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- ItemChanges of snow cover in Poland(Heidelberg : Springer, 2017) Szwed, Małgorzata; Pin´skwar, Iwona; Kundzewicz, Zbigniew W.; Graczyk, Dariusz; Mezghani, AbdelkaderThe present paper examines variability of characteristics of snow cover (snow cover depth, number of days with snow cover and dates of beginning and end of snow cover) in Poland. The study makes use of a set of 43 long time series of observation records from the stations in Poland, from 1952 to 2013. To describe temporal changes in snow cover characteristics, the intervals of 1952–1990 and of 1991–2013 are compared and trends in analysed data are sought (e.g., using the Mann–Kendall test). Observed behaviour of time series of snow-related variables is complex and not easy to interpret, for instance because of the location of the research area in the zone of transitional moderate climate, where strong variability of climate events is one of the main attributes. A statistical link between the North Atlantic Oscillation (NAO) index and the snow cover depth, as well as the number of snow cover days is found.
- ItemEvolving climate network perspectives on global surface air temperature effects of ENSO and strong volcanic eruptions(Berlin ; Heidelberg : Springer, 2021) Kittel, Tim; Ciemer, Catrin; Lotfi, Nastaran; Peron, Thomas; Rodrigues, Francisco; Kurths, Jürgen; Donner, Reik V.Episodically occurring internal (climatic) and external (non-climatic) disruptions of normal climate variability are known to both affect spatio-temporal patterns of global surface air temperatures (SAT) at time-scales between multiple weeks and several years. The magnitude and spatial manifestation of the corresponding effects depend strongly on the specific type of perturbation and may range from weak spatially coherent yet regionally confined trends to a global reorganization of co-variability due to the excitation or inhibition of certain large-scale teleconnectivity patterns. Here, we employ functional climate network analysis to distinguish qualitatively the global climate responses to different phases of the El Niño–Southern Oscillation (ENSO) from those to the three largest volcanic eruptions since the mid-20th century as the two most prominent types of recurrent climate disruptions. Our results confirm that strong ENSO episodes can cause a temporary breakdown of the normal hierarchical organization of the global SAT field, which is characterized by the simultaneous emergence of consistent regional temperature trends and strong teleconnections. By contrast, the most recent strong volcanic eruptions exhibited primarily regional effects rather than triggering additional long-range teleconnections that would not have been present otherwise. By relying on several complementary network characteristics, our results contribute to a better understanding of climate network properties by differentiating between climate variability reorganization mechanisms associated with internal variability versus such triggered by non-climatic abrupt and localized perturbations.
- ItemVariability of snow cover and frost depth at the Potsdam station, Germany(Praha : Česká geografická společnost, 2016) Szwed, Małgorzata; Kundzewicz, Zbigniew W.; Mezghani, AbdelkaderThe presented paper examines variability of characteristics of snow cover (snow cover depth, number of days with snow cover and dates of beginning and end of snow cover) and frost depth in Potsdam. The study makes use of a unique long time series of data from the secular meteorological station in Potsdam (Germany), covering the time interval from 1893 to date. The observed behaviour of time series of snow is complex, and not easy to interpret. Even if shrinking snow cover is typically expected in the warming climate of the moderate zone, the change in Potsdam is largely dominated by inter-winter and intra-winter variability, rendering trend detection difficult. Nevertheless, an increasing, statistically significant trend for winter precipitation was detected with almost no changes in the snow fall. A statistical link between the NAO index and the snow cover depth as well as the number of snow cover days was found.
- ItemThe Optical Variability of the BL Lac AO 0235+164(Basel : MDPI, 2016) Fan, Junhui; Kurtanidze, Omar; Liu, Yi; Liu, Xiang; Richter, Gotthard; Nikolashvili, Maria; Kurtanidze, Sophia; Chanishvili, Revaz; Wang, Hongtao; Sasada, Mahito; Zhou, Aiying; Lin, Chao; Yuan, YuhaiIn this work, we present optical R band observations of AO 0235+164 carried out during the period of November 2006 to December 2012 using the Ap6E CCD camera attached to the primary focus of the 70 cm meniscus telescope at Abastumani Observatory, Georgia. It shows a large variation of ΔR = 4.88 mag (14.19–19.07 mag) and a short time scale of ΔTv = 73.5 min during our monitoring period. When periodicity analysis methods are applied to the R-band data from both historic and our observations, periods P1 = 8.26 yr and P2 = 0.54 yr are found.
- ItemTackling long-term climate change together: The case of flexible CCS and fluctuating renewable energy(Amsterdam [u.a.] : Elsevier, 2011) Ludig, S.; Haller, M.; Bauer, N.The present study aims at shedding light into the interaction of fluctuating renewables and the operational flexibility of post-combustion capture plants in the framework of a long-term model. We developed a model of the electricity sector taking into account both long-term investment time scales to represent plant fleet development under economic and climate constraints as well as short time scales to consider fluctuations of demand and renewable energy sources. The LIMES model allows us to determine the respective roles of renewables and CCS in climate change mitigation efforts within the electricity sector. Furthermore, we assess the influence of natural gas prices on fuel choice and investigate the shares of competing CCS approaches in the technology mix. We find that the optimal technology mix includes large shares of renewables and simultaneously different competing CCS technologies, depending on emission constraints and fuel prices.