bluuebunny/crossref_metadata_2025 huggingface dataset:
On the prospects of a future GNSS constellation on the global terrestrial reference frame
Authors: Glaser Susanne , Michalak Grzegorz , Koenig Rolf , Maennel Benjamin , Schuh Harald
Published: March 2020

Global terrestrial reference frames (TRFs), as one of the most important geodetic products, currently miss the imperative requirements of 1 mm accuracy and 1mm/decade long-term stability. In this study, the prospects of a future Global Navigation Satellite System (GNSS) to improve global TRFs is assessed by simulations. The future constellation, named “Kepler”, is proposed by the German Aerospace Center DLR in view of the next generation Galileo system. In addition to a contemporary Medium Earth Orbit (MEO) segment with 24 satellites in three orbital planes, Kepler consists of six Low Earth Orbit (LEO) satellites in two near polar planes, all carrying long-term stable optical clocks. The MEO satellites in one orbital plane and the LEO and MEO satellites in different planes are connected with optical two-way inter-satellite links (ISLs) as the innovative key feature. The ISLs allow very precise range measurements and time synchronization (at the picosecond-level) between the satellites. Different simulation scenarios are set up to evaluate the impact of the Kepler features on the TRF-defining parameters origin and scale as well as on the Earth rotation parameters (ERPs). The origin of a Kepler-only TRF improves considerably by factors of 8, 8, and 43 in X, Y, and Z direction, respectively, w.r.t. a Galileo-only solution. The scale realized by a Kepler-TRF shows improvements of 34% w.r.t. Galileo-only. In a combination with simulated observations of Very Long Baseline Interferometry the impact on multi-technique TRFs is assessed as well. The ERPs of both techniques are combined as global ties and benefits especially on the determination of UT1-UTC are expected.
Measurements and modelling of the impacts of light absorbing impurities during two contrasted snow seasons at Col du Lautaret
Authors: Dumont Marie , Tuzet Francois , Picard Ghislain , Lamare Maxim , Voisin Didier , Nabat Pierre , Lafaysse Matthieu , Larue Fanny , Revuelto Jesus , Arnaud Laurent
Published: March 2020

Light absorbing impurities (LAP) in snow, such as dust or black carbon, trigger potent snow-climate feedbacks. However, detailed measurements of the evolution of LAPs in seasonal snow are scarce, especially in the Alps. Here, we conducted detailed measurements of LAP in snow, snow physical and optical properties in the French Alps at a high altitude site. The dataset includes chemical measurements of mineral dust and black carbon (precisely elemental carbon and refractory black carbon), as well as spectral albedo measurements. The analysis of this dataset reveals strong discrepancies between elemental carbon and refractory black carbon measured concentrations, making it challenging to link the content of LAP to their radiative impacts. Using the dataset, the ensemble version of the Crocus snow model is evaluated and used to estimate the impacts of light-absorbing particles on snow cover evolution. Their impact on snowmelt turns out to be extremely sensitive to both meteorological conditions and uncertainties of the snow model, with a median shortening of 10 days for both snow seasons.
PLANTENNA: 3D-sensor networks monitoring plant environment. An application for fruit frost protection
Authors: Ten Veldhuis Marie-Claire , Van de Wiel Bas , Fan Qinwen , Steeneken Peter
Published: March 2020

Environmental field conditions are highly variable in three-dimensions and unsuitable to be probed by a single sensor or weather station. In PLANTENNA, a team of electronics, precision and microsystems engineers and plant and environmental scientists collaborate to develop and implement 3D-sensor networks that measure plant and environmental parameters at high resolution and low cost. A first problem we aim to tackle in the field is 3D-monitoring of fruit farms for detection and mitigation of fruit frost damage. The objectives are two-fold:

- To quantify the time-dependent effects of frost mitigation measures on the 3D temperature profile, and to determine the resulting plant-physiological response to get a better understanding of the underlying mechanisms leading to frost damage.

- To develop low-cost, low power, wireless, distributed sensor networks, with automated mathematical data handling to give real-time visualization of subzero temperature regions as decision support system for the farmer.

Field implementation: A fruit farm will be equipped with optical fibre cables for Distributed Temperature Sensing, along horizontal and vertical profiles in the field. This will reveal how cooling penetrates the canopy as a function of time, and how this is influenced by changing atmospheric conditions and mitigation efforts. Detailed temperature monitoring is related to spatio-temporal physiological monitoring at the level of individual trees.

In a next step, the cables will be replaced by a 3D-network of  temperature sensors. The aim is to develop an accurate (±0.5°C accuracy with a resolution << 0.1°C), low cost sensor with ultra-low power consumption (~ 100 nW). The sensor is based on a PCB-based node that consists of a PV module to collect solar energy, a power management integrated circuit (PMIC), a supercapacitor to store energy, a temperature sensor, a microcontroller (µC), a timing control unit (TCU) to enable/disable the system, and a radio frequency IC (RFIC) + antenna to transmit data to the network. To reduce energy consumption, it should operate in low-power “sleep mode” as much as possible, while still being able to capture sudden temperature changes as by ventilator activation: the sensor must decide when to “wake up” and how frequently to measure. The often “power-hungry” MCU and RF radio should operate in an event-driven mode and only “awakened” when the sensor detects a temperature change above a certain threshold.
We chose LoRa for its low power consumption and long-distance capability, which is a perfect match with our application.
Soil organic carbon sequestration potential of reforesting riparian areas in an agricultural watershed in the state of São Paulo, Brazil
Authors: Galera Leonardo de Aro , Martinelli Luiz Antonio
Published: March 2020

Fighting climate change has never been so urgent as today. As geoscientific research advances, more realistic and appalling future climate scenarios are unraveled. Decreasing greenhouse gases (GHG) emissions is not sufficient to avoid a bad outcome; hence, mitigation actions are needed to reduce climate-related risks in the future. The depletion of the soil organic carbon (SOC) pool due to land use change and soil degradation have substantially contributed to the increase in the atmospheric CO2 concentration. Likewise, the sequestration of C by the soil is crucial to reverse this issue. These are especially important processes in the tropics where the replacement of native vegetation by agriculture still occurs at a high rate. Brazil is one of the biggest agricultural producers in the world. In 2018, agriculture and land use change represented 70% of the total Brazilian GHG emissions. Fortunately, Brazil also has opportune mitigation options. Since 1965, the Brazilian Forest Code requires landowners to conserve native vegetation by means of Riparian Preservation Areas, among other categories. Riparian forests provides several ecosystem services like water protection, biodiversity conservation and carbon sequestration. Frequently, the discussion over the carbon sequestration potential of riparian forests focus on the aboveground carbon, nevertheless, SOC stocks are more stable and protected from natural and anthropogenic hazards. We consider that the mandatory reforestation of riparian zones is a significant mitigation strategy in Brazil, owing to the potential of SOC sequestration by Brazilian biomes and the extensive area to be reforested. The objective of this study was to assess the SOC stocks of the main land uses of an agricultural watershed located in the state of São Paulo, Southeastern Brazil, and estimate the change in the SOC stocks that would occur with the reforestation of the riparian areas of this watershed. In order to achieve this goal, we compared the SOC stocks of riparian forests with the two main agricultural uses of the region, namely pasture and sugarcane. The mean SOC stock at 30 cm for riparian forests was of 44 Mg.ha-1, for pastures was of 26 Mg.ha-1 and for sugarcane was of 27 Mg.ha-1. Although the riparian forests of the region are often poorly preserved, they contained considerably more SOC at 30 cm than the agricultural uses. Based on the estimates of the SOC stocks of the main land uses and the extent of the riparian zones of the sampled sites, we could foresee an accretion of 20% of organic carbon in the 30 cm soil layer of those areas. We hope that this study highlight the importance of the riparian forests and the ecosystem services they provide, and the relevance of the Brazilian Forest Code in the mitigation of climate change.
Tectonic structures vs genesis and activity of mud volcanoes: examples from Emilia and Marche (Northern Apennines, Italy)
Authors: Bonini Marco , Maestrelli Daniele , Sani Federico
Published: March 2020

Mud volcanism is known to be strictly linked to anticlines, since these structures have the ability to trap hydrocarbons and other fluids into reservoirs placed at their core, where large overpressures may be generated. Despite mud volcanoes have been widely studied, a central and still debated theme is (i) how fluids are able to migrate upward bypassing the overburden and erupt at surface, and (ii) which role near-structures (i.e. structure directly linked to the mud volcano system, or located not far from it) and far-structures (i.e. faults located far away from the mud volcano system) may play in this process. In an effort to address these questions, we investigated the role of both types of structures in the genesis and evolution of mud volcanoes. In particular, we show six mud volcano case studies from the Emilia-Romagna and Marche pede-Apennine margin, in Italy. We integrated fieldwork data and interpretation of available seismic reflection profiles whit aerial photo analysis. Our results support the intimate link of the investigated mud volcano systems with anticline structures on top of which they are typically emplaced. We then discuss two distinct settings for fluid migration and mud volcano formation, particularly: (i) mud volcanoes emplaced on outcropping anticlines, and (ii) mud volcanoes located on top of buried structures, discerning when fluids are likely to exploit anticline-related fracture sets, or secondary structures and porosity. Finally, we speculate on how far-structures may still play a crucial role, via seismic triggering, in the occurrence of historical eruptions of some of the investigated mud volcano systems.
No Evidence for Brown Carbon Formation in Ambient Particles Undergoing Atmospherically Relevant Drying
Authors: Pratap Vikram , Battaglia Jr. Michael , Carlton Annmarie , Hennigan Christopher
Published: March 2020

Recent laboratory studies have reported the formation of light-absorbing organic carbon compounds (brown carbon, BrC) in aqueous particles undergoing drying.  Atmospheric particles undergo cycles of humidification and drying during vertical transport and through daily variations in temperature and humidity, which implies particle drying could potentially be an important source of BrC globally.  In this work, we investigated BrC formation in ambient particles undergoing drying at a site in the eastern United States during summer.  Aerosol BrC concentrations were linked to secondary organic aerosol (SOA) formation, consistent with seasonal expectations for this region.  Measurements of water-soluble organic aerosol concentrations and light absorption (365 nm) were alternated between an unperturbed channel and a channel that dried particles to 41% or 35% relative humidity (RH), depending on the system configuration. The RH maintained in the dry channels was below most ambient RH levels observed throughout the study.  We did not observe BrC formation in particles that were dried to either RH level. The results were consistent across two summers, spanning ~5 weeks of measurements that included a wide range of RH conditions and organic and inorganic aerosol loadings.  This work suggests that mechanisms aside from humidification-drying cycles are more important contributors to ambient particle BrC loadings.  The implications of this work on the atmospheric budget of BrC are discussed.
A tribute to Marie Tharp: Mapping the seafloor of back-arc basins, mid-ocean ridges, continental margins and plate boundaries
Authors: Gràcia Eulàlia , Martínez Loriente Sara , Diez Susana , Gómez de la Peña Laura , Serra Cristina S. , Bartolome Rafael , Sallarès Valentí , Lo Iacono Claudio , Perea Hector , Roger Urgeles , Ingo Grevemeyer , Ranero Cesar R.
Published: March 2020

Marie Tharp (1920-2006) was a pioneer of modern oceanography. She was an American geologist and oceanographic cartographer who, together with his husband Bruce Heezen, generated the first bathymetric map of the Atlantic Ocean floor. Tharp's work revealed the detailed topography and geological landscape of the seafloor. Her work revealed the presence of a continuous rift valley along the Mid-Atlantic Ridge axis, causing a paradigm in earth sciences that led to the acceptance of plate tectonics and continental drift theories. Piecing maps together in the late 1940s and early 1950s, Marie and his partner Bruce Heezen discovered the 75.000 km underwater ridge bounding around the globe. By this finding, they laid the conclusion from geophysical data that the seafloor spreads from mid-ocean ridges and that continents are in motion with respect to one another—a revolutionary geological theory at that time. Many years later, satellite images demonstrate that Tharp’s maps were accurate. In this contribution, we focus on detailed bathymetric maps collected from year 1992 to today, which include bathymetric maps from diverse parts of the world. For instance, we will show a) Back-arc basins (i.e. the Bransfield Basin, Antarctica; and the North Fiji Basin, SW Pacific); b) Mid-ocean ridges and fracture zones (i.e. the MAR at the South of Azores, the MAR at the Oceanographer-Hayes, and the St. Paul Fracture Zone at the Equator), and c) Active tectonic structures from the Gulf of Cadiz and Alboran Sea, located at the Africa-Eurasia plate boundary (Gibraltar Arc). Regarding this last area, we will characterize the seafloor expression of the fault systems, as well as the subsurface structure of the faults in the Gulf of Cadiz and Alboran Sea. This zone is characterized by a moderate seismicity, mainly reverse and strike-slip focal mechanisms; although large historical (AD1755, AD1829) and instrumental earthquakes or large/great magnitude also occurred, such as the earthquakes of 1969, 1994, 2004 and 2016. In addition, the Gulf of Cadiz-Alboran Sea area is compartmentalized in different crustal domains, bounded by active strike-slip fault systems. We adopted a multi-scale approach, including morphological analysis of shipboard multibeam bathymetry, near-bottom bathymetry obtained with Autonomous Underwater Vehicles (AUVs) at a resolution of 1-2 m, and medium to deep penetration multi-channel seismic (MCS) data. Finally, we will also show a couple of videos from recent marine cruises in the Gibraltar Arc (SHAKE-2015 and INSIGHT-2018), both using state-of-the-art high-resolution marine technologies.
Long-term properties of the solar wind and their relation to solar cycles
Authors: Salohub Anna , Šafránkova Jana , Němeček Zdeněk , Přech Lubomír , Ďurovcová Tereza
Published: March 2020

The solar wind variations during particular solar cycles have been described in many previous studies including the solar cycle 23 that was characterized by a long, deep, and very complex solar minimum with very low values of many solar wind parameters.

Using statistical methods, we analyzed 25 years of Wind spacecraft measurements with motivation to reveal differences and similarities in magnetic field components and solar wind plasma parameters in individual solar cycles. We tracked the changes of the solar magnetic field strength, and components, solar wind speed, density, dynamic pressure, temperature, and composition). Except quiet solar wind conditions during solar minima and maxima, we also selected significant discontinuities (ICME and CIRs) and investigated their influence on profiles of average parameters. For this, we followed other quantities connected with their presence as their average front normals, regions of transitions between high and slow wind streams, special interplanetary magnetic field orientations, etc.). We discuss a behavior of investigated parameters over solar cycles as well as on shorter time scales (in the order of days and hours).
Community Water Watch: Measurements, Forecasts and Impacts
Authors: van de Giesen Nick , Annor Frank , Hagenaars Rick , Izeboud Petra , Shoo Vivaoliva , Trambauer Patricia , Vaidya Shristi , Wagemaker Jurjen , Winsemius Hessel
Published: March 2020

Dar es Salaam is subject to regular flooding, especially from the Msimbazi River, causing tens of deaths and over $100 million damages per year. Dar es Salaam is not an exceptional case, as many cities in the Global South face rapid urban expansion, which causes increased impermeable services, clogging of drains by sediment and solid waste, as well as encroachment of the floodplains. Although in the long term, structural measures are needed, much is to be gained short term by a flood early warning system that aims to increase situational awareness and optimise allocation of resources during and after floods. The Community Water Watch project, which contributes to the Tanzania Urban Resilience Program, addresses these aspects through a mixture of data streams.

In an online dashboard, these three data streams come together to create meaningful information. First, a dense network of TAHMO weather stations and two hydrological stations report in near-real time the atmospheric input and state of the system. Second, a hydraulic model uses this information to provide forecasts in terms of discharge, flood levels, and flood extents. Finally, social media platforms, such as Twitter, Telegram, WhatsApp, and JAMII Forums, are continuously searched for texts and photos concerning flooding to provide an overview of flood impacts and ways in which people are dealing with them. Tailor-made dashboards have been built to cater to different users such as the Tanzania Red Cross Society and the local transportation company DART. Due to the intense co-creation processes during the design of the system, these dashboards have already produced actionable information that has prevented damages and possibly has saved lives. The solution is very scalable to any city dealing with similar flood problems.
Magnitude estimation of a landslide-triggered debris flow in the Serra do Mar Mountain Range, Brazil
Authors: Carvalho Cabral Victor , Mazo D'Affonseca Fernando , Fischer Gramani Marcelo , Tadashi Ogura Agostinho , Santos Corrêa Claudia , Martinez Mendoza Carolina , Veloso Vinicius , Vieira Reis Fábio
Published: March 2020

Debris flows represent great hazard to communities and infrastructures, since they move quickly and are very destructive. In Brazil, debris flows mainly occur in the Serra do Mar Mountain Range, where thousands of casualties were reported in the last two decades due to these phenomena. This study aims at estimating the magnitude of a debris-flow event that occurred in Serra do Mar on February 2017, at the Pedra Branca watershed in the State of Paraná. Debris-flow magnitude refers to the volume of material discharged during an event and is an important aspect of debris-flow hazard assessment. The Pedra Branca event was initiated by rainfall-triggered shallow landslides, damaging local oil pipelines and farms. The magnitude estimation is based on the combination of empirically based equations and the geomorphic features of the debris flow, acquired from in situ and aerial investigation. 28 cross-sections were made along the river channel, considering post-event channel width, erosion and accumulation depth, as well as depositional features. Sediment sources and accumulation areas were identified and delimitated based on high-resolution (1:500) aerial drone photographs. The results indicate that the landslides that initiated the event released approximately 26,884.5 m3 of sediments (Vi) into the main channel of Pedra Branca and that the volume eroded (Ve) and accumulated (Vd) along the channel are, respectively, 82,439 m3 and 22,012 m3. The estimated total solids volume (Vs) is 87,274 m3, assuming that Vs = Vi + Ve - Vd. Moreover, considering a solids concentration of 57% calculated according to empirically-based equations for Serra do Mar, the debris flow had a total magnitude of 153,113 m3. These estimations suggest that the February 2017 debris flow mobilised great volume of material and that 15% of the total volume accumulated on the channel bed, which can be remobilised by future events. Further research on debris-flow dynamics and recurrence at the Serra do Mar Mountain Range is recommended to mitigate future hazards.
Dynamic Seepage Meter: Theory with Application Examples
Authors: Zlotnik Vitaly A. , Solomon D. Kip , Gilmore Troy E. , Genereux David P. , Humphrey C. Eric
Published: March 2020

Most single-point methods of measuring seepage fluxes across the surface water-groundwater interface in lakes, streams, and estuaries (e.g., volumetric, head-based, and thermal) have one trait in common: they produce seepage rate values, averaged over substantial periods of time, thereby limiting resolution of the intra-day dynamics. Recently, Solomon et al. (Water Resources Research, 2019, in review) presented a new instrument and modification to a previously tested concept (Solder et al., Groundwater, 2016). This instrument has an open-bottom permeameter (OBP) design, which is commonly used for investigating hydraulic conductivity of the interface with falling or rising head tests, but historically not used for flux estimates. The novel dynamic seepage meter (DSM) evaluates the transient water level in the OBP-based instrument with submillimeter accuracy, exceeding the performance of traditional pressure transducers. The initial dynamics of the water level response over fractions of an hour holds the necessary information to infer the natural seepage rate in both gaining and losing conditions. The tests can be repeated frequently in an automatic regime. If a single test lasts long enough, hydraulic conductivity, in addition to the seepage rate can also be accurately determined. Here, a detailed hydrodynamic theory of the flow systems inside and outside the OBP is presented and the accuracy of measured water fluxes is investigated with emphasis on interpretation of the data with ambient noise. The results of this study will facilitate rapid, accurate, and massive data collection in diverse field conditions. (Research was supported by the NSF grant EAR 1744719.)
Combining in situ observations and high resolution VENμS data to monitor temperate deciduous shrub and tree phenology
Authors: Donnelly Alison , Yu Rong
Published: March 2020

Direct in situ phenological observations of co-located trees and shrubs help characterize the phenological profile of ecosystems, such as, temperate deciduous forests. Accurate determination of the start and end of the growing season is necessary to define the active carbon uptake period for use in reliable carbon budget calculations. However, due to the resource intensive nature of recording in situ phenology the spatial coverage of sampling is often limited. In recent decades, the use of freely available satellite-derived phenology products to monitor ‘green-up’ at the landscape scale have become commonplace. Although these data sets are widely available they either have (i) high temporal resolution but low spatial resolution, such as, MODIS (daily return time; 250m) or (ii) low temporal resolution but high spatial resolution, such as, Landsat (16-day return time; 30m). However, the recently (2017) launched VENμS (Vegetation and Environment monitoring on a New Micro-Satellite) satellite combines both high temporal (two-day return time) and spatial (5-10m) resolution at a local scale thus providing an opportunity for small scale comparison of a range of phenometrics. The next challenge is to determine what in situ phenophase corresponds to the satellite-derived phenology. Our study site is a temperate deciduous woodlot on the campus of the University of Wisconsin-Milwaukee, USA, where we monitored in situ phenology on a range of (5) native (N) and (3) non-native invasive (NNI) shrub species, and (6) tree species for a 3-year period (2017-2019) to determine the timing and duration of key spring (bud-open, leaf-out, full-leaf unfolded) and autumn (leaf color, leaf fall) phenophases. The monitoring campaign coincided with the 2-day return time of VENμS to enable direct comparison with the satellite data. The shrubs leafed out before the trees and the NNIs, in particular, remained green well into the autumn season when the trees were leafless. The next step will be to determine what exact in situ phenophses correspond to NDVI (Normalized Difference Vegetation Index) and EVI (Enhanced Vegetation Index) derived start, peak and end of season from MODIS and VENμS data. In addition, we will determine if VENμS can detect differences in phenological profile between N and NNI shrubs at seasonal extremes. We anticipate that the high resolution VENμS data will increase the accuracy of phenological determination which could help improve carbon budget determination and inform forest management and conservation plans.
Theory of low-temperature deuteric oxidation with application to time evolution of ocean magnetic anomalies
Authors: Shcherbakov Valera , Fabian Karl
Published: March 2020

The NRM of the ocean floor is carried by titanomagnetite grains that undergo low-temperature oxidation after initial cooling. Progressing oxidation is known to generate shrinkage cracks in   grains larger than approximately 5 mkm, and is suspected to   control the long wavelength variation of NRM-intensity across the ocean floor. Here we develop a quantitative theory of single-phase oxidation and crack formation by solving the vacancy-diffusion equation that describes the oxidation process for spherical titanomagnetite particles, where the diffusion coefficient strongly decreases with vacancy concentration. The latter dependence has been experimentally demonstrated and is essential to explain the peculiarities of the observed variations of oxidation-degree with ocean-floor age. The calculated diffusion profiles provide the exact stress distributions inside oxidized titanomagnetite spheres, and  predict a size limit for shrinkage-crack formation that agrees   with   microscopic observations of crack appearance in ocean-floor basalt samples. The new diffusion model provides a unified explanation of long-known experimental facts that 1) temperatures for the onset of low-temperature oxidation during laboratory heating are theoretically estimated as 200-400 °C, depending on grain size, and 2) that heating to 400-500 °C is required to obtain a sufficiently high degree of oxidation z about 0.8  for the development of  high-temperature exsolution lamellae. Calculations for ocean-floor conditions    quantitatively suggest that a rapid decrease of NRM intensity during the first 40 ka  results from  a deflection of magnetization by strong stresses that emerge in titanomagnetite grains of sub-critical sizes, and randomization of domain-state by crack formation in larger grains. This work was supported by Russian Science Foundation grant 19-47-04110401 (VS)
Aircraft campaigns in support of the North Atlantic Climate System Integrated Studies (ACSIS)
Authors: Archibald Alexander ,   The NERC ACSIS Team
Published: March 2020

The North Atlantic is witnessing major changes during the Anthropocene. These include changes in the physical climate system: in ocean and atmosphere temperatures and circulation; in sea ice thickness and extent; and in atmospheric composition, where ozone, ozone precursors and aerosols have undergone significant changes over the last few decades. Changes in aerosols over the North Atlantic have been linked to changes in sea surface temperatures (SST) and North Atlantic climate variability. A long-term research project, The North Atlantic Climate System Integrated Study (ACSIS), involving data collection and interpretation, has begun to better understand the processes and composition-climate interactions associated with these changes. Here we report on one of the major observational components of the ACSIS programme which involves repeated measurements of the composition of the North Atlantic using the NERC FAAM BAe146. To date six campaigns have taken place including three which coincided with the NASA ATom campaigns (2-4). 

In this presentation we will discuss the rationale for the aircraft project and recent results including the observation of transport of biomass burning plumes into the North Atlantic that are estimated to have originated from fires sampled as part of the NASA FIREX campaigns during the summer of 2019. We will highlight results from an intercomparison with the NASA DC-8 during our second campaign and ATom 3, which reveal good agreement in measurements of O3, CO and NOx between the two aircraft but large differences in measurements of non-methane VOCs, and we will summarise our results to-date including the comparison against chemical transport models. 

 
Winter draining lakes on the Greenland ice sheet observed by Sentinel-1
Authors: Benedek Corinne , Willis Ian
Published: March 2020

Supraglacial lakes on the Greenland Ice Sheet influence surface mass balance, the delivery of water from the surface to the bed, and the rate of basal sliding.  Summertime lake drainage behavior has been catalogued thoroughly through the use of optical remote sensing with a variety of satellites.  Radar results from Operation IceBridge demonstrated the presence of liquid water buried in lakes under ice lids but this platform is limited in its capability to examine short-term changes over the winter season.  This study describes the drainage of multiple buried lakes through the winter season using Sentinel-1 C-Band SAR.  Sudden positive anomalous changes in mean backscatter of surface lakes that are sustained over time are used to pick out wintertime (October through May) lake drainages over a four-year study period.  These changes are confirmed using late-Autumn and early-Spring Landsat-8 photoclinometry changes.  Drainages are detected from November through February, pointing to the likelihood of water injection to the bed through the winter season.  Our automated techniques involve quantifying patterns and trends in SAR backscatter and are also being developed to contribute to our understanding of water storage vs. refreezing in lakes and firn on the surface and in the shallow sub-surface regions of the Greenland Ice Sheet throughout the year.
Prominent influence of salinity on Atlantic hurricane rapid intensification
Authors: Balaguru Karthik , Foltz Gregory , Leung Ruby , Kaplan John , Xu Wenwei , Reul Nicolas , Chapron Bertrand
Published: March 2020

Rapid Intensification (RI) of hurricanes is difficult to predict and poses a formidable threat to coastal populations. While a warm upper-ocean is well-known to favor RI, the role of salinity is less clear. In this study, using a suite of observations, we demonstrate that the subsurface oceans' influence on Atlantic hurricane RI exhibits two regimes. In the western region, which includes the Gulf of Mexico and the western Caribbean Sea, temperature stratification plays an important role in hurricane RI with little impact from salinity. On the other hand, in the eastern region dominated by the Amazon-Orinoco plume, salinity stratification prominently impacts RI. While a weak temperature stratification aids cold wake reduction for hurricanes in the western region, a strong salinity stratification causes less hurricane-induced mixing and surface cooling in the eastern region. Finally, in both regions, the relevance of the cold wake, and consequently the ocean sub-surface, is enhanced during RI compared to weaker intensification.
A Review of Monsoon Responses to Warm Climates
Authors: Seth Anji , Giannini Alessandra , Rojas Maisa , Rauscher Sara , Bordoni Simona , Singh Deepti , Camargo Suzana
Published: March 2020

Knowledge of how monsoons will respond to external forcings through the twenty-:rst century has been confounded by incomplete theories of tropical climate and insuZcient representation in climate models. This talk will overview recent insights from past warm climates and historical trends that can inform our understanding of monsoon evolution in the context of an emerging energetic framework. A theoretical framework interprets monsoons as an integral part of the global atmospheric overturning circulation, and associated energy, angular momentum, and moisture budgets, rather than regional land-sea breeze circulations. The discussion will include monsoon responses to (1) external forcing in paleoclimate records, (2) external forcing and internal variations in observed records, and (3) anthropogenic forcing in future projections. Lines of evidence from warm climate analogues indicate that while monsoons respond in globally coherent and predictable ways to orbital forcing and interhemispheric thermal gradients, there are differences in response to these forcings and also between land and ocean. Re:ning the energetic framework to incorporate zonal asymmetries will be critical to gain further insights into monsoon evolution at regional scales.
A high resolution ultraviolet spectroradiometer and its application in solar radiation measurement
Authors: Min Qilong , Yin Bangsheng , Berdnt Jerry , Lee Harrison , Zhu Lei
Published: March 2020

An ultraviolet (UV) spectroradiometer is refurbished and upgraded with a fore-optical module. In addition to measuring total UV irradiance, the UV spectroradiometer can measure solar direct beam and sky radiance at any preset azimuth and elevation angle. This double Czerny-Turner spectroradiometer, with an ion-etched holographic grating operating in the first order with 3600 lines per mm, enables wavelength scanning range from 290 nm to 410 nm, with a nominal bandwidth of 0.1 nm.  It can operate with a step-size of 0.0005 nm and a full width at half maximum of 0.1 nm. It has an out-of-band rejection ratio of approximately 10–10. This high resolution spectroradiometer can be used as a reference instrument for UV radiation measurements and to monitoring atmospheric gases (O3, SO2, NO2). Recently laboratory work suggests that water vapor displays structured absorption features over 290-350 nm region with maximum and minimum cross-sections of 8.4×10-25 and 1.4×10-25 cm2/molecule. To investigate the water vapor absorption features in UV region in real atmosphere, we did a series of field observations by using this high resolution spectroradiometer. A residual analysis method is developed to analyze the absorption of atmospheric components and to retrieve the atmospheric optical depth. The residual spectra of multiple cases have spectral features similar to that of in-lab measured water vapor absorption in some wavelength regions, and the inferred ozone amount from residual analysis agrees with OMI retrievals. Through multiple case studies, the magnitude of residual optical depth from observed UV spectra is sensitive to the atmospheric water vapor amount. The greater the water vapor path, the larger the difference between observational spectra and calculated spectra without considering water vapor absorption.
Unstructured Grid based Fuzzy Cooperative Resistivity Tomography for Electrical and Electromagnetic data
Authors: Singh Anand
Published: March 2020

There are many inversion algorithms that have been developed in the literature to obtain the resistivity distribution of the subsurface. Recovered resistivity values are usually lower/higher than the actual resistivity as a consequence of the inversion algorithms. As a consequence, Identification of geologic units based on resistivity distribution can be done on a relative scale. In general, identification of different geologic units is a post step inversion process based on resistivity distribution in the study region.  I have presented a technique to enhance the resistivity image using cooperative inversion (named as fuzzy cooperative resistivity tomography) where two additional input parameters are added as the number of geologic units in the model (i.e. number of cluster) and the cluster center values of the geologic units (mean resistivity value of each geologic unit). Fuzzy cooperative resistivity tomography fulfills three needs: (1) to obtain a resistivity model which will satisfy the fitting between measured and modeled data, (2) the recovered resistivity model will be guided by additional a priori parametric information, and (3) resistivity distribution and geologic separation will be accomplished simultaneously (i.e. no post inversion step will be needed). Fuzzy cooperative resistivity tomography is based on fuzzy c-means clustering technique which is an unsupervised machine learning algorithm. The highest membership value which is a direct outcome from the FCRT corresponds to a geology separation result. To obtain a geology separation result, I adopted the defuzzification method to assign a single geologic unit for each model cell based on the membership values. Various synthetic and field example data show that FCRT is an effective approach to differentiate between various geologic units. However, I have also noted that this approach is only effective when measured data sets are sensitive to particular geologic units. This is the limitation of the presented FCRT.
Capturing the 2018 Monsoon Onset in the Bay of Bengal from in-situ ship and mooring network observations
Authors: Tandon Amit , Shroyer Emily , Venkatesan Ramasamy , Lucas Andrew , Farrar J. Thomas , McPhaden Michael
Published: March 2020

Air-Sea interaction in the Bay of Bengal has a strong coupling with the Monsoon rains over the South Asian region. The wet and dry spells, or active-break cycles of the Asian summer monsoon are governed by different modes of intra-seasonal variability with implied northward and westward propagation. Multiple hypotheses exist as to how air-sea interaction and the ocean mixed layer influence the propagation of Monsoon Intra-seasonal Oscillations (MISO), but the multi-scale nature of atmosphere-ocean coupling is not well understood. Multi-country collaborative initiatives MISOBOB (Oceanic Control of Monsoon Intra-seasonal Oscillations in the Tropical Indian Ocean and the Bay of Bengal-USA), RIO-MISO (Role of the Indian Ocean on Monsoon Intra-Seasonal Oscillations-USA), and OMM (Ocean Mixing and Monsoons-India) have led to a combination of ocean observations, atmospheric observations, and associated modeling to study this phenomenon.

 

We present observations analyzed using the OMNI (Ocean Moored Buoy Network for Northern Indian Ocean) buoy network of India and RAMA 15N mooring along with MISOBOB field program in June 2018, which captured the onset of the 2018 Monsoon from a heavily instrumented ship that simultaneously made measurements in the atmospheric and oceanic boundary layers. The shortwave and net heat fluxes show dramatic changes during the active phase with the in-situ net heat flux reversing sign. The Monsoon onset cooled all of the Central and North Bay of Bengal by 1.5 K, leading to large heat losses in the Bay, as the oceanic surface mixed layer deepened from 20m to about 40m. This talk will also explore the role of sub-surface salinity stratification in modulating cooling of the upper ocean at multiple locations across the Bay, providing a basin-wide view. Observations suggest that the air-sea interaction and ocean stratification in the Bay likely has strong feedback on the organized convection in the atmosphere.
Determination of homogenous GRACE FOLLOW-ON monthly displacements based on available solutions
Authors: Lenczuk Artur , Klos Anna , Bogusz Janusz
Published: March 2020

Presently, Gravity Recovery and Climate Experiment (GRACE) mission data is widely used in various fields of science. The longest satellite gravimetric mission regularly explored changes of the gravity field from April 2002 to October 2017. Nowadays, its follow-on mission (GRACE-FO) observes gravity changes from May 2018, providing new greater research opportunities. In the following research, we present a completely new vertical deformations changes model of the first 14 months GRACE-FO observations. The study’s aim is to reduce the signal noise left after Gauss spatial smoothing. In this study, we use monthly gravity field in spherical harmonics form up to degree and order 96, provided by three different centers, i.e. the NASA’s Jet Propulsion Laboratory (JPL), the German Research Center for Geosciences (GFZ) and the Center for Space Research (CSR). In following study, we use all sets of data (JPL, GFZ and CSR) to test three various algorithms: (1) coefficient-wise and (2) field-wise non-iterative weighting methods and further, (3) estimation by iterative variance component method.  Finally, we obtain joined spherical harmonics changes by a weighted average scheme, which are converted to Earth crust vertical deformations. The used weighting methods reduce root mean square scatter of monthly deformation fields by nearly 5% for continental areas (excluding Amazon basin and Hudson Bay region) and by 10-15% changes for the ocean areas. However, with respect to each new-created model, differences in monthly deformation changes are in the range from ±3 mm to ±6 mm depending on the data center (JPL, GFZ or CSR). Furthermore, the analysis of signal information contained in each degree allows us to assess the quality of the created models. The highest signal variations in our models occur up to the degree and order 25. Additionally, the high differences in the signal are obtained for sectoral harmonics up to the maximum degree. Analysis showed that the applied field-wise weights much more effectively remove remaining noise after spatial averaging than per-order/degree weighting. Whereas, the obtained results indicate that observations provided by GFZ center have the smallest weights for each algorithm.
Experiments and interpretations on unsaturated hydraulic properties using water retention tests based on the membrane in Korea
Authors: Oh Seboong , Kim Sungjin , Son Kwang Ik
Published: March 2020

In unsaturated soils, the soil water retention curve (SWRC) is most important in the fundamental hydraulic properties. In order to measure SWRCs through an alternative method in Korea, high air entry disks were replaced by micro membranes. Micro membranes are thin in which the air entry value is around 100kPa. Tests with the membrane are fast to reduce the duration of infiltration through the high air entry disk.

The water retention curves using the membrane were compared with the data using high air entry disks from the volumetric pressure plate extractor and Tempe pressure cell for samples of various sites. As a result, the SWRCs using the membrane were very similar for most cases and the micro membrane was verified as a useful tool to measure SWRCs.

The unsaturated hydraulic behavior could be measured easily using the membrane than ceramic disks and the huge amount of data could have been obtained in Korea. Using DB of SWRCs, the hydraulic properties were interpreted based on the parameters of the van Genuchten SWRC model. The void ratio and density are correlated to SWRCs under the same classification soil.

Acknowledgements This research is supported by grant from Korean NRF (2019R1A2C1003604) and MOE (79608), which are greatly appreciated.
Detection of S-wave reflectors beneath aftershock area of the 2016 Kaikoura earthquake
Authors: Matsumoto Satoshi , Kawamura Yuta , Okada Tomomi , Matsuno Miu , Iio Yoshihisa , Sibson Rick , Savage Martha , Graham Kenny , Suzuki Manami , Bannister Stephen
Published: March 2020

S wave reflectors in the crust may be caused by strong heterogeneous structures such as ones containing  fluid. Especially, fluid around an earthquake fault could play an important role for initiation of the earthquake rupture as a mechanism for reducing fault strength. The location and geometry of the reflector can be determined from the travel time of the reflected phases. For detecting the reflections, we need to observe at stations located close to the hypocentre because of sufficient phase separation of the small lapse time of the reflected phases due to a reflector in the crust from direct S wave. In this study, we attempted to detect reflected waves in observed seismograms at the seismic stations in and around the 2016 Kaikoura earthquake (Mw7.6). Seismic records were obtained from the permanent GeoNet stations as well as from seismic stations deployed before the Kaikoura earthquake in the northern South Island. We applied reflection seismology techniques to the data obtained by the network. We used seismograms with smaller epicentral distance than 30 km and obtained dip move-out sections for each station. We detected several reflectors in the mid and lower crust from the sections. Strong reflected phases were observed at the southern edge of the focal area (from a reflector with depth about 20 km). Weak reflectors were detected in/beneath the aftershock area (in the mid- to lower-crust). In addition, the subducting slab might be imaged with dipping angle 20 degree.  Reflectors parallel to the slab were also found below the interface.
Quantitative measurement of OH radical using Faraday rotation spectroscopy at 2.8 µm
Authors: Zhao Weixiong , Fang Bo , Wei Nana , Yang Nana , Zhang Weijun , Chen Weidong
Published: March 2020

Hydroxyl (OH) radicals play a vital role in the degradation of trace gases and pollutants in the troposphere and in controlling the atmospheric oxidation capacity. Due to its short lifetime and low concentration, interference-free high sensitivity in situ OH monitoring by laser spectroscopy represents a challenge. In this presentation, we will report the development of Faraday rotation spectroscopy (FRS) instruments operating at 2.8 µm for quantitative measurement of OH concentrations in an atmospheric simulation chamber and the total atmospheric OH reactivity (k’OH). The Q (1.5) double lines (2Π3/2 (ν=1<-0)) at 3568 cm-1 were selected for the detection. Different detection methods have been studied. The FRS technology relies on the particular magneto-optic effect observed for paramagnetic species (including most radicals and some compounds with unpaired electrons), which can significantly reduce excess laser noise and makes it capable of enhancing the detection sensitivity and mitigation of spectral interferences from diamagnetic species in the atmosphere. With the use of a multipass enhanced FRS, a detection limit of 3.2 × 106 OH/cm3 (2σ, 4s) was achieved with an absorption path length of 108 m. We demonstrated that FRS method provides a unique method for atmospheric chemistry research.