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Geophysical Research Letters

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
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
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
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
Christopher R Hain, Martha C Anderson
Observations of land surface temperature (LST) are crucial for the monitoring of surface energy fluxes from satellite. Methods that require high temporal resolution LST observations (e.g., from geostationary orbit) can be difficult to apply globally because several geostationary sensors are required to attain near-global coverage (60°N to 60°S). While these LST observations are available from polar-orbiting sensors, providing global coverage at higher spatial resolutions, the temporal sampling (twice daily observations) can pose significant limitations...
October 16, 2017: Geophysical Research Letters
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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