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Geophysical Research Letters

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https://www.readbyqxmd.com/read/29937608/warming-and-inhibition-of-salinization-at-the-ocean-s-surface-by-cyanobacteria
#1
O Wurl, K Bird, M Cunliffe, W M Landing, U Miller, N I H Mustaffa, M Ribas-Ribas, C Witte, C J Zappa
This paper describes high-resolution in situ observations of temperature and, for the first time, of salinity in the uppermost skin layer of the ocean, including the influence of large surface blooms of cyanobacteria on those skin properties. In the presence of the blooms, large anomalies of skin temperature and salinity of 0.95°C and -0.49 practical salinity unit were found, but a substantially cooler (-0.22°C) and saltier skin layer (0.19 practical salinity unit) was found in the absence of surface blooms...
May 16, 2018: Geophysical Research Letters
https://www.readbyqxmd.com/read/29937607/bayesian-analysis-of-the-glacial-interglacial-methane-increase-constrained-by-stable-isotopes-and-earth-system-modeling
#2
Peter O Hopcroft, Paul J Valdes, Jed O Kaplan
The observed rise in atmospheric methane (CH4 ) from 375 ppbv during the Last Glacial Maximum (LGM: 21,000 years ago) to 680 ppbv during the late preindustrial era is not well understood. Atmospheric chemistry considerations implicate an increase in CH4 sources, but process-based estimates fail to reproduce the required amplitude. CH4 stable isotopes provide complementary information that can help constrain the underlying causes of the increase. We combine Earth System model simulations of the late preindustrial and LGM CH4 cycles, including process-based estimates of the isotopic discrimination of vegetation, in a box model of atmospheric CH4 and its isotopes...
April 28, 2018: Geophysical Research Letters
https://www.readbyqxmd.com/read/29937606/unprecedented-2015-2016-indo-pacific-heat-transfer-speeds-up-tropical-pacific-heat-recharge
#3
Michael Mayer, Magdalena Alonso Balmaseda, Leopold Haimberger
El Niño events are characterized by anomalously warm tropical Pacific surface waters and concurrent ocean heat discharge, a precursor of subsequent cold La Niña conditions. Here we show that El Niño 2015/2016 departed from this norm: despite extreme peak surface temperatures, tropical Pacific (30°N-30°S) upper ocean heat content increased by 9.6 ± 1.7 ZJ (1 ZJ = 1021  J), in stark contrast to the previous strong El Niño in 1997/1998 (-11.5 ± 2.9 ZJ). Unprecedented reduction of Indonesian Throughflow volume and heat transport played a key role in the anomalous 2015/2016 event...
April 16, 2018: Geophysical Research Letters
https://www.readbyqxmd.com/read/29937605/a-century-of-stability-of-avannarleq-and-kujalleq-glaciers-west-greenland-explained-using-high-resolution-airborne-gravity-and-other-data
#4
L An, E Rignot, J Mouginot, R Millan
The evolution of Greenland glaciers in a warming climate depends on their depth below sea level, flow speed, surface melt, and ocean-induced undercutting at the calving front. We present an innovative mapping of bed topography in the frontal regions of Sermeq Avannarleq and Kujalleq, two major glaciers flowing into the ice-choked Torssukatak Fjord, central west Greenland. The mapping combines a mass conservation algorithm inland, multibeam echo sounding data in the fjord, and high-resolution airborne gravity data at the ice-ocean transition where other approaches have traditionally failed...
April 16, 2018: Geophysical Research Letters
https://www.readbyqxmd.com/read/29937604/vulnerability-of-southeast-greenland-glaciers-to-warm-atlantic-water-from-operation-icebridge-and-ocean-melting-greenland-data
#5
R Millan, E Rignot, J Mouginot, M Wood, A A Bjørk, M Morlighem
We employ National Aeronautics and Space Administration (NASA)'s Operation IceBridge high-resolution airborne gravity from 2016, NASA's Ocean Melting Greenland bathymetry from 2015, ice thickness from Operation IceBridge from 2010 to 2015, and BedMachine v3 to analyze 20 major southeast Greenland glaciers. The results reveal glacial fjords several hundreds of meters deeper than previously thought; the full extent of the marine-based portions of the glaciers; deep troughs enabling warm, salty Atlantic Water (AW) to reach the glacier fronts and melt them from below; and few shallow sills that limit the access of AW...
March 28, 2018: Geophysical Research Letters
https://www.readbyqxmd.com/read/29937603/spatial-representativeness-error-in-the-ground-level-observation-networks-for-black-carbon-radiation-absorption
#6
Rong Wang, Elisabeth Andrews, Yves Balkanski, Olivier Boucher, Gunnar Myhre, Bjørn Hallvard Samset, Michael Schulz, Gregory L Schuster, Myrto Valari, Shu Tao
There is high uncertainty in the direct radiative forcing of black carbon (BC), an aerosol that strongly absorbs solar radiation. The observation-constrained estimate, which is several times larger than the bottom-up estimate, is influenced by the spatial representativeness error due to the mesoscale inhomogeneity of the aerosol fields and the relatively low resolution of global chemistry-transport models. Here we evaluated the spatial representativeness error for two widely used observational networks (AErosol RObotic NETwork and Global Atmosphere Watch) by downscaling the geospatial grid in a global model of BC aerosol absorption optical depth to 0...
February 28, 2018: Geophysical Research Letters
https://www.readbyqxmd.com/read/29937602/irrigation-as-a-potential-driver-for-anomalous-glacier-behavior-in-high-mountain-asia
#7
Remco J de Kok, Obbe A Tuinenburg, Pleun N J Bonekamp, Walter W Immerzeel
Many glaciers in the northwest of High Mountain Asia (HMA) show an almost zero or positive mass balance, despite the global trend of melting glaciers. This phenomenon is often referred to as the "Karakoram anomaly," although strongest positive mass balances can be found in the Kunlun Shan mountain range, northeast of the Karakoram. Using a regional climate model, in combination with a moisture-tracking model, we show that the increase in irrigation intensity in the lowlands surrounding HMA, particularly in the Tarim basin, can locally counter the effects of global warming on glaciers in Kunlun Shan, and parts of Pamir and northern Tibet, through an increase in summer snowfall and decrease in net radiance...
February 28, 2018: Geophysical Research Letters
https://www.readbyqxmd.com/read/29937601/fat-plumes-may-reflect-the-complex-rheology-of-the-lower-mantle
#8
A Davaille, Ph Carrez, P Cordier
Recent tomographic imaging of the mantle below major hot spots shows slow seismic velocities extending down to the core-mantle boundary, confirming the existence of mantle plumes. However, these plumes are much thicker than previously thought. Using new laboratory experiments and scaling laws, we show that thermal plumes developing in a visco-plastic fluid present much larger diameters than plumes developing in a Newtonian fluid. Such a rheology requiring a yield stress is consistent with a lower mantle predominantly deforming by pure dislocation climb...
February 16, 2018: Geophysical Research Letters
https://www.readbyqxmd.com/read/29937600/fast-adjustments-of-the-asian-summer-monsoon-to-anthropogenic-aerosols
#9
Xiaoqiong Li, Mingfang Ting, Dong Eun Lee
Anthropogenic aerosols are a major factor contributing to human-induced climate change, particularly over the densely populated Asian monsoon region. Understanding the physical processes controlling the aerosol-induced changes in monsoon rainfall is essential for reducing the uncertainties in the future projections of the hydrological cycle. Here we use multiple coupled and atmospheric general circulation models to explore the physical mechanisms for the aerosol-driven monsoon changes on different time scales...
January 28, 2018: Geophysical Research Letters
https://www.readbyqxmd.com/read/29576667/multimodel-evidence-for-an-atmospheric-circulation-response-to-arctic-sea-ice-loss-in-the-cmip5-future-projections
#10
G Zappa, F Pithan, T G Shepherd
Previous single-model experiments have found that Arctic sea ice loss can influence the atmospheric circulation. To evaluate this process in a multimodel ensemble, a novel methodology is here presented and applied to infer the influence of Arctic sea ice loss in the CMIP5 future projections. Sea ice influence is estimated by comparing the circulation response in the RCP8.5 scenario against the circulation response to sea surface warming and CO2 increase inferred from the AMIPFuture and AMIP4xCO2 experiments, where sea ice is unperturbed...
January 28, 2018: Geophysical Research Letters
https://www.readbyqxmd.com/read/29576666/electron-crescent-distributions-as-a-manifestation-of-diamagnetic-drift-in-an-electron-scale-current-sheet-magnetospheric-multiscale-observations-using-new-7-5-ms-fast-plasma-investigation-moments
#11
A C Rager, J C Dorelli, D J Gershman, V Uritsky, L A Avanov, R B Torbert, J L Burch, R E Ergun, J Egedal, C Schiff, J R Shuster, B L Giles, W R Paterson, C J Pollock, R J Strangeway, C T Russell, B Lavraud, V N Coffey, Y Saito
We report Magnetospheric Multiscale observations of electron pressure gradient electric fields near a magnetic reconnection diffusion region using a new technique for extracting 7.5 ms electron moments from the Fast Plasma Investigation. We find that the deviation of the perpendicular electron bulk velocity from E × B drift in the interval where the out-of-plane current density is increasing can be explained by the diamagnetic drift. In the interval where the out-of-plane current is transitioning to in-plane current, the electron momentum equation is not satisfied at 7...
January 28, 2018: Geophysical Research Letters
https://www.readbyqxmd.com/read/29503484/re-examining-the-non-linear-moisture-precipitation-relationship-over-the-tropical-oceans
#12
S S Rushley, D Kim, C S Bretherton, M-S Ahn
Bretherton et al. (2004) used the Special Sensor Microwave Imager (SSM/I) version 5 product to derive an exponential curve that describes the relationship between precipitation and column relative humidity (CRH) over the tropical oceans. The curve, which features a precipitation pickup at a CRH of about 0.75 and a rapid increase of precipitation with CRH after the pickup, has been widely used in the studies of the tropical atmosphere. This study re-examines the moisture-precipitation relationship by using the version 7 SSM/I data, in which several biases in the previous version are corrected, and evaluates the relationship in the Coupled Model Intercomparison Project phase 5 (CMIP5) models...
January 28, 2018: Geophysical Research Letters
https://www.readbyqxmd.com/read/29713108/volcano-and-ship-tracks-indicate-excessive-aerosol-induced-cloud-water-increases-in-a-climate-model
#13
Velle Toll, Matthew Christensen, Santiago Gassó, Nicolas Bellouin
Aerosol-cloud interaction is the most uncertain mechanism of anthropogenic radiative forcing of Earth's climate, and aerosol-induced cloud water changes are particularly poorly constrained in climate models. By combining satellite retrievals of volcano and ship tracks in stratocumulus clouds, we compile a unique observational dataset and confirm that liquid water path (LWP) responses to aerosols are bidirectional, and on average the increases in LWP are closely compensated by the decreases. Moreover, the meteorological parameters controlling the LWP responses are strikingly similar between the volcano and ship tracks...
December 28, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/29622852/effects-of-el-ni%C3%A3-o-on-summertime-ozone-air-quality-in-the-eastern-united-states
#14
Lu Shen, Loretta J Mickley
We investigate the effect of El Niño on maximum daily 8-hour average surface ozone over the eastern United States in summer during 1980-2016. El Niño can influence the extra-tropical climate through the propagation of stationary waves, leading to (1) reduced transport of moist, clean air into the mid- and southern Atlantic states and greater subsidence, reduced precipitation, and increased surface solar radiation in this region, as well as (2) intensified southerly flow into the south central states, which here enhances flux of moist and clean air...
December 28, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/29540941/strong-dependence-of-u-s-summertime-air-quality-on-the-decadal-variability-of-atlantic-sea-surface-temperatures
#15
Lu Shen, Loretta J Mickley, Eric M Leibensperger, Mingwei Li
We find that summertime air quality in the eastern U.S. displays strong dependence on North Atlantic sea surface temperatures, resulting from large-scale ocean-atmosphere interactions. Using observations, reanalysis data sets, and climate model simulations, we further identify a multidecadal variability in surface air quality driven by the Atlantic Multidecadal Oscillation (AMO). In one-half cycle (~35 years) of the AMO from cold to warm phase, summertime maximum daily 8 h ozone concentrations increase by 1-4 ppbv and PM2...
December 28, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/29398736/inflated-uncertainty-in-multimodel-based-regional-climate-projections
#16
Marianne Sloth Madsen, Peter L Langen, Fredrik Boberg, Jens Hesselbjerg Christensen
Multimodel ensembles are widely analyzed to estimate the range of future regional climate change projections. For an ensemble of climate models, the result is often portrayed by showing maps of the geographical distribution of the multimodel mean results and associated uncertainties represented by model spread at the grid point scale. Here we use a set of CMIP5 models to show that presenting statistics this way results in an overestimation of the projected range leading to physically implausible patterns of change on global but also on regional scales...
November 28, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/29398735/the-signature-of-southern-hemisphere-atmospheric-circulation-patterns-in-antarctic-precipitation
#17
Gareth J Marshall, David W J Thompson, Michiel R van den Broeke
We provide the first comprehensive analysis of the relationships between large-scale patterns of Southern Hemisphere climate variability and the detailed structure of Antarctic precipitation. We examine linkages between the high spatial resolution precipitation from a regional atmospheric model and four patterns of large-scale Southern Hemisphere climate variability: the southern baroclinic annular mode, the southern annular mode, and the two Pacific-South American teleconnection patterns. Variations in all four patterns influence the spatial configuration of precipitation over Antarctica, consistent with their signatures in high-latitude meridional moisture fluxes...
November 28, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/29263561/bedmachine-v3-complete-bed-topography-and-ocean-bathymetry-mapping-of-greenland-from-multibeam-echo-sounding-combined-with-mass-conservation
#18
M Morlighem, C N Williams, E Rignot, L An, J E Arndt, J L Bamber, G Catania, N Chauché, J A Dowdeswell, B Dorschel, I Fenty, K Hogan, I Howat, A Hubbard, M Jakobsson, T M Jordan, K K Kjeldsen, R Millan, L Mayer, J Mouginot, B P Y Noël, C O'Cofaigh, S Palmer, S Rysgaard, H Seroussi, M J Siegert, P Slabon, F Straneo, M R van den Broeke, W Weinrebe, M Wood, K B Zinglersen
Greenland's bed topography is a primary control on ice flow, grounding line migration, calving dynamics, and subglacial drainage. Moreover, fjord bathymetry regulates the penetration of warm Atlantic water (AW) that rapidly melts and undercuts Greenland's marine-terminating glaciers. Here we present a new compilation of Greenland bed topography that assimilates seafloor bathymetry and ice thickness data through a mass conservation approach. A new 150 m horizontal resolution bed topography/bathymetric map of Greenland is constructed with seamless transitions at the ice/ocean interface, yielding major improvements over previous data sets, particularly in the marine-terminating sectors of northwest and southeast Greenland...
November 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/29568141/distinguishing-remobilized-ash-from-erupted-volcanic-plumes-using-space-borne-multi-angle-imaging
#19
Verity J B Flower, Ralph A Kahn
Volcanic systems are comprised of a complex combination of ongoing eruptive activity and secondary hazards, such as remobilized ash plumes. Similarities in the visual characteristics of remobilized and erupted plumes, as imaged by satellite-based remote sensing, complicate the accurate classification of these events. The stereo imaging capabilities of the Multi-angle Imaging SpectroRadiometer (MISR) were used to determine the altitude and distribution of suspended particles. Remobilized ash shows distinct dispersion, with particles distributed within ~1...
October 28, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/29263560/a-dynamic-model-of-mercury-s-magnetospheric-magnetic-field
#20
Haje Korth, Catherine L Johnson, Lydia Philpott, Nikolai A Tsyganenko, Brian J Anderson
Mercury's solar wind and interplanetary magnetic field environment is highly dynamic, and variations in these external conditions directly control the current systems and magnetic fields inside the planetary magnetosphere. We update our previous static model of Mercury's magnetic field by incorporating variations in the magnetospheric current systems, parameterized as functions of Mercury's heliocentric distance and magnetic activity. The new, dynamic model reproduces the location of the magnetopause current system as a function of systematic pressure variations encountered during Mercury's eccentric orbit, as well as the increase in the cross-tail current intensity with increasing magnetic activity...
October 28, 2017: Geophysical Research Letters
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