Die Sonne ist ein wichtiger Klimafaktor, auch in Amerika. Im Mai 2014 bekräftigten Gorji Sefidmazgi und Kollegen dies in einer Arbeit in Nonlinear Processes in Geophysics. Die Forscher untersuchten die Temperaturentwicklung des US-Bundesstaats North Carolina für die vergangenen 60 Jahre. Dabei fanden sie, dass die Schwankungen fast vollständig mit Sonnenaktivitätsschwankungen und Ozeanzyklen erklärbar wären. Hier die Kurzfassung:
Trend analysis using non-stationary time series clustering based on the finite element method
In order to analyze low-frequency variability of climate, it is useful to model the climatic time series with multiple linear trends and locate the times of significant changes. In this paper, we have used non-stationary time series clustering to find change points in the trends. Clustering in a multi-dimensional non-stationary time series is challenging, since the problem is mathematically ill-posed. Clustering based on the finite element method (FEM) is one of the methods that can analyze multidimensional time series. One important attribute of this method is that it is not dependent on any statistical assumption and does not need local stationarity in the time series. In this paper, it is shown how the FEM-clustering method can be used to locate change points in the trend of temperature time series from in situ observations. This method is applied to the temperature time series of North Carolina (NC) and the results represent region-specific climate variability despite higher frequency harmonics in climatic time series. Next, we investigated the relationship between the climatic indices with the clusters/trends detected based on this clustering method. It appears that the natural variability of climate change in NC during 1950–2009 can be explained mostly by AMO and solar activity.
Einige Monate später, im Oktober 2014, publizierte ein Forscherteam um Erich Osterberg im Journal of Geophysical Research eine Studie zum Einfluss von solaren Aktivitätsschwankungen auf das Aleuten-Tief im Golf von Alaska. Das Ergebnis lässt aufhorchen: Die Veränderungen des Aleuten-Tiefs während der vergangenen 1500 Jahre korrelieren stark mit der Sonnenaktivität. Eine starke Sonnenaktivität geht dabei typischerweise mit einem schwachen Aleuten-Tief und tropischen La Nina-Bedingungen einher. Hier der Abstract:
Mount Logan ice core record of tropical and solar influences on Aleutian Low variability: 500–1998 A.D.
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.
Noch einen Monat später, im November 2014, berichtete eine Forschergruppe um Keyan Fang im Journal of Climate über einen Bezug der Sonnenaktivität mit der Klimaentwicklung in Nordamerika und Asien. Anhand eines Datensatzes der letzten 600 Jahre konnten die Autoren zeigen, dass eine enge klimatische Kopplung zwischen den Kontinenten bestand, und zwar umso intensiver, je stärker die Sonne strahlte. Hier die Kurzfassung:
Covarying Hydroclimate Patterns between Monsoonal Asia and North America over the Past 600 Years
Proxy data with large spatial coverage spanning to the preindustrial era not only provide invaluable material to investigate hydroclimate changes in different regions but also enable studies on temporal changes in the teleconnections between these regions. Applying the singular value decomposition (SVD) method to tree-ring-based field reconstructions of the Palmer drought severity index (PDSI) over monsoonal Asia (MA) and North America (NA) from 1404 to 2005, the dominant covarying pattern between the two regions is identified. This pattern is represented by the teleconnection between the dipole pattern of southern–northern latitudinal MA and the dipole of southwest NA (SWNA)–northwest NA (NWNA), which accounts for 59.6% of the total covariance. It is dominated by an antiphase low MA and SWNA teleconnection, driven by the El Niño–Southern Oscillation (ENSO), and is most significant at an interannual time scale. This teleconnection is strengthened (weakened) in periods of increased (decreased) solar forcing and high (low) temperature, which is associated with intensified (weakened) ENSO variability. Additional forcing by SST anomalies in the Indian and western Pacific Oceans appears to be important too.
Springen wir nun auf die Südhalbkugel nach Südamerika. Im Juni 2015 veröffentlichte eine Forschergruppe um C. Turney von der University of New South Wales in Sydney im Fachblatt Climate of the Past Discussions eine Arbeit zum Klimageschehen der Falklandinseln. Anhand einer Torfabfolge rekonstruierten die Wissenschaftler die Stärke der Westwinde für die vergangenen 2600 Jahre. Im Rahmen einer Spektralanalyse fanden Turney und Kollegen einen charakteristischen Zyklus von 250 Jahren, der in den Bereich des solaren Suess-de Vries fällt. Ein faszinierendes Ergebnis: Die Westwinde der Südhalbkugel wehten ganz offensichtlich im Takte der Sonne. Hier der Abstract:
A 250 year periodicity in Southern Hemisphere westerly winds over the last 2600 years
Southern Hemisphere westerly airflow has a significant influence on the ocean–atmosphere system of the mid- to high-latitudes with potentially global climate implications. Unfortunately historic observations only extend back to the late nineteenth century, limiting our understanding of multi-decadal to centennial change. Here we present a highly resolved (30 yr) record of past westerly air strength from a Falkland Islands peat sequence spanning the last 2600 years. Situated under the core latitude of Southern Hemisphere westerly airflow, we identify highly variable changes in exotic pollen derived from South America which can be used to inform on past westerly air strength and location. The results indicate enhanced airflow over the Falklands between 2000 and 1000 cal. yr BP, and associated with increased burning, most probably as a result of higher temperatures and/or reduced precipitation, comparable to records in South America. Spectral analysis of the charcoal record identifies a 250 year periodicity within the data, suggesting solar variability has a modulating influence on Southern Hemisphere westerly airflow with potentially important implications for understanding global climate change through the late Holocene.
Wie wir bereits vor einiger Zeit an dieser Stelle berichteten, steuerte die Sonnenaktivität auch den südamerikanischen Monsunregen während der letzten 1500 Jahre.
