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Geophysical Research Letters

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
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
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
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
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
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
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
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
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
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
Lukas Brunner, Nathalie Schaller, James Anstey, Jana Sillmann, Andrea K Steiner
The impact of atmospheric blocking on European heat waves (HWs) and cold spells (CSs) is investigated for present and future conditions . A 50-member ensemble of the second generation Canadian Earth System Model is used to quantify the role of internal variability in the response to blocking. We find that the present blocking-extreme temperature link is well represented compared to ERA-Interim, despite a significant underestimation of blocking frequency in most ensemble members. Our results show a strong correlation of blocking with northern European HWs in summer, spring, and fall...
June 28, 2018: Geophysical Research Letters
Piercarlo Giacomel, Elena Spagnuolo, Manuela Nazzari, Andrea Marzoli, François Passelegue, Nasrrddine Youbi, Giulio Di Toro
The safe application of geological carbon storage depends also on the seismic hazard associated with fluid injection. In this regard, we performed friction experiments using a rotary shear apparatus on precut basalts with variable degree of hydrothermal alteration by injecting distilled H2 O, pure CO2 , and H2 O + CO2 fluid mixtures under temperature, fluid pressure, and stress conditions relevant for large-scale subsurface CO2 storage reservoirs. In all experiments, seismic slip was preceded by short-lived slip bursts...
June 28, 2018: Geophysical Research Letters
X Ma, H Jia, F Yu, J Quaas
The Moderate Resolution Imaging Spectroradiometer (MODIS) C6 L3 and the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis data from 2003 to 2016 are employed to study aerosol-cloud correlations over three industrial regions and their adjacent oceans, as well as explore the impact of meteorological conditions on the correlations. The analysis focusing on liquid and single-layer clouds indicates an opposite aerosol-cloud correlation between land and ocean; namely, cloud effective radius is positively correlated with aerosol index over industrial regions (positive slopes), but negatively correlated over their adjacent oceans (negative slopes), for a quasi-constant liquid water path...
June 16, 2018: Geophysical Research Letters
Catherine A Rychert, Nick Harmon
The ocean lithosphere is classically described by the thermal half-space cooling (HSC) or the plate models, both characterized by a gradual transition to the asthenosphere beneath. Scattered waves find sharp seismic discontinuities beneath the oceans, possibly from the base of the plate. Active source studies suggest sharp discontinuities from a melt channel. We calculate synthetic S -to- P receiver functions and SS precursors for the HSC and plate models and also for channels. We find that the HSC and plate model velocity gradients are too gradual to create interpretable scattered waves from the base of the plate...
June 16, 2018: Geophysical Research Letters
Krzysztof Wargan, Clara Orbe, Steven Pawson, Jerald R Ziemke, Luke D Oman, Mark A Olsen, Lawrence Coy, K Emma Knowland
1998-2016 ozone trends in the lower stratosphere (LS) are examined using the Modern-Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2) and related NASA products. After removing biases resulting from step-changes in the MERRA-2 ozone observations, a discernible negative trend of -1.67±0.54 Dobson units per decade (DU/decade) is found in the 10-km layer above the tropopause between 20°N and 60°N. A weaker but statistically significant trend of -1.17±0.33 DU/decade exists between 50°S and 20°S...
May 28, 2018: Geophysical Research Letters
W T Crow, F Chen, R H Reichle, Y Xia, Q Liu
Accurate partitioning of precipitation into infiltration and runoff is a fundamental objective of land surface models tasked with characterizing the surface water and energy balance. Temporal variability in this partitioning is due, in part, to changes in pre-storm soil moisture, which determine soil infiltration capacity and unsaturated storage. Utilizing the NASA Soil Moisture Active Passive Level-4 soil moisture product in combination with streamflow and precipitation observations, we demonstrate that land surface models (LSMs) generally underestimate the strength of the positive rank correlation between pre-storm soil moisture and event runoff coefficients (i...
May 28, 2018: Geophysical Research Letters
C Köhn, O Chanrion, T Neubert
Bursts of X-rays and γ -rays are observed from lightning and laboratory sparks. They are bremsstrahlung from energetic electrons interacting with neutral air molecules, but it is still unclear how the electrons achieve the required energies. It has been proposed that the enhanced electric field of streamers, found in the corona of leader tips, may account for the acceleration; however, their efficiency is questioned because of the relatively low production rate found in simulations. Here we emphasize that streamers usually are simulated with the assumption of homogeneous gas, which may not be the case on the small temporal and spatial scales of discharges...
May 28, 2018: Geophysical Research Letters
Tom Goren, Daniel Rosenfeld, Odran Sourdeval, Johannes Quaas
This study examines the relationships between marine stratocumulus clouds (MSC) coupling state with the ocean surface, their precipitation rate and fractional cloud cover (CF). This was possible by developing a novel methodology for satellite retrieval of the clouds coupling state. Decks of overcast MSC were reported in previous studies to break up often as their precipitation rate increases significantly, thus reducing CF and cloud radiative effect substantially. Here we show that decks of precipitating decoupled MSC have larger CF compared to similarly precipitating coupled MSC...
May 28, 2018: Geophysical Research Letters
Clemens Schwingshackl, Martin Hirschi, Sonia I Seneviratne
The evolution of near-surface air temperature is influenced by various dynamical, radiative, and surface-atmosphere exchange processes whose contributions are still not completely quantified. Applying stepwise multiple linear regression to Coupled Model Intercomparison Project phase 5 (CMIP5) model simulations and focusing on radiation (diagnosed by incoming shortwave and incoming longwave radiation) and land surface conditions (diagnosed by soil moisture and albedo) about 79% of the interannual variability and 99% of the multidecadal trend of monthly mean daily maximum temperature over land can be explained...
May 28, 2018: Geophysical Research Letters
Tianle Yuan, Lazaros Oreopoulos, Steven E Platnick, Kerry Meyer
Modeling studies have shown that cloud feedbacks are sensitive to the spatial pattern of sea surface temperature (SST) anomalies, while cloud feedbacks themselves strongly influence the magnitude of SST anomalies. Observational counterparts to such patterned interactions are still needed. Here we show that distinct large-scale patterns of SST and low-cloud cover (LCC) emerge naturally from objective analyses of observations and demonstrate their close coupling in a positive local SST-LCC feedback loop that may be important for both internal variability and climate change...
May 16, 2018: Geophysical Research Letters
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