pinecone/core-2020-05-10-deduplication huggingface dataset:
First satellite measurements of carbon dioxide and methane emission ratios in wildfire plumes

Supporting information available with version of record.Using methane and carbon dioxide atmospheric mixing\ud
ratios retrieved using SWIR spectra from the Greenhouse\ud
Gases Observing SATellite (GOSAT), we report the first\ud
wildfire plume CH4 to CO2 emission ratios (ERCH4/CO2)\ud
determined from space. We demonstrate the approach’s\ud
potential using forward modeling and identify a series of\ud
real GOSAT spectra containing wildfire plumes. These\ud
show significantly changed total-column CO2 and CH4\ud
mixing ratios, and from these we calculate ERCH4/CO2 for\ud
boreal forest, tropical forest, and savanna fires as 0.00603,\ud
0.00527, and 0.00395 mol mol 1\ud
, respectively. These ERs\ud
are statistically significantly different from each other and\ud
from the “normal” atmospheric CH4 to CO2 ratio and\ud
generally agree with past ground and airborne studies.We thank JAXA, NIES, and MOE for GOSAT data and their support as part of the Joint Research Agreement. R.P. and M.J.W are supported by the NERC National Centre for Earth Observation (NCEO). R.P. is also supported by the ESA Climate Change Initiative, and M.J.W by the EU Seventh Research Framework Programme (MACC-II project, contract 283576). We also thank BADC for providing ECMWF Operational Analyses data used in retrievals.Peer-reviewedPublisher Versio
Role of subsea permafrost and gas hydrate in postglacial Arctic methane releases

The papers of this thesis are not available in Munin.<br>Paper I: 'Offshore permafrost decay and massive seabed methane escape in water depths > 20 m at the South Kara Sea shelf.' Alexey Portnov, Andrew J. Smith, Jürgen Mienert, Georgy Cherkashov, Pavel Rekant, Peter Semenov, Pavel Serov, Boris Vanshtein. Available in <a href=http://dx.doi.org/10.1002/grl.50735> Geophysical Research Letters, vol. 40, 1–6</a><br>Paper II: 'Modeling the evolution of climate-sensitive Arctic subsea permafrost in regions of extensive gas expulsion at the West Yamal shelf.' Alexey Portnov, Jurgen Mienert, Pavel Serov. Available in <a href=http://dx.doi.org/10.1002/2014JG002685> Journal of Geophysical Research: Biogeosciences, vol. 119, issue 11, 2014</a>
<br>Paper III: 'Methane release from pingo-like features across the South Kara Sea shelf, an area of thawing offshore permafrost'. Pavel Serov, Alexey Portnov, Jurgen Mienert, Peter Semenov, Polina Ilatovskaya. (Manuscript). Published version available in <a href=http://dx.doi.org/10.1002/2015JF003467> Journal of Geophysical Research: Earth Surface, vol. 120, issue 8, 2015</a>
<br>Paper IV: 'Ice-sheet driven methane storage and release in the Arctic.' Alexey Portnov, Sunil Vadakkepulyambatta, Jurgen Mienert, Alun Hubbard. (Manuscript)Greenhouse gas methane is contained as gas hydrate, an icy structure, under the seabed in enormous amounts of Arctic regions. West Svalbard continental margin, which we investigated here, is one of these regions. Also, in the Russian Kara Sea the subsea permafrost is acting as a cap for the gas to be released in the future. But continuous expulsions of methane have been already observed in both places. This study shows how the subsea permafrost in the Kara Sea, and gas hydrate systems offshore West Svalbard, have evolved from the last ice age to the present day. The conclusions are based on integrated field geophysical and gas-geochemical studies as well as modeling of permafrost, gas hydrate reservoirs and Barents Sea ice sheet dynamics. It shows that continuous permafrost of the Kara Sea is more fragile than previously thought. It is likely to be limited to the shallow water depths of 20 meters on this Arctic shelf region, allowing expulsions of methane from an area of 7500 sq km. Offshore Svalbard almost 2000 active and inactive gas expulsion sites are associated with melting of gas hydrate and thawing of shallow permafrost from past to present. Our research approach shows that natural climate drivers such as methane release can change and that they are connected to the ice sheet retreat since the last ice age. These processes triggered widespread seafloor gas discharge, observed in Arctic shelf and upper continental margins to this day
Cassini CAPS-ELS observations of negative ions in Titan's ionosphere: trends of density with altitude

Observations with the Electron Spectrometer sensor of the Cassini Plasma Spectrometer (CAPS-ELS) have revealed the existence of negative ions in Titan's ionosphere. Negative ions are observed during encounters whenever the instrument points in the ram direction at altitudes 950–1400 km. Complex hydrocarbon and nitrile chemical processes are believed to take place which play a role in haze formation. The heaviest ions observed so far have masses up to 13,800 amu/q. Using data from 34 Titan encounters, we show for the first time negative ion density trends of different mass groups, including total densities, with altitude. We determine peak densities and the associated altitudes at which they are observed and the highest altitudes at which individual mass groups are found
An agent-based model of dune interactions produces the emergence of patterns in deserts

Crescent-shaped barchan dunes are highly mobile dunes which are ubiquitous on Earth and other solar system bodies. Although they are unstable when considered separately, they form large assemblies in deserts and spatially organize in narrow corridors that extend in the wind direction. Collision of barchans has been proposed as a mechanism to redistribute sand between dunes and prevent the formation of very large dunes. Here we use an agent-based model with elementary rules of sand redistribution during collisions to access the full dynamics of very large barchan fields. We tune the dune field density by changing the sand load/lost ratio and follow the transition between dilute fields, where barchans barely interact, and dense filds, where dune collisions control and stabilize the dune field. In this dense regime, barchans have a small, well-selected size and form flocks: the dune field self-organizes in narrow corridors of dunes, as it is observed in real dense barchan deserts
Advective timescales and pathways of Agulhas leakage

Current research indicates an increase in Agulhas leakage for the past and coming decades. This change potentially alters the strength of the Atlantic meridional overturning circulation, in particular, through advection of positive density anomalies into the North Atlantic. To explore the fate of Agulhas leakage, results from a Lagrangian analysis were evaluated, with virtual floats advected within an eddy-permitting ocean model (ORCA025). A considerable fraction of Agulhas leakage reached the subtropical North Atlantic: of a mean Agulhas leakage transport of 15.3 Sv entering the South Atlantic, 9.7, 7.7, and 6.1 Sv crossed sections at 6 degrees S, 6 degrees N, and 26 degrees N, respectively. The most probable transit time of leakage to reach the respective latitudes is one to two decades. We suggest that changes in Agulhas leakage could manifest in the Gulf Stream regime most probably within two decades. These results were supported by an eddy-resolving implementation of the ocean model (INALT01
Postmidnight depletion of the high‐energy tail of the quiet plasmasphere

The Van Allen Probes Helium Oxygen Proton Electron (HOPE) instrument measures the high‐energy tail of the thermal plasmasphere allowing study of topside ionosphere and inner magnetosphere coupling. We statistically analyze a 22 month period of HOPE data, looking at quiet times with a Kp index of less than 3. We investigate the high‐energy range of the plasmasphere, which consists of ions at energies between 1 and 10 eV and contains approximately 5% of total plasmaspheric density. Both the fluxes and partial plasma densities over this energy range show H+ is depleted the most in the postmidnight sector (1–4 magnetic local time), followed by O+ and then He+. The relative depletion of each species across the postmidnight sector is not ordered by mass, which reveals ionospheric influence. We compare our results with keV energy electron data from HOPE and the Van Allen Probes Electric Fields and Waves instrument spacecraft potential to rule out spacecraft charging. Our conclusion is that the postmidnight ion disappearance is due to diurnal ionospheric temperature variation and charge exchange processes.Key PointsOne to ten eV ion depletion in quiet time postmidnight sectorDepletion varies by ion species not ordered by massStrong diurnal variation in high‐energy tail of plasmaspher
Ecosystem-scale measurements of biomass water using cosmic ray neutrons

Accurate estimates of biomass are imperative for understanding the global carbon cycle. However, measurements of biomass and water in the biomass are difficult to obtain at a scale consistent with measurements of mass and energy transfer, ~1 km, leading to substantial uncertainty in dynamic global vegetation models. Here we use a novel cosmic ray neutron method to estimate a stoichiometric predictor of ecosystem-scale biomass and biomass water equivalent over tens of hectares. We present two experimental studies, one in a ponderosa pine forest and the other in a maize field, where neutron-derived estimates of biomass water equivalent are compared and found consistent with direct observations. Given the new hectometer scale of nondestructive observation and potential for continuous measurements, we anticipate this technique to be useful to many scientific disciplines
Initiation of the West Antarctic ice sheet and estimates of total Antarctic ice volume in the earliest Oligocene.

Reconstructions of Antarctic paleotopography for the late Eocene suggest that glacial erosion and thermal subsidence have lowered West Antarctic elevations considerably since then, with Antarctic land area having decreased ~20%. A new climate-ice sheet model based on these reconstructions shows that the West Antarctic Ice Sheet first formed at the Eocene-Oligocene transition (33.8–33.5 Ma, E-O) in concert with the continental-scale expansion of the East Antarctica Ice Sheet and that the total volume of East and West Antarctic ice (33.4–35.9 × 106 km3) was >1.4 times greater than previously assumed. This larger modeled ice volume is consistent with a modest cooling of 1–2°C in the deep ocean during the E-O transition, lower than other estimates of ~3°C cooling, and suggests the possibility of substantial ice in the Antarctic interior before the Eocene-Oligocene boundary
First magnetic seismology of the CME reconnection outflow layer in the low corona with 2.5-D MHD simulations of the Kelvin-Helmholtz instability

Copyright © 2013 American Geophysical UnionFor conditions observed in the low corona, we perform 2.5-D magnetohydrodynamic (MHD) simulations of the Kelvin-Helmholtz instability (KHI) at the surface of a coronal mass ejection (CME). We match the observed time development of the KHI with simulated growth from 110 MHD experiments representing a parametric range of realistic magnetic field strengths and orientations and two key values of the velocity shear, ΔV, inferred from observations. The results are field strengths Be≈ 8–9 G and Bs≈ 10–11 G in the CME reconnection outflow layer and the surrounding sheath, respectively, for ΔV≈770kms−1; for nearly perpendicular orientation (1° tilt) of Bs with respect to the flow plane, Be can be tilted between 3 and 10°; tilting Bs up to 15° would slow the growth of the KHI by too much. Our simulations also reveal hidden dynamics and structure of the CME ejecta layer such as plasma mixing via reconnection in the vortices
Plutonium-238 observations as a test of modelled transport and surface deposition of meteoric smoke particles

There are large uncertainties in the transport and surface deposition of upper atmospheric particles used to construct climate proxies. Here we use a 3-D chemistry-climate model (CCM) to simulate the transport and deposition of plutonium-238 oxide nanoparticles formed after the ablation of a power unit in the upper stratosphere (~11°S) in 1964. The model reproduces both the observed hemispheric asymmetry and time scale of Pu-238 deposition. We then use the CCM to investigate the transport of meteoric smoke particles (MSPs) from the upper mesosphere. The strongest MSP deposition is predicted to occur at middle latitudes, providing a significant source of Fe fertilization to the Southern Ocean. The model also predicts substantially more deposition in Greenland than in Antarctica (by a factor of ~15, in agreement with ice core measurements), showing that climate proxy measurements from a limited number of sites must be interpreted with care
Impact of future Arctic shipping on high-latitude black carbon deposition

The retreat of Arctic sea ice has led to renewed calls to exploit Arctic shipping routes. The diversion of ship traffic through the Arctic will shorten shipping routes and possibly reduce global shipping emissions. However, deposition of black carbon (BC) aerosol emitted by additional Arctic ships could cause a reduction in the albedo of snow and ice, accelerating snowmelt and sea ice loss. Here we use recently compiled Arctic shipping emission inventories for 2004 and 2050 together with a global aerosol model to quantify the contribution of future Arctic shipping to high-latitude BC deposition. Our results show that Arctic shipping in 2050 will contribute less than 1% to the total BC deposition north of 60°N due to the much greater relative contribution of BC transported from non-shipping sources at lower latitudes. We suggest that regulation of the Arctic shipping industry will be an insufficient control on high-latitude BC deposition
Characteristics of a tsunamigenic megasplay fault in the Nankai Trough

Slip on the shallow part of a megasplay fault that is an out-of-sequence thrust and branch of the main subduction plate boundary can cause devastating tsunamis after earthquakes. We analyzed the three-dimensional geometry, including dip amount and azimuths, roughness distributions, and thickness variations, of the shallow part of a megasplay fault in the Nankai Trough using a three-dimensional seismic data set. The fault is divided into three zones based on its geometry: thick, smooth, and simply convex in the east; complexly curved in the middle; and thin and kinked in the west. Results of scientific drilling indicate that the eastern region of the fault is most active, and local heterogeneities in fault geometry, including roughness and thickness, may control the slip on this part of the fault. The present findings can be used to evaluate the risk of future tsunamis arising from movement on shallow thrust faults at subduction margins
Tomographic image of melt storage beneath Askja volcano, Iceland using local microseismicity

[1] We use P wave and S wave arrivals from microseismic earthquakes to construct 3-D tomographic Vp and Vs images of the magma storage region beneath Askja's central volcano in the Northern Volcanic Zone of Iceland. A distinctive ellipsoidal low-velocity anomaly, with both Vp and Vsvelocities 8-12% below the background, is imaged at 6-11 km depth beneath the caldera. The presence of a shallow magma chamber is corroborated by geodetic and gravity studies. The small Vp/Vs anomaly suggests a lack of pervasive melt. We interpret this anomaly as a region of multiple sills, some frozen but hot, others containing partial melt. A second, smaller low-velocity anomaly beneath the main magma storage region may represent a magma migration pathway. This interpretation is supported by the close proximity to the anomaly of clusters of deep, magmatically induced earthquakes. However, the location and shape of this deep anomaly are poorly constrained by the current data set
Mechanism of column and carrot sprites derived from optical and radio observations

International audience[1] The lightning current waveforms observed simultaneously with high-speed video records of a column and a carrot sprite event are incorporated in a plasma fluid model to provide quantitative explanation of these two distinct morphological classes of transient luminous events. We calculate the strength of the lightning-induced electric field at sprite altitudes using a time integral of the ionization frequency R t 0 i (E/N)dt. For the studied two events, modeling results indicate that these integral values never exceed 18 in the lower ionosphere, which is the minimum value required for the initiation of streamers from single seed electrons according to the Raether-Meek criterion. It is therefore suggested that the presence of electron inhomogeneities is a necessary condition for the initiation of sprite streamers. It is further demonstrated using streamer modeling that a minimum value of the integral 10 is necessary to initiate upward negative streamers from inhomogeneities, corresponding to a minimum charge moment change of 500 C km under typical nighttime conditions. If the integral values in the entire upper atmosphere are smaller than 10, only column sprites can be produced, dominated by downward positive streamers. Citation: Qin, (2013), Mechanism of column and carrot sprites derived from optical and radio observations , Geophys
Numerical and statistical evidence for long-range ducted gravity wave propagation over Halley, Antarctica

Abundant short‒period, small‒scale gravity waves have been identified in the mesosphere and lower thermosphere over Halley, Antarctica, via ground‒based airglow image data. Although many are observed as freely propagating at the heights of the airglow layers, new results under modeled conditions reveal that a significant fraction of these waves may be subject to reflections at altitudes above and below. The waves may at times be trapped within broad thermal ducts, spanning from the tropopause or stratopause to the base of the thermosphere (∼140 km), which may facilitate long‒range propagation (∼1000s of km) under favorable wind conditions
Atmosphere drives recent interannual variability of the Atlantic meridional overturning circulation at 26.5°N

The Atlantic meridional overturning circulation (AMOC) has been observed at 26.5°N since 2004. During 2009/2010, there was a transient 30% weakening of the AMOC driven by anomalies in geostrophic and Ekman transports. Here, we use simulations based on the Met Office Forecast Ocean Assimilation Model (FOAM) to diagnose the relative importance of atmospheric forcings and internal ocean dynamics in driving the anomalous geostrophic circulation of 2009/2010. Data-assimilating experiments with FOAM accurately reproduce the mean strength and depth of the AMOC at 26.5°N. In addition, agreement between simulated and observed stream functions in the deep ocean is improved when we calculate the AMOC using a method that approximates the observing array at 26.5°N. The main features of the geostrophic circulation anomaly are captured by an ensemble of simulations without data assimilation. These model results suggest that the atmosphere played a dominant role in driving recent interannual variability of the AMOC
Detection of acoustic-gravity waves in lower ionosphere by VLF radio
  waves

We present a new method to study harmonic waves in the low ionosphere (60 -
90 km) by detecting their effects on reflection of very low frequency (VLF)
radio waves. Our procedure is based on amplitude analysis of reflected VLF
radio waves recorded in real time, which yields an insight into the dynamics of
the ionosphere at heights where VLF radio waves are being reflected. The method
was applied to perturbations induced by the solar terminator motions at
sunrises and sunsets. The obtained results show that typical perturbation
frequencies found to exist in higher regions of the atmosphere are also present
in the lower ionosphere, which indicates a global nature of the considered
oscillations. In our model atmosphere, they turn out to be the acoustic and
gravity waves with comparatively short and long periods, respectively
Projections of global changes in precipitation extremes from CMIP5 models

Precipitation extremes are expected to increase in a warming climate, thus it is essential to characterise their potential future changes. Here we evalu- ate eight high-resolution Global Climate Model simulations in the twenti- eth century and provide new evidence on projected global precipitation ex- tremes for the 21st century. A significant intensification of daily extremes for all seasons is projected for the mid and high latitudes of both hemispheres at the end of the present century. For the subtropics and tropics, the lack
of reliable and consistent estimations found for both the historical and fu- ture simulations might be connected with model deficiencies in the repre- sentation of organised convective systems. Low inter-model variability and good agreement with high-resolution regional observations are found for the twentieth century winter over the Northern Hemisphere mid and high lat- itudes
Paleogeographic controls on the onset of the Antarctic\ud
circumpolar current

Development of the Antarctic Circumpolar Current (ACC) during the Cenozoic is controversial in terms of timing and its role in major climate transitions. Some propose that the development of the ACC was instrumental in the continental scale glaciation of Antarctica and climate cooling at the Eocene/Oligocene boundary. Here we present climate model results that show that a coherent ACC was not possible during the Oligocene due to Australasian paleogeography, despite deep water connections through the Drake Passage and Tasman Gateway and the initiation of Antarctic glaciation. The simulations of ocean currents compare well to paleoenvironmental records relating to the physical oceanography of the Oligocene and provide a framework for understanding apparently contradictory dating of the initiation of the ACC. We conclude that the northward motion of the Australasian land masses and the reconfiguration of the Tasman Seaway and Drake Passage are necessary preconditions for the formation of a strong, coherent ACC
The role of synoptic eddies in the tropospheric response to stratospheric variability

The tropospheric response to sudden stratospheric warmings (SSWs) is analyzed in an idealized model setup regarding the respective roles of planetary-scale and synoptic-scale waves. The control model run includes a full interactive wave spectrum, while a second run includes interactive planetary-scale waves but only the time-mean synoptic-scale wave forcing from the control run. In both runs, the tropospheric response is characterized by the negative phase of the respective tropospheric annular mode. But given their different latitudinal structure, the control run shows the expected response, i.e., an equatorward shift of the tropospheric jet, whereas the response in the absence of interactive synoptic eddies is characterized by a poleward jet shift. This opposite jet shift is associated with a different planetary wave variability that couples with the zonal flow between the stratosphere and the surface. These results indicate that the synoptic eddy feedback is necessary for the observed tropospheric response to SSWs
Land use change and nitrogen feedbacks constrain the trajectory of the land carbon sink

Our understanding of Earth's carbon climate system depends critically upon interactions between rising atmospheric CO2, changing land use, and nitrogen limitation on vegetation growth. Using a global land model, we show how these factors interact locally to generate the global land carbon sink over the past 200 years. Nitrogen constraints were alleviated by N2 fixation in the tropics and by atmospheric nitrogen deposition in extratropical regions. Nonlinear interactions between land use change and land carbon and nitrogen cycling originated from three major mechanisms: (i) a sink foregone that would have occurred without land use conversion; (ii) an accelerated response of secondary vegetation to CO2 and nitrogen, and (iii) a compounded clearance loss from deforestation. Over time, these nonlinear effects have become increasingly important and reduce the present-day net carbon sink by ~40% or 0.4 PgC yr−1