bluuebunny/crossref_metadata_2025 huggingface dataset:
FAST satellite observations of electric field structures in the auroral zone
Authors: Ergun R. E. , Carlson C. W. , McFadden J. P. , Mozer F. S. , Delory G. T. , Peria W. , Chaston C. C. , Temerin M. , Elphic R. , Strangeway R. , Pfaff R. , Cattell C. A. , Klumpar D. , Shelley E. , Peterson W. , Moebius E. , Kistler L.
Published: February 2004

Electric field and energetic particle observations by the Fast Auroral Snapshot (FAST) satellite provide convincing evidence of particle acceleration by quasi‐static, magnetic‐field‐aligned (parallel) electric fields in both the upward and downward current regions of the auroral zone. We demonstrate this by comparing the inferred parallel potentials of electrostatic shocks with particle energies. We also report nonlinear electric field structures which may play a role in supporting parallel electric fields. These structures include large‐amplitude ion cyclotron waves in the upward current region, and intense, spiky electric fields in the downward current region. The observed structures had substantial parallel components and correlative electron flux modulations. Observations of parallel electric fields in two distinct plasmas suggest that parallel electric fields may be a fundamental particle acceleration mechanism in astrophysical plasmas.
Subducted lithosphere or 530 km discontinuity?
Authors: Oreshin Serge , Vinnik Lev , Treussov Alexandr , Kind Rainer
Published: February 2004

Tomographic images of the mantle west of Japan and south Kuril islands suggest that in this region the subducted lithospheric slabs instead of penetrating the lower mantle, lie flat on top of it [van der Hilst et al., 1991; Fukao et al., 1992]. To test these models with independent data and techniques, we analyse the slowness of the P arrivals of Kuril‐Japan seismic events at a seismic network in Baikal region. Relative to IASP91 standard earth model, the flat lying slab should generate an additional refraction line at epicentral distances less than 30°. The presence of this line is very clear in our data. The slope of the line and its position relative to the other lines are qualitatively consistent with the estimates of the slab velocity and thickness in the tomographic models. However, a similar wavefield can be generated by 530 km discontinuity, the presence of which is established by long‐range refraction profiling in the neighbouring regions of northern Eurasia.
Initial response and complex polar cap structures of the aurora in response to the January 10, 1997 magnetic cloud
Authors: Spann J. F. , Brittnacher M. , Elsen R. , Germany G. A. , Parks G. K.
Published: February 2004

On January 10th, 1997, a magnetic cloud originating at the Sun was incident on the Earth. The initial disturbance to the magnetosphere, as reflected in the activities of the aurora, was measured by the Ultraviolet Imager on the Polar Spacecraft. During this event we have observed the development of several unusual unique auroral forms that to our knowledge are unexplained in current models and theories. The observations were made on a global scale with unprecedented spatial and temporal resolution. The first activation of the aurora at local noon occurred within minutes of the arrival of the shock at 0107 UT. The substorm onset was observed at 0334 UT. During the intervening time significant polar cap precipitation occurred.
FAST observations of VLF waves in the auroral zone: Evidence of very low plasma densities
Authors: Strangeway R. J. , Kepko L. , Elphic R. C. , Carlson C. W. , Ergun R. E. , McFadden J. P. , Peria W. J. , Delory G. T. , Chaston C. C. , Temerin M. , Cattell C. A. , Möbius E. , Kistler L. M. , Klumpar D. M. , Peterson W. K. , Shelley E. G. , Pfaff R. F.
Published: February 2004

The Fast Auroral SnapshoT (FAST) explorer frequently observes the auroral density cavity, which is the source region for Auroral Kilometric Radiation (AKR). An important factor in the generation of AKR is the relative abundance of hot and cold electrons within the cavity, since hot electrons introduce relativistic modifications to the wave dispersion. VLF wave‐form data acquired by FAST within the auroral density cavity show clear signatures of whistler‐mode waves propagating on the resonance cone. This allows us to obtain the electron plasma frequency, and the cavity often has densities <1 cm−3. Moreover, the hot electrons can be the dominant electron species, enabling AKR to be generated below the cold electron gyro‐frequency.
Simultaneous observations of solar wind plasma entry from FAST and POLAR
Authors: Peterson W. K. , Tung Y.‐K. , Carlson C. W. , Clemmons J. H. , Collin H. L. , Ergun R. E. , Fuselier S. A. , Kletzing C. A. , Klumpar D. M. , Lennartsson O. W. , Lepping R. P. , Maynard N. C. , McFadden J. P. , Onsager T. G. , Peria W. J. , Russell C. T. , Shelley E. G. , Tang L. , Wygant J.
Published: February 2004

On November 15, 1996, NASA FAST and POLAR satellites obtained data in the cusp/cleft region for extended intervals. POLAR sampled a narrow range of local times. FAST observed cusp/cleft plasma for more than 5 hours in local time. At 07:51 UT the satellites were in near magnetic conjunction, and the interplanetary magnetic field was steady for an extended interval before this time. We confirm prior observations that show solar wind plasma often enters the magnetosphere over extended regions of local time. For the one hour interval of steady solar wind conditions when POLAR encountered cusp/cleft plasma, irregularly spaced ion injections interspersed with intervals of nearly constant cusp/cleft ion fluxes were observed. The data are consistent with temporal variations in the reconnection rate. At the time of the near conjugate observations the data suggest that solar wind plasma entered the magnetosphere over an extended region of the magnetopause, i.e. not in small discontinuous patches.
Magnetic cloud field intensities and solar wind velocities
Authors: Gonzalez W. D. , de Gonzalez A. L. Clúa , Dal Lago A. , Tsurutani B. T. , Arballo J. K. , Lakhina G. K. , Buti B. , Ho C. M. , Wu S.‐T.
Published: February 2004

For the sets of magnetic clouds studied in this work we have shown the existence of a relationship between their peak magnetic field strength and peak velocity values, with a clear tendency that clouds which move at higher speeds also possess higher core magnetic field strengths. This result suggests a possible intrinsic property of magnetic clouds and also implies a geophysical consequence. The relatively low field strengths at low velocities is presumably the cause of the lack of intense storms during low speed ejecta. There is also an indication that this type of behavior is peculiar for magnetic clouds, whereas other types of non cloud‐driver gas events do not seem to show a similar relationship, at least for the data studied in this paper. We suggest that a field/speed relationship for magnetic clouds, as that obtained in our present study, could be associated with the cloud release and acceleration mechanism at the sun.

Since for magnetic clouds the total field tyically has a substantial southward component, Bs, our results imply that the interplanetary dawn‐dusk electric field, given by v×Bs (where v is the cloud's velocity), is enhanced by both factors. Therefore, the consequent magnetospheric energization (that is governed by this electric field) becomes more efficient for the occurrence of magnetic storms.
The observed fingerprint of 1980–1997 ENSO evolution in the NCAR CSM equilibrium simulation
Authors: Liang Xin‐Zhong , Wang Wei‐Chyung
Published: February 2004

General circulation models (GCMs) are capable of simulating certain statistical characteristics of the composite El Niño‐Southern Oscillation (ENSO) cycle. Here we demonstrate that the NCAR Climate System Model (CSM), in absence of external forcing and data assimilation, simulates both temporal variations and spatial patterns associated with the observed ENSO cycles during 1980s. The model also produces a distinct decadal change of ENSO variations that resembles the observed shift from 1980s (strong and well‐defined cycles) to the early 1990s (weak and short‐lived warm phases) followed by the strong 1997 El Niño. The study thus suggests that the ENSO evolution during 1980s and the decadal shift in 1990s might be a result of natural variability intrinsic to the interactive climate system. Given the perceived capability to simulate natural variations, the CSM can be used to supplement observational data to better understand climate variability on interannual‐to‐decadal timescales.
Chemical fluxes in the Tonga Subduction Zone: Evidence from the Southern Lau Basin
Authors: Bach Wolfgang , Hegner Ernst , Erzinger Jörg
Published: February 2004

Chemical and isotopic data for volcanic glasses from the Valu Fa Ridge (VFR) in the southern Lau Basin closely resemble the composition of volcanics from the nearby Tonga arc. The most primitive basalts from the VFR were used to reconstruct the primary magma composition which is believed to reflect the composition of the bulk crust. The magma production rate at the Valu Fa Ridge was estimated (0.7−1.5×106 kg/a/m), and chemical fluxes of various elements have been calculated based on these values and the primary magma composition. The chemical and isotopic composition of VFR lavas is totally consistent with the release of fluid‐soluble elements from the subducting altered oceanic crust and sediments. Mass balance calculations indicate the important role of the altered basaltic basement as a source of H2O, K, Rb, Cs, Sr, U, and Pb in supra‐subduction zone rocks.
Solar wind density intercomparisons on the WIND spacecraft using WAVES and SWE experiments
Authors: Maksimovic M. , Bougeret J.‐L. , Perche C. , Steinberg J. T. , Lazarus A. J. , Viñas A. F. , Fitzenreiter R. J.
Published: February 2004

We present solar wind density comparisons using three different instruments on the WIND spacecraft: The thermal noise receiver (TNR) on the WAVES experiment which yields the total electron density from the detection and the analysis of the electron plasma peak; the SWE Faraday cup detectors which measure ion energy per charge spectra and yield the proton and alpha particle densities in the solar wind; and finally the SWE electron spectrometer which provides 3D electron velocity distribution functions and thus the total electron density. The density comparison between the TNR and the SWE Faraday cups shows a remarkably good agreement, with a systematic offset which is lower than 1% and fluctuations of up to ≈ 5% around this value. Due to the well known spacecraft electrical potential effects, the SWE electron spectrometer densities, uncorrected from the potential, exhibit larger differences when compared with the TNR or the SWE Faraday cups measurements. Using these latter densities as reference, we compute a rough estimation of the spacecraft potential.
Validation of hydrometeor occurrence predicted by the ECMWF Model using millimeter wave radar data
Authors: Mace Gerald G. , Jakob Christian , Moran Kenneth P.
Published: February 2004

Validation of hydrometeor prediction by global models is an important issue as it pertains to the accuracy of climate predictions. In this study we use data from a continuously operating millimeter wave radar at a research site in north central Oklahoma, USA to validate output from the operational ECMWF forecast model. We demonstrate that the ECMWF model shows good overall skill at predicting the vertical distribution of the clouds and precipitation that occurred over this site during winter 1997. However, we also show that the model tended to predict the onset of deep cloud events too soon, made the layers too deep and predicted dissipation somewhat later than observed.
Decadal variability of temperature at a depth of 400 meters in the North Pacific Ocean
Authors: Zhang Rong‐Hua
Published: February 2004

The gyre‐scale structure and evolution of decadal ocean thermocline variability in the North Pacific is described by analyzing historical temperature data at a depth of 400 meters. Decadal thermocline anomalies are characterized by a distinct see‐saw pattern in the midlatitudes and subtropics that appears to circulate coherently in the North Pacific basin, with a period on the order of 20 years. There are coherent spatial and temporal relationships between temperature anomalies around the subtropical gyre, with phase differences at depth and at the sea surface, suggesting that thermocline variability evolves independently of local SST anomalies. In the subtropics, subsurface anomalies can be seen to propagate all the way across the basin and thereby lead SST anomalies, providing a possible phase transition mechanism for SST. The basinwide anomaly pathways suggest a clockwise advection of subsurface temperature anomalies around the subtropical gyre, an active role played by the mean geostrophic flow in decadal variability.
New particle formation: Nucleation rates and spatial scales in the clean marine coastal environment
Authors: O'Dowd Colin D. , Geever Michael , Hill Martin K. , Smith Michael H. , Jennings S. Gerard
Published: February 2004

Nucleation of new, ultra‐fine, aerosol particles has been observed in the clean marine coastal atmosphere under a variety of conditions. These nucleation events were observed to occur frequently over spatial scales of 10's–100' of metres and temporal scales of seconds to minutes. Two conditions appeared to be necessary for nucleation event to occur: low tide and solar irradiation. The requirement of low tide conditions suggests that the exposed shore area provides the source of new particle precursors. It is speculated that VOC and/or alkyl halide derivatives contribute to nucleation under these conditions. Nucleation rates were calculated to be ≈ 10³ − 104 cm−3 s−1, suggesting that the coastal zone is an important source of atmospheric nuclei.
Permeability porosity relationships from numerical simulations of fluid flow
Authors: Dardis Orla , McCloskey John
Published: February 2004

Numerical calculations of permeability are obtained from a lattice Boltzmann simulation of flow in simplified 2D porous media over a range of solid fractions. The evolution equation governing the flow behaviour incorporates the effect of porous medium geometry through the definition of solid density ns, a real number, at each node of the simulation grid. The results obtained for homogeneous media are compared to commonly used theoretical and empirical relationships relating rock properties to permeability. Behaviour consistent with a Kozeny‐Carman type relationship between porosity ϕ and permeability k is obtained for low to intermediate solid fractions. At high solid fractions the rapid decrease in k is consistent with a percolation process giving a power‐law relationship for ϕ and k. Both the critical porosity and power‐law exponent are in agreement with quoted values for the lattice geometry used. A comparison of the results for homogeneous media with k values, obtained by embedding a spanning planar fracture into the matrix, illustrates the importance of matrix‐fracture flow interactions. The results for this case are consistent with experimental observations and illustrate the difficulties involved in using simplified assumptions to predict permeability from porosity in fractured porous rock.
Temporal variation in the interhemispheric 14C offset
Authors: McCormac F. G. , Hogg A. G. , Higham T. F. G. , Lynch‐Stieglitz J. , Broecker W. S. , Baillie M. G. L. , Palmer J. , Xiong L. , Pilcher J. R. , Brown D. , Hoper S. T.
Published: February 2004

Contemporaneous tree‐ring dated wood, from trees in the northern and southern hemispheres, gives different 14C dates. Previous studies [Vogel et al., 1986; 1993] using wood from South Africa and The Netherlands have shown depletion's of −4.56 ± 0.85‰ and −5.12±0.62‰ respectively. This translates to age differences of 36±7 and 41±5 years (yrs) with the southern hemisphere giving the older dates. More recently, Stuiver and Braziunas [1998] have shown that an offset of 23±4 yrs exists between combined 19th century wood measurements from Tasmania and Chile in the southern hemisphere and the west coast of the U.S. (Washington) in the northern hemisphere. In this study measurements on contemporaneous decadal samples of oak from the British Isles and cedar from New Zealand over the period 1725 to 1885 AD show a depletion of −3.4±0.58‰ (27.2±4.7 yrs). However, data after 1895 AD has a mean offset of 0.66±1.06‰ (−5.3±8.5 yrs) with increased variance compared to 19th century data. This, we believe, is attributable to anthropogenic fossil fuel, which, due to its long residence time in the earth, has long since lost any 14C component and when burned preferentially depletes the northern hemisphere atmosphere of 14C.
The auroral oval boundaries on January 10 1997: A comparison of global magnetospheric simulations with UVI images
Authors: Elsen R. K. , Winglee R. M. , Spann J. F. , Germany G. A. , Brittnacher M. , Parks G. K.
Published: February 2004

We present a global magnetospheric simulation of the initial period of the January 10–11, 1997 magnetic cloud event. Model magnetospheric boundaries mapped to the ionosphere are compared to UVI images of the auroral oval from 1:00 to 4:30 UT. The convection reversal boundary generally matches the UVI equatorward boundary and is almost always poleward of the boundary separating Region 1 and Region 2 currents. The separatrix between open and closed magnetic field lines matches the poleward boundary of the UVI images well during quiet periods. During dynamic periods when the separatrix moves several degrees in latitude in some sectors, the poleward boundary of the Region 1 currents matches the UVI images better.
Detection of biomass burning combustion products in Southeast Asia from backscatter data taken by the GOME Spectrometer
Authors: Thomas W. , Hegels E. , Slijkhuis S. , Spurr R. , Chance K.
Published: February 2004

We show that atmospheric UV/visible backscatter spectra obtained by the Global Ozone Monitoring Experiment (GOME) spectrometer on board the ESA ERS‐2 satellite may be used to retrieve column amounts of key trace species associated with smoke cloud combustion from biomass burning events. This paper focuses on the recent rain forest burning in SE Asia (August–October 1997). For ground scenes with low cloudiness, differential absorption fitting applied to backscatter spectra yields column distributions of NO2 and H2CO in and around smoke‐polluted regions. A two‐fold increase in the vertical NO2 content is apparent over large parts of the smoke cloud; this clearly indicates the ability of GOME to measure tropospheric NO2 content. H2CO is detected only in areas closest to combustion sources. Slant column amounts in the range 2.5 ‐ 4 × 1016 mol cm−2 have been determined; these correspond with previous estimations of vertical columns of H2CO for biomass Savannah burning.
DP 2 electric field fluctuations in the dusk‐time dip equatorial ionosphere
Authors: Abdu M. A. , Sastri J. H. , Luhr H. , Tachihara H. , Kitamura T. , Trivedi N. B. , Sobral J. H. A.
Published: February 2004

We have studied the geomagnetic and ionospheric manifestations of the DP 2 activity that occurred on April 7, 1995 using high time resolution magnetometer data of IMAGE network in Scandinavia and of Alcantara (dip 1.2° N), Brazil, and F layer vertical plasma drift, Vz measured by an HF Doppler radar at Kodaikanal (dip 4° N), India. Quasi‐periodic fluctuations in dusk‐time (1730–1900 LT) F layer vertical plasma drift (eastward electric field) occurred over Kodaikanal coherent with DP 2 type magnetic fluctuations (period≈25 min) at the day‐side dip equator and auroral/subauroral latitudes. This first‐ever observation at the dusk‐side equator is in agreement with the two‐cell equivalent current system previously proposed for DP 2 fluctuations. The results strongly suggest that the magnetospheric electric field responsible for DP 2 fluctuations penetrates to equatorial ionosphere on the dusk‐side as on the day‐side. An additional observation is that the electric field fluctuation amplitude increases towards the nightside suggesting the influence of dusk sector electrodynamics in the observed signature of the DP 2 electric field.
The auroral current circuit and field‐aligned currents observed by FAST
Authors: Elphic R. C. , Bonnell J. W. , Strangeway R. J. , Kepko L. , Ergun R. E. , McFadden J. P. , Carlson C. W. , Peria W. , Cattell C. A. , Klumpar D. , Shelley E. , Peterson W. , Moebius E. , Kistler L. , Pfaff R.
Published: February 2004

FAST observes signatures of small‐scale downward‐going current at the edges of the inverted‐V regions where the primary (auroral) electrons are found. In the winter pre‐midnight auroral zone these downward currents are carried by upward flowing low‐ and medium‐energy (up to several keV) electron beams. FAST instrumentation shows agreement between the current densities inferred from both the electron distributions and gradients in the magnetic field. FAST data taken near apogee (∼4000‐km altitude) commonly show downward current magnetic field deflections consistent with the observed upward flux of ∼109 electrons cm−2 s−1, or current densities of several µA m−2. The electron, field‐aligned current and electric field signatures indicate the downward currents may be associated with “black aurora” and auroral ionospheric cavities. The field‐aligned voltage‐current relationship in the downward current region is nonlinear.
NDVI relationship to monthly evaporation
Authors: Szilagyi J. , Rundquist D. C. , Gosselin D. C. , Parlange M. B.
Published: February 2004

Normalized difference vegetation indices (NDVI), calculated from Landsat‐MSS images, were correlated with monthly total precipitation and estimates of monthly evaporation in a prairie environment. The highest value of the correlation coefficient (r=.80) was obtained between the monthly mean NDVI and estimated evaporation of the preceding month. The de‐seasoned NDVI and evaporation values retained a correlation coefficient of .53 corresponding to half of the originally explained variance (r²=.64) between NDVI and evaporation suggesting that NDVI indices may be useful for estimating regional‐scale evaporation in a water‐limited environment.
Cloud droplet effective radius from spaceborne polarization measurements
Authors: Bréon François‐Marie , Goloub Philippe
Published: February 2004

The spaceborne POLDER instrument provided the first quantitative measurements of the Earth reflectance polarization characteristics. Many POLDER images of polarized light show cloudbow type features over cloud fields for scattering angles between 150 and 170°. This unexpected observation is attributed to the polarized radiance generated by single scattering by cloud droplets. It shows that, in many cases, the cloud droplet size distribution is very narrow. The multidirectional polarized radiance measurements can be inverted for an accurate estimate of the cloud droplet radius.
Lower tropospheric ozone trend observed in 1989–1997 at Okinawa, Japan
Authors: Lee ShanHu , Akimoto Hajime , Nakane Hideaki , Kurnosenko Sergey , Kinjo Yoshikatsu
Published: February 2004

In order to elucidate recent tropospheric ozone trends in Northeast Asia, 8 year‐long ozone sounding data obtained between 1989 and 1997 at Naha (Okinawa Island), Japan, were analyzed incorporating with backward trajectory categorization. Focusing on the regionally polluted continental outflow, only data associated with air masses that reached Naha from northern, northwestern, and western directions during autumn/winter/early spring seasons (from October to March) were selected for analysis. The concentration of ozone shows an increase of about 2.5±0.6% (one standard deviation) per year for a 0‐2 km layer from the ground representing the planetary boundary. The surface ozone concentrations obtained at Cape Hedo (northern tip of Okinawa Island) at the same timing as the selected ozone sounding also showed an increasing trend of 2.6% per year but with a large statistical uncertainty of ±2.0%. This result is in accordance with the 22‐year period (1969–1990) of tropospheric ozone trends, 1.5–2.5% per year, obtained previously at three other Japanese ozone sounding stations, Kagoshima, Tsukuba, and Sapporo [Akimoto et al. 1994], demonstrating the continuous increase of tropospheric ozone in Northeast Asia in 1990s. It is suggested that this tropospheric ozone trend would be related to the increasing emission of NOx from Northeast Asian region (China, Japan, South Korea, Taiwan) during this period with a rate of 3.9% per year.
Microwave dielectric properties of the ice core from Dome Fuji, Antarctica
Authors: Matsuoka Takeshi , Mae Shinji , Fukazawa Hiroshi , Fujita Shuji , Watanabe Okitsugu
Published: February 2004

Measurements of relative complex dielectric permittivities, ε*=ε′−iε″, of ice core recovered from Dome Fuji, Antarctica were carried out at 33 GHz in the temperature range 210–260 K. The open resonator method was used for precise measurement of temperature dependence of the real part, ε′, and imaginary part, ε″, of dielectric permittivities. The following results were obtained: small dielectric anisotropy, Δε′=|ε′∥c ‐ ε′⟂c|, was observed (Δε′ = 0.0104±0.0004) and was independent of temperature. The increase rate of ε′ with increase of temperature changed at around 238 K. The increase rate, dε′/dT, above 238 K was three times larger than that below 238 K and the values were 0.0011 and 0.0003 above and below 238 K, respectively. Also, Raman spectra measurements were carried out and the result showed that the increase rate of frequency of translational lattice vibrations with increase of temperature changed at around 238 K.
The North Atlantic Oscillation and its imprint on precipitation and ice accumulation in Greenland
Authors: Appenzeller C. , Schwander J. , Sommer S. , Stocker T. F.
Published: February 2004

Interannual to decadal fluctuations in net precipitation and ice accumulation are examined over Greenland. It is shown that in western Greenland these fluctuations are correlated with the North Atlantic Oscillation. The analysis is based on two complementary data sources: A highly resolved net precipitation and accumulation history over 15 years derived form the reanalysis data of the European Centre for Medium‐Range Weather Forecasts and a composite ice accumulation record representative for the western part of Central Greenland. It is suggested that western Greenland snow accumulation is a good proxy for the NAO index with the potential for the reconstruction of a long time series.
X‐ray coronal changes during Halo CMEs
Authors: Hudson H. S. , Lemen J. R. , St. Cyr O. C. , Sterling A. C. , Webb D. F.
Published: February 2004

Using the Yohkoh soft X‐ray images, we examine the coronal structures associated with “halo” coronal mass ejections (CMEs). These may correspond to events near solar disk center. Starting with a list of eleven confirmed halo CMEs over the time range from December 1996 through May 1997, we find seven with surface features identifiable in soft X‐rays, with GOES classifications ranging from A1 to M1.3. These have a characteristic pattern of sigmoid → arcade development. In each of these events, the pre‐flare structure disrupted during the flare, leaving the appearance of compact transient coronal holes. The four remaining events had weak or indistinguishable signatures in the X‐ray images. For the events for which we could see well‐defined coronal changes, we confirm our previous result that the estimated mass loss inferred from the soft X‐ray dimming is a small fraction of typical CME masses [Sterling & Hudson 1997].
The January 10, 1997 auroral hot spot, horseshoe aurora and first substorm: A CME loop?
Authors: Tsurutani B. T. , Arballo J. K. , Lakhina G. S. , Ho C. M. , Ajello J. , Pickett J. S. , Gurnett D. A. , Lepping R. P. , Peterson W. K. , Rostoker G. , Kamide Y. , Kokubun S.
Published: February 2004

The January 10, 1997 interplanetary high‐speed stream and the resultant first substorm (∼0332 to 0334 UT onset) is studied. A 47 minute interval of relatively intense southward interplanetary magnetic field (IMF) (BS = 4 to 8 nT) bounded by two tangential discontinuities (TDs) is identified between the interplanetary shock and the magnetic cloud. The two discontinuities arrive at the magnetopause at ∼0219 and ∼0302 UT. The IMF BS event served primarily to transfer solar wind energy to the magnetosphere/magnetotail, as no substorm expansion phase occurred during the event. The eventual energy release was in the form of a large substorm expansion phase which occurred after (∼15–17 min.) a second IMF northward turning (after the end of the BS interval). The interplanetary BS event came after a prolonged northward IMF interval. During the initial part of the BS event, both polar cap Sun‐Earth aligned arcs formed (part of a theta aurora) and an auroral hot spot along the main arc took place. Later, during the BS interval, an aurora in the shape of a horseshoe developed at lower (60°) latitudes (an oval with a gap in the noon sector). The dawnside portion of the horseshoe aurora became much brighter than the duskside with increasing time. The dawnside polar cap boundary layer (PCBL) broadband waves were well correlated with low energy ion fluxes (H+, He++, O+) during the event. It is speculated that this IMF BS structure may be an outer loop of the CME coming from the Sun. Another similar loop is identified just adjacent to the cloud.
Mean hydrographic and velocity sections near Pipe Organ Vent at Juan de Fuca Ridge
Authors: Helfrich K. R. , Joyce T. M. , Cannon G. A. , Harrington S. A. , Pashinski D. J.
Published: February 2004

A composite cross‐ridge hydrographic and velocity section near the Pipe Organ vent site on the Juan de Fuca Ridge is presented. The hydrographic section is composed of surveys obtained from 1990 to 1994. The potential temperature field shows pronounced downward sloping of the isotherms below 1.9° (centered at about 150 m above the bottom) on either side of the ridge crest. The horizontal scale is about 2 km, comparable to the local Rossby deformation radius. The maximum potential temperature anomaly is greater than 0.03°C. Significant light attenuation anomalies are also present. The mean along‐ridge velocity section is constructed from the records of 85 current meters. The mean flow is southward at and to the east of the vent and northward to the west. Largest velocities occur at the depth of the neutrally buoyant plume. The cross‐ridge shear is thus anti‐cyclonic with a characteristic value of −0.05f. Geostrophic velocity fields obtained from the density section differ significantly from the field produced from the current meter data. An estimate of the net mean flux of anomalous heat gives 780 (±400) MW to the south.
Vertical and temporal vorticity observations at Juan de Fuca Ridge: Hydrothermal signatures
Authors: Joyce Terrence M. , Cannon Glenn A. , Pashinski Dave , Helfrich Karl R. , Harrington Stephanie A.
Published: February 2004

Moored current measurements made from April 1994 to June 1995 reveal the vertical and temporal structure of the vorticity over the northern segment of the Juan de Fuca Ridge. At a depth of 2100m, near the thermal and particle maximum associated with the neutrally buoyant hydrothermal plume, the relative vorticity is anticyclonic with a mean value of nearly −0.09f, with variability of the same magnitude. This arises from cross‐ridge shear in the horizontal currents at this level. In the vertical, the anticyclonic shear has a peak value at plume level decreasing in magnitude both upward and downward from depths of 2100–2150m. As the bottom is approached, the transverse shear changes sign with cyclonic values of up to 0.09f below 2250m depth. This vorticity signature is suggestive of dynamics of a line source of buoyant fluid entering the plume at its neutral density horizon and not due to individual point sources.
Relativistic electrons and magnetic storms: 1992–1995
Authors: Reeves Geoffrey D.
Published: February 2004

This paper examines the relationship between relativistic electron enhancements at geosynchronous orbit and magnetic storms measured by the Dst index. We analyzed the 30 most intense relativistic electron events from 1992 to 1995 and all events that occurred in 1993. Every relativistic electron event was associated with a magnetic storm in the Dst index, but, magnetic storms could occur with no appreciable enhancement of the relativistic electron fluxes. By correlating the maximum electron flux in each event with the minimum Dst value we found that the maximum relativistic electron fluxes and maximum ring current intensity are roughly correlated but that there is considerable variation. These results suggest that the solar wind conditions that are necessary to generate a ring current response are also necessary to generate a strong relativistic electron response but that there is some additional factor, either in the solar wind or in the magnetosphere, that determines whether a given storm will produce relativistic electrons or not and how strong that response will be.
The discovery of trapped energetic electrons in the outer cusp
Authors: Sheldon R. B. , Spence H. E. , Sullivan J. D. , Fritz T. A. , Chen Jiasheng
Published: February 2004

We report on the POLAR/CEPPAD discovery of a trapped, 60°<θ<120° pitch angle electron population in the outer cusp (7−9+ Re), whose energetic electron component extends from below 30 keV to ∼2 MeV. Because the time variability in the outer cusp precludes mapping with POLAR, we have carried out test particle simulations using the Tsyganenko 1996 model (T96) to demonstrate the trapping of these energy electrons in the outer cusp region and the resonant frequencies of its trapped motion. We discuss the boundaries and regions of the cusp trap and show that it is analogous to the dipole trap. We show that the phase space densities observed there are equal or greater than the phase space densities observed in the radiation belts at constant magnetic moment, thus allowing the possibility of diffusive filling of the radiation belts from the cusp.
Dynamics of the seasonal variations in the Indian Ocean from TOPEX/POSEIDON sea surface height and an ocean model
Authors: Yang Jiayan , Yu Lisan , Koblinsky Chester J. , Adamec David
Published: February 2004

Observations from the TOPEX/POSEIDON (T/P) altimeter reveal that the sea level in the Indian Ocean varies strongly with season. Surface undulations propagate eastward along the equator and westward outside the equatorial waveguide. The forcing mechanisms responsible for such variations are investigated in this paper by analyzing T/P data and surface wind‐stress forcing, and by using a nonlinear, 2.5‐layer, reduced gravity model. Both the data and the model show that Kelvin and Rossby waves forced by the Indian Ocean monsoon are primarily responsible for the seasonal sea‐level change in the tropical and the subtropical Indian Ocean.
Concurrent observations of solar wind oxygen by Geotail in the magnetosphere and wind in interplanetary space
Authors: Christon S. P. , Cohen C. S. , Gloeckler G. , Eastman T. E. , Galvin A. B. , Ipavich F. M. , Ko Y.‐K. , Lui A. T. Y. , Lundgren R. A. , McEntire R. W. , Roelof E. C. , Williams D. J.
Published: February 2004

We present an initial report on the first direct, concurrent measurements of solar wind oxygen (O) charge state variations inside and outside Earth's magnetosphere. On 10‐11 Jan 1997 a magnetic cloud, with a spatial scale of at least ∼100 RE engulfed the magnetosphere. At ∼1200 UT on 10 Jan 1997, the Wind/SWICS ion charge‐state spectrometer, at ∼90 RE upstream of Earth, detected an increase in the solar wind O charge state ratio Γo = (O+7 + O+8) / O+6 at ∼0.5‐30 keV/e which persisted until ∼2400 UT on 10 Jan 1997. After ∼1110 UT on 10 Jan 1997, Geotail was in and near the mid‐afternoon to dusk magnetosphere. The ∼9.4‐210 keV/e Γo value from the Geotail/STICS spectrometer showed a longer‐term, gradual increase over ∼8–10 hr. Then, after ∼0600 UT on 11 Jan 1997, Wind observed a Γo decrease at a high speed solar wind stream onset. About 6 hr later Γo decreased promptly at Geotail during a plasma sheet substorm injection. Both instances are long durations compared to nominal 3‐hr substorm time‐scales.
Magma acoustics and time‐varying melt properties at Arenal Volcano, Costa Rica
Authors: Garcés Milton A. , Hagerty Michael T. , Schwartz Susan Y.
Published: February 2004

The similarity of acoustic and seismic spectra recorded during Strombolian activity of Arenal Volcano provides conclusive evidence that pressure waves are generated and propagated within the magma‐gas mixture inside volcanic conduits. These pressure waves are sensitive to the flow velocity and to small changes in the gas content of the magma‐gas mixture, and thus can provide useful indicators of the time‐varying properties of the unsteady flow regime and the chemical composition of the melt. The dominant features of the observed explosion and tremor signals are attributed to the source excitation functions and the acoustic resonance of a magma‐gas mixture inside the volcanic conduit. We postulate that explosions are triggered in the shallow parts of the magma conduit, where a drastic pressure drop with depth creates a region where violent degassing can occur. Tremor may be sustained by unsteady flow fluctuations at depth. Equilibrium degassing of the melt creates a stable, stratified magma column where the void fraction increases with decreasing depth. Disruption of this equilibrium stratification is thought to be responsible for observed variations in the seismic efficiency of explosions and enhanced acoustic transmission from the interior of the conduit to the atmosphere.
Plate tectonic framework for the October 9, 1996, Cyprus Earthquake
Authors: Arvidsson Ronald , Ben‐Avraham Zvi , Ekström Göran , Wdowinski Shimon
Published: February 2004

We determine the centroid depths for the Mw=6.8, October 9, 1996, Cyprus earthquake and its largest after‐shock to 32 and 27 km, respectively, by modeling P and SH waveforms. These depths are consistent with shallow subduction as the African plate, west of Cyprus, penetrates beneath the Anatolian plate. We calculate the pole of rotation between Anatolia and Africa and determine their relative motion. The result indicates that, along the Cyprean Arc, convergence between the African and Anatolian plate, in agreement with the observed seismicity, decreases from west to east. The northeasterly striking nodal plane is suggested as the plane on which the Cyprus earthquake ruptured since its strike agrees well with the derived plate motion vector. The faulting geometry suggests the emergence of a strike‐slip tear fault within the African plate separating the continental Eratosthenes seamount south of Cyprus from the oceanic African lithosphere that subducts west of Cyprus.
Some new aspects for the modelling of isothermal remanent magnetization acquisition curves by cumulative log Gaussian functions
Authors: Stockhausen Hagen
Published: February 2004

Rock samples containing (ferri)magnetic minerals acquire an isothermal remanent magnetization (IRM) after exposure to a direct magnetic field. Measuring IRM(B) allows to produce IRM acquisition curves which were modelled by cumulative log Gaussian (CLG) functions (Robertson and France, 1994) to discriminate the different magnetic phases. An approach of how to find the best model has been added to this method. From the investigation of a magnetite sample it is inferred that with the method the remanence acquisition coercive force for each magnetic component in a sample can be deduced. The method allows to detect minute concentrations of magnetically hard material in a predominant magnetically soft sample and vice versa. It furthermore allows to extrapolate the IRM behaviour of samples that do not reach saturation IRM in the experiment. The study of a natural hematite renders it possible that even well‐defined hematite may be contaminated by (ferri)magnetic impurities biasing the remanence acquisition coercive force of the sample towards lower values.
The pH of deliquesced sea‐salt aerosol in polluted marine air
Authors: Keene William C. , Savoie Dennis L.
Published: February 2004

The pH of deliquesced sea‐salt aerosol was derived from the Cl phase partitioning measured in marine air, corresponding meteorological conditions, and the thermodynamic properties of HCl. Under moderately polluted conditions at Bermuda during spring 1996, calculated sea‐salt aerosol pH ranged from the mid‐2s to the mid‐3 s. Cl− and NO3−concentrations in the lower half of the sea‐salt size distribution were near thermodynamic equilibrium with respect to HClg and HNO3g; shorter aerosol lifetimes and slower reaction kinetics involving larger aerosol sustained moderate phase disequilibria. The active multiphase cycling of HCl buffered sea‐salt aerosol pH to approximately the same value across the particle size spectrum.
Analysis of fluid pressure propagation in heterogeneous rocks: Implications for hydrologically‐induced earthquakes
Authors: Lee Ming‐Kuo , Wolf Lorraine W.
Published: February 2004

Mathematical models are developed to study the propagation of excess pore pressure in heterogeneous and fractured rocks. For a homogeneous rock, the time needed for a pore pressure front to migrate downward is directly proportional to the square of the depth, and inversely proportional to the permeability of the rock. Variational studies show that pore pressure propagation is highly influenced by the permeability heterogeneity of the crust. The results argue for the importance of accounting for geologic complexity when using mathematical models to estimate the extent of downward transmission of increases in hydraulic heads. The models presented in the paper are used to estimate a range of possible hypocentral depths of periodic seismicity observed near Mt. Ogden on the Alaska‐British Columbia border. The time lag between these earthquakes and hydrologic loading is on the order of days or weeks, indicating a quick response of seismicity to the increased surface water input from rainfall or glacial discharge, if such a causal relationship exists. Our models estimate that the hypocentral depths of these earthquakes could be on the order of several kilometers, if a high degree of vertical interconnectivity of fractures exists.
Asymmetry of occurrence‐frequency and intensity of AKR between summer polar region and winter polar region sources
Authors: Kumamoto Atsushi , Oya Hiroshi
Published: February 2004

The statistical analyses of intensity and occurrence‐frequency of auroral kilometric radiation (AKR) observed by the plasma wave and sounder experiment (PWS) onboard the Akebono (EXOS‐D) satellite have been carried out for the seven‐year period from March 1989 to February 1996. The results show clear seasonal variations of AKR intensity and occurrence‐frequency both in the northern and southern polar regions. AKR exhibits an increase in the intensity and occurrence‐frequency of intense emissions in the winter polar regions; thus there is a distinct north‐south asymmetry of AKR. This tendency of asymmetry feature of AKR emission sources becomes more prominent in the high frequency range. These results have given strong confirmation to the GEOTAIL observation reported by Kasaba et al. [1997]. The origin of this asymmetry of AKR emissions are plausibly related with the seasonal dependence of the acceleration processes of the auroral electrons as has been suggested by Newell et al. [1996].
Monitoring of the Palu‐Koro Fault (Sulawesi) by GPS
Authors: Walpersdorf A. , Vigny C. , Subarya C. , Manurung P.
Published: February 2004

5 years of GPS measurements across the Palu‐Koro fault (Sulawesi, Indonesia) state left lateral strike‐slip (3.4 cm/yr) with a small normal component (0.4 cm/yr). The measurements on intermediate points of the transect show that the fault is locked, at a depth estimated around 8–16 km by a very simple model. The best measured baseline linking the two most separate sites (Watatu and Toboli) shows very interestingly a constant rate of 2.6 cm/yr from 1992 to 1995, and an increased rate of 6.3 cm/yr since then. This increase is due to an earthquake on January 1, 1996 in the Minahasa trench, presumably affecting station Toboli's position by 2 cm of co‐seismic and 2 cm of post‐seismic displacement, which is added to its long term velocity. We interpret this phenomenon as additional stress loading on the Palu fault, driven by the slip during the earthquake 100 km to the North‐East.
Mg‐Fe partitioning between olivine and mafic‐ultramafic melts
Authors: Kushiro Ikuo , Walter Michael J.
Published: February 2004

The partitioning of Mg and Fe between olivine and mafic‐ultramafic melts has been examined based on previous and new experimental data. We find that the exchange partition coefficient, KD, changes primarily as a function of melt composition, expressed either as MgO+FeO content or degree of polymerization, NBO/T, rather than temperature or pressure. KD increases from about 0.23±0.02 at an NBO/T of ∼0 to a maximum of 0.35±0.02 at an NBO/T of ∼ 2, and then decreases to 0.23±0.02 for the pure olivine system (NBO/T=4). We suggest that the following empirical relation yields a reliable estimate of KD for mantle derived melts: KD = 0.235 + 0.120·(NBO/T) ‐ 0.031·(NBO/T)². The change of KD shown here should be taken into account when calculating the composition of olivine coexisting with basaltic to ultramafic melts.
Morphologic dating of slowly evolving scarps using a diffusive analogue
Authors: Niviére Bertrand , Marquis Guy , Maurin Jean‐Christophe
Published: February 2004

Morphologic dating techniques that have been applied successfully in arid and semi‐arid areas are also suitable for slowly evolving scarps that are usually found in temperate climate environments. Two approaches, based on diffusion, to relate the present‐day shape of a scarp to its age are used here. The first assumes a model of scarp degradation based on a diffusive process (D method). The second evaluates the state of scarp degradation using the slope distribution along a topographic profile (SD method). Based on an anthropic scarp of known age, we have obtained a mass diffusivity close to 1.5 m²/ka, a reasonable value for areas characterized by a continuous vegetation cover and a temperate climate. We show that the SD method requires an age correction, since it does not take into account the earliest stage for which the mid‐height point is not yet affected by erosion. However only the SD method reveals that at several profiles a later scarp reactivation event has occurred. Such information can be important when trying to identity the recent geological or environmental events that have affected a region.
Modulation of middle and upper tropospheric ozone at northern midlatitudes by the El Niño/Southern Oscillation
Authors: Langford A. O. , O'Leary T. J. , Masters C. D. , Aikin K. C. , Proffitt M. H.
Published: February 2004

A five‐year time series of lidar profiles from a site in Colorado is used to investigate the sources and scales of variability for ozone in the free troposphere. Analysis of 475 daily mean profiles derived from more than 25,000 individual profiles shows that ∼66% of the total variance is due to fluctuations on time scales from 1 day to 1 month, ∼30% on time scales from 1 month to 1 year, and ∼4% on time scales greater than 1 year. The analysis also identifies low‐frequency fluctuations correlated with the El Niño/Southern Oscillation (ENSO) (following a ∼6‐month lag) that may account for as much as 5% of the total variance in the data. The ENSO‐related changes can also lead to apparent ozone trends that range from −0.2 to +0.5 ppbv/yr for different 10‐year intervals between 1970 and 1990.