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Geophysical Research Letters

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
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
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
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
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
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
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
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
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
A V Grayver, F D Munch, A V Kuvshinov, A Khan, T J Sabaka, L Tøffner-Clausen
We present a new global electrical conductivity model of Earth's mantle. The model was derived by using a novel methodology, which is based on inverting satellite magnetic field measurements from different sources simultaneously. Specifically, we estimated responses of magnetospheric origin and ocean tidal magnetic signals from the most recent Swarm and CHAMP data. The challenging task of properly accounting for the ocean effect in the data was addressed through full three-dimensional solution of Maxwell's equations...
June 28, 2017: Geophysical Research Letters
H Lievens, R H Reichle, Q Liu, G J M De Lannoy, R S Dunbar, S B Kim, N N Das, M Cosh, J P Walker, W Wagner
SMAP (Soil Moisture Active and Passive) radiometer observations at ~40 km resolution are routinely assimilated into the NASA Catchment Land Surface Model to generate the 9-km SMAP Level-4 Soil Moisture product. This study demonstrates that adding high-resolution radar observations from Sentinel-1 to the SMAP assimilation can increase the spatio-temporal accuracy of soil moisture estimates. Radar observations were assimilated either separately from or simultaneously with radiometer observations. Assimilation impact was assessed by comparing 3-hourly, 9-km surface and root-zone soil moisture simulations with in situ measurements from 9-km SMAP core validation sites and sparse networks, from May 2015 to December 2016...
June 28, 2017: Geophysical Research Letters
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