bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of dissolved and atmospheric methane concentrations along a freshwater-seawater transect from the River Elbe into the North Sea
Authors: Bussmann Ingeborg , Brix Holger , Kamjunke Norbert , Ködel Uta , Koschorreck Matthias , Schütze Claudia
Published: March 2021

Surface waters are known to be significant sources of greenhouse gases (CH4 and CO2), but our understanding of large scale patterns is still incomplete. The greenhouse gases in rivers originate both from in-stream processes and interactions with the catchment. For coastal seas, rivers are suspected to be one of the main source of greenhouse gases, while the role of the interjacent tidal flats is still ambiguous. Especially the reaction of the entire system on terrestrial hydrological extremes such as low flow situations are still under consideration. The functional understanding of such events and their impacts on the water chemistry along its transition pathway in the terrestrial and limnic compartment as well as in the coastal marine environment is crucially needed for the evaluation of its relevance in the Earth system. As part of a MOSES campaign (Modular Observation Solutions for Earth Systems) spanning disciplines as well as earth system compartments we investigated the aquatic as well as the atmospheric compartemt in and above the Elbe River from inland waters through the tidal section of the river and the estuary to the North Sea with the goal to explore spatial heterogeneity of CO2 and CH4 concentrations in the water and in ambient air above the water during a low water period in summer 2020.

 

Overall, dissolved CH4 concentrations ranged over three orders of magnitude. Along the freshwater part of the transect, dissolved CH4 increased and weirs and harbors appeared to be hot spots of elevated CH4 concentrations both for the dissolved and atmospheric phase. We observed a longitudinal gradient of CO2 in the river which was closely linked to primary production. In the estuary and the marine part, dissolved CH4 concentrations of the transect were determined by the variability of temperature and salinity. Correlations with other water parameters revealed the complex regulation of dissolved CH4 concentrations along the freshwater-seawater continuum. For atmospheric CH4 above the North Sea, wind direction and wind speed proved to be crucial. Besides the typical diurnal fluctuations of atmospheric CO2 and CH4, an observed link between dissolved and atmospheric concentrations has to  be further clarified.
Scale factors of the thermospheric neutral density – a comparison of SLR and accelerometer solutions
Authors: Zeitler Lea , Corbin Armin , Vielberg Kristin , Rudenko Sergei , Löcher Anno , Bloßfeld Mathis , Schmidt Michael , Kusche Jürgen , Forootan Ehsan
Published: March 2021

The aerodynamic drag depending on the neutral density of the thermosphere is the largest non-gravitational force that decelerates Low Earth Orbiting (LEO) satellites with altitudes lower than 1000 km.  Consequently, the knowledge of the thermospheric neutral density is of crucial importance for many applications in geo-scientific investigations, such as precise orbit determination (POD), re-entry prediction, manoeuvre planning or satellite lifetime predictions. The accuracy of existing thermosphere models depends on observation data of the thermosphere, which are quite sparse. Evaluations of different thermosphere models indicate considerable differences, especially for time epochs of severe space weather events. Hence, an improvement of thermosphere models is absolutely necessary.

In this study, discrepancies between the empirical thermosphere model NRLMSISE-00 and the results of two geodetic observation techniques are discussed. For this purpose, two approaches are applied to calculate scale factors between the modelled density from the NRLMSISE-00 model and those from geodetic techniques. The first approach applies the POD of LEO satellites to estimate scale factors with a time resolution of 12 hours derived from Satellite Laser Ranging (SLR) tracking measurements. The SLR missions used here include the spherical satellites Starlette, Westpac, Blits, Stella and Larets. As our second approach, scale factors are computed by evaluating the aerodynamic acceleration using the on-board accelerometer data of the Challenging Mini-satellite Payload (CHAMP) mission and the Gravity Recovery and Climate Experiment (GRACE) mission. Here, the time resolution of scale factors is fixed to be 12 hours to be comparable with the first approach. Finally, we investigate the resulting scale factors from the above mentioned satellites at various altitudes, e.g. 960 km for Starlette and 400 km for GRACE. Especially, the temporal variation as well as the altitude dependency of the scale factors will be discussed.
The Climatic Significance of Organic Aerosol in the Boreal Region
Authors: Mielonen Tero , Yli-Juuti Taina , Heikkinen Liine , Arola Antti , Ehn Mikael , Isokääntä Sini , Keskinen Helmi-Marja , Kulmala Markku , Laakso Anton , Lipponen Antti , Luoma Krista , Mikkonen Santtu , Nieminen Tuomo , Paasonen Pauli , Petäjä Tuukka , Romakkaniemi Sami , Tonttila Juha , Kokkola Harri , Virtanen Annele
Published: March 2021

Biogenic secondary organic aerosol (BSOA) constitutes a major fraction of aerosol over boreal forests. As the emissions of BSOA precursors are temperature dependent, changes in temperature have potentially important implications on regional aerosol radiative forcing. Here, we have used long-term aerosol composition and temperature data measurements from a boreal forest site together with remote sensing observations of aerosol and cloud properties to investigate the effect of increasing temperature on organic aerosol mass loadings, and further on aerosol direct and indirect radiative effects. The analysis was based on 7 years of measurements done at Hyytiälä, Southern Finland, and they cover the summer months (July-August) between 2012-2018. We limited the analyses to these summer months to isolate the temperature dependence of the organic mass loadings from the seasonal effects arising from the vegetation growth cycle. Our analysis showed that organic aerosol loadings and cloud condensation nuclei concentrations increased in concert with surface temperature. Furthermore, we found that cloud reflectivity increased when the organic aerosol loadings increased. This research presents the first direct observational evidence on the effect of BSOA on cloud properties and their climatic significance.
Visualisation of fluid flow mechanisms through a viscous-porous rock-analogue medium – experiment and model results
Authors: van Noort Reinier , Wang Lawrence Hongliang , Yarushina Viktoriya
Published: March 2021

Understanding fluid flow patterns in the shallow and deep earth is one of the major challenges of modern earth sciences. Fluid flow may be slow and pervasive, or fast and focused. In the deep earth, focused fluid flow may result in, for example, dikes, veins, volcanic diatremes and gas venting systems. In the shallow Earth, focused fluid flow can be found in the form of fluid escape pipes and gas conducting chimneys, mud volcanoes, sand injectites, pockmarks, hydrothermal vent complexes, etc.

Focused fluid flow has been reproduced in visco-plastic models of flow through porous materials. However, the mechanisms that cause fluid flow to focus along such relatively narrow channels, with transiently elevated permeability, have not been investigated thoroughly in experiments. We have carried out experiments in a transparent Hele-Shaw cell. In our experiments, a hydrous fluid is injected into an aggregate of viscous grains, and the mechanisms by which this injected fluid flows are recorded using a digital camera. Our experiments demonstrate a dependence of fluid flow mechanisms on the injection rate. At low injection rate, we observe the formation of a slowly-rising diapir. As this diapir slowly rises through the porous medium, it is fed by transient, focused fluid flow following the path of the rising diapir. Once the diapir escapes through the surface of our aggregate, continued fluid flow through the porous aggregate is focused and transient. At high injection rate, instead of a diapir fed by focused fluid flow, an open channel forms as a result of local fluidization of the granular material.

Our experimental observations are interpreted through visco-plastic models simulating the experimental conditions. These numerical models can reproduce the diapirs observed in our experiments at low flow rate by assuming flow through a layered porous aggregate, with a layer with relatively high bulk viscosity overlying a layer with relatively low bulk viscosity. For low injection rates, such a model reproduces focused fluid flow in the low-viscosity layer, that feeds into a slowly rising diapir in the high-viscosity layer. This model observation thus suggests that the passage of the rising diapir in our experiments leaves a trail, where the aggregate bulk viscosity is lowered and along which ongoing fluid flow can focus transiently.
Communicating water-related climate change hazards to local stakeholders
Authors: Müller Laura , Döll Petra
Published: March 2021

Due to climate change, the water cycle is changing which requires to adapt water management in many regions. The transdisciplinary project KlimaRhön aims at assessing water-related risks and developing adaptation measures in water management in the UNESCO Biosphere Reserve Rhön in Central Germany. One of the challenges is to inform local stakeholders about hydrological hazards in in the biosphere reserve, which has an area of only 2433 km² and for which no regional hydrological simulations are available. To overcome the lack of local simulations of the impact of climate change on water resources, existing simulations by a number of global hydrological models (GHMs) were evaluated for the study area. While the coarse model resolution of 0.5°x0.5° (55 km x 55 km at the equator) is certainly problematic for the small study area, the advantage is that both the uncertainty of climate simulations and hydrological models can be taken into account to provide a best estimate of future hazards and their (large) uncertainties. This is different from most local hydrological climate change impact assessments, where only one hydrological model is used, which leads to an underestimation of future uncertainty as different hydrological models translate climatic changes differently into hydrological changes and, for example, mostly do not take into account the effect of changing atmospheric CO2 on evapotranspiration and thus runoff.   

The global climate change impact simulations were performed in a consistent manner by various international modeling groups following a protocol developed by ISIMIP (ISIMIP 2b, www.isimip.org); the simulation results are freely available for download. We processed, analyzed and visualized the results of the multi-model ensemble, which consists of eight GHMs driven by the bias-adjusted output of four general circulation models. The ensemble of potential changes of total runoff and groundwater recharge were calculated for two 30-year future periods relative to a reference period, analyzing annual and seasonal means as well as interannual variability. Moreover, the two representative concentration pathways RCP 2.6 and 8.5 were chosen to inform stakeholders about two possible courses of anthropogenic emissions.

To communicate the results to local stakeholders effectively, the way to present modeling results and their uncertainty is crucial. The visualization and textual/oral presentation should not be overwhelming but comprehensive, comprehensible and engaging. It should help the stakeholder to understand the likelihood of particular hazards that can be derived from multi-model ensemble projections. In this contribution, we present the communication approach we applied during a stakeholder workshop as well as its evaluation by the stakeholders.
Induced and triggered seismicity from Nov 2019 to Dec 2020 below the city of Strasbourg, France
Authors: Schmittbuhl Jean , Lengline Olivier , Lambotte Sophie , Grunberg Marc , Doubre Cécile , Vergne Jérôme , Cornet François , Masson Frédéric
Published: March 2021

Since Nov 2019, a series of seismic of events were felt by the population of the city of Strasbourg, France. The first main event (Ml3.0) on Nov 12, 2019 was part of a seismic swarm that has been initiated a few days before, lasted four month and was located by the BCSF-RéNaSS (EOST) in the northwestern part of the town (Robertsau area) at a depth of 5 km. Its location in the vicinity of the deep geothermal wells (GEOVEN), the temporal correlation with the injection activity on site, the similarity of the depth between the bottom of the wells and the hypocenter of the event, the lack of local seismicity before the event occurrence, the known geological structures including crustal faults in the area, all strongly support the possible triggering of the events by the deep geothermal activities despite the relatively large distance (4-5km). Template matching has been applied and allowed for a significant improvement of the detections. Double-difference relocations evidenced a complex fault zone in the swarm area that extends over 800m. Focal mechanisms of the two main events are consistent with the known orientation of the fault zone. The regional stress field in combination with the fault orientation and a Coulomb failure criterion, shows that the swarm location is in an unstable domain if the cohesion of the fault is weak, particularly sensitive to stress perturbations. Since Oct 2020, hydraulic tests were initiated and a second cluster of seismic events with more felt earthquakes developed closer to the geothermal wells. It includes the largest event (Ml3.6) that was induced on Dec 4, 2020 and caused the definitive arrest of the project. A preliminary analysis shows that most of the largest events happened along the same fault zone as in Nov 2019 but very close to the injection well, where a significant over-pressure has been maintained over time.

This presentation is dedicated to the memory of Prof. François Cornet.
The Method of Forced Probabilities: a Computation Trick for Bayesian Model Evidence
Authors: Walter Peter , Banerjee Ishani , Guthke Anneli , Mumford Kevin , Nowak Wolfgang
Published: March 2021

Bayesian model selection (BMS) can be used to objectively rank competing models of different structure and with different parameters upon comparison with validation data sets. This technique requires the evaluation of Bayesian Model Evidence (BME). BME is the likelihood of the data to occur under the assumed models, where the likelihood is averaged over the probability distribution of the model and its parameters.

Exact and fast analytical solutions for BME exist only with strong assumptions. For that reason, other techniques and approximations for BMS/BME have been developed. While mathematical approximations via information criteria may suffer from strong biases in real-world applications, numerical methods do not rely on any assumptions but require high computational effort. This becomes prohibitive if the data set is very large, e.g. highly resolved in space and time.

To still enable the use of BME as a probabilistic and rigorous model performance metric, we have developed the “Method of Forced Probabilities”: this method is a fast way to numerically compute BME for models that predict time series and fulfill the Markov Chain property in time. The core idea is to swap the direction of evaluation: instead of comparing thousands of forward runs of the model with the observed data (many model runs on random parameter realizations), we force the model to follow the data during each time step and record the individual probabilities of the model performing these exact transitions (single evaluation).

As a test case for demonstration, we use invasion percolation (IP) models to simulate multiphase flow in porous media. The underlying, highly resolved data set was obtained from an experiment of a slow gas injection into water-saturated, homogeneous sand in a 25cmx25cm acrylic glass cell. Images were obtained at a rate of 30 images per second using the light transmission technique. Since IP models fulfill the Markov chain property, the Method of Forced Probabilities can be applied to evaluate their BME. Results confirm that the proposed method presents a scalable, inexpensive alternative to standard Monte Carlo methods for analyzing the model-data mismatch.
Water vapour monitoring with E-band microwave links of cellular backhaul
Authors: Fencl Martin , Bares Vojtech
Published: March 2021

Water vapour observations represent an important input e.g. for predicting mesoscale initiation of convective precipitation or estimating evapotranspiration. E-band commercial microwave links (CMLs), which are increasingly used in cellular backhaul, might be used as unintentional water vapour sensors accessible remotely from a network operation centre. E-band CMLs operate at frequencies between 71 and 86 GHz where water vapour causes substantial attenuation of electromagnetic waves. This attenuation can be related to water vapour density along a CML path, nevertheless, it has to be properly separated from other sources of attenuation, especially rainfall-induced attenuation, and wet antenna attenuation caused by wet surface of antenna radomes. Moreover, the relation between attenuation and water vapour density is also dependent on temperature (Fencl et al., 2020).

This contribution evaluates capability to estimate water vapour density on a 4.86 km long full-duplex CML being operated within cellular backhaul at frequencies 73.5 GHz and 83.5 GHz. Three rain gauges are deployed along its path, two of them being equipped with an air humidity sensor. The evaluation period is between August to December 2018. The results show that estimation of water vapour density is feasible when there is now rain and antenna radomes are dry, which is only about 50% of time. Estimated water vapour density during dry weather is highly correlated with humidity observations (r = 0.7). The highest correlations are observed during summer season (r = 0.9) and lowest during December (r = 0.3) when amplitude of water vapour fluctuations are small. In contrast, mean absolute error is highest during August (approx. 1 g/m3) and lowest in December (0.2 g/m3). Most of the outliers were encountered during October, probably due to multipath inferences occurring during clear-sky conditions.

Unintentional sensing of water vapour density with E-band CMLs is feasible by sufficiently (several kilometres) long CMLs. Currently, 20 % of new CML deployments are operated E-band. E-band CMLs might thus greatly increase continental coverage of water vapour ground observations.

 

Fencl, M., Dohnal, M., Valtr, P., Grabner, M. and Bareš, V.: Atmospheric observations with E-band microwave links – challenges and opportunities, Atmospheric Measurement Techniques, 13(12), 6559–6578, https://doi.org/10.5194/amt-13-6559-2020, 2020.
The impact of the COVID-19 lockdown measures on the seismic monitoring in the Bucharest (Romania) metropolitan area
Authors: Grecu Bogdan , Tiganescu Alexandru , Poiata Natalia , Borleanu Felix , Dinescu Raluca , Tataru Dragos
Published: March 2021

The lockdown measures taken to control and stop the spread of the novel coronavirus (COVID-19) in cities around the globe caused an unprecedented reduction of anthropic activities. The signature of this reduction, different from one place to another, has been captured by the seismic stations installed in the urban areas where lockdown restrictions have been implemented. Bucharest, the capital of Romania, was no exception from this phenomenon.

In this paper, we investigate the effect of the COVID-19 lockdown measures imposed by the Romanian authorities on the high-frequency ambient seismic noise (ASN) data recorded by the Bucharest Metropolitan Seismic Network (BMSN). BMSN consists of 26 stations of which 19 are equipped with strong motion sensors and 7 have both short-period velocity and accelerometer sensors. All the stations are continuously recording the ground motion and the data is sent in real-time to the data center of the National Institute for Earth Physics.         

The reduction of ASN was first observed at stations installed in educational units (kindergartens, schools) starting with 11th of March 2020, when the Romanian government decided to close the schools in Romania. For these stations, the largest reduction of ASN, up to 82%, was noticed in the 25-40 Hz frequency band. On 16th of March the state of emergency was imposed in Romania and a few days later, on 25th of March, the stay-at-home order was issued. These new restrictions caused substantial reduction in urban traffic and people’s mobility and reflected in significant reduction of ASN at almost all the other BMSN stations, located either free-field or in buildings. For these stations, we observed a decrease of the noise levels by as much as 66% in the 15-25 Hz frequency band. We also correlated the ambient seismic noise with other types of data that might be affected by human activity, such as the mobility data from Google and Apple, and we found good correlation between ASN in different frequency bands and various mobility data categories. Finally, we showed that the noise reduction due to lockdown measures improved the signal-to-noise ratio of the stations in the Bucharest area, allowing us to record smaller earthquakes which otherwise would not have been recorded.
Gas monitoring of a hydrothermal-magmatic volcano in a tropical environment: the example of La Soufriere de Guadeloupe (FWI)
Authors: Moune Severine , Moretti Roberto , Burtin Arnaud , Jessop David , Didier Tristan , Robert Vincent , Bonifacie Magali , Tamburello Giancarlo , Komorowski Jean-Christophe
Published: March 2021

Fumarolic gas survey of dormant volcanoes is fundamental because the compositional and flux changes in gas emissions are recognised signals of unrest and may even be precursors of eruptions on several dormant volcanoes in hydrothermal unrest [1-5].

Here we report on the chemical compositions (CO2, H2S, SO2, H2) and mass fluxes of fumarolic gas emissions from the low-temperature (from 97° to 104°C) volcanic-hydrothermal system of La Soufrière de Guadeloupe (Lesser Antilles). This present study covers the period 2016 to present, encompassing the peak activity of April 2018. Long-term trends are acquired from both portable MultiGAS measurements (performed monthly) and two permanent MultiGAS stations (4 automated 20’ measurements per day). These MultiGAS data are discussed along with other geochemical and geophysical parameters monitored at OVSG, such as complete fumarole chemistry via Giggenbach bottles, fumarole temperatures, volcanic seismicity and deformation in order to track the deep-sourced magmatic signal contribution compared to the one of the hydrothermal system and detect potential signs of unrest [6].

Dealing with MultiGAS data from a low-T fumarolic system in a tropical environment is not straightforward due to external forcing effect of meteoric water on gas composition. Hence, interpretation of the observed chemical changes must consider (i) the role of water-gas-rock interactions and gas scrubbing processes by the hydrothermal system and the perched volcanic pond [7], which particularly affect sulphur precipitation and remobilization and (ii) how these processes vary with rainfall and groundwater circulation (i.e. rainy vs non-rainy seasons, extreme events).

[1] Giggenbach and Sheppard, 1989; [2] Symonds et al., 1994; [3] Hammouya et al., 1998; [4] De Moor et al., 2016; [5] Allard et al., 2014; [6] Moretti et al., submitted; [7] Symonds et al., 2001
Integration between data collection through field and UAV-based surveys in volcano-tectonic environments: an example from the Krafla Fissure Swarm (NE Iceland)
Authors: Bressan Sofia , Corti Noemi , Rigoni Valentina , Russo Elena
Published: March 2021

Due to its strategic position at the boundary between European and American plates, Iceland is extraordinarily well suited for the investigation of various geological processes, like the interaction between active rifting processes and magmatic stresses. In this study, we focused on surveying with very high detail different key areas located within the Krafla Fissure Swarm (KFS), an active volcanic system located in the Northern Volcanic Zone, NE Iceland.

The Krafla volcanic rift is characterized by the presence of a central volcano and by a 100 km-long swarm of extension fractures, normal faults and eruptive fissures mainly affecting post-LGM (Late Glacial Maximum) Holocene lavas. Our work focuses on three different areas, located in the northernmost sector of the rift, about 5 km north of the central caldera, and south of the central volcano. All these areas have been investigated through field surveys performed both with classical methods and through two Unmanned Aerial Vehicles (UAVs), the DJI Phantom 4 PRO and DJI Spark: thanks to Structure from Motion (SfM) photogrammetry techniques, we obtained Orthomosaics, Digital Surface Models (DSMs) and 3D models of the study area, with centimetric resolution.

 The integration of the above cited methodologies allowed us to collect a huge amount of data, also overcoming difficulties due to logistics, which can sometimes impede classical field survey. More in detail, we collected 2476 structural measurements at 918 sites along extension fractures, and at 185 sites along normal faults. At extension fractures, we measured local fracture strike, dilation and, whenever possible, opening direction. On the other hand, along normal faults we measured local fault strike and the vertical offset. From our data, we obtained an average opening direction of N101°E, thus observing the presence of lateral components of motion along extension fractures. Finally, considering both extension fractures and normal faults, we quantified the cumulative dilation along these sectors, in order to assess the stretch value along the rift.
3D modelling of Isbræ-type glaciers and temperate-zone processes 
Authors: Law Robert , Christoffersen Poul , Cook Samuel , MacKie Emma , Haseloff Marianne
Published: March 2021

The majority of Greenland’s outlet glaciers are Isbræ-type, with high driving stresses, steep surface slopes, flow through deep channels, and with a basal layer of temperate ice theorised to thicken towards the coastal margin. Understanding the formation processes and thermodynamic influence of this temperate ice is important as limited laboratory testing indicates temperate ice has a viscosity 5-10 times lower than cold ice with no liquid phase. Furthermore, limited field data suggests lower rates of deformation within basal temperate ice than in the cold ice directly overlying it, which is presently unexplained. Here, we present preliminary results from a 3D finite-element model of an idealised Isbrae-type glacier built with Elmer/Ice, incorporating water-content-dependent ice viscosity, basal melting, and a parameterization of basal crevassing, and use it to investigate the formation and thermodynamic behaviour of temperate ice in response to varying bedforms and model parameters. We find that the observed decrease in strain in temperate ice close to the glacier base can be explained by a high strain area close to the cold-temperate transition zone. We further compare our model results to temperate ice variability observed at Sermeq Kujalleq (Store Glacier) to determine key temperate ice parameters requiring further investigation. These results provide a more complete understanding of the heterogeneous ice deformation behind the fast movement of Greenland’s Isbræ-type glaciers and can therefore help to improve predictions of future glacier flow.
A coupled model of rapidly-evolving subglacial hydrology with ice dynamics
Authors: McPhail Michael , Hewitt Ian
Published: March 2021

The presence of subglacial water can have a significant effect on the motion of an ice sheet. The rate at which the ice slides over the bedrock is mediated by subglacial water pressure. Meltwater on the surface of the sheet can drain through cracks and moulins; drastically increasing the amount of water under the sheet. This source of water fluctuates seasonally and diurnally, much faster than the timescale associated with large-scale glacier evolution. We are interested in the effect that this short-term variation in the subglacial hydrology, and therefore water pressure, has on the long-term behaviour of the ice sheet.  In particular, we are interested in how important it is to resolve the short-timescale variations in ice sliding speed.

 

We use a mathematical model to study the response of the subglacial drainage system to time-varying surface melt input. By coupling this subglacial hydrology through an effective-pressure-dependent sliding law to the momentum equation for the overlying ice sheet, we study the impact of short-term meltwater fluctuations on the ice velocity.  We study these interactions using a one-dimensional (1D) flowline model representing a confined glacier, allowing us to explore a range of couplings between the ice flow and hydrology.  This enables us to assess the influence of the fluctuating meltwater input on the long-term behaviour of the ice sheet. We find that using a time-averaged effective pressure with an asynchronous coupling to the momentum equation gives a reasonable estimate for the time-averaged ice-sheet velocity, despite the nonlinearity of the governing equations. We use the results to suggest how hydrological coupling might be achieved in larger-scale models where resolving the short-term fluctuations is likely to be infeasible.  
Understanding the role of the troposphere in the surface impact of the 2018 sudden stratospheric warming event
Authors: González-Alemán Juan J. , Grams Christian M. , Ayarzagüena Blanca , Zurita-Gotor Pablo , Domeisen Daniela I. V. Domeisen , Gómara Íñigo , Rodríguez-Fonseca Belén
Published: March 2021

Sudden stratospheric warmings (SSWs) are impressive phenomena that consist of a rapid stratospheric polar vortex breakdown. SSWs can have a strong impact on the tropospheric weather and are mainly associated with the negative phases of the Arctic and North Atlantic Oscillations (AO, NAO), and with northern European cold outbreaks, thus causing high societal impact. However, the mechanisms behind the downward impact from the stratosphere are insufficiently understood, especially the role played by the troposphere. In this work, we investigate this coupling and its associated predictability limits by studying the 2018 SSW event.

By analyzing ECMWF 15-day ensemble forecasts and partitioning them into different weather regimes, we search for possible dynamical tropospheric events that may have favored the downward stratosphere-troposphere coupling during and after the SSW. It is found that two cyclogenesis events were the main drivers of the negative NAO pattern associated with a Greenland Blocking, causing a rapid change from prevailing westerlies into a blocked state in the North Atlantic region. Unless these cyclogenesis events are simulated in the forecasts, the prediction of a Greenland Blocking does not become highly prevalent. No important stratospheric differences between WRs were found. A possible oceanic contribution to this blocked state is also found. This work corroborates that individual synoptic events might constitute a “predictability barrier" for subsequent forecast lead times. It also sheds light, on the specific topic of troposphere-stratosphere coupling.
Dansgaard-Oeschger Tipping Events (TEs): Towards determining if IPCC-relevant models represent these TEs.
Authors: Sime Louise , Malmierca Vallet Irene , Valdes Paul
Published: March 2021

Dansgaard-Oeschger (DO) events are abrupt, large climate swings that punctuated the last glacial period. There is uncertainty whether current IPCC-relevant models can effectively represent the processes that cause DO events. This has implications for whether these models are also capable of simulating future TEs,  and more in general, for the delivery of accurate climate change projections. Here we present progress on possible pathways to a DO Paleoclimate Modelling Intercomparison Project (PMIP) protocol. This is broad interest to the climate community since (1), there is currently no PMIP common guidance to investigate DO events, (2) it could help carry out simulations in Earth system models under a common framework, and (3) it will help guide a more methodical search for DO events in current models. A protocol could help investigate cold-period TEs through a range of insolation-, freshwater-, green-house-gas-, and Northern Hemisphere ice sheet-related forcings, as well as evaluating the possibility of spontaneous TEs. MIS3 was a period of noticeable millennial-scale climate variability, characterised by the most regular incidence of DO events (Schulz et al., 1999). Although most abrupt DO events happened during MIS3, only few studies investigate TEs in coupled general circulation models under MIS 3 conditions (e.g., Kawamura et al., 2017; Zhang and Prange, 2020). Here, we therefore suggest that the MIS3 period could be the focus of such a DO-event focussed modelling protocol. Experiments performed under MIS 3 boundary conditions may help (1) explore variability under intermediate glacial conditions, (2) better understand the mechanisms behind millennial-scale TEs, (3) look for spontaneous DO-type oscillations, and (4) help answer the question: “are models too stable?”.
Change in thunderstorm activity in a projected warmer future climate over Bangladesh
Authors: Esha Shahana Akter , Jahan Nasreen
Published: March 2021

Thunderstorms can have a wide range of impacts on modern societies and their assets. Severe thunderstorms associated with thunder squall, hail, tornado, and lightning cause extensive damage and losses to lives, especially in the densely populated sub-tropical countries like Bangladesh. In this study the future changes in thunderstorm conducive environments, in terms convective available potential energy (CAPE), have been assessed under the RCP 8.5 scenario for the selected major cities of Bangladesh. Results show an increase in CAPE for all the selected cities and in the range of 44%–106%. Later, a statistical thunderstorm frequency prediction model has been developed based on CAPE and convective precipitation and the probable scenario of thunderstorm frequency in the 21st century under future climate has been projected. The simulations were carried out for three different time slices (Early, Mid and Late 21st century) with CMCC-CM (Centro Euro-Mediterraneo per Cambiamenti Climatici Climate Model) model data. The future projection of thunderstorm shows an increase in thunderstorm frequency for all the season in a warmer future climate. But pre-monsoon and monsoon are found to be the most thunderstorm frequent season. Given the substantial damage from severe thunderstorms in the current climate, such increases imply an increasing risk of thunderstorm-related damage in this disaster-prone region of the world.
A Feature Track Correction (FTC) Observation Operator applied to Aeolus-AMV Collocations
Authors: Hoffman Ross N. , Lukens Katherine , Ide Kayo , Garrett Kevin
Published: March 2021

In this study we propose and test a feature track correction (FTC) observation operator for atmospheric motion vectors (AMVs).  The FTC has four degrees of freedom corresponding to wind speed multiplicative and additive corrections (γ and δV), a vertical height assignment correction (h), and an estimate of the depth of the layer that contributes to the AMV (Δz).  Since the effect of the FTC observation operator is to add a bias correction to a weighted average of the profile of background winds an alternate formulation is in terms of a profile of weights (wk) and δV .

The FTC observation operator is tested in the context of a collocation study between AMVs projected onto the collocated Aeolus horizontal line-of-sight (HLOS) and the Aeolus HLOS wind profiles.  This is a prototype for an implementation in a variational data assimilation system and here the Aeolus profiles act as the background in the FTC observation operator.  Results were obtained for ten days of data using modest QC.  The overall OMB or collocation difference SD for a global solution applied to the independent sample is 5.49 m/s with negligible mean.  For comparison the corresponding simple (or pure) collocation SD is 7.85 m/s, and the null solution, which only interpolates the Aeolus profile to the reported height of the AMV and removes the overall bias, has an OMB SD of 7.23 m/s. These values correspond to reductions of variance of 51.0% and 42.3%, due to the FTC observation operator in comparison to the simple collocation and null solution, respectively.

These preliminary tests demonstrate the potential for the FTC observation operator for 

Improving AMV collocations (including triple collocation) with profile wind data.

Characterizing AMVs. For example, summary results for the HLOS winds show that AMVs compare best with wind profiles averaged over a 4.5 km layer centered 0.5 km above the reported AMV height.

Improving AMV observation usage within data assimilation (DA) systems. Lower estimated error and more realistic representation of AMVs with variational FTC (VarFTC) should result in greater information extracted.  The FTC observation operator accomplishes this by accounting for the effects of h and Δz. 
Drivers of Surface Downwelling Longwave Irradiance Changes from 1984 through 2017
Authors: Clark Joseph
Published: March 2021

Relatively few studies have taken observationally driven approaches toward understanding the impact that atmospheric gases and temperatures have on surface downwelling longwave irradiance (SDLI) changes. This is despite the fact that changes in SDLI contribute significantly to climate change. Using reanalysis, observations, and the Rapid Radiative Transfer Model Global (RRTMG; Mlawer et al. 1997; Iacono et al. 2008), we linearly separate the contributions to SDLI changes from 1984 through 2017 caused by the following variables: atmospheric temperature, H2O, CO2, CH4, N2O, CFC-11, and CFC-12. The results show that spatial and temporal variations in SDLI are primarily caused by spatial and temporal variations in atmospheric temperatures and water vapor amounts. Specifically, we find that atmospheric temperatures and water vapor amounts contribute about 10 times more to SDLI variations from 1984 through 2017 than the remaining greenhouse gases. Climatologically, spatial variability in atmospheric temperature and water vapor also play a role in determining the impact on SDLI of CO2, CH4, N2O, CFC-11, and CFC-12. SDLI trends directly attributable to CO2, CH4, N2O, CFC-11, and CFC-12 are strongest over regions with climatologically high temperatures and low water vapor amounts. In other words, the impact of the greenhouse gases varies in space, with its strength depending on the background temperature and moisture fields, even if the change in gas mixing ratio is spatially uniform. Finally, CO2 contributed 10 times more to the SDLI trends of 0.05-0.30 W m-2 / decade (depending on location) from 1984 through 2017 than any other greenhouse gas.

 

References
Raindrop driven erosion – what is in the black box ?
Authors: Kinnell Peter
Published: March 2021

Raindrop driven erosion – what is in the black box ?

P.I.A. Kinnell

Faculty of Science and Technology, University of Canberra, Canberra, Australia

Many experiments applying rainfall to produce erosion on soil surfaces consider the inputs and outputs in a black box situation where little or no consideration is given to the actual mechanisms controlling erosion. It is well known that rainfall erosion is caused by raindrop impact and flow forces acting singly or together. Raindrops impacting directly or through surface water detaches soil material from where it is held within the soil surface by cohesion and inter-particle friction  and erosion occurs if the detached material is transported away from the site of detachment. The movement of detached material downslope may be in the air by splash or more importantly in surface water flows where raindrop impact may induce coarse sediment may to move when sediment transport normally associated with undisturbed flow does not occur. These transport processes vary in space and time during laboratory and field experiments. How this influences the amounts of soil loss during these experiments is the subject of  this presentation .
Evaluating the stability and evolution of a proposed post mining landform.
Authors: Welivitiya Welivitiyage Don Dimuth Prasad , Willgoose Garry , Hancock Gregory
Published: March 2021

Evaluating the future stability and land denudation rates of natural or anthropogenic landforms is paramount for sustainable land use practices. Landform evolution models can be powerful tools in this endeavour.  In this study we used the well-established landform evolution model SIBERIA and the newly developed coupled soilscape-landform evolution model SSSPAM to simulate the evolution of a proposed post mining landform. SIBERIA uses a cellular digital elevation model to simulate annual average fluvial and diffusive erosion on landforms using annual average precipitation. However it does not simulate the soil profile evolution on the evolving landform. The new SSSPAM coupled soilscape-landform evolution model has the ability to assess the overall erosion rates of catchment scale landforms either using short term precipitation events, variable precipitation or time averaged precipitation rates. In addition, SSSPAM is able to simulate the evolution of the soil profile of the evolving landform using pedogenetic processes such as physical weathering and armouring.

            To assess the reliability of SSSPAM, model predictions at 100 and 10000 years were compared with SIBERIA predictions at the same times. During the long term (10000yr) simulation the effect of armouring and weathering on the landform evolution was also assessed. The results obtained from these different simulations were compared and contrasted. Comparison of the short term simulations revealed that SSSPAM results compare well with the simulation results of the more established SIBERIA model. Long term simulation showed that SSSPAM simulation results also compares well with SIBERIA simulations while the erosion rates predicted by both models are close to the land denudation rates measured in the field. The soil profile characteristics and channel forms simulated by SSSPAM long term simulations were examined using several landform cross-sections. This analyses revealed that SSSPAM produces deep incised channels with very low soil thickness in upper reaches of the catchment and shallow channels with relatively thick soil layers in the lower reaches of the catchment. These SSSPAM simulated channels match well with the channel forms and distribution of bedrock channels and alluvial channels observed in the field. The analysis of the catchment cross-sections also showed that SSSPAM is capable of reproducing complex subsurface soil evolution and stratification and spatial variability of soil profile characteristics typically observed in the field.
Validation of Multi-Model-based Deterministic and Probabilistic Clear-Air Turbulence (CAT) Forecasts 
Authors: Lee Dan-Bi , Chun Hye-Yeong , Kim Jung-Hoon
Published: March 2021

Clear-Air Turbulence (CAT) is small-scale eddies in clear sky conditions that affect cruising aircraft directly. The current turbulence prediction systems mostly produce deterministic forecasts. To consider inherent uncertainties and provide reliable probabilities for turbulence forecasts, it is also essential to produce probabilistic turbulence forecasts. In this study, we calculate multi-model-based ensemble mean CAT forecast (MMEM) and multi-model-based probabilistic CAT forecast (MMP) based on Ellrod-Knox Index (EKI) diagnostic using seven global NWP model outputs with a 0.5o x 0.5o resolution from The International Grand Global Ensemble (TIGGE) database. The EKI is a representative CAT diagnostic, which adding a divergence trend term for detecting CAT related to inertia gravity waves and anticyclonic flows to a combination term of vertical wind shear and total horizontal deformation to detect CAT related to frontogenesis. The 24-h and 30-h forecasts at 200, 250, and 300 hPa levels valid at 1800 UTC for a 6-month period (2016.10–2017.03) are used to calculate the 30-h EKI forecast at 250 hPa. MMEM is simply derived by averaging EKIs from seven TIGGE NWP models at a given grid point, while MMP is derived by calculating the percentage agreement of how often EKIs exceed a certain EKI threshold for moderate-or-greater (MOG)-level turbulence among seven EKIs based on different TIGGE model outputs at a given grid point. Three EKI thresholds based on the 95th-, 98th-, and 99th-percentile values of each of the seven EKI probability density functions are tested to represent better reliability and spread of the MMP. The performance skills of MMEM and MMP are validated based on the probability of detection method and reliability test, respectively, against turbulence observations from pilot reports and in-situ flight eddy dissipation rate (EDR) data. In the validation result of deterministic forecasts, the MMEM has better performance skills than any single-model-based EKI forecasts. In the validation result of probabilistic forecasts, all MMPs show an over-forecasting, although with better reliability when applying a higher-percentile of EKI values as a threshold.
Impact of flow conditions on pore-scale solute mixing: experiments in heterogeneous 2D porous media
Authors: Borgman Oshri , Régis Turuban , Géraud Baudouin , Tanguy Le Borgne , Yves Méheust
Published: March 2021

Solute mixing mediated by flow in porous media plays a significant role in controlling reaction rates in subsurface environments. In many practical cases, incomplete mixing—inhomogeneous solute concentrations—occurs at the pore-scale, limiting local and thus upscaled reaction rates, and renders their prediction based on effective dispersion coefficients derived from dispersion models (or by assuming Taylor-Aris dispersion) inaccurate. We perform solute transport experiments in transparent, quasi-two-dimensional, soil analog models to investigate the relationships between pore-scale solute dispersion and mixing under different flow conditions. We use Fluorescein as a conservative tracer and record its fluorescence intensity in monochrome images at fixed time intervals. We convert the fluorescence intensity to solute concentration fields based on a calibration curve obtained with various homogeneous solute concentrations and subsequently compute concentration gradients. Our images provide evidence for incomplete mixing at the pore-scale and show strong gradients transverse to the overall flow direction. We fit the mean longitudinal concentration profile to an analytical solution of the advection-dispersion equation and compute the effective longitudinal dispersion coefficient. Based on the lamellar mixing theory, we also infer an effective diffusion coefficient relevant to the mean concentration gradient’s dynamics. By comparing these two diffusion/dispersion coefficients in saturated flow conditions, we show that while their values are similar at low Péclet, their scaling behaviors as a function of Péclet are different. Hence, as pointed out by several previous studies, modeling reactive transport processes requires accounting for a mixing behavior driven by a diffusive process that cannot entirely be described by the solute dispersion coefficient. We extend this work by varying the saturation degree in the experiments and our samples' structural heterogeneity to investigate how flow desaturation and porous medium structure impact solute mixing.