bluuebunny/crossref_metadata_2025 huggingface dataset:
Preliminary results from POAM II: Stratospheric ozone at high northern latitudes
Authors: Randall C. E. , Rusch D. W. , Bevilacqua R. M. , Lumpe J. , Ainsworth T. L. , Debrestian D. , Fromm M. , Krigman S. S. , Hornstein J. S. , Shettle E. P. , Olivero J. J. , Clancy R. T.
Published: February 2004

We present results from the first 18 months of measurements by the Polar Ozone and Aerosol Measurement experiment (POAM II;) in the northern hemisphere. POAM II was launched on 25 September 1993, onboard the SPOT‐3 satellite into a sun‐synchronous polar orbit. The results presented here span a latitude range from about 55° to 71°, and an altitude range from about 18 to 35 km. Our results compare well with SAGE II data from 1986 to 1991. The observed variability in the zonally‐averaged ozone retrievals is due to a convolution of the true seasonal variation in ozone with the seasonal variation in latitude of the POAM II measurements. The seasonal variations in ozone at different altitudes reflect a transition between summer‐time photochemical and dynamical control around 25 km. The longitudinal variation in ozone densities correlates well with the position of the measurement with respect to the polar vortex. Mixing ratios inside the vortex during the winters of 1993–1994 and 1994–1995 are indicative of enhanced descent within the vortex, as well as other dynamical processes and possibly chemical depletion.
Shoreward intrusion of upper‐layer warm water by prescribed shelf‐break temperature perturbation and surface wind stress
Authors: Xie L. , Pietrafesa L. J.
Published: February 2004

A new mechanism for mid‐shelf frontogenesis in shelf waters off the Carolina Capes is proposed based on results from three numerical experiments using a three‐dimensional coastal ocean model. We find that quasi‐geostrophic currents induced by a density (temperature) anomaly at the shelf break may advect upper‐layer waters from the shelf break to the mid shelf. This process can cause mid‐shelf frontogenesis even in the absence of favorable wind forcing. However, persistent northerly winds can substantially enhance mid‐shelf frontogenesis, and increase the along‐shore scale of the mid‐shelf fronts off the Carolina Capes.
A two‐layer attenuation model for the upper mantle at short periods
Authors: Sharrock D. S. , Main I. G. , Douglas A.
Published: February 2004

Estimates of maximum mean P‐wave attenuation (described by the quality factor Qα) are used to make a two‐layer model of Qα in the period range 0.125–1 s for the northwest Pacific subducting region. A shallow highly attenuating layer (Qα ≈ 150) of only 85 km thickness overlays a less attenuating layer to a depth of 450 km (Qα > 1000). The added bandwidth made available by the use of array data yields key information for testing the validity of textbook models predominantly based on extrapolation from longer period data. We find that seismic attenuation at short periods appears to behave differently to long‐period attenuation. This reversal is represented by a modification to the absorption band model obtained from longer period data.
Using chlorofluorocarbons to assess ocean climate models
Authors: England Matthew H.
Published: February 2004

The potential for using chlorofluorocarbons (CFCs) to assess ocean climate models is explored within a series of global ocean experiments. The ocean model simulations are run under identical wind stress and thermohaline forcing, but with three different formulations of subgrid‐scale mixing. Two passive tracers are included in the equilibrated models, representing the dissolved concentrations of CFC‐11 and CFC‐12 in seawater. The resulting model simulations are then compared directly with observed CFC levels in key areas for deep and bottom water formation. CFC‐11 uptake is found to be overestimated in the Southern Ocean when mixing rates are defined in traditional Cartesian co‐ordinates. The inclusion of an isopycnal mixing scheme (which is often used in coupled ocean‐atmosphere models) actually degrades the CFC‐11 simulation by blending water masses too strongly, particularly in the Southern Ocean. The spurious uptake of CFC‐11 at 55°–70°S suggests that certain climate models might overestimate the role of the Southern Ocean in moderating climate change. A more sophisticated mixing parameterization that simulates the effects of subgrid‐scale eddies on the mean ocean flow (and allows for zero lateral diffusion) is seen to greatly reduce CFC‐11 uptake in the Southern Ocean. Climate models that adopt this new mixing scheme are likely to predict a more rapid CO2‐induced warning over the Southern Hemisphere.
Differences between the 0.35–1.0 MeV/nucleon H/He ratio in solar and Co‐rotating events at high heliolatitude
Authors: Simnett G. M. , Sayle K. A. , Roelof E. C.
Published: February 2004

We discuss measurements from the Ulysses spacecraft of the 0.35–1.0 MeV/nucleon H/He intensity ratio at high heliolatitudes. In early 1994 two transient solar events were detected in the gaps between particle intensity increases associated with the passage at low latitude of a co‐rotating interaction region. The H/He ratio was ≳ one order‐of‐magnitude lower in the co‐rotating events than in the transient solar events. Several similar instances, but not so cleanly separated, were observed from mid‐1992 to the end of 1993. We interpret the lower H/He ratio in recurrent events as the result of efficient acceleration of interstellar pickup He+ at corotating reverse shocks to which Ulysses remains connected even at high heliolatitudes.
Distant tail plasma jetting and Bz properties at slow‐mode shocks: A model of reconnection during northward IMFs
Authors: Ho C. M. , Tsurutani B. T.
Published: February 2004

Previous distant geotail studies find a difference in the locations where the plasma flow reverses direction (x ≈ −120 Re) and where the magnetic field Bz reverses (x ≈ −200 Re). These results raise some questions about the standard Petchek reconnection model and its applicability. In this study, we use 66 slow‐mode shock events to study the flow properties both earthward and tailward of the x‐type neutral line. The location of the neutral line relative to the spacecraft is determined by: a) use of the measured slow‐mode shock orientation, and b) the magnetic Bz polarity. We find that plasmasheet flow speeds downstream of slow shocks are similar, using either of the above two methods. On average, for events tailward of the neutral line, the tailward flow speed is statistically higher than for earthward cases by ∼100–150 km/s. This is consistent with magnetic reconnection where jetting plasma flows of 50–75 km/s are superposed on top of a more‐or‐less continuous high speed tailward convection flow of ∼ 600 km/s. By examining the relationship between these slow shock events in the distant tail and upstream IMF orientations, we also find that a significant amount (40%) of slow shock events occurs during northward IMFs. Thus, we propose a distant tail model of reconnection during northward IMF periods. Using this model and the standard substorm reconnection model (southward IMF cases), we believe we can explain all observations in this paper.
A new technique to model plasmoid magnetic field signatures
Authors: Nakamura T. K. , Nagai T. , Kazama Y. , Amano K. , Yamamoto T. , Kokubun S.
Published: February 2004

A new fitting method has been developed and applied to the plasmoid observations of the GEOTAIL satellite. This method, which we call “soft fitting”, is regarded as one kind of least square method, and can determine both the fitting function and fitting parameters simultaneously. Its application to magnetic field observations by the GEOTAIL satellite gives an average shape of plasmoid Bz bipolar structures. The method can also provide information about the velocity and spatial size of plasmoids from the optimal fitting parameters. The result indicates that the velocity and size become larger as a plasmoid propagates tailward.
Meteor‐3/TOMS observations of the 1994 ozone hole
Authors: Herman Jay R. , Newman Paul A. , Larko David
Published: February 2004

The development of the 1994 springtime (September–November) Antarctic ozone hole was observed by the Meteor‐3/TOMS (Total Ozone Mapping Spectrometer) to result in a very low minimum ozone value, 90±5 DU (Dobson Units) on September 28, 1994. During late September and early October, the region of extremely low ozone values was centered on the geographical pole between 85°S and 90°S. The geographical extent of the ozone hole region, the area within the 220 DU contour, reached a maximum during the first week in October with an elliptical area covering 24 × 106 km², reaching to the southern tip of South America. This approximately matched previous area records. After the maximum area was reached in early October, the 1994 ozone hole region was very similar to the 1993 ozone hole throughout the remainder of the month. The area of low temperatures (<196 K), where polar stratospheric clouds (PSCs) can form and heterogeneous chemistry is significant, has not increased over the past 16 years. During this period, the large trends in the area and minimum ozone amounts of the Antarctic ozone hole do not appear to be related to atmospheric temperature trends.
Behavior of the East Antarctic Ice Sheet as deduced from a coupled GCM/ice‐sheet model
Authors: Verbitsky Mikhail , Saltzman Barry
Published: February 2004

While the possible instability of the West Antarctic ice sheet has been widely recognized for some time as a potential source of sea‐level rise in an enhanced greenhouse warming, the stability of the East Antarctic ice sheet has only recently become the subject of such a conjecture. We approach an aspect of this issue using a numerical experiment with an atmospheric general circulation model (GCM) coupled to a 3‐dimensional ice‐sheet model. Response of the ice sheet model to the external forcing generated by an atmospheric GCM due to doubling the CO2 concentration does not show any appreciable changes in the horizontal extent of the ice sheet due to normal creep and topographic instabilities, suggesting that an Antarctic collapse resulting from these factors is unlikely. The mechanics of basal sliding, non‐isothermal effects, and ice shelves are as yet too poorly understood to make quantitative estimates of possible instabilities due to these processes.
Tailward flowing energetic oxygen ion bursts associated with multiple flux ropes in the distant magnetotail: GEOTAil observations
Authors: Wilken B. , Zong Q. G. , Daglis I. A. , Doke T. , Livi S. , Maezawa K. , Pu Z. Y. , Ullaland S. , Yamamoto T.
Published: February 2004

An event of tailward flowing energetic (144–7959 keV) oxygen ion bursts was observed in the distant magnetotail (X=−63, Y=+7, Z=−3.8 RE) on February 13, 1994. The observations were made with the HEP‐LD spectrometer on board the GEOTAIL spacecraft. The event was associated with magnetic field signatures characteristic of multiple flux ropes. During the event, which lasted from 1847 to 1907 UT, strong impulsive increases in the oxygen flux were observed. From 1846 to 1900 UT the proton counting rate also exhibited an increase, followed by a decrease until the end of the oxygen event. The oxygen flux was confined to a rather narrow range in polar and azimuthal angle (only 7–10% of 4π was occupied). This implies a streaming distribution or beam‐like structure. Comparison of the particle flow angles with the polar and azimuthal angles of the magnetic field indicates that the ion beam may have been embedded in flux ropes, which may be connecting the polar ionosphere and the distant magnetotail. During the observed oxygen event the ratio
is significantly higher than the ratios usually found in the center of the distant magnetotail. There is some evidence that the observed oxygen ions were more efficiently accelerated in this event than hydrogen and helium ions.
Anisotropy of inertial range turbulence in the polar heliosphere
Authors: Horbury T. S. , Balogh A. , Forsyth R. J. , Smith E. J.
Published: February 2004

A variance analysis of high frequency, inertial range fluctuations in the polar magnetic field as recorded by the Ulysses spacecraft indicates that they are largely transverse to the ambient magnetic field direction and highly anisotropic. Despite large changes in the mean field direction caused by the presence of large amplitude Alfvén waves, alignment of minimum variance vectors of 5 minute intervals of linearly detrended data with the mean field direction was good, with around 75% of minimum variance vectors lying within 26° of the mean field direction during a typical 5 day interval. Such fluctuations transverse to the mean field have anisotropies—the ratio of power transverse to the field to that parallel—of around 30. We find a small tendency for the field‐transverse fluctuations to become more isotropic with distance. Intervals whose minimum variance directions are not field‐aligned appear to be indicative of a significantly different type of fluctuations, with higher total variances and lower anisotropy.
Observation of polar mesospheric clouds in summer, 1993 by the WINDII Instrument on UARS
Authors: Evans W. F. J. , Laframboise L. R. , Sine K. R. , Wiens R. H. , Shepherd G. G.
Published: February 2004

Satellite images of polar mesospheric clouds (PMCs) were taken in support of the 1993 ANLC campaign. In July, 1993, they were common at latitudes north of 65°N but increased in abundance poleward to the limit of our viewing horizon of 72°N. The southern boundary edge of the PMCs was observed to move northwards as the season progressed in 1993. Compared with the climatology of other years, the ANLC campaign observations were taken towards the end of a season in a year of modest PMC activity. WINDII, the wind imaging interferometer on the UARS satellite, is a new effective tool in the study of polar mesospheric clouds. Images of the limb give vertical distributions of the light scattered by the molecular and the particle atmosphere. Detection of the PMCs against the Rayleigh background showed that the peak altitude was around 83 km in 1993.
Observations of spectra of intensity fluctuations of the OH Meinel nightglow during ALOHA‐93
Authors: Hecht James H. , Ramsay Howat Suzanne K. , Walterscheid Richard L. , Isler Joseph R.
Published: February 2004

Observations of the frequency and 2D horizontal wave number spectra are reported from airglow observations taken at Hawaii on October 8, 1993. The average values for the slopes of the frequency and wave number spectra are −2.2±0.3 and −2.6±0.2, respectively. These results are consistent with the predictions of the separable model of Gardner et al. [1993a] but inconsistent with the diffusive filtering theory of Gardner [1994]. The average frequency spectrum shows little evidence of significant power at periods below 5 minutes, the Brunt‐Vaisala period. However, during a single one hour observation period there is increasing power at periods below 3 minutes. This could indicate the presence of acoustic waves at mesopause altitudes.
Stress drop distribution of the aftershocks of the 1993 Hokkaido‐Nansei‐Oki Earthquake
Authors: Fujita Eisuke , Iio Yoshihisa , Fukuyama Eiichi
Published: February 2004

The Hokkaido‐Nansei‐Oki earthquake (M=7.8) occurred off the south‐west coast of Hokkaido, Japan, at 22:17 (JST) on July 12, 1993. We observed its aftershocks by broad‐band seismometers at five stations for about four months. Our analysis of the broad‐band data indicates that the stress drops of aftershocks have a regional dependency. The stress drops in the central part of the aftershock zone are larger than those in the northern and the southern parts. This result suggests that the stress field in this region is closely related to some previous seismic events that occurred in the vicinity.
Detection of auroral activity using GPS satellites
Authors: Coker Clayton , Hunsucker Robert , Lott Gus
Published: February 2004

GPS (Global Positioning System) satellites and a receiver located at Fairbanks, Alaska are used to detect auroral activity. A technique for using GPS total electron content (TEC) data to detect auroral‐E ionization (AEI) at all satellite line‐of‐sight elevations is presented. The location of AEI during auroral substorms is determined and is consistent with simultaneous magnetometer data. Maps of detected AEI events reveal the distribution of AEI in space and time. Additionally, a technique is presented for identifying the effects of the auroral oval E‐layer on the TEC data. Particle precipitation measured by the TIROS satellite is closely related to variations in the TEC data. The effects of the oval are consistently seen in the TEC data for a variety of magnetic conditions. The location of the equatorward edge of the oval is determined during auroral substorms and compares well with a model of the oval and with individual TIROS passes.
Reconstruction of solar irradiance since 1610: Implications for climate change
Authors: Lean Judith , Beer Juerg , Bradley Raymond
Published: February 2004

Solar total and ultraviolet (UV) irradiances are reconstructed annually from 1610 to the present. This epoch includes the Maunder Minimum of anomalously low solar activity (circa 1645–1715) and the subsequent increase to the high levels of the present Modern Maximum. In this reconstruction, the Schwabe (11‐year) irradiance cycle and a longer term variability component are determined separately, based on contemporary solar and stellar monitoring. The correlation of reconstructed solar irradiance and Northern Hemisphere (NH) surface temperature is 0.86 in the pre‐industrial period from 1610 to 1800, implying a predominant solar influence. Extending this correlation to the present suggests that solar forcing may have contributed about half of the observed 0.55°C surface warming since 1860 and one third of the warming since 1970.
Magnetosheath flow near the subsolar magnetopause: Zwan‐Wolf and Southwood‐Kivelson theories reconciled
Authors: Southwood David J. , Kivelson Margaret G.
Published: February 2004

We reconcile the superficially contradictory theories of flow immediately upstream of the subsolar magnetopause. We show that the formation of a layer of enhanced field and depressed density immediately adjacent to the magnetopause as predicted by Zwan and Wolf appears to require the presence upstream of a region of enhanced pressure and field rarefaction as predicted by Southwood and Kivelson. We thus argue that the detached regions of enhanced density and the depletion layer adjacent to the magnetopause are actually manifestations of a single phenomenon.
Earthquakes as a coupled shear stress‐high pore pressure dynamical system
Authors: Miller Stephen A. , Nur Amos , Olgaard David L.
Published: February 2004

The migration, coalescence and localization of slip, seismicity, and zones of high pore pressure are modeled using a porosity reduction mechanism to drive pore pressure within a fault zone in excess of hydrostatic. Increased pore pressure in discrete cells creates zones of low effective stress, which induces slip that may propagate to surrounding cells depending on the local state of stress. At slip, stress is transferred using the solution for a rectangular dislocation in an elastic half‐space, and pore pressures are redistributed by conserving fluid mass. Using simple assumptions about fault rheology and permeability, it is shown that the interaction between shear stress and effective stress evolves to a state of earthquake clustering with repeated events, locked zones, and large variations in fault strength. The model evolves from a uniform shear stress state on a strong fault, to a heterogeneous shear stress state on a weak fault.
The effects of low frequency waves on ion trajectories in the Earth's magnetotail
Authors: Cattell Cynthia , Roth Ilan , Linton Mark
Published: February 2004

The trajectories of ions in the Tsyganenko magnetic field model with a convection electric field have been compared to the trajectories when a perturbation electric field based on ISEE‐1 and Geotail observations of lower hybrid frequency waves is included. The inclusion of waves dramatically modifies the characteristics of the ion trajectories. For example, initial conditions which result in adiabatic orbits in the absence of waves are often non‐adiabatic when waves are included. In addition, both the regions of space accessible to the particles and the energization are changed. Although only individual trajectories were examined in this study, it is argued that the effect of the waves is to mix previously distinct regions of phase space.
Polar ice stratigraphy from laser‐light scattering: Scattering from ice
Authors: Ram Michael , Illing Matthias , Weber Peter , Koenig Gerson , Kaplan Michael
Published: February 2004

We demonstrate that laser‐light scattering (LLS) off glacial (pre‐Holocene) polar ice can be used to measure variations in dust concentration along sections of bubble‐free ice core. We have used this technique with considerable success on the GISP2 ice core that was retrieved from central Greenland down to bedrock. The technique is fast, non‐destructive and has a very high resolution (1 mm or less).
Ulysses observations of opposed tilts of solar wind corotating interaction regions in the northern and southern solar hemispheres
Authors: Gosling J. T. , Feldman W. C. , McComas D. J. , Phillips J. L. , Pizzo V. J. , Forsyth R. J.
Published: February 2004

Data obtained during Ulysses' rapid northbound traverse across the heliographic equator provide evidence for predicted, opposed north‐south tilts of corotating interaction regions formed from streams originating in the northern and southern solar hemispheres respectively. In both hemispheres, reverse waves that were propagating poleward were observed poleward of the latitudes where the fast‐slow wind interaction occurred. Forward waves, on the other hand, were observed only within the low‐latitude band of wind variability, consistent with the prediction of systematic, opposed tilts. However, the evidence for opposed north‐south tilts within the low‐latitude band of variability was less conclusive.
An additional low layer transport of Sahelian and Saharan dust over the north‐eastern Tropical Atlantic
Authors: Chiapello I. , Bergametti G. , Gomes L. , Chatenet B. , Dulac F. , Pimenta J. , Suares E. Santos
Published: February 2004

Mineral dust concentrations have been measured from a monitoring aerosol station set up at Sal, Cape Verde Island between December 1991 and December 1994 in order to assess the transport process of African dust over the North‐eastern Tropical Atlantic. These measurements indicate a pronounced seasonal pattern, with maximum dust concentrations observed during winter. A meteorological analysis shows that the transport of dust occurs at low altitudes, in the trade winds layer, during this season. Large quantities of dust are carried out of North‐western Africa, in particular from the Sahel at these altitudes. Such process could constitute the major supply of atmospheric mineral matter to the surface sea water of the Eastern Atlantic.
Comparison of broadband and short‐period seismic waveform stacks: Implications for upper‐mantle discontinuity structure
Authors: Ritsema Jeroen , Hagerty Michael , Lay Thorne
Published: February 2004

Stacks of short‐period and broadband seismic waveforms from four deep (h > 550 km) earthquakes in South America recorded in California exhibit small amplitude signals between the direct P and surface‐reflected pP phases. The anomalous and variable slownesses of these signals in short‐period stacks, as well as differences between short‐period and broadband stacks suggest that the weak arrivals originate by reflection from laterally varying structure in the mantle near the subduction zone. The only structure consistently producing near‐source and near‐receiver reflections is the “410 km” discontinuity, which varies in depth by ±10 km, and has an impedance contrast comparable with that predicted by reference Earth models.
Model calculations of ozone depletion in the Arctic Polar Vortex for 1991/92 to 1994/95
Authors: Chipperfield M. P. , Lee A. M. , Pyle J. A.
Published: February 2004

We have used a 3D chemical transport model to investigate the potential for chemical ozone depletion in the Arctic polar vortex for the past 4 winters. By using the same chemical initial conditions for each winter we have isolated the effects of meteorological variability on polar ozone loss. These calculations show that during 1994/95 conditions in the Arctic polar vortex were the most conducive to ozone depletion in recent years. Our numerical experiments show that at 475 K (around 18 km) in the lower stratosphere the chemical ozone destruction between late December and mid March was greater than 30% over a large area of the polar vortex. Larger percentage losses, reaching 50%, occur at slightly lower altitudes. The average model depletion in the entire region poleward of 60°N over the same period was around 22% at 475 K. Similar calculations for the preceding three Arctic winters show less depletion. The large depletion for 1994/95 is a consequence of the extreme meteorological conditions during this winter.
Volatile inorganic Cl in surface air over eastern North America
Authors: Maben John R. , Keene William C. , Pszenny Alexander A. P. , Galloway James N.
Published: February 2004

Volatile inorganic Cl in surface air over eastern North America was selectively measured using a tandem‐mist‐chamber technique with known collection efficiencies for HCl, HOCl, and Cl2. Mixing ratios of total alkaline‐reactive inorganic Cl (Clt) and HCl* (including HCl and possibly NOCl, ClNO2, and ClNO3) were statistically indistinguishable ranging from <39 to ≈ 2800 pptv; most were <300 pptv. Those of Cl* (including Cl2 and 56% HOCl) were <26 pptv Cl; anthropogenic influences were undetected. In addition, pre‐ and post‐sunrise concentrations of HCl* were similar suggesting insignificant Cl photochemistry at dawn. HCl appears to be the dominant form of volatile inorganic Cl over eastern North America. Atomic chlorine is probably not an important oxidant in the polluted continental boundary layer.
Vertical motion and ice thickness variation in western North America
Authors: Trupin Andrew S. , Easson Damien A. , Han DaZhong
Published: February 2004

Maps of the ice covered area of western North America and records of mass balance of 23 mountain glaciers in this region, were used to construct a gridded data set of average mass balance and to calculate a detailed description of time averaged radial displacement (uplift) in the region for the period, 1961–1990. While the region studied is tectonically active, there is some agreement between the rates of vertical uplift at several tide gauge sites along the Inside Passage of Alaska, and the measured sea level drop at these stations. The average sea level contribution from the melting of western North American glaciers, calculated from these gridded data is 0.4±0.2 mm/yr, and is greater than prior estimates for the same time period.
VAN: Candidacy and validation with the latest laws of the game
Authors: Mulargia Francesco , Gasperini Paolo
Published: February 2004

We reassess the set of VAN predictions in the period 1987–1989 with the latest laws of the game [Varotsos et al., 1996]. This reassessment does not modify our previous conclusions: VAN predictions have alarm and success rates too low to accept them as candidate precursors, and a degree of time association with earthquakes which suggests rejection of any precursor nomination. At the same time, this reassessment confirms the tendency of predictions in the period 1987–1989 to significantly follow earthquakes, with 13 earthquakes tracked by a spatially close prediction within 11 days. A validation study of the independent set of VAN predictions in the period 1990–1992, leaving the laws of the game unchanged while restricting the operative region to account for network reduction, denies any significant association of VAN predictions with earthquakes, but confirms the tendency of VAN predictions to follow rather than precede earthquakes.
High altitude discharges and gamma‐ray flashes: A manifestation of runaway air breakdown
Authors: Taranenko Yuri , Roussel‐Dupré Robert
Published: February 2004

γ‐ray flashes of atmospheric origin as well as blue jets and red sprites are naturally explained by high‐altitude discharges produced by runaway air breakdown. We present the first detailed model of the development of upward propagating discharges and compute optical and γ‐ray emissions that are in excellent agreement with observations. According to our theory, such discharges represent the first known manifestation of runaway air breakdown, a fundamental new process in plasma physics.
Large scale structures in the magnetosheath: Exogenous or endogenous in origin?
Authors: Zhang X. X. , Song P. , Stahara S. S. , Spreiter J. R. , Russell C. T. , Le G.
Published: February 2004

Observations of the solar wind and the interplanetary magnetic field from ISEE‐3 are used as input to the gasdynamic convected field model, as implemented in a new space weather forecast model. Then the model output, for three case studies, is compared with the magnetosheath quantities observed at ISEE‐2 in order to identify the sources of the observed variations of the magnetosheath. It is found that some variations in the magnetosheath plasma and magnetic field are well correlated with corresponding variations in the solar wind and hence have their sources in the solar wind. However, some variations in the magnetosheath magnetic field correlate well with those in the solar wind but not variations in plasma density. Finally, we find that other variations in both plasma and magnetic field in the magnetosheath do not have appreciable correlations with variations in the solar wind. Most of these latter variations occur in the inner magnetosheath, indicating that they are endogenous in origin. Our results show that the forecast model can provide an accurate estimate of the timeshift from the solar wind monitor to the magnetosheath, of the instantaneous locations of the bow shock and magnetopause, and of the properties of the plasma and magnetic field in the outer and middle magnetosheath.
Refractive index and density of vapor‐deposited ice
Authors: Berland B. S. , Brown D. E. , Tolbert M. A. , George S. M.
Published: February 2004

The refractive indices of vapor‐deposited ice films were measured versus substrate temperature from 35–140 K and H2O pressure from 1.9 × 10−7–9.5 × 10−5 Torr using optical interference techniques. The refractive indices were measured for ice films deposited on a cooled, single‐crystal Al2O3 substrate in vacuum. Ice densities were calculated from these refractive indices using the Lorentz‐Lorenz relationship. Above 120 K, the ice films had a refractive index of n=1.31 and a density of ρ=0.93 g/cm³. Significantly lower refractive indices and densities were found at lower temperatures and higher H2O fluxes that were consistent with microporous ices. A refractive index of n=1.24 and density of ρ=0.68 g/cm³ were determined at 35 K and an H2O pressure of 4 × 10−6 Torr. Above 35 K, the refractive index and density progressively increased with increasing temperature and decreasing H2O flux. The ice densities observed can be explained qualitatively using a ballistic deposition model. Estimates are also obtained for the surface diffusion of H2O on vapor‐deposited ice.
The VAN Method: Contradictory and misleading results since 1981
Authors: Stavrakakis George N. , Drakopoulos John
Published: February 2004

We reexamine the VAN‐telegrams available to us, in terms of the seismological data observed in the candidate region before and after the relevant telegram. For the time period 1981–1985, the correlations are random. Earthquakes of any magnitude, from an extremely low threshold (i.e., M=2.5) at very short distances (i.e., a few kilometers), to large magnitudes (i.e., M=7.0) at very large distances (i.e., 500 km), or even teleseismic events (i.e., the Iran earthquake of 1981, at a distance of about 2000 km) were correlated by VAN with “apparent” SES, on the basis of the occurrence of an earthquake, anywhere, (from Italy to Aegean Sea, and from Albania to Crete island) and usually based on telegrams exchanged between the VAN‐researchers. From 1986 onwards, the VAN‐telegrams were restricted mostly to the area of Western Greece, which has the highest seismicity in Europe. By analyzing all of the VAN‐telegrams available to us, we conclude that in no case was a mainshock predicted. Whenever the reported VAN‐correlation seems to be satisfactory, the correlated event was either an aftershock or the correlation was not unique, meaning that any of several earthquakes in the same focal region could be arbitrarily correlated with the telegram.
Observations of evolving turbulence in the polar solar wind
Authors: Horbury T. S. , Balogh A. , Forsyth R. J. , Smith E. J.
Published: February 2004

The Ulysses magnetic field experiment has measured the heliospheric magnetic field in solar wind flows from the Sun's Southern polar coronal hole over a wide range of heliolatitudes and distances. We present an analysis of more than one year of data, covering a latitude range of 40° to 80°S and a distance range of 4.0 to 1.7 AU. We extend an earlier analysis of Ulysses magnetic field data and, by calculating structure functions, demonstrate that the spectrum of fluctuations in the magnetic field changed along the orbit of Ulysses within polar flows and that this change is a result of the variation in Ulysses' distance from the Sun, rather than its latitude. We interpret this change as being due to the development of turbulence in the polar solar wind.
Ulysses observations from pole‐to‐pole: An introduction
Authors: Smith Edward J. , Marsden Richard G.
Published: February 2004

Recent results from the Ulysses spacecraft as it observed particles and fields above the Sun's south polar cap, returned rapidly across the equator and traversed the northern solar hemisphere are presented in subsequent articles. This introduction provides a brief description of the spacecraft, the experiments, the unique trajectory and highlights of some of the principal scientific results.
A Comparison of Climate Forcings Due to Chlorofluorocarbons and Carbon Monoxide
Authors: Sinha Ashok , Toumi Ralf
Published: February 2004

The direct radiative forcing of climate by carbon monoxide (CO) is generally considered to be negligible. However, a recent study of localised clear‐sky surface irradiances asserts that the forcing by CO may be comparable to that by CFC‐11. Nevertheless no detailed comparison of CO and CFC climate forcings has yet been made. Thus the present study estimates the radiative impact of the increases in CO, CFC‐11 and CFC‐12 that have occurred since industrialisation. A radiative transfer model is used to reproduce the results of the earlier study. Clouds are then added, and the stratosphere‐adjusted forcing at the tropopause (the “climate forcing”) calculated. Global‐mean anthropogenic climate forcing by CO is determined to be 32% of that by CFC‐11, 12% of that by CFC‐12, and 9% of that by the CFCs combined. Even if the contemporary global‐mean CO concentration is increased by a factor of three, the climate forcing by CO is still only 75% of that due to CFC‐11. Regarding instantaneous clear‐sky forcings, further analysis shows that surface measurements can give a misleading impression of effects at the tropopause. While the indirect effects of CO on climate change are not yet properly quantified, the direct radiative effects appear, as previously thought, to be of only minor significance.
Positive ion depletion in a noctilucent cloud
Authors: Balsiger F. , Kopp E. , Friedrich M. , Torkar K. M. , Wälchli U. , Witt G.
Published: February 2004

With a Mattauch‐Herzog type of mass spectrometer the positive ion composition was measured in the mesosphere between 80 and 98.4 km over Kiruna, Sweden, in summer 1993. During the rocket flight an intense noctilucent cloud (NLC) was present and detected by a particle impact sensor at 83.0–83.6 km and 82.5–85.6 km on ascent and descent, respectively. For the first time a significant depletion of the main positive proton hydrates was observed on ascent and a complete disappearance of these ions on descent in the entire NLC‐layer. The observation is associated with an atypical low ion production of 0.01–0.1 cm−3s−1, which favors the ion loss by particle attachment and/or vertical transport. In order to explain the loss of mobile charge a second population of at least 105 cm−3 1–2 nm ice particles is required in the NLC.
The heliolatitudinal gradient of the solar wind during solar minimum conditions modelled by exact hydrodynamic solutions
Authors: Lima J. , Tsinganos K.
Published: February 2004

The heliolatitudinal dependence of observations of the solar wind macroscopic quantities such as the averaged proton speed and density is modelled during solar minimum conditions when the rotational and magnetic axes roughly coincide. Published observations via the technique of interplanetary scintillations for the previous two solar cycles were used, as well as recent data from the plasma experiment aboard the ULYSSES spacecraft, which also refer to the declining phase of the present solar cycle. A class of exact, two‐dimensional solutions of the full set of steady HD equations is used which is obtained analytically through a nonlinear separation of the variables. The three parameters which emerge in these solutions are fixed from such observations, as well as from observations of solar rotation. The solutions are consistent with observational inferrences that during solar minimum and the declining phase of the solar activity cycle, there is a strong heliolatitudinal gradient in rotation averaged proton speed between about 400–800 km s−1 from equator to pole. This modelling also agrees with previous findings that the gradient in wind speed with the latitude is offset by a gradient in density such that the mass and momentum flux vary relatively little.
The appearance of plasmaspheric plasma in the outer magnetosphere in association with the substorm growth phase
Authors: Moldwin M. B. , Thomsen M. F. , Bame S. J. , McComas D. J. , Weiss L. A. , Reeves G. D. , Belian R. D.
Published: February 2004

Short intervals (<2.5 hrs) of dense (≥10 cm−3), cold (≤ 10 eV) plasmaspheric plasma are observed at synchronous orbit in association with the growth phase of geomagnetic substorms. We interpret the strong correlation between these phenomena in terms of the reconfiguration of the duskside/nightside magnetosphere during the growth phase of geomagnetic substorms. This reconfiguration moves plasmaspheric plasma outward to synchronous orbit, occasionally even in the midnight region.
Soil magnetism, an approach for examining archaeological landscapes
Authors: Dalan Rinita A. , Banerjee Subir K.
Published: February 2004

To investigate archaeological landscapes and the extent to which humans have influenced them, we have developed an innovative approach that employs complementary geophysical methods drawn from the fields of exploration geophysics and soil magnetism. Integrating soil magnetic techniques with exploration surveys and more standard archaeological procedures (i.e., topographic mapping, excavation, coring, and soil‐chemical studies) at the Cahokia Mounds site has helped us to better understand the formation of this premier North American mound center and has also demonstrated a scientific methodology of great potential for subsurface investigations of archaeological terrains.
Potential impact of SO2 emissions from stratospheric aircraft on ozone
Authors: Weisenstein Debra K. , Ko Malcolm K. W. , Sze Nien‐Dak , Rodriguez Jose M.
Published: February 2004

Renewed interest in the potential impact of stratospheric aircraft on atmospheric ozone has focused on emissions of nitrogen oxides (NOx). This work shows that enhancement of the sulfate aerosol layer by aircraft emissions of sulfur could be more significant to the ozone impact than emission of NOx, especially when emissions of NOx in future engines are reduced by a factor of three from present engine designs. Our calculations show that increases in the aerosol surface area of the stratosphere by factors of two to three are expected if significant amounts of aircraft‐emitted sulfur are converted to sulfuric acid and undergo homogeneous nucleation in the aircraft plume. This possibility is supported by both in situ stratospheric observations and plume/wake modeling.
Intrusion of ice into porous media by regelation: A mechanism of sediment entrainment by glaciers
Authors: Iverson Neal R. , Semmens Darius J.
Published: February 2004

Unlithified sediment at glacier beds should be entrained in ice as a result of melting above individual grains and refreezing below grains (regelation). To test this hypothesis, a device that simulates subglacial conditions was used to push ice downward through idealized and natural porous media in contact with a flat bed. Ice regelated toward the bed at speeds proportional to the gradient in ice pressure across the thickness of particles. Ice temperatures responded predictably to changes in driving stress and demonstrated that the ice‐particle mixtures were at or very near the pressure‐melting temperature. A theory of pore ice motion by regelation predicted the measured speed usually to within a factor of two, although at low driving stresses the speed was less than the predicted value by as much as a factor of five. The low speeds were probably caused by imperfect temperature control that resulted either in heat loss from the ice‐particle mixtures or in slightly subfreezing pore ice temperatures that were not detected by thermistors. Ice should intrude the pores of underlying sediment to a steady depth at which the downward regelation speed equals the rate of basal melting. Departures from the steady state should cause release of debris from ice or further entrainment. An approximate calculation of the steady intrusion depth yields values comparable to typical thicknesses of debris in basal ice, a few centimeters to more than a meter. Intrusion of sediment by regelation is consistent with the isotopic composition of debris‐bearing ice, if melting exceeds refreezing.
A thermoconvective interpretation of heat flow data in the area of Ocean Drilling Program Leg 116 in a distal part of the Bengal Fan
Authors: Ormond Anne , Boulègue Jacques , Genthon Pierre
Published: February 2004

We present the results of a numerical simulation study of the thermo‐convective circulation in a sedimentary pile, in the distal part of the Bengal Fan. The occurrence of faults and the variability of surface heat flow data led previous workers to suggest hydrothermal circulation in this area. According to the purpose of Ocean Drilling Program survey Leg 116, data were collected which are adequate to constrain a model for the comprehension and the quantification of the relationship between ocean basin heat flow and pore fluid circulation. In this paper the sedimentary pile is modeled as an anisotropic and inclined porous layer interrupted by faults with a periodic distribution. An important observation the model tries to reproduce is the shift of approximately 2–3 km between the surface expression of the heat flow maximum and the fault zone near site 718. The influence of permeability anisotropy and of permeability within those fault zones is analyzed. When the maximum vertical permeability in the fault zones is 5 times greater than the vertical permeability of the porous block, the circulation consists of longitudinal rolls (i.e., rolls with their axis oriented downslope), with more vigorous convection in fault zones. When the maximum permeability of the fault zone is 10 or more times greater than the vertical permeability of the porous layer, convection is primarily restricted to the fault plane. In all cases maximum heat flow values are located directly above faults. This paper shows that the best agreement between those data suggests a 1 m yr−1 forced convection and a permeability of the sediments of 0.5 darcy (5 × 10−13 m2) and 5 mdarcy respectively, in the horizontal and vertical derictions.
Thermal constraints on the seismogenic portion of the southwestern Japan subduction thrust
Authors: Hyndman R. D. , Wang K. , Yamano M.
Published: February 2004

For coastal cities an important factor in earthquake hazard from subduction zone earthquakes is the landward extent of the seismogenic portion of the subduction thrust fault. In this study we test the hypothesis that the maximum downdip extent is defined by a critical temperature. We have developed a transient thermal model for the Nankai subduction zone of southwest Japan to allow comparison of the thermally estimated downdip extent of the seismogenic zone with that from (1) seismicity and tsunami data for two great subduction earthquakes, (2) the coseismic faulting extent of these events estimated from geodetic deformation data, and (3) the interseismic locked zone determined from interseismic geodetic data. The Nankai margin has extensive heat flow and heat production data to control thermal models and thus crustal temperatures. It has earthquake, tsunami, and geodetic data that constrain the coseismic rupture portion of the subduction thrust fault for past great earthquakes and the portion of the thrust fault that is locked and storing interseismic elastic strain. On the Nankaido margin off Shikoku Island, the thermal model indicates that a temperature of 350°C (taken to be the limit for seismic initiation from laboratory and field data) is reached on the subduction thrust fault 150 km from the trench. A transition zone into which rupture may extend with decreasing offset (taken to be 450°C) extends an additional 45 km downdip. The thermal model results are in excellent agreement with the maximum downdip extent of coseismic displacement for the 1946 Nankaido Ms = 8.2 earthquake off Shikoku Island and with the downdip extent of the present locked zone. In the region of the 1944 Tonankai Ms = 8.2 earthquake to the northeast, the subduction angle is much steeper and the thermal models indicate a narrower downdip seismogenic extent. The seismogenic‐locked zone from earthquake and geodetic data is also narrower. Thus our analysis of the southwest Japan margin indicates that all three constraints on the downdip extent of the seismogenic zone, thermal, coseismic and interseismic geodetic data, are in general agreement. The study also supports the hypothesis that the seismogenic portion of subduction thrust faults is limited primarily by temperature. The thermal control implies that subduction thrust faults with shallow dip have wider seismogenic zones compared to those with steep dip. The subducting plate age and thus heat flow, and the thickness of the insulating sediments on the incoming plate, are also very important to the thermal regime and thus to the seismogenic width. The relation of the maximum seismic rupture area to the interseismic locked zone is particularly important for earthquake hazard estimation on subduction margins such as Cascadia where there have been no great historical events.