bluuebunny/crossref_metadata_2025 huggingface dataset:
Wind-driven Oscillations in the Meridional Overturning Circulation near the equator
Authors: Blaker Adam , Bell Michael , Hirschi Joel , Bokota Amy
Published: March 2021

Numerical model studies have shown the meridional overturning circulation (MOC) to exhibit variability on near-inertial timescales, and also indicate a region of enhanced variability on the equator. We present an analysis of a set of integrations of a global configuration of a numerical ocean model, which show very large amplitude oscillations in the MOCs in the Atlantic, Indian and Pacific oceans confined to the equatorial region. The amplitude of these oscillations is proportional to the width of the ocean basin, typically about 100 (200) Sv in the Atlantic (Pacific). We show that these oscillations are driven by surface winds within 10°N/S of the equator, and their periods (typically 4-10 days) correspond to a small number of low mode equatorially trapped planetary waves. Furthermore, the oscillations can be well reproduced by idealised wind-driven simulations linearised about a state of rest. Zonally integrated linearised equations of motion are solved using vertical normal modes and equatorial meridional modes representing Yanai and inertia-gravity waves. Idealised simulations capture between 85% and 95% of the variance of matching time-series segments diagnosed from the NEMO integrations. Similar results are obtained for the corresponding modes in the Atlantic and Indian Oceans. Our results raise questions about the roles of inertia-gravity waves near the equator in the vertical transfer of heat and momentum and whether these transfers will be explicitly resolved by ocean models or need to be parametrised.
Variability of the aerosol content in the tropical lower stratosphere from 2013 to 2019 as influenced by moderate volcanic eruptions
Authors: Tidiga Mariam , Berthet Gwenaël , Jegou Fabrice , Bossolasco Adriana , Kloss Corinna , Bègue Nelson , Renard Jean-Baptiste , Vernier Jean-Paul , Clarisse Lieven , Taha Ghassan , Portafaix Thierry , Metzger Jean-Marc , Payen Guillaume
Published: March 2021

The cumulative impacts of frequent moderate-magnitude eruptions on stratospheric aerosols were identified among the factors in recent decadal climate trends. Moderate volcanic eruptions are a recurrent source of sulfur dioxide (SO2) in the Upper Troposphere and Lower Stratosphere (UTLS) region and the resulting formation of sulfuric acid aerosol particles from the SO2 emitted provides sites for chemical reactions leading to enhancement of stratospheric optical depth (SAOD) and ozone depletion. Modelling properly the volcanic aerosol content and its evolution in this region is important for radiative impact issues. In this work, we explore the variability of the tropical UTLS aerosol content between 2013 and 2019, a period which was particularly impacted by moderate tropical and mid-latitude volcanic eruptions. For that purpose, space-borne observations from OMPS (version 2, datasets from GES DISC), and IASI, together with simulations by the Whole Atmosphere Community Climate Model (WACCM) coupled with the Community Aerosol and Radiation Model for Atmospheres (CARMA), are used. Different model sensitive experiments, particularly for the injection altitude and timing, have been conducted to evaluate how the model captures the aerosol plume in terms of content, optical and microphysical properties, transport and residence time. We find that the decay of the Calbuco and Kelud plumes observed by OMPS version 2 is well reproduced by the model. Comparisons with unique datasets in the tropical southern hemisphere from the NDACC Maïdo observatory (Reunion Island, France, 20.5°S, 55.5°E) show good agreement between the lidar SAOD observations and WACCM-CARMA SAOD simulations although we observe a difference in the altitude of the maximum aerosol concentration between the model and the in situ profile after Calbuco eruption in April 2015. A particular focus is also made on recent eruptions like Raikoke, Ambae and Ulawun. The plume of the Ambae volcano (15°S, 167°E) which erupted in July 2018 is shown to propagate to the northern hemisphere with some influence until summer 2019 in the Asian monsoon region. For the year 2019, we investigate how the Ulawun (5°S, 151°E; ~0.14 Tg of SO2) tropical eruption and the Raikoke mid-latitude eruption (48°N, 153°E; ~1.5Tg of SO2), have influenced the aerosol burden in the tropics.
Disintegration of the K1 internal tide in the South China Sea due to parametric subharmonic instability
Authors: Liu Kun , Zhao Zhongxiang
Published: March 2021

The disintegration of the equatorward-propagating K1 internal tide in the South China Sea (SCS) by parametric subharmonic instability (PSI) at its critical latitude of 14.52ºN is investigated numerically. The multiple-source generation and long-range propagation of K1 internal tides are successfully reproduced. Using equilibrium analysis, the internal wave field near the critical latitude is found to experience two quasi-steady states, between which the subharmonic waves develop constantly. The simulated subharmonic waves agree well with classic PSI theoretical prediction. The PSI-induced near-inertial waves are of half the K1 frequency and dominantly high modes, the vertical scales ranging from 50 to 180 m in the upper ocean. From an energy perspective, PSI mainly occurs in the critical latitudinal zone from 13–15ºN. In this zone, the incident internal tide loses ~14% energy in the mature state of PSI. PSI triggers a mixing elevation of O(10-5–10-4 m2/s) in the upper ocean at the critical latitude, which is several times larger than the background value. The contribution of PSI to the internal tide energy loss and associated enhanced mixing may differ regionally and is closely dependent on the intensity and duration of background internal tide. The results elucidate the far-field dissipation mechanism by PSI in connecting interior mixing with remotely generated K1 internal tides in the Luzon Strait.
Aerosol characterization in an oceanic context around Reunion island (AEROMARINE field campaign)
Authors: Mascaut Faustine , Pujol Olivier , Brioude Jérôme , Verreyken Bert , Peroni Raphaël , Blarel Luc , Podvin Thierry , metzger Jean-Marc , Sellegri Karine , Goloub Philippe
Published: March 2021

We present the results of the AEROMARINE field campaign which took place in the boreal spring 2019 off the coast of Reunion island in the South West Indian Ocean basin. The southern Indian Ocean is of major interest for the study of marine aerosols, their distribution and variability [1]. Nine instrumented light plane flights and a ground-based microwave radiometer were used during the AEROMARINE field campaign. These measurements were compared with the long-term measurements of the AERONET sun-photometer (based in Saint Denis, Reunion Island) and various instruments of the high altitude Maido Observatory (2200m above sea level, Reunion island). These results were analyzed using different model outputs: (i) the AROME mesoscale weather forecast model to work on the thermodynamics of the boundary layer, (ii) the FLEXPART-AROME Lagrangian particle dispersion model to assess the geographical and vertical origin of air masses, and (iii) the chemical transport model CAMS (Copernicus Atmosphere Monitoring Service) to work on the aerosol chemical composition of air masses. These measurements allowed us to determine the background concentration of natural marine aerosols and to highlight that (1) the atmospheric layers above 1500m are in the free troposphere and are mainly composed of aerosols from the regional background and (2) that the local environment (ocean or island) has little impact on the measured concentrations. Marine aerosols emitted locally are mostly measured in the lower atmospheric layers (below 500m). The daytime marine aerosol distributions in the free troposphere measured by the aircraft were compared to the aerosol distribution measured at the high altitude Maido observatory at night when the observatory is located in the free troposphere.  We also found that the CAMS reanalyses overestimated the aerosol optical depth in this region. Finally, our study confirms, with no ambiguity, that the AERONET station in Saint Denis (Reunion island) can be considered as a representative marine station in the tropics [2]. 

References
[1]  I.  Koren,  G.  Dagan,  and  O.  Altaratz.   From  aerosol-limited  to  invigoration  of  warm  convective clouds. Science, 344 (6188) : 1143–1146, 2014.
[2]  P. Hamill, M. Giordano, C. Ward, D. Giles, and B. Holben.  An aeronet-based aerosol classification using the mahalanobis distance. Atmospheric Environment, 140 : 213–233,2016.
How to deliver information on induced seismicity to the authorities and general public? 
Authors: Junno Niina , Bäcklund Pia , Tuomisaari Johanna , Oinonen Kati , Veikkolainen Toni , Korja Annakaisa , Working Group Seismic Risk
Published: March 2021

Alternative, carbon-free energy sources are essential to regulate the global climate crisis. Geothermal energy – i.e., heat harvested by geothermal systems by drilling geothermal wells to circulate water in a fractured hot rock mass at the depth of 1-7 km – has a huge potential as an environmentally friendly carbon-free energy source. One of the drawbacks is that geothermal systems can induce small-magnitude earthquakes that pose seismic risk to critical sensitive infrastructure. SEISMIC RISK - Mitigation of induced seismic risk in urban environments -project focuses on how to evaluate, mitigate and communicate seismic hazard and risk in an urban environment. Some of the associated challenges are the unclear regulatory, administrative and policy processes and unclear roles of the different actors. Another problem concerns defining what constitutes relevant information and how it should be disseminated to the public.

One part of the project is to carry out interviews of stakeholders (energy companies, municipalities and state authorities) on, how they perceive the current situation. These will give information on 1) the extent to which different actors have a common understanding of the situation and potential risks, 2) who should be responsible for coordinating risk management, and 3) how citizens should be informed of potential risks and should they be able to participate in location decisions of such geothermal power plants. Another part of the project is focusing on, how social media can better be used for rapid communication of induced seismic events and for the gathering of observations. Currently social media (Twitter) is already used for rapid notification of seismic events to the public. Gathering of macroseismic observations is handled online.
Using machine learning techniques to predict beaching of marine debris on the Galapagos Islands
Authors: Ypma Stefanie , Kaandorp Mikael , Jones Jen , Donnelly Andy , van Sebille Erik
Published: March 2021

The Galapagos Archipelago and the Galapagos Marine Reserve host one of the world’s most unique ecosystems. Although being a UNESCO world heritage site and being isolated from any dense population, over 8 tonnes of plastic are collected on the islands each year. To decrease the impact of plastic waste in the region, scientific evidence is needed on the sources and fate of the marine debris. Here, we will assess the skill of machine learning techniques to predict beaching events on these islands. In order to do so, we combine various hydrodynamic fields from ocean-, wave-, wind- and tide-models using the OceanParcels particle tracking framework to track virtual particles through the marine reserve. In addition, a beaching parameterization has been developed and implemented to quantify where and when virtual particles wash ashore. The results show that the particle pathways and beaching probabilities strongly depend on the dry and wet seasons characteristic for the Galapagos Islands. 

Therefore, it is expected that the beaching events can to some extent be predicted from the forecasts of currents, tides and waves - without performing a Lagrangian simulation. To test this hypothesis, PCA analysis and random forests are applied to a set of over 100 variables and their skill to explain the beaching variability given by the particle model is determined. In addition, the results are compared to a timeseries of observed beached litter on one of the Island of San Cristobal to apply the models in a realistic case study. This work, in combination with a growing observational data set, will form the basis of a predictive model that will support the Galapagos National Park in their efforts to free the Galapagos Archipelago from marine debris.
Nonlocal soil moisture effects during European heatwaves
Authors: Bohnenblust Ronja , Merrifield Anna L. , Sippel Sebastian , Simpson Isla R. , McKinnon Karen A. , Fischer Erich M. , Deser Clara , Knutti Reto
Published: March 2021

It has been shown that European heatwaves can be significantly intensified by dry land surface conditions. While local temperature intensification through soil moisture feedbacks are well understood, the role of nonlocal soil moisture conditions has yet to be studied in more detail. Studies suggest that through modification of the atmospheric circulation, soil moisture conditions can enhance local temperatures and even evoke a remote temperature response. 

In this study, we analyze how nonlocal soil moisture – atmosphere feedbacks contribute to the development of high temperature extremes during a seasonally persistent European heatwave. We use a CESM-based global circulation model framework described in Merrifield et al. (2019), in which near-identical heatwave-inducing atmospheric circulation patterns encounter different land surface conditions. In one ensemble the whole atmosphere is constrained, allowing only local temperature intensification by the land surface. In the other ensemble only the upper atmosphere is constrained, enabling the land surface to modify the atmospheric circulation below 300hPa.

To understand what variables and processes contribute to regional heatwave intensification in some members and damping in others on a daily timescale, a refined spatio-temporal analysis of the data set was performed. We find that local daily temperature spread across ensemble members amounts to 5°C in the ensemble with unconstrained lower atmosphere, which is 4°C more than in the ensemble where the whole atmosphere is constrained, highlighting the importance of nonlocal land – atmosphere interactions. We identify atmospheric pathways through which the land surface state in one region affected the intensity of the heatwave in another region during the initiation, peak, and decay phases of the event. These heatwave intensification storylines may help to inform seasonal prediction and improve preparedness for future European heat events.

 
Quasiperiodic emissions and related particle precipitation bursts observed by the DEMETER spacecraft
Authors: Nemec Frantisek , Hajoš Mychajlo , Bezděková Barbora , Santolík Ondřej , Parrot Michel
Published: March 2021

Electromagnetic waves observed in the inner magnetosphere at frequencies between about 0.5 and 4 kHz sometimes exhibit a quasiperiodic (QP) time modulation of the wave intensity with modulation periods from tens of seconds up to a few minutes. Such waves are typically termed “QP emissions” and their origin is still not fully understood. We use a large set of more than 2,000 of these events identified in the low-altitude DEMETER spacecraft data to analyze how the wave properties (modulation period, intensity) depend on relevant controlling factors. Moreover, in-situ measurements of energetic electron precipitation are used to check for precipitation peaks matching the individual QP elements. We successfully identified several such events and we perform their detailed analysis. Most importantly, while the waves may propagate unducted across L-shells, the precipitating particles follow magnetic field lines from the interaction region down to the observation point. They can thus be used to deduce important information about the location and spatial extent of the anticipated generation region of the emissions.
Application of an optimality-based model to operate at half-hourly timestep to implement plant acclimation within a land-surface modelling framework
Authors: Mengoli Giulia , Agustí-Panareda Anna , Boussetta Souhail , Harrison Sandy P. , Trotta Carlo , Prentice Iain Colin
Published: March 2021

Vegetation and atmosphere are linked through the perpetual exchange of water, carbon and energy. An accurate representation of the processes involved in these exchanges is crucial in forecasting Earth system states. Although vegetation has become an undisputed key component in land-surface modelling (LSMs), the current generation of models differ in terms of how key processes are formulated. Plant processes react to environmental changes on multiple time scales. Here we differentiate a fast (minutes) and a slower (acclimated – weeks to months) response. Some current LSMs include plant acclimation, even though they require additional parameters to represent this response, but the majority of them represent only the fast response and assume that this also applies at longer time scales. Ignoring acclimation in this way could be the cause of inconsistent future projections. Our proposition is to include plant acclimation in a LSM schema, without having to include new plant-functional-type-dependent parameters. This is possible by using an alternative model development strategy based on eco-evolutionary theory, which explicitly predicts the acclimation of photosynthetic capacities and stomatal behaviour to environmental variations. So far, this theory has been tested only at weekly to monthly timescales. Here we develop and test an approach to apply an existing optimality-based model of gross primary production (GPP), the P model, at the sub-daily timestep necessary for use in an LSM, making an explicit differentiation between the fast and slow responses of photosynthesis and stomatal conductance. We test model performance in reproducing the diurnal cycle of GPP as recorded by flux tower measurements across different biomes, including boreal and tropical forests. The extended model requires only a few meteorological inputs, and a satellite-derived product for leaf area index or green vegetation cover. It is able to manage both timescales of acclimation without PFT-dependent photosynthetic parameters and has shown to operate with very good performance at all sites so far investigated. The model structure avoids the need to store past climate and vegetation states. These findings therefore suggest a simple way to include both instantaneous and acclimated responses within a LSM framework, and to do so in a robust way that does not require the specification of multiple parameters for different plant functional types.
Deriving Nitrogen Oxide emissions from inland waterway vessels using MAX-DOAS measurements
Authors: Lukosiunaite Simona , Dörner Steffen , Donner Sebastian , Lauster Bianca , Beirle Steffen , Remmers Julia , Wagner Thomas
Published: March 2021

Inland waterway shipping is an important mode of freight transport in Europe with an extended network especially in Germany, e.g. the Rhine and Danube Rivers, and a variety of artificial channels. Nitrogen oxides (NOx = NO + NO2), which are also emitted by ships, play an important role in tropospheric chemistry. NOx contributes to the formation of tropospheric ozone and thus photochemical smog. Moreover, NOx affects human health and increases the acidification of ecosystems.  Monitoring of NOx emissions from inland waterway vessels could provide cities that are located along the rivers with valuable information about ship contribution to the pollution.

In this study, ground-based MAX-DOAS (Multi AXis-Differential Optical Absorption Spectroscopy) measurements were performed along the Rhine River. The aim is to derive NO2 emissions from individual ships. First sensitivity measurements showed that our Tube MAX-DOAS instrument is sensitive enough to detect a NO2 signal that can be attributed to passing ships. However, finding the optimal measurement mode to determine the emissions proves to be a challenging endeavour.
Scaling of extreme precipitation records in Antarctica from 1 day to 2 years
Authors: Gonzalez Sergi , Vasallo Francisco
Published: March 2021

Extreme weather records are important in determining the boundaries of the atmospheric system and in determining whether the Earth’s climate is changing or becoming more extreme (Cerveny, 2007). For this reason, the WMO Commission for Climatology decided to create a database to archive and verify the world weather extreme records. Due to the lack of an extensive database of reliable precipitation measurements in Antarctica, the only continental value in this table that has yet to be determined is the greatest precipitation in the Antarctic Region (average annual), which is estimated at more 800 mm. In order to evaluate the extreme precipitation records in Antarctica, in this communication the most extreme records are determined on different timescales, from 1 day to 2 years, using the RACMO2.3p2 model reanalysis (van Wessem et al. 2014), whose evaluation indicates that it performs well concerning the precipitation estimates. Records of extreme precipitation in Antarctica are found on the west side of the Antarctic Peninsula and are likely produced by utmost atmospheric river events (Gorodetskaya 2014). Extreme precipitation records closely follow a potential scaling such as the global precipitation records (Galmarini, 2004). Extreme precipitation in Antarctica has a higher exponent, indicating that small timescales (days) have less impact with respect to the large timescales (years) in relation to the global extreme precipitation. In addition, we show the regional variability of the extreme values and scaling in Antarctica. Although the values shown in this research emanate from model simulations and are not effectively measured, they help to constrain the upper limit of the maximum annual precipitation on the continent to well above one thousand millimeters.

 

References

Cerveny, R. S., Lawrimore, J., Edwards, R., & Landsea, C. (2007). Extreme weather records: Compilation, adjudication, and publication. Bulletin of the American Meteorological Society, 88(6), 853-860.

Galmarini, S., Steyn, D. G., & Ainslie, B. (2004). The scaling law relating world point‐precipitation records to duration. International Journal of Climatology: A Journal of the Royal Meteorological Society, 24(5), 533-546.

Gorodetskaya, I. V., Tsukernik, M., Claes, K., Ralph, M. F., Neff, W. D., & Van Lipzig, N. P. (2014). The role of atmospheric rivers in anomalous snow accumulation in East Antarctica. Geophysical Research Letters, 41(17), 6199-6206.

Van Wessem et al., 2014. Improved representation of East Antarctica surface mass balance in a regional climate model. J. Glac., 60(222), 761-770

 
IFPICS: Combining the advantages of hyperspectral imaging and filter cameras for trace gas imaging
Authors: Nies Alexander , Fuchs Christopher , Kuhn Jonas , Bobrowski Nicole , Platt Ulrich
Published: March 2021

Imaging of atmospheric trace gases in the UV and visible wavelength range provides insight into the spatial distribution of physical and chemical processes in the atmosphere. Instruments for this purpose ideally combine a high spatio-temporal resolution with a high trace gas selectivity. In addition, they have to be built robust and compact for field measurements.

Atmospheric trace gas remote sensing by Differential Optical Absorption Spectroscopy (DOAS) is common and allows to measure several trace gases simultaneously with high selectivity and sensitivity. On the downside, image acquisition requires spatial scanning as for instance implemented in so-called hyperspectral cameras (also known as Imaging DOAS, IDOAS). This, however, results in reduced spatio-temporal resolution. Another approach to trace gas imaging is to use band pass filters, as for example in SO2 cameras, which has the benefit of fast image acquisition combined with a high spatial resolution, but this advantage comes at the expense of low spectral sensitivity. Hence, only very high trace gas abundances can be reliably quantified, and the measurement is vulnerable to broadband interferences e.g. by aerosol.

We report an imaging technique combining the IDOAS and filter-based cameras’ advantages by utilizing the periodic transmission features of a Fabry-Perot-Interferometer (FPI). The FPI is tuned to two positions, so that its transmission either correlates or anti-correlates with the approximately periodic absorption structures of the target trace gas. From the measured intensities the differential optical density and the column density of the trace gas can be obtained with a high selectivity. Compared to IDOAS (or hyperspectral cameras) we only measure two different wavelength channels, however with maximum trace gas specific information. This reduces the amount of recorded data by at least two orders of magnitude for the same measurement resolution. This can be crucial for the feasibility of field measurements.

We present a compact and field-ready Imaging-FPI-Correlation-Spectroscopy (IFPICS) prototype. The FPI settings (or different FPIs) can be adapted to detect several different trace gases, our set-ups have been optimized for sulphur dioxide (SO2), bromine monoxide (BrO) or formaldehyde (HCHO).

We anticipate from laboratory studies using scattered skylight and HCHO cuvettes a detection limit of 4.7x1016 molec cm-2 for an image of about 90x90 pixel and an integration time of 6s. Because of the similar absorption features of BrO we expect a detection limit of 1.6x1014 molec cm^-2. Additionally, an outlook on the application of BrO imaging in volcanic plumes is given.

 
First validation results of the new TROPOMI/S5P Total Column Water Vapor product using AERONET ground-based measurements
Authors: Garane Katerina , Chan Ka Lok , Koukouli Maria Elissavet , Loyola Diego , Balis Dimitris
Published: March 2021

The very important role of water vapor on the greenhouse effect makes it a species that needs to be continuously and globally monitored, as well as thoroughly studied. The TROPOMI/S5P Total Column Water Vapor (TCWV) is a new product retrieved from the blue wavelength band (435 –455nm), using an algorithm that was originally developed for GOME-2. The algorithm is based on the DOAS technic and is separately presented in this session*.

The TROPOMI/S5P TCWV product is available for the time period May 2018 to August 2020, almost 2.5 years. For the validation purposes of this work, the co-located precipitable water Level 2.0 (quality-assured) measurements from the NASA AERONET (AErosol RObotic NETwork) were used. The network uses CIMEL sunphotometers located at about 1300 stations globally to monitor precipitable water, among other products. The two datasets, satellite and ground-based, were co-located and the percentage differences of the comparisons were calculated and statistically analyzed. The correlation coefficient of the two products is found to be 0.9 and the mean bias of the relative percentage differences is of the order of 2% for the mid-latitudes and the tropics but increases close to the poles. The effect of various influence quantities, such as air mass factor, solar zenith angle, clouds and albedo are also studied.

*see the respective abstract by Ka Lok Chan (EGU21-2673)
On the interaction of interplanetary shocks and solar wind turbulence
Authors: Pitna Alexander , Šafránková Jana , Němeček Zdeněk
Published: March 2021

The propagation of collisionless shocks through the turbulent magnetized plasmas has been investigated for decades. The processes connected with the formation and propagation of Interplanetary (IP) shocks play a key role in the acceleration of particles and in the coupling to the Earth’s magnetosphere. However, many aspects of the interactions are poorly understood, e.g., the regime of turbulence in downstream/upstream medium, heating of the downstream plasma via turbulent dissipation, etc. Recently, a few authors have addressed the nature of fluctuations within the downstream regions of IP shocks and sheaths of ICMEs. In general, they have found that an IP shock enhances the fluctuation energy within the downstream plasma. Consequently, this should lead to the enhanced heating of the shocked plasma. In this study, we investigate whether the downstream region exhibits such a heating. In the analysis, we stress that the downstream region (in situ observation by a spacecraft) of an IP shock is an evolutionary record of the shocked plasma, i.e., the leading edge of a sheath is plasma that has been just shocked, while the plasma recorded 1 hour after the shock passage has been shocked roughly 5–6 hours earlier, on average. We illustrate this point investigating the relation of the enhanced levels of turbulent fluctuations by the IP shocks and the temperature evolution in the downstream plasma. Preliminary results suggest that the level of enhanced fluctuations affects the temperature profile in this region.
Study of alpha particle properties across rarefaction regions
Authors: Durovcova Tereza , Šafránková Jana , Němeček Zdeněk
Published: March 2021

Two large-scale interaction regions between the fast solar wind emanating from coronal holes and the slow solar wind coming from streamer belt are usually distinguished. When the fast stream pushes up against the slow solar wind ahead of it, a compressed interaction region that co-rotates with the Sun (CIR) is created. It was already shown that the relative abundance of alpha particles, which usually serve as one of solar wind source identifiers can change within this region. By symmetry, when the fast stream outruns the slow stream, a corotating rarefaction region (CRR) is formed. CRRs are characterized by a monotonic decrease of the solar wind speed, and they are associated with the regions of small longitudinal extent on the Sun. In our study, we use near-Earth measurements complemented by observations at different heliocentric distances, and focus on the behavior of alpha particles in the CRRs because we found that the large variations of the relative helium abundance (AHe) can also be observed there. Unlike in the CIRs, these variations are usually not connected with the solar wind speed and alpha-proton relative drift changes. We thus apply a superposed-epoch analysis of identified CRRs with a motivation to determine the global profile of alpha particle parameters through these regions. Next, we concentrate on the cases with largest AHe variations and investigate whether they can be associated with the changes of the solar wind source region or whether there is a relation between the AHe variations and the non-thermal features in the proton velocity distribution functions like the temperature anisotropy and/or presence of the proton beam.
Hybrid modeling using multivariate, discrete probability distributions 
Authors: Ehret Uwe
Published: March 2021

In this contribution, I will suggest an approach to build models as ordered and connected collections of multivariate, discrete probability distributions (dpd's). This approach can be seen as a Machine-Learning (ML) approach as it allows very flexible learning from data (almost) without prior constraints. Models can be built on dpd's only (fully data-based model), but they can also be included into existing process-based models at places where relations among data are not well-known (hybrid model). This provides flexibility for learning similar to including other ML approaches - e.g. Neural Networks - into process-based models, with the advantage that the dpd's can be investigated and interpreted by the modeler as long as their dimensionality remains low. Models based on dpd's are fundamentally probabilistic, and model responses for out-of-sample situations can be assured by dynamically coarse-graining the dpd's: The farther a predictive situation is from the learning situations, the coarser/more uncertain the prediction will be, and vice versa.

I will present the main elements and steps of such dpd-based modeling at the example of several systems, ranging from simple deterministic (ideal spring) to complex (hydrological system), and will discuss the influence of i) the size of the available training data set, ii) choice of the dpd priors, and iii) binning choices on the models' predictive power.
Basin-scale evaporation rate estimation based on isotopic approach: adaptation to the Mediterranean conditions
Authors: Mattei Alexandra , Huneau Frédéric , Garel Emilie , Santoni Sebastien , Vystavna Yuliya
Published: March 2021

Being a proxy for water stress monitoring and as a key element of sustainable water management, evaporation helps to assess the vulnerability of Mediterranean ecosystems to droughts. Estimation of annual basin-scale evaporation rate can be done using cost-effective isotope mass balances approaches that exploit the integrative nature of the river isotopic signal.

In Mediterranean regions, the marked climatic seasonality and uneven precipitation distribution complicates the use of isotope mass balances to obtain basin-scale estimation of average evaporation rates. For example, a mass balance approach carried out on the Tavignanu River watershed in Corsica (France), showed unrealistic evaporation rate estimates of 10% for 2017-2018 and 1% for 2018-2019. These results suggest that not only does evaporation alter the seasonal isotopic composition in the river, but that there is a complex variability of the dominant water reservoirs contributing to the streamflow. Therefore, we propose a modified mass balance approach that includes monthly contribution of the different water sources to the river discharge. This allows the discrimination of isotopic variation occurring by evaporation from that originating by mixing processes. By applying this modified approach, we estimated evaporation rates on the Tavignanu River watershed that were in good agreement with results obtained by hydrological modelling: 40% for 2017-2018 and 46% for 2018-2019, respectively.

The proposed approach can be used to determine evaporation rates in river basins in other semi-arid climates where estimating evaporation is of major concern for water management. More generally, these results should encourage investigations of details in water source contributions to river flow prior to conducing isotope mass balance evaporation estimates. Consequences are expected in several research fields where the portioning of evapotranspiration into components is of interest, including hydrology (e.g. water budget estimations), ecology (e.g. carbon budget estimations) and climatology.

 
The GCRF Living Deltas Hub: using water quality monitoring and lived experiences to achieve the UN Sustainable Development Goals 
Authors: Roberts Lucy R. , Moorhouse Heather L. , Truong Oanh , Nguyen Thanh Phong , McGowan Suzanne , Panizzo Virginia N. , Barker Phillip , Do Nga T. , Rahman Feisal M.F. , Salgado Jorge , Ghosh Tuhin , Das Sourav , Salehin Mashfiquas , Amin Chowdhury Ahmed Ishtiaque , Henderson Andrew C.G. , Large Andrew R.G.
Published: March 2021

The Living Deltas Hub is a UKRI GCRF-funded community investigating the environmental, societal, and natural-cultural heritage of three South and Southeast Asian mega-deltas; the Ganges-Brahmaputra-Meghna delta spanning India and Bangladesh, and the Mekong Delta and Red River Delta of Vietnam. Globally, deltas occupy only 1% of the total land area, but support the livelihoods of ~500 million citizens. As a consequence of growing human populations and intensified anthropogenic activity these deltas face multiple challenges, such as eustatic sea level rise, land subsidence, saline intrusion, unsustainable extraction of natural resources, habitat loss, pollution, and are currently on a trajectory towards collapse. The waterscape of the deltas place SDG 6 (clean water and sanitation) at the heart of sustainable development. Thus, the Hub aims to quantify and assess human impacts on the water quality of major river channels, canals, and ponds by establishing catchment-wide water quality monitoring supplemented by historical data, biomonitoring networks, community science projects (including water quality and participatory GIS) and local knowledge of water quality. This will result in improved understanding of the impacts of the multi-functionality of water sources in Asian mega-deltas from basic domestic use (bathing and drinking water) up to industrial scale aquaculture, and can lead to the success of SDG 6 (clean water), SDG 3 (good health and wellbeing), SDG 2 (zero hunger – here, through sustainable aquaculture), and SDG 14 (life below water). In addition, the combined methodology of water quality monitoring and understanding lived experiences can be used to identify the concerns of local communities, identify inequalities in the access to safe water (working towards SDG 10 reduced inequalities) and understand the female experience (working towards SDG 5 gender inequality). Using a literature review of pond water quality and use in the delta regions and data from household surveys conducted in three regions of the Mekong Delta (Ben Tre, An Giang and Can Tho), we will use ponds as a case study to demonstrate how this approach can be used to improve understanding of community access to safe water. 

 
Explicit landslide characterization using high-resolution and multi-trajectory airborne UAVSAR data
Authors: Hu Xie , Bürgmann Roland , Fielding Eric , Handwerger Alexander
Published: March 2021

The spatial resolution and deformation-mapping capability of SAR remote sensing fit into the scope of scientific investigations of landslides that move slowly at millimeters to meters per year. The SAR technique has become an efficient tool to detect, monitor and characterize slow-moving landslides. However, north-south motions are nearly unresolvable for the present-day, spaceborne, polar-orbiting and side-looking Interferometric SAR (InSAR) line-of-sight (LOS) mapping systems, and unstable slopes may often not face favorable directions of SAR satellites. In addition, a complete 3D displacement field cannot be obtained with only two distinct InSAR LOS measurements from ascending and descending satellite orbits. Arbitrary assumptions such as simply no north-south motions or constraints imposed by topographic gradients can provide a quasi-3D displacement estimate, yet this is subject to large bias. The Uninhabited Aerial Vehicle SAR (UAVSAR) is an airborne SAR system deployed by NASA/JPL that can acquire measurements along user-specified flight paths. UAVSAR operates with an L-band wavelength (0.24 m) and the single-look pixel spacings along the azimuth and the range directions are as small as 0.6 m and 1.67 m, respectively. Here we will focus on the contributions of UAVSAR and satellite SAR systems to studying the Slumgullion landslide in Colorado, USA with persistent movements at 1-2 cm/day, and even slower-moving landslides (cm to m per year) in the San Francisco East Bay Hills and the Eel River catchment in California, USA. As a complement to InSAR LOS measurements, the high-resolution UAVSAR data and appreciable velocity at a level of m/yr (e.g., Slumgullion landslide and numerous Eel River landslides) make it possible to extract motions by tracking pixel offsets in both azimuth and LOS directions. The flexible trajectory of the aircraft and the additional information from UAVSAR’s sub-meter resolution and multiple flight trajectories allows for an optimal 3D displacement solution, which can be further used for quantitative analysis of the formation of morphological structures, landslide-fault interactions, inferring rheology, understanding slope channel modulation, and capturing the spatiotemporally dependent sensitivity to hydroclimatic variability. New knowledge gained on the precipitation thresholds, landslide volume, and the identification of potential nucleation zones of slope failures will directly assist landslide hazard mitigation and reduction.
Simulation of hydrocarbon generation and expulsion for the dark mudstone with Type-Ⅲ kerogen in the Pinghu Formation of Xihu Sag in East China Sea Shelf Basin
Authors: Xu Chenjie
Published: March 2021

In order to finely describe the hydrocarbon generation and expulsion process of source rocks and provide reasonable key parameters for quantitative evaluation of oil and gas resources, we carried out a simulation research under semi-open system on hydrocarbon generation and expulsion for the dark mudstone with Type-Ⅲ kerogen in the Eocene Pinghu Formation in the Xihu Sag, East China Sea Shelf Basin. The results show that the process of hydrocarbon generation and expulsion can be divided into five stages as follows:

Ro = 0.5%~0.7%, oil was generated slowly without expulsion;

Ro = 0.7%~1.0%, oil was generated and expelled rapidly;

Ro = 1.0%~1.5%, oil began to be cracked into hydrocarbon gas;

Ro = 1.5%~2.3%, gas generation predominated;

Ro > 2.3%, only dry gas was generated.

Oil expulsion threshold (Ro) of the source rock of this type is about 0.7% (Ro = 0.7%), having a wide gas-window of Ro = 1.0%~3.0%. So it can maintain relatively strong gas generation ability at high- and over-mature stages, belonging to gas-prone source rock. Following the study on experimental results and the characteristics of hydrocarbon generation and expulsion in samples, we established a set of mathematical models for the evaluation of the process and potential of gas generation and oil generation and expulsion of the dark mudstone with Type-Ⅲ kerogen in the study area. Compared with the thermal simulation experiment in a closed system, the cumulative yield of oil in the semi-open system is higher and closer to that under actual geological conditions. Accordingly, we may conclude that more oil and gas resources may exist in the Xihu Sag.
Improving Arctic Sea Ice Prediction Though Freeboard Assimilation
Authors: Sievers Imke , Rasmussen Till , Stenseng Lars
Published: March 2021

With the presented work we aim to improve sea ice forecasts and our understanding of Arcitc sea ice formation though freeboard assimilation. Over the last years understanding Arctic sea ice changes and being able to make a reliable sea ice forecast has gained in importance. The central roll of Arctic sea ice extent in climate warming makes it a highly discussed topic in the climate research community. However a reliable Arctic sea ice forecast both on short term to seasonal time scales remains a challenge to be mastered, hinting that there are still many processes at play to be better understood.
One promising approach to improve forecasts has been to assimilate satellite sea ice data into numerical sea ice models. Mainly two parameters measured by satellites have been used for assimilation: Sea ice concentration, which is competitively easy to obtain from satellites measuring passive microwave emissions as for example obtained by the SMOS satellite, and sea ice thickness, which is not directly measured, but has to be calculated from surface elevation measurements, as for example obtained by Cryosat 2. Compering the skill, of assimilation products using sea ice thickness and sea ice concentration shows that sea ice thickness has a longer memory and is over all leading to a better performance then sea ice concentration assimilation. Knowing this, sea ice thickness assimilation is far from being straight forward. Surface elevation measurements, obtained from satellite altemitry measurements, have to be separated into snow and ice freeborad, by assuming a snow thickness, to derive sea ice thickness from. Most of the time this is done using a snow thickness climatology obtained from Soviet drift stations measuring snow over multi year ice during the period 1954-1991 with adaption over first year sea ice, where this climatology has proven to be overestimating snow thickness. The technique is widely used jet known to introduce an error.
To avoid errors caused by wrongly assumed snow covers the DMI and Aalborg University and DTU are at the moment collaborating on assimilating freebord instead of sea ice thickness into the CICE-NEMO modeling frame work using LARS NGen (LARS the Advanced Retracking System, Next Generation) sate of the art retracing software. In the presented work we will show first results of freeboard assimilation with a focus how this assimilation influences winter sea ice formation as well as the upper Arctic Ocean dynamics.
How Well Does Grain Boundary Sliding Represent Densification Rates in the Upper Firn?
Authors: Schultz Timm , Humbert Angelika , Müller Ralf , Gross Dietmar
Published: March 2021

The simulation of firn densification, although first models were already developed in the 1960s, is still a work in progress. Various models and variants of earlier models developed throughout the decades testify for this (e.g. Lundin et al. 2017, Stevens et al, 2020). Here we focus on the first stage of firn densification up to the density of 550 kg m−3, hence the first few meters of the firn column. Describing the early stage of the process well is crucial as it proceeds fastest and influences further densification. Alley first applied the process of grain boundary sliding to firn in 1987 and thereby provided a physics based material model for the densification of firn at low densities. Despite being used in many firn densification models, it is sometimes debated if grain boundary sliding is governing the densification at low densities as there are very few observations of intra-crystalline deformation in firn.

We aim to test to which extent grain boundary sliding can be used to reproduce measured firn density profiles and to constrain the parameter range in the constitutive relation. To this end, we conduct a high number of simulations for various locations, stepping through the parameter space and select the best match with corresponding measured density profiles. By doing so, we are following Alley’s original approach, but we make use of a much larger firn density dataset provided by the SUMup working group (Koenig & Montgomery, 2020).

Forcing data provided by the regional climate model RACMO (van Wessem et al., 2014, Noël et al., 2015) allows not only to simulate steady state solutions but transient simulations. Our model implementation provides a very fast, complete and flexible simulation environment, allowing to test wide parameter ranges in short time and hence enables us to cover a great amount of firn properties. The broad testing approach allows to evaluate if and in which ways grain boundary sliding might play a role in firn densification at low densities.
Using Satellite Altimeter and SST Observations of the 1997-1998 El Nino to Check the Key Ocean Processes Involved in a Strong El Nino.
Authors: Webb David , Coward Andrew , Snaith Helen
Published: March 2021

A recent high-resolution ocean model study of the strong El Ninos of 1982-1983 and 1997-1998 highlighted a previously neglected ocean mechanism which was active during their growth.   The mechanism involved a weakening of both the Equatorial Current and the tropical instability eddies in mid-ocean.  It also involved an increase in the strength of the North Equatorial Counter Current due to the passage of the annual Rossby wave.

      This presentation reports how satellite altimeter and satellite SST data was used to validate the model results the key areas, confirming the changes in the current and eddy fields and the resulting eastward extension of the region of highest SST values.  The SST changes were sufficient to trigger new regions deep-atmospheric convection and so had the potential to have a significant impact on the development of the El Nino and the resulting changes in the large scale atmospheric circulation.