The Adams Event, a geomagnetic-driven environmental crisis 42,000 years ago

Geological archives record multiple reversals of Earth’s magnetic poles, yet the potential impacts of these events remain unknown. The lack of any obvious association between the last major inversion, the Laschamps Excursion ~41 thousand years ago (ka), and polar ice paleoclimate records has underpinned the view that geomagnetic reversals do not have major environmental consequences. We find this is not the case. Importantly, the weakened geomagnetic field causes rapid production of atmospheric radiocarbon, and the lack of accurate calibration records has complicated dating of environmental and archaeological events in other parts of the world. Here we exploit the first detailed record of radiocarbon levels across the Laschamps Excursion using New Zealand swamp kauri (Agathis australis) trees to precisely align Pacific Basin environmental changes with polar paleoclimate records (via 10Be). Comprehensive radiocarbon-dated and glacial sequences are consistent with global chemistry climate modelling, and show synchronous climate changes across the mid to low latitudes that are concentrated during the geomagnetic field minima (42.2-41.5 ka) in the transitional phase that precedes the Laschamps Excursion. Critically, the revised timing reveals associations with a wide range of extinction events and major changes in the global archaeological record, which we hereby term the Adams Event. The climatic, environmental, and evolutionary impacts of past magnetic reversals now form a critical issue for future investigation

Nonvolatile particulate matter emissions of a business jet measured at ground level and estimated for cruising altitudes

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Environmental Science & Technology, copyright © American Chemical Society after peer review and technical editing by the publisher.Business aviation is a relatively small but steadily growing and little investigated emission source. Regarding emissions, aircraft turbine engines rated at and below 26.7 kN thrust are certified only for visible smoke and are excluded from the nonvolatile particulate matter (nvPM) standard. Here, we report nvPM emission characteristics of a widely used small turbofan engine determined in a ground test of a Dassault Falcon 900EX business jet. These are the first reported nvPM emissions of a small in-production turbofan engine determined with a standardized measurement system used for emissions certification of large turbofan engines. The ground-level measurements together with a detailed engine performance model were used to predict emissions at cruising altitudes. The measured nvPM emission characteristics strongly depended on engine thrust. The geometric mean diameter increased from 17 nm at idle to 45 nm at take-off. The nvPM emission indices peaked at low thrust levels (7 and 40% take-off thrust in terms of nvPM number and mass, respectively). A comparison with a commercial airliner shows that a business jet may produce higher nvPM emissions from flight missions as well as from landing and take-off operations. This study will aid the development of emission inventories for small aircraft turbine engines and future emission standards

Surface ozone in the Southern Hemisphere : 20 years of data from a site with a unique setting in El Tololo, Chile

The knowledge of surface ozone mole fractions and their global distribution is of utmost importance due to the impact of ozone on human health and ecosystems and the central role of ozone in controlling the oxidation capacity of the troposphere. The availability of long-term ozone records is far better in the Northern than in the Southern Hemisphere, and recent analyses of the seven accessible records in the Southern Hemisphere have shown inconclusive trends. Since late 1995, surface ozone is measured in situ at "El Tololo", a high-altitude (2200ma.s.l.) and pristine station in Chile (30°S, 71°W). The dataset has been recently fully quality controlled and reprocessed. This study presents the observed ozone trends and annual cycles and identifies key processes driving these patterns. From 1995 to 2010, an overall positive trend of ∼ 0.7ppb decade−1 is found. Strongest trends per season are observed in March and April. Highest mole fractions are observed in late spring (October) and show a strong correlation with ozone transported from the stratosphere down into the troposphere, as simulated with a model. Over the 20 years of observations, the springtime ozone maximum has shifted to earlier times in the year, which, again, is strongly correlated with a temporal shift in the occurrence of the maximum of simulated stratospheric ozone transport at the site. We conclude that background ozone at El Tololo is mainly driven by stratospheric intrusions rather than photochemical production from anthropogenic and biogenic precursors. The major footprint of the sampled air masses is located over the Pacific Ocean. Therefore, due to the negligible influence of local processes, the ozone record also allows studying the influence of El Niño and La Niña episodes on background ozone levels in South America. In agreement with previous studies, we find that, during La Niña conditions, ozone mole fractions reach higher levels than during El Niño conditions

Springtime arctic ozone depletion forces northern hemisphere climate anomalies

Large-scale chemical depletion of ozone due to anthropogenic emissions occurs over Antarctica as well as, to a lesser degree, the Arctic. Surface climate predictability in the Northern Hemisphere might be improved due to a previously proposed, albeit uncertain, link to springtime ozone depletion in the Arctic. Here we use observations and targeted chemistry–climate experiments from two models to isolate the surface impacts of ozone depletion from complex downward dynamical influences. We find that springtime stratospheric ozone depletion is consistently followed by surface temperature and precipitation anomalies with signs consistent with a positive Arctic Oscillation, namely, warm and dry conditions over southern Europe and Eurasia and moistening over northern Europe. Notably, we show that these anomalies, affecting large portions of the Northern Hemisphere, are driven substantially by the loss of stratospheric ozone. This is due to ozone depletion leading to a reduction in short-wave radiation absorption, when in turn causing persistent negative temperature anomalies in the lower stratosphere and a delayed break-up of the polar vortex. These results indicate that the inclusion of interactive ozone chemistry in atmospheric models can considerably improve the predictability of Northern Hemisphere surface climate on seasonal timescales

Multidecadal variations of the effects of the Quasi-Biennial Oscillation on the climate system

Effects of the Quasi-Biennial Oscillation (QBO) on tropospheric climate are not always strong or they appear only intermittently. Studying them requires long time series of both the QBO and climate variables, which has restricted previous studies to the past 30–50 years. Here we use the benefits of an existing QBO reconstruction back to 1908. We first investigate additional, newly digitized historical observations of stratospheric winds to test the reconstruction. Then we use the QBO time series to analyse atmospheric data sets (reconstructions and reanalyses) as well as the results of coupled ocean–atmosphere-chemistry climate model simulations that were forced with the reconstructed QBO. We investigate effects related to (1) tropical-extratropical interaction in the stratosphere, wave-mean flow interaction and subsequent downward propagation, and (2) interaction between deep tropical convection and stratospheric flow. We generally find weak connections, though some are statistically significant over the 100-year period and consistent with model results. Apparent multidecadal variations in the connection between the QBO and the investigated climate responses are consistent with a small effect in the presence of large variability, with one exception: the imprint on the northern polar vortex, which is seen in recent reanalysis data, is not found in the period 1908-1957. Conversely, an imprint in Berlin surface air temperature is only found in 1908-1957 but not in the recent period. Likewise, in the model simulations both links tend to appear alternatingly, suggesting a more systematic modulation due to a shift in the circulation, for example. Over the Pacific warm pool, we find increased convection during easterly QBO, mainly in boreal winter in observation-based data as well as in the model simulations, with large variability. No QBO effects were found in the Indian monsoon strength or Atlantic hurricane frequency

Large eddy simulations of low-level turbulence caused by tree lines in the vicinity of an airfield

Obstacles in the vicinity of an airfield are sources of low-level turbulence that can adversely affect air traffic in critical flight phases close to the ground. The airfield in Yverdon in western Switzerland is surrounded by tall tree lines and is notorious for turbulence during take-offs and landings. This situation is even more pronounced when a strong northwesterly local wind, the Joran, prevails. Some parts of the tree lines to the north and to the west of the airfield were removed around 2017. To analyze the effect of the tree lines before and after their removal with respect to low-level turbulence, large eddy simulation tools can be applied to gain valuable insights. In this study, the flow patterns in the vicinity of the airfield in Yverdon were analyzed by means of high-resolution large-eddy simulations with the PALM model system. This was conducted for different wind scenarios, as well as for two different tree line configurations. In PALM, a nested simulation approach was chosen, where the smallest domain was configured to a resolution of four meters and the larger domain to a resolution of 32 meters. The simulations were forced by COSMO-1 model reanalysis fields, in order to factor in the synoptic weather conditions of the respective days. We validated the model results by comparing the simulated fields with measurement data that were recorded by a sonic anemometer close to the airfield in July 2019, during which period one Joran event was captured. The results of the simulations show in general good coherence with the measurement data at the mast position. The onset of the Joran event was also well captured in amplitude as well as in time. For each scenario, wind speed, wind direction and turbulence intensity were analyzed with the aim to investigate the effect of the removal of parts of the existing tree lines. The simulations show that the removal of the tree lines change the characteristics of the winds experienced by air traffic significantly. During the simulated Joran case, over the runway, the turbulence intensity is reduced by 0.12 (-27 %), while the mean wind speed increases by 1.78 m/s (+62 %). Furthermore, the lack of wind breaking from the tree lines introduces large crosswind components that were not present before. Similar effects were identified for the other analyzed wind directions. These results show that the placement of obstacles in the vicinity of an airfield matters to aviation safety and large eddy simulation tools like PALM can produce very helpful insights into how they do so. This is an especially encouraging message regarding future airport infrastructure projects, as costly mistakes can be effectively avoided already during planning phases

Comparing large eddy simulations with sonic anemometer and LIDAR measurement data during Foehn events in complex terrain

Simulations of turbulent wind flows in complex, mountainous terrain prove to be challenging tasks for today’s numerical simulation models. However, knowing about these wind flow patterns and speeds would be beneficial to assess potential environmental risks for various stakeholders – aviation, wind farms, ski resorts, cable cars or others. With the PALM model system, a state-of-the-art turbulence resolving meteorological model for atmospheric boundary layer flows is available, that can be used to assess these types of questions. By treating topography on a cartesian grid, complex terrain can be accurately represented in simulations. In this study, the complex local flow patterns in mountainous terrain were analyzed by means of high-resolution large eddy simulations with the PALM model system. This was conducted for the Rhine valley region focusing on a small peculiar topographic feature upstream of Balzers in the area of the border between the Principality of Liechtenstein and Switzerland, were flow splitting is known to occur. There, Foehn events lead to pronounced local wind maxima and pose a damaging risk to the upwind part of the village. The model results were compared with data from measurement masts equipped with sonic and cup-anemometers at the position of assumed wind speed maxima. As well, measurements of a continuous-wave LIDAR system located at the outflow of the side valley were integrated in our study. The validation measurements for the Foehn events in Balzers were taken in December 2020, during which two pronounced Foehn events took place. In PALM, a nested simulation approach was chosen, with the smallest domain having a resolution of only a few meters. The simulation was forced by COSMO-1 model results in order to factor in the synoptic weather conditions of the respective days. We show model results of the flow patterns that occur in this complex topography, analyze the wind maxima present in the valley and compare the results with local measurement data. This study demonstrates how large eddy simulation tools like PALM can produce insights into complex flow structures in mountainous terrain, and how these insights can be used to make more informed decisions to protect residents from damaging outcomes of environmental risks

Building a new high-density air temperature measurement network in two Swiss cities

With progressive climate change, weather extremes are very likely to become more frequent. While rural regions may suffer from more intense and longer drought periods, urban spaces are going to be particularly affected by severe heat waves. This urban temperature anomaly, also known as “urban heat island” (UHI), can be traced back to different factors, the most prominent being soil sealing, lower albedo and lack of effective ventilation. City planners have started developing mitigation strategies to reduce future forecasted heat stress in urban regions. While some heat reduction strategies are currently intensely scrutinized and applied within pilot projects, the efficiency of latter mitigation actions can be overseen due to the low density of reference in situ air temperature measurements in urban environments. The same problem applies when trying to benchmark modeling studies of UHI as the amount of benchmarking data may be insufficient. To overcome this lack of data, over the last two years, a dense air temperature measurement network has been installed in the Swiss cities of Basel and Zurich, counting more than 450 sensors. The low-cost air temperature sensors are installed on street lamps and traffic signs in different local climate zones of the city with an emphasis on street canyons, where air temperatures are expected to be the largest and most of the city’s population lives and works. These low-cost sensors add valuable meteorological information in cities and complement the WMO reference stations. Air temperature measurements from the low-cost sensor network were controlled for accuracy, reliability and robustness and homogenized in order to minimize radiation errors, although 40% of the stations were equipped with self-built radiation shields, allowing an efficient passive ventilation of the installed sensors. We demonstrate the strength of our network by presenting first results of two exemplary heat waves that occurred in July 2019 and August 2020 and show that a) the radiation-error corrected datasets correlate well with different high-quality reference WMO stations, and b) the existence of urban heat islands in Zurich and Basel can be well confirmed, showing significant air temperature differences of several degrees between rural and urban areas. The results demonstrate the advantages of a high-density low-cost air temperature network as a benchmark for future urban heat islands modelling studies

Surface ozone in the Southern Hemisphere: 20 years of data from a site with a unique setting in El Tololo, Chile

The knowledge of surface ozone mole fractions and their global distribution is of utmost importance due to the impact of ozone on human health and ecosystems and the central role of ozone in controlling the oxidation capacity of the troposphere. The availability of long-term ozone records is far better in the Northern than in the Southern Hemisphere, and recent analyses of the seven accessible records in the Southern Hemisphere have shown inconclusive trends. Since late 1995, surface ozone is measured in situ at "El Tololo", a high-altitude (2200ma.s.l.) and pristine station in Chile (30 degrees S, 71 degrees W). The dataset has been recently fully quality controlled and reprocessed. This study presents the observed ozone trends and annual cycles and identifies key processes driving these patterns. From 1995 to 2010, an overall positive trend of similar to 0.7 ppbdecade(-1) is found. Strongest trends per season are observed in March and April. Highest mole fractions are observed in late spring (October) and show a strong correlation with ozone transported from the stratosphere down into the troposphere, as simulated with a model. Over the 20 years of observations, the springtime ozone maximum has shifted to earlier times in the year, which, again, is strongly correlated with a temporal shift in the occurrence of the maximum of simulated stratospheric ozone transport at the site. We conclude that background ozone at El Tololo is mainly driven by stratospheric intrusions rather than photochemical production from anthropogenic and biogenic precursors. The major footprint of the sampled air masses is located over the Pacific Ocean. Therefore, due to the negligible influence of local processes, the ozone record also allows studying the influence of El Nino and La Nina episodes on background ozone levels in South America. In agreement with previous studies, we find that, during La Nina conditions, ozone mole fractions reach higher levels than during El Nino conditions.Federal Office of Meteorology and Climatology MeteoSwiss through the project Capacity Building and Twinning for Climate Observing Systems (CATCOS) 81025332 Swiss Agency for Development and Cooperation (SDC) MeteoSwiss FONDAP 1511000