bluuebunny/crossref_metadata_2025 huggingface dataset:
Long-term Variations in Ozone Levels over Beijing: Observations and Model Simulations
Authors: Zhang Yuli , Tao Mengchu , Zhang JinQiang , Liu Yi , Chen Hongbin , Cai Zhaonan , Konopka Paul
Published: March 2020

Tropospheric ozone is a major pollutant and a short-lived greenhouse gas and has therefore attracted much concern in recent years. The ozone concentration in the troposphere and lower stratosphere over Beijing has been observed since 2002 by ozonesondes developed by the Institute of Atmospheric Physics. We used these balloon-based observations to analyze the long-term variability of ozone over Beijing during the whole period from 2002 to 2018. The ozonesondes measured increasing concentrations of ozone from 2002 to 2012 in both the troposphere and lower stratosphere. There was a sudden decrease in observed ozone between 2011 and 2012. After this decrease, the increasing trend in ozone concentrations slowed down, especially in the mid-troposphere, where the positive trend became neutral. We used the Chemical Lagrangian Model of the Stratosphere (CLaMS) to determine the influence of the transport of ozone from the stratosphere to the troposphere on the observed ozone profiles. Because there is no tropospheric chemistry in CLaMS, the sudden decrease simulated by CLaMS indicates that a smaller downward transport of ozone from the stratosphere after 2012 may explain a significant part of the observed decrease in ozone in the mid-troposphere and lower stratosphere. However, the influence of stratospheric ozone in the lower troposphere is negligible in CLaMS and the hiatus in the positive trend after 2012 can be attributed to a reduction in ozone precursors as a result of stronger pollution control measures in Beijing.
Probing the oceanic upper mantle using M2 tidal magnetic field, waveform tomography, satellite gravity field, surface elevation and heat flow data
Authors: Martinec Zdenek , Fullea Javier , Velimsky Jakub
Published: March 2020

Conventional methods of seismic tomography, surface topography and gravity data analysis constrain distributions of seismic velocity and density at depth, all depending on temperature and composition of the rocks within the Earth. WINTERC-grav, a new global thermochemical model of the lithosphere-upper mantle constrained by state-of-the-art global waveform tomography, satellite gravity (geoid and gravity anomalies and gradiometric measurements from ESA's GOCE mission), surface elevation and heat flow data has been recently released. WINTERC-grav is based upon an integrated geophysical-petrological approach where all relevant rock physical properties modelled (seismic velocities and density) are computed within a thermodynamically self-consistent framework allowing for a direct parameterization of the temperature and composition variables. In this study, we derive a new three dimensional distribution of the electrical conductivity in the Earth's upper mantle combining WINTERC-grav's thermal and compositional fields along with laboratory experiments constraining the conductivity of mantle minerals and melt. We test the derived conductivity model over oceans by simulating a tidally induced magnetic field. Here, we concentrate on the simulation of M2 tidal magnetic field induced by the ocean M2 tidal flow that is modelled by two different assimilative barotropic models, TPXO8-atlas (Egbert and Erofeeva, 2002) and DEBOT (Ein\v spigel and Martinec, 2017). We compare our synthetic results with the M2 tidal magnetic field estimated from 5 years of Swarm satellite observations and CHAMP satellite data by the comprehensive inversion of Sabaka et al. (2018).
Impact of the low/high Alfven Mach number regime of the solar wind on the Aflven transition Layer of the cusp for IMF North: 3D global PIC simulation.
Authors: Cai DongSheng , Lembege Bertrand
Published: March 2020

 CLUSTER experimental observations of  Lavraud et al. (2005) have evidenced the presence of a particular layer (so –called herein Alfven Transition Layer or ATL) almost adjacent to the upper edge of the stagnant exterior cusp (SEC), through which the plasma flow transits from super-(from magnetosheath) to sub- (to SEC) Alfvenic regime as the interplanetary magnetic field (IMF) is northward. Three dimensional globa PIC simulations have been recently used  (Cai et al., 2015) to analyze the main features of the cusp for an IMF configuration similar that in the observations. These simulations have allowed us to complete the global view of the cusp region  (in particular the features not accessible by MHD approach).  A  detailed analysis has allowed to retrieve the features of the ATL which reveals to be associated to the complicated 3D particles entry into the cusp region and exhibit an internal conic depletion region (CDR) where the ion fluxes concentrate and are very strong (which suggests very local ion precipitation). Moreover, simulation results show that the ATL expands towards areas out and even far from the cusp region and outside the meridian plane.

                     In the present work, the study is extended for different Ma regimes of the solar wind, as the IMF stays in northward  configuration. Results show the impact of this Ma variation on the 3D features of the overall magnetosphere and in particular on the cusp region, i.e. (i) on the 3D ATL structures/spatial scales, (ii) on the extension of the region surrounded by the ATL, and (iii) on the structures, the spatial scales and the dynamics of the CDR itself.

 

 
The forced response of Asian Summer Monsoon precipitation during the past 1500 years
Authors: Wang Zhiyuan , Wang Jianglin , Jia Jia , Liu Jian
Published: March 2020

Asian summer monsoon (ASM) is one of the critical elements of the global climate system, and strongly affects food production and security of most people over Asia. However, the characteristics and the forcing drivers of the ASM system at decadal to centennial time scales remain unclear. To address these issues, we report four 1500-yr long climate model simulations based on the Community Earth System Model (CESM), including full-forced run (ALLR), control run (CTRL), natural run (NAT), and anthropogenic run (ANTH). After evaluating the performances of the CESM in simulating ASM precipitation, a 10-100 bandpass filter is applied to obtain the decadal-centennial signals in ASM precipitation. The main conclusions are (1) the variation of ASM intensity shows significant decadal to centennial periodicities in the ALLR, such as ~15, ~25, ~40, and ~70 years. (2) the major spatial-temporal ASM precipitation distributions in the ALLR show an external forced mode and climate internal variability mode, respectively. (3) The leading forced mode of ASM precipitation is mainly affected by natural forcing over the past 1500 years and characterizes a meridional spatial 'tripole' mode. In the NAT (solar irradiation and volcanic eruptions), the substantial warming (cooling) over the western tropical Pacific enhances (or reduces) the SST gradient change in the tropical Pacific, and modifying the ASM rainfall distribution. Our findings contribute to better understanding of the ASM in the past, and provide implications for future projections of the ASM under global warming.
Impact of revegetation of the Loess Plateau of China on the regional growing season water balance
Authors: Guo Weidong , Pitman Andrew , Ge Jun , Zan Beilei , Fu Congbin
Published: March 2020

To resolve a series of ecological and environmental problems over the Loess Plateau, the was initiated at the end of 1990s. Following the conversion of croplands and bare land on hillslopes to forests, the Loess Plateau has displayed a significant greening trend with soil erosion being reduced. However, the GFGP has also affected the hydrology of the Loess Plateau which has raised questions whether the GFGP should be continued in the future. We investigated the impact of revegetation on the hydrology of the Loess Plateau using high resolution simulations and multiple realisations with the Weather Research and Forecasting (WRF) model. Results suggests that land cover change since the launch of the GFGP has reduced runoff and soil moisture due to enhanced evapotranspiration. Further revegetation associated with the GFGP policy is likely to increase evapotranspiration further, and thereby reduce runoff and soil moisture. The increase in evapotranspiration is associated with biophysical changes, including deeper roots that deplete deep soil moisture stores. However, despite the increase in evapotranspiration our results show no impact on rainfall. Our study cautions against further revegetation over the Loess Plateau given the reduction in water available for agriculture and human settlements, without any significant compensation from rainfall.
Seasonal variation of microplastics in seawater and zooplankton in Jiaozhou Bay, the Yellow Sea
Authors: Sun Xiaoxia
Published: March 2020

Plastic pollution is a globally concerning issue in marine environments. There is currently little research about the seasonal changes in microplastics in coastal areas. Here, we report a seasonal study on the concentrations and characteristics of microplastics in the surface seawater and zooplankton of Jiaozhou Bay, a typical bay in the west Yellow Sea. The concentrations of microplastics in the surface water of Jiaozhou Bay were 0.063, 0.174, 0.094, and 0.050 pieces/m3 in February, May, August and November, respectively, with an annual average concentration of 0.095 pieces/m3, a low value compared with the plastic concentrations of other coastal areas. The size of the collected microplastics ranged from 346 to 155200 μm, with an average of 5093 μm. The overall percentages of fibers, fragments and plastic foams were 29%, 55% and 16%, respectively. Fragments were the most dominant shape in four seasons. Nine plastic polymers were detected from the surface water of Jiaozhou Bay. The dominant chemical composition was polypropylene (PP), accounting for 51.04% of polymers, followed by polyethylene (PE), accounting for 26.04% of polymers. The seasonal variation of plastic characteristics in Jiaozhou Bay, including the shape, color and chemical composition, was significant. The highest concentration of plastics occurred in May and the lowest concentration of plastics occurred in November. Strong rainfall resulted in an increase in the plastic concentration in May, and winds and eddies affected the spatial distribution of plastics in Jiaozhou Bay. Focused on the dominant zooplankton groups in Jiaozhou Bay, the morphology, color, size, chemical composition and quantity of MPs in zooplankton were investigated in Jiaozhou Bay. The results showed that the MPs in zooplankton of the Jiaozhou Bay were dominated by fibers. The proportions of fiber in February, May, August and November were 91%, 88%, 89% and 88%, respectively. The average size of MPs in zooplankton was 441±2, 468±2, 576±2, and 379±4μm in the four seasons. For the 2 common zooplankton groups in the 4 seasons, the MP/zooplankton was 0.3, 0.26, 0.17, 0.19 for copepod, and 0.22, 0.19, 0.17, 0.45 for chaetognath, respectively.
Evaluating the dynamic resilience process of a regional water resource system through the nexus approach and resilience routing analysis
Authors: Liu Dedi
Published: March 2020

The increasing magnitude and frequency of undesirable events, driven by climate and anthropogenic changes, have given rise to various approaches for quantifying the resilience of regional water resource systems. However, the deficiencies of these approaches in describing linkages among subsystems and disturbance-dependent resilience have hindered the assessment and prediction of resilience in water resource management. The nexus approach enables the propagation of a disturbance to be simulated (a process called surrogate disturbance generation). An approach analogous to a unit hydrograph is developed, and resilience routing (strain flow routing), which is a novel framework and model of the dynamic resilience process, is proposed for the evaluation of a regional water resource system. The proposed framework and model are applied to the Jinghong regional water resource system. Taking a pollution event as a disturbance, the responses of the water supply, fishery and electricity subsystems are simulated to test the validity of the proposed methods. The linkages among subsystems are determined according to the sink-source dynamic using the nexus approach, and the levels of surrogate disturbance transformed from the disturbance event can be quantified by the processes of dynamic resilience evaluation. The shape of the dynamic resilience process is quantified by the parameters of unit resilience routing with disturbance independence and reflects the characteristics of the system responding to the disturbance. The proposed method helps to assess the adaptive capacity of a water system to alleviate and regulate disturbances. Furthermore, after the calibration and validation of the assumptions of linearity inherent in the method, it can also be used to predict the dynamic resilience processes of every subsystem in response to any disturbance event affecting a regional water resource system.
‘Little Ice Age’ maxima and glacier retreat in northern Troms and western Finnmark, northern Norway
Authors: Leigh Joshua , Stokes Chris , Evans David , Carr Rachel , Andreassen Liss
Published: March 2020

Glaciers are important indicators of climate change and observations worldwide document increasing rates of mountain glacier recession. Here we present ~200 years of change in mountain glacier extent in northern Troms and western Finnmark. This was achieved through: (1) mapping recent (post-1980s) changes in ice extent from remotely sensed data and (2) lichenometric dating and mapping of major moraine systems within a sub-set of the main study area (the Rotsund Valley). Lichenometric dating reveals that the Little Ice Age (LIA) maximum occurred as early as AD 1814 (±41 years), which is before the early-20th century LIA maximum proposed on the nearby Lyngen Peninsula, but younger than the LIA maximum limits in southern and central Norway (ca. AD 1740-50). Between LIA maximum and AD 1989, the reconstructed glaciers (n = 15) shrank by 3.9 km2 (39%), with those that shrank by >50% fronted by proglacial lakes. Between AD 1989 and 2018, the total area of glaciers within the study area (n = 219 in AD 1989) shrank by ~35 km2. Very small glaciers (<0.5 km2 in AD 1989) show the highest relative rates of shrinkage, and 90% of mapped glaciers within the study area are <0.5 km2 as of AD 2018.
First Results of the 2019 Algerian Magnetic Repeat Station Network
Authors: Lemgharbi Abdenacuer , Abtout Abdeslam , Hamoudi Mohamed , Bendekken Abdelhamid , Annad Fatma , Hemmi Abderrahman , Mansouri Abdallah , Aganou Ener , Allili Moussa , Mazari Anis
Published: March 2020

Abstract:

The second part of the history of the Algerian magnetic repeat station network goes back to 1989 when the new one was started with 37 stations. It was then followed by three other networks in 1993, 1997 and 2005. The first part of this history started at the beginning of the XXth and ended ca 1956.

After a 14-year break, we launched a new repeat stations network in February 2019. The number of carried out stations was increased to 51 to try to cover all the territory.

Each repeat station network consists of stations of periodically, say  5-6 years, measured of three components of the Earth's magnetic field. to try to derive the spatial distribution of the geomagnetic field of Algeria and it's secular variation. This periodicity is also very important for the need to update local as well as global geomagnetic field models such as the International Geomagnetic Reference Field (IGRF).

In this work we describe the new 2019 Algerian repeat station network. Then we will discuss the steps of the absolute measurements using two methods. The first one is called the ‘method of zero’ and the second one ‘method of residuals’. The accuracy and resolution of the instruments and data reduction used and their effect on the final results will as well be discussed. We derive the spatial distribution of the geomagnetic field, and its secular variation. Finally, we will show how local, for instance regional polynomial modeling, is the key issue.

Key words: geomagnetic repeat network, absolute measurements, zero method, residual method, magnetic maps of Algeria, secular variation.
Proposing "analogy experiment" as a sub-category of "analog experiment" in earth science
Authors: Ichihara Mie
Published: March 2020

In the earth and planetary sciences, the term "analog experiment" indicates laboratory experiments that use analog materials to investigate natural processes. Scaled experiments constitute a representative sub-category of analog experiments. They are designed to have the same dominant dimensionless parameter in the same range as the targeted natural processes. Other primary uses of analog experiments are education and outreach. Reproducing similar phenomena in front of the audience is useful in explaining the essence of the complex dynamics of natural processes. However, it is often the case that we do not fully understand the physics of the experimental systems or the targeted natural phenomena. In such cases, especially when the process is complex, it is difficult to guarantee the scaling similarity. When we take such laboratory phenomena as a research subject of earth science, we encounter critical comments about the scaling issue.

Nevertheless, I think it scientifically important to consider questions like follows. What is the mechanism of the experimental phenomena? Why the behaviors of the experiment look similar to the natural phenomena? To what extent the laboratory and the natural systems are similar. To indicate experimental studies to elucidate these questions, I would like to define "analogy experiment" as a new sub-category of analog experiments.  Some recent experiments are presented as examples.
On the Resonances and Teleconnections of the North Atlantic and Madden-Julian Oscillations
Authors: Brunet Gilbert , Martinez Yosvany , Lin Hai , Bernier Natacha
Published: March 2020

The key to better prediction of S2S variability and weather regimes in a changing climate lies with improved understanding of the fundamental nature of S2S phase space structure and associated predictability and dynamical processes. The latter can be decomposed into a finite number of relatively large-scale discrete-like Rossby waves with coherent space-time characteristics using Empirical Normal Mode (ENM) analysis. ENM analysis is based on principal component analysis, conservation laws and normal mode theories. These modes evolve in a complex manner through nonlinear interactions with themselves and transient eddies and weak dissipative processes. Within this atmospheric dynamic framework, we will discuss the teleconnections and the 35-day wave resonance of the North Atlantic Oscillation using recent diagnostics and numerical experiments.

References

Brunet, G. and J. Methven, 2018: Identifying wave processes associated with predictability across time scales: An empirical normal mode approach. Book chapter in Sub-seasonal to seasonal prediction: The gap between weather and climate forecasting. Editors A.W. Robertson and F. Vitart, Elsevier. p.1-42

Brunet, G. 1994:  Empirical normal mode analysis of atmospheric data. J. Atmos. Sci., 51, 932-952.

Lin, H., G. Brunet, and J. Derome, 2009: An observed connection between the North Atlantic Oscillation and the Madden-Julian Oscillation.  J. Climate, 22, 364-380.

Lin, H., G. Brunet and J. Derome 2007: Intraseasonal Variability in a Dry Atmospheric Model, J. Atmos. Sci., 64, 2442-2441.
Nitrate isotopic constraints on routes of nutrient supply to global ocean pycnocline
Authors: Fripiat Francois , Martinez-Garcia Aflredo , Marconi Dario , Fawcett Sarah E. , Sigman Daniel M. , Haug Gerald H.
Published: March 2020

The circulation of the ocean plays a fundamental role in restoring the surface nutrients necessary to maintain global ocean biological production. However, our quantitative understanding of the physical mechanisms that return deep-ocean water and nutrients to the upper ocean is currently limited. The nitrate isotopes are investigated here as a new data constraint on the percentage of gross water transport into the global pycnocline that derives from the Southern Ocean as opposed to the deep ocean (which we term the “pycnocline recipe”). Based on a comparison between large-scale observations of nitrate isotopes and the output of a box model, we estimate that the pycnocline recipe is 75 ± 10%; this result implies that ~ 64% of the nutrients supplied to the low latitude pycnocline pass through the Southern Ocean. Our simulations also highlight the shortcomings of a purely advective view of the ocean’s transport of water and nutrients, confirming that mixing with both the deep ocean and the Southern Ocean ventilating area are key to the exchange of water and nutrients between the pycnocline and higher-density deep and polar surface waters. Our calculations support a pure advective-diffusive balance in the deep ocean. In contrast, in the Southern Ocean, our findings provide independent evidence for the importance of air-sea fluxes of momentum and buoyancy in driving the circulation.
Potential consequences of water limitation and drought-induced tree mortality on carbon and nitrogen cycling
Authors: Solly Emily F. , Jaeger Astrid C. H. , Six Johan , Hartmann Martin
Published: March 2020

Water limiting conditions for the growth and physiology of trees as well as episodes of tree mortality triggered by drought have recently been documented in several bioregions across the world. In parallel to these major vegetation alterations, the impact of water scarcity also has prominent effects on soil processes mediated by the microbiome such as the transformation of organic matter, heterotrophic respiration, microbial uptake as well as nutrient mineralization. Although currently little explored, shifts in the interplay occurring between tree functioning and soil microbial processes may be crucial during tree mortality events and may feed back on ecosystem carbon and nitrogen cycling. We will present a multidisciplinary setup to mechanistically explore how water limitation acts synergistically on the interplay between trees and soil microorganisms, with potential consequences for ecosystem biogeochemical fluxes.

The experimental setup focusses on a key temperate forest species, Scots pine (Pinus sylvestris L.), which is currently facing high mortality rates in several inner-Alpine valleys of Europe due to drier climatic conditions during parts of the year. We make use of small scale mesocosms featuring young trees and soil collected from a drought-affected natural forest. The mesocosms are treated with different levels of water availability under controlled conditions. Plant growth and physiological changes related to water limitation are investigated in parallel to various soil properties. State-of-the-art isotopic labelling techniques are used to trace alterations in carbon and nitrogen transfers within the plant-soil-microbe continuum. We will specifically test whether extended periods of drought suppress the flux of carbon from plants to soil and lead plants to invest more in the maintenance of fine root systems. Moreover, we will follow the potential changes in the rates of decomposition, mineralization and incorporation of plant debris into soil organic matter over time and link them to potential alterations of the soil microbiota. These experimental observations will be validated by measurements in drought-affected Scots pine forests in inner-Alpine valleys. We expect the outcomes of this work to advance the fundamental understanding of the alterations occurring in the plant-soil-microbe system related to drought as well as to improve the detection of mechanisms leading to Scots pine mortality.
Energy of a tsunami in the framework of an irreversible deformation of the ocean bottom
Authors: Okal Emile , Synolakis Costas
Published: March 2020

The classic approach to tsunami simulation by earthquake sources consists
of computing the vertical static deformation of the ocean bottom due to
the dislocation, using formalisms such as Mansinha and Smylie's [1971] or
Okada's [1985], and of transposing that field directly to the ocean's
surface as the initial condition of the numerical simulation.
We look into the limitations of this approach by developing a very
simple general formula for the energy of a tsunami, expressed as the
work performed against the hydrostatic pressure at the bottom of
the ocean, in excess of the simple increase in potential energy
of the displaced water, due to the irreversibility of the process.
We successfully test our results against the exact analytical solution
obtained by Hammack [1972] for the amplitude of a tsunami generated
by the exponentially-decaying uplift of a circular plug on the ocean
bottom. We define a "tsunami efficiency" by scaling the resulting energy
to its classical value derived, e.g., by Kajiura [1963]. As expected, we
find that sources with shorter rise times are more efficient tsunami
generators; however, an important new result is that the efficiency is
asymptotically limited, for fast sources, to a value depending on the
radius of the source, scaled to the depth of the water column; as this
ratio increases, it becomes more difficult to flush the water out of
the source area during the generation process, resulting in greater
tsunami efficiency. Fortunately, this result should not affect
significantly the generation of tusnamis by mega-earthquakes.
L-band Radiometry Measurement in the Tibetan Plateau
Authors: Wen Jun , Su Zhongbo , Zheng Donghai , Wang Xin
Published: March 2020

Surface soil moisture and freeze/thaw state monitoring is essential for quantifying water and heat exchanges in cold regions, e.g. the Tibetan Plateau. L-band (1.4 GHz, 21 cm) radiometry is recognized as one of the best suitable techniques for global monitoring of soil moisture and freeze-thaw dynamics. This study reports a long term ground-based L-band radiometry measurements conducted in a seasonally frozen grassland site located in the northeastern part of the Tibetan Plateau. The ESA funded ELBARA-III radiometer is deployed in a Tibetan meadow ecosystem where a well-instrumented in-situ soil moisture and soil temperature (SMST) monitoring network was developed. The network holds 20 SMST profile measurement stations, and each station records every 15-min readings of 5TM ECH2O probes installed at soil depths of 5, 10, 20, 40, and 80 cm. The ELBARA-III radiometer has been deployed in the center of the SMST network at the beginning of 2016. The L-band radiometer is mounted on a tower with a height of 4.8m, and the antenna beam waist is about 6.5m above the surface. Brightness temperature (TB) measurements with vertical and horizontal polarizations are performed every 30 min at observation angles of 40° to 70° in steps of 5°. A sky measurement with an observation angle of 155° is performed once per day for calibration purposes next to the internal calibration sequence performed as part of every measurement run. The internal calibration adopted to derive the TB from the raw data is based on a two-point calibration strategy using a resistive load (RL) and an active cold load (ACL). A vertically dense SMST measurement profile is installed next to the radiometer tower. Concurrent measurements of micrometeorological variables are also performed in vicinity of the radiometer tower, such as solar radiation, wind speed, air temperature, air pressure, and humidity. A rain gauge and eddy-covariance system are setup in the ELBARA-III field site at the end of 2016 providing precipitation and surface heat flux measurements. Preliminary analysis of the ELBARA-III TB measurements will be given in this study.
Framboidal pyrites flourished in sulfate-methane transition zones of cored sediments in the northern South China Sea
Authors: Wang Jiasheng , Wei Qing
Published: March 2020

The diameter of framboidal pyrites was widely used as a measure of redox condition in modern and ancient sedimentary environments, the proposed critical values of average size and standard deviation of framboids are about 8μm and 3μm respectively. However, a few reports proposed that the exceptionally large size and standard deviation of framboidal pyrites in cored sediments from northeastern South China Sea is closely related to the anaerobic oxidation of methane (AOM) processes mainly dominated in sulfate-methane transition zones (SMTZ). Here we investigate the occurrence of framboidal pyrites in two cored sediments of sites SC-W02B-2017 and SC-W03B-2017 at Shenhu area during the first offshore gas hydrate production test in northern South China Sea. Combined with the statistics of size and standard deviation of framboidal pyrites, the relative concentrations and sulfur isotopic compositions of bulk pyrites, we verified that the AOM could enhance the framboidal pyrite formation. Our data show that both the size and the standard deviation of framboidal pyrite present an unusual positive excursion in cored sediment column. By interpreting the coupling occurrence of positive excursions both pyrite concentrations and sulfur isotopes, four main paleo-sulfate-methane transition zones (Paleo-SMTZ) are roughly recognized in depths around 50 meter below seafloor (mbsf), 90-100 mbsf, 135-225 mbsf and 180 mbsf, where unusual strong AOM and unusual methane releases might happened. The morphology shows most of the pyrite framboids occur in framboidal cluster with a rod-like, irregular block shape and secondary overgrowth. The size of pyrite framboids in site W02B ranges from 8.1μm to 40.1μm with maximal about 40.1μm and in site W03B from 8.6μm to 25.3μm with maximal about 101.2μm (n=2686 from 13 samples). Our data show the average size and the standard deviation of pyrite framboids are more than 20μm and 3.0μm respectively, and the higher δ34S value and larger size of framboid mainly occur near the intervals of paleo-SMTZs in marine sediment columns. Therefore, we propose again that the enhancing AOM in SMTZs could flourish the growth of pyrite framboids and enlarge the standard deviation of framboidal size, which might be implication for more precise interpretation of redox condition of sedimentary environments using framboidal pyrite diameter.
Diverse effects of climate at different times on grassland phenology in mid-latitude of the Northern Hemisphere
Authors: Ren Shilong , Li Yating , Peichl Matthias
Published: March 2020

Studying grassland phenology and its relationships to climate would deepen our understanding of vegetation-air interactions under global climate change. To date, however, our knowledge of the responses of grassland phenology to climatic factors is still limited at the continental scale. In this study, we retrieved the start (SOS) and end (EOS) of the growing season for mid-latitude (30°N~55°N) grasslands of the Northern Hemisphere during 1981-2014, and investigated their relations with previous temperature, rainfall, and snowfall (only for SOS) through trends analysis and time window analysis. Results illustrated a predominant significant advancing/delaying trend of SOS/EOS in 23.2%/20.5% of the study region. They jointly resulted in a primarily significant prolongation trend of growing season length in 22.7% of the study region. Next, a dominated negative correlation between air temperature/rainfall and SOS was found in 62.4%/57.6% of areas. Snowfall showed converse effects (positive/negative) among different grasslands. The time window opening date for air temperature to start to affect SOS was identified as the day 1-90 before the multi-year average SOS in 76.1% of areas, while the time window opening date for the effect of rainfall/snowfall on SOS was relatively evenly distributed between the 1st and 180th day before the multi-year average SOS. EOS was found to be significantly negatively/positively correlated with air temperature/precipitation in 74.8%/83.7% of areas. The time window opening date for the effect of air temperature on EOS was identified as the 90-180th day before the multi-year average EOS in 66.9% of areas, while the time window opening date for the effect of precipitation on EOS was mainly concentrated on the 60-120th day before the multi-year average EOS in 51.5% of areas. Overall, this study highlights the distinctly different time windows for the thermal-moisture effects on grassland vegetation phenology and this should be considered when establishing process-based phenological models.
SMOS-IC L-VOD reveals that tropical forests did not recover from the strong 2015–2016 El Niño event
Authors: Fan Lei , Wigneron Jean-pierre , Ciais Philippe , Bastos Ana , Brandt Martin , Chave Jérome , Saatchi Sassan , Baccini Alessandro , Fensholt Rasmus
Published: March 2020

Severe drought and extreme heat associated with the 2015–2016 El Niño event have led to large carbon emissions from the tropical vegetation to the atmosphere. With the return to normal climatic conditions in 2017, tropical forest aboveground carbon (AGC) stocks are expected to partly recover due to increased productivity, but the intensity and spatial distribution of this recovery are unknown. Simulations from land-surface models used in the global carbon budget (GCB) suggest a strong reinvigoration of the tropical land sink after the 2015–2016 El Niño. However, models and atmospheric inversions display large divergences in tropical CO2 fluxes during the 2017 recovery event. For instance, models predict a total net land sink recovery (2017 sink minus the 2015–2016 average sink) ranging from 0.3 to 2.6 Pg C, and the land sink recovery estimated from five atmospheric inversions ranges from −0.08 to +1.92 Pg C. The results of different inversions show a large spread in the tropics due to the scarcity of stations and uncertainties in atmospheric transport simulations.

We used low-frequency microwave satellite data (L-VOD) to feature precise monitoring of AGC changes and show that the AGC recovery of tropical ecosystems was slow and that by the end of 2017, AGC had not reached predrought levels of 20141. From 2014 to 2017, tropical AGC stocks decreased by 1.3 Pg C due to persistent AGC losses in Africa (-0.9 Pg C) and America (-0.5 Pg C). Pantropically, drylands recovered their carbon stocks to pre–El Niño levels, but African and American humid forests did not, suggesting carryover effects from enhanced forest mortality.

 

Reference

J.-P. Wigneron, L. Fan, P. Ciais, A. Bastos, M. Brandt, J. Chave, S. Saatchi, A. Baccini, R. Fensholt, Tropical forests did not recover from the strong 2015–2016 El Niño event. Science Advances. 6, eaay4603 (2020).
Mapping groundwater recharge in Vilnius urban and peri-urban area (Lithuania)
Authors: Miksa Katazyna , Inacio Miguel , Kalinauskas Marius , Gomes Eduardo , Pereira Paulo
Published: March 2020

Urban sprawl is decreasing the groundwater recharge by sealing the soils. In several cases, this expansion occurs were soils have the highest quality and infiltration capacity.  Soil sealing destroys the soil functions and reduces drastically the capacity to store water and regulate floods. The objective of this work is to map groundwater recharge capacity in Vilnius urban and peri-urban areas (urban atlas). To model groundwater recharge capacity, we used several variables such as lithology, geomorphology, slope, topographic wetness index, river network, tectonic faults, topographic position index, soil sand content and depth, precipitation, and land use. The model was validated using soil clay content. Drainage and tectonic faults density were calculated using the line density tool. Data was reclassified and overlaid applying the fuzzy overlay method. The results showed that the areas most urbanized and located in steeper slopes have the lowest values of groundwater recharge capacity. On the other hand, flat areas in sandy soil areas had the highest capacity. The model had an acceptable validation performance (r2=0.52).

This work was funded by the European Social Fund project LINESAM No. 09.3.3-LMT-K-712-01-0104 under grant agreement with the Research Council of Lithuania (LMTLT).
Discrete changes in fault free-face roughness: constraining past earthquakes characteristics
Authors: Zielke Olaf , Benedetti Lucilla , Mai P. Martin , Rizza Magali , Fleury Jules , Pousse Beltran Lea , Puliti Irene , Pace Bruno
Published: March 2020

A driving motivator in many active tectonics studies is to learn more about the recurrence large and potentially destructive earthquakes, providing the means to assess the respective fault’s future seismic behavior. Doing so requires long records of earthquake recurrence. The lack of sufficiently long instrumental seismic records (that would be best suited for this task) has led to the development of other approaches that may constrain the recurrence of surface rupturing earthquakes along individual faults. These approaches take different forms, depending on the specific tectonic and geographic conditions of an investigated region.

For example, around the Mediterranean Sea, we frequently find bedrock scarps along normal faults. Assuming that bedrock (i.e., fault free-face) exposure is caused by the occurrence of sub-sequent large earthquakes, we may measure certain rock properties to constrain the time and size of past earthquakes as well as the fault’s geologic slip-rate. A now-classic example in this regard is the measurement of 36Cl concentrations along exposed fault scarps in limestones.

For the presented study, we looked at another property of the exposed fault free-face, namely its morphologic roughness. We aim to identify whether fault free-face roughness contains information to constrain earthquake occurrence and fault slip-rates following the assumption that  sub-sequent exposure to the elements and sub-areal erosional conditions may leave a signal in how rough (or smooth) the fault free-face is (assuming a somewhat uniform pre-exposure roughness). Here, we present observations of fault free-face surface roughness for the Mt. Vettore fault (last ruptured in 2016) and the Rocca Preturo fault (The underlying models of fault free-face morphology were generated using the Structure-from-Motion approach and a large suite of unregistered optical images.). Employing different metrics to quantify morphologic roughness, we were indeed able to observe a) an increase in surface roughness with fault scarp height (i.e., longer exposure to sub-areal erosion causes higher roughness), and b) distinct (rather than gradual) changes in surface roughness, suggesting a correlation to individual exposure events such as earthquakes. Hence, fault free-face morphology of bedrock faults may serve as an additional metric to reconstruct earthquake recurrence patterns.
Bottom pressure induced by the long nonlinear internal waves
Authors: Talipova Tatiana , Pelinovsky Efim
Published: March 2020

The bottom pressure sensors are widely used for the purpose of registration of the sea surface movement. They are particularly efficient to measure long surface waves like tsunami and storm surges. The bottom pressure gauges can be also used to record internal waves in coastal waters. For instance, the perspective system of the internal wave warning in the Andaman Sea is based on the bottom pressure variation data. Here we investigate theoretically the relation between long internal waves and induced bottom pressure fluctuations. Firstly, the linear relations are derived for the multi-modal internal wave field. Then, the weakly nonlinear theory is developed. Structurally, the obtained formula for the bottom pressure induced by the long internal waves is similar to those known for the surface waves within the Green-Naghdi system framework, but the coefficients are determined through the integrals for the water density stratification and vertical mode wave functions. In particular, the bottom pressure variations are calculated for solitary waves in two- and three-layer flows described by the Gardner equation.
The research is supported by RFBR grants No. 19-55-15005 and 19-05-00161.
Assessment of the Running Slope Difference (RSD) t-Test, a new statistical method for detecting climate trend turning
Authors: Zuo Bin , Hou Zhaolu , Zheng Fei , Sheng Lifang , Gao Yang , Li Jianping
Published: March 2020

Global mean surface air temperature (GMT) rose roughly 0.85 °C from 1880 to 2012 (IPCC 2013), attributing mainly to an increase in atmospheric greenhouse gases. For different decadal timescale periods in the past 100 years, the warming rate of different periods may significantly different. For example, IPCC AR1 (1990) point out that GMT between 1910-1940 and 1975-1990 are significantly warming, meanwhile GMT stay nearly constant between 1940 and early 1970. The phenomenon of two nearby periods showing significantly different trends is knowing as trend turning, this phenomenon is common in climate time series and crucial when climate change is investigated. However, the available detection methods for climate trend turnings are relatively few, especially for the methods which have the ability of detecting multiple trend turnings. We propose a new methodology named as the running slope difference (RSD) t-test to detect multiple trend turnings. This method employs a t-distributed statistic of slope difference to test the sub-series trends difference of the time series, thereby identify the turning-points. We compare the RSD t-test method with some other existing trend turning detection methods with an idealized time series case and several climate time series cases. And we also report the Monte Carlo simulation used to evaluate this method’s detection ability. Results show that the RSD t-test method is an effective tool for detecting trend turning in time series, and this method has three major advantages: ability to detect multiple turning-points, capacity to detect all three types of trend turning, and great performance of avoiding false alarm.
Low-level cloud feedbacks in CMIP6 models and EUREC4A observations
Authors: Albright Anna Lea , Bony Sandrine , Dufresne Jean-Louis , Vial Jessica
Published: March 2020

How will low-level clouds respond to global warming? We approach this question by first investigating the spread of climate sensitivity and cloud feedbacks in CMIP6 models. We stratify the cloud response by circulation regime and focus in greater detail on the cloud response in tropical regimes of subsidence and weak ascent  (i.e., their vertical structure in the present-day and future climate, how cloud profile changes relate to changes in cloud-controlling factors). This CMIP6 model analysis dovetails with an observational analysis of low cloud responses from the EUREC4A field campaign. We seek to employ a simple model of low cloud behavior, constrained with observations from EUREC4A and longer time series from the Barbados Cloud Observatory, to better constrain the range of low cloud behavior spanned by CMIP6 models. 
Improved understanding on flash droughts: from a perspective of the rapid intensification rate
Authors: Liu Yi
Published: March 2020

The rapid intensification rate and short duration are currently two different notions in defining flash droughts. Here we make a thorough evaluation on these two approaches and illustrate which approach can provide more accurate information of flash drought and why. Based on the conception of intensification rate, a new method focusing on soil moisture depletion during the onset-development phase is proposed, and its performance in monitoring flash drought events, their onset time and spatial dynamics are compared with those from the short-duration method. Results show that the proposed rapid-intensification approach is superior to the short-duration approach in capturing the continuous evolution process of drought. Since the short-duration approach ignores the change of soil moisture with time, it can hardly ensure the identified flash drought events all have the rapid evolving characteristic. Meanwhile, the miss monitoring for flash drought onset is also observed for the short-duration approach. The unreasonable selections of hydro-meteorological variables and corresponding thresholds, particularly refers to that of temperature, is the main reason for the poor behavior of the short-duration approach.
Evidence for atmosphere-ocean meridional energy transport compensation in the past decades
Authors: Hazeleger Wilco , Liu Yang , Attema Jisk
Published: March 2020

We present evidence of compensation between the atmosphere and ocean's meridional energy transport variations, also known as Bjerknes compensation. Motivated by previous studies with mostly numerical climate models, we analyze compensation using a range of atmosphere and ocean reanalysis datasets. We show that Bjerknes compensation is present at almost all latitudes from 40 degrees North to 70 degrees North in the Northern Hemisphere from interannual to decadal time scales. In contrast to results from some numerical climate models, which attribute the compensation to variations of eddy energy transports in the atmosphere in response to changes of ocean heat transport and sea ice at multi-decadal time scales, we find a response of the zonal mean of poleward energy transport to ocean heat transport variability that leads to compensation. This is apparent in a meridional shift of the Ferrel Cell at midlatitudes at decadal time scales in winter. This shift in the cell itself is driven by changes in the eddy momentum flux and related baroclinicity. The oceanic response to atmospheric heat transport variations associated by the shift is primarily wind driven. In summer, there is hardly compensation and the proposed mechanism is not at work. Interestingly, these results are robust among all reanalysis datasets and can provide a benchmark for climate modelling studies.