bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for under‐reported western European emissions of the potent greenhouse gas HFC‐23
Authors: Keller Christoph A. , Brunner Dominik , Henne Stephan , Vollmer Martin K. , O'Doherty Simon , Reimann Stefan
Published: August 2011

Western European emission inventories of the potent greenhouse gas trifluoromethane (HFC‐23) are validated at a country level by combining 2‐hourly atmospheric in‐situ measurements at Jungfraujoch (Switzerland) and Mace Head (Ireland) with Lagrangian transport simulations. HFC‐23 has an atmospheric lifetime of ∼270 yr and a 100‐yr global warming potential (GWP) of 14,800 and is unintentionally produced during the manufacture of chlorodifluoromethane (HCFC‐22). For the study region we derive emissions of 144–216 Mg/yr for July 2008–July 2010, which are 60–140% higher than the official emissions gathered from the national reports for the year 2009. The largest discrepancy is found for Italy, where our estimate of 26–56 Mg/yr exceeds the national inventory (2.6 Mg/yr) by more than an order of magnitude. These findings suggest that non‐reported emissions from Annex 1 countries partly explain the recently derived gap between global bottom‐up and top‐down HFC‐23 emission estimates. The results presented here provide independent information to relevant authorities on effective reporting of HFC‐23 emissions, and demonstrate the potential of atmospheric measurements for real‐world verification of greenhouse gas emissions.
Inter‐annual to multi‐decadal Arctic sea ice extent trends in a warming world
Authors: Kay Jennifer E. , Holland Marika M. , Jahn Alexandra
Published: August 2011

A climate model (CCSM4) is used to investigate the influence of anthropogenic forcing on late 20th century and early 21st century Arctic sea ice extent trends. On all timescales examined (2–50+ years), the most extreme negative observed late 20th century trends cannot be explained by modeled natural variability alone. Modeled late 20th century ice extent loss also cannot be explained by natural causes alone, but the six available CCSM4 ensemble members exhibit a large spread in their late 20th century ice extent loss. Comparing trends from the CCSM4 ensemble to observed trends suggests that internal variability explains approximately half of the observed 1979–2005 September Arctic sea ice extent loss. In a warming world, CCSM4 shows that multi‐decadal negative trends increase in frequency and magnitude, and that trend variability on 2–10 year timescales increases. Furthermore, when internal variability counteracts anthropogenic forcing, positive trends on 2–20 year timescales occur until the middle of the 21st century.
Intercomparison of aerosol climatologies for use in a regional climate model over Europe
Authors: Zubler E. M. , Lohmann U. , Lüthi D. , Schär C.
Published: August 2011

Many regional climate models (RCM) and numerical weather prediction (NWP) models use old aerosol data sets to calculate the direct aerosol effect. In this study, three multi‐year simulations with COSMO‐CLM using different aerosol climatologies and a simulation with monthly mean aerosol optical properties, stemming from a COSMO‐CLM simulation with coupled aerosol microphysics and transport, are evaluated. The climatologies of Tegen et al. (1997), the AEROCOM‐climatology for present‐day conditions, and the monthly mean optical properties from Zubler et al. (2011), with realistic patterns of aerosol optical depth (AOD), lead to an increase of downward surface shortwave radiation (SSR) of 35 W m−2 (20%) in the Mediterranean region in comparison with the climatology of Tanré et al. (1984). The former is known to strongly overestimate AOD over Europe. The associated bias in SSR exceeds the observed variations of the recent decades by up to a factor 5. Despite an annual mean temperature increase of 0.5 K above Southern European land surfaces owing to enhanced SSR, the newer climatologies yield colder temperatures in the mid‐troposphere because of a reduction of the shortwave absorption by desert dust. This reduced heating destabilizes the atmosphere relative to the simulation with the climatology of Tanré et al. (1984), enhancing cloud formation and precipitation in these simulations. It is recommended that the RCM community uses updated aerosol information for radiative transfer calculations.
Recent surface temperature trends in the interior of East Antarctica from borehole firn temperature measurements and geophysical inverse methods
Authors: Muto Atsuhiro , Scambos Ted A. , Steffen Konrad , Slater Andrew G. , Clow Gary D.
Published: August 2011

We use measured firn temperatures down to depths of 80 to 90 m at four locations in the interior of Dronning Maud Land, East Antarctica to derive surface temperature histories spanning the past few decades using two different inverse methods. We find that the mean surface temperatures near the ice divide (the highest‐elevation ridge of East Antarctic Ice Sheet) have increased approximately 1 to 1.5 K within the past ∼50 years, although the onset and rate of this warming vary by site. Histories at two locations, NUS07‐5 (78.65°S, 35.64°E) and NUS07‐7 (82.07°S, 54.89°E), suggest that the majority of this warming took place in the past one or two decades. Slight cooling to no change was indicated at one location, NUS08‐5 (82.63°S, 17.87°E), off the divide near the Recovery Lakes region. In the most recent decade, inversion results indicate both cooler and warmer periods at different sites due to high interannual variability and relatively high resolution of the inverted surface temperature histories. The overall results of our analysis fit a pattern of recent climate trends emerging from several sources of the Antarctic temperature reconstructions: there is a contrast in surface temperature trends possibly related to altitude in this part of East Antarctica.
Models of iron speciation and concentration in the stratified epipelagic ocean
Authors: Fan Song‐Miao , Dunne John P.
Published: August 2011

Surface ocean iron speciation is simulated using a time‐dependent box‐model of light‐mediated redox cycling over a range of aeolian inputs of soluble iron in the stratified epipelagic ocean. At steady‐state, Dissolved iron (DFe) concentration increases with aeolian input of soluble iron up to 0.1 μmol m−2 d−1, and is limited by the solubility of ferric hydroxide at higher fluxes which causes the formation of colloidal iron. We demonstrate that even in the presence of ample excess ligand, rapid conversion of dissolved iron between oxidized and reduced forms in the tropical surface ocean exposes DFe to colloid formation and scavenging. This result provides an explanation for the much smaller range of interregional variability in DFe measurements (0.05–0.4 nM) than soluble Fe fluxes (0.01–1 μmol m−2 d−1) and dust fluxes (0.1–10 g m−2 yr−1) predicted by atmospheric models. We incorporate the critical behavior of the full chemical speciation model into a reduced, computationally efficient model suitable for large scale calculations.
The impact of ENSO and the Arctic Oscillation on winter temperature extremes in the southeast United States
Authors: Lim Young‐Kwon , Schubert Siegfried D.
Published: August 2011

Interannual variations of the winter mean temperature and the number of days of warm and cold extremes were investigated for the southeast United States to identify the relative influence of El Niño‐Southern Oscillation (ENSO) and the Arctic Oscillation (AO). Generalized extreme value theory was used to estimate the probability distribution function (PDF) of warm and cold extremes and their return values for different phases of ENSO and the AO. An analysis of the temperature observations for the past 58 years (1951–2008) reveals that both the winter mean temperature anomalies and the number of days of extreme cold are most closely linked to variations in the AO especially in the recent past (1981–2008). In contrast, the number of days of extreme warmth are linked to both ENSO and the AO.
Climatic forcing and phytoplankton phenology over the subarctic North Pacific from 1998 to 2006, as observed from ocean color data
Authors: Sasaoka Kosei , Chiba Sanae , Saino Toshiro
Published: August 2011

We investigated phenological changes in phytoplankton in the subarctic North Pacific and the relationship to climatic forcing variability from 1998 to 2006, using ocean color satellite data combined with climatological data. The interannual to 9‐year mean variability in the timing, magnitude, and duration of phytoplankton blooms were examined using SeaWiFS data. Based on 10‐day composites of SeaWiFS data, the date of bloom initiation, peak chlorophyll a concentration, and bloom duration were estimated each year for every 2 × 2 degree grid within the range of 40–60°N and 130°E–120°W. The peak chlorophyll a concentration, date of bloom initiation, and bloom duration were derived by a Gaussian curve fitting technique. In addition, to investigate the geographic pattern of phytoplankton phenology, we classified the oceanic regions of the subarctic North Pacific into three groups based on K‐means clustering: group A was distributed in the coastal regions of marginal seas, waters around the Kamchatka Peninsula, and along the Aleutian Islands; group B was mainly distributed offshore in western and central regions; and group C was in southeastern and central regions. The timing of spring blooms of group A was earlier in El Niño phase and later in La Niña phase, whereas the opposite pattern was seen in group B. Our study clearly revealed regional differences in phytoplankton seasonality, phenology patterns, and relationships between interannual variability of phytoplankton phenology and El Niño Southern Oscillation‐scale variation.
Deep tremor in New Zealand triggered by the 2010 Mw8.8 Chile earthquake
Authors: Fry B. , Chao K. , Bannister S. , Peng Z. , Wallace L.
Published: August 2011

Deep non‐volcanic tremor (NVT) is usually associated with episodic slow‐slip events. New Zealand is one notable exception where numerous slow slip events have been identified, yet NVT has remained undetected. Here we present the first known case of triggered NVT at New Zealand's Hikurangi subduction margin. Following the Mw8.8 Chilean earthquake of February 27, 2010, we identify coherent high‐frequency tremor signals that are in phase with, and modulated by, the passing Rayleigh waves. This is consistent with the surface wave triggering potential for strike‐normal incidence on a low‐angle thrust fault. After constraining the tremor depth on the plate interface, we locate the tremor source within 20 km of the source area of episodic slow slip. The tremor location is also near the edge of a region with high seismic attenuation that marks the boundary between dehydrated subducted slab and inferred hydrated, underplated sediment. We speculate that reduced interface friction and high fluid pressures provided by fluid‐rich underplated sediment facilitates the tremor generation.
Land‐atmosphere coupling associated with snow cover
Authors: Dutra Emanuel , Schär Christoph , Viterbo Pedro , Miranda Pedro M. A.
Published: August 2011

This study investigates the role of interannual snow cover variability in controlling the land‐atmosphere coupling and its relation with near surface (T2M) and soil temperature (STL1). Global atmospheric simulations are carried out with the EC‐EARTH climate model using climatological sea surface temperature and sea ice distributions. Snow climatology, derived from a control run (COUP), is used to replace snow evolution in the snow‐uncoupled simulation (UNCOUP). The snow cover and depth variability explains almost 60% of the winter T2M variability in predominantly snow‐covered regions. During spring the differences in interannual variability of T2M are more restricted to the snow line regions. The variability of soil temperature is also damped in UNCOUP. However, there are regions with a pronounced signal in STL1 with no counterpart in T2M. These regions are characterized by a significant interannual variability in snow depth, rather than snow cover (almost fully snow covered during winter). These results highlight the importance of both snow cover and snow depth in decoupling the soil temperature evolution from the overlying atmosphere.
Magnetic signatures of a tenuous atmosphere at Dione
Authors: Simon Sven , Saur Joachim , Neubauer Fritz M. , Wennmacher Alexandre , Dougherty Michele K.
Published: August 2011

We present Cassini magnetic field observations from the only two close flybys (16DI and 129DI) of Saturn's icy satellite Dione which have been carried out so far. Data from 16DI show a weak field perturbation in the upstream region, indicative of a tenuous atmosphere around the satellite. By applying an analytical model of the perturbations caused by subalfvénic atmosphere‐magnetosphere interactions, we demonstrate that an atmospheric column density of approximately 1 · 1017 m−2 would be able to sustain the observed field signature. Magnetic field data from 16DI also contain hints that Dione's gas envelope might possess a slight asymmetry between the Saturn‐facing and the Saturn‐averted hemisphere. The detection of a thin atmosphere at Dione might be correlated to the occurrence of a transient radiation belt near the moon's L‐shell at the time of the 16DI flyby, as reported by Roussos et al. (2008b). On the other hand, magnetic field observations from the subsequent downstream encounter 129DI show no clear evidence of an atmosphere, probably due to the flyby trajectory being unsuitable for the detection of the associated perturbations.
Effects of physical forcing and particle characteristics on underwater imaging performance
Authors: Chang Grace , Twardowski Michael S.
Published: August 2011

We computed the modulation transfer function (MTF), which is the magnitude of the Fourier transform of the point spread function, for two different water bodies using measurements of optical properties and analytical formulations. Knowledge of the MTF is important for the interpretation of images from underwater electro‐optical systems. The data were collected from two field sites as part of the Office of Naval Research sponsored Radiance in a Dynamic Ocean program: (1) Scripps Institution of Oceanography (SIO) Pier, a shallow‐water, eutrophic environment, and (2) the Santa Barbara Channel (SBC), a deeper, mesotrophic environment. Wavelet analysis was employed to investigate the sources of variability of the MTF and the periodicities at which they occur. Results suggest that the MTF was strongly related to wind conditions and advection events and the optical properties serving as proxies for particle concentration and composition in the SBC. Increased wind speeds and stresses resulted in upper water column mixing, decreased water clarity, and reductions in image transmission. Rip currents accompanied by high concentrations of reflective particles observed at SIO Pier resulted in increases in the MTF. Optically derived particle composition characteristics such as the bulk particle real index of refraction and particle size distribution are shown to be related to the variability of imaging performance at both field sites.
Basement controls on the scale of giant polygons in Utopia Planitia, Mars
Authors: Cooke Michele , Islam Fariha , McGill George
Published: August 2011

We investigate the role of buried basement topography in controlling the scale of the giant polygons of Utopia Planitia (49°N, 233°W), Mars. Thermal Emission Imaging System (THEMIS) Infrared Daytime image mosaics reveal ∼6 km average spacing of polygon troughs along selected basin‐radial transects. If graben spacing correlates to thickness of the Utopia basin sediments, this measured trough spacing suggests ∼3 km of sediment, in contrast to inferences of 1–2 km thick sediments within this portion of the basin. Irregular basement topography can influence trough development within the contracting sediments by localizing stresses at the top of basement slopes so that the trough spacing correlates to topographic variations rather than layer thickness. Along the slopes, locally large strains responsible for graben development may develop with only modest levels of sediment contraction. Mars Orbiter Laser Altimeter (MOLA) data from the highlands region, which may represent the buried topography in Utopia basin, are used to create a stochastic suite of numerical simulations of the Utopia basin, where fracture seeds along the base of the model represent potential basement topography beneath the basin. At low strain, our models that simulate wet, fine sediment produce surface fractures with ∼4–7 km spacing, which matches the spacing of troughs in the polygonal terrain of the Utopia basin. This match supports the idea that buried topography below contracting wet sediments may exert primary control on the scale of polygonal troughs. Furthermore, volumetric contraction can produce locally high extensional strains with or without a contribution from tectonic uplift.
Pitted rock surfaces on Mars: A mechanism of formation by transient melting of snow and ice
Authors: Head James W. , Kreslavsky Mikhail A. , Marchant David R.
Published: August 2011

Pits in rocks on the surface of Mars have been observed at several locations. Similar pits are observed in rocks in the Mars‐like hyperarid, hypothermal stable upland zone of the Antarctic Dry Valleys; these form by very localized chemical weathering due to transient melting of small amounts of snow on dark dolerite boulders preferentially heated above the melting point of water by sunlight. We examine the conditions under which a similar process might explain the pitted rocks seen on the surface of Mars (rock surface temperatures above the melting point; atmospheric pressure exceeding the triple point pressure of H2O; an available source of solid water to melt). We find that on Mars today each of these conditions is met locally and regionally, but that they do not occur together in such a way as to meet the stringent requirements for this process to operate. In the geological past, however, conditions favoring this process are highly likely to have been met. For example, increases in atmospheric water vapor content (due, for example, to the loss of the south perennial polar CO2 cap) could favor the deposition of snow, which if collected on rocks heated to above the melting temperature during favorable conditions (e.g., perihelion), could cause melting and the type of locally enhanced chemical weathering that can cause pits. Even when these conditions are met, however, the variation in heating of different rock facets under Martian conditions means that different parts of the rock may weather at different times, consistent with the very low weathering rates observed on Mars. Furthermore, as is the case in the stable upland zone of the Antarctic Dry Valleys, pit formation by transient melting of small amounts of snow readily occurs in the absence of subsurface active layer cryoturbation.
Determination of seasonal variations in the Martian neutral atmosphere from observations of ionospheric peak height
Authors: Zou Hong , Lillis Robert J. , Wang Jin Song , Nielsen Erling
Published: August 2011

Radio occultation experiments allow us to measure electron and neutral densities in planetary atmospheres. Here we investigate such measurements from the Mars Global Surveyor Radio Science experiment in 2 consecutive Martian years (25 and 26). Using Chapman theory, we parameterize the ionospheric peak altitude in terms of the solar zenith angle, neutral scale height at the peak, neutral density at 20 km and the effective neutral scale height (n) between 20 km and the peak, finding the latter to be the primary driver of peak altitude. From the occultation data, we observe that altitudes of peak electron density at high northern latitudes show a clear seasonal trend, increasing from northern summer (Ls = 90°) to northern autumn (Ls = 180°), driven by substantial increases in n, despite neutral densities at 20 km steadily decreasing as surface temperatures drop. We find these trends to be consistent with neutral density predictions from the LMD Mars Global Circulation Model at both 20 km and 130 km. The primary mechanism responsible for this increase in the 20–130 km effective neutral scale height (and hence temperature) is the southward drift in subsolar latitude as northern summer becomes autumn. This drives the seasonal evolution of the Martian interhemispheric Hadley circulation. The downward branch of this circulation leads to an increasing warming in the middle atmosphere at high north latitudes from the northern summer to the northern autumn, causing an increase in neutral scale height at and below the ionospheric peak and thus an increase in the ionospheric peak height.
Radiative transfer modeling for quantifying lunar surface minerals, particle size, and submicroscopic metallic Fe
Authors: Li Shuai , Li Lin
Published: August 2011

The main objective of this work is to quantify lunar surface minerals (agglutinate, clinopyroxene, orthopyroxene, plagioclase, olivine, ilmenite, and volcanic glass), particle sizes, and the abundance of submicroscopic metallic Fe (SMFe) from the Lunar Soil Characterization Consortium (LSCC) data set with Hapke's radiative transfer theory. The mode is implemented for both forward and inverse modeling. We implement Hapke's radiative transfer theory in the inverse mode in which, instead of commonly used look‐up tables, Newton's method and least squares are jointly used to solve nonlinear questions. Although the effects of temperature and surface roughness are incorporated into the implementation to improve the model performance for application of lunar spacecraft data, these effects cannot be extensively addressed in the current work because of the use of lab‐measured reflectance data. Our forward radiative transfer model results show that the correlation coefficients between modeled and measured spectra are over 0.99. For the inverse model, the distribution of the particle sizes is all within their measured range. The range of modeled SMFe for highland samples is 0.01%–0.5%, and for mare samples it is 0.03%–1%. The linear trend between SMFe and ferromagnetic resonance (Is) for all the LSCC samples is consistent with laboratory measurements. For quantifying lunar mineral abundances, the results show that the R squared for the training samples (Is/FeO ≤ 65) are over 0.65 with plagioclase having highest correlation (0.94) and pyroxene having the lowest correlation (0.68). In future work, the model needs to be improved for handling more mature lunar soil samples.
Early Holocene temperature variability in the Nordic Seas: The role of oceanic heat advection versus changes in orbital forcing
Authors: Risebrobakken Bjørg , Dokken Trond , Smedsrud Lars Henrik , Andersson Carin , Jansen Eystein , Moros Matthias , Ivanova Elena V.
Published: August 2011

The separate roles of oceanic heat advection and orbital forcing on influencing early Holocene temperature variability in the eastern Nordic Seas is investigated. The effect of changing orbital forcing on the ocean temperatures is tested using the 1DICE model, and the 1DICE results are compared with new and previously published temperature reconstructions from a transect of five cores located underneath the pathway of Atlantic water, from the Faroe‐Shetland Channel in the south to the Barents Sea in the north. The stronger early Holocene summer insolation at high northern latitudes increased the summer mixed layer temperatures, however, ocean temperatures underneath the summer mixed layer did not increase significantly. The absolute maximum in summer mixed layer temperatures occurred between 9 and 6 ka BP, representing the Holocene Thermal Maximum in the eastern Nordic Seas. In contrast, maximum in northward oceanic heat transport through the Norwegian Atlantic Current occurred approximately 10 ka BP. The maximum in oceanic heat transport at 10 ka BP occurred due to a major reorganization of the Atlantic Ocean circulation, entailing strong and deep rejuvenation of the Atlantic Meridional Overturning Circulation, combined with changes in the North Atlantic gyre dynamic causing enhanced transport of heat and salt into the Nordic Seas.
Northeastern Pacific oxygen minimum zone variability over the past 70 kyr: Impact of biological production and oceanic ventilation
Authors: Cartapanis Olivier , Tachikawa Kazuyo , Bard Edouard
Published: August 2011

During the last glacial period, the Oxygen Minimum Zone (OMZ) within the northeastern Pacific Ocean strengthened and weakened on a millennial time scale, demonstrating a tight linkage with northern high latitude climate, although the precise mechanisms responsible remain unknown. Core MD02–2508, retrieved off Baja California, was analyzed for major and trace elements (Br, Ca, Ti, Fe, Mn, and Sr) using a XRF scanner and redox‐sensitive trace elements (Cu, Ni, Cd, As, V, Cr, Mo, and U) using the ICP‐MS. The trace element content, the Fe/Ti ratio, and Br‐based organic carbon exhibit higher values during the Holocene and during warm Dansgaard‐Oeschger events than during the Last Glacial Maximum (LGM), stadials, and Heinrich (H) events. A principal component analysis of the element/Al ratio indicated that the following two main factors controlled the chemical composition of the sediments: (1) export production, as represented by organic carbon, that was lower during cold periods; and (2) regional intermediate water oxygenation, as represented by U and Mo variability, that was not supported by a change in export production. The latter suggests that intermediate water oxygenation improved during H events, but slightly deteriorated during late Marine Isotope Stage (MIS) 3 and MIS 2. A local biogeochemical effect, forced by atmospheric processes, impacted the LGM and H events in the same manner. Whereas regional intermediate oceanic circulation varied in an opposite manner during the LGM and H events, possibly as a result of the global reorganization of intermediate water circulation during the LGM.
Effect of the deepening of the Tasman Gateway on the global ocean
Authors: Sijp Willem P. , England Matthew H. , Huber Matthew
Published: August 2011

We examine the effect of the deepening of the Tasman Seaway at the end of the Eocene in a climate model with realistic late Eocene bathymetry and winds. For this, we have constructed an Eocene numerical model based on the University of Victoria climate model with wind forcing derived from a fully coupled Eocene simulation. The model climate state is characterized by an oceanic meridional overturning circulation (MOC) involving Southern Hemisphere sinking and a northward atmospheric moisture transport across the equator. The deepening of the Tasman Seaway in the presence of an open Drake Passage and the associated establishment of the Antarctic Circumpolar Current (ACC) have a limited climatic impact on Antarctica. Nonetheless, the Antarctic deep sinking regions cool sufficiently to lead to a global deep ocean cooling of 3°C. No initiation of Northern Component Water is found, indicating that this may require the development of a more mature ACC. Previous studies suggest that the Ross Sea gyre cools the east coast of Australia, and expected the deepening of the Tasman Seaway to lead to a warming east of Australia due to the introduction of warmer water from the Australo‐Antarctic Gulf. We here find that this warming is limited to close to the Australian coast, and that widespread cooling prevails further off shore.
Florida Straits deglacial temperature and salinity change: Implications for tropical hydrologic cycle variability during the Younger Dryas
Authors: Schmidt Matthew W. , Lynch‐Stieglitz Jean
Published: August 2011

The prevailing paradigm of abrupt climate change holds that rapid shifts associated with the most extreme climate swings of the last glacial cycle were forced by changes in the strength and northward extension of Atlantic Meridional Overturning Circulation (AMOC), resulting in an abrupt reorganization of atmospheric circulation patterns with global teleconnections. To determine the timing of tropical Atlantic atmospheric circulation changes over the past 21 ka BP, we reconstruct high resolution sea surface temperature and δ18OSW (a proxy for surface salinity) records based on Mg/Ca ratios and oxygen isotope measurements in the planktonic foraminifera Globigerinoides ruber from a sediment core located on the western margin of the Florida Straits. As a proxy for meltwater discharge influence on Florida Straits surface water salinity, we also measured Ba/Ca ratios in G. ruber from the same core. Results show that riverine influence on Florida Straits surface water started by 17.2 ka BP and ended by 13.6 ka BP, 600 years before the start of the Younger Dryas (YD) cold interval. The initiation of the YD is marked by an abrupt increase in Florida Straits δ18OSW values, indicating a shift to elevated sea surface salinity occurring in 130 years, most likely resulting from increased regional aridity and/or reduced precipitation. In order to resolve the timing of tropical atmospheric circulation change relative to AMOC variability across this transition, we compare the timing of surface water changes to a recently published record of Florida Current variability in the same core reconstructed from benthic oxygen isotope measurements. We find synchronous changes in atmospheric and ocean circulation on the transition into the YD, consistent with an abrupt reduction in AMOC as the driver of tropical Atlantic atmospheric circulation change at this time.
THE EXTRATROPICAL UPPER TROPOSPHERE AND LOWER STRATOSPHERE
Authors: Gettelman A. , Hoor P. , Pan L. L. , Randel W. J. , Hegglin M. I. , Birner T.
Published: August 2011

The extratropical upper troposphere and lower stratosphere (Ex‐UTLS) is a transition region between the stratosphere and the troposphere. The Ex‐UTLS includes the tropopause, a strong static stability gradient and dynamic barrier to transport. The barrier is reflected in tracer profiles. This region exhibits complex dynamical, radiative, and chemical characteristics that place stringent spatial and temporal requirements on observing and modeling systems. The Ex‐UTLS couples the stratosphere to the troposphere through chemical constituent transport (of, e.g., ozone), by dynamically linking the stratospheric circulation with tropospheric wave patterns, and via radiative processes tied to optically thick clouds and clear‐sky gradients of radiatively active gases. A comprehensive picture of the Ex‐UTLS is presented that brings together different definitions of the tropopause, focusing on observed dynamical and chemical structure and their coupling. This integral view recognizes that thermal gradients and dynamic barriers are necessarily linked, that these barriers inhibit mixing and give rise to specific trace gas distributions, and that there are radiative feedbacks that help maintain this structure. The impacts of 21st century anthropogenic changes to the atmosphere due to ozone recovery and climate change will be felt in the Ex‐UTLS, and recent simulations of these effects are summarized and placed in context.
ON THE DETERMINISTIC DESCRIPTION OF EARTHQUAKES
Authors: Bizzarri Andrea
Published: August 2011

The quantitative estimate of earthquake damage due to ground shaking is of pivotal importance in geosciences, and its knowledge should hopefully lead to the formulation of improved strategies for seismic hazard assessment. Numerical models of the processes occurring during seismogenic faulting represent a powerful tool to explore realistic scenarios that are often far from being fully reproduced in laboratory experiments because of intrinsic, technical limitations. In this paper we discuss the prominent role of the fault governing model, which describes the behavior of the fault traction during a dynamic slip failure and accounts for the different, and potentially competing, chemical and physical dissipative mechanisms. We show in a comprehensive sketch the large number of constitutive models adopted in dynamic modeling of seismic events, and we emphasize their prominent features, limitations, and specific advantages. In a quantitative comparison, we show through numerical simulations that spontaneous dynamic ruptures obeying the idealized, linear slip‐weakening (SW) equation and a more elaborated rate‐ and state‐dependent friction law produce very similar results (in terms of rupture times, peaks slip velocity, developed slip, and stress drops), provided that the frictional parameters are adequately comparable and, more importantly, that the fracture energy density is the same. Our numerical experiments also illustrate that the different models predict fault slip velocity time histories characterized by a similar frequency content; a feeble predominance of high frequencies in the SW case emerges in the frequency ranges [0.3, 1] and [11, 50] Hz. These simulations clearly indicate that, even forgiving the frequency band limitation, it would be very difficult (virtually impossible) to discriminate between two different, but energetically identical, constitutive models, on the basis of the seismograms recorded after a natural earthquake.
Mars ionosphere: A review of experimental results and modeling studies
Authors: Haider S. A. , Mahajan K. K. , Kallio E.
Published: August 2011

In this paper we review results from atmospheric and ionospheric experiments on the early planetary missions like the Mariners, Mars, and Viking 1 and 2 Orbiters/Landers. We then discuss the new results obtained from the two latest missions, namely, the Mars Global Surveyor (MGS) and Mars Express (MEX). The MGS had three ionospheric and atmospheric related experiments, namely, (1) the radio science experiment, which generated 5600 electron density profiles covering a major portion of sunspot cycle 23; (2) the magnetometer/electron reflectometer experiment, which very clearly answered the question about the presence or absence of Martian intrinsic magnetic field; and (3) the accelerometer experiment, which provided a large database of atmospheric density at various Martian locations during the aerobraking phases. The topside sounder on the MEX provided electron density profiles for altitudes above the primary ionospheric peak with a very high time resolution, thereby providing opportunity for exploring ionospheric conditions during events of rapid changes like solar flares. Unlike Venus, where simultaneous electron density, ion density, and magnetic field measurements were made, Mars lacks this kind of information. Consequently, most of our current understanding of Mars' plasma environment is based on theoretical models. We therefore review the various atmospheric and ionospheric models for Mars, which have been generated during the last 4 decades.
Universal and local time variations deduced from simultaneous Schumann resonance records at three widely separated observatories
Authors: Nickolaenko A. P. , Yatsevich E. I. , Shvets A. V. , Hayakawa M. , Hobara Y.
Published: August 2011

A technique is applied to experimental Schumann resonance intensity that separates the universal (UT) and local time (LT) variations. Two orthogonal horizontal magnetic field components were recorded simultaneously at the observatories of Moshiri, Japan (44.4°N, 142.2°E), Lehta, Russia (64.4°N, 34°E), and West Greenwich, Rhode Island, United States (41.6°N, 71.6°W). We use the cumulative magnetic field power integrated over the first three Schumann resonance modes. Diurnal variations were averaged over a month for the period from August 1999 to December 2001 at each site. These records were combined to obtain estimates for the UT daily patterns of the global thunderstorm activity. Diurnal variations of particular months repeat year after year, indicating that space‐time distributions of global thunderstorms are annually replicated with minor deviations. Another technique, based on geometric averaging of records, was used to obtain alternative estimates of the global thunderstorm intensity. Results acquired with both techniques showed an outstanding similarity.
Microwave vector radiative transfer equation of a sea foam layer by the second‐order Rayleigh approximation
Authors: Wei En‐Bo
Published: August 2011

The microwave vector radiative transfer (VRT) equation of a coated spherical bubble layer is derived by means of the second‐order Rayleigh approximation field when the microwave wavelength is larger than the coated spherical particle diameter. Meanwhile, the perturbation method is developed to solve the second‐order Rayleigh VRT equation for the small ratio of the volume scattering coefficient to the extinction coefficient. As an example, the emissive properties of a sea surface foam layer, which consists of seawater coated bubbles, are investigated. The extinction, absorption, and scattering coefficients of sea foam are obtained by the second‐order Rayleigh approximation fields and discussed for the different microwave frequencies and the ratio of inner radius to outer radius of a coated bubble. Our results show that in the dilute limit, the volume scattering coefficient decreases with increasing the ratio of inner radius to outer radius and decreasing the frequencies. It is also found that the microwave emissivity and the extinction coefficient have a peak at very thin seawater coating and its peak value decreases with frequency decrease. Furthermore, with the VRT equation and effective medium approximation of densely coated bubbles, the mechanism of sea foam enhancing the emissivity of a sea surface is disclosed. In addition, excellent agreement is obtained by comparing our VRT results with the experimental data of microwave emissivities of sea surface covered by a sea foam layer at L‐band (1.4 GHz) and the Camps' model.
GNSS‐R ground‐based and airborne campaigns for ocean, land, ice, and snow techniques: Application to the GOLD‐RTR data sets
Authors: Cardellach E. , Fabra F. , Nogués‐Correig O. , Oliveras S. , Ribó S. , Rius A.
Published: August 2011

Several ground‐based and airborne data sets taken with the Global Navigation Satellite System Reflectometry (GNSS‐R) technique are made available to the research community. This paper reviews the potential applications of these bistatic radar observations, including a list of possible approaches and algorithms described in the literature for oceanic measurements (altimetric and scatterometric), soil moisture sensing, and sea ice and snow characterization. A list of applicable models complements the review. The paper continues with descriptions of the campaigns included in the initial data set, together with the basic information required to understand the instrumental issues of the data. Finally, some parameters and observables provided in the data are detailed.
Electromagnetic wave propagation in inhomogeneous, moving media: A general solution of the problem
Authors: Ferencz Csaba
Published: August 2011

The exact computation, the exact modeling of the propagation of electromagnetic signals through inhomogeneous moving media, is an old theoretical and measuring/data interpretation problem, because in a lot of practical problems, such as the accurate space‐time determination in satellite positioning systems, the occultation measurements, or the accurate tracking of the interplanetary probes, the electromagnetic wave (signal) traverses moving, inhomogeneous media, where the moving velocity of the media and the media itself are inhomogeneous in space, i.e., the Earth's high and low atmosphere, the planetary atmospheres, the interplanetary matter in the inner and outer solar system, etc. In other important cases of electromagnetic wave propagation, as the propagation in inhomogeneous media or the propagation of short impulses (ultrawide‐band (UWB) signals), the application of the method of inhomogeneous basic modes (MIBM) was successful. In this paper it is demonstrated that the application of MIBM in the case of inhomogeneous moving media produces an exact, full‐wave solution of monochromatic or UWB signals propagating through these media. The solutions are valid inside the special relativity.
Improving the accuracy of sea surface salinity retrieval using GNSS‐R data to correct the sea state effect
Authors: Valencia E. , Camps A. , Rodriguez‐Alvarez N. , Ramos‐Perez I. , Bosch‐Lluis X. , Park H.
Published: August 2011

Reflectometry using GNSS signals of opportunity (GNSS‐R) has stood as a powerful technique for ocean remote sensing. Particularly, the use of these techniques has been proposed to retrieve sea state information (i.e. sea surface roughness) among other applications. Precise knowledge of the sea state is a key issue to process L‐band radiometric measurements for sea surface salinity retrieval. It has been recently shown that GNSS‐R data can be directly linked to the brightness temperature variations caused by the sea state effect, without the use of emission/scattering models or sea spectra models. In this study, this approach is applied to CoSMOS 2007 flights data. Firstly, the radiometric and GNSS‐R data sets are presented. Secondly, measured brightness temperature is corrected using the collocated GNSS‐R data. In particular, the area under the normalized waveforms is used to directly compute the required brightness temperature correction. Thirdly, the salinity retrievals are presented (achieving an error reduction from 2.8 psu for the raw measurements down to 0.51 psu). Finally, the obtained results are compared with the WISE correction approach, based on the wind speed correction, and the conclusions of this work are presented.
Analysis of time‐of‐arrival observations performed during ELF/VLF wave generation experiments at HAARP
Authors: Fujimaru S. , Moore R. C.
Published: August 2011

Modulated high frequency (HF) heating of the lower ionosphere in the presence of auroral electrojet currents has become an important method for generating electromagnetic waves in the extremely‐low frequency (ELF) and very‐low frequency (VLF) bands. Recent research efforts focus on improving the efficiency of ELF/VLF wave generation. One method to do so involves the spatial mapping of modulated currents that result from HF heating for comparison with HF heating models. As a first step toward providing a spatial map of the modulated ionospheric currents, we introduce time‐of‐arrival (TOA) observations performed during a series of experimental research campaigns conducted at the High‐frequency Active Auroral Research Program (HAARP) in Gakona, Alaska. The TOA method provides a measurement of the ELF/VLF amplitude and phase detected at a ground‐based receiver as a function of time, and this information may be used to estimate the distribution of ELF/VLF source currents within the HF heated region. In an effort to test and improve the TOA method, the University of Florida conducted ELF/VLF wave generation experiments using the HAARP HF transmitter under varying ionospheric conditions and using various transmission formats. In this paper, we summarize our experimental results and compare observations with the predictions of a theoretical model.
Assimilation of autoscaled data and regional and local ionospheric models as input sources for real‐time 3‐D International Reference Ionosphere modeling
Authors: Pezzopane M. , Pietrella M. , Pignatelli A. , Zolesi B. , Cander L. R.
Published: August 2011

This paper describes how the joint utilization of autoscaled data such as the F2 peak critical frequency foF2, the propagation factor M(3000)F2, and the electron density profile coming from two reference ionospheric stations (Rome and Gibilmanna), and the regional (Simplified Ionospheric Regional Model Updated) and global (International Reference Ionosphere) ionospheric models can provide a valid tool for obtaining a real‐time three‐dimensional (3‐D) electron density mapping of the ionosphere. Preliminary results of the proposed 3‐D model are shown by comparing the electron density profiles given by the model with the ones measured at three testing ionospheric stations (Athens, Roquetes, and San Vito).
Evaluating predictions of ICME arrival at Earth and Mars
Authors: Falkenberg T. V. , Taktakishvili A. , Pulkkinen A. , Vennerstrom S. , Odstrcil D. , Brain D. , Delory G. , Mitchell D.
Published: August 2011

We present a study of interplanetary coronal mass ejection (ICME) propagation to Earth and Mars. Because of the significant space weather hazard posed by ICMEs, understanding and predicting their arrival and impact at Mars is important for current and future robotic and manned missions to the planet. We compare running ENLILv2.6 with coronal mass ejection (CME) input parameters from both a manual and an automated method. We analyze shock events identified at Mars in Mars Global Surveyor data in 2001 and 2003, when Earth and Mars were separated by <80° in heliocentric longitude. The shocks identified at Mars were also identified at Earth, and the majority of the shock sources were identified through the Solar and Heliospheric Observatory–Large Angle and Spectrometric Coronagraph catalogue. We find that arrival times predicted by the two methods at both planets are statistically similar, dynamic pressures predicted when using the automated method are better, and the automated method tends to underestimate both CME width and speed. Using the location of the related flare as the CME direction did not improve results. In addition, changing the CME speed toward the plane‐of‐sky speed at 20 RS improves the match to observations, mainly because the speed found by the automated method is underestimated. The time lapse between the shock arrival at Earth and Mars, for the events studied here, is shorter than expected from simulations, and the presence of high speed streams can enable an ICME to arrive almost simultaneously at Earth and Mars. This work will be applied to improve the input parameter methods for ENLIL.
Quantifying extreme behavior in geomagnetic activity
Authors: Thomson Alan W. P. , Dawson Ewan B. , Reay Sarah J.
Published: August 2011

Understanding the extremes in geomagnetic activity is an important component in understanding just how severe conditions can become in the terrestrial space environment. Extreme activity also has consequences for technological systems. On the ground, extreme geomagnetic behavior has an impact on navigation and position accuracy and the operation of power grids and pipeline networks. We therefore use a number of decades of one‐minute mean magnetic data from magnetic observatories in Europe, together with the technique of extreme value statistics, to provide a preliminary exploration of the extremes in magnetic field variations and their one‐minute rates of change. These extremes are expressed in terms of the variations that might be observed every 100 and 200 years in the horizontal strength and in the declination of the field. We find that both measured and extrapolated extreme values generally increase with geomagnetic latitude (as might be expected), though there is a marked maximum in estimated extreme levels between about 53 and 62 degrees north. At typical midlatitude European observatories (55–60 degrees geomagnetic latitude), compass variations may reach approximately 3–8 degrees/minute, and horizontal field changes may reach 1000–4000 nT/minute, in one magnetic storm once every 100 years. For storm return periods of 200 years the equivalent figures are 4–11 degrees/minute and 1000–6000 nT/minute.