bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial and temporal variation of snow cover in the Himalayan and Karakorum region using MODIS data (2000-2019)
Authors: Dharpure Jaydeo Kumar , Goswami Ajanta , Kulkarni Anil V.
Published: March 2020

The Himalayan and Karakorum (H-K) region comprise the highest amount of snow and ice cover outside the Polar Regions. The H-K region is grouped into four-part, i.e., the Karakorum (KK), Western (WH), Central (CH), and Eastern Himalayas (EH), based on climate and geographic location. The EH and CH mainly feed by summer-monsoon snowfall, whereas the KK and WH are winters accumulated. This regional variability of climate will affect the water availability for hydropower generation, agriculture, and ecosystem. Therefore, the mapping and monitoring of snow cover change over the study area played an essential role in the context of climate change. The snow cover area (SCA) was observed using Moderate-resolution Imaging Spectroradiometer (MODIS) daily snow cover products version 6 during 2000-2019. Different cloud removal techniques (e.g., multi-sensor, temporal, spatial, regional snow line, multiday backward) are applied to reduce the cloud cover pixels over snow pixels of the MODIS data. The mean annual SCA of the H-K region is ∼26.4% of the total geographical area during the study period. The statistical trend analysis of mean monthly, seasonal, and annual SCA is examined using Mann-Kendal and Sen’s slope test. The mean yearly SCA of the H-K region shows an increasing trend during 2000-2009 and start decreasing significantly during 2009-2019. Similar results are observed in the KK, WH, CH, and EH, which shows a decreasing trend of mean annual SCA since 2009. The mean seasonal SCA shows a significant decreasing trend in summer (June to September) and winter (December to February) since 2009, suggesting a seasonal shift or change in snow cover. Overall, the winter shows an insignificant decreasing trend in comparison to the other seasons during 19 hydrological years (2000-01 to 2018-19). The mean monthly minimum SCA observed in August for the KK and WH, July for the CH, and June for the EH. However, the mean maximum SCA in February for the KK, WH, CH, and March for the EH. The snow cover depletion curve suggests that the maximum SCA in February and minimum in August of the entire region during the study period. The seasonal variation of SCA can be highly related to the influence of monsoonal patterns in the region.
Improving GNSS Zenith Wet Delay Interpolation by Utilizing Tropospheric Gradients: Results from the dense station network in Japan
Authors: Zus Florian , Balidakis Kyriakos , Pikridas Christos , Dick Galina , Wickert Jens
Published: March 2020

In a recent study we have shown how GNSS Zenith Wet Delay (ZWD) interpolation and therefore Integrated Water Vapor (IWV) maps can be improved by utilizing tropospheric gradients (Zus et al., 2019). For a station configuration with an average distance of 50 km in Germany and a period of two months in the summer 2013 we demonstrated an average improvement of 10% in interpolated ZWDs. We extended this work by a new study. It differs from the previous one in two respects: (1) we consider more than 1,200 stations with an average distance of 20 km in Japan and (2) ZWDs and tropospheric gradients are taken from the Nevada Geodetic Laboratory (NGL) (Blewitt et al., 2018). We present results and propose future directions. For example, we may consider a mixed approach where ZWDs and tropospheric gradients from a numerical weather prediction model are utilized as well.

Zus, F.; Douša, J.; Kačmařík, M.; Václavovic, P.; Balidakis, K.; Dick, G.; Wickert, J. Improving GNSS Zenith Wet Delay Interpolation by Utilizing Tropospheric Gradients: Experiments with a Dense Station Network in Central Europe in the Warm Season. Remote Sens. 2019, 11, 674. 

Blewitt, G., W. C. Hammond, and C. Kreemer (2018), Harnessing the GPS data explosion for interdisciplinary science, EOS, 99, https://doi.org/10.1029/2018EO104623.
Locating fault tips to aid fault length identification: an example from the Gulf of Corinth rift
Authors: Robertson Jenni , Roberts Gerald , Iezzi Francesco , Meschis Marco , Gheorghiu Delia , Sahy Diana , Bristow Chris , Sgambato Claudia
Published: March 2020

Crustal-scale active normal faults dominate seismic hazard in some regions and have been intensely studied. However, the lateral tips of these structures have received relatively little attention in the literature so their geometries are poorly known. This is an important omission because locating the tips of normal faults is vital in order to define fault lengths and calculate maximum expected earthquake magnitudes. Identifying tips will be challenging if their geometries, kinematics and rates of deformation are poorly known. Consequently, incorrectly identified tips and hence fault lengths may contribute to uncertainty in Probabilistic Seismic Hazard Assessment.

We investigate the geometry, rates and kinematics of active normal faulting in the western tip zone of the South Alkyonides Fault System (SAFS) (Gulf of Corinth, Greece) by detailed fault mapping and fault offset dating using a combination of new 234U/230Th coral ages and in situ 36Cl cosmogenic exposure ages on wave-cut platforms deformed by faults.

Our results reveal that there is no clear singular fault tip and that distributed deformation in the tip zone of the SAFS occurs across as many as eight faults arranged within ~700 m across strike, each of which deforms deposits and landforms associated with the 125 ka marine terrace of Marine Isotope Stage 5e. Summed throw-rates across strike achieve values as high as 1.6 mm/yr, values that approach those close to the centre of the crustal-scale fault of 2-3 mm/yr from Holocene palaeoseismology and 3-4 mm/yr from GPS geodesy. Considering the uncertainty in the location of the western tip induced by distributed faulting, the SAFS fault length is uncertain by up to ± 6%, which equates to a total maximum magnitude uncertainty of Mw 0.1.

The calculated tip displacement gradient summed across parallel faults since 125 ka for the western tip zone of the SAFS is within the upper range compared to data from other normal crustal-scale faults. We discuss stress interaction between the SAFS and a neighbouring along-strike crustal-scale fault as a potential cause of the observed fault complexity and anomalously high throw and investigate this by undertaking Coulomb stress transfer modelling. The results from the study are discussed within the context of fault-based seismic hazard assessment.

 We conclude that identifying the locations of fault tips is challenging. While the results of this study may or may not be typical of other tip zones owing to the interaction, there is a need for further studies that explore the geometry of both non-interacting and interacting fault tip zones.
Indication of glacially-induced fault reactivation in Latvia, Lithuania and the Kaliningrad District of Russia from models of glacial isostatic adjustment
Authors: Steffen Holger , Steffen Rebekka , Tarasov Lev
Published: March 2020

We model the change of Coulomb Failure Stress (δCFS) during the Weichselian glaciation up until today at 12 locations in Latvia, Lithuania and Russia that are characterised by soft-sediment deformation structures (SSDS). If interpreted as seismites, these SSDS may point to glacially-induced fault reactivation. The δCFS suggests a high potential of such reactivation when it reaches the instability zone. We show that δCFS at all 12 locations reached this zone several times in the last 120,000 years. Most notably, all locations exhibit the possibility of reactivation after ca. 15 ka BP until today. Another time of possible activity likely happened after the Saalian glaciation until ca. 96 ka BP. In addition, some models suggest unstable states after 96 ka BP until ca. 28 ka BP at selected locations but with much lower positive δCFS values than during the other two periods. For the Valmiera and Rakuti seismites in Latvia, we can suggest a glacially-induced origin, whereas we cannot exactly match the timing at Rakuti. Given the (preliminary) dating of SSDS at some locations, at Dyburiai and Ryadino our modelling supports the interpretation of glacially-induced fault reactivation, while at Slinkis, Kumečiai and Liciškėnai they likely exclude such a source. Overall, the mutual benefit of geological and modelling investigations is demonstrated. This helps in identifying glacially-induced fault reactivation at the south-eastern edge of the Weichselian glaciation and in improving models of glacial isostatic adjustment.

This work has been published in Steffen et al. (2019).

Reference:

Steffen, H., Steffen R., Tarasov L. 2019. Modelling of glacially-induced stress changes in Latvia, Lithuania and the Kaliningrad District of Russia. Baltica, 32 (1), 78–90.
The effect of the photomineralization mechanism on ambient organic aerosols' cloud condensation nuclei and ice nucleation abilities
Authors: Müller Silvan , Borduas-Dedekind Nadine
Published: March 2020

Organic aerosol (OA) is an important component of the atmospheric submicron particulate mass, consisting of a complex mixture of organic compounds from natural and anthropogenic sources. During its lifetime of approximately one week in the atmosphere, OA is exposed to sunlight and thus undergoes atmospheric processing through photochemistry. This photochemical aging mechanism is thought to have a substantial effect on the propensity of OA to participate in cloud-forming processes by increasing its cloud condensation nuclei (CCN) activity. However, this effect is not well-constrained, and the influence of photochemistry on the ice nucleation (IN) activity of OA is uncertain. In this study, we aim to better understand how the photomineralization mechanism changes the cloud-forming properties of OA by measuring the CCN and IN abilities of photochemically aged OA of different sources: (1) Laboratory-generated ammonium sulfate-methylglyoxal (a proxy for secondary OA), and ambient OA bulk solutions collected from (2) wood smoke and (3) urban particulate matter in Padua (Italy). The solutions are exposed to UV-B radiation in a photoreactor for up to 25 hour and subsequently analyzed for their IN ability and, following aerosolization, for their CCN ability. To correlate changes in cloud-forming properties with changes in chemical composition due to photomineralization, we measure total organic carbon, UV-Vis absorbance, and CO, CO2, acetic acid, formic acid, pyruvic acid and oxalic acid production. Indeed, preliminary data of wood smoke OA highlights photomineralization as an important atmospheric aging process that modifies the CCN ability of OA. By characterizing both the CCN and IN abilities of photochemically aged OA, our study may thus provide important insights into the atmospheric evolution and cloud-forming properties of OA, potentially establishing photomineralization of OA as an important mechanism to consider in regional and global climate model predictions.
National glacier monitoring – strengths and weaknesses, responsibilities and priorities
Authors: Gärtner-Roer Isabelle , Nussbaumer Samuel U. , Hüsler Fabia , Zemp Michael
Published: March 2020

Glaciers impact the lives of millions of people whose drinking water supply, energy production, and irrigation-dependent agriculture is disrupted as the glaciers melt. Knowledge on glacier distribution and quantification of glacier changes is crucial to assessing the impact of glacier shrinkage on the society. Therefore, glacier monitoring is vital to the development of sustainable adaptation strategies in regions with glaciated mountains.

Detailed information on national glacier monitoring, including data on glacier distribution as well on as glacier changes, is compiled in a standardized procedure to summarize and also compare the situation in each of the glacierized countries. The resulting country profiles are assessed in relation to the existing monitoring strategy of the Global Terrestrial Network for Glaciers (GTN-G). Gaps between the current implementation of glacier monitoring and implementation targets are analyzed in a solid gap analysis, which allows countries to be categorized as having poorly developed monitoring, needing improvement, or having well-developed monitoring. By this, it is intended to raise awareness of the challenges for the individual national monitoring systems and to illuminate what future needs might be to improve the situation.

The study is meant to provide a baseline for scientists and decision-makers in international organizations, national governments, and local communities, as they take responsibilities to improve glacier monitoring systems and care about their relevance in decision-making processes.
A tale of two peats: characterizing ecosystem-driven differences in chemical composition with depth in natural and drained Finnish mires using Py-GC/MS analytical techniques
Authors: Klein Kristy , Groβ-Schmölders Miriam , Alewell Christine , Leifeld Jens
Published: March 2020

Intact accumulating peatlands are a globally important terrestrial carbon sink. Climate change and agricultural drainage are degrading these ecosystems, and through increases in aerobic decomposition, shifting their C balance from sink to source. To argue the effectiveness of restoration activities (such as rewetting), techniques are needed that clearly show differences between drained and natural (or drained and rewetted) peatlands. Because these changes are not always macroscopically visible, molecular analysis methods are especially needed to distinguish between ecosystems experiencing net pet growth (sequestering carbon), and those where aerobic decomposition is still a primary driving mechanism. Molecular biomarkers are a useful way to use chemical composition to distinguish these mechanisms.

This study aimed to compare differences in chemical composition with depth between two peatland sites from a large ombrotrophic mire in Lakkasuo Finland – one natural and one drained. To characterize these chemical shifts, pyrolysis gas chromatography mass spectrometry was used to track changes in relative abundance of various molecular biomarkers and compound classes (ie., aromatics, Sphagnum phenols, lignin, N-containing compounds, n-alkanes, etc.) with depth across both sites. Three replicate cores per site were collected, allowing for statistical evaluation of the relative abundances of these compounds. Using radiocarbon dating at three depths per core, the drained and natural sites were also matched by age for reference purposes. Significant differences were found for the Sphagnum-specific biomarker, p-isopropenylphenol, aromatics, and lignin, to the approximate current depth of the drained peatland water table. Higher phenolic compound class abundance indicated inhibited aerobic decomposition in the natural cores. An increasing trend in lignin biomarker relative abundance with depth was observed in the natural site, despite the identification of comparatively fewer vascular plants during the macroscopic analysis. Rather than a higher abundance of palaeo-ecological vascular plants, this trend is considered to be an indicator of preferential preservation of lignin compounds with anaerobic conditions. Below the depth of the water table, the relative abundances of most biomarkers stabilized, indicating the existance of similar environmental conditions in both sites prior to drainage. These data were compared and are in agreement with findings from elemental analysis (CHNO) and bulk isotopic (13C and 15N) data measured on the same cores. Collectively, these data suggest that observed shifts in chemical composition in the natural and drained cores reflect the effect of different hydrological conditions between the two sites.
The Arctic Ocean Observation Operator for 6.9 GHz (ARC3O)
Authors: Burgard Clara , Notz Dirk , Pedersen Leif T. , Tonboe Rasmus T.
Published: March 2020

The diversity in sea-ice concentration observational estimates retrieved from brightness temperatures measured from space is a challenge for our understanding of past and future sea-ice evolution as it inhibits reliable climate model evaluation and initialisation. To address this challenge, we introduce a new tool: the Arctic Ocean Observation Operator (ARC3O). 

ARC3O allows us to simulate brightness temperatures at 6.9 GHz at vertical polarisation from standard output of an Earth System Model to be compared to observations from space at this frequency. We use simple temperature and salinity profiles inside the snow and ice column based on the output of the Earth System Model to compute these brightness temperatures. 

In this study, we evaluate ARC3O by simulating brightness temperatures based on three assimilation runs of the MPI Earth System Model (MPI-ESM) assimilated with three different sea-ice concentration products. We then compare these three sets of simulated brightness temperatures to brightness temperatures measured by the Advanced Microwave Scanning Radiometer Earth Observing System (AMSR-E) from space. We find that they differ up to 10 K in the period between October and June, depending on the region and the assimilation run. However, we show that these discrepancies between simulated and observed brightness temperature can be mainly attributed to the underlying observational uncertainty in sea-ice concentration and, to a lesser extent, to the data assimilation process, rather than to biases in ARC3O itself. In summer, the discrepancies between simulated and observed brightness temperatures are larger than in winter and locally reach up to 20 K. This is caused by the very large observational uncertainty in summer sea-ice concentration but also by the melt-pond parametrisation in MPI-ESM, which is not necessarily realistic. 

ARC3O is therefore capable to realistically translate the simulated Arctic Ocean climate state into one observable quantity for a more comprehensive climate model evaluation and initialisation, an exciting perspective for further developing this and similar methods.
Effects of Urbanization on Regional Extreme-Temperature Change in China，1960-2016
Authors: Qiu Junliang , Yang Xiankun , Cao Bowen , Chen Zhilong , Li Yuxuan
Published: March 2020

Fast urbanization is one of the aggrandizement factors to global warming, but the effects of urbanization on extreme temperature change is still not quantitatively assessed. Based on high-resolution land cover map, this study classified 613 meteorological stations in China into three classes, namely, urban station, suburban station and rural station to simulate the trends of extreme minimum temperature (TNN), mean temperature (Tavg) and extreme maximum temperature (TXX) of each meteorological station. The roles of urbanization in temperature change in the period 1960-2016 were then assessed. The results indicated that annual temperature increased significantly, but seasonal temperature increased with varied degrees. Temperature in high latitudes increased faster than that in low latitudes. Temperature in summer increased slower than that in other seasons. The effects of urbanization on TNN, Tavg and TXX were all statistically significant, but the effects on TNN and Tavg were more noticeable than TXX. The aggrandizement effects of urbanization presented by low-altitude meteorological stations are significant in South China and East China for all temperature indices, despite no statistical significance presented by high-altitude meteorological stations in Southwest China. This paper can provide a reference for understanding the regional temperature changes and the effects of urbanization on its changes in China.
Towards consistent seismological models of the core-mantle boundary landscape
Authors: Koelemeijer Paula
Published: March 2020

The dynamic topography of the core-mantle boundary (CMB) provides important constraints on dynamic processes in the mantle and core. However, inferences on CMB topography are complicated by the uneven coverage of data with sensitivity to different length scales and strong heterogeneity in the lower mantle. Particularly, a trade-off exists with density variations, which ultimately drive mantle flow and are vital for determining the origin of mantle structures. Here, I review existing models of CMB topography and lower mantle density, focusing on seismological constraints (Koelemeijer, 2020). I develop average models and vote maps with the aim to find model consistencies and discuss what these may teach us about lower mantle structure and dynamics.

While most density models image two areas of dense anomalies beneath Africa and the Pacific, their exact location and relationship to seismic velocity structure differs between studies. CMB topography strongly influences the retrieved density structure, which partially helps to resolve differences between recent studies based on Stoneley modes and tidal measurements. CMB topography models vary both in pattern and amplitude and a discrepancy exists between models based on body-wave and normal-mode data. As existing models typically feature elevated topography below the Large-Low-Velocity Provinces (LLVPs), very dense compositional anomalies may be ruled out as possibility.

To achieve a similar consistency as observed in lower mantle models of S-wave and P-wave velocity, future studies should combine multiple data sets to break existing trade-offs between CMB topography and density. Important considerations in these studies should be the choice of theoretical approximation and parameterisation. Efforts to develop models of CMB topography consistent with both body-wave and normal-mode data should be intensified, which will aid in narrowing down possible explanations for the LLVPs and provide additional insights into mantle dynamics.

Koelemeijer, P. (2020), “Towards consistent seismological models of the core-mantle boundary landscape”. Book chapter in revision for AGU monograph "Mantle upwellings and their surface expressions", edited by Marquardt, Cottaar, Ballmer and Konter
Stress State and Fault Strength Variation along Xiaojiang Fault Zone Revealed by Seismicity
Authors: Zhou Yijian , Zhou Shiyong , Zhang Hao , Hou Yu , Pei Weilai , Wang Longtan , Yun Naidan
Published: March 2020

Xiaojiang Fault (XJF) lies at the southeastern edge of the rhombic Sichuan-Yunnan block, and has an extent for over 400km from Qiaojia to Shanhua district. The Sichuan-Yunnan block experiences clockwise rotation and southwestward escaping from the Tibetan Plateau, producing complex fault geometry and seismicity pattern. The strong variation along fault segments provides a special opportunity to study the relationship between fault zone properties and seismicity pattern. However, the fine structure of XJF remains unknown due to the sparse observational stations.

Seismic data has its unique advantage of resolving fault zone properties at depth. We deployed 48 broad-band seismometers along XJF in order to capture detailed seismicity patterns. Our seismic network covers the northern and middle part of XJF, with an average aperture of 20km; the continuous observation from 2015 to 2019 guarantees enough data volume. We detected about 12,000 earthquakes by STA/LTA phase picking and association, and augmented the detection to over 50,000 events with template matching. The relocated catalog has lateral and vertical resolution of 500m and 1km, respectively; the magnitude of completeness (Mc) reaches ML0.3

This high-resolution catalog depicts detailed 3D fault geometry. The seismicity shows clustered lateral distribution, with the clusters’ depth extension ranging from 20km at northern to 35km at southern segments. Unmapped orthogonal faults on northern XJF are illuminated by seismicity, which matches orthogonal topography characteristics. Repeating events are detected from 8 seismicity clusters, under a threshold of 5 repeating families, indicating a creeping slip mode, while the separated low-seismicity segments exhibit a high locking rate. Taking advantage of the high detectability, we got reliable b-value estimation for different segments of XJF. The low-b regions correlate well with the margins of locking patches, which points to a high stress concentration. Velocity structure extracted from ambient noise and fault zone head wave present similar spatial variation, which further proved the seismicity pattern. The high heterogeneous characteristics of XJF may produce stress barriers, preventing future earthquake rupture from propagating to a large scale. 
Effects of air pollution, urbanization and temperature on chronic kidney disease
Authors: Liang Chenyu
Published: March 2020

The prevalence of chronic kidney disease in China is around 11%, which is a serious public health challenge. Air pollution and personal habits have been cited as major causes of chronic kidney disease, but a number of studies have suggested that urbanization and meteorological factors may also play a role. Therefore, this study established a longitudinal population cohort composed of 47,204 Chinese residents, combined with geographical means to obtain PM2.5 and temperature data, and used multiple regression model and random forest algorithm to explore the impact of air pollution, urbanization and temperature on chronic kidney disease. The results showed that the contribution of temperature, urbanization and PM2.5 to CKD was second only to individual factors such as age and BMI, and the contribution of temperature and urbanization to eGFR was higher than that of PM2.5. This provides a new way of thinking for the study of non-communicable diseases such as chronic kidney disease. With the acceleration of climate warming and urbanization, more attention should be paid to the impact of urbanization and temperature on diseases.
Exploring the relationships among ecosystem services and their drivers in the Beijing-Tianjin-Hebei urban agglomeration
Authors: Shen Jiashu
Published: March 2020

Understanding the relationships among multiple ecosystem services and their drivers is crucial for the sustainability of ecosystem services provision. Different ecosystem services were quantified using different models, and the relationships among ecosystem services and their drivers were analyzed using different statistical methods in the Beijing-Tianjin-Hebei urban agglomeration. Our results showed that the spatially concordant supply of regulating services and cultural services decreased from northwest to southeast, whereas the delivery of provisioning services decreased from southeast to northwest in the region. The provisioning service was  antagonistic with both the regulating services and the cultural service, and the relationships among the regulating services and the cultural service were mostly synergistic. Different combinations of ecosystems provided seven types of ecosystem services bundles with different compositions and quantities of ecosystem services. Different drivers had different impacts on different ecosystem services. On the basis of  our findings, we suggested that the features of ecosystem service relationships and their drivers should be considered to ensure the efficiency of the  management of natural capital.
Did tropical precipitation improve in CMIP6 simulations?
Authors: Fiedler Stephanie , Crueger Traute , D’Agostino Roberta , Peters Karsten , Becker Tobias , Leutwyler David , Paccini Laura ,   project team
Published: March 2020

Climate models are known to have biases in tropical precipitation. We assessed to what extent simulations of tropical precipitation have improved in the new Coupled Model Intercomparison Project (CMIP) phase six, using state-of-the-art observational products and model results from the earlier CMIP phases three and five. We characterize tropical precipitation with different well-established metrics. Our assessment includes (1) general aspects of the mean climatology like precipitation associated with the Intertropical Convergence Zone and shallow cloud regimes in the tropics, (2) solar radiative effects including the summer monsoons and the time of occurrence of tropical precipitation in the course of the day, (3) modes of internal variability such as the Madden-Julian Oscillation and the El Niño Southern Oscillation, and (4) changes in the course of the 20th century. The results point to improvements of CMIP6 models for some metrics, e.g., the occurrence of drizzle events and consecutive dry days. However, no improvements of CMIP6 models are identified for other aspects of tropical precipitation. These include the area and intensity of the global summer monsoon as well as the diurnal cycle of the tropical precipitation amount, frequency and intensity.

All our metrics taken together, CMIP6 models show no systematic improvement of tropical precipitation across different temporal and spatial scales. The model biases in the spatial distribution of tropical precipitation are typically larger than the changes associated with anthropogenic warming. Given the pace of climate change as compared to the pace of climate model improvements, we suggest to use novel modeling approaches to understand the responseof tropical precipitation to changes in atmospheric composition.
Imminent re-opening of the Weddell Polynya detectable days ahead by spaceborne infrared
Authors: Heuzé Céline , Lemos Adriano
Published: March 2020

The Weddell Polynya, a large hole in the winter sea ice cover, has intrigued researchers since satellite observations began in the late 70s. There is no consensus regarding the mechanisms leading to its opening, not least because there never was an instrument deployed early enough at the right location and with the right sampling interval. But what if we could predict imminent openings, by detecting early-warning signs from space?

The leading theory among oceanographers is that the polynya opens after the sea ice is melted from below by upwelled warm waters. We argue that such upwelling, or at least the increased heat flux through a thinning ice, should be visible on spaceborne thermal infrared imagery. Using microwave-based sea ice products to determine past polynya openings, we first found that there were in fact 83 Weddell / Maud Rise Polynya occurrences since winter 2000, 19 of which reaching an area larger than 1000 km2. We then created a timeseries of (cloud-filtered) daily mean brightness temperature at 3.7, 10.5 and 12 μm from Advanced Very High Resolution Radiometer datasets and found a significant warm temperature anomaly at least 10 days before the polynya opened, peaking at 4K for all bands 5-6 days before the opening. The anomaly is on average 2K stronger for the large polynyas (> 1000 km2). Moreover, the band ratios brutally change magnitude, which suggests lead formation rather than progressive melting – a hypothesis that would agree with meteorologists' theory that the polynya opens because of winds, and that we are now checking with spaceborne radar.

Six days is not much, but it would be enough to re-route expeditions or autonomous sensors so that the opening can be monitored in details. And this is only the first step of our ongoing project... stay tuned to see if we can predict weeks or months ahead!
Temporal Multi-Looking of SAR Image Series for Glacier Velocity Determination and Speckle Reduction
Authors: Leinss Silvan , Li Shiyi , Bernhard Philipp , Frey Othmar
Published: March 2020

The velocity of glaciers is commonly derived by offset tracking using pairwise cross correlation or feature matching of either optical or synthetic aperture radar (SAR) images.  SAR images, however, are inherently affected by noise-like radar speckle and require therefore much larger images patches for successful tracking compared to the patch size used with optical data. As a consequence, glacier velocity maps based on SAR offset tracking have a relatively low resolution compared to the nominal resolution of SAR sensors. Moreover, tracking may fail because small features on the glacier surface cannot be detected due to radar speckle. Although radar speckle can be reduced by applying spatial low-pass filters (e.g. 5x5 boxcar), the spatial smoothing reduces the image resolution roughly by an order of magnitude which strongly reduces the tracking precision. Furthermore, it blurs out small features on the glacier surface, and therefore tracking can also fail unless clear features like large crevasses are visible.

In order to create high resolution velocity maps from SAR images and to generate speckle-free radar images of glaciers, we present a new method that derives the glacier surface velocity field by correlating temporally averaged sub-stacks of a series of SAR images. The key feature of the method is to warp every pixel in each SAR image according to its temporally increasing offset with respect to a reference date. The offset is determined by the glacier velocity which is obtained by maximizing the cross-correlation between the averages of two sub-stacks. Currently, we need to assume that the surface velocity is constant during the acquisition period of the image series but this assumption can be relaxed to a certain extend.

As the method combines the information of multiple images, radar speckle are highly suppressed by temporal multi-looking, therefore the signal-to-noise ratio of the cross-correlation is significantly improved. We found that the method outperforms the pair-wise cross-correlation method for velocity estimation in terms of both the coverage and the resolution of the velocity field. At the same time, very high resolution radar images are obtained and reveal features that are otherwise hidden in radar speckle.

As the reference date, to which the sub-stacks are averaged, can be arbitrarily chosen a smooth flow animation of the glacier surface can be generated based on a limited number of SAR images. The presented method could build a basis for a new generation of tracking methods as the method is excellently suited to exploit the large number of emerging free and globally available high resolution SAR image time series.
Geodesy and Mathematics: Interactions in Multiscale Mollifier Regularization Methods
Authors: Freeden Willi
Published: March 2020

The lecture highlights arguments that, coming from Mathematics, have fostered the advancement of Geodesy, as well as those that, generated by geodetic problems, have contributed to the enhancement in Mathematics.

We particularly deal with novel applications to Geodesy in the context of multiscale approximation (MA). In fact, multiscale reconstruction and decorrelation methods are a research field originated in geophysics for, e.g., earthquake modeling some decades ago, in which today's Geodesy and Mathematics show mutual influences, especially on the subject of spectral and space data sampling.

We particularly focus the attention on inverse problems of Geodesy and multiscale mollifier regularization strategies. Two examples are studied in more detail:

(i) Vening Meinesz multiscale surface mollifier regularization to determine locally the Earth's disturbing potential from deflections of vertical,

(ii) Newton multiscale volume mollifier regularization of the inverse gravimetry problem to derive locally the density contrast distribution from functionals of the Newton integral and to detect fine particulars of geological relevance.

Neither extreme depth to explain all facets of the geodetic observational situation nor penetrative handling of mathematical obligations and technicalities can be expected. The lecture is just an \lq \lq appetizer'' served to enjoy the tasty meal "Mathematical Geodesy Today'' to be shared by geodesists and mathematicians.
The Pulsating Magnetosphere at Jupiter
Authors: Manners Harry , Masters Adam
Published: March 2020

The magnetosphere of Jupiter is the largest planetary magnetosphere in the solar system, and plays host to internal dynamics that remain, in many ways, mysterious. Prominent among these mysteries are the ultra-low-frequency (ULF) pulses ubiquitous in this system. Pulsations in the electromagnetic emissions, magnetic field and flux of energetic particles have been observed for decades, with little to indicate the source mechanism. While ULF waves have been observed in the magnetospheres of all the magnetized planets, the magnetospheric environment at Jupiter seems particularly conducive to the emergence of ULF waves over a wide range of periods (1-100+ minutes). This is mainly due to the high variability of the system on a global scale: internal plasma sources and a powerful intrinsic magnetic field produce a highly-compressible magnetospheric cavity, which can be reduced to a size significantly smaller than its nominal expanded state by variations in the dynamic pressure of the solar wind. Compressive fronts in the solar wind, turbulent surface interactions on the magnetopause and internal plasma processes can also all lead to ULF wave activity inside the magnetosphere.

To gain the first comprehensive view of ULF waves in the Jovian system, we have performed a heritage survey of magnetic field data measured by six spacecraft that visited the magnetosphere (Galileo, Ulysses, Voyager 1 & 2 and Pioneer 10 & 11). We found several-hundred wave events consisting of wave packets parallel or transverse to the mean magnetic field, interpreted as fast-mode or Alfvénic MHD wave activity, respectively. Parallel and transverse events were often coincident in space and time, which may be evidence of global Alfvénic resonances of the magnetic field known as field-line-resonances. We found that 15-, 30- and 40-minute periods dominate the Jovian ULF wave spectrum, in agreement with the dominant “magic frequencies” often reported in existing literature.

We will discuss potential driving mechanisms as informed by the results of the heritage survey, how this in turn affects our understanding of energy transfer in the magnetosphere, and potential investigations to be made using data from the JUNO spacecraft. We will also discuss the potential for multiple resonant cavities, and how the resonance modes of the Jovian magnetosphere may differ from those of the other magnetized planets.
Clouds and Aerosols observed during EUREC4A by the UK Twin Otter aircraft.
Authors: Lachlan-Cope Tom , Blyth Alan , Boeing Steven , Rosenberg Philip , Barrett Paul , Bower Keith , Flynn Michael , Dorsey James , Lloyd Gary , Denby Leif
Published: March 2020

The EUREC4A project took place during January and February of 2020 and involved aircraft and ships from Germany, France, the United States of America and the United Kingdom. The aim of the project is to advance the understanding of the interplay between clouds, convection and circulation and their role in climate change. The Twin Otter belonging to the British Antarctic Survey (BAS) has been used to take observations of clouds and aerosols to the East of Barbados in conjugation with the French ATR-42 and the German Halo aircraft. Here we report the preliminary results of the observations made by the British aircraft. These observations will include aerosols from 10nm to 10micron and numbers of cloud condensation nuclei as well as detailed in-situ measurements of clouds microphysical properties. The observations have been taken over a one month period and taken as a whole can be used to provide a statistical view of the aerosols and clouds observed during EUREC4A by the BAS Twin Otter Aircraft.
The influence of soil fertility on carbon cycling and storage in temperate tree bioenergy crops
Authors: Kemp Leigh-Anne
Published: March 2020

LA Kemp, Supervisors: A. Karley, A. Bennett, A. Taylor, N. McNamara, E.J Sayer

Short – rotation woody perennials such as Populus and Salix are often selected for bioenergy crops in temperate climates. In conjunction with providing a renewable crop, bioenergy crops can improve carbon storage in previously degraded soils and associate with beneficial mycorrhizal fungi. Applying nitrogen fertilizers to bioenergy crops can increase yield and carbon sink but may also increase CO2 emissions through increased soil respiration and N2O through increased microbial activity which alter population and community dynamics.

Changing environmental conditions due to climate change such as prolonged droughting and increasing intensity of rewetting are also impacting plant-soil interactions. However, there are gaps in the understanding of the mechanisms responsible for plant responses to changing abiotic conditions. Therefore, the scale of future carbon cycling, CH4 and N2O emissions by temperate tree species are still very unclear.

To address this my experiment, focuses on two temperate tree species used in bioenergy production known to associate with mycorrhizal fungi. The study will run over two growing seasons, using a randomized block design with four fungal treatments, four nutrient treatments and then implementing two abiotic treatments during the second growing season. I aim to determine how soil nutrient availability influences: i) plant – mycorrhiza associations, ii) plant carbon cycling and storage, iii) soil respiration rates, iv) plant and soil GHG emission rates. v) carbon cycling and GHG emissions under different climate controls.
Human-induced changes to the global ocean water masses and their time of emergence
Authors: Silvy Yona , Guilyardi Eric , Sallée Jean-Baptiste , Durack Paul
Published: March 2020

The World Ocean is rapidly changing, with global and regional modification of temperature and salinity evident at the surface and depth. These changes have widespread and irreversible impacts including sea-level rise, changes to the oxygen and carbon contents of the ocean interior, or changing habitats, diversity and resilience of ecosystems. While the most pronounced temperature and salinity changes are located in the upper few hundred metres, changes in water-masses at depth are already observed and will likely strengthen and persist in the future as water-masses form at the surface and propagate in the deep ocean along density surfaces, storing the anthropogenic signal away from the atmosphere for decades to millennia. Here, using 11 climate models, we define when anthropogenic temperature and salinity changes are expected to emerge from natural background variability in the ocean interior. On a basin-scale zonal average, the model simulations predict that in 2020, 20–55% of the Atlantic, Pacific and Indian basins have an emergent anthropogenic signal; reaching 40–65% in 2050, and 55–80% in 2080. The well-ventilated Southern Ocean water-masses emerge very rapidly, as early as the 1980s-1990s, while the Northern Hemisphere emerges in the 2010s to 2030s. Additionally, dedicated idealized simulations of the IPSL coupled climate model are examined to study the role of each separate surface forcing on the time scales associated with the patterns of temperature and salinity change under a global warming scenario, and the influence of excess versus redistributed heat and salt. Our results highlight the importance of maintaining and augmenting an ocean observing system capable of detecting and monitoring anthropogenic changes. 
Revisiting the Linkages between the Variability of Atmospheric Circulations and Arctic Melt-Season Sea Ice Cover at Multiple Time Scales
Authors: Yu Lejiang , Zhong Sharon
Published: March 2020

The sharp decline of Arctic sea ice in recent decades has captured the attention of the climate science
community. A majority of climate analyses performed to date have used monthly or seasonal data. Here,
however, we analyze daily sea ice data for 1979–2016 using the self-organizing map (SOM) method to further
examine and quantify the contributions of atmospheric circulation changes to the melt-season Arctic sea ice
variability. Our results reveal two main variability modes: the Pacific sector mode and the Barents and Kara
Seas mode, which together explain about two-thirds of the melt-season Arctic sea ice variability and more
than 40% of its trend for the study period. The change in the frequencies of the two modes appears to be
associated with the phase shift of the Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation
(AMO). The PDO and AMO trigger anomalous atmospheric circulations, in particular, the
Greenland high and the North Atlantic Oscillation and anomalous warm and cold air advections into the
Arctic Ocean. The changes in surface air temperature, lower-atmosphere moisture, and downwelling longwave
radiation associated with the advection are consistent with the melt-season sea ice anomalies observed
in various regions of the Arctic Ocean. These results help better understand the predictability of Arctic sea ice
on multiple (synoptic, intraseasonal, and interannual) time scales.
Biomass burning decline causes large reductions in NO2 burden over north equatorial Africa in spite of growing fossil fuel use
Authors: Hickman Jonathan , Andela Niels , Ossohou Money , Galy-Lacaux Corinne , Tsigaridis Kostas , Bauer Susanne
Published: March 2020

Socio-economic development in low and middle-income countries has been accompanied by increased emissions of air pollutants such as nitrogen oxides (NOx: nitrogen dioxide (NO2) + nitric oxide (NO)), which affect human health.  In sub-Saharan Africa, fossil fuel combustion has nearly doubled since 2000.  At the same time, biomass burning—another important NOx source—has declined in Africa’s northern biomass burning region, attributed to changes in climate and anthropogenic fire management associated with agricultural development. Here we use satellite observations of tropospheric NO2 vertical column densities (VCDs) and burned area to identify NO2 trends and drivers over Africa. Across the northern ecosystems where biomass burning occurs—home to over 350 million people—mean annual tropospheric NO2 VCDs decreased by 4.5% from 2005 through 2017 during the biomass burning season of November through February. Reductions in burned area explained the majority of these change in NO2 VCDs, but there were also weaker relationships between changes in NO2 VCDs and fossil fuel emissions over parts of West Africa, which were stronger during rainy season. Over Africa’s biomass burning regions, NO2 VCDs tended to decrease with increasing population density up to a threshold of approximately 180 people per km2, suggesting that anthropogenic activity causes a net reduction in NO2 emissions across roughly 90% of the continent’s biomass burning regions. In contrast to the widely-held perception that socio-economic development worsens air quality in low and middle-income nations, our results suggest that countries in Africa’s northern biomass burning region are following a different pathway, resulting in regional air quality benefits. However, these benefits may be lost with increasing fossil fuel use.