Real-time pollen monitoring using digital holography Atmospheric Measurement Techniques DOI 10.5194/amt-13-1539-2020 9 April 2020 We present the first validation of the only operational automatic pollen monitoring system based on holography, the Swisens Poleno. The device produces real-time images of coarse aerosols, and by applying a machine learning algorithm we identify a range of pollen taxa with accuracy >90 %. The device was further validated in controlled chamber experiments to verify the counting ability and the performance of additional fluorescence measurements, which can further be used in pollen identification. Read more
Technical note: LIMS observations of lower stratospheric ozone in the southern polar springtime of 1978 Atmospheric Chemistry and Physics DOI 10.5194/acp-20-3663-2020 7 April 2020 The Nimbus 7 limb infrared monitor of the stratosphere (LIMS) instrument operated from October 25, 1978, through May 28, 1979. This note focuses on the lower stratosphere of the southern hemisphere, subpolar regions in relation to the position of the polar vortex. Both LIMS ozone and nitric acid show reductions within the edge of the polar vortex at 46 hPa near 60° S from late October through mid-November 1978, indicating that there was a chemical loss of Antarctic ozone some weeks earlier. Read more
Terrestrial methane emissions from the Last Glacial Maximum to the preindustrial period Climate of the Past DOI 10.5194/cp-16-575-2020 7 April 2020 We investigate the changes in natural methane emissions between the Last Glacial Maximum and preindustrial periods with a methane-enabled version of MPI-ESM. We consider all natural sources of methane except for emissions from wild animals and geological sources. Changes are dominated by changes in tropical wetland emissions, high-latitude wetlands play a secondary role, and all other natural sources are of minor importance. We explain the changes in ice core methane by methane emissions only. Read more
Methane emissions from the Munich Oktoberfest Atmospheric Chemistry and Physics DOI 10.5194/acp-20-3683-2020 3 April 2020 We demonstrate for the first time that large festivals can be significant methane sources, though they are not included in emission inventories. We combined in situ measurements with a Gaussian plume model to determine the Oktoberfest emissions and show that they are not due solely to human biogenic emissions, but are instead primarily fossil fuel related. Our study provides the foundation to develop reduction policies for such events and new pathways to mitigate fossil fuel methane emissions. Read more
Deconvolution of boundary layer depth and aerosol constraints on cloud water path in subtropical stratocumulus decks Atmospheric Chemistry and Physics DOI 10.5194/acp-20-3609-2020 3 April 2020 Cloud water content and the number of droplets inside clouds covary with boundary layer depth. This covariation may amplify the change in water content due to a change in droplet number inferred from long-term observations. Taking this into account shows that the change in water content for increased droplet number in observations and high-resolution simulations agrees in shallow boundary layers. Meanwhile, deep boundary layers are under-sampled in process-scale simulations and observations. Read more
Back to the future II: tidal evolution of four supercontinent scenarios Earth System Dynamics DOI 10.5194/esd-11-291-2020 31 March 2020 We have confirmed that there is a supertidal cycle associated with the supercontinent cycle. As continents drift due to plate tectonics, oceans also change size, controlling the strength of the tides and causing periods of supertides. In this work, we used a coupled tectonic–tidal model of Earth’s future to test four different scenarios that undergo different styles of ocean closure and periods of supertides. This has implications for the Earth system and for other planets with liquid oceans. Read more
Scaling carbon fluxes from eddy covariance sites to globe: synthesis andevaluation of the FLUXCOM approach Biogeosciences DOI 10.5194/bg-17-1343-2020 26 March 2020 We test the approach of producing global gridded carbon fluxes based on combining machine learning with local measurements, remote sensing and climate data. We show that we can reproduce seasonal variations in carbon assimilated by plants via photosynthesis and in ecosystem net carbon balance. The ecosystem’s mean carbon balance and carbon flux trends require cautious interpretation. The analysis paves the way for future improvements of the data-driven assessment of carbon fluxes. Read more
“This bookmark gauges the depths of the human”: how poetry can help to personalise climate change Geoscience Communication DOI 10.5194/gc-3-35-2020 24 March 2020 To many non-specialists, the science behind climate change can appear confusing and alienating, yet in order for global mitigation efforts to be successful it is not just scientists who need to take action, but rather society as a whole. This study shows how poets and poetry offer a method of communicating the science of climate change to the wider society using language that they not only better understand, but which also has the potential to stimulate accountability and inspire action. Read more
Methanethiol, dimethyl sulfide and acetone over biologically productive waters in the southwest Pacific Ocean Atmospheric Chemistry and Physics DOI 10.5194/acp-20-3061-2020 24 March 2020 Methanethiol (MeSH) is a reduced sulfur gas originating from phytoplankton, with a global ocean source of ~ 17 % of dimethyl sulfide (DMS). It has been little studied and is rarely observed over the ocean. In this work, MeSH was measured at much higher levels than previously observed (3–36 % of parallel DMS mixing ratios). MeSH could be a significant source of atmospheric sulfur over productive regions of the ocean, but its distribution, and its atmospheric impact, requires more investigation. Read more
Changing suspended sediment in United States rivers and streams: linking sediment trends to changes in land use/cover, hydrology and climate Hydrology and Earth System Sciences DOI 10.5194/hess-24-991-2020 17 March 2020 Between 1992 and 2012, concentrations of suspended sediment decreased at about 60 % of 137 US stream sites, with increases at only 17 % of sites. Sediment trends were primarily attributed to changes in land management, but streamflow changes also contributed to these trends at > 50 % of sites. At many sites, decreases in sediment occurred despite small-to-moderate increases in the amount of anthropogenic land use, suggesting sediment reduction activities across the US may be seeing some success. Read more
Assimilation of surface observations in a transient marine ice sheet model using an ensemble Kalman filter The Cryosphere DOI 10.5194/tc-14-811-2020 17 March 2020 Marine-based sectors of the Antarctic Ice Sheet are increasingly contributing to sea-level rise. The basal conditions exert an important control on the ice dynamics. For obvious reasons of inaccessibility, they are an important source of uncertainties in numerical ice flow models used for sea-level projections. Here we assess the performance of an ensemble Kalman filter for the assimilation of transient observations of surface elevation and velocities in a marine ice sheet model. Read more
Time-lapse monitoring of root water uptake using electrical resistivitytomography and mise-à-la-masse: a vineyard infiltration experiment SOIL DOI 10.5194/soil-6-95-2020 17 March 2020 The use of non-invasive geophysical imaging of root system processes is of increasing interest to study soil–plant interactions. The experiment focused on the behaviour of grapevine plants during a controlled infiltration experiment. The combination of the mise-à-la-masse (MALM) method, a variation of the classical electrical tomography map (ERT), for which the current is transmitted directly into the stem, holds the promise of being able to image root distribution. Read more
Ultra-clean and smoky marine boundary layers frequently occur in the same season over the southeast Atlantic Atmospheric Chemistry and Physics DOI 10.5194/acp-20-2341-2020 12 March 2020 Using observations from instruments deployed to a small island in the southeast Atlantic, we study days when the atmospheric concentrations of particles near the surface are exceptionally low. Interestingly, these ultra-clean boundary layers occur in the same months as the smokiest boundary layers associated with biomass burning in Africa. We find evidence that enhancements in drizzle scavenging, on top of a seasonal maximum in cloudiness and precipitation, likely drive these conditions. Read more
Temperature controls production but hydrology regulates export of dissolved organic carbon at the catchment scale Hydrology and Earth System Sciences DOI 10.5194/hess-24-945-2020 12 March 2020 Lateral carbon fluxes from terrestrial to aquatic systems remain central uncertainties in determining ecosystem carbon balance. This work explores how temperature and hydrology control production and export of dissolved organic carbon (DOC) at the catchment scale. Results illustrate the asynchrony of DOC production, controlled by temperature, and export, governed by flow paths; concentration–discharge relationships are determined by the relative contribution of shallow versus groundwater flow. Read more
On the alignment of velocity and magnetic fields within magnetosheath jets Annales Geophysicae DOI 10.5194/angeo-38-287-2020 12 March 2020 Jets of solar-wind plasma commonly hit the Earth’s magnetosphere. Using data from the four Magnetospheric Multiscale (MMS) spacecraft, we show statistically that within jets the magnetic field is more aligned with the plasma flow direction than outside of these jets. Our study confirms prior simulation results, but it also shows that the average effect is moderate. The jets’ magnetic field is important with respect to their impact on space weather. Read more
Earth system data cubes unravel global multivariate dynamics Earth System Dynamics DOI 10.5194/esd-11-201-2020 10 March 2020 The ever-growing availability of data streams on different subsystems of the Earth brings unprecedented scientific opportunities. However, researching a data-rich world brings novel challenges. We present the concept of Earth system data cubes to study the complex dynamics of multiple climate and ecosystem variables across space and time. Using a series of example studies, we highlight the potential of effectively considering the full multivariate nature of processes in the Earth system. Read more
Modelling global tropical cyclone wind footprints Natural Hazards and Earth System Sciences DOI 10.5194/nhess-20-567-2020 10 March 2020 Assessing tropical cyclone (TC) wind risk is challenging due to a lack of historical TC wind data. This paper presents a novel approach to simulating landfalling TC winds anywhere on Earth. It captures local features such as high winds over coastal hills and lulls over rough terrain. A dataset of over 700 global historical wind footprints has been generated to provide new views of historical events. This dataset can be used to advance our understanding of overland TC wind risk. Read more
The substructure of extremely hot summers in the Northern Hemisphere Weather and Climate Dynamics DOI 10.5194/wcd-1-45-2020 10 March 2020 In this study we quantify how much the coldest, middle and hottest third of all days during extremely hot summers contribute to their respective seasonal mean anomaly. This extreme-summer substructure varies substantially across the Northern Hemisphere and is directly related to the local physical drivers of extreme summers. Furthermore, comparing re-analysis (i.e. measurement-based) and climate model extreme-summer substructures reveals a remarkable level of agreement. Read more
Measuring compound flood potential from river discharge and storm surge extremes at the global scale Natural Hazards and Earth System Sciences DOI 10.5194/nhess-20-489-2020 3 March 2020 When a high river discharge coincides with a high storm surge level, this can exarcebate flood level, depth, and duration, resulting in a so-called compound flood event. These events are not currently included in global flood models. In this research, we analyse the timing and correlation between modelled discharge and storm surge level time series in deltas and estuaries. Our results provide a first indication of regions along the global coastline with a high compound flooding potential. Read more
TRAPPIST-1 Habitable Atmosphere Intercomparison (THAI):motivations and protocol version 1.0 Geoscientific Model Development DOI 10.5194/gmd-13-707-2020 3 March 2020 Atmospheric characterization of rocky exoplanets orbiting within the habitable zone of nearby M dwarf stars is around the corner with the James Webb Space Telescope (JWST), expected to be launch in 2021. Global climate models (GCMs) are powerful tools to model exoplanet atmospheres and to predict their habitability. However, intrinsic differences between the models can lead to various predictions. This paper presents an experiment protocol to evaluate these differences. Read more