bluuebunny/crossref_metadata_2025 huggingface dataset:
Three‐dimensional numerical simulation of Martian global dust storms
Authors: Murphy James R. , Pollack James B. , Haberle Robert M. , Leovy Conway B. , Toon Owen B. , Schaeffer James
Published: February 2004

We present results from the first numerical simulations of simultaneously evolving three‐dimensional thermal, dynamical, and radiatively active suspended dust fields in the Martian atmosphere. Simulations of southern summer dust storms (arising from a prescribed southern subtropical surface dust source) conducted with a Mars general circulation model (GCM) illustrate the important role of dust transport by atmospheric eddies. Both traveling and stationary eddies contribute to dust transport to high latitudes in both hemispheres. These hemispheric differences arise from seasonal and topographic effects. Transport into the south polar regions is accomplished primarily by thermally and topographically forced standing eddies. Both traveling and stationary eddies transport dust to middle and high northern (winter) latitudes. Atmospheric wave motions are affected by the developing storms. Thermal tidal amplitudes increase at storm onset, with the calculated pressure response at a model grid point corresponding to the location of the Viking Lander 1 site in good agreement with observations. In qualitative agreement with observations, winter hemisphere baroclinic waves weaken during the early stages of the storm, but as the storm wanes, amplitudes of these waves increase. A slowly westward propagating (9 degrees of longitude per sol) zonal wavenumber one feature in the temperature and geopotential fields at middle northern latitudes amplifies rapidly during the initial sols (Martian solar days) of the simulated storms. This feature is suggestive of the observed north polar warming which occurred during the 1977B global dust storm, but the simulations produce a much weaker polar warming (∼10 K at 0.5 mbar) than was observed (40–50 K). The globally integrated CO2 condensation rate decreases by 15–20% during the simulated dust storm onset and would likely be decreased more if a stronger polar warming were produced. During the initial stages of the simulated storms, surface stress values in the southern subtropics intensify due primarily to the intensification of the Hadley circulation and thermally driven tides. This supports the hypothesis that these components of the general circulation contribute strong positive feedbacks to the developing storms.
Compositional variations on the Moon: Recalibration of Galileo solid‐state imaging data for the Orientale region and farside
Authors: Gaddis Lisa R. , McEwen Alfred S. , Becker Tammy L.
Published: February 2004

Updated radiometric calibration and systematic processing procedures for Galileo solid‐state imaging (SSI) data from the first (1990) Earth‐Moon encounter are presented. These procedures were applied to a whole‐disk imaging sequence of the Moon centered near Mare Orientale, called Lunmap 14 (L14). Processing of L14 data included radiometric calibration, subpixel coregistration, scattered light removal, geometric control and reprojection, photometric normalization, and calibration to Earth‐based spectra. Coregistration and scattered‐light removal procedures are improvements over the initial calibration of the SSI mosaics. The effects of scattered light correction are best seen using a whole‐Moon view such as L14; resolution of the debated amounts of light scattering from within or outside the camera field of view is not necessary. Scattered light removal particularly affects the 1‐μm spectral region and has implications for interpretation of mafic mineral signatures in mare deposits of the lunar limb and farside. Recalibrated spectra indicate that mare ponds of the limb show moderately deep 1‐μm absorptions, and thus mafic mineral contents, comparable to those of other nearside basalts. Mafic mineral contents of Schiller‐Shickard cryptomaria are higher than previously thought and are similar to some low‐Ti nearside basalts. Many of the recalibrated spectra from South Pole/Aitken are similar to those of Schiller‐Schickard cryptomaria, suggesting that many of these soils represent a mixed mare/highland lithology. The hypothesis that there is an olivine enrichment in southern South Pole/Aitken basin is not supported strongly by spectra shown here.
A mechanism for episodic subduction on Venus
Authors: Fowler A. C. , O'Brien S. B. G.
Published: February 2004

We propose a mechanism previously developed as a hypothetical cause of the initiation of subduction in the Earth's mantle, to describe a situation where such subduction may occur transiently, at irregular intervals of time. It has been suggested that tectonics on Venus may be described by such a scenario. In our model, a subduction event is followed by resumption of high Rayleigh number mantle convection below a stagnant lithosphere which thickens due to conductive cooling. As it thickens, differential buoyancy causes large lithospheric stresses which eventually lead to (plastic) failure in the upper portions of the lithosphere. This plastic zone thickens faster than the lithosphere, so that at some critical time, it reaches the base of the lithosphere. At this point, the effective lithosphere viscosity decreases to that of the underlying mantle, and subduction can occur. We suggest that this is mechanistically consistent with the postulated Venusian tectonic style.
Stagnant lid convection on Venus
Authors: Solomatov V. S. , Moresi L.‐N.
Published: February 2004

The effect of strongly temperature‐dependent viscosity on convection in the interior of Venus is studied systematically with the help of finite element numerical models. For viscosity contrasts satisfying experimental constraints on the rheology of rocks, Venus is likely to be in the regime of stagnant lid convection. This regime is characterized by the formation of a slowly creeping, very viscous lid on top of the mantle‐Venusian lithosphere and is in agreement with the tectonic style observed on Venus. Stagnant lid convection explains large geoid to topography ratios on Venus by the thermal thinning of a thick lithosphere. The thickness of the lithosphere can be as large as 400–550 km for Beta Regio and 200–400 km on average. Geoid and topography data and experimental data on the rheology of rocks provide constraints on the viscosity of the mantle, 1020–1021 Pa s; the convective stresses in the interior, 0.2–0.5 MPa; the stresses in the lid, 100–200 MPa; the velocity in the interior, 0.5–3 cm yr−1; and the heat flux beneath the lithosphere, 8–16 mW m−2. Parameterized convection calculations of thermal history of Venus are difficult to reconcile with a thick present‐day lithosphere. However, a sufficiently thick lithosphere can be formed if a convective regime with mobile plates was replaced by stagnant lid convection around 0.5 b.y. ago. One of the possible explanations for the cessation of Venusian late tectonics is that during the evolution of Venus, stresses in the lid dropped below the yield strength of the lithosphere. This model predicts a drastic drop in the heat flux, thickening of the lithosphere, and suppression of melting and is consistent with the hypothesis of cessation of resurfacing on Venus around 0.5 b.y. ago.
Suprathermal electron fluxes in the Venus nightside ionosphere at moderate and high solar activity
Authors: Spenner K. , Knudsen W. C. , Lotze W.
Published: February 2004

Suprathermal electron fluxes up to energies of 50 eV measured at moderate solar activity (MSA) during the Pioneer Venus Orbiter entry mission are presented and compared with measurements made during high solar activity (HSA). The median height profiles measured at these two seasons do not significantly differ from each other in the Venus nightside ionosphere. At HSA the fluxes decrease significantly with increasing solar zenith angel (SZA). At MSA, only a small decrease in flux is suggested from individual orbits and a statistical study. Flux changes between different orbits and locations during MSA are usually less than an order of magnitude, a relatively small value compared with the spread of the thermal plasma density of more than 2 orders of magnitude at altitudes above 200‐km altitude. Independent of altitude and SZA, the shape of the spectrum of the suprathermal electrons is similar to the spectrum of the dayside photoelectrons with a characteristic energy of about 7 eV in many cases, but the flux is an order of magnitude smaller. In other cases the suprathermal electrons are approximately twice as energetic as photoelectrons of the dayside, comparable with the characteristic energy of solar wind electrons and assumed to originate there. The results indicate that the source of high thermal plasma densities, which occur especially at HSA, is mainly plasma transport from the dayside ionosphere. The median total plasma density above 200‐km altitude in the central nightside sector at MSA is depleted by a factor of 5 compared with that at HSA. Between HSA and MSA, plasma transport is typically reduced by a factor of 6. At MSA, transport and particle precipitation contribute about equally to the nightside ionization.
Glacial enrichments of authigenic Cd And U in subantarctic sediments: A climatic control on the elements' oceanic budget?
Authors: Rosenthal Y. , Boyle E. A. , Labeyrie L. , Oppo D.
Published: February 2004

We examine the possibility that glacial increase in the areal extent of reducing sediments might have changed the oceanic Cd inventory, thereby decoupling Cd from PO4. We suggest that the precipitation of Cd‐sulfide in suboxic sediments is the single largest sink in the oceanic Cd budget and that the accumulation of authigenic Cd and U is tightly coupled to the organic carbon flux into the seafloor. Sediments from the Subantarctic Ocean and the Cape Basin (South Atlantic), where oxic conditions currently prevail, show high accumulation rates of authigenic Cd and U during glacial intervals associated with increased accumulation of organic carbon. These elemental enrichments attest to more reducing conditions in glacial sediments in response to an increased flux of organic carbon. A third core, overlain by Circumpolar Deep Water (CPDW) as are the other two cores but located south of the Antarctic Polar Front, shows an approximately inverse pattern to the Subantarctic record. The contrasting patterns to the north and south of the Antarctic Polar Front suggest that higher accumulation rates of Cd and U in Subantarctic sediments were driven primarily by increased productivity. This proposal is consistent with the hypothesis of glacial stage northward migration of the Antarctic Polar Front and its associated belt of high siliceous productivity. However, the increase in authigenic Cd and U glacial accumulation rates is higher than expected simply from a northward shift of the polar fronts, suggesting greater partitioning of organic carbon into the sediments during glacial intervals. Lower oxygen content of CPDW and higher organic carbon to biogenic silica rain rate ratio during glacial stages are possible causes. Higher glacial productivity in the Cape Basin record very likely reflects enhanced coastal up welling in response to increased wind speeds. We suggest that higher productivity might have doubled the areal extent of suboxic sediments during the last glacial maximum. However, our calculations suggest low sensitivity of seawater Cd concentrations to glacial doubling of the extent of reducing sediments. The model suggests that during the last 250 kyr seawater Cd concentrations fluctuated only slightly, between high levels (about 0.66 nmol kg−1) on glacial initiations and reaching lowest values (about 0.57 nmol kg−1) during glacial maxima. The estimated 5% lower Cd content at the last glacial maximum relative to modern levels (0.60 nmol kg−1) cannot explain the discordance between Cd and δ13C, such as observed in the Southern Ocean. This low sensitivity is consistent with foraminiferal data, suggesting minimal change in the glacial Cd mean oceanic content.
Modern and Last Glacial Maximum eolian sedimentation patterns in the Atlantic Ocean interpreted from sediment iron oxide content
Authors: Balsam William L. , Otto‐Bliesner Bette L. , Deaton Bobby C.
Published: February 2004

Eolian dust derived from the desert regions of North Africa is blown far into the tropical Atlantic Ocean by persistent easterly and northeasterly winds. In this paper, we demonstrate that the iron oxides, hematite and goethite, are a worthwhile addition to proxy monitors of eolian sedimentation in the tropical Atlantic. Iron oxides are identified by diffuse reflectance spectrophotometry, a technique capable of identifying these minerals in concentrations as low as 0.01% by weight. We analyze samples from both the modern and last glacial maximum (LGM) synoptic levels from 178 sample locations yielding a total of 356 samples distributed throughout the Atlantic Ocean. To determine the relative contribution of the iron oxides, we factor analyzed the modern and LGM levels as a single data set. The iron oxide factor explains about 25% of the variance in the combined core top and LGM data set. Mapped factor scores for the LGM and modern ocean indicate high iron oxide values are present in just two regions, one off eastern North America and the other off northwest Africa. In the region off eastern North America, iron oxide occurs primarily during the LGM as the previously noted “brick red lutite,” a unique sediment type derived from the erosion of Permo‐Carboniferous red beds in Atlantic Canada. A larger, lobe‐shaped area of iron oxide rich sediment is present off northwest Africa in both the modern and LGM levels. The modern iron oxide lobe is coincident with the distribution of eolian dust as determined by observations from ships, satellites, and analysis of air samples. During the LGM, iron oxides exhibit a similar distribution except the southern margin of the region shifts equatorward and iron oxide concentration increases.
Nannofossil assemblages, fine fraction stable isotopes, and the paleoceanography of the Valanginian‐Barremian (Early Cretaceous) North Sea Basin
Authors: Williams John R. , Bralower Timothy J.
Published: February 2004

Calcareous nannofossil assemblages have been investigated in three sections from around the margins of the Early Cretaceous North Sea Basin. Both absolute (number of nannofossils per gram) and relative (percent of the assemblage of different taxa) abundance data have been collected. Absolute abundances (up to 10 billion nannofossils per gram) are somewhat higher than those reported previously from other stratigraphic intervals. Stratigraphic correlation of trends in assemblage data in different sections points toward the existence of large, uniform water masses, stable over long (0.5 to 1 m.y.) time periods. These water masses contained a characteristic nannoplankton, which appears to have been driven largely by variations in fertility possibly tied to changes in sources of surface waters, which in turn may have been controlled by relative sea level. Fine fraction isotopic data show fluctuations on shorter time periods (0.1 to 0.5 m.y.). We postulate that some of these isotopic fluctuations were controlled by relative changes in sea level which affected the balance of surface waters derived from runoff and those imported from the Boreal Sea. These oceanographic changes appear to have affected nannofossil assemblages only in discrete intervals.

Data are available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009. Document P95‐001; $2.50 payment must accompany order.
Glacial‐interglacial differences in circulation and carbon cycling within the upper western North Atlantic
Authors: Slowey Niall C. , Curry William B.
Published: February 2004

We investigated glacial‐interglacial changes in the circulation and carbon cycling in the western North Atlantic subtropical gyre using hydrographic data and downcore records of the stable isotopic compositions of individual shells of Bahamian benthic foraminifera. Potential temperature‐salinity‐depth relations show that modern thermocline (∼200–1000 m) and deep (∼1000–2000 m) waters in the Providence Channels, Bahamas, originate in the Sargasso Sea and are typical of the subtropical gyre. Gradients in the stable isotopic compositions of late Holocene Planulina and Cibicidoides species from the bank margins (∼400 to 1500 m depth) reflect temperature, nutrient, and isotopic gradients of modern subtropical gyre waters. The difference between the δ18O of glacial maximum and late Holocene foraminifera is ∼2.1‰ for the upper 900 m of the water column and ∼1.6‰ for deeper waters, indicating that these waters were ∼4°C and ∼2°C cooler, respectively, during glacial time. The glacial temperature gradient (dT/dz) was similar to today, while the base of the thermocline was ∼100 m shallower. These results differ significantly from our earlier results from multiple shell δ18O analyses, which implied upper thermocline waters were only ∼1°C cooler and dT/dz was greater during the glacial maximum. The difference occurs because bioturbation adversely affects multiple shell analyses of glacial‐aged samples from shallow water depths. At all depths above 1500 m, foraminiferal δ13C are greater during the glacial maximum than the late Holocene by at least 0.1 to 0.2‰ (as much as 0.6‰ in the lower thermocline), indicating that nutrient concentrations throughout the thermocline were reduced and there was no oxygen minimum zone during the glacial maximum. This suggests greater, more uniform ventilation of the thermocline. Results of single and multiple shell δ13C analyses of glacial age foraminifera compare favorably because samples most affected by mixing correspond to water depths where the glacial‐interglacial change of δ13C was small. Cooler upper ocean waters during the glacial maximum reflect cooler temperatures at the ocean surface where isopycnal surfaces outcrop, including large areas of the subtropical ocean. A shallower thermocline base is consistent with southward migration of the northern edge of the subtropical gyre or increased mode water production. Enhanced thermocline ventilation is consistent with more vigorous winds and all isopycnal surfaces outcropping in the area of Ekman downwelling.
A “simulation” of Mid‐Cretaceous climate
Authors: Barron Eric J. , Fawcett Peter J. , Peterson William H. , Pollard David , Thompson Starley L.
Published: February 2004

A series of general circulation model experiments utilizing GENESIS have been completed for the mid‐Cretaceous based on geography, variable atmospheric carbon dioxide concentrations (2 to 6 times present‐day concentrations), and variable poleward oceanic heat flux (.6 to 1.2 × 1015 W increased from present day). By combining all three major variables (CO2, geography, and oceanic heat flux), the distribution of mid‐Cretaceous temperatures can be achieved. In the simulations, increased CO2 is required to promote global warmth, and increased oceanic heat flux is required to prevent the tropics from overheating with higher levels of CO2. Four times present‐day CO2 with 1.2 × 1015 W provided the best match to the distribution of mid‐Cretaceous data. The best match to the Cretaceous observations was achieved with a globally averaged surface temperature increase of 6.2°C, at the lower end of past estimates of mid‐Cretaceous warmth. This value may be a better estimate of mid‐Cretaceous global warming. Finally, the model experiments can be used to provide a “paleocalibration” of the global warming expected for a doubling of atmospheric carbon dioxide. The best estimates for the mid‐Cretaceous appear to be a 2.5 to 4.0°C sensitivity, in the mid to upper range of the sensitivity of current climate models used to assess future global change.
Hydrographic changes of the Southern Ocean (southeast Indian Sector) Over the last 230 kyr
Authors: Labeyrie Laurent , Labracherie Monique , Gorfti Nabila , Pichon Jean Jacques , Vautravers Maryline , Arnold Maurice , Duplessy Jean‐Claude , Paterne Martine , Michel Elizabeth , Duprat Josette , Caralp Michelle , Turon Jean‐Louis
Published: February 2004

Hydrographical changes of the southern Indian Ocean over the last 230 kyr, is reconstructed using a 17‐m‐long sediment core (MD 88 770; 46°01′S 96°28′E, 3290m). The oxygen and carbon isotopic composition of planktonic (N. pachyderma sinistra and G. bulloides) and benthic (Cibicidoides wuellerstorfi, Epistominella exigua, and Melonis barleeanum) foraminifera have been analysed. Changes in sea surface temperatures (SST) are calculated using diatom and foraminiferal transfer functions. A new core top calibration for the Southern Ocean allows an extension of the method developed in the North Atlantic to estimate paleosalinities (Duplessy et al., 1991). The age scale is built using accelerator mass spectrometry (AMS) 14C dating of N. pachyderma s. for the last 35 kyr, and an astronomical age scale beyond. Changes in surface temperature and salinity clearly lead (by 3 to 7 kyr) deep water variations. Thus changes in deep water circulation are not the cause of the early response of the surface Southern Ocean to climatic changes. We suggest that the early warming and cooling of the Southern Ocean result from at least two processes acting in different orbital bands and latitudes: (1) seasonality modulated by obliquity affects the high‐latitude ocean surface albedo (sea ice coverage) and heat transfer to and from the atmosphere; (2) low‐latitude insolation modulated by precession influences directly the atmosphere dynamic and related precipitation/ evaporation changes, which may significantly change heat transfer to the high southern latitudes, through their control on latitudinal distribution of the major frontal zones and on the conditions of intermediate and deep water formation.
Tracking the sources of icebergs with lead isotopes: The provenance of ice‐rafted debris in Heinrich layer 2
Authors: Gwiazda Roberto H. , Hemming Sidney R. , Broecker Wallace S.
Published: February 2004

The provenance of ice‐rafted debris (IRD) deposited in the North Atlantic before, during, and after Heinrich event 2 has been determined through measuring the lead isotopic composition of single feldspar grains and multiple‐grain composites from the larger than 150‐µm size fraction, from cores from the eastern and western North Atlantic and from the Labrador Sea. Single‐grain analyses are used to identify the specific continental sources of the IRD, whereas composite samples are used to assess the relative IRD contributions from different sources. All single grains from Heinrich layer 2 (H 2) as well as H 2 composites plot along a correlation line on a 207Pb/204Pb versus 206Pb/204Pb diagram characteristic of the Churchill province of the Canadian shield. This is yet another strong piece of evidence that this Heinrich event was dominated by a massive iceberg discharge of the Laurentide ice sheet lobe located over Hudson Bay. In contrast, single grains from the ambient glacial sediment (above and below H 2) have multiple sources: many of them also lie along the correlation line with H 2 grains, but many others have Pb signatures consistent with derivation from the Grenville province and the Appalachian range in North America and possibly from Scandinavia and Greenland. Composites from the ambient sediment generally lie well to the right of the H 2 reference line in agreement with the results of the single‐grain analyses. The evidence provided by lead isotopes regarding the dominant role played by the Hudson Bay lobe of the Laurentide ice sheet in the development of the Heinrich events lends support to the binge/purge model advanced by MacAyeal [1993a, b] that invokes trapping of geothermal heat by the base of the icecap and subsequent basal melting as the mechanism that triggered the Heinrich events.
Turbulence and mixing in the ocean
Authors: Caldwell Douglas R. , Mourn James N.
Published: February 2004

Without turbulence and the mixing it causes, we would not have the same ocean that we do now, nor indeed the same climate. Turbulent mixing brings nutrients into the surface layer from below so that plankton can grow. Turbulence near the surface, driven by surface winds and cooling, transmits heat in and out of the ocean to create the reservoir of heat that governs climate. It is turbulence that diffuses the permanent pycnocline separating the cold bottom waters of polar origin from the atmosphere‐connected upper ocean, either directly, or indirectly by local mixing followed by distribution along isopycnals (surfaces of constant density). Turbulence in the bottom layer affects the deposition, resuspension and movement of sediments. Turbulence creates micro‐environments for the small creatures that form the basis for life in the oceans.
Solar wind corotating interaction regions: The third dimension
Authors: Gosling J. T.
Published: February 2004

A new dimension has recently been added to our understanding of solar wind structure ‐ the dimension out of the solar equatorial plane. Measurements made by the Ulysses space probe at high heliographic latitudes and powerful new 3‐dimensional numerical simulations have revealed that solar wind corotating interaction regions (CIRs) tend to be tilted systematically relative to the solar equatorial plane, at least on the declining phase of the ∼11‐year solar activity cycle. One consequence of this tilt is that with increasing heliocentric distance the forward waves associated with the CIRs tend to propagate toward and across the equator while the reverse waves tend to propagate to higher heliographic latitudes. It has been shown that tilted interaction regions are a natural consequence of the tilt of the solar magnetic dipole relative to the solar rotation axis. This new understanding of the 3‐dimensional nature of CIRs is essential to the interpretation of energetic particle measurements at high solar latitudes, and is useful for explaining certain puzzling aspects of Voyager observations in the very distant heliosphere at lower latitudes. Closer to home, there is an awakening perception of the important role played by CIRs in stimulating recurrent geomagnetic activity. The present paper provides a limited review of recent U.S. work on these topics and on other aspects of corotating interaction regions in the solar wind.
An example of fisheries oceanography: Walleye pollock in Alaskan waters
Authors: Schumacher Jim , Kendall Arthur W.
Published: February 2004

A major area of research in fisheries oceanography examines relationships between recruitment dynamics of fish populations and the marine environment. A primary goal is to understand the natural causes of variability in year‐class strength of commercially valuable species and apply this knowledge to management [Perry, 1994]. The paradigm that the majority of mortality occurs during transport of early life history stages from spawning to nursery grounds [Rothschild, 1986; Houde, 1987] provides an initial temporal focus for most research. The spatial domain includes the region occupied by early life history stages. Since global climate variability impacts regional ecosystem dynamics, however, the spatial domain often must be expanded. The relative importance and manifestation of biological factors [starvation and predation] that limit survival varies each year. Marked interannual and longer period variations in temperature (an influence on metabolic rates and behavior), transport of planktonic stages, and turbulence can exert an influence on both survival of early life history stages, and distribution of juveniles and adults. To understand how these environmental factors influence reproductive success of fish stocks also requires knowledge of the impact of these factors on predators and prey throughout the food web.
The use of isotopes and environmental tracers in subsurface hydrology
Authors: Phillips Fred M.
Published: February 2004

The term “isotope hydrology” is, perhaps, unfortunate. It refers to the application of techniques that measure isotopic abundances (i.e., relative numbers of atoms of an element having different numbers of neutrons in the nucleus) to problems in hydrology. However, “isotopic” techniques can be applied to a very wide range of hydrological problems. For example, isotopic abundances may be used as conservative tracers for transport by flowing groundwater, for estimating amounts of materials going from one phase of a system to another, for determining extents of chemical reactions in the subsurface, for identifying recharge areas of aquifers, or for estimating subsurface residence times. In general, neither the analytical techniques used nor the physical processes involved have much in common from application to application. Instead, the common thread throughout the field is a basic application of simple nuclear physics and a generally understood (within the specialty) jargon and notation.
Environmental geophysics
Authors: Phillips Jeffrey D. , Fitterman David V.
Published: February 2004

In this review we discuss selected publications during the last quadrennium (1991–1994) that involved the use or development of geophysical methods for environmental applications. The topic of environmental geophysics did not appear in the previous IUGG quadrennial report [Shea, 1991]. The principal annual conference proceedings volume related to environmental geophysics since 1988 (the Proceedings of the Symposium on the Application of Geophysics to Engineering and Environmental Problems) increased in size from just under four hundred pages in 1991 [Anonymous, 1991] to over one thousand pages in 1994 [Bell and Lepper, 1994]. These facts attest to the rapid growth of this new field.
Recent progress in snow hydrology
Authors: Bales Roger C. , Harrington Robert F.
Published: February 2004

Though limited in extent, seasonal snowpacks in the Earth's mountain ranges account for the major source of the runoff for stream flow and groundwater recharge over wide areas of the mid‐latitudes. In most alpine regions, snowmelt runoff is responsible for the annual maximum instantaneous discharge and most of the annual flow. It is therefore important to understand the processes controlling snowmelt runoff and its chemical composition for both water resources as well as ecological reasons.

Progress in snow hydrology over the past quadrennium has been heavily influenced by the availability and anticipated future availability of remote sensing data at times and spatial scales appropriate for addressing local, regional and global hydrologic issues [Dozier, 1992]. Recent research has examined topics contributing to better estimation of snowpack properties, snow distribution, snowmelt, and related chemical and biological questions. This review focuses mainly on seasonally snow‐covered alpine areas, but includes other research potentially applicable to alpine areas of the Earth.
The atmospheric oxygen cycle: The oxygen isotopes of atmospheric CO2 and 02 and the 02/N2 ratio
Authors: Keeling Ralph F.
Published: February 2004

Oxygen is the most abundant element in the earth's crust, it accounts for 89% of the mass of the ocean, and it is the second most abundant element in the earth's atmosphere. Much work on the oxygen cycle has focused on the question of the origin of atmospheric 02 and its variations over geologic time [see Kump et al, 1991, and references therein]. This review focuses on several other aspects of the oxygen cycle including the short‐term controls on the oxygen isotopic abundance of atmospheric CO2 and O2, and the short‐term variabilitiy in the O2/N2 ratio.

These aspects of the oxygen cycle depend mainly on material exchanges between the atmosphere and living organisms at the earth's surface or in the ocean. Like several other atmospheric variables which have received much attention recently, e.g., the abundances of CO2, CH4, and N2O, the oxygen isotopic content of CO2 and O2 and the O2/N2 ratio have atmospheric lifetimes that are long relative to the time scale of atmospheric mixing and thus reflect an integration of material exchanges over the globe. Recently, our knowledge of these variables has expanded through laboratory experiments exploring the exchange pathways, and through measurements on contemporary air samples or in ancient air samples extracted from polar ice cores. This review summarizes recent literature on these subjects, and also emphasizes how these aspects of the global oxygen cycle can provide new information on the material exchanges between the atmosphere and biota integrated over large areas.
Space weather prediction
Authors: Maynard Nelson C.
Published: February 2004

Energy from the Sun impacts the near‐Earth environment to create a myriad of hazards to systems operating in and through space, and even to ground based activities. Costly systems are at risk. Already space storms cause averaged annual losses estimated to exceed $100M. The space weather effects from the severe magnetic storms during this past solar maximum and the recent failure (1994) of the Anik satellite have emphasized the risk. The Solar‐Terrestrial predictions Workshop, held in Ottawa in 1992, brought forecasters, customers and the physics community together in a common forum to present and discuss recent advancements. The proceedings of these meetings [Solar‐Terrestrial Predictions ‐ IV, 1993[ provide a source book of effects and attempts to mitigate those effects.
Loess magnetism
Authors: Heller Friedrich , Evans Michael E.
Published: February 2004

Loess is a wind‐blown Quaternary silt deposit that blankets vast tracts of land and in places reaches thicknesses in excess of 300 m. Over the last decade it has emerged that certain loess sections have recorded the polarity history of the geomagnetic field and now provide essentially continuous magnetostratigraphic archives covering the last 2–3 m.y. Indeed, it is the chronology provided by the magnetic polarity signature itself that was largely responsible for establishing the timing of the initiation of loess accumulation, particularly in the celebrated Chinese loess plateau, where a starting date close to the Gauss‐Matuyama chron boundary (2.6 Ma) is now firmly established. This coincides with a widely documented global climatic shift and accelerated uplift of the Tibetan plateau. Many loess sections contain fossil soils (paleosols) that bear witness to warmer and wetter climatic conditions corresponding to interglacial periods in contrast to the cold, arid environments in which pristine loess accumulated and which correspond to glacial intervals. The resulting sequences of alternating loess and paleosols also manifest themselves magnetically, in this case in terms of susceptibility changes, entirely distinct from the remanence characteristics, which encode the geomagnetic polarity. The susceptibility time series obtained from localities in Alaska and China correlate remarkably well with the oceanic oxygen isotope signal and yield spectral power estimates in agreement with those predicted by the astronomical (Milankovitch) theory of ice ages. Comparison of susceptibility patterns with corresponding profiles of 10Be concentration in loess allows major changes in rainfall to be estimated. In China, for example, data spanning the last 130 kyr (corresponding to oxygen isotope stages 1–5) indicate that paleoprecipitation was almost halved (from ∼540 to ∼310 mm yr−1) as the warm interglacial during which paleosol S1 formed gave way to the following glacial interval in which loess layer L1 accumulated. It has also been found that increased amounts of continent‐derived dust delivered to the deep ocean correlate with loess formation and thereby permit certain broad features of atmospheric circulation (paleowinds) to be worked out. Debate continues over the actual mechanism by which magnetic susceptibility becomes a climate proxy. The current consensus is that some form of in situ process must be responsible, at least in part. Detailed laboratory investigations, both on whole samples and on magnetic extracts, indicate that the enhancement observed in midlatitude weathered loess and paleosols is largely due to a magnetically “soft” mineral which is either magnetite (Fe3O4) or maghemite (γ‐Fe2O3). Experimental evidence is accumulating that tiny (<100 nm) ferromagnetic particles probably generated by the activity of magnetotactic bacteria in the soil are responsible.
Recent developments in hydrologic data assimilation
Authors: McLaughlin Dennis
Published: February 2004

Data assimilation is a term that is most closely associated with the atmospheric sciences. It arises from the meteorological custom of constructing daily weather maps which show how environmental variables such as pressure and wind velocity vary over space (see Daley [1991] for a good historical review). Such maps are useful both for short‐term forecasting, where they provide initial conditions for numerical weather prediction models, and for more long‐term climatic analysis, where they can be used to reveal regional trends [Bengtson and Shukla, 1988; National Research Council, 1991; Shubert et al, 1993].

For many years weather maps were derived from a limited number of measurements collected from surface stations and radiosondes. The mapping process required a good understanding of atmospheric physics and was typically carried out by hand, using the methods of ‘subjective analysis’. In the first half of the twentieth century efforts were made to standardize and automate meteorological mapping. The quantitative procedures which grew out of these efforts were commonly called ‘objective analysis’ methods [Gandin, 1963]. Objective analysis algorithms provide spatially distributed descriptions of atmospheric conditions which are consistent both with observed data and with kinematic (‘diagnostic’) principles (such as the geostrophic requirement that the pressure gradient and Coriolis force must balance). These algorithms produce ‘snapshots’ portraying conditions everywhere in a given region at a particular time.
Recent advances associated with flood forecast and warning systems
Authors: Krzysztofowicz Roman
Published: February 2004

Floods remain one of the most frequent and devastating natural hazards worldwide. In the United States alone, there are 20,000 flood‐prone communities; 3,000 of them receive site‐specific flood forecasts from the National Weather Service (NWS), and 1,000 have local warning systems; the remaining communities receive county‐wide warnings. Between 1965 and 1985, floods accounted for 63% of the federally declared disasters (337 out of 531), took 1,767 lives, and caused $5 billion worth of damage annually, on the average.

The Great Flood of 1993, documented by the National Oceanic and Atmospheric Administration [NOAA, 1994], provided a vivid demonstration of Cromwell's rule: one should never assign the exceedance probability of zero to any prior observation. The duration (from March to November), the extent (over nine states) and the magnitude (exceeding previous floods of record at 95 forecast points) made this the most catastrophic flooding in modern U.S. history: 54,000 persons were evacuated, 50,000 homes were damaged, and economic losses of $15–20 billion have been estimated. The event also tested the limits of the Nation's forecast and warning services as flood stages were exceeded at about 500 forecast points.
Marine biological diversity: Some important issues, opportunities and critical research needs
Authors: Butman Cheryl Ann , Carlton James T.
Published: February 2004

Marine biological diversity is changing, dramatically in some cases, and most recent changes are due to broad‐scale human activities. Knowledge of “biodiversity” — the variety of genomes (the genetic material specifying all characteristics and functions within an organism), species and ecosystems — is the foundation for understanding and predicting how human and natural effects can change the ocean's ecosystems. Evaluating the scale and ultimate consequences to life in the sea of a plethora of anthropogenic effects is difficult, however, because there is inadequate knowledge of both the patterns of and the processes that control marine biodiversity.

Recognizing change and evaluating its consequences require sufficient knowledge of present and historical natural patterns of biodiversity, and sufficient understanding of how and why these patterns vary in space and time. Data on biodiversity patterns and their causes are sorely lacking for most marine ecosystems. Adequate understanding of what creates and maintains diversity must be the scientific underpinning for policy decisions regarding pollutant and waste disposal, habitat alteration, fisheries management and the preservation of threatened or endangered species. The inability, at this time, to provide such information to policy makers may have important implications for the conservation of marine life [Norse, 1993].
Geometry of heat and mass transfer in dry snow: A review of theory and experiment
Authors: Arons E. M. , Colbeck S. C.
Published: February 2004

Porous materials are common on the Earth's surface and in the crust. Accordingly, their physical properties have received a lot of attention. A century ago, Maxwell and Rayleigh each modeled the physical properties of aggregate materials as discrete spheres embedded in continuous matrices. Although the particles of interest in snow are not spheres and do have interconnections, these basic models give first‐order predictions of the thermal conductivity. In the last 3 decades, scientists have attempted to make the predictions more precise by determining the effect of geometry on heat and mass flow using basic physical models and data collected from images of planar sections of aggregates. Under favorable circumstances, physical parameters and quantitative microscopic parameters of an aggregate may be highly correlated, but physical understandings of the geometric effects are not likely to arise from such studies until physical models can be based on measurable fundamental parameters. In snow, as in other aggregates, that goal seems to be a long way from realization.
A brief history of magnetospheric physics during the space age
Authors: Stern David P.
Published: February 2004

After 1958, when scientific satellites began exploring the Earth magnetic environment, many puzzling phenomena could be directly examined, especially the polar aurora and disturbances of the Earth's magnetic field [see Stern, 1989a]. The notion of the solar wind, also introduced in 1958, helped clarify the role of the Sun in driving such phenomena. The large‐scale structure of the magnetosphere, the space region dominated by the Earth's magnetic field, was gradually revealed within the next decade: its trapped particles, its boundary, and its long magnetic tail on the nightside. Inevitably, however, at a more fundamental level, the new discoveries led to new questions about the transfer of energy, the flow patterns of plasmas and electric currents, the acceleration of the aurora, and transient events such as magnetic substorms and storms, which energized ions and electrons. Though significant progress has occurred in some of these areas, many unresolved issues still remain. This review outlines the history of magnetospheric research, draws some general conclusions, and provides an extensive bibliography.
Comparison of simultaneous wind measurements using colocated VHF meteor radar and MF spaced antenna radar systems
Authors: Cervera Manuel A. , Reid Iain M.
Published: February 2004

Comparisons of wind velocities at heights from 80 to 98 km have been made using two different techniques. The first method involves the determination of winds using meteor drifts (e.g., Avery et al., 1990; Stubbs, 1973). This was done by observing meteors using the University of Adelaide VHF radar situated approximately 40 km north of Adelaide, Australia, at Buckland Park. The second method used to determine winds was the spaced antenna technique (e.g., Briggs, 1984) using an MF radar at the same site. The two radar systems are independent, the VHF radar operating at 54.1 MHz and the MF radar at 1.98 MHz. The spatial separation of the two radars is approximately 600 m. Simultaneous data obtained from September 10 to 20, 1993, are presented here. The agreement between the two techniques is good below 90 km, while above 90 km we find that the spaced antenna technique yields smaller wind speeds than the meteor drift technique. Several possible reasons for these discrepancies are discussed.
A simple model of atmospheric radar backscatter: Description and application to the full correlation analysis of spaced antenna data
Authors: Holdsworth David A. , Reid Iain M.
Published: February 2004

A model has been developed for simulating the effects of backscatter from scatterers advected with a mean background wind. This model has been designed to be as simple yet as realistic as possible, allowing the simulation of both spaced antenna and Doppler radars, and includes features such as aspect sensitivity, gravity wave perturbations, and turbulent motions. The model simulates the characteristics of radar backscatter very well at both MF and VHF. Results of the application of the full correlation analysis to model data generated for the spaced antenna configuration are presented, revealing good agreement with the model input velocity. The effects of the sampling time upon the full correlation analysis are investigated, suggesting an upper limit for the successful application of the technique. The triangle size effect of the full correlation analysis is also investigated, confirming that the major cause is the failure to properly compensate for the effects of noise. The application of techniques for the estimation of turbulent velocities and aspect sensitivity from model‐generated data have also proven successful.
Fine structure of the auroral kilometric radiation: A Fermi acceleration process?
Authors: Farrell W. M.
Published: February 2004

The fine structure of the auroral kilometric radiation is explained as a nonlinear interaction between the locally generated cyclotron emission created in an electron plasma cavity and the cavity boundary. Specifically, it is demonstrated that broadband cyclotron emission can form discrete tones after numerous interactions with an oscillating boundary that has quasi‐monochromatic wavelike motion. This boundary will Doppler shift most radio photons in a stochastic way, creating a diffuse background radio component. However, some radio photons will have regular, stable frequencies that form discrete tones that overlie on the diffuse background emission. The discrete tones are created in situations where the photon travel time in the cavity is an integer multiple of the boundary oscillation period, this effect establishing a resonance between the boundary oscillations and photon. A set of coupled nonlinear equations is used to describe the radio photon/cavity boundary interaction. Effects of wave growth in the local density cavity and boundary reflections are also included. As the character of the cavity slowly changes, the resonance condition also changes in an adiabatic way, shifting the resonance to different frequencies. The net result is the creation of drifting radio tones which are comparable to those actually observed on radio spectrograms of the auroral kilometric radiation.
Inference of raindrop size distributions from measurements of rainfall rate and attenuation at infrared wavelengths
Authors: Maitra A. , Gibbins C. J.
Published: February 2004

A new technique is proposed to infer the parameters in a generalized three‐parameter gamma function model for the distribution of drop sizes in rain, from measurements of rainfall rate and path attenuation through the rain at infrared wavelengths, where raindrop cross sections are essentially independent of frequency, and comparison with simultaneously measured rain attenuations in the millimetric wavebands. The technique is shown to be single‐valued and stable, for a particular form of the gamma function. The resultant drop size distributions have been used to calculate millimeter‐wave rain attenuations which are in excellent agreement with those measured.