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Describes experiments involving simple machines that follow the scientific method, and can be completed in an hour or less. Explore using levers to control motion and lift, and how the steepness of inclined planes affects the force needed to move something. Most experiments also include ideas for science fair projects.

The Northern Annular Mode (NAM) induces anomalous wintertime weather over the extratropical Northern Hemisphere as the leading mode of atmospheric circulation variability. Yet, modulations of its statistical properties in a changing climate need elucidating. This study investigates the seasonality of NAM variability and its modulations under global warming with a large‐ensemble atmospheric simulation data set. We find that the Aleutian Low anomaly associated with the NAM strengthens in a warmer climate, which is linked to a seasonally earlier emergence of the Aleutian‐Icelandic Low seesaw (AIS). The El Niño‐Southern Oscillation (ENSO) teleconnection extends more eastward under global warming, which increases the ENSO‐NAM correlation through the earlier AIS development. Our findings suggest increased predictability of the NAM under global warming, with uncertainties due to potential ENSO changes.

The last glacial cycle provides the opportunity to investigate large changes in the Atlantic Meridional Overturning Circulation (AMOC) beyond the small fluctuations evidenced from direct measurements. Paleotemperature records from Greenland and the North Atlantic show an abrupt variability, called Dansgaard–Oeschger (DO) events, which is associated with abrupt changes of the AMOC. These DO events also have Southern Hemisphere counterparts via the thermal bipolar seesaw, a concept describing the meridional heat transport leading to asynchronous temperature changes between both hemispheres. However, temperature records from the North Atlantic show more pronounced DO cooling events during massive releases of icebergs known as Heinrich (H) events, contrary to ice-core–based temperature records from Greenland. Here, we present high-resolution temperature records from the Iberian Margin and a Bipolar Seesaw Index to discriminate DO cooling events with and without H events. We show that the thermal bipolar seesaw model generates synthetic Southern Hemisphere temperature records that best resemble Antarctic temperature records when using temperature records from the Iberian Margin as inputs. Our data-model comparison emphasizes the role of the thermal bipolar seesaw in the abrupt temperature variability of both hemispheres with a clear enhancement during DO cooling events with H events, implying a relationship that is more complex than a simple flip-flop between two climate states linked to a tipping point threshold.

The last glacial interval experienced abrupt climatic changes called Dansgaard–Oeschger (DO) events. These events manifest themselves as rapid increases followed by slow decreases of oxygen isotope ratios in Greenland ice core records. Despite promising advances, a comprehensive theory of the DO cycles, with their repeated ups and downs of isotope ratios, is still lacking. Here, based on earlier hypotheses, we introduce a dynamical model that explains the DO variability by rapid retreat and slow regrowth of thick ice shelves and thin sea ice in conjunction with changing subsurface water temperatures due to insulation by the ice cover. Our model successfully reproduces observed features of the records, such as the sawtooth shape of the DO cycles, waiting times between DO events across the last glacial, and the shifted antiphase relationship between Greenland and Antarctic ice cores. Our results show that these features can be obtained via internal feedbacks alone. Warming subsurface waters could have also contributed to the triggering of Heinrich events. Our model thus offers a unified framework for explaining major features of multimillennial climate variability during glacial intervals.

Future experiments such as SHiP and high-intensity e + e - colliders will have a superb sensitivity to heavy Majorana neutrinos with masses below M Z . We show that the measurement of the mixing to electrons and muons of one such state could establish the existence of CP violating phases in the neutrino mixing matrix, in the context of low-scale seesaw models. We quantify in the minimal model the CP reach of these future experiments, and demonstrate that CP violating phases in the mixing matrix could be established at 5 σ CL in a very significant fraction of parameter space.

Temperature and precipitation are the most important factors responsible for agricultural productivity variations. In 2018 spring/summer growing season, Europe experienced concurrent anomalies of both. Drought conditions in central and northern Europe caused yield reductions up to 50% for the main crops, yet wet conditions in southern Europe saw yield gains up to 34%, both with respect to the previous 5-year mean. Based on the analysis of documentary and natural proxy-based seasonal paleoclimate reconstructions for the past half millennium, we show that the 2018 combination of climatic anomalies in Europe was unique. The water seesaw, a marked dipole of negative water anomalies in central Europe and positive ones in southern Europe, distinguished 2018 from the five previous similar droughts since 1976. Model simulations reproduce the 2018 European water seesaw in only 4 years out of 875 years in historical runs and projections. Future projections under the RCP8.5 scenario show that 2018-like temperature and rainfall conditions, favorable to crop growth, will occur less frequent in southern Europe. In contrast, in central Europe high-end emission scenario climate projections show that droughts as intense as 2018 could become a common occurrence as early as 2043. While integrated European and global agricultural markets limited agro-economic shocks caused by 2018's extremes, there is an urgent need for adaptation strategies for European agriculture to consider futures without the benefits of any water seesaw.

Neutrinos are ghost-like particles that interact only very weakly with other particles. As ongoing experiments to measure their properties improve, Ohlsson and Zhou review neutrino mass models and the renormalization group running of neutrino parameters that aim to understand the origin of neutrino mass. Neutrinos are the most elusive particles in our Universe. They have masses at least one million times smaller than the electron mass, carry no electric charge and very weakly interact with other particles, meaning that they are rarely captured in terrestrial detectors. Tremendous efforts in the past two decades have revealed that neutrinos can transform from one type to another as a consequence of neutrino oscillations—a quantum mechanical effect over macroscopic distances—yet the origin of neutrino masses remains puzzling. The physical evolution of neutrino parameters with respect to energy scale may help elucidate the mechanism for their mass generation.

Dansgaard‐Oeschger (DO) events are a dominant mode of millennial‐scale climate variability during the last glacial period with most pronounced impacts in the North Atlantic region. In Antarctica, they manifest primarily as a muted and phase‐shifted temperature signal, but recent studies suggest an additional in‐phase component. Here, we analyze the Southern Hemisphere (SH) response to spontaneous DO‐type oscillations in a general circulation model. The dominant Antarctic temperature mode is phase‐shifted compared to Greenland temperature variations and consistent with the oceanic pathway described by the bipolar seesaw model. However, the leading SH atmospheric circulation mode varies synchronously with Greenland temperatures. A westward‐shifted Walker circulation and strengthened Hadley cell during Greenland temperature maxima cause zonally heterogeneous jet stream anomalies differing from the Southern Annular Mode pattern. Comparison of simulated δ18${\\delta }^{18}$ O with speleothems and ice cores indicates a good agreement in the tropics and SH mid‐latitudes but deviations in Antarctica warrant further research. Plain Language Summary Dansgaard‐Oeschger (DO) events are pronounced North Atlantic temperature oscillations during glacial climate, lasting typically around 1,500 years. In Greenland, they are characterized by abrupt warming phases of up to 15°C within decades, followed by a slower cooling process. Impacts of DO events have been detected in paleoclimate records across the globe, including temperature changes over Antarctica. These can be explained by modified heat transport from the Southern to the Northern Hemisphere in the Atlantic Ocean. Yet, recent ice core analyses suggest that changes in the atmospheric circulation are also involved in transmitting the DO signal from the North Atlantic to the Southern Hemisphere. In this study, we investigate such changes using simulations with a global climate model that shows oscillations resembling DO events. We find separate atmospheric and oceanic pathways that drive the Southern Hemisphere climate response to North Atlantic warming. Notably, the response patterns of the atmospheric pathway differ from the climate changes observed on short timescales. We compare the simulations with speleothems and Antarctic ice cores and find a good agreement in the tropics and mid‐latitudes but differences for Antarctica. More research is needed to understand the factors that are responsible for this ambiguity. Key Points Simulations of spontaneous Dansgaard‐Oeschger‐type oscillations show a synchronous atmospheric and a phase‐shifted oceanic Southern Hemisphere climate mode The synchronous mode features zonally heterogeneous atmospheric circulation anomalies which differ from the leading interannual modes Simulated water isotopes largely agree with speleothems from the low and Southern Hemisphere mid‐latitudes but their patterns differ from Antarctic ice cores

Extending across three major plateaus, namely the Qinghai-Tibetan Plateau, the Inner Mongolia-Xinjiang Plateau and the Loess Plateau, Northwest China has the complex terrain and spatio-temporal climate variations, and is affected by the interactions among different circulation systems, such as the summer monsoon, the westerlies and the plateau monsoon. The understanding of the climate variability, as well as its characteristics and evolution mechanisms in this area has been limited so far. In this paper, the precipitation characteristics and mechanisms in the eastern and western parts of Northwest China during the flood season are compared and analyzed based on the data from 192 national meteorological observational sites in Northwest China in 1961–2016. The results show that, divided by the northern boundary of the East Asian summer monsoon, there are huge differences in the precipitation variation characteristics between the eastern and western parts. The inter-annual variations, inter-decadal variations and total trends in the two parts all show a significant seesaw phenomenon. Moreover, it is found that the seesaw phenomenon of precipitation variation is closely related to the opposite variation between the East Asian summer monsoon index (MI) and the westerly circulation index (WI). In addition, the inverse variations on different time scales are only related to the contributions of precipitation at specific grades. Besides, in the two matching patterns of precipitation in the seesaw phenomenon, the middle and high latitudes are occupied by the “high-low-high” wave trains in the precipitation increases in the east of Northwest China (ENWC) and decreases in the west of Northwest China (WNWC) pattern, meaning precipitation increases in ENWC and decreases in WNWC. Whereas the opposite “low-high-low” wave trains at 500 hPa height are observed in the middle and high latitudes in the WH-EA pattern at 500 hPa height, meaning precipitation increases in WNWC and decreases in ENWC. Thus, the atmosphere circulation situation with two wave train types can support both the precipitation seesaw phenomenon and the opposite variation between MI and WI. Moreover, the seesaw phenomenon is shown to be related to the separate or joint effects of the South Asian High, ENSO and the plateau heating on the common but opposite effect on the summer monsoon and the westerlies, in which the South Asian High probably plays a more critical role. This study could deepen the scientific understanding of precipitation mechanisms and improve the weather forecast technology in Northwest China during the flood season.

Antarctic climate changes prior to 2000 were characterized by a strong zonally asymmetric pattern. Over 90% of the land ice mass loss occurred around a limited area in West Antarctica, accompanied by a rapid surface warming rate about three times the global mean. In contrast, surface warming and glacier mass loss around East Antarctica are not significant, until the decades since 2000 when several individual stations show that the temperature trends might have reversed. The asymmetric climate changes between East- and West-Antarctica are largely attributable to the inter-decadal variabilities over the Pacific and Atlantic Oceans through tropical–polar teleconnections, leaving open the question of whether the post-2000 phase shift of the lower-latitude decadal variability causes a flip of the asymmetric Antarctic changes. Here, by synthesizing 26 in-situ observations and 6 reanalysis datasets using a statistical method and integrating the results with a series of climate model experiments, we find that the West-warming, East-cooling trend over Antarctica has systematically reversed in austral spring since the early 21st century, largely due to the atmospheric circulation anomaly over the Antarctic Peninsula–Weddell Sea region, which is associated to the teleconnection with Pacific and atmospheric internal variability. This reversal of the temperature seesaw suggests that substantial decadal-scale fluctuations of the Antarctic climate system exist, including for sea-ice and land-ice systems, superimposed on and modifying longer term changes.