bluuebunny/crossref_metadata_2025 huggingface dataset:
The occurrence of lower hybrid cavities in the upper ionosphere
Authors: Dovner P. O. , Eriksson A. I. , Boström R. , Holback B. , Waldemark J. , Eliasson L. , Boehm M.
Published: February 2004

Lower hybrid cavities (LHC', i. e., small‐scale density depletions coinciding with enhanced lower hybrid waves, are frequent in the upper ionosphere. It is found that they exist in all regions the Freja satellite has scanned, as long as lower hybrid waves are present. They are found most frequently at magnetic latitudes between 55° to 65°, preferably on the morning side. In the auroral oval, the LHCs do not occur as densely as at lower latitudes but they usually form larger structures.
Alkenone sea surface temperature in the Southern Ocean for the last two deglaciations
Authors: Ikehara Minoru , Kawamura Kimitaka , Ohkouchi Naohiko , Kimoto Katsunori , Murayama Masafumi , Nakamura Toshio , Oba Tadamichi , Taira Asahiko
Published: February 2004

A piston core taken from the Tasman Plateau in the Southern Ocean has been studied for organic compounds to reconstruct the late Pleistocene marine environments. Here we report paleo sea surface temperature (SST) for the last two deglaciations using the unsaturation degree of alkenones (Uk37′) preserved in the marine sediments. The Uk37′ record indicates that the SST was at least 4°C lower than the present SST at the last glacial maximum (LGM), and the amplitude of paleo‐SST is at most 5.2°C from the penultimate glacial (MIS‐6) to the last interglacial warm period (the Eemian). Our results also demonstrate that the Eemian warm period in the Southern Ocean lasted only 3,000 years followed by a sharp cooling at around 120 kyr BP. The sharp cooling in the Southern Ocean seemed to occur a few millennia (2‐3 kyrs) before the beginning of continental ice‐sheet growth.
Geodetic investigation of the 13 May 1995 Kozani‐Grevena (Greece) Earthquake
Authors: Clarke P. J. , Paradissis D. , Briole P. , England P. C. , Parsons B. E. , Billiris H. , Veis G. , Ruegg J.‐C.
Published: February 2004

The Ms=6.6 13 May 1995 Kozani‐Grevena earthquake struck a region of low historical seismic activity which includes a 10‐year‐old triangulation network in northern Greece. After the earthquake, monuments from this network were occupied with GPS to measure co‐seismic displacements. Inversion of the co‐seismic displacement field to yield a source mechanism is achieved by use of a hybrid simplex‐Monte‐Carlo method which requires no a priori constraints. The model focal mechanism agrees well with the global CMT solution and locally observed aftershocks, but implies a significantly higher scalar moment than do seismological or SAR interferometry studies, and has a longer fault length than the model based on SAR interferometry.
A water well sensitive to seismic waves
Authors: Ohno Masao , Wakita Hiroshi , Kanjo Kenji
Published: February 2004

The water level in an observation well (EDY) has been monitored with high frequency sampling (1/sec). Large changes in the water level are observed in this well, which correspond to dynamic strain changes due to the passage of long period seismic waves. For example, fluctuations of more than 200 cm were observed after a M 8.1 earthquake, 1200 km from the observation site. The response characteristic of the water level to strain change was investigated by comparison with nearby volumetric strain changes: the response curve has a peak of sensitivity and a phase transition at periods of 18∼19 seconds. At the resonant period, the sensitivity is as large as 15 mm per 10−9 strain.
CUPRI observations of the east‐west power asymmetry in oblique type‐I echoes from the equatorial electrojet above Alcântara, Brazil
Authors: Swartz Wesley E.
Published: February 2004

Radar observations of the equatorial electrojet at oblique incidence made by the Cornell University Portable Radar Interferometer (CUPRI) from Alcântara, Brazil show the same east‐west asymmetry in the echo strength seen previously at Jicamarca, Peru, namely type‐I echoes from the west are stronger than those from the east [Balsley, 1965]. One early theory attributed the results at Jicamarca to topographical asymmetries with the Andes Mountains to the east and the Pacific Ocean to the west [Ierkic et al., 1980]. However, the lack of comparable topographical features at Alcântara now implies that this postulate is no longer tenable. Other proposed theories are then examined, but none has so far been found to be fully consistent with both the CUPRI and the Jicamarca data.
A novel method for compound specific determination of δ13C in volatile organic compounds at ppt levels in ambient air
Authors: Rudolph J. , Lowe David C. , Martin R. J. , Clarkson T. S.
Published: February 2004

A novel method for the compound specific determination of δ13C in VOC is presented. It combines a cryogenic preconcentration procedure with gas chromatographic separation, on‐line combustion and isotope ratio mass spectrometry. The method allows the determination of δ13C values of VOC at sub ppb levels with a precision of 0.5‰. The procedure is suitable for routine operation. The accuracy of the method is of the same quality as the reproducibility of the measurements. The first ever measurements of δ13C in selected VOC in clean air are presented and compared with data from samples of contaminated air. The variability in the δ13C values of atmospheric VOC is much larger than the accuracy and precision of the measuring method. Hence the technique will be a very valuable tool to complement concentration measurements of VOC and to improve our understanding of the processes governing the distribution of VOC in the atmosphere.
The Latitudinal Structure of the Solar Wind in the Vicinity of the Solar Equator near Solar Minimum: 1986 and Predictions for 1997
Authors: Gazis P. R.
Published: February 2004

In situ observations by different spacecraft have shown that the heliospheric current sheet (HCS) is associated with a narrow band of low speed high density solar wind. The inclination of the HCS and the three‐dimensional structure of solar wind streams is related to the inclination of the coronal neutral line. Observations from the Ulysses spacecraft during the descending phase of solar cycle 22, when Wilcox Solar Observatory coronal field models suggest that the inclination of the coronal neutral line was between 50° and 70°, showed that the inclination of the HCS was ≃20° while solar wind streams were confined to heliographic latitudes less than 35°. At higher latitudes, low and medium speed solar wind disappeared and the solar wind speed was uniformly high. Observations from the Pioneer 11 ‐ Voyager 2 spacecraft pair near the time of the 1986 solar minimum revealed a different structure. At that time the inclination of the coronal neutral line was unusually low (<10°–15°). Solar wind streams vanished near the solar equator and may have disappeared at most heliographic latitudes in the outer heliosphere. This has implications for the forthcoming Ulysses equatorial pass at the end of 1997, when the inclination of the coronal neutral line and the HCS are again expected to be low. If the HCS is sufficiently flat, conditions may resemble those observed near the time of the 1986 solar minimum and the solar wind stream structure may disappear at Ulysses near the solar equator.
Contribution of particulate sulfate and organic carbon to cloud condensation nuclei in the marine atmosphere
Authors: Matsumoto Kiyoshi , Tanaka Hiroshi , Nagao Ippei , Ishizaka Yutaka
Published: February 2004

To identify the source of cloud condensation nuclei(CCN) in the marine atmosphere, simultaneous measurements of aerosol chemical components and CCN concentration were made over more than a year at Hahajima, the Ogasawara Islands, located on the Northwest Pacific Ocean in the lee of Eastern Asian large pollution sources. Large loading of CCN in continental air mass and long‐distance transportation to the remote ocean were confirmed. Non‐seasalt sulfate and water soluble organic carbon were dominant in fine aerosols and their concentration revealed significant relationships with CCN concentration, suggesting that not only sulfate but also organic aerosols play a key role in CCN formation, especially in the background atmospheric condition.
Variations of tropospheric HCl amounts over northern Sweden
Authors: Wegner A. , Stiller G. P. , von Clarmann T. , Trieschmann O. , Fischer H. , Reimer E.
Published: February 2004

Unexpectedly large variations of tropospheric HCl zenith column amounts were observed over Kiruna, Northern Sweden, in the arctic winters of 1991/92 and 1992/93. Trajectory calculations prove a strong dependence of tropospheric HCl variation on the origin of the air mass observed. This effect cannot be explained by different altitudes of the tropopause caused by dynamical processes. Polar maritime air contains 0.67 ± 0.11 × 1015 more HCl molecules cm−2, in terms of tropospheric zenith column amounts, than maritime midlatitudinal air. The latter contains 0.39 ± 0.16 × 1015 more HCl molecules cm−2 than continental air from midlatitudes. The HCl loading of arctic air is comparable to that of maritime polar air, except for one measurement on January 28, 1993, which showed significantly less tropospheric HCl. Tropospheric chlorine activation, along with ozone destruction in the troposphere, is considered a candidate for explanation. Furthermore, HCl strongly correlates with CH2O.
Sedimentation of barium ions from the CRRES G‐9 release
Authors: Frey H. U. , Haerendel G. , Valenzuela A.
Published: February 2004

The CRRES G‐9 barium release was designed for the investigation of the field line tracing between the release point at 17.4°N latitude and the area of ion cloud sedimentation at about −41°S latitude. Very recently published images of the ion cloud after the release showed the development of at least two weak filaments between the release point and the main ion cloud [Zaitsev et al., 1996]. Observations made from an aircraft in the south Atlantic region verify that at least one of these filaments survived the transequatorial transit and was still separated from the main barium cloud during sedimentation.
Recent abnormal changes in wintertime atmospheric response to tropical SST forcing
Authors: Kawamura Ryuichi , Sugi Masato , Kayahara Takahiro , Sato Nobuo
Published: February 2004

An ensemble of climate experiments has been performed using a T42 GCM version of the Japan Meteorological Agency global model to examine abnormal changes in the wintertime extratropical atmospheric response to anomalous sea surface temperature (SST) forcing in recent decades. Three independent 39‐year integrations for the period 1955–1993 are forced by the same observed SST boundary condition. Although the tropical Pacific SST anomalies since the late 1980s indicate El Nino‐like patterns, the Pacific/North American teleconnection (PNA) pattern is found to be hardly simulated, which stands in sharp contrast with that for the period 1977–1983. The SSTs in the vicinity of the maritime continent (the Indonesian region), including the tropical Indian Ocean, are very high during the period 1987–1993 and associated model atmosphere does undergo pronounced zonal heating over almost the entire tropics. Such tropical heating does not necessarily favor the barotropic Rossby wave dispersion into the extratropics emanating out of convective forcing since weakened Walker circulation is not capable of producing localized strong divergence anomalies, hence inhibiting generation of apparent vorticity sources in the subtropics. If the prevailing tendency of high SSTs in the vicinity of the maritime continent persists from now on, it is anticipated that a good correlation between El Nino‐Southern Oscillation (ENSO) and PNA, which has been pointed out by previous numerous studies, becomes insignificant. This anomalous feature may be viewed as a signature of global warming.
Electron density fluctuations in the equatorial mesosphere: Neutral Turbulence or plasma instabilities?
Authors: Lehmacher G. A. , Goldberg R. A. , Schmidlin F. J. , Croskey C. L. , Mitchell J. D. , Swartz W. E.
Published: February 2004

Electron density fluctuations were measured with rocket borne nose‐tip probes launched on August 19, 1994 at 12:08 LT and August 24, 1994 at 10:39 LT from Alcântara, Brazil (2.3°S, 44.4°W) during the MALTED/Guará campaign. The spectral analysis of the fluctuations shows evidence for neutral turbulence in the region of 85 to 90 km for both flights. Falling spheres launched 44 and 13 minutes prior to the main payloads indicate superadiabatic lapse rates in this height region. Also for the two flights, the electron density fluctuations between 90 and 110 km are dominated by the equatorial electrojet which has been observed simultaneously by the 50‐MHz CUPRI VHF radar. The in situ data show significant plasma irregularities associated with the electrojet at altitudes well below those that return detectable radar echoes, and where they can interfere with the fluctuations attributed to neutral turbulence.
Melting of CaSiO3 perovskite to 430 kbar and first in‐situ measurements of lower mantle eutectic temperatures
Authors: Zerr A. , Serghiou G. , Boehler R.
Published: February 2004

Melting temperatures of CaSiO3 perovskite were measured between 160 and 430 kbar in a diamond anvil cell under hydrostatic, inert conditions using CO2‐laser heating. The melting temperatures are higher than those obtained in previous YAG‐laser heating experiments [Shen and Lazor, 1995], where chemical reactions of the sample with rhenium might have caused a lowering in the melting temperatures. The melting temperatures of CaSiO3 perovskite are slightly higher than those of (Mg,Fe)SiO3 perovskite [Zerr and Boehler, 1993], thus making the two major minerals of the lower mantle Mg‐Si‐perovskite and magnesiowüsite the low‐melting components. First in‐situ measurements of the eutectic melting temperatures of these two minerals are presented. The data suggest that eutectic melting depression in the lower mantle may be insignificant. An alternate solution for the extrapolation of the measured melting temperatures to higher pressures, based on recent observations on the highly compressible alkali halides, yields melting temperatures at the bottom of the lower mantle below 6000 K.
Imaging spread‐F structures using GPS observations at Alcântara, Brazil
Authors: Musman S. , Jahn J.‐M. , LaBelle J. , Swartz W. E.
Published: February 2004

During October 1994, a dual‐frequency GPS receiver was operated in Alcântara, Brazil, at the same site where the Cornell University Portable Radar Interferometer (CUPRI) was performing spread‐F measurements for an ongoing rocket campaign. We present data for two nights during which several spread‐F plumes drifted through the field‐of‐view of CUPRI. Fluctuations in the total electron content (TEC) measured with the GPS receiver were correlated with those plumes. We define a “roughness” measure from a specialized high frequency filter. Plots of “roughness” in a magnetic longitude versus time space show initially low activity followed by regions of dramatic localized onsets and a slower subsequent decline. Features in the roughness image are well‐correlated with plumes in the CUPRI backscatter power map.
Magma budgets and steady‐state activity of Vulcano and Stromboli
Authors: Harris Andrew J. L. , Stevenson David S.
Published: February 2004

We present three models for magma budget during steady‐state volcanic activity, by which non‐erupted magma is emplaced as dykes or cumulates or crystallises in place. Using gas and thermal data we apply our models at Vulcano to calculate degassing, cooling and crystallisation of magma at a rate of 40–375 kg s−1 within a magma body with an upper surface at a ∼2 km depth. At Stromboli we calculate a steady magma supply of 300–1300 kg s−1 to shallow (<1 km) depths.
Observation of NO and NO2 in the young plume of an aircraft jet engine
Authors: Haschberger P. , Lindermeir E.
Published: February 2004

For the first time the emission indices of NO and NO2 were measured simultaneously in‐flight by a non‐intrusive spectrometric measurement setup. Moreover the method described here is capable of determining the (static) temperature of the exhaust gas and emission indices for H2O and CO at the same time with a precision of 1–4%. After a very brief description of the experimental setup, results of measurements are shown. They reveal mean emission indices for EI(NO2) of 1 g/kg and 3–5 g/kg for EI(NO) (estimated accuracy: 20–25%). The ratio of concentrations [NO2]/[NOx] of 12–22% is by a factor of approximately two higher than most values cited for other engines. Based on the bulk mean properties of the plume it is shown that the temperature determination is accurate to several Kelvin.
Alfvén modulation of the substorm magnetotail transport
Authors: Sánchez E. R. , Kelly J. D. , Angelopoulos V. , Hughes T. , Singer H.
Published: February 2004

This work explores the proposition that magnetic field resonances modulate the transport of particle and magnetic flux in the earth's magnetotail. Coordinated high‐ and low‐altitude measurements during a substorm show periodic variations of magnetic field, plasma density and flow bursts in the magnetotail with frequencies that correlate well with those of magnetic field oscillations at geosynchronous altitude and pulsations measured by ground‐based stations. The pulsations' frequency is in the Pc 5 range. The example presented here occurred during the substorm period of May 19–20, 1996, that was chosen as the first ISTP/GGS campaign for the ground‐based and theory investigations. There appears to be a resonance between modes sustained by the near‐Earth magnetic field and compressional and flapping pulsations that can be sustained by the magnetotail.
Structure and crystal chemistry of Phase G, A new hydrous magnesium silicate synthesized at 22 GPa and 1050°C
Authors: Kudoh Y. , Nagase T. , Mizohata H. , Ohtani E. , Sasaki S. , Tanaka M.
Published: February 2004

A single crystal of phase G, Mg1.24Si1.76H2.48O6 synthesized at conditions of 1050°C and 22 GPa, using a multi‐anvil apparatus was studied at the Photon Factory BL‐10A beamline at the National Laboratory for High Energy Physics, Tukuba, Japan. With a (111) Si double‐crystal monochromator and a single crystal measuring 47 × 35 × 12 µm, intensities of 95 independent reflections were collected with sin θ/λ <0.72 Å−1 and Io >1.5 σ Io at a wave length of 0.6990 Å. The unit cell parameters obtained through the refinement of 23 reflections are: Trigonal, a=4.790 (3) Å, c=4.344 (3) Å, V=86.3 (2) Å³. The result of structure analysis in space group P
1m (No. 162) indicates that the structure of phase G has close structural similarity to that of stishovite,SiO2. The calculated density of phase G is 3.43 g/cm³, which is larger than any other known dense hydrous magnesium silicate, suggesting that phase G might be stable even under lower mantle conditions.
Why do North American climate anomalies differ from one El Niño event to another?
Authors: Hoerling Martin P. , Kumar Arun
Published: February 2004

This study explores the cause of the appreciable variations in North American climate from one El Niño event to another. Two competing sources of inter‐El Niño variations are examined; one associated with differences in sea surface temperature (SST) forcing between El Niño events, and the other associated with purely internal atmospheric processes that operate independently of El Niño. The analysis is based upon a large ensemble of atmospheric general circulation model (AGCM) simulations that are forced with the observed variations in global SSTs during 1950–1994. From investigation of the seven strongest warm events in this record, the AGCM is shown to possess only one dominant large‐scale pattern over the Pacific‐North American region. The case‐to‐case variability seen in nature is thus claimed to be primarily due to atmospheric processes, and the inter‐El Niño differences in SST appear to be of secondary importance. The significance of these results for an atmosphere‐ocean forecasting system are discussed.
CUPRI observations of persistence asymmetry reversals in up‐down vertical type‐I echoes from the equatorial electro jet above Alcântara, Brazil
Authors: Swartz Wesley E.
Published: February 2004

High resolution vertical radar measurements of the equatorial electrojet above Alcântara, Brazil, were made with the Cornell University Portable Radar Interferometer (CUPRI) as part of the Guará Dip Equator Campaign. Type‐I spectra obtained from the main body of the electrojet during strong daytime conditions show a preponderance of upward phase velocities as a function of time. However, the data from a few kilometers higher show a persistence of downward phase velocities. This reversal in sign of the most persistent type‐I peak occurs regularly in our data whenever the electrojet is strongly driven. The persistence of upward phase velocities is similar to that seen earlier at Jicamarca but the reversal in sign of the dominating mode has not been previously observed, nor is it consistent with current electrojet theories. Another unexpected result from the Alcântara data set is that the absolute values of the phase velocities of the type‐I spectra peaks decrease with altitude. This is through a region where the temperature (and hence the acoustic velocity) should be increasing with altitude. Hence, the saturation of the type‐I peak phase velocities is not just a simple function of the acoustic velocity.
Observations of ultrafine aerosol particle formation and growth in boreal forest
Authors: Mäkelä J. M. , Aalto P. , Jokinen V. , Pohja T. , Nissinen A. , Palmroth S. , Markkanen T. , Seitsonen K. , Lihavainen H. , Kulmala M.
Published: February 2004

Number size distribution of ambient submicron and ultrafine aerosol particles have been measured on a continuous basis (every 10 minutes) for three quarters of the year 1996, at a forest site in Southern Finland. Continuous monitoring offers additional insight over the diurnal dynamics of the submicron size distribution, including existence of clearly separate size modes as well as events of new particle formation. Selected examples of the measured size distributions are presented, including the particle formation events observed at the measurement site. Typical characteristics of days with particle formation events versus days of no events are discussed.
Achieving zero current for polar wind outflow on open flux tubes subjected to large photoelectron fluxes
Authors: Wilson G. R. , Khazanov G. , Horwitz J. L.
Published: February 2004

In this study we investigate how the condition of zero current on open flux tubes with polar wind outflow, subjected to large photoelectron fluxes, can be achieved. We employ a steady state collisionless semikinetic model to determine the density profiles of O+, H+, thermal electrons and photoelectrons coming from the ionosphere along with H+, ions and electrons coming from the magnetosphere. The model solution attains a potential distribution which both satisfies the condition of charge neutrality and zero current. For the range of parameters considered in this study we find that a 45–60 volt discontinuous potential drop may develop to reflect most of the photoelectrons back toward the ionosphere. This develops because the downward flux of electrons from the magnetosphere to the ionosphere on typical open flux tubes (e.g. the polar rain) appears to be insufficient to balance the photoelectron flux from the ionosphere.
Cyclicity and NRM acquisition in the armantes section (Miocene, Spain): Potential for an astronomical polarity time scale for the continental record
Authors: Krijgsman W. , Delahaije W. , Langereis C. G. , de Boer P. L.
Published: February 2004

The results are presented of a detailed study of a short (250 kyr) interval from a cyclically bedded continental sequence that is composed of alternating reddish silts and whitish limestones (Armantes section, Central Spain). The lithology as well as the carbonate and gamma‐ray records indicate that five small‐scale cycles are developed in one large‐scale cycle, implying that the small‐scale cyclicity is related to precession and thus caused by climate forcing. Rock magnetic experiments show that the NRM is carried by hematite and magnetite/maghemite and that the relative contribution of hematite is related to lithology. The positions of the reversal boundaries can reliably be determined, even though reversals of the magnetite and hematite components appear to be recorded at slightly different levels. We conclude that the well‐developed cyclicity and the good paleomagnetic properties of the sediments will enable the construction of an astronomical polarity time scale (APTS) for the continental realm.
Sound velocities of clinohumite, and implications for water in Earth's upper mantle
Authors: Fritzel Theresa L. Beckman , Bass Jay D.
Published: February 2004

The velocities of longitudinal and shear acoustic waves were measured for clinohumite, a possible host for water in the upper mantle. Brillouin scattering measurements on a natural crystal under ambient conditions indicate that the hydration of olivine to clinohumite lowers most of the single‐crystal elastic moduli, as well as the bulk and shear moduli of a polycrystalline aggregate. However, the velocities of mantle rocks in which all olivine is hydrated to clinohumite are only 1–1.5% lower than those of the equivalent dry rocks under ambient conditions. These results suggest that in shallow, cold portions of the uppermost mantle (for example the seismic lid), water may be difficult to identify seismologically if all of it is bound up in humite‐group minerals. Negative velocity anomalies in the shallow mantle may require a different explanation than the presence of hydrous minerals.
Horizontally propagating quasi‐sinusoidal tropospheric waves observed in the lee of the Andes
Authors: Liziola Luis E. , Balsley Ben B.
Published: February 2004

VHF profiler observations of the troposphere obtained over a flat desert in northern Perú show the presence of strong, quasi‐sinusoidal oscillations in the vertical wind velocity with periods of around 8–18 minutes. These oscillations are a very consistent feature of the vertical velocities over Piura, and are also observed at other profiler locations. This paper presents an overview of the wave characteristics obtained at Piura until this point, including results obtained using a second antenna built a few hundreds meters to the west of the main antenna to measure horizontal wavelengths and phase velocities. Briefly, the Piura waves appear to have horizontal wavelengths in the zonal direction of 5–10 m, with either westward or eastward phase velocities (in a ground‐based reference frame) of 5–15 m s−1. Their occurrence appears to be causally related to the magnitude of the easterly wind, which blows over the Andean Cordillera some 60 km to the east of the site.
Some remarks on the estimation of fractal scaling parameters from borehole wire‐line logs
Authors: Dolan Seán S. , Bean Christopher J.
Published: February 2004

Well‐logging provides a direct means of assessing fluctuations in petrophysical properties with depth, and thus allows for the statistical characterisation of crustal heterogeneity. Using records from three super‐deep boreholes (KTB and Cajon Pass) and synthetic data, we assess three different techniques for estimating fractal dimension and correlation length. Inaccurate correlation lengths may result from the way in which the autocorrelation is calculated for well‐logs, leading to an incorrect application of the von Kármán function. Analysis of the rescaled range, power spectra and autocorrelation allow us to model the data as k−β (where k = wavenumber and exponent β=5–2D, for fractal dimension D) process with values of fractal dimension displaying anti‐persistence.
Climatic impact of aircraft induced ozone changes
Authors: Sausen Robert , Feneberg Brigitte , Ponater Michael
Published: February 2004

The effect of aircraft induced ozone changes on the global climate is studied by means of the general circulation model ECHAM4. We focus on the zonal mean temperature signal. In order to estimate the statistical significance of the climatic impact a multivariate statistical test hierarchy combined with the fingerprint method has been applied. Our sensitivity experiments suggest the existence of a coherent temperature response pattern for northern hemisphere summer conditions. The signal is highly significant in case of an artificially enhanced forcing, but it retains its characteristic structure for present‐day forcing conditions, when statistical significance becomes more moderate. The signal consists of a tropospheric warming of about 0.2 K and a corresponding stratospheric cooling of similar magnitude.
Recent observations of a spring‐summer surface warming over the Arctic Ocean
Authors: Martin Seelye , Munoz Esther , Drucker Robert
Published: February 2004

For the Arctic Ocean, a 1961–1990 trend analysis of the 2‐m, 6‐hourly air temperatures from the Russian North Pole (NP) drifting ice stations shows a significant warming in May and June, or seasonally in summer. In this analysis, if we choose temperatures from only those stations which report at least 95% of the time, and define an anomaly field by removal of a mean temperature field, then for both the temperature and anomaly fields, we obtain statistically significant May and June warmings of respectively 0.8 and 0.4°C/decade, and a summer seasonal warming of 0.2°C/decade. For the other seasons, although our trends are not statistically significant, they match the trends derived for the same period from the Arctic land stations.
Significant P wave attenuation for a specific frequency range beneath Kirishima Volcano, Japan
Authors: Yamamoto K. , Ida Y.
Published: February 2004

The three‐dimensional P wave attenuation structure beneath Kirishima Volcano, southwest Japan, was obtained through tomographic inversion of 469 P wave seismograms from 41 regional events recorded at 14 stations. Using band‐pass filtered P wave amplitude data, the inversion determined the deviatoric attenuation constants of 4 km × 4 km × 5 km (SW‐NE, SE‐NW, depth) blocks in the study volume as a function of seismic wave frequency. The result delineates strikingly high attenuation at the depth of about 5 km beneath the highest cinder cone, Karakuni‐dake, in the central region of Kirishima Volcano. The attenuation constant in this region shows strong frequency dependence with greatest absorption around 8 Hz. This result is interpreted to represent the absorption of seismic waves by an 80 m thick sill‐like magma body there.
First energetic neutral atom images from Polar
Authors: Henderson M. G. , Reeves G. D. , Spence H. E. , Sheldon R. B. , Jorgensen A. M. , Blake J. B. , Fennell J. F.
Published: February 2004

Energetic neutral atoms are created when energetic magnetospheric ions undergo charge exchange with cold neutral atoms in the Earth's tenuous extended atmosphere (the geocorona). Since they are unaffected by the Earth's magnetic field, these energetic neutrals travel away in straight line trajectories from the points of charge exchange. The remote detection of these particles provides a powerful means through which the global distribution and properties of the geocorona and ring current can be inferred. Due to its 2 × 9 RE polar orbit, the Polar spacecraft provides an excellent platform from which to observe ENAs because it spends much of its time in the polar caps which are usually free from the contaminating energetic charged particles that make observations of ENAs more difficult. In this brief report, we present the first ENA imaging results from Polar. Storm‐time ENA images are presented for a northern polar cap apogee pass on August 29, 1996 and for a southern polar cap perigee pass on October 23, 1996. As well, we show with a third event (July 31, 1996) that ENA emissions can also be detected in association with individual substorms.
Statistical evidence links exceptional 1995 Atlantic Hurricane season to record sea warming
Authors: Saunders Mark A. , Harris Andrew R.
Published: February 2004

Tropical cyclones rank above earthquakes as the major geophysical cause of loss of life and property (Bryant, 1991; Houghton, 1994). In the United States alone, the damage bill from mainland landfalling hurricanes over the last 50 years averages $2.0 billion per year (Hebert et al., 1996). Years with high numbers of hurricanes provide new insight on the environmental factors influencing interannual variability; hence the interest in the exceptional 1995 Atlantic season which saw 11 hurricanes and a total of 19 tropical storms, double the 50‐year average. While most environmental factors in 1995 were favourable for tropical cyclone development, we show that a factor not fully explored before, the sea surface temperature (SST) was the most significant. For the 10°–20°N, 20°–60°W region where 93% of the anomalous 1995 hurricanes developed, ∼45 year statistical regressions show that SST is the dominating influence, independent of all known other factors, behind the interannual variance in Atlantic hurricance numbers. With this SST experiencing record warm levels in 1995, 0.66°C above the 1946–1995 mean, these regressions indicate that sea warming explains 61±34% of the anomalous hurricane activity in 1995 to 95% confidence.
Evidence of currents and unstable particle distributions in an extended region around the lunar plasma wake
Authors: Bale S. D. , Owen C. J. , Bougeret J.‐L. , Goetz K. , Kellogg P. J. , Lepping R. P. , Manning R. , Monson S. J.
Published: February 2004

We report observations of electrostatic ion acoustic waves and Langmuir waves during a recent lunar encounter by the Wind spacecraft. These waves are observed when Wind is magnetically connected to the nominal wake and at distances greater than 8 lunar radii from the wake. When interpreted in the context of a simple time‐of‐flight model, these observations imply the existence of a system of currents and disturbed particle distributions that extends far into solar wind.
Ion cyclotron waves in the Io torus during the Galileo encounter: Warm plasma dispersion analysis
Authors: Huddleston D. E. , Strangeway R. J. , Warnecke J. , Russell C. T. , Kivelson M. G. , Bagenal F.
Published: February 2004

During the Galileo‐Io flyby, nearly field‐aligned, left‐hand circularly polarized ion cyclotron waves were observed in a band near the sulfur‐dioxide ion gyrofrequency. We have performed a warm plasma dispersion analysis using nominal Io torus composition ratios, pickup ion “ring”‐type velocity‐space distributions, and a thermal background plasma of typical torus temperature. Analysis shows that the SO2+ wave is dominant, particularly as the ring begins to broaden. The observed spectral peak indicates that the ring distribution of pickup SO2+ is highly unstable and generates waves, but there is unlikely to be sufficient time for ions to fully thermalize before dissociation occurs. Assuming wave‐particle scattering of ions towards a “bispherical” shell‐type distribution, a free energy analysis and comparison with observed wave amplitudes suggests that the ions are not scattered far from the ring and/or that the SO2+ composition ratio in the Io torus falls off considerably from Io wake values.
Bromine emissions from leaded gasoline
Authors: Thomas V. M. , Bedford J. A. , Cicerone R. J.
Published: February 2004

Gasoline lead additives contain brominated compounds. When leaded gasoline is combusted, some of the bromine can be emitted as methyl bromide which can contribute to stratospheric ozone depletion. Based on world use of lead in gasoline and on gasoline scavenger formulations, we estimate that worldwide use of bromine in gasoline peaked in the early 1970s at 170±20 kT/yr and that by 1995 this had decreased to 23±2.5 kT/yr. The fraction of bromine in leaded gasoline that is emitted as methyl bromide ranges over two orders of magnitude. At the upper end of this range, the decrease in methyl bromide emissions from the 1970s to the 1990s could have equaled the increase in emissions from use of methyl bromide as a fumigant in the same period.
Subsurface creep on the Hayward Fault, Fremont, California
Authors: Bilham Roger , Whitehead Scott
Published: February 2004

Surface creep on the Hayward fault at Fremont has been sustained for the past century at 8.2±0.1 mm/year. Two surface creepmeters record a similar mean creep rate in the past 3 years, but the data show significant irregularity despite being anchored at depths of 10–28 m. The serendipitous piercing of the subsurface fault by one of the creepmeter anchors, whose deflection at depth has been regularly monitored with a biaxial inclinometer system, reveals two fault traces dipping at ≈ 70°. At 21 m depth the Hayward fault slips dextrally at 8.1±0.4 mm/yr, and at ≈ 7 m depth a subsidiary fault slips bidirectionally adding noise to the surface creep data. Surface creep on this segment of the Hayward fault was arrested by stress changes following the 1989 Loma Prieta earthquake, but resumed in 1994. Tilt of the borehole, and a similar borehole east of the fault, is 3 orders of magnitude too large to be driven by uniform creep extending to depths of several km, and we conclude that irregular slip on the fault occurs in the uppermost few hundred meters. Cumulative dilatational strain since 1868 near segments of the fault NW of the creepmeter may exceed 200 µstrain, unless absorbed by undocumented slip off the main fault trace.
The Complex Rupture Process of the 1996 Deep Flores, Indonesia Earthquake (Mw 7.9) from teleseismic P‐waves
Authors: Goes Saskia , Ruff Larry , Winslow Nathan
Published: February 2004

From an analysis of broadband teleseismic P‐waveforms we resolve the complex rupture characteristics of the 17 June 1996, Flores earthquake (Mw 7.9, depth 590 km). This earthquake was unusual because of its large rupture length and the variation in rupture velocity and stress drop. The 20 s rupture propagated westward at 2–3 km/s to a distance of 20–30 km, and eastward at 4 km/s over 75 km. Average static stress drop was about 15 MPa, but the stress drop during the episode of main moment release was a factor of four higher. The oblique normal faulting mechanism is consistent with the stress expected as the slab descends along a highly curved trench. Significant rupture complexity is also reported for the deep 1994 Mw 7.7 Fiji and Mw 8.2 Bolivia earthquakes and is evident in the source‐time functions of many smaller earthquakes at depths >300 km. Thus source complexity of deep earthquakes appears no less common than for shallow earthquakes, and requires the existence of significant heterogeneity in the physical properties that control deep earthquake rupture.
Surface wave waveform inversions for local shear‐wave velocities under eastern Australia
Authors: Passier M. L. , van der Hilst R. D. , Snieder R. K.
Published: February 2004

The waveform inversion method developed by Kushnir et al. [1989] and expanded by Passier and Snieder [1995b] yields estimates of structure along short interstation paths and of average velocity gradients. In contrast, 3D tomographic inversions yield local estimates of the earth structure by combining the information contained in a large set of long propagation paths. Both approaches lead to estimates of the local earth structure, but the two methods are subject to different types of artifact. As a test case of the consistency of the two approaches we consider the recent S‐velocity model of the Australian region by Zielhuis and Van der Hilst [1996]. We invert 20 Rayleigh wave waveforms between 20 and 110 s recorded on the Australian continent, most of them by the mobile Skippy network. From the data, we directly extract measurements of the S‐velocity structure at various short interstation paths in Australia and obtain estimates of the average velocity gradient along long paths. The estimates of the local interstation structure and the estimates of the velocity gradient are consistent with the 3D model of Zielhuis and Van der Hilst [1996]. These results provide illustrative examples of how specific features of a complex velocity structure can be determined using only a few waveforms.
The permeability of young oceanic crust east of Juan de Fuca Ridge Determined using borehole thermal measurements
Authors: Fisher A. T. , Becker K. , Davis E. E.
Published: February 2004

Temperature measurements made in Ocean Drilling Program (ODP) Hole 1026B, drilled into a sediment‐buried basement ridge in 3.5 m.y. old crust on the eastern flank of Juan de Fuca Ridge, revealed fluid flow from the formation and into the overlying ocean. This flow indicates that the upper basaltic crust at this site is naturally overpressured relative to hydrostatic. This finding is consistent with output from previously published numerical models of hydrothermal circulation in the upper crust that include appropriate crustal geometry, sediment thickness, and basal heat flow. The fluid flowing into Hole 1026B enters the hole through the upper 10 m of basalt below the sediment‐basement contact. The flow rate estimated from the thermal data (80–120 m/hr), in combination with the inferred basement overpressure relative to hydrostatic (about 20–30 kPa), was used to estimate the bulk permeability of the shallowest oceanic crust: 5 to 9 × 10−12 m². Such high bulk permeability would allow regionally significant hydrothermal circulation, consistent with thermal homogenization of upper basement in this area.
Bifurcated cusp ion signatures: Evidence for re‐reconnection?
Authors: Fuselier S. A. , Shelley E. G. , Peterson W. K. , Lennartsson O. W. , Collin H. L. , Drake J. F. , Ghielmetti A. G. , Balsiger H. , Burch J. L. , Johnstone A. , Rosenbauer H. , Steinberg J. T.
Published: February 2004

Toroidal Imaging Mass‐Angle Spectrograph (TIMAS) ion composition measurements during a pass of the POLAR spacecraft through the Earth's magnetospheric cusp show a bifurcated ion signature. High energy (several keV/e) solar wind ions are observed simultaneously with a low energy (up to several hundred eV/e) component. The high energy component exhibits an energy‐latitude dispersion consistent with magnetic reconnection at the dayside magnetopause and velocity filtering in the cusp. The low energy component exhibits no such dispersion. Simultaneous observations of the solar wind ion composition from the WIND spacecraft indicate that the high and low energy components in the cusp have a higher He2+/H+ density ratio than that in the solar wind. Additional solar wind data show that the IMF was southward and the solar wind plasma and magnetic field were relatively steady. These POLAR and WIND observations are interpreted as evidence for continuous re‐reconnection of magnetospheric field lines that thread the high latitude cusp.
Initial POLAR MFE observation of substorm signatures in the polar magnetosphere
Authors: Kawano H. , Le G. , Russell C. T. , Rostoker G. , Mukai T. , Spence H.
Published: February 2004

This paper studies substorm influences in the polar magnetosphere using data from the POLAR magnetic field experiment (MFE). The POLAR spacecraft remains in the high altitude polar magnetosphere for extended periods around apogee. There it can stay at nearly constant altitude through all phases of a substorm, which was not possible on previous missions. We report such an event on March 28, 1996. Ground magnetometers monitored substorm activity, while the POLAR spacecraft, directly over the pole at (−0.8, −0.6, 8.5) RE in GSM coordinates, observed a corresponding perturbation in the total magnetic field strength. The total magnetic field first increased, then recovered toward quiet levels, consistent with erosion of magnetic flux from the dayside magnetosphere, followed by transport of that flux to the magnetotail, and eventual onset of tail reconnection and the return of that magnetic flux to the dayside magnetosphere.
A new upshifted spectral stimulated electromagnetic emission structure, observed between electron cyclotron harmonics
Authors: Frolov V. L. , Ermakova E. N. , Erukhimov L. M. , Komrakov G. P. , Sergeev E. N. , Stubbe P.
Published: February 2004

Observations are reported of a new upshifted stimulated electromagnetic emission (SEE) feature, termed broad upshifted structure (BUS). This wideband emission is found to be upshifted by up to 170 kHz above the pump frequency if the pump frequency lies in a frequency range far from a gyroharmonic frequency. The dependence of the BUS feature on the pump frequency and pump power, as well as its temporal evolution, are investigated. The experiments were carried out at the Sura heating facility in Russia by modification of the ionospheric F region, using a HF ordinary mode pump wave.
DC polarization electric field, current density, and plasma density measurements in the daytime equatorial electrojet
Authors: Pfaff Robert F. , Acuña Mario H. , Marionni Paul A. , Trivedi Nalin B.
Published: February 2004

Measurements of the vector DC electric field, current density, and plasma number density were gathered in the daytime equatorial electrojet on a sounding rocket launched from Alcântara, Brazil. The data set provides a self‐consistent picture of the electrodynamics of the daytime electrojet, permitting a detailed comparison of the altitude profiles of the vertical component of the DC electric field, Evert, the current density, J, and the plasma number density, Ne. Good agreement in the upper electrojet region between both the magnitude and the profile of the plasma drifts, calculated independently from Evert/B and Jzonal/qNe, demonstrates that the equatorial electrojet is a Hall current consisting of electron motion driven by a vertical DC electric field. The data support the basic Cowling conductivity ideas of electron flow at the dip equator within a narrow conducting layer in which the ions are at rest.
Electrical conductivity anomalies beneath the Western Sea of Kyushu, Japan
Authors: Shimoizumi M. , Mogi T. , Nakada M. , Yukutake T. , Handa S. , Tanaka Y. , Utada H.
Published: February 2004

Geomagnetic depth soundings have been made in the area covering Kyushu island and its neighboring islands in the western sea of Kyushu to investigate the back‐arc conductivity structure. The in‐phase induction arrows derived from geomagnetic variations are found to point roughly southwestwards at most sites on Kyushu island for the period range 300–7200 sec. This is quite different from some other areas of Japan. The non‐uniform thin sheet model calculation indicates that the induction arrows in this area are strongly influenced by the surrounding seas. However, the observed arrows have much more intense westward components than indicated by the model calculations. This strongly suggests existence of highly conducting layers (HCLs) beneath the East China Sea. And the existence of HCLs in the upper mantle are confirmed by a two‐dimensional finite element modeling. These HCLs may be considered to be a part of mantle upwelling extended to East China Sea.
Noctilucent clouds: One‐ and two‐color lidar observations
Authors: von Cossart G. , Fiedler J. , von Zahn U. , Hansen G. , Hoppe U.‐P.
Published: February 2004

From early July until mid‐August 1995 we observed six noctilucent clouds (NLC) above the ALOMAR observatory in Northern Norway (69°N, 16°E) with ground based lidar. The NLC layers had maximum backscatter ratios between 17 and 190 at 532 nm, their mean altitude was 83.0 km. The latest of these events (August 12/13, 1995) was observed by two lidars, both, the Rayleigh‐ and the ozone lidar, located in the ALOMAR observatory, on wavelengths of 532 nm and 308 nm, respectively. During the period of common‐volume observations from 23:55 UT until 01:30 UT, maximum averaged backscatter ratios of 56 and 28 were measured at 532 and 308 nm, respectively. If we assume spherical particles and a lognormal particle size distribution of width s, standard Mie theory yields median radii rm of the NLC particles between 16 nm and 44 nm with number densities between 2780 cm−3 and 160 cm−3 for assumed values of s between 1.6 and 1.2, respectively.