bluuebunny/crossref_metadata_2025 huggingface dataset:
Remotely sensed quantification of non-fire-related disturbances and their contribution to global forest dynamics
Authors: Acil Nezha , Pugh Thomas , Sadler Jonathan , Senf Cornelius
Published: March 2021

Stand-replacing disturbances vary in their type, frequency and severity across regions, with consequent heterogeneity in their effects on forest stand age, structure and carbon cycling. These effects can be assessed using dynamic global vegetation models (DGVMs), but representations of disturbances in these models are generally limited to wildfire, with other major natural agents, such as windthrow and biotic outbreaks, typically neglected. Furthermore, human actions, such as harvest and forest management, may intensify or dampen disturbance regimes and modulate forest susceptibility to certain agents. Here, we assess the relative importance of non-fire-related disturbances in canopy turnover, as opposed to fire-related, accounting for human influence across the world. Using the Landsat-derived Global Forest Change product, we delineate contiguous patches of tree cover loss at 30m resolution for the period 2001-2016 and combine them with different global satellite-based data products to identify fire disturbances, land conversion and exposure to human activities. We then calculate disturbance rates by forest ecoregion, excluding land use change and differentiating by fire association and forest intactness. We find that the rate of non-fire-related disturbances in intact forests, mainly windthrow and biotic outbreaks, exceeds the rate of fire in most tropical regions, as well as in British Columbia’s coastal and mountain temperate conifer forests and West Scandinavian and Russian taiga, whereas wildfire dominates in remaining boreal regions. Outside intact forests, the rate of non-fire-related disturbances, with the addition of anthropogenic disturbances, mainly harvest, exceeds the rate of fire in most regions of the world, apart from the fire-prone boreal Siberia, Mediterranean Australia, boreal North America and West American mountain temperate conifer and Mediterranean forests. The dominant disturbance agent shifts from fire in intact forests to non-fire outside intact forests, mainly in West Siberian taiga, East Australian temperate broadleaf and mixed forests, and some North American boreal forests. This analysis shows the potential of leveraging satellite remote sensing for assessing disturbance regimes and provides a globally consistent dataset that can help achieve more realistic disturbance simulations in DGVMs and reduce uncertainties in projections appraising the future role of forests in global carbon cycling.
Field and numerical study of solute transport under evaporation in a subtropical tidal wetland
Authors: Liu Yue , Zhang Chenming , Liu Xiaocheng , Li Ling , Scheuermann Alexander , Lockington David
Published: March 2021

Tidal wetlands are critical intertidal ecosystem which accommodates a large range of flora and fauna species. The intertidal subsurface environment is subjected to continuous groundwater-seawater mixing which results in dynamic solute transport in the aquifer and to the ocean. Salt distribution and transport play a vital role in the wetland ecology and near-shore biogeochemical activities. While many field and simulation studies have been presented to characterize the salt distribution in the intertidal beach aquifer under the influence of tidal inundation, salt distribution in the tidal wetland subsurface system yet requires more investigation. Moreover, the impact of evaporation on porewater salt distribution could be essential in subtropical areas with numerous coastal wetlands as evaporation extracts porewater from the soil surface and leaves salt in the surface and wetland root zone. However, this parameter was commonly ignored by previous studies.

In this study, field monitoring was carried out to map the groundwater level and spatial salt distribution in a subtropical wetland located in Southeastern Queensland, Australia. Two dimensional, variable-density, saturated-unsaturated groundwater flow and solute transport model was used to examine the pore water flow and salt distribution patterns in a cross-shore section of the field site under the influences of the spring-neap tide and evaporation. Field and simulation results consistently showed that salinity is greatly impacted by evaporation and showed different distributions from the saline seawater intrusion patterns displayed by most of the former studies. 
Characterization of GEMS level 1B based on inter-comparison using the visible channel of AMI
Authors: Lee Yeeun , Ahn Myoung-Hwan , Eo Mijin , Kang Mina , Moon Kyung-jung , Ko Dai-Ho , Kim Jhoon , Lee Dong-won
Published: March 2021

             The Geostationary Korean Multi-Purpose Satellite (GK-2) program consisting of GK-2A and GK-2B provides consistent monitoring information in the Asia Pacific region, including the Korean peninsula. The Geostationary Environment Monitoring Spectrometer (GEMS) onboard GK-2B in particular provides information on the atmospheric composition and aerosol properties, retrieved from the calibrated radiance (Level 1B) with high spectral resolution in 300-500 nm. GEMS started its extended validation measurement after the in-orbit test (IOT) in October following the launch of the satellite in February 2020. One of issues found during the IOT is that GEMS shows a spatial dependence in the measured solar irradiance along the north-south direction, albeit the solar irradiance does not have such a dependency. Thus, such a dependence should be from the optical system or the solar diffuser which is placed in front of the scan mirror. To clarify the root cause of the dependence, we utilize inter-comparison of the Earth measurement between GEMS and the Advanced Meteorological Imager (AMI), a multi-channel imager onboard GK-2A for meteorological monitoring. As the spectral range of GEMS fully covers the spectral response function (SRF) of the AMI visible channel having a central wavelength of 470 nm, spectral matching is properly done by convolving the SRF with the hyperspectral data of GEMS. By taking advantage of the fact that the position of GK-2A and GK-2B is maintained within a 0.5 degree square box centered at 128.2°E, match-up data set for the inter-comparison is prepared by temporal and spatial collocation. To reduce spatio-temporal mis-match and increase the signal to noise, zonal mean is applied to the collocated data. Results show that the north-south dependence occurs in the comparison of reflectance, the ratio between the earth radiance and solar irradiance, while not in the comparison of radiance. This indicates the dependence occurs due to the characteristics of the solar diffuser, not because of optical system. It is further deduced that dependence of diffuser transmittance on the solar azimuth angle is the main cause of the north-south dependency which was not characterized during the pre-flight ground test.
Greenhouse gas dynamics in an anthropogenically modified tropical river continuum
Authors: Sarkar Siddhartha , Rathi Ajayeta , Kumar Sanjeev
Published: March 2021

Recent decades have witnessed large scale modifications in the natural flow regime of river systems. What follows are shifts in various instream processes that ultimately govern the air-water fluxes of major greenhouse gases (GHGs) like CH4, CO2, and N2O. However, due to paucity of data, the process dynamics and controls on fluxes of GHGs in tropical rivers are understudied, contributing to uncertainty in their global budget. In this study, an attempt was made to estimate the fluxes of GHGs and thereby decipher the controls on evasive processes in an anthropogenically affected Sabarmati River (catchment ~ 27,674 km2 and channel length ~371 km) located in semi-arid western India. After originating from a relatively pristine region, Sabarmati passes through a major twin city (Ahmedabad-Gandhinagar), where construction of a riverfront resulted in increased residence time of water within the city limits.

To compare and understand changes in in-stream biogeochemical processes as a result of human interventions, sampling was carried out at 50 sites along the Sabarmati river continuum and a parallel running, but not so anthropogenically modified, Mahi River along with their tributaries. Results indicated relatively lower fluxes of GHGs in pristine upstream of Sabarmati and Mahi River continuum with CH4, CO2 and N2O fluxes at 0.99 ± 0.35 mg C m-2 d-1, 4250.99 ± 477.74 mg C m-2 d-1 and 0.055 ± 0.026 mg N m-2 d-1 respectively. The effect of higher residence time of water could be seen in the riverfront with increased CH4 and N2O fluxes at 3.27 ± 1.02 mg C m-2 d-1 and 0.129 ± 0.024 mg N m-2 d-1, respectively. However, the CO2 flux did not show much increase. The fluxes increased significantly post city limits until its mouth in the Arabian Sea with extremely large flux for methane (CH4: 102.84 ± 41.32 mg C m-2 d-1, CO2: 9563.58 ± 1252.43 mg C m-2 d-1, and N2O: 0.16 ± 0.11 mg N m-2 d-1, respectively). Overall, it appeared that even within the anthropogenically stressed river, the nature of flow regime, exerts significant control on cycling of elements leading to differential fluxes. Also, the level of coupling between nitrogen and carbon appeared to change within the course of the river.
Modeling Water Distribution Systems with Graph Neural Networks
Authors: Garzón Alexander , Bentivoglio Roberto , Isufi Elvin , Kapelan Zoran , Taormina Riccardo
Published: March 2021

Water management has recently explored data-driven models to improve the adaptability of Water Distribution Systems (WDS) and strengthen decision making under uncertain conditions. The focus on these tools is motivated by the increasing availability of information and their proven performance in other fields. Modeling WDS with these techniques has been demonstrated to be useful; however, the traditional machine learning tools do not account for the graph structure present in the WDS. Considering this essential information offers the possibility to increase performance and to help the learning process. In this work, we introduce Graph Neural Networks (GNNs) for modeling WDS. GNNs are processing architectures to perform neural network tasks for data related to a graph. We first present the definitions and interpretations for using this framework in water networks. Then we compare the GNN approach against standard neural networks to predict an overall resilience metric in a benchmark system. The benefits of including the network structure in the learning process by the GNN are shown in the analysis of the obtained results.
Solar forcing on the Northern Hemisphere weather and climate extremes during summer
Authors: Rimbu Norel , Ionita Monica , Lohmann Gerrit
Published: March 2021

The effects of solar irradiance forcing on weather and climate extremes have received relatively less attention compared to the solar-induced changes in the mean climate. In this respect, here we investigate the possible impact of solar irradiance forcing on the Northern Hemisphere extreme weather and climate variability during summer, from a potential vorticity (PV) perspective. The generation of severe weather events in the extra-tropical regions is often related to intrusions of high PV originating from the polar lower stratosphere. Various two-dimensional PV indices, similar to those characterizing surface temperature and precipitation extremes, are defined to measure the frequency of upper level PV intrusion events. Based on long-term reanalysis data, we show that upper level high PV intrusions over Asia (Europe) are more (less) frequent during high relatively to low solar irradiance summers. Consistent with this PV pattern more (less) frequent surface extreme precipitation events are recorded during high relative to low solar irradiance summers in Asia (Europe). Patterns in the frequency of extreme temperatures are largely opposite to the corresponding extreme precipitation. Furthermore, extreme climate anomaly patterns associated with high solar irradiance forcing are similar to the corresponding patterns associated with strong monsoon circulation over Asia during summer. A preliminary analysis reveals the dominant role of upper level solar related PV anomalies in generation of extreme precipitation in the Asian monsoon region during high solar irradiance summers. A persistent blocking like circulation in the Caspian Sea region during low solar irradiance summers is associated more frequent high PV intrusions and extreme precipitation over Europe. The stability of the solar related extreme precipitation and temperature patterns in the last millennium perspective is also discussed based on proxy data as well as model simulations.

 
How to model enhanced firn densification due to strain softening
Authors: Oraschewski Falk , Grinsted Aslak
Published: March 2021

Most classical firn densification models merely consider temperature and accumulation rate as variable input parameters. However, in locations with high horizontal strain rates, such as the shear margins of ice streams, a reduced firn thickness can be observed. This is explained by an enhancement of power-law creep due to the effect of strain softening, which is not yet captured by existing firn models. We present a model extension that corrects the densification rate, predicted by any classical, climate-forced firn model, for the effect of strain softening caused by horizontal strain rates. With the presented model firn densities measured along a cross-section of the North-East Greenland ice stream (NEGIS) are reproduced with good agreement, validating the accuracy of the developed model. The results further indicate the general importance of considering strain rates in firn densification modeling and pave the way for the development of a firn model that inherently uses temperature, accumulation rate and horizontal strain rates as forcing parameters.
Shifts in the frequency of sequentially occurring late-spring frost and drought impact the dynamics of non-structural carbohydrates in European beech
Authors: Meyer Benjamin F. , Rammig Anja , Buras Allan , Zang Christian S.
Published: March 2021

In the past, terrestrial ecosystems have largely functioned as carbon sinks, capturing nearly 30% of anthropogenic carbon dioxide emissions (Le Quéré et al. 2009). Forest ecosystems, which cover roughly 30% of the land surface, play a fundamental role in maintaining this sink by storing nearly half of all terrestrial carbon (Pan et al. 2011; Bonan 2008). Over large parts of Europe, these forest ecosystems are dominated by European beech. Consequently, the reaction of beech to climate extremes is central to the ability of European forests to act as carbon sinks. Disconcertingly, the projected – and indeed already observed – increase in frequency and severity of drought across Europe threatens to shift forest ecosystems from carbon sinks to carbon sources (Ciais et al. 2005). Concurrently, the incidence of late-spring frost events in Europe is on the rise. While these events are considerably more localized and do not result in the same widespread reduction of ecosystem productivity as droughts, the damage to the photosynthetic apparatus of affected trees forces the mobilization of non-structural carbohydrates (NSC) to ensure tree survival. We analyze high-resolution historical (E-OBS 0.1°) and projected (EURO-CORDEX RCP 2.6 & RCP 8.5 0.11°) climate data to identify localized changes in the frequency of sequentially occurring drought and late-spring frost events across Europe. Subsequently, we use a modified version of the standalone NSC-model SUGAR (Jones et al. 2020) to ascertain the effect of sequentially occurring climate extremes on the carbon reserves of European beech forests. Here, we identify differences in the impact of isolated extremes (either frost or drought) and sequential extremes (frost followed by drought and vice versa) on the regulation of the NSC pool. Through the integration of SUGAR with the LPJ-GUESS DGVM (Smith et al. 2014; Sitch et al. 2003) we further quantify the effect of sequentially occurring climate extremes on the productivity of beech forest ecosystems in central Europe.

 
Enhancement of 3D GPR datasets using singular value decomposition applied in 2D the spectral domain for clutter noise removal
Authors: Oliveira Rui Jorge , Caldeira Bento , Teixidó Teresa , Borges José Fernando
Published: March 2021

The ground-penetrating radar (GPR) datasets obtained in archaeological environments have substantial problems related the presence of clutter noise. These noisy reflections are generated by the heterogeneities of the ground and by the collapses of structures buried in the ground, that can prevent a good assessment of the subsurface with this method. The classic filtering operations available can fail to remove it effectively. This work presents an approach to filtering the GPR data in the 2D spectral domain through the singular value decomposition (SVD) factorization technique. The spectral domain present advantages such as the circular symmetry of the transformed data that turns easy the filter parametrisation and the constant computational effort whatever the amount of data considered. SVD allows the decreasing of the user dependency to parametrize the filter. The main propose of this method is to classify automatically the datasets into useful information, corresponding to buried structures, and noise, to remove the last. This approach was conceived based on the study of the GPR signal in the 2D spectral domain and the manual filter design. The tests were performed with different datasets, one from a laboratory experiment (controlled environment) and the other from a field acquisition in an archaeological site (uncontrolled environment) with subsequent excavation to proof the results. The proposed approach is effective to remove the clutter noise in the GPR datasets and constitutes a complementary operation to those already existing in the commercial software.

 

Acknowledgment: The work was supported by the Portuguese Foundation for Science and Technology (FCT) project UIDB/04683/2020 - ICT (Institute of Earth Sciences) and by the INTERREG 2014-2020 Program, through the "Innovación abierta e inteligente en la EUROACE" Project, with the reference 0049_INNOACE_4_E.
The role of irrigation on potato yields in Northern Germany under climate change
Authors: Egerer Sabine , Fajardo Andrea , Peichl Michael , Rakovec Oldrich , Samaniego Luis , Schneider Uwe
Published: March 2021

The agricultural sector is particularly vulnerable to changing weather and climate conditions. Climate projections for Germany until the end of this century demonstrate higher temperatures and a substantial net water deficit during the summer months when agriculture is in high demand for water. Additionally, the frequency and length of dry periods increase as a consequence of climate change. Irrigation was introduced in the 1960s in Northeast Lower Saxony (Germany) to become more resilient to changing weather and climate conditions and prevent yield losses. The region involves today the largest irrigated area in Germany. However, during the drought in 2018 water extractions for irrigation by far exceeded the institutional limit. Water using conflicts are likely to strengthen in the future as the irrigation demand will increase.

In this study, we explore the importance of irrigation as a climate change adaptation measure in the region. First, we employ a statistical regression model to investigate whether regional climate, hydrological, and irrigation data on a monthly and county level scale are adequate to describe potato yield changes between 1978 and 2018. Soil moisture information originates from the mesoscale hydrologic model (mHM). Irrigation is estimated based on the climatic water balance and crop water demand. These estimations are scaled with irrigation data from local authorities to account for realistic monthly water withdrawals. Second, we use the process-based crop model EPIC to estimate potato crop yields and to validate the performance of the statistical approach.

We analyze future yield changes based on climate model projections for the 21st century using the two approaches. We investigate different irrigation scenarios as a potential climate change adaptation measure. By comparing the statistical and process-based approaches we explore whether a rather simplistic statistical approach captures the main processes of the climate change impact on yields.
Effects of channel engineering on flood dynamics along the middle and lower Rhône over the last two centuries.
Authors: Lucas Mathieu , Lang Michel , Le Coz Jérôme , Renard Benjamin , Piegay Hervé
Published: March 2021

The Rhône River has undergone many anthropogenic transformations to improve his navigability and produce hydroelectricity since the mid-19th century. From the longitudinal dikes of the 1850’s to the hydroelectric diversion schemes of the 1950’s and 1960’s, these structures had a direct impact on the channel geometry along the 300km of river course between Lyon (France) and the Mediterranean Sea. An indirect consequence could be a change in the flood dynamics along the channel course, caused by the simplification of the channel patterns and the floodplain accretion. This communication aims to assess the potential changes in the flood propagation along the middle and lower Rhône valley throughout a century of anthropogenic reconfigurations of the channel. The possible impact of these human pressures on the inundation risk and the attenuation of the flood peak discharge is also discussed. Through the use of digitized hydrometric data recorded since 1840 on multiple stream gauges of the Rhône river, a variety of floods of the same type and magnitude are selected. The oceanic flood types (as described by Pardé, 1925) that take their origin from heavy rainfalls upstream of the area of interest are preferred. Thus, complex flood waves due to floods from the lower Rhône valley tributaries are avoided, to keep the analysis as simple as possible. The flood travel time and the peak discharge attenuation of the selected events are compared over the years of channel transformations, permitting us to estimate the impact of anthropogenic pressures on the flood dynamics.
Incorporating missing volcanic impacts into future climate impact assessments
Authors: Outten Stephen , Bethke Ingo , Thorne Peter
Published: March 2021

Future climate projections for the 21st century generally do not include the effects of volcanic eruptions. While some attempt has been made to account for the integrated effect of multiple eruptions by incorporating a small continuous volcanic forcing, a recent study (http://nature.com/articles/doi:10.1038/nclimate3394) has already shown that this approach is insufficient to resolve the increased climate variance caused by individual eruptions, especially on decadal timescales. Increased climate variance exerts stresses on ecosystems and society, thus resolving the impacts of plausible future volcanic eruptions is of importance for certain adaptation and mitigation decisions.

While previous work has used a modelling approach to address this problem, in this talk we demonstrate a computationally inexpensive method to incorporate the effects of plausible volcanic eruptions into future climate projections. This method uses stochastic volcanic emulators based on 2,500 years of past volcanic activity and the characterization of the response of the climate system to individual eruptions. We will demonstrate not only this methodology, but also describe the requirements and potential for its application to the wider future projections of CMIP6.
Anticipating cascading risks at the imminent Hochvogel peak failure
Authors: Leinauer Johannes , Meindl Manfred , Jacobs Benjamin , Stammberger Verena , Krautblatter Michael
Published: March 2021

Climatic changes are exacerbating the risk of alpine mass movements for example through more frequent and extreme heavy precipitation events. To cope with this situation, the monitoring, anticipation, and early warning of rock slope failures based on process dynamics is a key strategy for alpine communities. However, only investigating the release area of an imminent event is insufficient, as the primary hazard can trigger or increase secondary hazards like debris flows or the damming of a river. Nevertheless, recent case studies dealing with successive hazards are rarely existent for the Calcareous Alps. In this study, we precisely investigate the cascading effects resulting from an imminent rock fall and perform a pre-event analysis instead of back-modelling of a past event.

The Hochvogel summit (2592 m a.s.l., Allgäu Alps, Germany/Austria) is divided by several pronounced clefts that separate multiple instable blocks. 3D-UAV point clouds reveal a potentially instable mass of 260,000 m³ in six main subunits. From our near real time monitoring system (Leinauer et al. 2020), we know that some cracks are opening at faster pace and react differently to heavy rainfall, making a successive failure of subunits likely. However, pre-deformations are not yet pronounced enough to decide on the exact expected volume whereas secondary effects are likely as the preparing rock fall mass will be deposited into highly debris-loaded channels. Therefore, we developed different rock fall scenarios from the gathered monitoring information, which we implemented into a RAMMS modelling of secondary debris flows. To obtain best- and worst-case results, each scenario is calculated with different erosion parameters in the runout channel. The models are calibrated with a well-documented debris flow event at Roßbichelgraben (10 km NW and similar lithology) and are supported by field investigations in the runout channel including electrical resistivity tomography profiles (ERT) for determination of the depth of erodible material as well as a drone survey for mapping the area and the generation of an elevation model.

Here we show a comprehensive scenario-based assessment for anticipating cascading risks at the Hochvogel from initial rock failure volume estimation to debris flow evolution and potential river damming. This recent case study from an alpine calcareous peak is an excellent and rare chance to gain insights into cascading risks modelling and an improved hazard evaluation.
Application of the Regional Ocean Modelling System (ROMS) for Baltic Sea area
Authors: Muzyka Maciej , Jakacki Jaromir , Przyborska Anna
Published: March 2021

The Regional Ocean Modelling System has been begun to implement for region of Baltic Sea.  A preliminary curvilinear grid with horizontal resolution ca. 2.3 km has been prepared based on the grid, which was used in previous application in our research group (in Parallel Ocean Program and in standalone version of Los Alamos Sea Ice Model - CICE).  Currently the grid has 30 sigma layers, but the final number of levels will be adjusted accordingly.

So far we’ve successfully compiled the model on our machine, run test cases and created Baltic Sea case, which is working with mentioned Baltic grid. The following parameters: air pressure, humidity, surface temperature, long and shortwave radiation, precipitation and wind components are used as an atmospheric forcing. The data arrive from our operational atmospheric model - Weather Research and Forecasting Model (WRF).

Our main goal is to create efficient system for hindcast and forecast simulations of Baltic Sea together with sea ice component by coupling ROMS with CICE. The reason for choosing these two models is an active community that takes care about model’s developments and updates. Authors also intend to work more closely with the CICE model to improve its agreement with satellite measurements in the Baltic region.

Calculations were carried out at the Academic Computer Centre in Gdańsk.
Studying uncertainty in LUT-based aerosol retrieval employing Bayesian statistical approach applied to TROPOMI/S5P measurements
Authors: Kauppi Anu , Kukkurainen Antti , Lipponen Antti , Laine Marko , Tamminen Johanna
Published: March 2021

In this presentation we consider uncertainty in Look-up table (LUT) based technique for retrieving aerosol optical depth (AOD) and aerosol type using TROPOMI/S5P measurements.
The LUTs are multi-dimensional tables containing aerosol microphysical properties and they have been constructed using libRadtran simulations. 
Especially we study difficulty in aerosol microphysical model selection that reflects the retrieval uncertainty. As a source of uncertainty we have also acknowledged so called model discrepancy originating from imperfect forward modeling. 
The methodology considered is based on Bayesian inference where the retrieved AOD estimate is given as maximum a posterior (MAP) value and uncertainties are described as posterior density functions. We have also combined statistically the most appropriate aerosol microphysical models by Bayesian model averaging when the selection of single best-fitting model is not clear.
The motivation is to consider difficulty in aerosol model selection and obtain realistic uncertainty estimates.
We have applied this methodology to OMI/Aura measurements in our earlier studies. Here we present results when used higher resolution measurements from TROPOMI/S5P and studied the methodology covering various aerosol conditions including wild fire and dust events.
Striking repercussions of the Australian "Black Summer" bushfires on the stratospheric composition and dynamical circulation
Authors: Khaykin Sergey , Legras Bernard , Bucci Silvia , Sellitto Pasquale , Isaksen Lars , Tencé Florent , Bekki Slimane , Bourassa Adam , Rieger Landon , Zawada Daniel , Jumelet Julien , Godin-Beekmann Sophie
Published: March 2021

Wildfire-driven pyro-convection (PyroCb) is capable of lofting combustion products into the stratosphere, polluting it with smoke aerosols at hemispheric and yearly scales. This realization has emerged after the record-breaking British Columbia PyroCb event in August 2017 that approached moderate volcanic eruptions in terms of stratospheric aerosol load perturbation. The Australian “Black Summer” bushfires in 2019/20 have surpassed the previous record by a factor of 3 and rivaled the strongest volcanic eruptions in the XXI century. Here we exploit a synergy of various satellite observations, ECMWF meteorological analysis and radiative transfer modeling to quantify the perturbation of stratospheric particulate and gaseous composition, dynamical circulation and radiative balance caused by the Australian New Year’s PyroCb outbreak. One of the most striking repercussions of this event was the generation of several persistent anticyclonic vortices that provided confinement to the PyroCb plumes and preserved them from rapid dilution in the environment. The most intense vortex measured 1000 km in diameter, persisted in the stratosphere for over 13 weeks and lifted a confined bubble of combustion gases, aerosols and moisture to 35 km altitude. It was accompanied by a synoptic-scale ozone hole with the total column reduction by about 30%. The startling consequences of the Australian event provide new insights into climate-altering potential of the wildfires, that have increased in frequency and strength over the recent years.
The Greenland Clipper: a fast ocean connection between Greenland and the Southern Ocean
Authors: Andreasen Laurits , Jochum Markus , von der Heydt Anna , Vettoretti Guido , Nuterman Roman
Published: March 2021

The glacial Dansgaard-Oeschger (DO) events are thought to result in a global reorganization of oceanic heat fluxes and heat content.

DO events originate in the North Atlantic, but are communicated all the way to the pole of the other hemisphere. This interhemispheric coupling is known as the bipolar seesaw. A striking feature of the bipolar seesaw is the ~100 year time lag between the initial onset at high northern latitudes and the following adjustments at high southern latitudes.

Here, we focus on this time lag.

Ultimately high southern latitudes are expected to begin their adjustment, when the sea ice margin in the Southern Ocean (SO) shift position due to cooling/warming in the ocean below. But how is the northern signal propagated into the SO, and what processes control the time it takes the SO to change its state?

We expect the SO adjustment to have four components: Planetary waves, geostrophic adjustments in the Atlantic, vertical mixing and finally heat fluxes from baroclinic eddies in the SO.

To investigate the relative importance of these components on the adjustment time in the SO, we apply a fresh water perturbation at high northern latitude in an idealized setup of the Atlantic basin and the Southern Ocean using the newly developed OGCM VEROS. We measure the time it takes the model's Southern Ocean to adjust to the perturbation as a function of different model parameters associated with the components mentioned above.

We find that the adjustment time - which we believe is related to the bipolar seesaw time lag - is dominated by two components. The first is associated with geostrophic adjustment in the South Atlantic, and the second with the eddy heat fluxes in the Southern Ocean. Interestingly we find that in the limit of a high (realistic) eddy transfer (Gent-McWilliams) coefficient, the geostrophic component constitutes the main part of the the adjustment time and quantitatively matches the observed time lag in the bipolar seesaw.

This make us suggest that the bipolar seesaw time lag could be caused mainly by adjustments in the South Atlantic.
Incorporating the North Atlantic Oscillation into the post-processing of MOGREPS-G wind speed forecasts
Authors: Allen Sam , Evans Gavin , Buchanan Piers , Kwasniok Frank
Published: March 2021

Changes in the North Atlantic Oscillation (NAO) heavily influence the weather across the UK and the rest of Europe. Due to an imperfect reconstruction of the polar jet stream and associated pressure systems, there is reason to believe that errors in numerical weather prediction models may also depend on the prevailing behaviour of the NAO. To address this, information regarding the NAO is incorporated into statistical post-processing methods through a regime-dependent mixture model, which is then applied to wind speed forecasts from the Met Office's global ensemble prediction system, MOGREPS-G. The mixture model offers substantial improvements upon conventional post-processing methods when the wind speed depends strongly on the NAO, but the additional complexity of the model can hinder forecast performance in other instances. A measure of regime-dependency is thus defined that can be used to differentiate between situations when the numerical model output is, and is not, expected to benefit from regime-dependent post-processing. Implementing the regime-dependent mixture model only when this measure exceeds a certain threshold is found to further improve predictive performance, while also producing more accurate forecasts of extreme wind speeds.
Cosmic-ray muography applications in underground tunnelling
Authors: Kuusiniemi Pasi , Holma Marko , Zhang Zongxian
Published: March 2021

The novel geophysical remote imaging method of muography is based on cosmic-ray induced muon particles that are detected after passing through the media of interest. If the studied objects are solid, their sizes can vary from meters to up to kilometres. In terms of penetration capability, muography can be placed between methods based on X-rays and those using seismic waves. The most famous objects imaged with muography are pyramids (e.g., Khufu's Pyramid at Giza in Egypt) and volcanoes (e.g., Mt Etna in Italy). One clear advantage of muography compared with seismic methods is that muons, unlike seismic waves, do not reflect from geological interfaces. In addition, the scattering phenomenon is a minor issue and needs consideration only at low-energy muons. Raw data must be corrected according to topography. On the basis of extensive numeric simulations of Hivert et al. (2017), the lowest density variations observable for muography with a significant level of 3σ (a typical significance level in physics) are around 2% at 150 m, 4% at 300 m, and 10% at 700 m of depth, respectively. If these numbers are extrapolated to depths below 100 m, the mean density differences in the range of 1% are likely within the observation capability of muography. It is also worth to note that the 1% difference in a mean rock density results in an approximately 3% difference in the muon flux. This indicates that muon flux measurements are very sensitive to the density variations of rocks.

In underground tunnelling, muography has at least four applications: (1) muography can be used to detect a potential risk (such as a water reservoir, a weak zone with loose rocks, boulders, etc.) before or during tunnelling, (2) muography can be employed to monitor overburden rock behaviour during tunnelling operation to avoid risks like the roof cave-ins, (3) muography can be applied to monitor the overburdening rock masses in tunnels after they are excavated to predict and avoid the collapse of rock mass, and (4) muography can be used to estimate the size and volume of a rock mass collapse in a tunnel since the volume of the collapsed rocks must have markedly smaller density than original overburden rock mass. In an excavating tunnel project using a tunnel boring machine (TBM), a muon detector can be installed in the TBM during tunnelling. If there occurs a tunnel cave-in, muography can be employed in undamaged tunnels nearby (sideways or below) the collapse. If possible, the collapse can also be approached safely via an undamaged part of the collapsed tunnel. If none of these are available, borehole muography can be applied as a substitute solution. Whereas an undamaged underground tunnel is either filled by air or water, a collapsed tunnel segment is characterized by air and rock, or water and rock. In either case, the average density of the tunnel segment is increased. We are currently planning simulations and real-world tests to validate these assumptions.
How radial and quasi radial IMF impact the Earth's magnetopause's size, location, and shape. Does this impact generate Dawn-Dusk asymmetry in the magnetosheath?: Global 3D Kinetic Simulations. 
Authors: Baraka Suleiman , Le Contel Olivier , Ben-Jaffel Lotfi , Moore Bill
Published: March 2021

The boundary between the solar wind (SW) and the Earth’s magnetosphere, named the magnetopause (MP), is highly dynamic. Its location and shape can vary as a function of different SW parameters such as density, velocity, and interplanetary magnetic field (IMF) orientations. We employ a 3D kinetic Particle-In-Cell (IAPIC) code to simulate these effects.  We investigate the impact of radial (B = Bx) and quasi-radial (Bz < Bx, By) IMF on the shape and size of Earth’s MP for a dipole tilt of 31o using both maximum density steepening and pressure system balance methods for identifying the boundary. We find that, compared with northward or southward-dominant IMF conditions, the MP position expands asymmetrically by 8 to 22% under radial IMF. In addition, we construct the MP shape along the tilted magnetic equator and the OX axes showing that the expansion is asymmetric, not global, stronger on the MP flanks, and is sensitive to the ambient IMF. Finally, we investigate the contribution of SW backstreaming ions by the bow shock to the MP expansion, the temperature anisotropy in the magnetosheath, and a strong dawn-dusk asymmetry in MP location.
The Earth energy imbalance – new advances and remaining challenges
Authors: von Schuckmann Karina
Published: March 2021

Human-induced atmospheric composition changes cause a radiative imbalance at the top of the atmosphere which is driving global warming. This simple number, the Earth energy imbalance (EEI), is the most fundamental metric that the scientific community and public must be aware of as the measure of how well the world is doing in the task of bringing climate change under control. Combining multiple measurements and approaches in an optimal way holds considerable promise for estimating EEI and continued quantification and reduced uncertainties can be best achieved through the maintenance of the current global climate observing system, its extension into areas of gaps in the sampling, advance on instrumental limitations, and the establishment of an international framework for concerted multidisciplinary research effort. This talk will provide an overview on the different approaches and their challenges for estimating the EEI. A particular emphasis will be drawn on the heat gain of the Earth system over the past half of a century – and particularly how much and where the heat is distributed – which is fundamental to understanding how this affects warming ocean, atmosphere and land; rising surface temperature; sea level; and loss of grounded and floating ice, which are critical concerns for society.

 
Impact of land-use on soil structure and soil ecological properties in a long-term field experiment
Authors: Schlüter Steffen , Roussety Tim , Rohe Lena , Guliyev Vusal , Blagodatskaya Evgenia , Reitz Thomas
Published: March 2021

Land use is known to exert a dominant impact on a range of essential soil functions like water retention, carbon sequestration, matter cycling and plant growth. In addition, land use management is known to have a strong influence on soil structure, e.g. through tillage and compaction. While the difference in topsoil structure between grassland and agricultural soil is huge, differences among different farming or grassland management practices can be more subtle. At the same time, soil structure is known to be a suitable indicator for many soil functions. That is, differences in carbon content or plant-available field capacity between different land uses can often be explained by different structural properties.

This impact of land use on the relationship between soil structure and biological indicators for soil processes was explored in the Global Change Exploratory Facility, a well-established (>5 years) field experiment in Bad Lauchstädt, Germany, comprising five land use types (conventional farming, organic farming, intensive meadow, extensive meadow, extensive pasture). 15 intact topsoil cores were sampled from each land use type in spring 2020 and soil structure and microbial activity were measured using X-ray CT and respirometry, respectively. Microbial activity was estimated by basal respiration at field moisture and by substrate-induced respiration with glucose solution under wet conditions. The aims of this study were to (1) quantify the impact of land use on these structural and biological soil properties and (2) to assess in how far microbial activity can be predicted by the structural properties.

Surprisingly, image-derived macroporosity did not differ between farming and grassland plots mainly due to the huge variability among compacted and non-compacted samples in the farming plots. Other pore metrics like pore distance and pore connectivity followed the same trend, whereas mean pore size was larger in the grassland plots due to more large biopores. Basal respiration increased in the order farming < meadow < pasture, whereas the order was reversed for substrate-induced respiration. The predictability of basal respiration (R2=0.29) and substrate-induced respiration (R2=0.5) with explanatory variables based on pore metrics and bulk soil properties was rather low, with root mass and bulk density being the best predictors.
El Niño as a predictor of round sardinella distribution along the northwest African coast
Authors: López-Parages Jorge , Auger Pierre-Amaël , Rodríguez-Fonseca Belén , Keenlyside Noel , Gaetan Carlo , Rubino Angelo , Arisido Maeregu Woldeyes , Brochier Timothée
Published: March 2021

The El Niño Southern Oscillation (ENSO) produces global marine environment conditions that can cause changes in abundance and distribution of distant fish populations worldwide. Understanding mechanisms acting locally on fish population dynamics is crucial to develop forecast skill useful for fisheries management. The present work addresses the role played by ENSO on the round sardinella population biomass and distribution in the central-southern portion of the Canary Current Upwelling System (CCUS). A combined physical-biogeochemical framework is used to understand the climate influence on the hydrodynamical conditions in the study area. Then, an evolutionary individual-based model is used to simulate the round sardinella spatio-temporal biomass variability. According to model experiments, anomalous oceanographic conditions forced by El Niño along the African coast cause anomalies in the latitudinal migration pattern of the species. A robust anomalous increase and decrease of the simulated round sardinella biomass is identified in winter off the Cape Blanc and the Saharan coast region, respectively, in response to El Niño variations. The resultant anomalous pattern is an alteration of the normal migration between the Saharan and the Mauritanian waters. It is primarily explained by the mod- ulating role that El Niño exerts on the currents off Cape Blanc, modifying therefore the normal migration of round sardinella in the search of acceptable temperature conditions. This climate signature can be potentially predicted up to six months in advance based on El Niño conditions in the Pacific.
Glaciation cycle models and their pullback attractors
Authors: Riechers Keno , Boers Niklas , Ghil Michael , Mitsui Takahito
Published: March 2021

The Pleistocene climate was dominated by alternating retreat and regrowth of massive ice sheets accompanied by large variations in the global mean temperature and sea level. Partial agreement between the power spectra of global ice volume proxies and high-latitude summer insolation provides evidence that quasi-periodic changes in the earth’s orbital configuration affect the timing of glaciations and deglaciations. It remains, however, a topic of active debate whether the main cause of glacial cycles is an internal self-sustained oscillation of the climate system that merely phased locked, more or less, to orbital forcing or whether glacial cycles could not exist at all in the absence of orbital forcing. Furthermore, it is unclear whether past ice volume records should be regarded as the result of a purely deterministic process or as a randomly selected trajectory of a stochastic process. To study plausible paths of the earth’s climate system given the orbital forcing, we compute the pullback attractors of several conceptual Pleistocene models. The results are confronted with the power spectra, as well as the time series of proxy records and conclusions will be drawn about the role of internal vs. forced variability and the possible contribution of stochastic processes to the mix of causes. We argue, moreover, that the explanatory power of either a deterministically chaotic or a dynamic-stochastic model cannot be assessed by comparing the model output to observations in the time domain alone.