Showing papers in "Reviews of Geophysics in 2007"

The Shuttle Radar Topography Mission

Abstract: [1] The Shuttle Radar Topography Mission produced the most complete, highest-resolution digital elevation model of the Earth. The project was a joint endeavor of NASA, the National Geospatial-Intelligence Agency, and the German and Italian Space Agencies and flew in February 2000. It used dual radar antennas to acquire interferometric radar data, processed to digital topographic data at 1 arc sec resolution. Details of the development, flight operations, data processing, and products are provided for users of this revolutionary data set.

Measuring surface water from space

Abstract: [1] Surface fresh water is essential for life, yet we have surprisingly poor knowledge of the spatial and temporal dynamics of surface freshwater discharge and changes in storage globally. For example, we are unable to answer such basic questions as “What is the spatial and temporal variability of water stored on and near the surface of all continents?” Furthermore, key societal issues, such as the susceptibility of life to flood hazards, cannot be answered with the current global, in situ networks designed to observe river discharge at points but not flood events. The measurements required to answer these hydrologic questions are surface water area, the elevation of the water surface (h), its slope (∂h/∂x), and temporal change (∂h/∂t). Advances in remote sensing hydrology, particularly over the past 10 years and even more recently, have demonstrated that these hydraulic variables can be measured reliably from orbiting platforms. Measurements of inundated area have been used to varying degrees of accuracy as proxies for discharge but are successful only when in situ data are available for calibration; they fail to indicate the dynamic topography of water surfaces. Radar altimeters have a rich, multidecadal history of successfully measuring elevations of the ocean surface and are now also accepted as capable tools for measuring h along orbital profiles crossing freshwater bodies. However, altimeters are profiling tools, which, because of their orbital spacings, miss too many freshwater bodies to be useful hydrologically. High spatial resolution images of ∂h/∂t have been observed with interferometric synthetic aperture radar, but the method requires emergent vegetation to scatter radar pulses back to the receiving antenna. Essentially, existing spaceborne methods have been used to measure components of surface water hydraulics, but none of the technologies can singularly supply the water volume and hydraulic measurements that are needed to accurately model the water cycle and to guide water management practices. Instead, a combined imaging and elevation-measuring approach is ideal as demonstrated by the Shuttle Radar Topography Mission (SRTM), which collected images of h at a high spatial resolution (∼90 m) thus permitting the calculation of ∂h/∂x. We suggest that a future satellite concept, the Water and Terrestrial Elevation Recovery mission, will improve upon the SRTM design to permit multitemporal mappings of h across the world's wetlands, floodplains, lakes, reservoirs, and rivers.

On the driving processes of the Atlantic meridional overturning circulation

Abstract: Because of its relevance for the global climate the Atlantic meridional overturning circulation (AMOC) has been a major research focus for many years. Yet the question of which physical mechanisms ultimately drive the AMOC, in the sense of providing its energy supply, remains a matter of controversy. Here we review both observational data and model results concerning the two main candidates: vertical mixing processes in the ocean's interior and wind-induced Ekman upwelling in the Southern Ocean. In distinction to the energy source we also discuss the role of surface heat and freshwater fluxes, which influence the volume transport of the meridional overturning circulation and shape its spatial circulation pattern without actually supplying energy to the overturning itself in steady state. We conclude that both wind-driven upwelling and vertical mixing are likely contributing to driving the observed circulation. To quantify their respective contributions, future research needs to address some open questions, which we outline.

Slow slip events and seismic tremor at circum-Pacific subduction zones

Abstract: [1] It has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements. However, only recently has a fuller spectrum of strain release processes, including normal, slow, and silent earthquakes (or slow slip events) and continuous and episodic slip, been observed and generated by numerical simulations of the earthquake cycle. Despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive. The concurrence of seismic tremor with slow slip episodes in Cascadia and southwestern Japan provides insight into the process of slow slip. A perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface. Alternatively, evidence is accumulating to support the notion that tremor results from shear failure during slow slip. Global observations of the location, spatial extent, magnitude, duration, slip rate, and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation. Most slow slip events occur just downdip of the seismogenic zone, consistent with rate- and state-dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation. At a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation. Slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault, bringing it closer to or farther from earthquake failure, respectively. This paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide, with a focus on circum-Pacific subduction zones. Trends in global observations of slow slip events suggest that (1) slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it, (2) different frictional properties likely control fast versus slow slip, (3) the depth range of slow slip may be related to the thermal properties of the plate interface, and (4) the equivalent seismic moment of slow slip events is proportional to their duration (Moατ), different from the Moατ3 scaling observed for earthquakes.

Atmospheric bridge, oceanic tunnel, and global climatic teleconnections

Abstract: [1] We review teleconnections within the atmosphere and ocean, their dynamics and their role in coupled climate variability. We concentrate on teleconnections in the latitudinal direction, notably tropical-extratropical and interhemispheric interactions, and discuss the timescales of several teleconnection processes. The tropical impact on extratropical climate is accomplished mainly through the atmosphere. In particular, tropical Pacific sea surface temperature anomalies impact extratropical climate variability through stationary atmospheric waves and their interactions with midlatitude storm tracks. Changes in the extratropics can also impact the tropical climate through upper ocean subtropical cells at decadal and longer timescales. On the global scale the tropics and subtropics interact through the atmospheric Hadley circulation and the oceanic subtropical cell. The thermohaline circulation can provide an effective oceanic teleconnection for interhemispheric climate interactions.

Impact of El Niño–Southern Oscillation on European climate

Abstract: [1] El Nino–Southern Oscillation (ENSO) is arguably the most important global climate pattern. While the effects in the Pacific–North American sector and the tropical regions are relatively well understood, the impacts on the circulation in the North Atlantic–European sector are discussed more controversially. Studies from the past 10 years demonstrate that ENSO does affect European climate. However, some of the effects undergo a seasonal modulation or are nonlinear. The signal can be modified by other factors and might be nonstationary on multidecadal scales, contributing to a large interevent variability. Here I review observational and model-based evidence for ENSO's effect on European climate and discuss possible mechanisms, also including troposphere-stratosphere coupling. The paper ends with a schematic depiction of the effects and a discussion of their relevance with respect to our scientific understanding of the climate system and of their relevance for seasonal climate forecasts.

Lunar surface: Dust dynamics and regolith mechanics

Abstract: [1] The lunar surface is characterized by a collisionally evolved regolith resulting from meteoroid bombardment. This lunar soil consists of highly angular particles in a broad, approximately power law size distribution, with impact-generated glasses. The regolith becomes densified and difficult to excavate when subjected to lunar quakes or, eventually, manned and unmanned activity on the surface. Solar radiation and the solar wind produce a plasma sheath near the lunar surface. Lunar grains acquire charge in this environment and can exhibit unusual behavior, including levitation and transport across the surface because of electric fields in the plasma sheath. The fine component of the lunar regolith contributes to the operational and health hazards posed to planned lunar expeditions. In this paper we discuss the mechanical response of the regolith to anticipated exploration activities and review the plasma environment near the lunar surface and the observations, models, and dynamics of charged lunar dust.

The early anthropogenic hypothesis: Challenges and responses

Abstract: [1] Ruddiman (2003) proposed that late Holocene anthropogenic intervention caused CH4 and CO2 increases that kept climate from cooling and that preindustrial pandemics caused CO2 decreases and a small cooling. Every aspect of this early anthropogenic hypothesis has been challenged: the timescale, the issue of stage 11 as a better analog, the ability of human activities to account for the gas anomalies, and the impact of the pandemics. This review finds that the late Holocene gas trends are anomalous in all ice timescales; greenhouse gases decreased during the closest stage 11 insolation analog; disproportionate biomass burning and rice irrigation can explain the methane anomaly; and pandemics explain half of the CO2 decrease since 1000 years ago. Only ∼25% of the CO2 anomaly can, however, be explained by carbon from early deforestation. The remainder must have come from climate system feedbacks, including a Holocene ocean that remained anomalously warm because of anthropogenic intervention.

Glacial/interglacial changes in mineral dust and sea‐salt records in polar ice cores: Sources, transport, and deposition

Abstract: [1] Sea-salt and mineral dust records as represented by Na+ and Ca2+ concentrations, respectively, in Greenland and Antarctic ice cores show pronounced glacial/interglacial variations. For the Last Glacial Maximum (LGM), mineral dust (sea salt) concentrations in Greenland show an increase of a factor of approximately 80 (15) compared to the Holocene and significant shifts by a factor of 15 (5) during Dansgaard-Oeschger events. In Antarctica the dust (sea salt) flux is enhanced by a factor of 15 (3) during the LGM compared to the Holocene, and variations by approximately a factor of 8 (1–2) exist in parallel to Antarctic warm events. Primary glacial dust sources are the Asian deserts for Greenland and Patagonia for Antarctica. Ice core evidence and model results show that both changes in source strength as well as atmospheric transport and lifetime contributed to the observed changes in Greenland ice cores. In Antarctica, changes in ice core fluxes are in large parts related to source variations both for sea salt and dust, where the formation of sea-salt aerosol from sea ice may play a pivotal role. Summarizing our latest estimates on changes in sources, transport, and deposition, these processes are roughly able to explain the glacial increase in sea salt in both polar regions, while they fall short by at least a factor of 4–7 for mineral dust. Future improvements in model resolution and in the formulation of source and transport processes together with new ice core records, e.g., on dust size distributions, will eventually allow convergence of models and observations.

Hierarchy of models for meandering rivers and related morphodynamic processes

Abstract: We review the importance of the physical mechanisms involved in river meandering by comparing some existing linear models and extensions thereof. Such models are hierarchically derived from a common and general mathematical framework and then analyzed with a detailed discussion of the physical processes and relevant hypotheses that are involved. Experiments and field data are also used to discuss the related morphodynamic processes. The analysis of the models shows the importance of the closure of secondary currents especially in the modeling of eddy viscosity. This aspect confirms the usefulness of using simplified models for some practical applications, provided the secondary currents are modeled in detail. On the other hand, the free response of the sediments, the phase lag of secondary currents, and the momentum redistribution due to the coupling between the main and the transverse flow are shown to be less relevant. Hence the second-order models, which neglect the effect of superelevation induced by the topography-driven lateral flow on the longitudinal flow, can reasonably be considered a good approximation for both predictive analysis and the computation of the resonant conditions. Finally, the analysis of higher harmonics suggests that the multilobed pattern can intrinsically be present in both second- and fourth-order models.

Silicate melt properties and volcanic eruptions

Abstract: [1] Knowledge about the properties of silicate melts is needed by volcanologists and petrologists to evaluate the dynamics of volcanic eruptions and magmatic processes. These properties include the solubility and diffusivity of volatile components in silicate melts, silicate melt viscosity, and the fragmentation condition. Data and models of each property are reviewed and assessed. For rhyolitic melts many properties are sufficiently well known to allow realistic modeling of volcanic and magmatic processes. One interesting example is the role of speciation in the solubility and diffusivity of H2O and CO2. Even though both H2O and CO2 are present in silicate melts as at least two species, the complexity in the solubility and diffusion behavior of H2O and the simplicity of CO2 are due to differences in the speciation reaction: For the H2O component the stoichiometric coefficient is one for one hydrous species (molecular H2O) but is two for the other hydrous species (OH) in the species interconversion reaction, whereas for CO2 the stoichiometric coefficients for all carbon species are one. The investigation of the species reaction not only helps in understanding the solubility and diffusion behavior, but the reaction among the hydrous species also serves as a geospeedometer (cooling rate indicator) for hydrous rhyolitic pyroclasts and glass and provides a method to infer viscosity. For melts other than rhyolite, a preliminary description of their properties is also available, but much more experimental and modeling work is necessary to quantify these properties more accurately.

Pleistocene hydrology of North America: The role of ice sheets in reorganizing groundwater flow systems

Abstract: [1] While the geomorphic consequences of Pleistocene megafloods have been known for some time, it has been only in the past 2 decades that hydrogeologists and glaciologists alike have begun to appreciate the important impact that ice sheet–aquifer interactions have had in controlling subsurface flow patterns, recharge rates, and the distribution of fresh water in confined aquifer systems across North America. In this paper, we document the numerous lines of geochemical, isotopic, and geomechanical evidence of ice sheet hydrogeology across North America. We also review the mechanical, thermal, and hydrologic processes that control subsurface fluid migration beneath ice sheets. Finite element models of subsurface fluid flow, permafrost formation, and ice sheet loading are presented to investigate the coupled nature of transport processes during glaciation/deglaciation. These indicate that recharge rates as high as 10 times modern values occurred as the Laurentide Ice Sheet overran the margins of sedimentary basins. The effects of ice sheet loading and permafrost formation result in complex transient flow patterns within aquifers and confining units alike. Using geochemical and environmental isotopic data, we estimate that the volume of glacial meltwater emplaced at the margins of sedimentary basins overrun by the Laurentide Ice Sheet totals about 3.7 × 104 km3, which is about 0.2% of the volume of the Laurentide Ice Sheet. Subglacial infiltration estimates based on continental-scale hydrologic models are even higher (5–10% of meltwater generated). These studies in sum call into question the widely held notion that groundwater flow patterns within confined aquifer systems are controlled primarily by the water table configuration during the Pleistocene. Rather, groundwater flow patterns were likely much more complex and transient in nature than has previously been thought. Because Pleistocene recharge rates are believed to be highly variable, these studies have profound implications for water resource managers charged with determining sustainable pumping rates from confined aquifers that host ice sheet meltwater.

Predictability: Recent insights from information theory

Abstract: [1] This paper summarizes a framework for investigating predictability based on information theory. This framework connects and unifies a wide variety of statistical methods traditionally used in predictability analysis, including linear regression, canonical correlation analysis, singular value decomposition, discriminant analysis, and data assimilation. Central to this framework is a procedure called predictable component analysis (PrCA). PrCA optimally decomposes variables by predictability, just as principal component analysis optimally decomposes variables by variance. For normal distributions the same predictable components are obtained whether one optimizes predictive information, the dispersion part of relative entropy, mutual information, Mahalanobis error, average signal to noise ratio, normalized mean square error, or anomaly correlation. For joint normal distributions, PrCA is equivalent to canonical correlation analysis between forecast and observations. The regression operator that maps observations to forecasts plays an important role in this framework, with the left singular vectors of this operator being the predictable components and the singular values being the canonical correlations. This correspondence between predictable components and singular vectors occurs only if the singular vectors are computed using Mahalanobis norms, a result that sheds light on the role of norms in predictability. In linear stochastic models the forcing that minimizes predictability is the one that renders the “whitened” dynamical operator normal. This condition for minimum predictability is invariant to linear transformation and is equivalent to detailed balance. The framework also inspires some new approaches to accounting for deficiencies of forecast models and estimating distributions from finite samples.

North American dynamics and western U.S. tectonics

Abstract: [1] Interest and controversy exist on the origin of forces that move and tectonically deform plates, especially regarding the relative importance of loads applied to the plate margins and base and those created internally (e.g., by elevated potential energy in uplifted regions). To quantify these loads, we evaluate predicted interplate stress through two-dimensional finite element analysis of the North American plate, finding that boundary loads are most important, followed by internal and basal loads. Craton root basal drag of ∼4 MPa opposes absolute plate motion, compared to basal tractions elsewhere that average ∼0.4 MPa, suggesting that North America is separated from a relatively static deep Earth mantle by a weak asthenosphere. San Andreas shear (∼1.5 TN/m), gravitational collapse, and southern Cascadia pull all contribute importantly to western U.S. deformation; the region also is relatively weak. Important future work includes incorporating three-dimensional plate structure onto global flow calculations and including the global set of plates.

Stellar Ablation of Planetary Atmospheres

Abstract: We review observations and theories of the solar ablation of planetary atmospheres, focusing on the terrestrial case where a large magnetosphere holds off the solar wind, so that there is little direct atmospheric impact, but also couples the solar wind electromagnetically to the auroral zones. We consider the photothermal escape flows known as the polar wind or refilling flows, the enhanced mass flux escape flows that result from localized solar wind energy dissipation in the auroral zones, and the resultant enhanced neutral atom escape flows. We term these latter two escape flows the "auroral wind." We review observations and theories of the heating and acceleration of auroral winds, including energy inputs from precipitating particles, electromagnetic energy flux at magnetohydrodynamic and plasma wave frequencies, and acceleration by parallel electric fields and by convection pickup processes also known as "centrifugal acceleration." We consider also the global circulation of ionospheric plasmas within the magnetosphere, their participation in magnetospheric disturbances as absorbers of momentum and energy, and their ultimate loss from the magnetosphere into the downstream solar wind, loading reconnection processes that occur at high altitudes near the magnetospheric boundaries. We consider the role of planetary magnetization and the accumulating evidence of stellar ablation of extrasolar planetary atmospheres. Finally, we suggest and discuss future needs for both the theory and observation of the planetary ionospheres and their role in solar wind interactions, to achieve the generality required for a predictive science of the coupling of stellar and planetary atmospheres over the full range of possible conditions.

Instability and surge development in debris flows

Abstract: [1] Debris flows are often described as a succession of surges, which are characterized by enhanced peak depth and velocity and therefore by a tremendous increase of their destructive power. For given characteristics of the base flow, if the channel is sufficiently long to allow an appreciable wave development, the linear stability analysis in shallow streams is shown to provide a reasonable prediction of the critical flow condition and of the instability growth rate. The one-dimensional (1-D) theory, however, does not allow the determination of the wave period of the fastest growing perturbations. Debris waves most frequently develop following a mechanism similar to water roll waves: Instabilities grow up becoming clearly distinguishable waves, and then waves overtake one another with increasing wave period and amplitude. The typical hydrograph of a multiple-peak event is shown to be composed of a first surge, which is usually characterized by the highest depth, the longest duration, the greatest erosive power, and the most symmetrical shape, and of secondary waves that burst on the flow tail in the recession phase. The characteristics of the first surge can be explained by two different mechanisms. All waves that rise up near the flood crest run faster than this first surge and coalesce into it, causing its high depth and great volume. Moreover, segregation during the flow induces the concentration of boulders at the fronts, contributing to its depth enhancement, erosive power, and symmetrical shape. When a debris surge impacts a structure, the force pattern can be interpreted as the superposition of the reflection of the bouldery front and the formation of a vertical muddy jet due to the impact of the front wedge. Wave reflection can be described by a 1-D mass and momentum balance across the front, whereas the pressure impulse, due to the incompressibility of the interstitial fluid, can be analyzed through inviscid formulations validated for the representation of tsunami forces.

Localized aurora beyond the auroral oval

Abstract: [1] Aurora is the result of the interaction between precipitating energetic electrons and protons with the upper atmosphere. Viewed from space, it generally occurs in continuous and diffuse ovals of light around the geomagnetic poles. Additionally, there are localized regions of aurora that are unrelated to the ovals and exhibit different morphological, spatial, and temporal properties. Some of these localized aurorae are detached from the oval poleward or equatorward of it. Others are located within the oval and are brighter than the surrounding diffuse aurora. Many of them occur only during preferred solar wind conditions and orientations of the interplanetary magnetic field. This review describes the different localized aurorae and their particle sources in the plasma sheet, at the plasmapause, or at the magnetopause. Their origin is still not completely understood, and the study of aurorae can teach a great deal about their underlying physical processes of reconnection, electrostatic acceleration, or wave-particle interactions.

Understanding coronal heating and solar wind acceleration: Case for in situ near‐Sun measurements

Abstract: The solar wind has been measured directly from 0.3 AU outward, and the Sun's atmosphere has been imaged from the photosphere out through the corona. These observations have significantly advanced our understanding of the influence of the Sun's varying magnetic field on the structure and dynamics of the corona and the solar wind. However, how the corona is heated and accelerated to produce the solar wind remains a mystery. Answering these fundamental questions requires in situ observations near the Sun, from a few solar radii (R_S) out to ∼20 R_S, where the internal, magnetic, and turbulent energy in the coronal plasma is channeled into the bulk energy of the supersonic solar wind. A mission to make such observations has long been a top priority of the solar and space physics community. The recent Solar Probe study has proven that such a mission is technically feasible and can be accomplished within reasonable resources.

Tracer interrelationships in the stratosphere

Abstract: [1] Relationships between long-lived stratospheric tracers, manifested in similar spatial structures on scales ranging from a few to several thousand kilometers, are displayed most strikingly if the mixing ratio of one is plotted against another, when the data collapse onto remarkably compact curves. Distinct curves form in the polar vortex, the midlatitude “surf zones”, and the tropics. Theory predicts such relationships for sufficiently rapid mixing along isentropic surfaces. Model results are used to illustrate the formation and seasonal evolution of distinct tracer relationships in the different regions. Using such relationships to associate departures from canonical forms with anomalous chemical or microphysical behavior must be done with care and with full awareness of the meteorological context of the data. Although the theory has been developed in the context of stratospheric tracers, the key requirement is that transport is predominantly two-dimensional. While the theory is thus inappropriate in the troposphere, it should be applicable to transport in the ocean interior.

Neural network emulations for complex multidimensional geophysical mappings: Applications of neural network techniques to atmospheric and oceanic satellite retrievals and numerical modeling

Abstract: [1] A group of geophysical applications, which from the mathematical point of view, can be formulated as complex, multidimensional, nonlinear mappings and which in terms of the neural network (NN) technique, utilize a particular type of NN, the multilayer perceptron (MLP), is reviewed in this paper. This type of NN application covers the majority of NN applications developed in geosciences like satellite remote sensing, meteorology, oceanography, numerical weather prediction, and climate studies. The major properties of the mappings and MLP NNs are formulated and discussed. Three particular groups of NN applications are presented in this paper as illustrations: atmospheric and oceanic satellite remote sensing applications, NN emulations of model physics for developing atmospheric and oceanic hybrid numerical models, and NN emulations of the dependencies between model variables for application in data assimilation systems.

Toward elucidating the microstructure of warm rainfall: a survey

Abstract: [1] Quantitative measurement, estimation, and prediction of precipitation remains one of the grand challenges in the hydrological and atmospheric sciences with far-reaching implications across the natural sciences. Although the roots of current research activity in this topic go back to the beginning of the twentieth century, advances in radar technology and in numerical modeling have provided the impetus for prolific research in the area of cloud and precipitation physics over the last 50 years. As radar rainfall measurements progressively became the staple of hydrometeorological observing systems, cloud and precipitation microphysics emerged as increasingly preeminent areas of research. Here we present a synthesis of the state of the science with respect to the physical dynamics of hydrometeors and, specifically, the transient processes that affect the temporal evolution of rainfall microstructure and that are directly relevant to the quantitative interpretation of radar rainfall measurements and explicit numerical simulations. The focus of our survey is on raindrop morphodynamics (equilibrium raindrop shape and raindrop oscillations), drop-drop interactions (bounce, coalescence, and breakup), and the dynamical evolution of raindrop size distributions in precipitating clouds.

Theoretical aspects of energetic neutral atoms as messengers from distant plasma sites with emphasis on the heliosphere

Abstract: [1] Ions after a local charge exchange with neutral atoms are not controlled anymore by magnetic or electric fields but instead move as neutral atoms with their instantaneous velocities along free-flight trajectories, unless they undergo further collisions of elastic or ionizing types. Atoms originating from a charge exchange process of energetic ions, so-called energetic neutral atoms, can serve as valuable messengers of plasma sites allowing for a remote sensing of distant plasma activities. Remote diagnostics is especially enabled in the case of resonant charge exchange processes at which only charge, but nearly no momentum or energy, is exchanged between collision partners. Most important in this respect and in our context here are charge exchange collisions between protons and hydrogen atoms. In this article we review several theoretical aspects of how this context can be used to study different plasma scenarios like the solar corona and the solar wind, corotating interaction regions, planetary or cometary ionospheres, plasmaspheres or magnetospheres or like the solar wind termination shock, the heliosheath, and the outer heliospheric bow shock. In particular, we address the following questions: Where do energetic atoms play a role, and what kind of role, a dynamic or thermodynamic one, do they play there? From which plasma sites can we expect to receive energetic neutral atom fluxes including even those located far outside these sites? Though we mention in brief presently available and upcoming techniques to measure and to resolve energetic neutral atom fluxes spectrally and spatially, we put the emphasis on theoretical model calculations predicting spectral flux features of energetic neutral atoms with different origins, which in the nearest future may be observed by the NASA Small Explorer mission IBEX and, hopefully, its successors.

Angular momentum in the global atmospheric circulation

Abstract: Angular momentum is a variable of central importance to the dynamics of the atmosphere both regionally and globally. Moreover, the angular momentum equations yield a precise description of the dynamic interaction of the atmosphere with the oceans and the solid Earth via various torques as exerted by friction, pressure against the mountains and the nonspherical shape of the Earth, and by gravity. This review presents recent work with respect to observations and the theory of atmospheric angular momentum of large-scale motions. It is mainly the recent availability of consistent global data sets spanning decades that sparked renewed interest in angular momentum. In particular, relatively reliable estimates of the torques are now available. In addition, a fairly wide range of theoretical aspects of the role of angular momentum in atmospheric large-scale dynamics is covered.

The study of Earth's magnetism (1269–1950): A foundation by Peregrinus and subsequent development of geomagnetism and paleomagnetism

Abstract: [1] This paper summarizes the histories of geomagnetism and paleomagnetism (1269–1950). The role of Peregrinus is emphasized. In the sixteenth century a debate on local versus global departures of the field from that of an axial dipole pitted Gilbert against Le Nautonier. Regular measurements were undertaken in the seventeenth century. At the turn of the nineteenth century, de Lamanon, de Rossel, and von Humboldt discovered the decrease of intensity as one approaches the equator. Around 1850, three figures of rock magnetism were Fournet (remanent and induced magnetizations), Delesse (remagnetization in a direction opposite to the original), and Melloni (direction of lava magnetization acquired at time of cooling). Around 1900, Brunhes discovered magnetic reversals. In the 1920s, Chevallier produced the first magnetostratigraphy and hypothesized that poles had undergone enormous displacements. Matuyama showed that the Earth's field had reversed before the Pleistocene. Our review ends in the 1940s, when exponential development of geomagnetism and paleomagnetism starts.

Correction to “Volcanic eruptions and climate”

Abstract: [1] In the paper ‘‘Volcanic eruptions and climate’’ by Alan Robock (Reviews of Geophysics, 38(2), 191–219, 2000), two errors have been found on page 197. [2] While preparing for a presentation on the 25th anniversary of the April 1982 El Chichon volcanic eruption, I found the original slide used for Plate 4 and discovered that it had been developed in July 1982 rather than the date of April 1983 given in the paper. I had had copies made of this slide and erroneously had used the date on a copy of the slide rather than the original date when writing the paper. Therefore the corrected caption should read as follows: [3] Plate 4. Sunset over Lake Mendota in Madison, Wisconsin, in July 1982, three months after the El Chichon eruption. Photograph by A. Robock. [4] On the same page as Plate 4, the statement, ‘‘The famous 1893 Edvard Munch painting, ‘The Scream,’ shows a red volcanic sunset over the Oslo harbor produced by the 1892 Awu eruption,’’ is incorrect with regard to the eruption that produced the red and yellow sky. As pointed out subsequently by Olson et al. [2004], it was the memory of the spectacular sunsets from the 1883 Krakatau eruption that inspired Munch to use a volcanic sunset 10 years later in ‘‘The Scream.’’

Groundwater table mounding, pore pressure, and liquefaction induced by explosions: Energy‐distance relations

Abstract: [1] Explosive-induced ground motion can alter well water levels and induce liquefaction in water-saturated cohesionless geological profiles. Analysis of underground detonations of chemical and nuclear explosives indicates that residual pore pressure and groundwater table mounding can be induced to maximum distances in meters equal to 0.087 J1/3 or 14 kg1/3, a zone where the estimated peak compressive strain exceeds 0.007% and peak particle velocity exceeds 0.11 m/s. Liquefaction can be induced to maximum distances in meters equal to 0.019 J1/3 or 3 kg1/3, a zone where the estimated peak compressive strain exceeds 0.07% and peak particle velocity exceeds 1.1 m/s. These relationships are linear over 11 orders of magnitude of energy (joules) or trinitrotoluene equivalent mass (kilograms). Maximum distances for residual pore pressure and liquefaction for surface explosions are about one third of those found for underground explosions.