ALBERT

Description: History of the circulation in the North Pacific marginal seas (NPMS), one of the largest shelf seas in the world, remains elusive. This is mainly attributed to the interaction between climatic processes and land-sea evolution since the last deglaciation when sea level is over 100 meters lower than the present. In this study, we apply a high-resolution regional ocean general circulation model and perform simulations based on stepwise sea-level rise from -90m to 0m of the present, while also measure radiolarians assemblages in sediment cores. Based on data-model intercomparison, our results show that the NPMS circulation mainly underwent 3 regimes during the evolution from 14,000 years ago to the modern state. Such nonlinear process is due to the existence of tipping points in the relationship between sea level and NPMS circulation on glacial-interglacial time scales

Description: Looking at the past sharpens our understanding of possible future climate changes. We focus on Earth system modeling, paleoclimate data analysis, and theoretical aspects. Predicting the future spread of possible climates, the risk of climate extremes and the risk of rapid transitions is of high relevance. The past provides evidence of abrupt climate change and the frequency of extremes. Earth system models applied both to past and future scenarios enhance our ability to detect regime shifts in climates and extremes. We consider the response of the system to long-term forcing and then focus on shorter time scales down to weather. Particular aspects are: Model resolution matters for climate change and extremes; recorder systems such as O, H, C-isotopes enable a suitable interpretation of the past; data assimilation can yield a dynamically consistent picture. New high-resolution models can quantify the feedbacks in the atmosphere-ocean-ice system and inform us about the full range of climate variability and extremes.With our holistic approach, we seek to overcome known biases of deep-time polar amplification, the stochastic nature of centennial-to-millennial climate variability, as well as extremes. Here, we put emphasis on the concept of a hierarchy of models as this provides a linkage between theoretical understanding and the complexity of the system. Lohmann, Butzin, Eissner, Shi, Stepanek, 2020: Abrupt climate and weather changes across timescales. Paleoc. Paleoclim., doi:10.1029/2019PA003782 Lohmann, 2020: Temperatures from energy balance models: the effective heat capacity matters. ESD, doi:10.5194/esd-11-1195-2020 Contzen, Dickhaus, Lohmann, 2023: Long-term temporal evolution of temperature extreme in a warming Earth. PLOS, doi:10.1371/journal.pone.0280503

Description: Past studies found that large-amplitude geomagnetically induced current (GIC) related to magnetospheric Ultra Low Frequency (ULF) waves tend to be associated with periods 〉120 s at magnetic latitudes 〉60°, with comparatively (a) smaller GIC amplitudes at lower latitudes and shorter wave periods and (b) fewer reports of waves associated with GIC at lower latitudes. ULF wave periods generally decrease with decreasing latitude; thus, we examine whether these trends might be due, in part, to the undersampling of ULF wave fields in commonly available measurements with 60 s sampling intervals. We use geomagnetic field (B), geoelectric field (E), and GIC measurements with 0.5–10 s sampling intervals during the 29–31 October 2003 geomagnetic storm to show that waves with periods 〈∼120 s were present during times with the largest amplitude E and GIC variations. These waves contributed to roughly half the maximum E and GIC values, including during times with the maximum GIC values reported over a 14-year monitoring interval in New Zealand. The undersampling of wave periods 〈120 s in 60 s measurements can preclude identification of the cause of the GIC during some time intervals. These results indicate (a) ULF waves with periods ≤120 s are an important contributor to large amplitude GIC variations, (b) the use of 0.1–1.0 Hz sampling rates reveals their contributions to B, E, and GIC, and (c) these waves' contributions are likely strongest at magnetic latitudes 〈60° where ULF waves often have periods 〈120 s.