) variability in influencing the rainfall variability in Indian Summer Monsoon Rainfall (ISMR) season.
We find that on an average during ‘drought’ (low ISMR) periods in India, GCR flux is decreasing, and during ‘flood’ (high ISMR) periods, GCR flux is increasing. The results of our analysis suggest for a possibility that the decreasing GCR flux during the summer monsoon season in India may suppress the rainfall. On the other hand, increasing GCR flux may enhance the rainfall. We suspect that in addition to real environmental conditions, significant levitation/dispersion of low clouds and hence reduced possibility of collision/coalescence to form raindrops suppresses the rainfall during decreasing GCR flux in monsoon season. On the other hand, enhanced collision/coalescence efficiency during increasing GCR flux due to electrical effects may contribute to enhancing the rainfall. Based on the observations, we put forward the idea that, under suitable environmental conditions, changing GCR flux may influence precipitation by suppressing/enhancing it, depending upon the decreasing/increasing nature of GCR flux variability during monsoon season in India, at least. We further note that the rainfall variability is inversely related to the temperature variation during ISMR season. We suggest an explanation, although speculative, how a decreasing/increasing GCR flux can influence the rainfall and the temperature. We speculate that the proposed hypothesis, based on the Indian climate data can be extended to whole tropical and sub-tropical belt, and that it may contribute to global temperature in a significant way. If correct, our hypothesis has important implication for the sun – climate link.

Weiterhin erwähnenswert ist eine Arbeit von L.Z. Biktash im Dezember 2014 in Advances in Space Research. In dieser Studie geht es ebenfalls um die kosmische Strahlung und ihr Bezug zur globalen Temperatur. Für die Phase 1965–2012 sollen sich die Temperaturmaxima während der Minima der kosmischen Strahlung ereignet haben. Hier die Kurzfassung:

Evolution of Dst index, cosmic rays and global temperature during solar cycles 20–23
We have studied conditions in interplanetary space, which can have an influence on galactic cosmic ray (CR) and climate change. In this connection the solar wind and interplanetary magnetic field parameters and cosmic ray variations have been compared with geomagnetic activity represented by the equatorial Dst index from the beginning 1965 to the end of 2012. Dst index is commonly used as the solar wind–magnetosphere–ionosphere interaction characteristic. The important drivers in interplanetary medium which have effect on cosmic rays as CMEs (coronal mass ejections) and CIRs (corotating interaction regions) undergo very strong changes during their propagation to the Earth. Because of this CMEs, coronal holes and the solar spot numbers (SSN) do not adequately reflect peculiarities concerned with the solar wind arrival to 1 AU. Therefore, the geomagnetic indices have some inestimable advantage as continuous series other the irregular solar wind measurements. We have compared the yearly average variations of Dst index and the solar wind parameters with cosmic ray data from Moscow, Climax, and Haleakala neutron monitors during the solar cycles 20–23. The descending phases of these solar cycles (CSs) had the long-lasting solar wind high speed streams occurred frequently and were the primary contributors to the recurrent Dst variations. They also had effects on cosmic rays variations. We show that long-term Dst variations in these solar cycles were correlated with the cosmic ray count rate and can be used for study of CR variations. Global temperature variations in connection with evolution of Dst index and CR variations is discussed.

Im Text der Arbeit heißt es:

We demonstrate that the detrended annual means of global surface air temperature in 1965–2012 show the maxima during CRs [Cosmic Rays] and Dst index [of the solar wind] minima. It proves that CRs [Cosmic Rays] play essential role in climate change and main part of climate variations can be explained by Pudovkin and Raspopov’s (1992) mechanism of action CRs [Cosmic Rays] modulated by the solar activity on the state of lower atmosphere and meteorological parameters. Following this we have to seek for another ways of looking for global warming reason, first of all, as a man impact on climate.”

Eine Gruppe um Nicolas Huneeus überraschte im Mai 2014 im Journal of Geophysical Research mit einer etwas versteckten Bestätigung des Sonne-Wolken-Bezugs. Im Rahmen von Modellierungen fanden sie eine bedeutende Beeinflussung der Wolken durch solare Aktivitätsschwankungen. Lesen Sie selbst im Abstract:

Forcings and feedbacks in the GeoMIP ensemble for a reduction in solar irradiance and increase in CO2
The effective radiative forcings (including rapid adjustments) and feedbacks associated with an instantaneous quadrupling of the preindustrial CO2 concentration and a counterbalancing reduction of the solar constant are investigated in the context of the Geoengineering Model Intercomparison Project (GeoMIP). The forcing and feedback parameters of the net energy flux, as well as its different components at the top-of-atmosphere (TOA) and surface, were examined in 10 Earth System Models to better understand the impact of solar radiation management on the energy budget. In spite of their very different nature, the feedback parameter and its components at the TOA and surface are almost identical for the two forcing mechanisms, not only in the global mean but also in their geographical distributions. This conclusion holds for each of the individual models despite intermodel differences in how feedbacks affect the energy budget. This indicates that the climate sensitivity parameter is independent of the forcing (when measured as an effective radiative forcing). We also show the existence of a large contribution of the cloudy-sky component to the shortwave effective radiative forcing at the TOA suggesting rapid cloud adjustments to a change in solar irradiance. In addition, the models present significant diversity in the spatial distribution of the shortwave feedback parameter in cloudy regions, indicating persistent uncertainties in cloud feedback mechanisms.

Hochinteressant auch die Studie einer Forscherguppe um Mai Mai Lam, die ihre Ergebnisse im September 2014 in den Geophysical Research Letters publizierte. Die Wissenschaftler untersuchten die Atmosphäre über der Antarktis und fanden deutliche Hinweise darauf, dass solar-modulierte kosmische Strahlung über das atmosphärische elektrische Feld die Wolken der unteren Troposphäre beeinflussen können. Lam und Kollegen sehen den Wolken-Solarverstärker parallel operierend zum UV-Solarverstärker der Stratosphäre. Anbei die Kurzfassung:

Solar wind-driven geopotential height anomalies originate in the Antarctic lower troposphere
We use National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data to estimate the altitude and time lag 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 time lags at the tropopause (6–8 days) and in the midtroposphere (4 days) than in the lower troposphere (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 time lag 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 ultraviolet radiation or energetic particle precipitation.

Die American Geophysical Union (AGU) fand das Paper so bemerkenswert, dass sie es in einem Nachrichtenbeitrag in ihrer Mitgliederzeitschrift Eos vorstellte:

How the Solar Wind May Affect Weather and Climate
The Sun’s influence on the Earth’s climate is complicated, but researchers are slowly figuring out how the solar wind can indirectly affect clouds over the poles.
The Sun plays a large role in providing the Earth with light and heat, but its more subtle effects on the Earth’s weather, climate and atmospheric processes are still a mystery. Scientists are especially puzzled by how the solar wind—streams of plasma ejected from the Sun—affects the Earth’s climate system.

Weiterlesen in Eos.

Licht und Schatten für Svensmark-Freunde in einem Paper in PNAS im März 2015. Dort veröffentlichte eine Gruppe um Anastasios Tsonis eine Untersuchung zum Zusammenhang zwischen kosmischer Strahlung und der globalen Temperatur. Zwar konnten die Forscher die Erwärmung des 20. Jahrhundert nicht in Einklang mit der kosmischen Strahlung bringen, jedoch fanden sie im Maßstab von einigen Jahren einen bedeutenden Zusammenhang zwischen kosmischer Strahlung und Temperatur. Hier der Abstract:

Dynamical evidence for causality between galactic cosmic rays and interannual variation in global temperature
As early as 1959, it was hypothesized that an indirect link between solar activity and climate could be mediated by mechanisms controlling the flux of galactic cosmic rays (CR) [Ney ER (1959) Nature 183:451–452]. Although the connection between CR and climate remains controversial, a significant body of laboratory evidence has emerged at the European Organization for Nuclear Research [Duplissy J, et al. (2010) Atmos Chem Phys 10:1635–1647; Kirkby J, et al. (2011) Nature 476(7361):429–433] and elsewhere [Svensmark H, Pedersen JOP, Marsh ND, Enghoff MB, Uggerhøj UI (2007) Proc R Soc A 463:385–396; Enghoff MB, Pedersen JOP, Uggerhoj UI, Paling SM, Svensmark H (2011) Geophys Res Lett 38:L09805], demonstrating the theoretical mechanism of this link. In this article, we present an analysis based on convergent cross mapping, which uses observational time series data to directly examine the causal link between CR and year-to-year changes in global temperature. Despite a gross correlation, we find no measurable evidence of a causal effect linking CR to the overall 20th-century warming trend. However, on short interannual timescales, we find a significant, although modest, causal effect between CR and short-term, year-to-year variability in global temperature that is consistent with the presence of nonlinearities internal to the system. Thus, although CR do not contribute measurably to the 20th-century global warming trend, they do appear as a nontraditional forcing in the climate system on short interannual timescales.

Ein komplettes Modell zur klimatischen Wirkungsweise kosmischer Strahlung beschrieb N.A. Kilifarska im August 2015 im Journal of Atmospheric and Solar-Terrestrial Physics. Ihr Prozess läuft im Maßstab von zwei Jahrzehnten ab und umfasst das Sonnenmagnetfeld, das die kosmische Strahlung moduliert, welche wiederum das Ozon und Wasserdampf in der unteren Stratosphäre verändert. Hier die Kurzfassung:

Bi-decadal solar influence on climate, mediated by near tropopause ozone
The Sun’s contribution to climate variations was highly questioned recently. In this paper we show that bi-decadal variability of solar magnetic field, modulating the intensity of galactic cosmic ray (GCR) at the outer boundary of heliosphere, could be easily tracked down to the Earth’s surface. The mediator of this influence is the lower stratospheric ozone, while the mechanism of signal translation consists of: (i) GCR impact on the lower stratospheric ozone balance; (ii) modulation of temperature and humidity near the tropopause by the ozone variations; (iii) increase or decrease of the greenhouse effect, depending on the sign of the humidity changes. The efficiency of such a mechanism depends critically on the level of maximum secondary ionisation created by GCR (i.e. the Pfotzer maximum) − determined in turn by heterogeneous Earth’s magnetic field. Thus, the positioning of the Pfotzer max in the driest lowermost stratosphere favours autocatalytic ozone production in the extra-tropical Northern Hemisphere (NH), while in the SH − no suitable conditions for activation of this mechanism exist. Consequently, the geomagnetic modulation of precipitating energetic particles – heterogeneously distributed over the globe – is imprinted on the relation between ozone and humidity in the lower stratosphere (LS). The applied test for causality reveals that during the examined period 1957–2012 there are two main centers of action in the winter NH, with tight and almost stationary ozone control on the near tropopause humidity. Being indirectly influenced by the solar protons, the variability of the SH lower stratospheric ozone, however, is much weaker. As a consequence, the causality test detects that the ozone dominates in the interplay with ULTS humidity only in the summer extra-tropics.

Eine spannende Entdeckung machte eine Gruppe um Il-Hyun Cho, die sie im August 2012 im Asia-Pacific Journal of Atmospheric Sciences beschrieben. Sie analysierten fünf solare Zyklen über gut 50 Jahre und fanden, dass die globale Temperatur jeweils geringer war, wenn die Nordhalbkugel der Sonne aktiver war als die solare Südhalbkugel. Die Autoren schlagen einen Mechanismus über die kosmische Strahlung vor. Hier der Abstract:

The global temperature anomaly and solar North-South asymmetry
We investigate whether the global temperature anomaly is associated with the solar North-South asymmetry using data archived approximately for five solar cycles. We are motivated by both the accumulating evidence for the connection of Galactic cosmic-rays (GCRs) to the cloud coverage and recent finding of the association of GCR influx and the solar North-South asymmetry. We have analyzed the data of the observed sunspot, the GCR influx observed at the Moscow station, and the global temperature anomaly. We have found that the mean global temperature anomaly is systematically smaller (0.56 in the unit of its standard deviation) during the period when the solar northern hemisphere is more active than the solar southern hemisphere. The difference in the mean value of the global temperature anomaly for the two data sets sub-sampled according to the solar North-South asymmetry is large and statistically significant. We suggest the solar North-South asymmetry is related to the global temperature anomaly through modulating the amount of GCR influx. Finally, we conclude by discussing its implications on a climate model and a direction of future work.

Zuguterletzt noch einen Hinweis auf das Erdmagnetfeld, das sich derzeit in einigen Teilen der Erde rapide abschwächt. Kommt bald die Umpolung? Hier ein Auszug aus einem Artikel in Spiegel Online vom 19. Juni 2014:

Dennoch hat sich das Magnetfeld der Erde in einem Tempo verändert, das Wissenschaftler stutzig gemacht hat. In den vergangenen 100 Jahren ist es global gesehen um rund fünf Prozent schwächer geworden. In bestimmten Gebieten, etwa im Atlantik vor der Küste Brasiliens, hat es noch deutlich mehr an Kraft verloren. Im Bereich dieser sogenannten Südatlantischen Anomalie war ein Minus von fünf Prozent in zehn bis fünfzehn Jahren zu beobachten. Drei europäische Satelliten haben nun in ungekannter Genauigkeit vermessen, wie schnell der Wandel vonstatten geht. Die “Swarm”-Satelliten fliegen seit vergangenem Herbst um die Erde. Die Europäische Weltraumorganisation (Esa) hat die ersten Ergebnisse der “Swarm”-Mission am Donnerstag auf einem Kongress in Kopenhagen vorgestellt. “Generell konnten wir eine Abschwächung beobachten”, berichtete Nils Olsen von Dänemarks Technischer Universität (DTU), “aber in manchen Bereichen gab es auch einen Anstieg”. So hat das Magnetfeld vor allem über Nord- und Südamerika innerhalb der sechs Monate der Mission an Stärke verloren, kräftiger geworden ist es über dem Indischen Ozean.

Ganzen Artikel auf Spiegel Online lesen.