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Geophysical Research Letters

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https://www.readbyqxmd.com/read/29200535/mjo-related-tropical-convection-anomalies-lead-to-more-accurate-stratospheric-vortex-variability-in-subseasonal-forecast-models
#1
C I Garfinkel, C Schwartz
The effect of the Madden-Julian Oscillation (MJO) on the Northern Hemisphere wintertime stratospheric polar vortex in the period preceding stratospheric sudden warmings is evaluated in operational subseasonal forecasting models. Reforecasts which simulate stronger MJO-related convection in the Tropical West Pacific also simulate enhanced heat flux in the lowermost stratosphere and a more realistic vortex evolution. The time scale on which vortex predictability is enhanced lies between 2 and 4 weeks for nearly all cases...
October 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/29104328/underlying-causes-of-eurasian-midcontinental-aridity-in-simulations-of-mid-holocene-climate
#2
Patrick J Bartlein, Sandy P Harrison, Kenji Izumi
Climate model simulations uniformly show drier and warmer summers in the Eurasian midcontinent during the mid-Holocene, which is not consistent with paleoenvironmental observations. The simulated climate results from a reduction in the zonal temperature gradient, which weakens westerly flow and reduces moisture flux and precipitation in the midcontinent. As a result, sensible heating is favored over evaporation and latent heating, resulting in substantial surface-driven atmospheric warming. Thus, the discrepancy with the paleoenvironmental evidence arises initially from a problem in the simulated circulation and is exacerbated by feedback from the land surface...
September 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/29104327/dayside-response-of-the-magnetosphere-to-a-small-shock-compression-van-allen-probes-magnetospheric-multiscale-and-goes-13
#3
C Cattell, A Breneman, C Colpitts, J Dombeck, S Thaller, S Tian, J Wygant, J Fennell, M K Hudson, Robert Ergun, C T Russell, Roy Torbert, Per-Arne Lindqvist, J Burch
Observations from Magnetospheric MultiScale (~8 Re) and Van Allen Probes (~5 and 4 Re) show that the initial dayside response to a small interplanetary shock is a double-peaked dawnward electric field, which is distinctly different from the usual bipolar (dawnward and then duskward) signature reported for large shocks. The associated E × B flow is radially inward. The shock compressed the magnetopause to inside 8 Re, as observed by Magnetospheric MultiScale (MMS), with a speed that is comparable to the E × B flow...
September 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/28989207/juno-uvs-approach-observations-of-jupiter-s-auroras
#4
G R Gladstone, M H Versteeg, T K Greathouse, V Hue, M W Davis, J-C Gérard, D C Grodent, B Bonfond, J D Nichols, R J Wilson, G B Hospodarsky, S J Bolton, S M Levin, J E P Connerney, A Adriani, W S Kurth, B H Mauk, P Valek, D J McComas, G S Orton, F Bagenal
Juno ultraviolet spectrograph (UVS) observations of Jupiter's aurora obtained during approach are presented. Prior to the bow shock crossing on 24 June 2016, the Juno approach provided a rare opportunity to correlate local solar wind conditions with Jovian auroral emissions. Some of Jupiter's auroral emissions are expected to be controlled or modified by local solar wind conditions. Here we compare synoptic Juno-UVS observations of Jupiter's auroral emissions, acquired during 3-29 June 2016, with in situ solar wind observations, and related Jupiter observations from Earth...
August 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/28966411/evidence-for-a-low-bulk-crustal-density-for-mars-from-gravity-and-topography
#5
Sander Goossens, Terence J Sabaka, Antonio Genova, Erwan Mazarico, Joseph B Nicholas, Gregory A Neumann
Knowledge of the average density of the crust of a planet is important in determining its interior structure. The combination of high-resolution gravity and topography data has yielded a low density for the Moon's crust, yet for other terrestrial planets the resolution of the gravity field models has hampered reasonable estimates. By using well-chosen constraints derived from topography during gravity field model determination using satellite tracking data, we show that we can robustly and independently determine the average bulk crustal density directly from the tracking data, using the admittance between topography and imperfect gravity...
August 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/28989206/pitted-terrains-on-1-ceres-and-implications-for-shallow-subsurface-volatile-distribution
#6
H G Sizemore, T Platz, N Schorghofer, T H Prettyman, M C De Sanctis, D A Crown, N Schmedemann, A Neesemann, T Kneissl, S Marchi, P M Schenk, M T Bland, B E Schmidt, K H G Hughson, F Tosi, F Zambon, S C Mest, R A Yingst, D A Williams, C T Russell, C A Raymond
Prior to the arrival of the Dawn spacecraft at Ceres, the dwarf planet was anticipated to be ice-rich. Searches for morphological features related to ice have been ongoing during Dawn's mission at Ceres. Here we report the identification of pitted terrains associated with fresh Cerean impact craters. The Cerean pitted terrains exhibit strong morphological similarities to pitted materials previously identified on Mars (where ice is implicated in pit development) and Vesta (where the presence of ice is debated)...
July 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/28943678/causes-of-accelerating-sea-level-on-the-east-coast-of-north-america
#7
James L Davis, Nadya T Vinogradova
The tide-gauge record from the North American East Coast reveals significant accelerations in sea level starting in the late twentieth century. The estimated post-1990 accelerations range from near zero to ∼0.3 mm yr(-2). We find that the observed sea level acceleration is well modeled using several processes: mass change in Greenland and Antarctica as measured by the Gravity Recovery and Climate Experiment satellites; ocean dynamic and steric variability provided by the GECCO2 ocean synthesis; and the inverted barometer effect...
May 28, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/28781391/microphysical-explanation-of-the-rh-dependent-water-affinity-of-biogenic-organic-aerosol-and-its-importance-for-climate
#8
N Rastak, A Pajunoja, J C Acosta Navarro, J Ma, M Song, D G Partridge, A Kirkevåg, Y Leong, W W Hu, N F Taylor, A Lambe, K Cerully, A Bougiatioti, P Liu, R Krejci, T Petäjä, C Percival, P Davidovits, D R Worsnop, A M L Ekman, A Nenes, S Martin, J L Jimenez, D R Collins, D O Topping, A K Bertram, A Zuend, A Virtanen, I Riipinen
A large fraction of atmospheric organic aerosol (OA) originates from natural emissions that are oxidized in the atmosphere to form secondary organic aerosol (SOA). Isoprene (IP) and monoterpenes (MT) are the most important precursors of SOA originating from forests. The climate impacts from OA are currently estimated through parameterizations of water uptake that drastically simplify the complexity of OA. We combine laboratory experiments, thermodynamic modeling, field observations, and climate modeling to (1) explain the molecular mechanisms behind RH-dependent SOA water-uptake with solubility and phase separation; (2) show that laboratory data on IP- and MT-SOA hygroscopicity are representative of ambient data with corresponding OA source profiles; and (3) demonstrate the sensitivity of the modeled aerosol climate effect to assumed OA water affinity...
May 28, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/29225384/the-role-of-sulfur-dioxide-in-stratospheric-aerosol-formation-evaluated-using-in-situ-measurements-in-the-tropical-lower-stratosphere
#9
A W Rollins, T D Thornberry, L A Watts, P Yu, K H Rosenlof, M Mills, E Baumann, F R Giorgetta, T V Bui, M Höpfner, K A Walker, C Boone, P F Bernath, P R Colarco, P A Newman, D W Fahey, R S Gao
Stratospheric aerosols (SAs) are a variable component of the Earth's albedo that may be intentionally enhanced in the future to offset greenhouse gases (geoengineering). The role of tropospheric-sourced sulfur dioxide (SO2) in maintaining background SAs has been debated for decades without in-situ measurements of SO2 at the tropical tropopause to inform this issue. Here we clarify the role of SO2 in maintaining SAs by using new in-situ SO2 measurements to evaluate climate models and satellite retrievals. We then use the observed tropical tropopause SO2 mixing ratios to estimate the global flux of SO2 across the tropical tropopause...
May 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/28713180/global-observations-of-magnetospheric-high-m-poloidal-waves-during-the-22-june-2015-magnetic-storm
#10
G Le, P J Chi, R J Strangeway, C T Russell, J A Slavin, K Takahashi, H J Singer, B J Anderson, K Bromund, D Fischer, E L Kepko, W Magnes, R Nakamura, F Plaschke, R B Torbert
We report global observations of high-m poloidal waves during the recovery phase of the 22 June 2015 magnetic storm from a constellation of widely spaced satellites of five missions including Magnetospheric Multiscale (MMS), Van Allen Probes, Time History of Events and Macroscale Interactions during Substorm (THEMIS), Cluster, and Geostationary Operational Environmental Satellites (GOES). The combined observations demonstrate the global spatial extent of storm time poloidal waves. MMS observations confirm high azimuthal wave numbers (m ~ 100)...
April 28, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/28503005/electron-acceleration-during-streamer-collisions-in-air
#11
Christoph Köhn, Olivier Chanrion, Torsten Neubert
High-voltage laboratory experiments show that discharges in air, generated over a gap of one meter with maximal voltage of 1 MV, may produce X-rays with photon energies up to 1 MeV. It has been suggested that the photons are bremsstrahlung from electrons accelerated by the impulsive, enhanced field during collisions of negative and a positive streamers. To explore this process, we have conducted the first self-consistent particle simulations of streamer encounters. Our simulation model is a 2-D, cylindrically symmetric, particle-in-cell code tracing the electron dynamics and solving the space charge fields, with a Monte Carlo scheme accounting for collisions and ionization...
March 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/28503004/factors-controlling-the-evaporation-of-secondary-organic-aerosol-from-%C3%AE-pinene-ozonolysis
#12
Taina Yli-Juuti, Aki Pajunoja, Olli-Pekka Tikkanen, Angela Buchholz, Celia Faiola, Olli Väisänen, Liqing Hao, Eetu Kari, Otso Peräkylä, Olga Garmash, Manabu Shiraiwa, Mikael Ehn, Kari Lehtinen, Annele Virtanen
Secondary organic aerosols (SOA) forms a major fraction of organic aerosols in the atmosphere. Knowledge of SOA properties that affect their dynamics in the atmosphere is needed for improving climate models. By combining experimental and modeling techniques, we investigated the factors controlling SOA evaporation under different humidity conditions. Our experiments support the conclusion of particle phase diffusivity limiting the evaporation under dry conditions. Viscosity of particles at dry conditions was estimated to increase several orders of magnitude during evaporation, up to 10(9) Pa s...
March 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/28405053/observed-strengthening-of-interbasin-exchange-via-the-indonesian-seas-due-to-rainfall-intensification
#13
Shijian Hu, Janet Sprintall
A proxy of the Indonesian Throughflow (ITF) transport, developed using in situ hydrographic measurements along with assimilations, shows a significant strengthening trend during the past decade. This trend is due to a freshening and subsequent increase in the halosteric component of the ITF transport associated with enhanced rainfall over the Maritime Continent over the same period. The strengthening of the ITF transport leads to a significant change in heat and freshwater exchange between the Pacific and Indian Oceans and contributes to the warming and freshening of the eastern Indian Ocean...
February 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/28344367/cross-saharan-transport-of-water-vapor-via-recycled-cold-pool-outflows-from-moist-convection
#14
Tomasz M Trzeciak, Luis Garcia-Carreras, John H Marsham
Very sparse data have previously limited observational studies of meteorological processes in the Sahara. We present an observed case of convectively driven water vapor transport crossing the Sahara over 2.5 days in June 2012, from the Sahel in the south to the Atlas in the north. A daily cycle is observed, with deep convection in the evening generating moist cold pools that fed the next day's convection; the convection then generated new cold pools, providing a vertical recycling of moisture. Trajectories driven by analyses were able to capture the direction of the transport but not its full extent, particularly at night when cold pools are most active, and analyses missed much of the water content of cold pools...
February 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/29200536/decade-long-deep-ocean-warming-detected-in-the-subtropical-south-pacific
#15
Denis L Volkov, Sang-Ki Lee, Felix W Landerer, Rick Lumpkin
The persistent energy imbalance at the top of the atmosphere, inferred from satellite measurements, indicates that the Earth's climate system continues to accumulate excess heat. As only sparse and irregular measurements of ocean heat below 2000 m depth exist, one of the most challenging questions in global climate change studies is whether the excess heat has already penetrated into the deep ocean. Here we perform a comprehensive analysis of satellite and in situ measurements to report that a significant deep-ocean warming occurred in the subtropical South Pacific Ocean over the past decade (2005-2014)...
January 28, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/28356606/stratospheric-variability-contributed-to-and-sustained-the-recent-hiatus-in-eurasian-winter-warming
#16
Chaim I Garfinkel, Seok-Woo Son, Kanghyun Song, Valentina Aquila, Luke D Oman
The recent hiatus in global-mean surface temperature warming was characterized by a Eurasian winter cooling trend, and the cause(s) for this cooling is unclear. Here we show that the observed hiatus in Eurasian warming was associated with a recent trend toward weakened stratospheric polar vortices. Specifically, by calculating the change in Eurasian surface air temperature associated with a given vortex weakening, we demonstrate that the recent trend toward weakened polar vortices reduced the anticipated Eurasian warming due to increasing greenhouse gas concentrations...
January 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/29200534/spread-in-the-magnitude-of-climate-model-interdecadal-global-temperature-variability-traced-to-disagreements-over-high-latitude-oceans
#17
Patrick T Brown, Wenhong Li, Jonathan H Jiang, Hui Su
Unforced variability in global mean surface air temperature can obscure or exaggerate global warming on interdecadal timescales, thus understanding both the magnitude and generating mechanisms of such variability is of critical importance for both attribution studies as well as decadal climate prediction. Coupled atmosphere-ocean general circulation models (climate models) simulate a wide range of magnitudes of unforced interdecadal variability in global mean surface air temperature (UITglobal), hampering efforts to quantify the influence of UITglobal on contemporary global temperature trends...
December 28, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/28239205/a-study-of-the-dissociative-recombination-of-cao-with-electrons-implications-for-ca-chemistry-in-the-upper-atmosphere
#18
D L Bones, M Gerding, J Höffner, Juan Carlos Gómez Martín, J M C Plane
The dissociative recombination of CaO(+) ions with electrons has been studied in a flowing afterglow reactor. CaO(+) was generated by the pulsed laser ablation of a Ca target, followed by entrainment in an Ar(+) ion/electron plasma. A kinetic model describing the gas-phase chemistry and diffusion to the reactor walls was fitted to the experimental data, yielding a rate coefficient of (3.0 ± 1.0) × 10(-7) cm(3) molecule(-1) s(-1) at 295 K. This result has two atmospheric implications. First, the surprising observation that the Ca(+)/Fe(+) ratio is ~8 times larger than Ca/Fe between 90 and 100 km in the atmosphere can now be explained quantitatively by the known ion-molecule chemistry of these two metals...
December 28, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/28275286/sources-of-cosmic-dust-in-the-earth-s-atmosphere
#19
J D Carrillo-Sánchez, D Nesvorný, P Pokorný, D Janches, J M C Plane
There are four known sources of dust in the inner solar system: Jupiter Family comets, asteroids, Halley Type comets, and Oort Cloud comets. Here we combine the mass, velocity, and radiant distributions of these cosmic dust populations from an astronomical model with a chemical ablation model to estimate the injection rates of Na and Fe into the Earth's upper atmosphere, as well as the flux of cosmic spherules to the surface. Comparing these parameters to lidar observations of the vertical Na and Fe fluxes above 87...
December 16, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/28190903/potential-negative-consequences-of-geoengineering-on-crop-production-a-study-of-indian-groundnut
#20
Huiyi Yang, Steven Dobbie, Julian Ramirez-Villegas, Kuishuang Feng, Andrew J Challinor, Bing Chen, Yao Gao, Lindsay Lee, Yan Yin, Laixiang Sun, James Watson, Ann-Kristin Koehler, Tingting Fan, Sat Ghosh
Geoengineering has been proposed to stabilize global temperature, but its impacts on crop production and stability are not fully understood. A few case studies suggest that certain crops are likely to benefit from solar dimming geoengineering, yet we show that geoengineering is projected to have detrimental effects for groundnut. Using an ensemble of crop-climate model simulations, we illustrate that groundnut yields in India undergo a statistically significant decrease of up to 20% as a result of solar dimming geoengineering relative to RCP4...
November 28, 2016: Geophysical Research Letters
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