Exploring gravity wave characteristics in 3-D using a novel S-transform technique: AIRS/Aqua measurements over the Southern Andes and Drake Passage Atmospheric Chemistry and Physics DOI 10.5194/acp-17-8553-2017 13 July 2017 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. Read more
On the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic Biogeosciences DOI 10.5194/bg-14-3337-2017 13 July 2017 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. Read more
HESS Opinions: A planetary boundary on freshwater use is misleading Hydrology and Earth System Sciences DOI 10.5194/hess-21-3455-2017 12 July 2017 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. Read more
Efficient retention of mud drives land building on the Mississippi Delta plain Earth Surface Dynamics DOI 10.5194/esurf-5-387-2017 12 July 2017 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. Read more
River logjams cause frequent large-scale forest die-off events in southwestern Amazonia Earth System Dynamics DOI 10.5194/esd-8-565-2017 11 July 2017 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. Read more
Detectability of Arctic methane sources at six sites performing continuous atmospheric measurements Atmospheric Chemistry and Physics DOI 10.5194/acp-17-8371-2017 11 July 2017 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. Read more
Geomorphometric delineation of floodplains and terraces from objectively defined topographic thresholds Earth Surface Dynamics DOI 10.5194/esurf-5-369-2017 10 July 2017 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. Read more
A weekly Arctic sea-ice thickness data record from merged CryoSat-2 and SMOS satellite data The Cryosphere DOI 10.5194/tc-11-1607-2017 6 July 2017 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. Read more
Non-linear intensification of Sahel rainfall as a possible dynamic response to future warming Earth System Dynamics DOI 10.5194/esd-8-495-2017 5 July 2017 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. Read more
WCRP’s Coupled Model Intercomparison Project: a remarkable contribution to climate science Geoscientific Model Development DOI 10.5194/gmd-9-1937-2016 4 July 2017 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. Read more
The importance of terrestrial weathering changes in multimillennial recovery of the global carbon cycle: a two-dimensional perspective Earth System Dynamics DOI 10.5194/esd-8-455-2017 30 June 2017 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. Read more
Opposite long-term trends in aerosols between low and high altitudes: a testimony to the aerosol–PBL feedback Atmospheric Chemistry and Physics DOI 10.5194/acp-17-7997-2017 30 June 2017 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. Read more
STRAPS v1.0: evaluating a methodology for predicting electron impact ionisation mass spectra for the aerosol mass spectrometer Geoscientific Model Development DOI 10.5194/gmd-10-2365-2017 27 June 2017 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. 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. Read more
The European 2015 drought from a hydrological perspective Hydrology and Earth System Sciences DOI 10.5194/hess-21-3001-2017 22 June 2017 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. Read more
Hypsometric amplification and routing moderation of Greenland ice sheet meltwater release The Cryosphere DOI 10.5194/tc-11-1371-2017 9 June 2017 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. Read more
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. Read more
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 Nonlinear Processes in Geophysics DOI 10.5194/npg-24-215-2017 22 May 2017 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. Read more
The polar amplification asymmetry: role of Antarctic surface height Earth System Dynamics DOI 10.5194/esd-8-323-2017 18 May 2017 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. Read more
Ozone and haze pollution weakens net primary productivity in China Atmospheric Chemistry and Physics DOI 10.5194/acp-17-6073-2017 16 May 2017 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. Read more