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Geophysical Research Letters

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https://read.qxmd.com/read/31068737/oxidation-of-volatile-organic-compounds-as-the-major-source-of-formic-acid-in-a-mixed-forest-canopy
#1
Hariprasad D Alwe, Dylan B Millet, Xin Chen, Jonathan D Raff, Zachary C Payne, Kathryn Fledderman
Formic acid (HCOOH) is among the most abundant carboxylic acids in the atmosphere, but its budget is poorly understood. We present eddy flux, vertical gradient, and soil chamber measurements from a mixed forest and apply the data to better constrain HCOOH source/sink pathways. While the cumulative above-canopy flux was downward, HCOOH exchange was bidirectional, with extended periods of net upward and downward flux. Net above-canopy fluxes were mostly upward during warmer/drier periods. The implied gross canopy HCOOH source corresponds to 3% and 38% of observed isoprene and monoterpene carbon emissions and is 15× underestimated in a state-of-science atmospheric model (GEOS-Chem)...
March 16, 2019: Geophysical Research Letters
https://read.qxmd.com/read/30983646/melting-of-casio-3-perovskite-at-high-pressure
#2
James Braithwaite, Lars Stixrude
Ab initio molecular dynamics simulations predict that CaSiO3 perovskite melts at 5600 K at 136 GPa, and 6400 K at 300 GPa, significantly higher than MgSiO3 perovskite. The entropy of melting (1.8 kB per atom) is much larger than that of many silicates at ambient pressure and of simple liquids and varies little with pressure. The volume of melting decreases rapidly with increasing pressure, to 3 % at 136 GPa, producing a melting slope that diminishes rapidly with pressure. We determine the melting temperature via the ZW method, combining the Z method, for which we clarify the theoretical basis, with a waiting time analysis...
February 28, 2019: Geophysical Research Letters
https://read.qxmd.com/read/31031452/soil-moisture-effects-on-afternoon-precipitation-occurrence-in-current-climate-models
#3
Heewon Moon, Benoit P Guillod, Lukas Gudmundsson, Sonia I Seneviratne
Soil moisture-precipitation feedbacks in a large ensemble of global climate model simulations are evaluated. A set of three metrics are used to assess the sensitivity of afternoon rainfall occurrence to morning soil moisture in terms of their spatial, temporal, and heterogeneity characteristics. Positive (negative) spatial feedback indicates that the afternoon rainfall occurs more frequently over wetter (drier) land surface than its surroundings. Positive (negative) temporal feedback indicates preference over temporally wetter (drier) conditions, and positive (negative) heterogeneity feedback indicates preference over more spatially heterogeneous (homogeneous) soil moisture conditions...
February 16, 2019: Geophysical Research Letters
https://read.qxmd.com/read/31007309/ferrous-iron-under-oxygen-rich-conditions-in-the-deep-mantle
#4
E Boulard, M Harmand, F Guyot, G Lelong, G Morard, D Cabaret, S Boccato, A D Rosa, R Briggs, S Pascarelli, G Fiquet
Recent experiments have demonstrated the existence of previously unknown iron oxides at high pressure and temperature including newly discovered pyrite-type FeO2 and FeO2 Hx phases stable at deep terrestrial lower mantle pressures and temperatures. In the present study, we probed the iron oxidation state in high-pressure transformation products of Fe3+ OOH goethite by in situ X-ray absorption spectroscopy in laser-heated diamond-anvil cell. At pressures and temperatures of ~91 GPa and 1,500-2,350 K, respectively, that is, in the previously reported stability field of FeO2 Hx , a measured shift of -3...
February 16, 2019: Geophysical Research Letters
https://read.qxmd.com/read/31007308/observational-constraints-reduce-likelihood-of-extreme-changes-in-multidecadal-land-water-availability
#5
Ryan S Padrón, Lukas Gudmundsson, Sonia I Seneviratne
Future changes in multidecadal mean water availability, represented as the difference between precipitation and evapotranspiration, remain highly uncertain in ensemble simulations of climate models. Here we identify a physically meaningful relationship between present-day mean precipitation and projected changes in water availability. This suggests that the uncertainty can be reduced by conditioning the ensemble on observed precipitation, which is achieved through a novel probabilistic approach that uses Approximate Bayesian Computation...
January 28, 2019: Geophysical Research Letters
https://read.qxmd.com/read/31007307/sensitivity-kernels-of-pp-precursor-traveltimes-and-their-limitations-for-imaging-topography-of-discontinuities
#6
Maria Koroni, Hanneke Paulssen, Jeannot Trampert
We analyze the sensitivity of PP precursor traveltimes that are often used to infer lateral variation in the depths of the 410- and 660-km discontinuities in the mantle. Previous results were inconclusive due to complex wave phenomena, such as multiple energy conversions and focusing/defocusing, that hamper their interpretation. Using spectral-element synthetics and Fréchet derivatives calculated with adjoint methods, we compute sensitivity kernels for volumetric and boundary parameters in a 1-D model for representative epicentral distances of past studies, and a dominant period of 11-25 s...
January 28, 2019: Geophysical Research Letters
https://read.qxmd.com/read/31007306/hamiltonian-nullspace-shuttles
#7
Andreas Fichtner, Andrea Zunino
We present a method to explore the effective nullspace of nonlinear inverse problems without Monte Carlo sampling. This is based on the construction of an artificial Hamiltonian system where a model is treated as a high-dimensional particle. Depending on its initial momentum and mass matrix, the particle evolves along a trajectory that traverses the effective nullspace, thereby producing a series of alternative models that are consistent with observations and their uncertainties. Variants of the nullspace shuttle enable hypothesis testing, for example, by adding features or by producing smoother or rougher models...
January 28, 2019: Geophysical Research Letters
https://read.qxmd.com/read/30853732/probing-jovian-broadband-kilometric-radio-sources-tied-to-the-ultraviolet-main-auroral-oval-with-juno
#8
Masafumi Imai, Thomas K Greathouse, William S Kurth, G Randall Gladstone, Corentin K Louis, Philippe Zarka, Scott J Bolton, John E P Connerney
Observations of Jovian broadband kilometric (bKOM) radiation and ultraviolet (UV) auroras were acquired with the Waves and Juno-UVS instruments for ∼2 hr over the northern and southern polar regions during Juno's perijoves 4, 5, and 6 passes (PJ4, PJ5, and PJ6). During all six time periods, Juno traversed auroral magnetic field lines connecting to the UV main auroral ovals, matching the estimates of bKOM radio source footprints. The localized bKOM radio sources for the PJ4 north pass map to magnetic field lines having distances of 10 to 12 Jovian radii (R J ) at the magnetic equator, whereas the extended bKOM radio sources for the other events map to field lines extending to 20-61 R J ...
January 28, 2019: Geophysical Research Letters
https://read.qxmd.com/read/30828110/comparing-electron-energetics-and-uv-brightness-in-jupiter-s-northern-polar-region-during-juno-perijove-5
#9
R W Ebert, T K Greathouse, G Clark, F Allegrini, F Bagenal, S J Bolton, J E P Connerney, G R Gladstone, M Imai, V Hue, W S Kurth, S Levin, P Louarn, B H Mauk, D J McComas, C Paranicas, J R Szalay, M F Thomsen, P W Valek, R J Wilson
We compare electron and UV observations mapping to the same location in Jupiter's northern polar region, poleward of the main aurora, during Juno perijove 5. Simultaneous peaks in UV brightness and electron energy flux are identified when observations map to the same location at the same time. The downward energy flux during these simultaneous observations was not sufficient to generate the observed UV brightness; the upward energy flux was. We propose that the primary acceleration region is below Juno's altitude, from which the more intense upward electrons originate...
January 16, 2019: Geophysical Research Letters
https://read.qxmd.com/read/30774167/estimating-subseasonal-variability-and-trends-in-global-atmosphere-using-reanalysis-data
#10
N Žagar, D Jelić, M J Alexander, E Manzini
A new measure of subseasonal variability is introduced that provides a scale-dependent estimation of vertically and meridionally integrated atmospheric variability in terms of the normal modes of linearized primitive equations. Applied to the ERA-Interim data, the new measure shows that subseasonal variability decreases for larger zonal wave numbers. Most of variability is due to balanced (Rossby mode) dynamics but the portion associated with the inertio-gravity (IG) modes increases as the scale reduces. Time series of globally integrated variability anomalies in ERA-Interim show an increase in variability after year 2000...
December 16, 2018: Geophysical Research Letters
https://read.qxmd.com/read/31007305/deep-transient-slow-slip-detected-by-survey-gps-in-the-region-of-atacama-chile
#11
E Klein, Z Duputel, D Zigone, C Vigny, J-P Boy, C Doubre, G Meneses
We detected a long-term transient deformation signal between 2014 and 2016 in the Atacama region (Chile) using survey Global Positioning System (GPS) observations. Over an ∼150 km along-strike region, survey GPS measurements in 2014 and 2016 deviate significantly from the interseismic trend estimated using previous observations. This deviation from steady state deformation is spatially coherent and reveals a horizontal westward diverging motion of several centimeters, along with a significant uplift. It is confirmed by continuous measurements of recently installed GPS stations...
November 28, 2018: Geophysical Research Letters
https://read.qxmd.com/read/30774166/sediment-characterization-at-the-equatorial-mid-atlantic-ridge-from-p-to-s-teleseismic-phase-conversions-recorded-on-the-pi-lab-experiment
#12
M R Agius, N Harmon, C A Rychert, S Tharimena, J-M Kendall
Accurate marine sediment characteristics, for example, thickness and seismic velocity, are important for constraining sedimentation rates with implications for climate variations and for seismic imaging of deeper structures using ocean bottom seismic deployments. We analyze P-to-S seismic phase conversions from the sediment-crust boundary recorded by the Passive Imaging of the Lithosphere-Asthenosphere Boundary (PI-LAB) experiment to infer the sediment thickness across the Mid-Atlantic Ridge covering 0- to 80-Myr-old seafloor...
November 28, 2018: Geophysical Research Letters
https://read.qxmd.com/read/30774165/infrared-radiation-in-the-thermosphere-near-the-end-of-solar-cycle-24
#13
Martin G Mlynczak, Linda A Hunt, B Thomas Marshall, James M Russell
Observations of thermospheric infrared radiative cooling by carbon dioxide (CO2 ) and nitric oxide (NO) from 2002 to 2018 are presented. The time span covers more than 6,000 days including most of solar cycle (SC) 23 and the entirety of SC 24 to date. Maxima of infrared cooling rate profiles (nW/m3 ) are smaller during SC 24 than SC 23, indicating a cooler thermosphere. Rates of global infrared power (W) from CO2 are now at levels observed during the deep solar minimum of 2009. Rates of NO power are still larger than those observed during 2009 and are being maintained at an elevated level by geomagnetic activity...
November 16, 2018: Geophysical Research Letters
https://read.qxmd.com/read/30686845/understanding-rapid-adjustments-to-diverse-forcing-agents
#14
C J Smith, R J Kramer, G Myhre, P M Forster, B J Soden, T Andrews, O Boucher, G Faluvegi, D Fläschner, Ø Hodnebrog, M Kasoar, V Kharin, A Kirkevåg, J-F Lamarque, J Mülmenstädt, D Olivié, T Richardson, B H Samset, D Shindell, P Stier, T Takemura, A Voulgarakis, D Watson-Parris
Rapid adjustments are responses to forcing agents that cause a perturbation to the top of atmosphere energy budget but are uncoupled to changes in surface warming. Different mechanisms are responsible for these adjustments for a variety of climate drivers. These remain to be quantified in detail. It is shown that rapid adjustments reduce the effective radiative forcing (ERF) of black carbon by half of the instantaneous forcing, but for CO2 forcing, rapid adjustments increase ERF. Competing tropospheric adjustments for CO2 forcing are individually significant but sum to zero, such that the ERF equals the stratospherically adjusted radiative forcing, but this is not true for other forcing agents...
November 16, 2018: Geophysical Research Letters
https://read.qxmd.com/read/31007304/fast-diffusion-of-ultrarelativistic-electrons-in-the-outer-radiation-belt-17-march-2015-storm-event
#15
A N Jaynes, A F Ali, S R Elkington, D M Malaspina, D N Baker, X Li, S G Kanekal, M G Henderson, C A Kletzing, J R Wygant
Inward radial diffusion driven by ULF waves has long been known to be capable of accelerating radiation belt electrons to very high energies within the heart of the belts, but more recent work has shown that radial diffusion values can be highly event-specific, and mean values or empirical models may not capture the full significance of radial diffusion to acceleration events. Here we present an event of fast inward radial diffusion, occurring during a period following the geomagnetic storm of 17 March 2015...
October 28, 2018: Geophysical Research Letters
https://read.qxmd.com/read/30774164/quantifying-the-importance-of-rapid-adjustments-for-global-precipitation-changes
#16
G Myhre, R J Kramer, C J Smith, Ø Hodnebrog, P Forster, B J Soden, B H Samset, C W Stjern, T Andrews, O Boucher, G Faluvegi, D Fläschner, M Kasoar, A Kirkevåg, J-F Lamarque, D Olivié, T Richardson, D Shindell, P Stier, T Takemura, A Voulgarakis, D Watson-Parris
Different climate drivers influence precipitation in different ways. Here we use radiative kernels to understand the influence of rapid adjustment processes on precipitation in climate models. Rapid adjustments are generally triggered by the initial heating or cooling of the atmosphere from an external climate driver. For precipitation changes, rapid adjustments due to changes in temperature, water vapor, and clouds are most important. In this study we have investigated five climate drivers (CO2 , CH4 , solar irradiance, black carbon, and sulfate aerosols)...
October 28, 2018: Geophysical Research Letters
https://read.qxmd.com/read/31031451/galveston-bay-and-coastal-ocean-optical-geochemical-response-to-hurricane-harvey-from-viirs-ocean-color
#17
Eurico J D'Sa, Ishan Joshi, Bingqing Liu
Dissolved and particulate organic carbon, suspended particulate matter concentrations, and their optical proxies colored dissolved organic matter absorption and backscattering coefficients were studied in Galveston Bay, Texas, following the extreme flooding of Houston and surrounding areas due to Hurricane Harvey (25-29 August 2017) using field and ocean color observations. A three-step empirical-semianalytic algorithm for determination of colored dissolved organic matter absorption and backscattering coefficients revealed the dynamics of dissolved organic carbon and particle distribution from Visible and Infrared Imaging Radiometric Suite ocean color...
October 16, 2018: Geophysical Research Letters
https://read.qxmd.com/read/31031450/surface-pond-energy-absorption-across-four-himalayan-glaciers-accounts-for-1-8-of-total-catchment-ice-loss
#18
Evan S Miles, Ian Willis, Pascal Buri, Jakob F Steiner, Neil S Arnold, Francesca Pellicciotti
Glaciers in High Mountain Asia, many of which exhibit surface debris, contain the largest volume of ice outside of the polar regions. Many contain supraglacial pond networks that enhance melt rates locally, but no large-scale assessment of their impact on melt rates exists. Here we use surface energy balance modeling forced using locally measured meteorological data and monthly satellite-derived pond distributions to estimate the total melt enhancement for the four main glaciers within the 400-km2 Langtang catchment, Nepal, for a 6-month period in 2014...
October 16, 2018: Geophysical Research Letters
https://read.qxmd.com/read/30546165/exacerbation-of-the-2013-2016-pan-caribbean-drought-by-anthropogenic-warming
#19
Dimitris A Herrera, Toby R Ault, John T Fasullo, Sloan J Coats, Carlos M Carrillo, Benjamin I Cook, A Park Williams
The Caribbean islands are expected to see more frequent and severe droughts from reduced precipitation and increased evaporative demand due to anthropogenic climate change. Between 2013 and 2016, the Caribbean experienced a widespread drought due in part to El Niño in 2015-2016, but it is unknown whether its severity was exacerbated by anthropogenic warming. This work examines the role of recent warming on this drought, using a recently developed high-resolution self-calibrating Palmer Drought Severity Index data set...
October 16, 2018: Geophysical Research Letters
https://read.qxmd.com/read/30487657/climatic-responses-to-future-trans-arctic-shipping
#20
Scott R Stephenson, Wenshan Wang, Charles S Zender, Hailong Wang, Steven J Davis, Philip J Rasch
As global temperatures increase, sea ice loss will increasingly enable commercial shipping traffic to cross the Arctic Ocean, where the ships' gas and particulate emissions may have strong regional effects. Here we investigate impacts of shipping emissions on Arctic climate using a fully coupled Earth system model (CESM 1.2.2) and a suite of newly developed projections of 21st-century trans-Arctic shipping emissions. We find that trans-Arctic shipping will reduce Arctic warming by nearly 1 °C by 2099, due to sulfate-driven liquid water cloud formation...
September 28, 2018: Geophysical Research Letters
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