Sonne

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.

weiter lesenNeues vom Svensmark-Wolken-Solarverstärker

Eines des großen ungelösten Rätsel der Klimawissenschaften ist die Frage, auf welchem Wege solare Aktivitätsschwankungen zu klimatischen Veränderungen führen. Eine Vielzahl von geologisch-paläoklimatologischen Untersuchungen belegt einwandfrei, dass es einen solaren Einfluss auf das Klima gibt. Allerdings wird hierzu ein solarer Verstärkermechanismus benötigt, da die Sonne-Schwankungen im sichtbaren Strahlungsbereich des Lichtes wohl zu gering sind, um den beobachteten Effekt zu erzeugen. In unserem Buch „Die kalte Sonne“ haben wir die beiden wahrscheinlichsten Verstärker-Kandidaten vorgestellt. Zum einen wäre hier der Svensmark-Wolkeneffekt zu nennen, wobei von der Sonne modulierte galaktische Strahlung Keime für Wolken bilden könnte. Zum anderen geht es um die UV-Strahlung, die viel stärker schwankt als der sichtbare Lichtanteil der Sonne. Das UV erzeugt in der Stratosphäre, Ozon. Mittlerweile gibt es sich verdichtenede Hinweise darauf, dass sich das Geschehen in der Stratosphäre auch in die tieferen Atmosphärenstockwerke durchpaust, wo das Wettergeschehen stattfindet. Im Folgenden wollen einen Streifzug durch die neuere Literatur unternehmen. Was gibt es Neues vom stratosphärischen Solarverstärker?

Im November 2012 wartete eine Gruppe um David Thompson in Nature mit einer großen Überraschung auf: Die Forscher hatten einen neuen Datensatz zur Temperaturentwicklung der mittleren und oberen Stratosphäre ermittelt, der sich signifikant von früheren Temperaturkurven unterschied. Hierdurch wurde nun alles durcheinandergewirbelt. Offenbar stimmten die früheren Modelle zur Entwicklung hinten und vorne nicht. Auch Modelle mussten nun plötzlich auf den Prüfstand, die nur die veraltete Temperaturkurve nachvollziehen konnten, nicht jedoch die neue. Dies ist insbesondere bedenklich, da hier Emissionen von CO2 und ozonzerstörenden Gasen eine Rolle spielen. Hier der Abstract der Arbeit:

The mystery of recent stratospheric temperature trends
A new data set of middle- and upper-stratospheric temperatures based on reprocessing of satellite radiances provides a view of stratospheric climate change during the period 1979–2005 that is strikingly different from that provided by earlier data sets. The new data call into question our understanding of observed stratospheric temperature trends and our ability to test simulations of the stratospheric response to emissions of greenhouse gases and ozone-depleting substances. Here we highlight the important issues raised by the new data and suggest how the climate science community can resolve them.

Auch Katja Matthes vom Kieler Geomar ist zusammen mit Kollegen an der Erforschung des stratosphärischen Solarverstärkers beteiligt. Hier gelangten in den letzten Jahren gleich drei Arbeiten zur Publikation, die wir hier vorstellen möchten. So erschien im September 2012 im Journal of Geophysical Research ein Paper, das von Christof Petrick angeführt wurde. In der Studie geht es um solare UV-Schwankungen, die stratosphärische Veränderungen hervorrufen, die sich über Ozeanzyklen in die Ozeane fortpflanzen. Die Matthes-Gruppe nennt dies „Top-Down-Mechanismus“. Hier der Abstract:

Impact of the solar cycle and the QBO on the atmosphere and the ocean
The Solar Cycle and the Quasi-Biennial Oscillation are two major components of natural climate variability. Their direct and indirect influences in the stratosphere and troposphere are subject of a number of studies. The so-called „top-down‘ mechanism describes how solar UV changes can lead to a significant enhancement of the small initial signal and corresponding changes in stratospheric dynamics. How the signal then propagates to the surface is still under investigation. We continue the „top-down‘ analysis further down to the ocean and show the dynamical ocean response with respect to the solar cycle and the QBO. For this we use two 110-year chemistry climate model experiments from NCAR’s Whole Atmosphere Community Climate Model (WACCM), one with a time varying solar cycle only and one with an additionally nudged QBO, to force an ocean general circulation model, GFZ’s Ocean Model for Circulation and Tides (OMCT). We find a significant ocean response to the solar cycle only in combination with a prescribed QBO. Especially in the Southern Hemisphere we find the tendency to positive Southern Annular Mode (SAM) like pattern in the surface pressure and associated wind anomalies during solar maximum conditions. These atmospheric anomalies propagate into the ocean and induce deviations in ocean currents down into deeper layers, inducing an integrated sea surface height signal. Finally, limitations of this study are discussed and it is concluded that comprehensive climate model studies require a middle atmosphere as well as a coupled ocean to investigate and understand natural climate variability.

Im April 2013 publizierte die Matthes-Gruppe mit Ermolli et al 2013 im Fachblatt Atmospheric Chemistry and Physics eine weitere Studie zum Thema. Die Hauptnachricht: Klimamodelle unterschätzten bislang die UV-Schwankungen um einen Faktor von 4-6. Das ist enorm. In Wirklichkeit waren die UV-Schwankungen also im Mittel 5 mal so hoch wie angenommen. Ermolli und Kollegen prognostizieren, dass auch die atmosphärischen Effekte entsprechend viel größer sind als zuvor modelliert. Hier der Abstract:

Recent variability of the solar spectral irradiance and its impact on climate modelling
The lack of long and reliable time series of solar spectral irradiance (SSI) measurements makes an accurate quantification of solar contributions to recent climate change difficult. Whereas earlier SSI observations and models provided a qualitatively consistent picture of the SSI variability, recent measurements by the SORCE (SOlar Radiation and Climate Experiment) satellite suggest a significantly stronger variability in the ultraviolet (UV) spectral range and changes in the visible and near-infrared (NIR) bands in anti-phase with the solar cycle. A number of recent chemistry-climate model (CCM) simulations have shown that this might have significant implications on the Earth’s atmosphere. Motivated by these results, we summarize here our current knowledge of SSI variability and its impact on Earth’s climate.
We present a detailed overview of existing SSI measurements and provide thorough comparison of models available to date. SSI changes influence the Earth’s atmosphere, both directly, through changes in shortwave (SW) heating and therefore, temperature and ozone distributions in the stratosphere, and indirectly, through dynamical feedbacks. We investigate these direct and indirect effects using several state-of-the art CCM simulations forced with measured and modelled SSI changes. A unique asset of this study is the use of a common comprehensive approach for an issue that is usually addressed separately by different communities.
We show that the SORCE measurements are difficult to reconcile with earlier observations and with SSI models. Of the five SSI models discussed here, specifically NRLSSI (Naval Research Laboratory Solar Spectral Irradiance), SATIRE-S (Spectral And Total Irradiance REconstructions for the Satellite era), COSI (COde for Solar Irradiance), SRPM (Solar Radiation Physical Modelling), and OAR (Osservatorio Astronomico di Roma), only one shows a behaviour of the UV and visible irradiance qualitatively resembling that of the recent SORCE measurements. However, the integral of the SSI computed with this model over the entire spectral range does not reproduce the measured cyclical changes of the total solar irradiance, which is an essential requisite for realistic evaluations of solar effects on the Earth’s climate in CCMs.
We show that within the range provided by the recent SSI observations and semi-empirical models discussed here, the NRLSSI model and SORCE observations represent the lower and upper limits in the magnitude of the SSI solar cycle variation.
The results of the CCM simulations, forced with the SSI solar cycle variations estimated from the NRLSSI model and from SORCE measurements, show that the direct solar response in the stratosphere is larger for the SORCE than for the NRLSSI data. Correspondingly, larger UV forcing also leads to a larger surface response.
Finally, we discuss the reliability of the available data and we propose additional coordinated work, first to build composite SSI data sets out of scattered observations and to refine current SSI models, and second, to run coordinated CCM experiments.

In unserer Monatskolumne “Die Sonne im August 2015“ hatten wir bereits eine weitere aktuelle Matthes-Arbeit besprochen, Thiéblemont et al., die im September 2015 in Nature Communications erschien. Laut der Arbeit ist die Nordatlantische Oszillation mit einer Verzögerung von 1-2 Jahren an die Sonnenaktivität gekoppelt. Die Forscher benutzten ein Klimamodell, das die Atmosphäre bis zu einer Höhe von 140 km modelliert  und somit die Wirkung der UV-Strahlung auf die Chemie der Stratosphäre, etwa der Ozonbildung, besser berücksichtigen kann. Hier der Abstract:

Solar forcing synchronizes decadal North Atlantic climate variability
Quasi-decadal variability in solar irradiance has been suggested to exert a substantial effect on Earth’s regional climate. In the North Atlantic sector, the 11-year solar signal has been proposed to project onto a pattern resembling the North Atlantic Oscillation (NAO), with a lag of a few years due to ocean-atmosphere interactions. The solar/NAO relationship is, however, highly misrepresented in climate model simulations with realistic observed forcings. In addition, its detection is particularly complicated since NAO quasi-decadal fluctuations can be intrinsically generated by the coupled ocean-atmosphere system. Here we compare two multi-decadal ocean-atmosphere chemistry-climate simulations with and without solar forcing variability. While the experiment including solar variability simulates a 1–2-year lagged solar/NAO relationship, comparison of both experiments suggests that the 11-year solar cycle synchronizes quasi-decadal NAO variability intrinsic to the model. The synchronization is consistent with the downward propagation of the solar signal from the stratosphere to the surface.

Mithilfe eines Klimamodells, das auch die Stratosphäre berücksichtigt, konnte ein Forscherteam um Lon Hood einen Einfluss des 11-Jahres-Sonnenzyklus in der winterlichen Temperaturentwicklung des Pazifiks nachweisen. Das macht Hoffnung. Die Arbeit erschien im Oktober 2013 im Journal of Climate. Hier der Abstract:

weiter lesenNeues vom stratosphärischen Solarverstärker