bluuebunny/crossref_metadata_2025 huggingface dataset:
Sub‐kilometer thermal plasma structure near 1750 km altitude in the polar cusp/cleft
Authors: Knudsen D. J. , Whalen B. A. , Yau A. W. , Greffen M. J. , Eriksson A. I. , Lloyd N. , Boehm M. , Clemmons J. , Blomberg L. G.
Published: February 2004

We present Freja Cold Plasma Analyzer (CPA) measurements from an encounter with the low altitude (∼1750 km) polar cusp during which the CPA measured 2‐D images of the thermal (0–16 eV) particle distributions at 1.2 s time resolution, and simultaneously made rapid estimates (600/s) of integrated thermal particle flux into the instrument. The high resolution data show bursty ion flux enhancements of the order of tens of percent on time scales of tens of ms, or alternatively, hundreds of m spatial scales. The flux of electrons from 0–16 eV also varied by tens of percent and on temporal/spatial scales comparable to those in the ion cases. There is some evidence that the thermal particle flux variations are associated with intense low‐frequency electromagnetic fluctuations with temporal/spatial scales identical to those seen by the CPA (tens of ms, hundreds of m).
Prospects for Jovian seismological observations following the impact of comet Shoemaker‐Levy 9
Authors: Deming Drake
Published: February 2004

The impact of each fragment of comet SL‐9 will produce a downward‐propagating pressure wave which will travel at the sound speed through the jovian interior. Since the sound speed increases with depth, most of the energy in the pressure pulse will be strongly refracted and return to the surface, as recently computed by Marley (1994). This wave may in principle be observable as it propagates into the stratosphere, using sufficiently sensitive thermal infrared imaging. If so, it will provide a unique opportunity to constrain models of the jovian interior. This paper extends Marley's calculations to include the effect of the limited spatial resolution which will be characteristic of real observations. The wave pattern on the disk will consist of closely spaced regions of alternating temperature increases and decreases. Spatial averaging will significantly reduce the observed amplitude for resolutions attainable using earth‐based telescopes, but the waves should remain above the detection limit.
Electrodynamical interaction between comet Shoemaker‐Levy 9 and Jupiter
Authors: Bolin O. , Brenning N.
Published: February 2004

The electrodynamical interaction between Jupiter and comet Shoemaker‐Levy 9, which is expected to impact on Jupiter around July 20, 1994, is investigated. The comet consists of a sequence of 21 or so nuclei, each surrounded by a neutral cloud of outgassed material. A model is constructed of one single such cloud which is subject to electron impact ionization during the passage through Jupiter's magnetosphere. The cloud is assumed to couple electrically to the surroundings either by means of Alfvén wings, or through a dc circuit that closes in Jupiter's ionosphere. The magnetic‐field‐aligned currents resulting from the Jupiter‐Io interaction are strongly connected to the Jovian Decametric Radiation. The Shoemaker‐Levy comet can theoretically supply ions to Jupiter's magnetosphere at a rate not so far below Io's, and will have a higher velocity relative to Jupiter, and could therefore conceivably drive similar processes. However, we find that, due to the high latitude trajectory of the comet, the resulting currents become very weak. The field‐aligned currents obtained in this study are a factor 500 below those driven by Io, while the dissipated power is almost a factor 106 below. It is therefore proposed that very little or no detectable electromagnetic radiation will arise during the comet's passage through Jupiter's magnetosphere.
Beaver impoundments in temperate forests as sources of atmospheric CO2
Authors: Yavitt Joseph B. , Fahey Timothy J.
Published: February 2004

Beaver impoundments trap large amounts of organic matter, and remineralization of the organic matter to CO2 could make them a significant source of atmospheric CO2. Measurements in two beaver impoundments in the Adirondack Park of New York State indicated that: (i) during the ice‐free season CO2 emission averaged 197 mmol m−2d−1; (ii) concentrations of dissolved inorganic carbon (DIC) in the water column were always >100 µM, reaching >1000 µM beneath ice cover and in midsummer; and (iii) the rate of CO2 production by sediment samples from beneath the water column could exceed 300 mmol m−2d−1 in midsummer. The CO2 emitted from the impoundments to the atmosphere is supplied both by the sediments beneath the impoundment and by transport into the water column from the surrounding uplands. If beaver impoundments cover 3% of the landscape in north temperate forests then the magnitude of the presumed CO2 sink in this landscape would be reduced by 7% compared with estimates based only on the terrestrial component.
Sensitivity of a coupled atmosphere‐dynamic upper ocean GCM to variations of CO2, solar constant, and orbital forcing
Authors: Syktus Jozef , Gordon Hal , Chappell John
Published: February 2004

Sensitivity of a coupled atmosphere‐dynamic upper ocean GCM to varying CO2, solar constant, and orbital forcing was examined. Response to atmospheric CO2 concentrations ranging from 100–3500 ppm is logarithmic at all latitudes and seasons, with highest sensitivity at high latitudes, during the winter season. Solar constant response is approximately linear over the range of values +2%, but the sensitivity at high latitudes is less than for equivalent CO2 forcing. Sensitivity to “cold northern summer” orbital forcing, which occurred at the start of the last glacial cycle, is strongly affected by CO2. For CO2 at or below the present level, perennial snow cover in the northern hemisphere expands dramatically with “cold summer” orbital forcing, but this effect becomes very small for CO2 levels in the range 410–460 ppm. This result suggests that the Quaternary “ice age” mode of climatic behaviour may have been initiated by an atmospheric CO2 decrease below a critical value, probably around 350–450 ppm.
Recent warming in global temperature series
Authors: Jones P. D.
Published: February 2004

Global mean temperature can be estimated from surface and from tropospheric measurements. Much has been written recently concerning trends in the various time series over short (10–15 year) periods. This paper compares the surface, 850–300 mb and the microwave sounding unit (MSU) channel 2R measurements on the ‘global’ scale. The various series show marked differences in their trends over the 1979–93 period with the surface data showing significant warming and the troposphere no change. The difference can be explained by the shortness of the record and by the transitory nature of volcanic and El Niño/Southern Oscillation effects on global temperatures. Correcting or factoring out these influences and extending the period of analysis leads to a greater conformity in the results, which show temperatures have risen by about 0.1°C per decade since 1958.
Ozone variations in the Scandinavian sector of the Arctic during the AASE Campaign and 1989
Authors: Henriksen K. , Larsen S. H. H. , Shumilov O. I. , Thorkelsson B.
Published: February 2004

The Airborne Arctic Stratospheric Expedition (AASE) carried out measurements from January 3 to February 15, 1989. Enhanced levels of chlorine compounds were found in the Arctic stratosphere, and on two single flights ozone decrease of 17% were measured, interpreted as essential features of the Arctic stratosphere, caused by a combined effect of enhanced amounts of chlorine compounds and presence of polar stratospheric clouds. Related model calculations also indicate extended ozone depletion maximizing in late March 1989 and amount to 5–8% in column at 70° N. Ground‐based ozone measurements, however, show that the most characteristic features during this period are temporal variations and a strong enhancement of ozone, probably due to an extended stratospheric warming. From these measurements it is hard to see any effect of an eventual enhanced burden of stratospheric chlorine, which might show up as an extended and long‐lasting decrease of stratospheric ozone, but its eventual existence is masked by the temporal variations.
Cerenkov excitation of whistler/helicon waves by ionospheric HF heating
Authors: Papadopoulos K. , Zhou H.‐B. , Chang C.‐L.
Published: February 2004

A novel scheme for exciting VLF waves and injecting them in the magnetosphere is presented. The scheme is based on Cerenkov excitation of whistler and helicon waves in an altitude range of 80–95 km. Contrary to the traditional Cerenkov excitation which relies on a charge moving at speeds exceeding the local phase velocity of the wave, the present scheme relies on currents moving transversely to its flow direction. The moving current source is created by changing the spatial location of the energy deposition of an ionospheric heater in phase with the wave motion. Representative estimates of the VLF power injected in the magnetosphere are presented.
Fine‐scale, poleward transport of tropical air during AASE 2
Authors: Waugh D. W. , Plumb R. A. , Newman P. A. , Schoeberl M. R. , Lait L. R. , Loewenstein M. , Podolske J. R. , Elkins J. W. , Chan K. R.
Published: February 2004

The poleward transport of tropical air in the lower stratosphere during the winter period of the second Airborne Arctic Stratospheric Expedition (December 1991–March 1992) is examined using contour advection calculations. These calculations show that filaments of tropical air extend into mid‐latitudes, and are wrapped around the equatorward edge of the polar jet. Simultaneously filaments are drawn from the polar vortex and are intermingled with the filaments of tropical air. The tropical filaments are consistent with measurements of chemical tracers taken aboard the ER‐2 and DC‐8 aircraft which show localized regions, in mid‐latitudes, of air with the characteristics of tropical air.
Stable chlorine isotopic composition of marine aerosol particles in the western Atlantic Ocean
Authors: Volpe Christopher , Spivack Arthur J.
Published: February 2004

The isotopic composition of chlorine sampled from the atmosphere has been measured for the first time. Eight aerosol samples collected on bulk filters at Bermuda are enriched in 37Cl relative to sea water. Stable chlorine isotopic compositions are reported in units of per mil as δ37Cl which is defined as 1000 × [(Rsample/Rsea water) ‐ 1] where R is the ratio of 37Cl to 35Cl. The δ37Cl of the aerosols range from +0.42 to +2.53 per mil and strongly correlate with chlorine deficit (based upon sea salt sodium) and non‐sea salt sulfate. The data trend is consistent with the fractional distillation (loss) of HCl from an acidified aerosol governed by a fractionation factor of 0.9972. Subsequent experiments support the hypothesis that HCl evaporation was most likely the primary mechanism of chlorine volatilization in the sampled aerosols. Furthermore, the data indicate that marine aerosols perturbed by anthropogenic NOx and SO2 are an important source of isotopically light chlorine in the free troposphere.
Evaluation of an empirical radar backscatter model for predicting backscatter characteristics of geologic units at Pisgah Volcanic Field, California
Authors: Gaddis Lisa R.
Published: February 2004

Comparison of radar backscatter coefficients (σ°, in dB), calculated by using the empirical model of Oh et al. [1992], to σ° extracted from AIRSAR data of four geologic units at Pisgah shows that the model predicts measured σ°vv and σ°hv to within ±3 dB. The model predicts higher σ°hh than those observed. For smooth surfaces (rms height=s, s<8 cm), model results depend strongly on the accuracy of the surface measurements ( s and dielectric constant, ϵr). For rougher surfaces, the model is less dependent on the accuracy of surface characterizations. The model may be inverted to estimate s from measured σ° for surfaces with ks<3 (k = wavenumber, or 2π/λ, where λ = radar wavelength). Model inversion for a pahoehoe unit at 30° to 50° incidence angles (θ) resulted in an estimate of s to within <1 cm of the measured 3 cm. The inability of the model to estimate accurately σ°hh and the anomalously high nadir Fresnel reflection coefficients (Γo) and ϵr required in the model inversion may both be due to ∼equal co‐polarized ratios (σ°hh/σ°vv=p∼1) of the soils used to derive the model. For effective application to many geologic surfaces, for which p<1 is often observed at θ>30°, the model will require modification to include surfaces with non‐unity σ°hh/σ°vv.
Fine structure of field‐aligned current sheets deduced from spacecraft and ground‐based observations: Initial FREJA results
Authors: Lühr H. , Warnecke J. , Zanetti L. J. , Lindqvist P. A. , Hughes T. J.
Published: February 2004

Due to its special orbit—over large segments tangential to the auroral oval and at altitudes around 1600 km—FREJA provides measurements from a sparsely sampled region. Here we will introduce initial results from the magnetic field experiment. For one event occurring about an hour after midnight we investigate the fine structure of the field‐aligned currents associated with a westward electrojet. From simultaneous ground‐based observations we deduce the orientation and the spatial and temporal variations of the electrojet. Space‐borne magnetic field measurements provide estimates of the field‐aligned current density. We deduce a lower limit of 1.75 km for the thickness of field‐aligned current filaments. The comparison between electric and magnetic field recordings on FREJA suggests a poor correlation of these quantities for this event.
DSM complete synthetic seismograms: P‐SV, spherically symmetric, case
Authors: Cummins Phil R. , Geller Robert J. , Takeuchi Nozomu
Published: February 2004

In a previous paper, [Cummins et al., 1994, hereafter referred to as DSMI], we presented theoretical and computational results for calculating complete SH (toroidal) synthetic seismograms for spherically symmetric, isotropic, media. We now extend our treatment to the P‐SV (spheroidal) part of the wavefield. No asymptotic approximations are used, and the synthetics, which include both body and surface waves, can be computed for a broad range of frequencies. Examples of synthetic profiles are presented for a 600km deep source in the IASP91 model for the period range 4‐5000s. Such synthetics can contribute greatly to the determination of earth structure from analyses of broadband seismograms.
Concentration of interstellar pickup H+ and He+ in the solar wind
Authors: Gloeckler G. , Jokipii J. R. , Giacalone J. , Geiss J.
Published: February 2004

We present observations of interstellar pickup hydrogen and helium in the solar wind which show large, highly‐correlated fluctuations in flux which are not correlated significantly with the solar‐wind hydrogen flux. The correlation of the fluctuations in the two species implies that the fluctuations are caused by transport after ionization. The lack of correlation with the thermal flux means they are not caused by compressions of the wind. We present a new model which can naturally produce the observed fluctuations in the pickup ions.
Increase in atmospheric CHF2Cl (HCFC‐22) over southern California from 1985 to 1990
Authors: Irion Fredrick W. , Brown Margaret , Toon Geoffrey C. , Gunson Michael R.
Published: February 2004

Column densities of CHF2Cl (HCFC‐22) have been measured over Table Mountain Facility (TMF), Wrightwood, California (34.4°N) using the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier‐transform infrared (FTIR) spectrometer. Between October 1985 and July 1990, the exponential column increase rate was (6.7±0.5)% yr−1. Additionally, column measurements of CHF2Cl over McMurdo Sound, Antarctica (78°S) in September and October 1986 by the MarkIV FTIR spectrometer were used to derive a south‐north interhemispheric ratio of (0.86±0.08). Model calculations investigated the feasibility of using CHF2Cl column measurements with a predicted global OH field to determine a globally averaged chemical lifetime for CHF2Cl, or equivalently, an estimate of the OH field using a predicted lifetime. The current uncertainty in historical CHF2Cl emissions is too large for CHF2Cl to be used to infer adequately either the lifetime or the OH field.
Convection and the formation of thin current sheets in the near‐Earth plasma sheet
Authors: Pritchett P. L. , Coroniti F. V.
Published: February 2004

Particle simulations are used to investigate plasma sheet convection in a realistic near‐Earth magnetic field model including dipolelike and taillike regions. Convection leads to the formation of a thin current region characterized by a strong electrostatic potential and a depressed equatorial magnetic field component in which the cross tail current is carried predominantly by the electrons as a result of their E × B and diamagnetic drifts. Implications for the thin current sheets observed in the near‐Earth magnetotail during substorm growth phase are discussed.
Freja's contribution to the ISTP event of October 27, 1992. A distorted magnetosphere
Authors: Potemra T. A. , Zanetti L. J. , Anderson B. J. , Bythrow P. F. , Ohtani S.
Published: February 2004

A unique arrangement of satellites and ground‐based magnetometers has provided the opportunity to study the distortion of the magnetosphere by conditions of elevated solar wind dynamic pressure and high geomagnetic activity on October 27, 1992. Data were acquired by the near‐Earth satellites Freja, UARS, DMSP‐F8 and DMSP‐F11, and by IMP‐8. This study will focus on patterns of large‐scale Birkeland currents deduced from the APL magnetic field experiments on Freja and UARS. Because of the relatively low inclinations of their orbits (63° for Freja and 57° for UARS) these satellites skim the current systems over a wide range of local time and provide a kind of “global image” of the Birkeland currents. Energetic particle data from the DMSP satellites are used in an attempt to complete the image of the auroral region. The principal findings of this study include the following. The dayside Birkeland current system is displaced 6° to 9° equatorward of the statistical pattern determined by Iijima and Potemra [1978] for undisturbed conditions (|AL|< 100 nT) and 3° equatorward of their disturbed statistical pattern (|AL|≥ 100 nT). The densities of these daytime Birkeland currents are estimated to be 1 to 2 µA/m², comparable to, but not larger than the statistical values determined by Iijima and Potemra for disturbed conditions. The nightside Birkeland currents are located close to the Iijima and Potemra disturbed statistical pattern and they are less intense than the dayside currents.
A study of type I polar stratospheric cloud formation
Authors: Tabazadeh A. , Turco R. P. , Drdla K. , Jacobson M. Z. , Toon O. B.
Published: February 2004

Mechanisms for the formation of Type I (nitric acid‐based) polar stratospheric clouds (PSCs) are discussed. If the pre‐existing sulfate aerosols are liquid prior to PSC formation, then nitric acid particles (Type Ib) form by HNO3 dissolution in aqueous H2SO4 solution droplets. This process does not require a nucleation step for the formation of HNO3 aerosols, so most pre‐existing aerosols grow to become relatively small HNO3‐containing particles. At significantly lower temperatures, the resulting supercooled solutions (Type Ib) may freeze to form HNO3 ice particles (Type Ia). If the preexisting sulfate aerosols are initially solid before PSC formation, then HNO3 vapor can be deposited directly on the frozen sulfate particles. However, because an energy barrier to the condensation exists a nucleation mechanism is involved. Here, we suggest a unique nucleation mechanism that involves formation of HNO3/H2O solutions on the sulfate ice particles. These nucleation processes may be highly selective, resulting in the formation of relatively small number of large particles.
Whistler mode waves observed by MGF search coil magnetometer—Polarization and wave normal features of upstream waves near the bow‐shock
Authors: Hayashi K. , Matsui H. , Kawano H. , Yamamoto T. , Kokubun S.
Published: February 2004

Whistler mode waves observed in the upstream region very close to the bow‐shock is focused from the initial survey for magnetic fed data in a frequency range between 1Hz and 50Hz observed by the search coil magnetometer on board the Geotail satellite. Based on the three component wave form data polarization and wave‐normal characteristics of foreshock waves is first shown as dynamic spectra for the whole Fourier components of the 50Hz band width. Intense whistler mode waves generated in the foot region of the bow‐shock are found strongly controlled in the observed polarization dependent on the angle between directions of the wave propagation and the solar wind flow but no much dependent on frequency. Our simple scheme to derive the wave characteristics which is effective to survey large amount of data continuously growing is also introduced.
Transition from slow flow to fast tailward flow in the distant plasma sheet
Authors: Nishida A. , Mukai T. , Saito Y. , Yamamoto T. , Hayakawa H. , Maezawa K. , Machida S. , Terasawa T. , Kokubun S. , Nagai T.
Published: February 2004

Transitions from slow flow to fast tailward flow are studied in the distant plasma sheet at downtail distances of ∼70 Re with the data from the GEOTAIL satellite. The speed of 300 km/s can be regarded as a reasonable measure that separates the fast and the slow flow. While the magnetic field tends to be northward during the slow flow, its polarity oscillates between northward and southward during the fast tailward flow. A case is studied in detail where the slow‐to‐fast transition of the flow velocity was observed when the spacecraft was very close to the neutral sheet, and it is seen that the pressure was balanced in the interface region between these flows. The observations are consistent with a model in which the fast tailward flow is associated with a plasmoid and the quiet plasma is pushed forward when a plasmoid approaches.
Diurnal variation of the ISCCP cloudiness
Authors: Kondragunta Chandrasekhara R. , Gruber Arnold
Published: February 2004

Seven January (1984 to 1990) months of three hourly monthly mean total cloud amount data were subjected to Empirical Orthogonal Function (EOF) analysis to study large scale features of the diurnal variation. The first two EOF modes explain two different types of diurnal variation. While the first EOF mode shows the diurnal variation contrast between land and ocean, the second EOF pattern shows diurnal variation over deep convective cloudy regions. In the second mode, maximum cloudiness occurs at around 2000 LST both over continental and oceanic regions, where deep convective cloudiness occurs. The first two EOF modes explain 78.4% of the total normalized variance. The time coefficients of these two EOF modes indicate that the diurnal variation of cloudiness undergoes non sinusoidal variation.
A hybrid simulation of contact discontinuity
Authors: Wu B. H. , Chao J. K. , Tsai W. H. , Lin Y. , Lee L. C.
Published: February 2004

Contact discontinuities in a collisionless plasma are studied by hybrid simulations, in which ions are treated as particles and electrons are considered as a fluid. It is demonstrated that contact discontinuity with a stable density ramp can exist in cases with a finite electron temperature. An electron pressure gradient is present across the contact discontinuity, leading to the presence of a parallel electric field and hence field‐aligned potential increase (ΔΦ∥) in the transition region. By reflecting ions at the discontinuity, this parallel electric potential peak reduces the interpenetration between hot and cold ions and maintains a stable density ramp across the contact discontinuity. The ratio of the field‐aligned electric potential energy to ion thermal energy, eΔΦ∥/kTi, is found to be an increasing function of Te/Ti, where Te and Ti are respectively the electron and ion temperature.
Dispersive Pc1 bursts observed by Freja
Authors: Mursula K. , Blomberg L. G. , Lindqvist P. ‐A. , Marklund G. T. , Bräysy T. , Rasinkangas R. , Tanskanen P.
Published: February 2004

Electric field measurements by the Freja double probe sensor are used to study equatorially generated ion cyclotron waves, also called Pc1 pulsations. We have examined the global occurrence and spectral properties of these waves in the upper ionosphere during 12‐hour period on Nov. 18, 1992, when a long chain of structured Pc1 waves (pearls) was observed on ground. In agreement with ground observations, Pc1 waves were found to occur as short bursts of 10–25 s in early morning to postnoon MLT sector. Most Pc1 activity was detected within a small latitudinal range, extending from 60° CGMlat at dawn to 63° CGMlat at noon. The latitudinal width of the source was only about 0.5° CGMlat. Observations give evidence for a plasmapause connected source region that was several hours wide in MLT and active during many hours. One burst displayed a fully developed classical dispersive Pc1 pearl, now detected for the first time above the ionosphere. In all studied Pc1 events, two spectral maxima (bands) were observed. The longer Pc1 wave bursts showed evidence for a small time delay between the lower and upper frequency bands, unveiling a new dispersive phenomenon.
Mid‐latitude incoherent scatter observations of helium and hydrogen ions
Authors: Erickson Philip J. , Swartz Wesley E.
Published: February 2004

We have successfully employed a constrained non‐linear least squares analysis of incoherent scatter data from the topside ionosphere over Arecibo, Puerto Rico to simultaneously deduce concentrations of helium ions, protons, and oxygen ions as well as ion and electron temperatures. The constraint encourages smooth temperature profiles, and its use avoids unrealistic parameter values in regions where light ions are more than 80% of the total. Here we report proton concentrations that remain higher than helium ion concentrations, even though the latter reach 30% of the total and exceed the oxygen ion densities at altitudes as low as 700 km at night and 1500 km in the day‐time. Before local sunrise the effects of conjugate‐point photoelectrons are clearly seen, while after sunrise the transition height between oxygen and helium rises much more rapidly than does the transition from oxygen to hydrogen.
Observation of hydration of single, modified carbon aerosols
Authors: Wyslouzil B. E. , Carleton K. L. , Sonnenfroh D. M. , Rawlins W. T. , Arnold S.
Published: February 2004

We have compared the hydration behavior of single carbon particles that have been treated by exposure to gaseous H2SO4 with that of untreated particles. Untreated carbon particles did not hydrate as the relative humidity varied from 0 to 80% at 23°C. In contrast, treated particles hydrated under subsaturation conditions; mass increases of up to 30% were observed. The mass increase is consistent with sulfuric acid equilibration with the ambient relative humidity in the presence of inert carbon. For the samples studied, the average amount of adsorbed acid was 14% ± 6% by weight, which corresponds to a surface coverage of ∼0.1 monolayer. The mass fraction of surface‐adsorbed acid is comparable to the soluble mass fraction observed by Whitefield et al. (1993) in jet aircraft engine aerosols. Estimates indicate this mass fraction corresponds to 0.1% of the available SO2 exiting an aircraft engine ending up as H2SO4 on the carbon aerosol. If this heterogeneous process occurs early enough in the exhaust plume, it may compete with homogeneous nucleation as a mechanism for producing sulfuric acid rich aerosols.
Tailward energetic ion streams observed at ∼100 RE by GEOTAIL‐EPIC associated with geomagnetic activity intensification
Authors: Jacquey C. , Williams D. J. , McEntire R. W. , Lui A. T. Y. , Angelopoulos V. , Christon S. P. , Kokubun S. , Yamamoto T. , Reeves G. D. , Belian R. D.
Published: February 2004

We report energetic particle (EPIC instrument) and magnetic field (MGF instrument) measurements collected onboard GEOTAIL located at ∼100 RE downstream in the magnetotail during a 13‐hour long active period on January 20–21, 1993. During this period, a series of 6 geomagnetic activity intensifications (breakup or pseudo‐breakup) have been studied with ground magnetograms and energetic particle data at geosynchronous orbit. We show that: (1) as a general trend, the level of the energetic ion fluxes was related to the intensity of the westward electrojet; (2) a systematic temporal (within a few minutes) correlation exists between energetic ion flux enhancements observed by GEOTAIL/EPIC in the distant tail and near‐Earth geomagnetic activity intensification onsets; and (3) for 5 of 6 cases, these energetic ion flux enhancements corresponded to strong tailward streams which included particles of both solar wind and ionospheric origin. Their amplitude seemed also to be related to the electrojet intensity change.
Magnetic field structures of the magnetotail as observed by GEOTAIL
Authors: Yamamoto Tatsundo , Shiokawa Kazuo , Kokubun Susumu
Published: February 2004

Global magnetic field structures of the earth's magnetotail are investigated by using magnetic field data obtained during the first one‐year observation of GEOTAIL. When the effect of the average solar wind aberration and the geomagnetic dipole tilt is taken into consideration, the tail lobe structures appear to be observed around the expected location even beyond −150RE. The flaring angle of magnetic field lines in the tail lobe is statistically larger than the expansion angle of the tail magnetopause, especially in X > −150RE, suggesting that the lobe magnetic field lines are linked with those in the magnetosheath across the magnetopause. Momentum and particles in the magnetosheath could enter the tail region across the magnetopause with high efficiency. The majority of observed Bz in the current sheet that separates the two distant tail lobes shows northward even beyond −150RE. This is contrary to the model of the quasi‐steady reconnection around −100RE but it cannot be readily concluded that the field lines in the plasma sheet are closed since the convection is predominantly directed tailward in the distant magnetotail.
Rotational evolution of potential vorticity associated with a strong blocking flow configuration over Europe
Authors: Nakamura Hisashi
Published: February 2004

Time evolution of a prominent tropospheric blocking flow configuration over Europe is examined based upon composites for the 15 strongest events observed during the last 27 winter seasons, from which the fluctuations associated with synoptic‐scale eddies have been filtered out. The blocking, initiated in the exit region of the Atlantic jet stream, forms into a domain of the very weak westerlies. The tropopause‐level potential vorticity (PV) exhibits a distinct, clockwise evolution within this domain, so that the negative correlation between PV and the meridional wind velocity associated with the amplifying blocking becomes positive as it decays, which signifies the convergence of the wave activity density flux and its subsequent divergence. Indeed, a quasi‐stationary wavetrain across the Atlantic is evident during the blocking amplification, and then another wavetrain becomes apparent to the east of the decaying ridge. It appears that the wave activity propagating across the Atlantic is obstructed and accumulated in the weak‐westerly domain associated with the developing blocking ridge until it is saturated, followed by the release of the activity to the east. The result suggests that the low‐frequency dynamics of the atmospheric flow plays an important role in the formation of a certain type of blocking.
The harmonic development of the Earth tide generating potential due to the direct effect of the planets
Authors: Hartmann Torsten , Wenzel Hans‐Georg
Published: February 2004

The time‐harmonic development of the Earth tide generating potential due to the direct effect of the planets Venus, Jupiter, Mars, Mercury and Saturn has been computed. The catalogue of the fully normalized potential coeffients contains 1483 waves. It is based on the DE102 numerical ephemeris of the planets between years 1900 and 2200. Gravity tides due to the planets computed from the catalogue at the surface of the Earth have an accuracy of about 0.027 pm/s² (1 pm/s² = 10−12 m/s² = 0.1 ngal) rms and 0.160 / 0.008 pm/s² at maximum in time / frequency domain using the new benchmark tidal gravity series (Wenzel 1994).
The effect of wave‐particle interactions on the polar wind O+
Authors: Barakat A. R. , Barghouthi I. A.
Published: February 2004

The escape of the polar wind plasma is an important element in the ionosphere‐magnetosphere coupling. Both theory and observations indicate that the wave‐particle interactions (WPI) play a significant role in the dynamics of ion outflow along open geomagnetic field lines. A Monte Carlo simulation was developed in order to include the effect of the WPI in addition to the factors that are traditionally included in the ‘classical‘ polar wind (i.e. gravity, electrostatic field, and divergence of geomagnetic field lines). The ion distribution function (fj), as well as the profiles of its moments (density, drift velocity, temperature, etc.) were found for different levels of WPI, that is, for different values of the normalized diffusion rate in the velocity space
. Although the model included O+, H+ and electrons, we presented only the results related to the O+ ion. We found that (1) both the density and drift velocity of O+ increased with the WPI strength, and consequently, the O+ escape flux was enhanced by a factor of up to 105; (2) The O+ ions could be energized up to a few electron volts; (3) for moderate and high levels of WPI
, the distribution function f(O+) displayed very pronounced conic features at altitudes around 3Re. Finally, the interplay between the downward body force, the upward mirror force, and the perpendicular heating resulted in the formation of the “pressure cooker” effect. This phenomena explained some interesting features of our solution, such as, the peak in the O+ temperature, and the formation of “ears” and conics for f(O+) around 2.5Re.
Global structures of Alfvén‐ballooning modes in magnetospheric plasmas
Authors: Vetoulis George , Chen Liu
Published: February 2004

We show that a steep plasma pressure gradient can lead to radially localized Alfvén modes, which are damped through coupling to field line resonances. These have been called drift Alfvén ballooning modes (DABM) by [Chen and Hasegawa, 1991] and are the prime candidates to explain Pc4–Pc5 geomagnetic pulsations observed during the recovery phase of geomagnetic storms. A strong dependence of the damping rate on the azimuthal wave number m is established, as well as on the equilibrium profile. A minimum azimuthal mode number can be found for the DABM to be radially trapped. We find that higher m DABMs are better localized, which is consistent with high‐m observations.
Three‐dimensional evolution of Kelvin‐Helmholtz billows in stratified compressible flow
Authors: Palmer Teresa L. , Fritts David C. , Andreassen Øyvind , Lie Ivar
Published: February 2004

We present results of an initial study of Kelvin‐Helmholtz instability in a stratified shear flow using a three‐dimensional, nonlinear, compressible, spectral collocation model. The simulation was performed at an intermediate Reynolds number and significantly extends previous studies of homogeneous and stratified shear flows. Our major findings include a secondary instability oriented along the two dimensional velocity field, with counter‐rotating vortices arising due to both buoyancy and shear sources of eddy kinetic energy within the billow structures. The vortices occupy the outer regions of the billows and contribute significant eddy transports of momentum and potential temperature within the billows. The resulting KH evolution differs in important respects from the corresponding two‐dimensional or unstratified flows.
ERS‐1 altimeter fast delivery data quality flagging over land surfaces
Authors: Strawbridge Fiona , Laxon Seymour
Published: February 2004

Over land ice and land, satellite altimeters provide valuable topographic information, in spite of having been designed primarily to operate over the ocean. There is a need, however, for careful data quality assessment and screening as erroneous elevation measurements can be included within the telemetered data, especially when the range tracker encounters complex echoes, or rapidly varying topography. The ERS‐1 Fast Delivery (FD) data product provides an excellent source of near real‐time data, which has already been used for ice sheet mapping. This is a reduced data set consisting of on‐board parameters generated once per second. In this paper we show that by applying thresholds to two parameters, significant amounts of poorly tracked data can be eliminated. The effectiveness of this filtering technique is demonstrated by a comparison of filtered and unfiltered altimeter data with a digital elevation model. This filtering technique is applied to the first 35 day repeat cycle of FD data obtained over land to produce the first map of global topography from ERS‐1.
Convective motions in the Earth's fluid core
Authors: Zhang K. , Jones C. A.
Published: February 2004

Convection in the Earth's core is affected by Lorentz and Coriolis forces. The relative importance of these is measured by the Elsasser number Λ. Previous work suggested that the optimum condition for convection occurs when the Elsasser number Λ is O(1); in particular, the critical modified Rayleigh number R* had a minimum value at some O(1) value of Λ. This gave rise to the view that the size of the magnetic field generated by the dynamo would adjust to this Λ‐value because it optimised the convection. We have investigated convection in a rotating spherical shell with magnetic field distributions satisfying appropriate boundary conditions in the form of the toroidal decay modes which we believe are more realistic for the Earth's core. Our results are rather different from the classical picture. We find no optimum Elsasser number that minimises R*, but instead a monotonic decay of R* as Λ increases. At Λ ∼ 10, R* goes negative, so that rolls are driven by magnetic instability rather than convection. Naturally, as this regime is entered the rolls must be destroying magnetic field rather than creating it by dynamo action. This suggests that in the Earth's fluid outer core, the field strength is such that 1 < Λ < 10, so that the magnetic field is stable and the corresponding convection is dominated by large scales and is efficient. Another important feature of these solutions is that the azimuthal flow is primarily two‐dimensional. This is surprising, as it has generally been believed that a magnetic field of this strength would break the Taylor‐Proudman constraint. However, it appears that the magnetic field adjusts to preserve two‐dimensionality even in the range 1 < Λ < 20.
Energy flux and characteristic energy of an elemental auroral structure
Authors: Lanchester B. S. , Palmer J. R. , Rees M. H. , Lummerzheim D. , Kaila K. , Turunen T.
Published: February 2004

Electron density profiles acquired with the EISCAT radar at 0.2 s time resolution, together with TV images and photometric intensities, were used to study the characteristics of thin (< 1 km) auroral arc structures that drifted through the field of view of the instruments. It is demonstrated that both high time and space resolution are essential for deriving the input parameters of the electron flux responsible for the elemental auroral structures. One such structure required a 400 mW m−2 (erg cm−2 s−1) downward energy flux carried by an 8 keV monochromatic electron flux equivalent to a current density of 50 µA m−2.
Cold crust in a hot spot
Authors: Menke William , Levin Vadim
Published: February 2004

Shear waves from locally‐recorded Icelandic earthquakes exhibit very little anelastic attenuation, even though they turn in 0–5 Ma lower (15–25 km) crust just above the Moho. Lower crustal shear wave quality factors are about Q=150‐225 for paths that cross central Iceland and about Q=300 for paths in southwestern Iceland, values that indicate that the temperature of the lower crust is at least 250–325°C below the solidus of gabbro (that is, about 875–950°C, based on published experimental studies of the effect of temperature on shear wave attenuation in gabbro). These low temperatures are not consistent with existing models of crustal accretion, which predict partial melt at lower crustal depths.
Small changes in the sea surface temperature during the last 20,000 years: Molecular evidence from the western tropical Pacific
Authors: Ohkouchi N. , Kawamura K. , Nakamura T. , Taira A.
Published: February 2004

One of the most controversial problems of glacial paleoclimatology is the conservative change in tropical sea surface temperature (SST) in contrast with the large high altitude temperature change in the western tropical Pacific. In this report SST was estimated for the last 20,000 years using alkenones preserved in marine sediments recovered from a site 800 km north of New Guinea. The UK37 (unsaturation degree of long‐chain alkenones synthesized by planktonic prymnesiophyte algae) record suggests that SST decreased at most 1.5°C at the last glacial maximum. This small changes in SST of the western tropical Pacific is concordant with results previously reported in UK37 studies from the eastern equatorial Pacific and the equatorial Atlantic. The UK37‐based SST estimates are in good agreement with the CLIMAP results and planktonic foraminifera δ18O, but much smaller than those (ca. −5°C) obtained from coral Sr/Ca and δ18O thermometries and glacial vegetation reconstruction.
Multiple‐wavelength Raman lidar measurements of atmospheric water vapor
Authors: Rajan Sumati , Kane Timothy J. , Philbrick C. Russell
Published: February 2004

Height profiles of atmospheric water vapor obtained using a multiple‐wavelength Raman lidar are examined. The water vapor profiles exhibit vertical structure with scales on the order of the resolution of the lidar (75 m). To determine whether such structure is atmospheric in origin, measurements obtained simultaneously in a common volume at two independent wavelengths were compared. Correlation of the gradients of the water vapor profiles obtained from these two wavelengths yielded an average correlation factor of 0.88. It was also observed that for the given meteorological conditions, the vertical structure decorrelated with a time constant of approximately three hours.
Comment on the Paper “Sondrestrom overview” by Wickwar et al.
Authors: Papitashvili V. O. , Clauer C. R.
Published: February 2004

Results of a reexamination of the geomagnetic coordinate system in the vicinity of the Sondrestrom radar corrects earlier estimates of the proper direction to the corrected geomagnetic pole [Wickwar et al., 1984]. We find the corrected geomagnetic pole direction at the Sondrestrom radar to be −17° geographic azimuth in contrast to the −27° value in common usage.
Magnetic properties of zero‐age oceanic crust; A new submarine lava flow on the Juan de Fuca Ridge
Authors: Johnson H. Paul , Tivey Maurice A.
Published: February 2004

A volcanic eruption that occurred in October, 1993 on the Juan de Fuca Ridge shows unusually high magnetization when compared with older samples from the off‐axis Juan de Fuca Ridge and other Pacific sites. These data, plus data from other young oceanic basalts, indicate that oceanic crustal magnetization may decay rapidly, by 10% in the first year. The considerably slower decrease in magnetization for rocks from older, off‐axis sites agrees with previous models of progressive low temperature oxidation of the mineral titanomagnetite. The magnetization for newly erupted submarine basalts, however, is not consistent with the exponential decay predicted from older sites, indicating that oxidation may not be the sole process responsible for the short‐term decay. Similarly, weak field magnetic susceptibility of the younger rocks does not show an obvious corresponding decrease with increasing age, as expected for the oxidation of titanomagnetite to titanomaghemite. These preliminary results indicate that decay of magnetization of oceanic crustal rocks with time may have two distinct stages, with only the later stage being due to the progressive oxidation of the magnetic minerals.
Effect of recent revisions to the geomagnetic reversal time scale on estimates of current plate motions
Authors: DeMets Charles , Gordon Richard G. , Argus Donald F. , Stein Seth
Published: February 2004

Recent revisions to the geomagnetic time scale indicate that global plate motion model NUVEL‐1 should be modified for comparison with other rates of motion including those estimated from space geodetic measurements. The optimal recalibration, which is a compromise among slightly different calibrations appropriate for slow, medium, and fast rates of seafloor spreading, is to multiply NUVEL‐1 angular velocities by a constant, α, of 0.9562. We refer to this simply recalibrated plate motion model as NUVEL‐1A, and give correspondingly revised tables of angular velocities and uncertainties. Published work indicates that space geodetic rates are slower on average than those calculated from NUVEL‐1 by 6±1%. This average discrepancy is reduced to less than 2% when space geodetic rates are instead compared with NUVEL‐1A.
Tropospheric HONO and reactions of oxides of nitrogen with NaCl
Authors: Vogt Rainer , Finlayson‐Pitts Barbara J.
Published: February 2004

Although nitrous acid is important in both the polluted and remote troposphere, as well as indoors, its mechanisms of production from oxides of nitrogen are not well known. The reactions of N2O5 with NaCl and NaBr in sea salt particles in the presence of water have been hypothesized recently to act as sources of particulate nitrite and which forms gaseous HONO. We report here the results of studies of the reactions of N2O5, HONO and NO2 with NaCl using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to follow the formation of products on the salt surface. The infrared bands arising from species formed on the salt surface can be attributed to nitrate ions associated with water molecules; the presence of NO3− was confirmed by chemical analysis of the reacted salts. No nitrite was detected either by DRIFTS or by chemical analysis. Thus the reactions of sea salt particles with N2O5 in the troposphere are not expected to be significant sources of particle nitrite nor of gaseous HONO via conversion of the particle nitrite.
3D geometry of the strain‐field at transform plate boundaries: Implications for seismic rupture
Authors: Bodin P. , Bilham R.
Published: February 2004

We examine the amplitude and distribution of slip on vertical frictionless faults in the zone of concentrated shear strain that is characteristic of transform plate boundaries. We study both a 2D and a 3D approximation to this strain field. Mean displacements on ruptures within the zone of concentrated shear strain are proportional to the shear strain at failure when they are short, and are limited by plate displacements since the last major earthquake when they are long. The transition between these two behaviors occurs when the length of the dislocation approaches twice the thickness of the seismogenic crust, approximately the breadth of the zone of concentrated shear strain observed geodetic ally at transform plate boundaries. This result explains the observed non‐linear scaling relation between seismic moment and rupture length. A geometrical consequence of the 3D model, in which the strain‐field tapers downward, is that moderate earthquakes with rupture lengths similar to the thickness of the crust tend to slip more at depth than near the surface. Seismic moments estimated from surface slip in moderate earthquakes (M≤7) will thus be underestimated. Shallow creep, if its along‐strike dimension is extensive, can reduce a surface slip deficit that would otherwise develop on faults on which M<7 events are typical. In the absence of surface creep or other forms of off‐fault deformation great earthquakes may be necessary features of transform boundaries with downward‐tapering strain‐fields.