bluuebunny/crossref_metadata_2025 huggingface dataset:
Relative contributions of North and South Pacific sea surface temperature anomalies to ENSO
Authors: Ding Ruiqiang , Tseng Yu-heng , Li Jianping
Published: March 2020

Variations in the sea surface temperature (SST) field in both the North Pacific [represented by the Victoria mode (VM)] and the South Pacific [represented by the South Pacific Quadrapole (SPQ) mode] are related to the state of the El Niño-Southern Oscillation (ENSO) three seasons later. Here, with the aid of observational data and numerical experiments, we demonstrate that both VM and SPQ SST forcing can influence the development of ENSO events through a similar air–sea coupling mechanism. By comparing ENSO amplitudes induced by the VM and SPQ, as well as the percentages of strong ENSO events followed by the VM and SPQ events, we find that the VM and SPQ make comparable contributions and therefore have similar levels of importance to ENSO. Additional analysis indicates that although VM or SPQ SST forcing alone may serve as a good predictor for ENSO events, it is more effective to consider their combined influence. A prediction model based on both VM and SPQ indices is developed, which is capable of yielding skillful forecasts for ENSO at lead times of three seasons.
A Study on the Operation of Early Warning System for Heat Waves in Gwangju Based on the Urban Climatic Environment Assessment Model System
Authors: Oh Byoungchull , Hwang Cheolho , Yun Won-tae , Kim Jongha
Published: March 2020

Damages in cities resulting from climate change are made irregularly and untypically, thus difficult to predict due to heavily concentrated buildings and population, etc. This study aims to introduce the results of our Urban Climatic Environment Assessment Model System(Model System hereinafter) as well as its construction, which is designed to provide impact assessment of heat waves in cities, to reduce damages, and to build capacities against it.

Our Model System is based on the Unified Model(UM : an integrated model of Korea Meteorological Administration), and satellite data is necessary to verify the Model System. However, we have developed high resolution (10m ~ 100m) urban assessment model to analyze the impacts of heat waves in city of Gwangju to help local government by developing and implementing environmental policies. The outputs of our Model System will contribute to the decision making.

Following two approaches were considered for impact assesment. Firstly, high spatial resolution model (in 10m to 100m level) using ensemble and down-scaling techniques can help identification of vulnerable areas in the city. Also, analyzed data can be linked to local GIS and land use map for analysis and assessment of the heat waves, which enables to make 48h heat wave forecast.

Secondly, CFD micro-scale analysis using super-computer enables to analyze the vulnerable areas with components of : temperature, wind, humidity, solar radiation quantity, cloud cover, etc. Data achieved via our Model System will be used as objective and scientific basis for developing heat wave policies. It will also give guidance for heat wave early warning.

It is expected that local governments can utilize our Model System to identify and analyze patterns and characteristics of heat waves in the city, and make decisions and develop environment-related policies on the objective and scientific basis preemptive response for vulnerable areas in the region.

Keywords : heat waves, Urban Climatic Environment Assessment Model System, spatial resolution, ensemble average, down-scaling, CFD, micro-scale, Early warning system

 

* This research was supported by a grant from Research Program funded by International Climate & Environment Center(ICEC).
Climatic Effects of Hygroscopic Growth of Sulfate Aerosols in the Stratosphere
Authors: Krishnamohan Krishna-Pillai Sukumara-Pillai , Bala Govindasamy , Cao Long , Duan Lei , Caldeira Ken
Published: March 2020

Deliberate climate intervention by injection of sulfate aerosols in the stratosphere is a method proposed to counter anthropogenic climate warming. In such an injection scenario, an improved understanding of the microphysical and optical properties of the injected aerosols is important as these properties alter the radiative forcing and resulting climate. Here we analyze the effect of a specific microphysical property of sulfate aerosols in the stratosphere: hygroscopic growth – the tendency of aerosol particles to grow by accumulating water. In the NCAR CESM model, using idealized climate simulations, we find that, for a given mass, stratospheric sulfate aerosols cause more cooling when prescribed at the lower levels of the stratosphere because of increased hygroscopic growth of the aerosols due to larger relative humidity. The relative humidity in the stratosphere typically decreases rapidly with the increasing altitude. The larger relative humidity in the lower stratosphere causes an increase in the aerosol size through hygroscopic growth, which leads to a larger scattering efficiency. The increase in shortwave back-scattering due to the size change is found to be the primary factor contributing to the additional surface cooling as the aerosols are prescribed in the lower levels of the stratosphere. In our simulations, hygroscopic growth provides an additional cooling of 23% (0.7 K) when 20 Mt-SO4 of sulfate aerosols are prescribed at 100 hPa, relative to a non-hygroscopic simulation where hygroscopic growth is not allowed in the stratosphere. This additional cooling due to hygroscopic effect becomes weaker higher in the stratosphere where relative humidity is lower. Hygroscopic growth also leads to additional warming in the layers where the aerosols are prescribed due to an increase in near-IR shortwave absorption. This warming causes secondary effects such as a decrease in high clouds and an increase in stratospheric water vapor, which affects the effective radiative forcing. This altitude dependence of the cooling effects of hygroscopic growth is opposite to the altitude dependence of sedimentation effects;  while the hygroscopic effect produces larger cooling when aerosols reside in the lower stratosphere, the sedimentation effect produces less cooling when aerosols are injected into the lower stratosphere as the residence time becomes shorter.
Research of Marine Geophysics Processing and Official Regulation for Underwater Culture Heritage in Taiwan
Authors: Lo Shu-Yunn , Song Gwo-shyh
Published: March 2020

In recent years, the Government of Taiwan has put considerable effort into the environment impact assessment for offshore wind potential area in Taiwan Strait, especially the research and regulation related to Underwater Cultural Heritage (UCH). From prehistorical evidence and historical record, it can be seen that Taiwan Strait is rich in archaeological character, which involves the traces of people living in 10,000 years ago (The Paleolithic Age), and the remains of human activities on the water before 100 years. Since the cultural and historical value of the material preserved under the sea, the Underwater Cultural Heritage Preservation Act, which follows the Convention on the Protection of the Underwater Cultural Heritage announced by UNESCO in 2001, was published by the Ministry of Culture to set an official standard for development and management in 2015. The guideline for UCH survey was soon be announced in the next year. All these acts lead Taiwan into the forefront of UCH survey in the world.
The techniques or methods used in UCH survey, as the rule in the UCH Preservation Act, must be non-destructive to reduce harm as much as possible. Marine geophysical techniques therefore become the major tools used in the UCH surveys in Taiwan. These tools include side-scan sonar for wide range seafloor mapping, multi-beam sonar for getting accurate position and 3-D image, magnetometer for finding ferromagnetic material, and sub-bottom profiler for searching buried objects. The requirements of using these techniques within UCH surveys are written in the official guideline.
After data analysis, the records from different instruments will be compared with others to identify the targets. However, the results of recognition involve objects unwanted, such as acoustic noise, rocks, or other nature features. Errors produced during the survey may also increase the difficulty of recognition. With the experience from previous research, this study will introduce some cases which were done before, and take a review of the official guideline to provide the suggestion that can help to improve the results of UCH survey in Taiwan.

Keywords: Underwater Cultural Heritage, marine geophysics, side-scan sonar
Characterization of aerosol composition and sources in a polluted city in Central China
Authors: Wang Qingqing , Sun Yele , Li Jie , Chen Yong , Li Yanyu
Published: March 2020

Air pollution problem in megacities in China has been significantly improved as annual average PM2.5 in 2019 in Beijing was 42 µg/m3. But is still a serious problem in many smaller cities. Sanmenxia is located in the Fen-Wei Plain, close to China's largest coal base. The annual average PM2.5 of Sanmenxia decreased from 72 µg/m3 in 2015 to 59 µg/m3 in 2019. The highly concentrated industries, especially coal industries, heavy traffic, and the typical terrain that it locates nearby the gorge of the Yellow river, make Sanmenxia a highly polluted city. The highest average PM2.5 was ~100 µg/m3 in winter. Non-refractory PM1 (NR-PM1) species including organic aerosol (Org), sulfate (SO4), nitrate (NO3), ammonium (NH4) and chloride (Chl) were measured at Sanmenxia Environmental Protection Bureau (34.794°N,111.171°E) by the ACSM at a time resolution of ~5 min from December 21, 2018 to January 21, 2019. High time resolution of online meteorological variables, as well as precursor gases, OC/EC, and trace elements were also collected at the site, aiming to characterize the pollution sources and evolution mechanisms of aerosol chemical composition. A long haze episode lasted for 16 days was observed with NR-PM1 = 76±33 µg/m3, PM2.5 = 180±89 µg/m3. During this episode, the primary species, nitrate accounted for 32% of NR-PM1 due to high emission of NOx. Positive matrix factorization (PMF) analysis indicates that industrial emission, coal combustion, traffic emission, and secondary species (sulfate + nitrate + ammonium + secondary organic aerosol) were the major sources of pollution. The diurnal variations of pollutants in Sanmenxia were affected significantly by the vertical movement of air flows, but were not sensitive to the regional transport.
Riverine Flooding and Landfalling Tropical Cyclones over China
Authors: Yang Long , Liu Maofeng , Wang Lachun , Ji Xiaomin , Li Xiang , Hou Aizhong
Published: March 2020

Riverine flooding associated with landfalling tropical cyclones (TCs) in the Western North Pacific basin is responsible for some of the most severe socioeconomic losses in East Asian countries. However, little is known about the spatial and temporal patterns of TC flooding and its synoptic controls, which constrain predictive understandings of flood risk in this highly populated region. In this study, we investigate hydrology, hydrometeorology, and hydroclimatology of riverine flooding over China induced by landfalling tropical cyclones, based on empirical analysis of dense networks of stream gauging and rainfall stations as well as downscaling simulations using the Weather Research and Forecasting (WRF) model driven by 20th Century Reanalysis fields. The most extreme floods in central and northeastern China are associated with TCs despite infrequent TC visits in these regions. Inter-annual variations in TC flooding demonstrate a mixture of climate controls tied to surface temperature anomalies in central tropical Pacific, western North Pacific and north Atlantic. We implement numerical modelling analysis of typhoon Nina (1975), typhoon Andy (1982) and typhoon Herb (1996) to further shed light on key hydro-meteorological features of landfalling TCs that are responsible for severe flooding over China. We highlight the important role of interactions of storm circulations with mid-latitude synoptic systems (e.g., upper-level trough) and complex terrains in producing extreme rain rates and flooding. Analytical framework developed in this study aims to explore utilization of hydro-meteorological approach in flood-control engineering designs by providing details on the key elements of flood-producing storms. We also highlight potential challenges of developing predictive tools of TC flood risk in east Asian countries.
Gravity Wave identification using GPS Total Electron Content in South East Asia
Authors: Srivastava Sarthak , Chandran Amal
Published: March 2020

Ionospheric Total Electron Content (TEC) data from ground-based Global Positioning System (GPS) receiver networks have been used previously to detect Travelling Ionospheric Disturbances (TIDs). The TIDs have been shown to arise through coupling of lower atmosphere with the Ionosphere with Gravity Waves as the coupling mechanism. Gravity Waves generated by earthquakes, tsunamis, volcanoes, topography, convection and even solar eclipses have been detected using GPS TEC data. In this study, we identify Gravity Wave signatures in GPS TEC data derived from the Sumatran GPS Array (SuGAr) network. SuGAr is a network of 49 ground-based GPS stations along the convergent plate boundary between Indo-Australian and Asian tectonic plates in western Sumatra, Indonesia. Since initiation in 2002, data from SuGAr has primarily been used to study earthquakes and plate-tectonics in south-east Asia. Due to its location along the seismically-active region, SuGAr can provide valuable data for studying co-seismic Gravity Waves triggered by terrestrial-atmosphere coupling. Frequent occurrence of deep convective clouds in tropical region implies that SuGAr data also provides a unique opportunity to study atmospheric waves generated by convection. 

We have identified Gravity Waves across a wide spectrum corresponding to seismic and tropical convection events in Sumatran region. Upon identifying the wave signatures, we characterized the wave parameters and identified the wave sources through suitable ray tracing calculations. In this paper we show acoustic-gravity waves generated by the 2012 Sumatra great earthquake sequence consisting of 2 largest strike slip earthquakes ever recorded. Spectral analysis indicates the presence of fundamental resonant frequencies for solid Earth-atmosphere coupling. Using a geometric ray tracing method, we also trace the waves very close to the reported epicentres of the double earthquake sequence. We also discuss inertia-gravity waves generated due to convection in South-East Asia using SuGAr TEC data for 2018. Indication of deep convective clouds is confirmed through satellite-based cloud top brightness temperature data.  Ray tracing is performed to further trace the observed waves to the convective system location.
A multiproxy approach to identify the Tambora volcanic fallout in 1810s from the Styx glacier in Victoria Land, Antarctica
Authors: Han Changhee , Kim Songyi , Han Yeongcheol , Moon Jangil , Hong Sang-Bum , Chang Chaewon , Hur Soon Do
Published: March 2020

Ice cores provide records of past aerosol composition and have been used to reconstruct the relative contribution of different emission sources changing in time. A precise age scale is essential to achieve this goal, for which annual layer counting of seasonal cycles in water stable isotope ratios (δ18O and δD) and major ion concentrations have been basically utilized. Introducing additional time markers are helpful for reducing the uncertainty of the depth-age scale, and the fallout of volcanic products has offered useful time markers when they are well-dated. Here, we report lead isotope ratios (206Pb/207Pb and 208Pb/207Pb) and concentrations of thallium (Tl) and major ions in a shallow ice core from the Styx Glacier (73°51 S, 163°41 E) in the Victoria Land, Antarctica, analyzed for discriminating volcanic products of the 1815 AD Tambora eruption, Indonesia from local volcanic inputs. Mechanically decontaminated 19 inner core pieces between the depth interval 40.8 – 42.4 m were analyzed. The results show that the increases of volcanic SO42- input are accompanied by either (1) input of more-radiogenic lead (higher 206Pb/207Pb) and Tl or (2) relatively 208Pb enriched lead. These results suggest that the Tambora volcanic input is overprinted by local volcanic aerosol input and that the isotope-based assessment of the Pb sources can help to discriminate between remote and local components of the volcanic input signals recorded in Victoria Land glaciers.
Detection and quantification of soil compaction in a post-mining landscape by geophysical methods
Authors: Weihermüller Lutz , Schmäck Jessica , Mertens Mario , Endenich Manuel , van der Kruk Jan , Vereecken Harry , Welp Gerd , Pätzold Stefan
Published: March 2020

Rhenish opencast mines located in the central west of Germany have used about 330 km2 of land so far. Of this, some 230 km2 have been recultivated, including 125 km2 of arable land. After recultivation, the land is cultivated for at least seven years by the mining company before let to the farmers. Where new farmland is envisaged, the stackers spread pure loess mixed with soil material of the original Luvisols (loess loam) at the top of the refilled mining areas. After a certain settling time, this layer must be at least two meters thick. In a next step, the loess is levelled in a soil-sparing fashion using caterpillars with extra-wide rawler tracks. Even if care is taken that the loess layer will not be heavily compacted during levelling, local soil compaction is one of the major problems, as leveling often is performed during unfavorable moist soil conditions. These local compactions lead to reduced crop growth during either wet or dry growing seasons and result in yield losses over periods of many years. Localizing and evaluating such compacted field zones would enable the mining company to perform a physical soil melioration before handing over the land to a farmer.

To identify local soil compaction, a field study was performed in 2019 on a selected field with known variability in crop performance within the recultivated area of the Garzweiler mine in North Rhine-Westphalia, Germany. Over the course of 5 months, the field was intensively investigated using geophysical methods such as electromagnetic induction (EMI) and electrical resistivity tomography (ERT). Additionally, soil samples were taken to determine soil water contents, bulk density, penetration resistance, and soil texture.

The geophysical maps gathered, clearly show zones of higher electrical conductivities in the soil, which were associated to conventionally measured subsoil compaction. Regression of bulk densities with EMI data yielded good results allowing to map out compacted zones within the field and also to quantify compaction. Hence, geophysical methods provide a promising approach to plan soil melioration measures.
Imaging Hales Discontinuity beneath India: Seismological and Petrological Model
Authors: Chaudhury Jashodhara , Mitra Supriyo , Sarkar Tapabrato
Published: March 2020

We model the depth and Vs structure of the Hales discontinuity (H-D) beneath Eastern Dharwar Craton (EDC) and Southern Granulite Terrain (SGT) using P-wave receiver function (P-RF) analysis and joint inversion with Rayleigh wave phase velocity dispersion. We calculate P-RFs at higher frequency (fmax 0.46 Hz), compared to previous studies, to show that the P-to-S converted phase from the H-D (Phs) is distinct from the crustal reverberations. The Phs at stations in the EDC arrive at ~10 s beneath GBA, and ~11 s beneath HYB. From joint inversion the H-D is modeled at 97 ± 5 km and 108 ± 5 km depth, with 5% and 3% Vs increase, beneath GBA and HYB, respectively. For KOD, in SGT, the Phs coincides with the mid-crustal PpSs+PsPs reverberation at most ray-parameters, causing destructive intereference. This explains the apparent absence of Phs in previous studies. We isolated P-RFs where Phs is distinct at ~10.5 s and model it at depth of 101 ± 5 km with Vs increase of 3%. We demonstrate through forward calculation that the spinel-garnet mineral transformation cannot explain the H-D Vs increase. From data of mantle xenoliths in the Wajrakarur kimberlite field, Southern India, we calculate Vs of mantle peridotite and eclogite, using published bulk rock compositions through Perple-X. At the H-D depth and temperature derived from Indian shield geotherm, we observed a perfect match to the Vs. We hypothesize that H-D marks the surface of a paleo-subducted eclogitic oceanic slab embeded within the upper mantle peridotite. Observations of mantle faults within the Canadian lithosphere, at similar depth, has been related to relict-subduction zones and therefore independently supports our model.
Reviewing the role of precipitation and soil moisture in driving the terrestrial carbon cycle variability in Europe: recent advances and known unknowns
Authors: Messori Gabriele , Ruiz-Pérez Guiomar , Manzoni Stefano , Vico Giulia
Published: March 2020

The terrestrial biosphere is a key component of the global carbon cycle and is heavily influenced by climate. This interaction spans a wide range of temporal (from sub-daily to paleoclimatic) and spatial (from local to continental and global) scales and a multitude of bio-physical processes. In part due to this complexity, a comprehensive picture of the physical links and correlations between climate drivers and carbon cycle metrics at different scales remains elusive, framing the scope of this contribution. Here, we specifically explore how precipitation, soil moisture and aggregated climate variability indices relate to the variability of the European terrestrial carbon cycle at sub-daily to interannual scales (i.e. excluding long-term trends). We first discuss broad areas of agreement and disagreement in the literature. For example, while most carbon cycle proxies tend to correlate positively with precipitation, responses to soil moisture and climate indices are more variable. In fact, soil moisture often correlates positively with productivity in water-limited environments, and negatively in light limited ones, or can exhibit nonlinear relations with the carbon cycle proxies. We then conclude by outlining some existing knowledge gaps and by proposing avenues for improving our holistic understanding of the role of climate drivers in modulating the terrestrial carbon cycle.
Nitrogen removal and nitrous oxide emissions in woodchips biofilters treating agricultural drainage waters
Authors: Audet Joachim , Zak Dominik , Hoffmann Carl Christian
Published: March 2020

Eutrophication of aquatic ecosystems provoked by excess nitrogen (N) concentration is still a major concern worldwide with severe consequences such as hypoxia, biodiversity loss, and degradation of drinking water quality. To face these challenges, a novel N mitigation measure has emerged in the last decades consisting of biofilters made of woodchips. Drainage water from agricultural areas infiltrate through a layer of woodchips before it discharges to an aquatic recipient such as a ditch or a stream. The goal with this technique is to provide optimal conditions for denitrification i.e. an easy degradable carbon source (the woodchips) and an anaerobic environment. There is, however, some concerns regarding the emissions of the greenhouse gas nitrous oxide (N2O) which can be a by-product of denitrification.

Here, we present results on N removal and N2O emissions from 9 biofilters differing in age (1–8 years) and representing a total of 18 years of monitoring. The biofilters were all located in agricultural catchments in Denmark (temperate climate conditions). Nitrogen removal in the biofilters was estimated using a mass balance approach measuring N species dissolved in the water (total N, nitrate, nitrite, ammonium) using time proportional automated samplers placed at inlet and outlet of the biofilters. Nitrous oxide emissions were measured every third week both as gaseous form at the surface of the biofilters (closed chamber technique and gas chromatography) and in dissolved form in the water phase at inlet and outlet of the biofilters (headspace technique and gas chromatography). We take advantage of this unique dataset to identify the factors enabling to maximize N removal while minimizing N2O emissions. Furthermore, we make a first assessment of the potential impact of the increasing number of biofilters on N2O emissions in agricultural landscapes.
Idealised satellite data assimilation experiments with clouds and precipitation
Authors: Cantarello Luca , Bokhove Onno , Inverarity Gordon , Migliorini Stefano , Tobias Steve
Published: March 2020

Operational data assimilation (DA) schemes rely significantly on satellite observations with much research aimed at their optimisation, leading to a great deal of progress. Here, we investigate the impact of the spatial-temporal variability of satellite observations for DA: is there a case for concentrating effort into the assimilation of small-scale convective features over the large-scale dynamics, or vice versa?

 

We conduct our study in an isentropic one-and-a-half layer model that mimics convection and precipitation, a revised and more realistic version of the idealised model based on the shallow water equations in [1,2]. Forecast-assimilation experiments are performed by means of a twin-setting configuration, in which pseudo-observations  from a high-resolution nature run are combined with lower-resolution forecasts. The DA algorithm used is the deterministic Ensemble Kalman Filter (see [3]). We focus our research on polar-orbit satellites regarding emitted microwave radiation.

 

We have developed a new observation operator and a representative observing system in which both ground and satellite observations can be assimilated. The convection thresholds in the model are used as a proxy for cloud formation, clouds, and precipitation. To imitate the use of weighting functions in real satellite applications, radiance values are computed as a weighted sum with contributions from both layers. In the presence of clouds and/or precipitation, we model the response of passive microwave radiation to either precipitating or non-precipitating clouds. The horizontal resolution of satellite observations can be varied to investigate the impact of scale-dependency on the analysis.

 

New, preliminary results from experiments including both transverse jets and rotation in a periodic domain will be reported and discussed.

 

References:

[1] Kent, T., Bokhove, O., & Tobias, S. (2017). Dynamics of an idealized fluid model for investigating convective-scale data assimilation. Tellus A: Dynamic Meteorology and Oceanography, 69(1), 1369332.

[2] Kent, T. (2016). An idealised fluid model for convective-scale NWP: dynamics and data assimilation (Doctoral dissertation, PhD Thesis, University of Leeds).

[3] Sakov, P., & Oke, P. R. (2008). A deterministic formulation of the ensemble Kalman filter: an alternative to ensemble square root filters. Tellus A: Dynamic Meteorology and Oceanography, 60(2), 361-371.

 
Trends of extreme temperature events over the Iberian Peninsula during the 21st century
Authors: Acero Francisco Javier , Portero Javier , García José Agustín
Published: March 2020

Heat waves are meteorological events exceptionally extremes that are increasing in frequency, duration and intensity. The Iberian Peninsula is characterized in the last decades by an increase in the trend of extreme temperature events and its consequences are important not only for the effects over the population but also for agriculture and biodiversity. The main objective in this study is to analyse future trends over the 21st century for extreme temperature using two events: heat waves and warm events. These are defined as the period of at least two consecutive days with temperatures over a certain threshold, the 95th percentile for heat waves and the 75th percentile for warm events. For this purpose, 14 different regionalized dynamic climate projections dataset are used. Firstly, to choose the better climate models, the common period 1961-2000 is used to compare with observational data obtained from SPAIN02 grid dataset. Once the better climate models are selected, trends in both events are analysed for the past (1961-2000) and the future (2011-2099). To estimate trends, Mann-Kendall test and Theil-Sen estimator were applied. Mann-Kendall test returns the significance of the trends for each grid point, while Theil-Sen estimator estimates the value of that trend. Moreover, max-stables processes are used to compare spatial dependence between dynamic projections. The results for the comparison period show that maximum temperature and moderate values of the maximum temperature are increasing smoothly, while low values of maximum temperatures are increasing even faster. This means that the variability of extreme temperature is decreasing, especially in the Mediterranean area of the Iberian Peninsula. For the 21st century, results reveal a significant positive trend in low values of the maximum temperatures that increases throughout the century over the whole study area. Warm events show a significant positive trend in frequency and intensity. This trend drastically increases from 2050 onwards.
Determining the ion velocity in the inner magnetosphere of comet 67P/Churyumov–Gerasimenko using Rosetta IES measurements
Authors: Nemeth Zoltan , Szego Karoly , Timar Aniko , Foldy Lajos , Burch Jim , Goldstein Raymond
Published: March 2020

Determining the ion bulk velocity is essential to understand the physics of the inner magnetosphere of comets. This velocity controls the strength of the ion-neutral drag force, which plays a very important role in the energy and momentum transfer processes of that region. Unfortunately there are no direct measurements of this quantity available. The energy thresholds of the ion instruments on board the Rosetta orbiter would prevent the direct detection of the bulk ion content of the plasma as long as the plasma is relatively slow and cold. The picture is further complicated by the spacecraft potential, which accelerates the thermal ions to energies higher than the measurement threshold, but effectively screens the magnitude and direction of their original velocity. That distortion effect is not arbitrary however; it is possible to recover the original ion velocity distribution from IES measurements by simulating the effects of the spacecraft potential on the ion motion. We performed these simulations for several bulk and thermal velocity as well as spacecraft potential values, and compared the results with IES measurements. From this we could determine the most probable values of the bulk and thermal speeds of the plasma ions in the inner magnetosphere of comet 67P/ Churyumov–Gerasimenko.
Crustal Structure Revealed by a Deep Seismic Sounding Profile of Baijing-Gaoming-Jinwan in the Pearl River Delta
Authors: Zhang Xiang , Ye Xiuwei , Lv Jinshui , Wang Xiaona
Published: March 2020

The Pearl River estuary area, located in the middle part of the southern China coastal seismic belt, has long been considered a potential source of strong earthquakes above magnitude 7.0. To scientifically assess the potential strong earthquake risk in this area, a three-dimensional artificial seismic sounding experiment, consisting of a receiving array and seabed seismograph, was performed to reveal the deep crustal structure in this region. We used artificial ship-borne air-gun excitation shots as sources, and fixed and mobile stations as receivers to record seismic data from May to August 2015. This paper presents results along a line from the western side of the Pearl River estuary to the western side of the Baijian–Gaoming–Jinwan profile. A two-dimensional velocity structure was constructed using seismic travel-time tomography. The inversion results show that the Moho depth is 27 km in the coastal area and 30 km in the northwest of the Pearl River estuary area, indicating that the crust thins from land to sea. Two structural discontinuities and multiple low-velocity anomalies appear in the crustal section. Inside both discontinuity zones, a low-velocity layer, with a minimum velocity of 6.05kms−1, exists at a depth of about 15 km, and another, with a minimum velocity of 6.37kms−1, exists at a depth of about 21.5 km between the middle and lower crust. These low velocities suggest that the discontinuities may consist of partly molten material. Earthquakes with magnitudes higher than 5.0 occurred in the low-velocity layer along the profile. The deep Kaiping-Enping fault, rooted in the crust, may be one of the most important channels for deep material upwelling and is related to tectonic movement since the Cretaceous in the Pearl River Delta tectonic rift basin.
Decadal changes in snow cover characteristics in Slovakia over the period 1921 – 2020
Authors: Fasko Pavel , Markovič Ladislav , Pecho Jozef , Bochníček Oliver
Published: March 2020

Long-term changes in air temperature regime have significant consequences for the atmospheric precipitation regime in Slovakia. Moreover, the combination of air temperature increase, changes in annual precipitation regime, as well as increasing proportion of liquid and mixed precipitation on its annual total, have had a profound effect on the snow cover occurrence. In majority of territory of Slovakia, with the exception of high altitudes, the stability of snow cover incidence has decreased. In the last decade of the 20th century and in the first two decades of the 21st century, there was a significant increase in mean values of the air temperature characteristics in every individual decade over the period. Very clear decline of amount of snow cover in Slovakia was recorded especially in the second decade of the 21st century however significant regional differences of measurable long-term trends have been affected by very complex natural conditions of Slovakia. The paper we analyze selected snow cover characteristics, such as the sum of snow depths as well as the number of days with snow cover in the decadal time scale for the period 1921 – 2020. The analysis is performed using the time series of daily values of snow cover at selected weather stations in different regions of Slovakia.
Data correlation of non-destructive testing methods to assess asphalt pavement thickness
Authors: Plati Christina , Loizos Andreas , Gkyrtis Konstantinos
Published: March 2020

Performing structural assessment at any time of asphalt pavements service life is an inherent process within pavement condition assessment. Layers thicknesses are among the major contributors to the overall pavement response and performance. Knowledge of layer thicknesses is imperative for both new and in-service pavements, because thickness data is usually combined with other response indicators (i.e. pavement deflections) in order to perform pavement evaluation during pavements service life. As such, inaccuracies in thickness assessment might result in erroneous response analysis and life expectancy estimation with a detrimental financial impact during maintenance planning.

Traditionally, layer thicknesses were retrieved through coring or digging test pits. Because of the limitations of these methods (including location-specific information, destructive nature, need for traffic disruptions), the pavement engineering community has consistently drawn its attention to a broadened utilization of advanced Non-Destructive Testing (NDT) systems in order to non-invasively determine the pavement cross-section. The most indicative NDT tool for that purpose is the Ground Penetrating Radar (GPR), which is systematically used for layers thickness evaluation. Within the framework of pavement evaluation processes, GPR is quite often combined with the Falling Weight Deflectometer (FWD), which provides with pavement response indications in terms of surface deflections.

It is worthwhile mentioning that GPR requires high expertise in order to reliably analyze the collected data and until now, there is none uniquely recognizable and universally accepted signal processing scheme. Supplementary to experienced users and analysts, investments in time and human resources are also needed to make reliable interpretations. Such reasons may potentially discourage related stakeholders from systematic GPR use, especially in cases where there are budgets constraints for the procurement and transportation logistics of multiple expensive equipment.

In light of the above, related research is pursed in respect to the investigation of the ability of FWD surface deflections indexes to provide with reliable information on the Asphalt Concrete (AC) layer thicknesses. For this purpose, Long-Term Pavement Performance (LTPP) data is analyzed including FWD and GPR data as well as sample coring. A nonlinear regression based relationship is under development that preliminarily exhibits a satisfactory performance both during model fit and model accuracy evaluation. Based on the above framework, it is suggested that the NDT analysis with deflection indexes seems promising in terms of roughly producing AC thickness, thereby balancing constraints at network level.
Ocean carbon cycle during the last deglaciation in the Max Planck Institute Earth System Model
Authors: Liu Bo , Six Katharina , Ilyina Tatiana
Published: March 2020

The deglacial atmospheric CO2 increase has been attributed to a combination of mechanisms, many of which relate to the ocean outgassing triggered by changing marine physical and biogeochemical states. To quantify the impact of proposed processes and feedback on the deglacial CO2 rise, previous modelling studies mostly conducted time-slice sensitivity experiments. Here, we present results from a transient deglaciation simulation (24 kB.P. - 1850) using the comprehensive Max Planck Institute Earth System Model (MPI-ESM). We force the model with the deglacial atmospheric greenhouse gases (CO2, CH4, N2O) concentrations, obital parameters, ice sheet reconstruction and transient dust deposition. The ocean biogeochemical component of MPI-ESM is using the same automatical adjustment of bathymetry and land-sea mask in response to deglacial continental runoff and melt water discharge. In and around the areas of changing land-sea mask, we redistribute the marine biogeochemical tracers in accord with the simulated salinity. Terrestrial organic matter is transferred from flooded land areas to the ocean, which guarantees mass conservation with respect to carbon. We also include 13C tracers in the ocean biogeochemical component to evaluate the simulated ocean state against proxy data. The initial marine nutrients and carbon inventories are set the same as those in the present-day ocean. 
During the first 3 kyr, the climate and ocean state show, as expected, only modest variations. Some flooding events of coastal areas bring terrestrial organic matter to the ocean and lead locally to CO2 outgassing for several decades. Terrestrial organic matter has a higher carbon to nutrient stoichiometry as compared to marine organic matter, thus its remineralization favours CO2 outgassing. Additionally, the accumulation of terrestrial organic matter in the top layers of the marine sediment reduces the replenishment of the water-column nutrients by the re-flux of remineralization products from marine sediment. Consequently, the strength of the local biological pump decreases. Further results will be presented and discussed. 
Assessment of future heat events for the city of Augsburg by means of a normal vector based analog approach
Authors: Merkenschlager Christian , Beck Christoph , Hertig Elke
Published: March 2020

Under enhanced anthropogenic greenhouse gas forcing heat waves are only one example of climatic risks mankind has to deal with. Especially in urban areas where most of the people will live until the end of the 21st century heat waves are a serious risk factor since the urban heat island will reinforce such events. For the city of Augsburg, new analog methods are utilized for assessing the development and impacts of heat waves taking into account the varying urban structure.

For model calibration the temperature data from the Augsburg-Mühlhausen weather station operated by the German Weather Service (DWD) and atmospheric circulation variables of the ERA5 reanalysis data set were used to analyze the recent temperature development. For this purpose, the least deviation of the normal vector was used to determine a subsample of analogs corresponding to the day of interest. The normal vector was derived from the regression plane of the prevailing circulation on the respective day. Subsequently, the temperature patterns were used to define the analog day from the subsample. For future periods, the same method was applied to model data for two representative concentration pathways (RCP4.5, RCP8.5) of different general circulation models (GCM: ACCESS1-0, CNRM-CM5, MPI-ESM-LR). Thus, we derive future time series of analogs corresponding to events prevailing in the observational period. To account for projected trends of the GCMs, the trends of all time-series were first removed and, after the analog selection process, added again according to the trends of the GCMs.

Temperature extremes are defined as days with temperatures exceeding the 90th quantile (Q90) and heat days are defined as days where at least two temperature indices (TMIN, TMEAN, TMAX) exceed Q90. When at least three consecutive days are defined as heat day a heat wave is proclaimed. Analysis have shown that under consideration of RCP8.5 (RCP4.5) and all model runs the number of heat days in the end of the 21st century will be nine (five) times higher than within the reference period 1970-2000. Furthermore, the mean duration of heatwaves will extend by factor four (two), whereby heat waves of more than 30 (15) consecutive days are possible.
A new educational seismic network in the city of Barcelona
Authors: Diaz Jordi , Schimmel Martin , Ruiz Mario , Carbonell Ramon
Published: March 2020

Connecting students with Earth Sciences in general, and seismology in particular, is challenging in countries not usually affected by strong earthquakes. In order to mitigate this problem, we have designed a citizen science experiment supported by the SANIMS research project (Spanish Ministry of Science, Research and Innovation, Ref.: RTI2018-095594-B-I00). The experiment is based on the deployment of a temporal network of 15 short-period seismometers within the city of Barcelona, mostly located in the basement of secondary schools, with a twofold objective; acquire new valuable scientific data and introduce the students in an Earth Science research project.

Many citizen activities produce vibrations that can be recorded seismically, and our experience shows that these records attract the attention of the students, press media and social networks. Our objective is to introduce secondary school students to seismology and Earth Sciences by exploring the data acquired in its own school, looking for earthquakes, but also for the ground vibrations generated by human activities. We will benefit from the low-cost and easy-to-use instruments developed by RaspberryShake, which provides online access to the data in real-time, hence making easier the implication of the students in the project. First results show that clear seismic arrivals from regional and distant earthquakes can be recorded within the city and that it is possible to identify ground vibrations generated by meteorological events, road traffic, transportation systems, fireworks or sports events.

Besides the educational motivation, the data acquired in this citizen science project is expected to provide valuable scientific results relative to the characterization of the uppermost crust using methods based in the analysis of the ambient background vibrations. 
Interactive stratospheric aerosol model experiments suggest a strong impact of climate change on the aerosol evolution and radiative forcing from future eruptions.
Authors: Aubry Thomas , Schmidt Anja , Haywood Jim
Published: March 2020

Radiative forcing from stratospheric volcanic sulfate aerosols is a key driver of climate variability. However, climate change may also impact volcanic forcing which remains largely unexplored. Atmospheric processes indeed control virtually all mechanisms that govern volcanic forcing, such as the rise of the volcanic column, the chemical and microphysical evolution of volcanic aerosols and their transport in the atmosphere.

Accordingly, we present novel numerical experiments combining chemistry-climate and volcanic plume modelling to investigate how climate change will affect volcanic forcing. We compare the aerosol evolution and radiative forcing following two eruption cases in two different climates (historical 1990’s and SSP5 8.5 2090’s). We chose two tropical eruptions: i) a strong intensity (i.e., mass flux), Pinatubo-like eruption emitting 10 Tg of sulfur dioxide (SO2); and ii) a moderate intensity eruption emitting 1 Tg of SO2, similar to eruptions such as those of Merapi in 2010, Nabro in 2011 or Kelud in 2014, which have had major impacts on the stratospheric aerosol background and are thought to have contributed to the global temperature hiatus in the early 21st century. The chemistry-climate model that we use (UM_UKCA version 11.2) has the capacity to interactively simulate the chemical and microphysical evolution of stratospheric sulfate aerosol given an initial injection of SO2. Furthermore, we use a plume model to calculate SO2 injection heights for a given eruption intensity and atmospheric conditions simulated by UM-UKCA.

In our experiments, the peak stratospheric aerosol optical depth (SAOD) of the high-intensity, Pinatubo-like eruption increases by 10% in the SSP5 8.5 2090 climate compared to the historical 1990 climate. Furthermore, the peak global-mean top-of-the-atmosphere radiative forcing of the same eruption increases by 30%. In contrast, the peak SAOD of the moderate intensity eruption decreases by a factor of 4 (with radiative forcing being small compared to simulated natural variability). Our results thus suggest that volcanic forcing will become more extreme and polarized in the future, with the forcing associated with moderate-intensity and relatively frequent eruptions being muted, but the forcing associated with high-intensity and relatively rare eruptions being amplified. We analyze which mechanisms are responsible for the simulated impacts of climate change on volcanic forcing, and discuss potential additional feedbacks expected in our future ocean-atmosphere coupled simulations.
Revisiting the Identification of Wintertime Atmospheric Circulation Regimes in the Euro-Atlantic Sector
Authors: Falkena Swinda , de Wiljes Jana , Weisheimer Antje , Shepherd Theodore G.
Published: March 2020

A number of methods exist for the identification of atmospheric circulation regimes. The most commonly-used method is k-means clustering. Often the clustering algorithm is applied to the first several principal components, instead of the full field data. In addition, many studies use a time-filter to get rid of high frequency oscillations before the clustering is executed. We discuss the consequences of these filtering techniques on the identified circulation regimes for the Euro-Atlantic sector in winter. Most studies identify four regimes: the Atlantic Ridge, the Scandinavian Blocking, and the two phases of the North Atlantic Oscillation. However, when k-means clustering is applied to the full field data of a reanalysis dataset, the optimal number of regimes is not found to be four, but six. This optimal number is based on the use of an information criterion, together with consistency arguments. The two additional regimes can be identified as the opposite phases of the Atlantic Ridge and Scandinavian Blocking, since they have a low-pressure area where the original regimes have a high-pressure area. Furthermore, the incorporation of a persistence constraint within the clustering algorithm is found to preserve the occurrence rates of the regimes, and thus maintains the consistency of the results. In contrast, applying a time-filter to enforce persistence of the regimes changes the occurrence rates. We conclude that care must be taken when filtering the data before the clustering algorithm is applied, since this can lead to biases in the identified circulation regimes and their occurrence rates.