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Simultaneous measurements of new particle formation at 1 s time resolution at a street site and a rooftop site

This study reports the distinct effects of street canyons on new particle formation (NPF) under warm or cold ambient temperature conditions because of on-road vehicle emissions; i.e., stronger condensation sinks are responsible for the reduced NPF in the springtime, but efficient nucleation and partitioning of gaseous species contribute to the enhanced NPF in the wintertime. The oxidization of biogenic organics is suggested to play an important role in growing new particles.

Has dyke development in the Vietnamese Mekong Delta shifted flood hazard downstream?

In this study we provide a numerical quantification of changes in flood hazard in the Vietnamese Mekong Delta as a result of dyke development. Other important drivers to the alteration of delta flood hazard are also investigated, e.g. tidal level. The findings of our study are substantial valuable for the decision makers in Vietnam to develop holistic and harmonized floods and flood-related issues management plan for the whole delta.

NOx emission trends over Chinese cities estimated from OMI observations during 2005 to 2015

We assess NO_x emission trends over Chinese cities based on satellite NO₂ observations using a method independent of chemical transport models. NO_x emissions over 48 Chinese cities have decreased significantly since 2011. Cities with different dominant emission sources (i.e. power, industrial, and transportation sectors) showed variable emission decline timelines that corresponded to the schedules for emission control in different sectors.

OMI observations during 2005 to 2015">Read more

An intercomparison of approaches for improving operational seasonal streamflow forecasts

Water supply forecasts are critical to support water resources operations and planning. The skill of such forecasts depends on our knowledge of (i) future meteorological conditions and (ii) the amount of water stored in a basin. We address this problem by testing several approaches that make use of these sources of predictability, either separately or in a combined fashion. The main goal is to understand the marginal benefits of both information and methodological complexity in forecast skill.

Every apple has a voice: using stable isotopes to teach about food sourcing and the water cycle

Fruits take up soil water as they grow, and thus the fruit water is related to the rain or irrigation the crop receives. We used a novel sampling system to measure the stable isotopes of H and O in the fruit water to determine its geographic origin by comparing it to maps of isotopes in rain. We used this approach to teach an audience of science students and teachers about water cycle concepts and how humans may modify the water cycle through agriculture and irrigation water diversions.

The double high tide at Port Ellen: Doodson’s criterion revisited

Some places experience double high tides, where the tide starts to ebb for a short while, only to briefly flood again before finally receding. The result is a very long high tide with weak currents, and is important for navigational purposes. The existing theory for when and where double high tides occur does not always capture them, and it can only be applied to double highs occurring on a twice-daily tide. Here, the criterion has been generalized to capture all double high or low tides.

Reviews and syntheses: Systematic Earth observations for use in terrestrial carbon cycle data assimilation systems

This paper briefly reviews data assimilation techniques in carbon cycle data assimilation and the requirements of data assimilation systems on observations. We provide a non-exhaustive overview of current observations and their uncertainties for use in terrestrial carbon cycle data assimilation, focussing on relevant space-based observations.

The CarbonTracker Data Assimilation Shell (CTDAS) v1.0: implementation and global carbon balance 2001–2015

The CarbonTracker Data Assimilation Shell (CTDAS) is the new modular implementation of the CarbonTracker Europe (CTE) data assimilation system. We present and document CTDAS and demonstrate its ability to estimate global carbon sources and sinks. We present the latest CTE results including the distribution of the carbon sinks over the hemispheres and between the land biosphere and the oceans. We show the versatility of CTDAS with an overview of the wide range of other applications.

CTDAS) v1.0: implementation and global carbon balance 2001–2015">Read more

Periodic input of dust over the Eastern Carpathians during the Holocene linked with Saharan desertification and human impact

We present the first record of dust input into an eastern European bog over the past 10 800 years. We find significant changes in past dust deposition, with large inputs related to both natural and human influences. We show evidence that Saharan desertification has had a significant impact on dust deposition in eastern Europe for the past 6100 years.

Young people’s burden: requirement of negative CO2 emissions

Global temperature now exceeds +1.25 °C relative to 1880–1920, similar to warmth of the Eemian period. Keeping warming less than 1.5 °C or CO₂ below 350 ppm now requires extraction of CO₂ from the air. If rapid phaseout of fossil fuel emissions begins soon, most extraction can be via improved agricultural and forestry practices. In contrast, continued high emissions places a burden on young people of massive technological CO₂ extraction with large risks, high costs and uncertain feasibility.

Analysis of single-Alter-shielded and unshielded measurements of mixed and solid precipitation from WMO-SPICE

Precipitation measurements were combined from eight separate precipitation testbeds to create multi-site transfer functions for the correction of unshielded and single-Alter-shielded precipitation gauge measurements. Site-specific errors and more universally applicable corrections were created from these WMO-SPICE measurements. The importance and magnitude of such wind speed corrections were demonstrated.

WMO-SPICE">Read more

Update of the Polar SWIFT model for polar stratospheric ozone loss (Polar SWIFT version 2)

The Polar SWIFT model is a fast scheme for calculating the chemistry of stratospheric ozone depletion in polar winter. It is intended for use in global climate models (GCMs) and Earth system models (ESMs) to enable the simulation of mutual interactions between the ozone layer and climate.

SWIFT model for polar stratospheric ozone loss (Polar SWIFT version 2)">Read more

Exploring gravity wave characteristics in 3-D using a novel S-transform technique: AIRS/Aqua measurements over the Southern Andes and Drake Passage

We introduce a novel 3-D method of measuring atmospheric gravity waves, based around a 3-D Stockwell transform. Our method lets us measure new properties, including wave intrinsic frequencies and phase and group velocities. We apply it to data from the AIRS satellite instrument over the Southern Andes for two consecutive winters. Our results show clear evidence that the waves measured are primarily orographic in origin, and that their group velocity vectors are focused into the polar night jet.

AIRS/Aqua measurements over the Southern Andes and Drake Passage">Read more

On the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic

We find that a big portion of the phytoplankton, zooplankton, and detrital organic matter produced near the northern African coast is laterally transported towards the open North Atlantic. This offshore flux sustains a relevant part of the biological activity in the open sea and reaches as far as the middle of the North Atlantic. Our results, obtained with a state-of-the-art model, highlight the fundamental role of the narrow but productive coastal ocean in sustaining global marine life.

HESS Opinions: A planetary boundary on freshwater use is misleading

In 2009, the “planetary boundaries” were introduced. They consist of nine global control variables and corresponding “thresholds which, if crossed, could generate unacceptable environmental change”. The idea has been very successful, but also controversial. This paper picks up the debate with regard to the boundary on “global freshwater use”: it argues that such a boundary is based on mere speculation, and that any exercise of assigning actual numbers is arbitrary, premature, and misleading.

HESS Opinions: A planetary boundary on freshwater use is misleading">Read more

Efficient retention of mud drives land building on the Mississippi Delta plain

Our work presents a novel method of measuring the capacity of deltaic landforms to trap and retain river-borne sediments, and we demonstrate that sediment retention is closely connected to sedimentary composition. Our results, supported by a unique high-resolution coring dataset in a major crevasse splay, show that finer sediments are a much larger component of the Mississippi Delta than is often acknowledged and that their abundance indicates exceptionally high rates of sediment retention.

River logjams cause frequent large-scale forest die-off events in southwestern Amazonia

In lowland Bolivia, satellite images show rivers collapsing and the replacement of forest with savannah. This was first described in 1996 as the result of logjams (river dams created by fallen trees). I have investigated how the logjams form and affect the forest through remote sensing and fieldwork. Logjams occur nearly every year and propagate upriver until the river changes course. This region offers a unique opportunity to study how frequent forest die-off events affect biodiversity.

Detectability of Arctic methane sources at six sites performing continuous atmospheric measurements

Atmospheric methane simulations in the Arctic have been made for 2012 and compared to continuous observations at six measurement sites. All methane sources significantly affect the measurements at all stations, at least at the synoptic scale, except for biomass burning. An appropriate modelling framework combined with continuous observations of atmospheric methane enables us to gain knowledge on regional methane sources, including those which are usually poorly represented, such as freshwater.

Geomorphometric delineation of floodplains and terraces from objectively defined topographic thresholds

Floodplains and fluvial terraces can provide information about current and past river systems, helping to reveal how channels respond to changes in both climate and tectonics. We present a new method of identifying these features objectively from digital elevation models by analysing their slope and elevation compared to the modern river. We test our method in eight field sites, and find that it provides rapid and reliable extraction of floodplains and terraces across a range of landscapes.

A weekly Arctic sea-ice thickness data record from merged CryoSat-2 and SMOS satellite data

We developed the first merging of CryoSat-2 and SMOS sea-ice thickness retrievals. ESA’s Earth Explorer SMOS satellite can detect thin sea ice, whereas its companion CryoSat-2, designed to observe thicker perennial sea ice, lacks sensitivity. Using these satellite missions together completes the picture of the changing Arctic sea ice and provides a more accurate and comprehensive view on the actual state of Arctic sea-ice thickness.

SMOS satellite data">Read more

Non-linear intensification of Sahel rainfall as a possible dynamic response to future warming

Monsoon systems have undergone abrupt changes in past climates, and theoretical considerations show that threshold behavior can follow from the internal dynamics of monsoons. So far, however, the possibility of abrupt changes has not been explored for modern monsoon systems. We analyze state-of-the-art climate model simulations and show that some models project abrupt changes in Sahel rainfall in response to a dynamic shift in the West African monsoon under 21st century climate change.

WCRP’s Coupled Model Intercomparison Project: a remarkable contribution to climate science

As part of the Coupled Model Intercomparison Project (CMIP) organized under the auspices of the World Climate Research Programme’s (WCRP) Working Group on Coupled Modelling (WGCM) many hundreds of climate researchers, working with modeling centres around the world, will share, compare and analyze the latest outcomes of global climate models. These model products will fuel climate research for the next 5 to 10 years, while its careful analysis will form the basis for future climate assessments and negotiations.

The importance of terrestrial weathering changes in multimillennial recovery of the global carbon cycle: a two-dimensional perspective

In this paper we describe the development and application of a new spatially explicit weathering scheme within the University of Victoria Earth System Climate Model (UVic ESCM). We integrated a dataset of modern-day lithology with a number of previously devised parameterizations for weathering dependency on temperature, primary productivity, and runoff. We tested the model with simulations of future carbon cycle perturbations and confirmed the importance of silicate weathering in the long term.

Opposite long-term trends in aerosols between low and high altitudes: a testimony to the aerosol–PBL feedback

Opposite trends in aerosol loading between the lower and upper planetary boundary layer are found on a wide range of timescales and from different types of data acquired by various platforms in China. The reversal trend is consistent with the strong vertical gradients in the aerosol-induced atmospheric heating rate that unevenly modifies the atmospheric temperature profile and alters the stability differently. The findings have multiple implications in understanding and combating air pollution.

STRAPS v1.0: evaluating a methodology for predicting electron impact ionisation mass spectra for the aerosol mass spectrometer

Our ability to model the chemical and thermodynamic processes that lead to secondary organic aerosol (SOA) formation is thought to be hampered by the complexity of the system. In this proof of concept study, the ability to train supervised methods to predict electron impact ionisation (EI) mass spectra for the AMS is evaluated to facilitate improved model evaluation. The study demonstrates the use of a methodology that would be improved with more training data and data from simple mixed systems.

STRAPS v1.0: evaluating a methodology for predicting electron impact ionisation mass spectra for the aerosol mass spectrometer">Read more

Statistical characteristics of convective wind gusts in Germany

Natural Hazards and Earth System Sciences
DOI 10.5194/nhess-17-957-2017
23 June 2017

Due to the small-scale and non-stationary nature of the convective wind gusts usually associated with thunderstorms, there is a considerable lack of knowledge regarding their characteristics and statistics. Thus, we investigated the temporal and spatial distribution, intensity, and return values of those wind events in Germany. The study constitutes a fundamental addition to an improved understanding of convective wind gusts and serves as basis for further risk assessments.

The European 2015 drought from a hydrological perspective

In 2015 large parts of Europe were affected by a drought. In terms of low flow magnitude, a region around the Czech Republic was most affected, with return periods > 100 yr. In terms of deficit volumes, the drought was particularly severe around S. Germany where the event lasted notably long. Meteorological and hydrological events developed differently in space and time. For an assessment of drought impacts on water resources, hydrological data are required in addition to meteorological indices.

Hypsometric amplification and routing moderation of Greenland ice sheet meltwater release

The Greenland ice sheet melts faster in a warmer climate. The ice sheet is flatter at high elevation, therefore atmospheric warming increases the melt area exponentially. For current climate conditions, we find that the ice sheet shape amplifies the total meltwater generation by roughly 60 %. Meltwater is not stored underneath the ice sheet, as previously found, but it does take multiple days for it to pass through the seasonally developing subglacial drainage channels, moderating discharge.

Debris-flow modeling at Meretschibach and Bondasca catchments, Switzerland: sensitivity testing of field-data-based entrainment model

Natural Hazards and Earth System Sciences
DOI 10.5194/nhess-17-801-2017
1 June 2017

This study describes a sensitivity analysis of the RAMMS debris-flow entrainment model, which is intended to help solve problems related to predicting the runout of debris flows. The results indicate that the entrainment model predicts plausible erosion volumes in comparison with field data. These eroded volumes are sensitive to the initial landslide volume, suggesting that this tool may be useful for both reconstruction of historical events and modeling of debris flow scenarios.

Non-linear effects of pore pressure increase on seismic event generation in a multi-degree-of-freedom rate-and-state model of tectonic fault sliding

The influence of fluid injection on tectonic fault sliding and generation of seismic events was studied in the paper by a multi-degree-of-freedom rate-and-state friction model with a two-parametric friction law. The considered system could exhibit different types of motion. The main seismic activity could appear directly after the start of fluid injection or in the post-injection phase (after some days or months). Such an influence of injection on seismicity is observed in the real cases.

The polar amplification asymmetry: role of Antarctic surface height

The Arctic has been warming much faster than the rest of the globe, including Antarctica. Here it was shown that one of the important mechanisms that sets Antarctica apart from the Arctic is heat transport from lower latitudes, and it was argued that a decrease in land height due to Antarctic melting would be favorable for increased atmospheric heat transport from midlatitudes. Other factors related to the larger Antarctic land height were also investigated.

Ozone and haze pollution weakens net primary productivity in China

While it is widely recognized that air pollutants adversely affect human health and climate change, their impacts on the regional carbon balance are less well understood. We apply an Earth system model to quantify the combined effects of ozone and aerosol particles on net primary production in China. Ozone vegetation damage dominates over the aerosol effects, leading to a substantial net suppression of land carbon uptake in the present and future worlds.

Process-level model evaluation: a snow and heat transfer metric

This work defines a metric for evaluation of a specific model snow process, namely, heat transfer through snow into soil. Heat transfer through snow regulates the difference in air temperature versus soil temperature. Accurate representation of the snow heat transfer process is critically important for accurate representation of the current and future state of permafrost. Utilizing this metric, we can clearly identify models that can and cannot reasonably represent snow heat transfer.

Divergence of seafloor elevation and sea level rise in coral reef ecosystems

We report regional-scale erosion of coral reef ecosystems in the Atlantic, Caribbean, and Pacific oceans determined by measuring changes in seafloor elevation. The magnitude of seafloor elevation loss has increased local sea level rise, causing water depths not predicted until near 2100, placing coastal communities at elevated and accelerating risk from hazards such as waves, storms, and tsunamis. Our results have broad implications for coastal resource and safety management.

Accounting for the climate–carbon feedback in emission metrics

Emission metrics such as GWP or GTP are used to put non-CO₂species on aCO₂-equivalentscale. In the fifth IPCC report the metrics are inconsistent, as the climate–carbon feedback is included only for CO₂but not for non-CO₂species. Here, we simulate a new impulse response function for the feedback, and we use it to correct the metrics. For instance, 1 g of CH₄is equivalent to 31 g of CO₂(instead of 28 g) following the corrected GWP100 metric. It is 34 g if other factors are also updated.

Constraining N2O emissions since 1940 using firn air isotope measurements in both hemispheres

Nitrous oxide is the third most important anthropogenic greenhouse gas with an increasing mole fraction. To understand its natural and anthropogenic sources we employ isotope measurements. Results show that while the N₂O mole fraction increases, its heavy isotope content decreases. The isotopic changes observed underline the dominance of agricultural emissions especially at the early part of the record, whereas in the later decades the contribution from other anthropogenic sources increases.

Characterization of the long-term radiosonde temperature biases in the upper troposphere and lower stratosphere using COSMIC and Metop-A/GRAS data from 2006 to 2014

Radiosonde observations (RAOBs) have provided the only long-term global in situ temperature measurements since 1958. In this study, we use Global Positioning System (GPS) radio occultation (RO) temperature data from 2006 to 2014 to characterize the inter-seasonal and interannual variability of temperature biases in the lower stratosphere. Results from this study also demonstrate the feasibility to use RO data to correct RAOB temperature biases for different sensor types.

COSMIC and Metop-A/GRAS data from 2006 to 2014">Read more

Drought and flood in the Anthropocene: feedback mechanisms in reservoir operation

There is still little understanding about the dynamics emerging from human–water interactions. As a result, policies and measures to reduce the impacts of floods and droughts often lead to unintended consequences. This paper proposes a research agenda to improve our understanding of human–water interactions, and presents an initial attempt to model the reciprocal effects between water management, droughts, and floods.

Surge dynamics and lake outbursts of Kyagar Glacier, Karakoram

Recent surging of Kyagar Glacier (Karakoram) caused a hazardous ice-dammed lake to form and burst in 2015 and 2016. We use remotely sensed glacier surface velocities and surface elevation to observe dramatic changes in speed and mass distribution during the surge. The surge was hydrologically controlled with rapid summer onset and dramatic termination following lake outburst. Since the surge, the potential outburst hazard has remained high, and continued remote monitoring is crucial.

Manganese in the west Atlantic Ocean in the context of the first global ocean circulation model of manganese

We ran a global ocean model to understand manganese (Mn), a biologically essential element. Our model shows that (i) in the deep ocean, dissolved [Mn] is mostly homogeneous ca. 0.10–0.15 nM. The model reproduces this with a threshold on MnO₂ of 25 pM, suggesting a minimal particle concentration is needed before aggregation and removal become efficient. (ii) The observed distinct hydrothermal signals are produced by assuming both a strong source and a strong removal of Mn near hydrothermal vents.

The European 2015 drought from a climatological perspective

This paper analyses the European summer drought of 2015 from a climatological perspective, including its origin and spatial and temporal development, and how it compares with the 2003 event. It discusses the main contributing factors controlling the occurrence and persistence of the event: temperature and precipitation anomalies, blocking episodes and sea surface temperatures. The results represent the outcome of a collaborative initiative of members of UNESCO’s FRIEND-Water program.

Structural uncertainty in air mass factor calculation for NO2 and HCHO satellite retrievals

Choices and assumptions made to represent the state of the atmosphere introduce an uncertainty of 42 % in the air mass factor calculation in trace gas satellite retrievals in polluted regions. The AMF strongly depends on the choice of a priori trace gas profile, surface albedo data set and the correction method to account for clouds and aerosols. We call for well-designed validation exercises focusing on situations when AMF structural uncertainty has the highest impact on satellite retrievals.

HCHO satellite retrievals">Read more

Characteristics and causes of Deep Western Boundary Current transport variability at 34.5∘ S during 2009–2014

This study investigates the variability of the Deep Western Boundary Current at 34.5° S. This current carries a large part of the cold deep limb of the Meridional Overturning Circulation, which is a crucial part of the ocean system and has impacts on global weather patterns. Study of this current in the South Atlantic has been limited in the past, and this new study provides insights into the strength and variability of the current as well as the causes for the observed changes.

Soil conservation in the 21st century: why we need smart agricultural intensification

SOIL
DOI 10.5194/soil-3-45-2017
1 March 2017

We discuss pathways towards better soil protection in the 21st century. The efficacy of soil conservation technology is not a fundamental barrier for a more sustainable soil management. However, soil conservation is generally not directly beneficial to the farmer. We believe that the solution of this conundrum is a rapid, smart intensification of agriculture in the Global South. This will reduce the financial burden and will, at the same time, allow more effective conservation.

A record of Neogene seawater δ11B reconstructed from paired δ11B analyses on benthic and planktic foraminifera

Understanding the boron isotopic composition of seawater (δ¹¹B_sw) is key to calculating absolute estimates of CO₂ using the boron isotope pH proxy. Here we use the boron isotope gradient, along with an estimate of pH gradient, between the surface and deep ocean to show that the δ¹¹B_sw varies by ~ 2 ‰ over the past 23 million years. This new record has implications for both δ¹¹B_sw and CO₂ records and understanding changes in the ocean isotope composition of a number of ions through time.

Multi-model simulations of aerosol and ozone radiative forcing due to anthropogenic emission changes during the period 1990–2015

Over the past decades, the geographical distribution of emissions of substances that alter the atmospheric energy balance has changed due to economic growth and pollution regulations. Here, we show the resulting changes to aerosol and ozone abundances and their radiative forcing using recently updated emission data for the period 1990–2015, as simulated by seven global atmospheric composition models. The global mean radiative forcing is more strongly positive than reported in IPCC AR5.

A new device to mount portable energy-dispersive X-ray fluorescence spectrometers (p-ED-XRF) for semi-continuous analyses of split (sediment) cores and solid samples

Geoscientific Instrumentation, Methods and Data Systems
DOI 10.5194/gi-6-93-2017
17 February 2017

This paper introduces a hands-on, low-cost device (German industrial property right no. 20 2014 106 048.0) that uses common adapters to mount p-ED-XRF devices so that these can provide bulk-sedimentary chemistry data from non-destructive measurements at the surface of a split sediment core or from other solid samples. The strength of combining p-ED-XRF analyses with this new sample chamber is demonstrated by exemplary sediment cores from an archaeological research project.

XRF) for semi-continuous analyses of split (sediment) cores and solid samples">Read more

How much can we save? Impact of different emission scenarios on future snow cover in the Alps

The Cryosphere
DOI 10.5194/tc-11-517-2017
16 February 2017

We simulate the future snow cover in the Alps with the help of a snow model, which is fed by projected temperature and precipitation changes from a large set of climate models. The results demonstrate that snow below 1000 m is probably a rare guest at the end of the century. Moreover, even above 3000 m the simulations show a drastic decrease in snow depth. However, the results reveal that the projected snow cover reduction can be mitigated by 50 % if we manage to keep global warming below 2°.

Brief communication: Glaciers in the Hunza catchment (Karakoram) have been nearly in balance since the 1970s

The Cryosphere
DOI 10.5194/tc-11-531-2017
15 February 2017

Previous geodetic estimates of glacier mass changes in the Karakoram have revealed balanced budgets or a possible slight mass gain since the year ∼  2000. We used old US reconnaissance imagery and could show that glaciers in the Hunza River basin (Central Karakoram) experienced on average no significant mass changes also since the 1970s. Likewise the glaciers had heterogeneous behaviour with frequent surge activities during the last 40 years.

Trend of atmospheric mercury concentrations at Cape Point for 1995–2004 and since 2007

Currently the Cape Point GAW GEM record is a very sought-after data record for international modelers and scientist alike, as the data set of 20 years represents the longest record in the Southern Hemisphere (SH). CPT was the only monitoring site on the African continent and one of eight GMOS ground-based monitoring sites located in the SH. The increasing Hg trend observed at CPT is of global importance as treaties such as the Minamata Convention on Mercury is there to combat Hg pollution.