bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of electromagnetic fpe and 2fpe waves in the Earth's electron foreshock via linear mode conversion
Authors: Yin L. , Ashour‐Abdalla M. , El‐Alaoui M. , Bosqued J. M. , Bougeret J. L.
Published: February 2004

This study examines the mode conversion from electrostatic to electromagnetic waves near the plasma frequency in the Earth's electron foreshock. The conversion and reflection coefficients are obtained by solving coupled differential equations in a weakly magnetized warm plasma with a longitudinal linear density gradient. Results indicate that the foreshock first harmonic electromagnetic emissions and the backward‐propagating Langmuir waves required for the generation of the second harmonic electromagnetic waves may be efficiently produced by the linear conversion process in an inhomogeneous plasma.
Plasma and magnetic field structure of a slow shock: Wind observations in interplanetary space
Authors: Whang Y. C. , Larson D. , Lin R. P. , Lepping R. P. , Szabo A.
Published: February 2004

This paper reports on the observation of an interplanetary slow shock on May 23, 1995 using 3‐s plasma and magnetic field data from the Wind spacecraft. Since the time to traverse the shock (∼15 s) is much greater than the 3‐s temporal resolution of the data, this observation can reveal the plasma and magnetic field structure through the interior of the shock. The 3‐s data also provide accurate preshock and postshock conditions immediately outside the shock layer. The flow speeds in the shock frame of reference Un < a cos Θ on both sides of the shock, Un1 >CS1, and Un2 < CS2. Here a and CS are, respectively, the Alfven speed and the slow speed, Θ is the acute angle between the magnetic field vector and the shock normal, and the subscripts 1 and 2 denote the preshock and the postshock conditions. Θ1 ∼47° and Θ2 ∼ 39°. The jump conditions B2/B1, N2/N1, and (Ti + Te)2/(Ti + Te)1 of the observational result are in good agreement with the Rankine‐Hugoniot solution. The thickness of the shock is of the order of 36 times of the preshock ion inertial length.
A characteristic time scale in the global temperature record
Authors: Tsonis A. A. , Roebber P. J. , Elsner J. B.
Published: February 2004

Using modern time series analysis we discover a characteristic time scale in the global temperature record. This time scale corresponds to about 20 months and separates processes that promote a trend in the past from processes that reverse this tendency. This characteristic scale has important implications one of which might be that the El Niño/La Niña cycle may act as a mechanism countering the tendency of shorter time scale events to organize a positive or a negative temperature trend.
Upwelling and convergence in the Middle Atlantic Bight Shelfbreak Front
Authors: Houghton Robert W. , Visbeck Martin
Published: February 2004

Convergent and up welling circulation within the shelfbreak front in the Middle Atlantic Bight are detected using a dye tracer injected into the bottom boundary layer at the foot of the front. From the three day displacement and dispersion of two dye injections within the front we infer Lagrangian isopycnal (diapycnal) velocities and diffusivities of 2 × 10−2 m/s (4 × 10−6 m/s) and 9 m²/s (6 × 10−6 m²/s). These results substantiate model predictions of Chapman and Lentz [1994] and previous dye tracer observations by Houghton [1997].
Observed linear and nonlinear K layer response
Authors: Eska V. , Höffner J.
Published: February 2004

Potassium densities and temperatures were measured on board the German Research Vessel ‘Polarstern’ with the containerized IAP (Institute of Atmospheric Physics) K‐lidar. Considerable wave activity was observed in the K density profiles as well as the temperature profiles, in particular during the night of May 23/24, 1996 over the South Atlantic ocean. A strong monochromatic wave was observed between 85 and 100 km. The calculated relative K density variations are in phase with the temperature variations at the bottom of the K layer and 180° out of phase at the top of the K layer as was to be expected from linear gravity wave theory. The height of change (92–93 km) between positive and negative correlation of temperatures and K densities is clearly dominated by the nonlinear layer response, which could be observed largely because of a strong monochromatic gravity wave with vertival wavelength of 30 km and a horizontal period close to 5 hours, quite similar to the predicted nonlinear layer response from theory. These data show that (1) chemical effects are negligible in the response of the K layer to the passage of an atmospheric gravity wave, and (2) that near the peak of the K layer non‐linear effects dominate the response.
A three‐dimensional hybrid simulation of magnetic reconnection
Authors: Nakamura M. S. , Fujimoto M.
Published: February 2004

We study magnetic reconnection in the magnetotail by a 3‐D hybrid simulation (ion particle, charge neutralizing massless electron fluid). Magnetic reconnection is initiated by putting anomalous resistivity localized in the plasma sheet. The resistive region is set up to have a finite dawn‐dusk extent so that 3‐D effects in the presence of ion particle dynamics are studied. Indeed, in the course of reconnection, plasma flow pattern and magnetic field configuration show highly asymmetric features in the dawn‐dusk direction due to ion kinetic responses. The initial dawn‐to‐dusk ion current is disrupted on the dawnside of the diffusion region, requiring electrons to flow into the diffusion region from the duskside of it to support the cross‐tail current, resulting in dawnward bending of field lines prior to reconnection. In contrast, reconnected field lines are transported by the reconnection jet which has substantial duskward flow component and eventually bend duskward.
Acid ions at triple junction of Antarctic ice observed by Raman scattering
Authors: Fukazawa Hiroshi , Sugiyama Ken , Mae Shinji , Narita Hideki , Hondoh Takeo
Published: February 2004

We measured the Raman spectra of the junctions where three crystal grains met (triple‐junctions) in polycrystalline ice from two Antarctic sites (Nansen ice and South Yamato ice) in order to obtain direct evidence that sulfuric and nitric acids are present as liquid at the triple‐junctions. We found that Raman spectra of Nansen ice have a peak (1050 cm−1) of HSO4− and NO3− in sulfuric and nitric acid solutions when the measured temperatures of the ice are −8 ∼ −35°C. Thus, sulfuric and nitric acids dissociate to HSO4− and NO3− at the triple‐junctions of Nansen ice. Raman spectra of South Yamato ice have a peak (980 cm−1) of SO42− in sulfuric acid solution when the measured temperatures of the ice are −8 ∼ −20°C. Thus, sulfuric acid dissociates to SO42− at the triple‐junctions of South Yamato ice. The results showed that aqueous solutions of the acids exist at Antarctic ice‐sheet temperatures.
Simulated interannual to decadal variability in the tropical and sub‐tropical North Atlantic
Authors: Delworth Thomas L. , Mehta Vikram M.
Published: February 2004

The dominant pattern of tropical and subtropical North Atlantic sea surface temperature (SST) anomalies simulated in the GFDL coupled ocean‐atmosphere model is identified and compared to observations. The spatial pattern and temporal variability of that pattern resemble observational results. On interannual time scales it is shown that anomalous surface heat fluxes, consistent with variations in the intensity of the subtropical high pressure system in the atmosphere and the associated Northeasterly Trade winds, appear to be the most important process for generating this SST pattern. This relationship is also true on decadal time scales, although the relative role of oceanic heat advection is somewhat larger than on the interannual time scales.
The first simulation of an ozone QBO in a general circulation model
Authors: Nagashima Tatsuya , Takahashi Masaaki , Hasebe Fumio
Published: February 2004

The quasi‐biennial oscillation (QBO) of ozone has been simulated for the first time in a general circulation model (GCM). The model employed is the first version GCM developed at the Center for Climate System Research / National Institute for Environmental Studies (CCSR/NIES). The model has a horizontal resolution of T21 and 60 layers in the vertical. Modified Chapman reactions of ozone photochemistry are included in the model, allowing the ozone to be fully interactive with the radiative and dynamical fields. The simulation is, for the most part, successful except that a deficiency of about 40 DU exists in the total ozone in comparison with observations. The simulated zonal wind QBO has a rather short period (about 1.5 years) and somewhat weak easterlies. The lower stratospheric ozone QBO over the equator is qualitatively similar to that observed, although the simulated amplitude of about 0.3 ppmv is somewhat less than that observed. The phase relationship between the equatorial upper and lower stratospheric ozone QBOs is successfully reproduced, although the phase of the modeled ozone QBO slightly precedes the observed phase in the upper stratosphere. The mid‐latitude ozone QBO is out of phase with the equatorial ozone QBO. The phase propagation of planetary‐scale structure in ozone from the mid‐latitudes to equatorial regions is more pronounced during the westerly than in the easterly phase of the stratospheric QBO, especially in the Northern Hemisphere winter.
Drain‐back process of basaltic magma in the summit conduit detected by microgravity observation at Izu‐Oshima Volcano, Japan
Authors: Watanabe Hidefumi , Okubo Shuhei , Sakashita Shikou , Maekawa Tokumitsu
Published: February 2004

Basalt magma sometimes moves through volcanic conduits causing only minor deformation. In that case, we may detect magma movements directly by microgravity observations. After the 1986 eruption of Izu‐Oshima volcano, we observed anomalous gravity variations localized at the summit. Based on a vertical cylindrical conduit model, we estimate the time variations of the head of magma in the summit conduit and clarify the magma drain‐back process after the 1986 eruption.
Sea surface salinity changes along the Fiji‐Japan shipping track during the 1996 La Niña and 1997 El Niño period
Authors: Delcroix Thierry , Gourdeau Lionel , Hénin Christian
Published: February 2004

Sea‐surface salinity (SSS) changes during the 1996 La Niña and 1997 El Niño events are analysed along the Fiji‐Japan shipping track, based on 20 thermosalinograph sections. In the equatorial band, above‐average SSS (35.2 to 35.4 instead of 35) were observed in 1996, consistent with a well‐marked south equatorial current, an unusually‐strong equatorial upwelling, and below‐average precipitation (P). From January to August 1997, the SSS decreased sharply from 35.2 to 33.8 (lowest recorded monthly value over the last 20 years), compatible with a reversal of zonal current, the occurrence of equatorial downwelling, and above‐average P. From September to November 1997, the SSS remained almost constant (34.2), consistent with the opposite effects of eastward current, likely bringing low saline water from the Pacific warm pool, and of evaporative cooling, vertical mixing and below‐average P which all tend to increase SSS. The potential impacts of the observed SSS changes on sea level are discussed.
Velocity‐shear origin of low‐frequency electrostatic ion‐gyroresonant waves
Authors: Carroll J. J. , Koepke M. E. , Zintl M. W. , Gavrishchaka V. , Ganguli G.
Published: February 2004

Electrostatic ion‐cyclotron waves with spectral features below the ion gyrofrequency and spaced by small fractions of the ion gyrofrequency are reported, a result not possible for waves associated with the well‐known current‐driven electrostatic ion‐cyclotron (CDEIC) instability. This is accomplished by producing a localized, transverse (to the magnetic field B ž)
electric field E(x) x) in a laboratory plasma to excite inhomogeneous energy‐density driven (IEDD) waves and by exploiting the kyνE dependence of the IEDD mode frequency, where ky and νE are the components of the IEDD wavevector and plasma drift speed, respectively, along the E × B direction. The IEDD frequency range is shown to reach down to one‐third of the ion gyrofrequency, a range usually reserved for other types of waves, e.g., ion‐acoustic waves. These results may be relevant to broadband ELF waves observed in the ionosphere.
Solar cycle correlations of substorm and auroral occurrence frequency
Authors: Nevanlinna H. , Pulkkinen T. I.
Published: February 2004

Recent results of Newell et al. [1998a] suggest that the polar cap integrated auroral occurrence frequency is independent of the solar cycle phase. This paper utilizes auroral all‐sky camera observations from Northern Finland during 1974–1996 to show that although the total number of auroral observations shows only a weak solar cycle dependence, the number of quiet auroral arcs is anticorrelated with the sunspot number, indicating that active auroral forms are less common during sunspot minima. A local index for geomagnetic substorm occurrence frequency and intensity is developed. It is shown that in long‐term averages this index is highly correlated with the planetary aa index, and that both show strong correlation with the sunspot number. We further demonstrate a clear correlation between the active auroral forms and the local geomagnetic disturbances.
Preliminary geodetic strain measurement from the South Fiordland Region of New Zealand using repeat GPS surveys: Implications for subduction on the Puysegur Trench
Authors: Pearson Chris
Published: February 2004

Comparing 1996 GPS data and data collected only one year earlier demonstrates that 50% of the instantaneous relative plate motion is accommodated between the west coast of the South Island and the eastern side of the Waiau Basin, a distance of about 75 km. The observed relative velocity vectors are nearly parallel to the inferred orientation of the plate boundary and rotated more than 30° clockwise compared to the relative plate motion vector, a difference that is significant at the 95% level of confidence. Modeling shows that the observed deformation rates are consistent with a model where nearly all the relative plate motion occurs on the plate boundary thrust as defined by the Benioff Zone associated with subduction on the Puysegur Trench.
Rate coefficient upper limits for the BrONO2 and ClONO2 + O3 reactions
Authors: Burkholder James B. , Orlando John J.
Published: February 2004

The gas phase reactions BrONO2 and ClONO2 + O3 → Products (k1 and k3) were examined at 235±2 K and 700 Torr N2 using a Fourier transform infrared spectrometer coupled to a temperature regulated long path absorption cell. The loss of BrONO2 and ClONO2 were measured to be independent of the O3 concentration yielding k1 < 1 × 10−20 cm³ molecule−1 s−1 and k3 < 4 × 10−21 cm³ molecule−1 s−1.
Enthalpy and density measurements of pressure‐amorphized GeO2 quartz
Authors: Akaogi M. , Suzuki T. , Kojima R. , Honda T. , Ito E. , Nakai I.
Published: February 2004

Quartz‐type GeO2 was compressed at room temperature up to pressures of 11, 15 and 18 GPa, and the samples recovered to 1 atm were mostly amorphized. Measured densities of the amorphous phases increased with increasing synthesis pressure: the amorphous phase synthesized at 18 GPa was 32 % denser than GeO2 quartz. Enthalpies of the amorphous phases relative to GeO2 quartz and glass prepared at 1 atm were measured by lead borate solution calorimetry. The enthalpies increased almost linearly with decreasing molar volumes from GeO2 quartz to the 18 GPa‐amorphous phase. The enthalpy of the 18 GPa‐amorphous phase was about 18 kJ/mol higher than GeO2 quartz, and about 4 kJ/mol higher than the 1 atm‐glass. The higher enthalpy relative to GeO2 quartz is interpreted as the energy associated with disordering of the quartz structure and collapse of the tetrahedral framework which lead to octahedral coordination of germanium atoms.
Estimating the influence of salinity on sea level anomaly in the ocean
Authors: Maes Christophe
Published: February 2004

Evidence is found over broad regions of the ocean that variations in salinity have sufficiently large effects on sea level such that they may be detectable by an altimeter. The mechanisms involve the salinity variability within the tropical mixed layer, the tropical and subtropical baroclinic response in the main halocline and the barotropic response in the Southern Ocean. All these processes lead to signals in sea level which range between 2 and 10 cm. An important result is that in the western tropical Pacific Ocean the effect of salinity variability on sea level may be equal to the effect of thermal variability.
Model calculations of stratospheric OBrO indicating very small abundances
Authors: Chipperfield M. P. , Glassup T. , Pundt I. , Rattigan O. V.
Published: February 2004

We have used a one‐dimensional photochemical model to investigate the potential role of OBrO in stratospheric photochemistry. The OBrO lifetime against photolysis is likely to be very short (around a few s) which prevents any appreciable concentration during sunlit hours. This rapid photolysis also prevents the gas‐phase production of significant OBrO in the model during twilight, as possible precursors (e.g. BrO) are converted to their nighttime reservoirs. Using a range of possible gas‐phase production reactions, the maximum (nighttime) OBrO volume mixing ratio produced in the model in the lower stratosphere is around 0.01 × 10−12 (0.01 pptv). These model results contradict recent tentative nighttime balloon observations of large OBrO [Renard et al., 1997, 1998]. We have used our model results to put constraints on the rates of gas‐phase and heterogeneous reactions that would be necessary to produce appreciable amounts of OBrO in the stratosphere. These constraints show that if OBrO is indeed present in the nighttime stratosphere at the pptv level, our current understanding of atmospheric bromine chemistry is severely flawed.
On the origin of relativistic electrons in the magnetosphere associated with some geomagnetic storms
Authors: Rostoker Gordon , Skone Susan , Baker Daniel N.
Published: February 2004

There has been considerable interest of late in the sudden appearance of large fluxes of relativistic electrons (E>1 MeV) at geostationary orbit due to the adverse effect these electrons can have on operational spacecraft. The question arises as to how these electrons are accelerated to relativistic energies in the relatively short time of a few hours. We shall show that large amplitude ULF pulsations are a unique feature of intervals of time in which the fluxes of relativistic electrons rise to high levels at radial distances beyond the normal L‐shell range occupied by the outer radiation belt. We use SAMPEX polar orbiter data for the magnetic storm of November 1993 to show that the fluxes of E>400 keV electrons increase simultaneously over a broad range of L‐shells and use this fact to suggest that large amplitude ULF pulsations have the potential to supply the energy necessary to create the relativistic electron fluxes.
Energetic (∼ 1 to 50 MeV) protons associated with Earth‐directed coronal mass ejections
Authors: Torsti J. , Anttila A. , Kocharov L. , Mäkelä P. , Riihonen E. , Sahla T. , Teittinen M. , Valtonen E. , Laitinen T. , Vainio R.
Published: February 2004

During the period from January through mid‐May, 1997, four large Earth‐directed CMEs were observed by the Large Angle Spectroscopic Coronograph (LASCO). These CMEs were associated with long‐lasting fluxes of >1.6 MeV protons detected by the Energetic and Relativistic Nuclei and Electron instrument (ERNE). However, the magnitudes of energetic proton events differed dramatically on different occasions. In strong proton events, production of 10‐50 MeV protons started during expansion of the coronal Moreton wave in the western hemisphere of the Sun. The new SOHO observations suggest that potentialities of CMEs to produce energetic particles in the interplanetary medium crucially depend on the previous evolution of the explosion below ∼2R⊙. Forecasting of the near‐Earth >10 MeV proton intensity requires multiwavelength observations of the early phase of an event particularly the Extreme‐ultraviolet Imaging Telescope (EIT) observations.
Geodetic observations of the M 5.1 January 29, 1994 Northridge aftershock
Authors: Donnellan Andrea , Webb Frank H.
Published: February 2004

Geodetic observations of the January 29, 1994 M 5.1 aftershock of the Northridge earthquake are consistent with seismic solutions showing left‐lateral oblique slip on a northeast striking steeply dipping fault. Thirty second solutions of the data from the station showing the maximum observed displacement (35 mm) indicate neither precursory nor immediate post‐seismic motion to the aftershock. The aftershock does appear to be superimposed over the longer term Northridge post‐seismic deformation field. Inversions of the data yield a potency of 2.6 ± 0.3 × 10−3km³ slightly higher than that determined by seismic methods. Combining the potency with estimates of rigidity from P‐ and S‐wave velocities yields a moment that is consistent with seismic moment solutions.
Observations of galactic cosmic ray modulation during Earth‐directed coronal mass ejections
Authors: Mäkelä P. , Torsti J. , Teittinen M. , Valtonen E. , Riihonen E. , Ipavich F.
Published: February 2004

We describe three cosmic‐ray decreases observed by the energetic particle telescope ERNE on board SOHO spacecraft during the period January–May, 1997. The decreases in cosmic‐ray proton intensities in the energy range above 50 MeV were observed after the passage of interplanetary shocks on February 9, April 10, and May 15. All the shocks were produced by Earth‐directed coronal mass ejections. The amplitudes of the decreases compared to the counting rates just before the shock arrival were 8.5%, 14%, and 7%, respectively. The observed recovery times were 1, 4.2, and 5 days, respectively. After the February and May events the pre‐shock levels were reached, but in the April event the recovery was only to 3% below this level. In each case, there were also clear indications of the passage of the ejecta. The energy dependences of the cosmic‐ray helium flux decreases at 12–100 MeV/n were similar to each other in the April and May events, while in the February event the decrease was less pronounced.
Microphysical and turbulent measurements of the Schmidt number in the vicinity of polar mesosphere summer echoes
Authors: Lübken Franz‐Josef , Rapp Markus , Blix Tom , Thrane Eivind
Published: February 2004

During the ECHO campaign in 1994 neutral and electron density fluctuations were measured together with charged aerosols on the same sounding rocket launched close to a VHF radar detecting polar mesosphere summer echoes (PMSE). For the first time this combination of measurements allows for an independent test of the microphysical and the turbulence interpretations of the Schmidt number (Sc). The Schmidt number characterizes the reduction of the electron diffusivity by charged aerosols, which leads to an enhancement of the electron density fluctuations at small spatial scales. In one of the flights charged aerosols were observed at ∼83–89km together with correlated depletions in electron density (‘biteouts’). We have applied a model of aerosol charging to the measured plasma profiles and determined a mean aerosol radius of ∼8nm and a mean aerosol charge of 1e‐. In the microphysical description of electron diffusion these parameters correspond to Sc∼420. Spectral analysis of the electron density fluctuations showed enhancements of spectral densities at small scales suggesting likewise a Schmidt number much larger than unity. Using an energy dissipation rate of 67mW/kg as derived from neutral air turbulence measurements on the same rocket we get from the electron spectra Sc=385 which is in excellent agreement with the microphysical result. Apart from this turbulent layer we observe no significant disturbances in neutral air number densities below ∼87km which confirms earlier indications that processes must exist to create PMSEs which are not directly coupled to neutral air turbulence.
Sources of crustal deformation associated with the Krafla, Iceland, eruption of September 1984
Authors: Árnadóttir Thóra , Sigmundsson Freysteinn , Delaney Paul T.
Published: February 2004

A decade‐long plate‐boundary rifting episode in northern Iceland ended with the September 1984 fissure eruption of Krafla volcano. We apply a nonlinear inversion method to geodetic data collected before and after the eruption to infer the location, geometry, and strengths of deformation sources associated with the eruption. The net outflow of magma from a 3‐km‐deep magma chamber beneath the Krafla caldera was 30−120× 106 m³. A similar volume of magma, 50−70×106 m³, was emplaced in a 1‐meter‐wide, ∼9‐km‐long dike extending from the surface to ∼7 km depth. Furthermore, at least 110×106 m³ of magma erupted. Accordingly, a surplus of magma must have been expelled from a second reservoir, the location of which, although uncertain, is likely to lie at depths greater than ∼5 km beneath Krafla volcano. It would be difficult to detect this deeper source because of the narrow aperture of the geodetic networks.
Persistently anomalous Pacific geomagnetic fields
Authors: Johnson Catherine L. , Constable Catherine G.
Published: February 2004

A new average geomagnetic field model for the past 3kyr (ALS3K) helps bridge a large temporal sampling gap between historical models and more traditional paleomagnetic studies spanning the last 5 Myr. A quasi‐static feature seen historically in the central Pacific has the opposite sign in ALS3K; its structure is similar to, but of larger amplitude than, that in the time‐averaged geomagnetic field for the last 5 Myr. Anomalous geomagnetic fields exist beneath the Pacific over timescales ranging from 10²‐106 years. It is unlikely that bias over such long time scales arises from electromagnetic screening, but conceivable that the Lorentz force is influenced by long wavelength thermal variations and/or localized regions of increased electrical conductivity (associated with compositional anomalies and possibly partial melt). This is consistent with recent seismic observations of the lower mantle.
Antineutrino geophysics with liquid scintillator detectors
Authors: Rothschild Casey G. , Chen Mark C. , Calaprice Frank P.
Published: February 2004

Detecting the antineutrinos emitted by the decay of radioactive elements in the mantle and crust could provide a direct measurement of the total abundance of uranium and thorium in the Earth. In calculating the antineutrino flux at specific sites, the local geology of the crust and the background from the world's nuclear power reactors are important considerations. Employing a global crustal map, with type and thickness data, and using recent estimates of the uranium and thorium distribution in the Earth, we calculate the antineutrino event rate for two new neutrino detectors. We show that spectral features allow terrestrial antineutrino events to be identified above reactor antineutrino backgrounds and that the uranium and thorium contributions can be separately determined.
A saturation mechanism for the Farley‐Buneman instability
Authors: Otani Niels F. , Oppenheim Meers
Published: February 2004

Studies with a reduced‐mode two‐fluid model have revealed a promising candidate for the saturation mechanism of the Farley‐Buneman instability in the daytime equatorial electrojet. The mechanism operates by redistributing the zero‐order electron E × B flow field. Secondary waves generated nonlinearly by the instability are responsible for the flow field modification. Saturation occurs because the modified flow reduces the principal charge transport responsible for the growth of the primary wave. Two‐dimensional particle simulations of the instability exhibit saturation via the same mechanism.
The quiet daily variation in the total magnetic field: Global curves
Authors: Hitchman A. P. , Lilley F. E. M. , Campbell W. H.
Published: February 2004

Most magnetic mapping exercises involve measuring the amplitude, or total‐field component, of Earth's magnetic field. Removing the time‐varying part of the field is a task of data reduction, and the most common time variation is the quiet daily variation, Sq. It is thus valuable to have for reference type curves of the quiet daily variation in the total field. To meet this need, global data obtained during the 1965 International Year of the Quiet Sun have been used to derive type curves describing the Sq variation of the total magnetic field, in addition to the traditional field components. As for the traditional components, the total‐field curves show significant seasonal and latitudinal variability in amplitude and phase. The effect of the equatorial electro‐jet is clearly evident. In both hemispheres of the globe there are bands of reduced amplitude in total‐field signal between the equator and the path of the Sq focus. These bands, here termed the total‐field “doldrums”, persist throughout the year.
Lateral asthenospheric viscosity variations and postglacial rebound: A case study for the Barents Sea
Authors: Kaufmann Georg , Wu Patrick
Published: February 2004

The effect of lateral asthenospheric viscosity variations on observable signatures related to postglacial rebound in the Barents Sea is studied. Using a finite‐element approach to discretize the problem, a comparison between a laterally homogeneous reference earth model and a laterally heterogeneous earth model is performed.

The results indicate that a change in asthenospheric viscosity of about three orders of magnitude influences predictions of land uplift up to 10–20 m, present‐day velocities up to 0.5–1.5 mm/a, and present‐day gravity anomalies up to 0.4–0.8 mGal in the northwestern part of the Barents Sea region.
The evolution of aircraft emissions in the stratosphere
Authors: Gettelman A.
Published: February 2004

Distributions of subsonic aircraft emissions are advected as an initial value problem in a 3D transport model to simulate the evolution of emissions in the stratosphere. The sensitivity of transport to season, analyzed tropopause height and aircraft emissions distribution is analyzed. The 1/e‐folding lifetime of the emissions of the current fleet is found to be about 50 days, within the range of previous estimates. The lifetime is shorter in January than in July. Within a 90 day period, approximately 7% of emissions in July and 2% in January are lofted into the stratosphere. Pathways for the stratosphere‐troposphere exchange of emissions are discussed.
Gas‐phase reaction of N2O5 with water vapor: Importance of heterogeneous hydrolysis of N2O5 and surface desorption of HNO3 in a large Teflon chamber
Authors: Wahner Andreas , Mentel Thomas F. , Sohn Martin
Published: February 2004

Laboratory measurements of the gas‐phase hydrolysis of N2O5 are always preturbed by wall reactions. Their contribution could be quantified in a large double‐walled teflon bag chamber by introducing HNO3 into the chamber and analysing its temporal evolution in the gas‐phase at low and high relative humidities, and by varying the surface‐to‐volume ratio of the chamber. By fitting a model to the experimental results, a consistent set of rate coefficients for adsorption and desorption of HNO3 from the chamber walls could be obtained. The desorption is so slow that the gas‐phase hydrolysis of N2O5 via the reactions N2O5 + H2O → 2HNO3 (k1 = 2.5 · 10−22cm³molec.−1s−1) and N2O5 + 2H2O → 2HNO3 + H2O (k2 = 1.8 · 10−39cm6molec.−2s−1) is influenced by wall effects to less than 5%. The importance of the gas‐phase N2O5 hydrolysis in the troposphere is discussed.
Predicting the '97 El Niño event with a global climate model
Authors: Oberhuber Josef M. , Roeckner E. , Christoph M. , Esch M. , Latif M.
Published: February 2004

A simple data assimilation technique has been applied for initializing coupled ocean‐atmosphere general circulation models, which is able to generate the three‐dimensional thermal state of the low‐latitude oceans by forcing the model with observed anomalies of sea surface temperature. The scheme has been tested in a multi‐year experiment in which the vertical temperature profiles in the equatorial Pacific measured by the TOGA‐TAO array have been successfully reproduced for the period '96 to '97. In a further series of eight hindcast experiments initialized between January '96 and September '97, the predictive skill of the model was tested. All experiments starting in '97 correctly simulated the evolution of the '97 El Niño, although the amplitude was slightly underestimated. While the ocean was pre‐conditioned to create an El Niño already in '96, the model correctly stayed in the cold (La Niña) phase initially. All experiments initialized in '97 forecast a La Niña event for the middle of'98.
Quantum interference in the Schumann‐Runge bands of molecular oxygen
Authors: Lewis B. R. , Gibson S. T. , Torop L. W. , McCoy D. G.
Published: February 2004

The photoabsorption cross section of O2 in the Schumann‐Runge bands is investigated theoretically using the coupled‐channel Schrödinger‐equations method. It is found that quantum interference between vibrational bands leads to significant asymmetry in the far line wings, a result supported by experimental evidence. Thus, Schumann‐Runge cross sections calculated with the usual band models based on Voigt line shapes may be in error in regions of weak absorption between vibrational band heads, suggesting the need to re‐evaluate aspects of atmospheric photochemistry sensitive to those regions.
Effect of the magnetic field on the energetics of Mars ionosphere
Authors: Choi Y. W. , Kim J. , Min K. W. , Nagy A. F. , Oyama K. I.
Published: February 2004

The coupled, one‐dimensional electron and ion energy equations, with a combination of small steady and fluctuating horizontal magnetic fields imposed, are solved for the Mars ionosphere, corresponding to conditions encountered during the Viking mission. A series of calculations with various boundary conditions and heat sources result in a range of electron and ion temperature profiles, which are compared with the results obtained by the RPA's carried aboard the Viking landers. It is shown that solar EUV heating alone does not lead to the observed temperature profiles and that assuming reasonable heat fluxes at the top result in good agreement. It is also found that the introduction of small steady and altitude dependent fluctuating horizontal magnetic fields, which modify the thermal conductivity, leads to electron temperatures in reasonably good agreement with the RPA data, but does not match the observed ion temperatures above about 240 km. The effects of chemical and Joule heating are also examined and found not to be significant.
The depth of the stably stratified internal boundary layer over the sea
Authors: Melas Dimitrios
Published: February 2004

As an air mass is advected from a heated land surface over a cooler sea, it is extensively modified by the underlying surface with the subsequent formation of a stably stratified internal boundary layer (SIBL). Due to weak turbulence, changes in surface forcing are communicated very slowly across the depth of the SIBL and its growth rate cannot be described in terms of local parameters. Therefore, it has been proposed that the growth of the SIBL is controlled by the fetch integrated value of surface heat flux. This approach is adopted in the present paper in order to develop a simple equation capable to describe the development of the SIBL as a function of downwind distance and external forcings, such as pressure gradient force, surface roughness and potential temperature difference between sea and land surface. The derived relationship is tested against a limited data set from the Öresund experiment.
Sub‐seasonal variations in lower stratospheric water vapor
Authors: Mote Philip W. , Dunkerton Timothy J. , Pumphrey Hugh C.
Published: February 2004

Observations of water vapor with high temporal and spatial resolution and good horizontal coverage just above the tropical tropopause have been scarce, but a preliminary version of such data has been developed using radiance measurements of the Microwave Limb Sounder. These data reveal distinct variations with periods in the ranges 10–25 days and 30–70 days, consistent with (respectively) slow Kelvin waves and the tropical intraseasonal oscillation.
A stochastic view of the solar modulation phenomena of cosmic rays
Authors: Yamada Yoshihiko , Yanagita Shohei , Yoshida Tatsuo
Published: February 2004

We report on a numerical method for solving the Fokker‐Planck equation (FPE) which describes the solar modulation of cosmic rays using Itô's stochastic differential equations (SDEs) and discuss on it's power and profound implications not easily attainable by standard methods. It is shown how easily the modulated energy spectrum of cosmic rays is calculated from the interstellar spectrum utilizing the momentum distribution function obtained by SDE method for particles with a fixed momentum of various values at 1 AU. The resultant modulated spectra are compared with the results by the standard numerical technique using the Crank‐Nicholson method to demonstrate the validity of our method.
Identification of the cloud pulse responsible for a trans‐ionospheric pulse pair
Authors: Russell C. T. , Zuelsdorf R. S. , Strangeway R. J. , Franz R.
Published: February 2004

The Blackbeard VHF radio receiver on the Alexis satellite detects pairs of broadband chirps, each lasting about four microseconds. These chirps are separated by several tens of microseconds and extend in frequency to over 166 MHz. The characteristics of these signals suggest that they are caused by electrical discharges in the Earth's atmosphere, but there is some debate as to whether the discharges occur in the middle atmosphere or within tropospheric clouds. Previously, by comparing the time of the occurrence of these Trans‐Ionsopheric Pulse Pairs (TIPPs) with the occurrence of electric pulses recorded by the National Lightning Detection Network, we have found that they are associated with events classified as positive cloud pulses. Herein we examine one TIPP event that is associated with a near simultaneous (0.75 ms) detection at two stations of the ground network allowing us to determine that the causative event occurred over southeastern Kansas. Knowing the longitude and latitude of the pulse, we show that the interchirp separation time is consistent with the generation of the first chirp of the pair at 8 km altitude followed by the ground reflection of that signal to produce the second chirp of the TIPP.
Analysis of record‐low ozone values during the 1997 winter over Lauder, New Zealand
Authors: Brinksma E. J. , Meijer Y. J. , Connor B. J. , Manney G. L. , Bergwerff J. B. , Bodeker G. E. , Boyd I. S. , Liley J. B. , Hogervorst W. , Hovenier J. W. , Livesey N. J. , Swart D. P. J.
Published: February 2004

Record‐low ozone (O3) column densities (with a minimum of 222 DU) were observed over the Lauder NDSC (Network for the Detection of Stratospheric Change) station (45°S, 170°E) in August 1997. Possible causes are examined using height‐resolvedO3measurements over Lauder, and high‐resolution reverse trajectory maps ofO3(initialised with Microwave Limb Sounder measurements) and of potential vorticity. The analysis shows thatO3poor air originated from two regions: Below the 550 K isentrope (∼22 km) subtropical air was observed, while between 600 and 1000 K (∼25–33.5 km) the polar vortex tilted over Lauder for several days. A rapid recovery of theO3column density was observed later, due to anO3rich polar vortex filament moving over Lauder between 18 and 24 km, while simultaneously theO3poor higher vortex moved away.
Dynamics of the Siple Coast ice streams, west Antarctica: Results from a thermomechanical ice sheet model
Authors: Payne A. J.
Published: February 2004

Most of the ice leaving the Antarctic Ice Sheet is discharged to the sea by ice streams. An understanding of the dynamics of these ice streams is therefore crucial if we are to predict the future evolution of the ice sheet and its effect on global sea level. The behavior of Ice Streams A to E of the Siple Coast, West Antarctica has attracted much attention with evidence of recent stagnation and numerous relict ice‐flow features. Here I present results from a three‐dimensional, thermodynamic ice sheet model of the West Antarctic Ice Sheet (WAIS). The model generates variability in the flow of the Siple Coast ice streams reminiscent of that mentioned above. This is caused by competition between several preferred ice flow pathways in the area. Individual ice streams interact through changes in catchment‐area size: a reduction in catchment area reduces the flow of ice entering a stream and can cause stagnation through the associated reduction in deformational heating.
Production of methyl bromide by terrestrial higher plants
Authors: Gan J. , Yates S. R. , Ohr H. D. , Sims J. J.
Published: February 2004

Methyl bromide (CH3Br) is considered to play an important role in stratospheric ozone depletion, but its sources are currently not well defined. We have observed that Brassica plants can take up Br− from soil, produce CH3Br and release it into the air. Emission of CH3Br was detected from plants grown in natural soils containing 0.06–0.31 mg/kg Br−; the emission increases with increasing soil Br− level. We estimate that cabbage produces 0.4±0.2 Gg/yr, and rapeseed plants 6.6±1.8 Gg/yr. Given the ubiquitous distribution of Br− in soil, CH3Br production by terrestrial higher plants is likely a large source for atmospheric CH3Br.
Influence of crustal viscosity on earthquake energy distribution in a viscoelastic Spring‐Block System
Authors: Yoshino Takashi
Published: February 2004

We show that viscosity of crust‐forming rocks makes the frequency curve of earthquake energy deviate from an empirical power law relation. To estimate the effect of viscosity, we consider a modified Burridge‐Knopoff type spring‐block model. The model consists of the blocks connected by Maxwell springs which represent the material property of crustal rocks. We applied a method of cellular automaton model to the system. The resulting earthquake sequences depend on the relaxation time τ of the Maxwell spring. For relatively small 1/τ, where elasticity dominates, the earthquake energy frequencies show the power law relation and deviate from the relation at large earthquake energies. The separation shifts to smaller energy with increase of 1/τ. For large 1/τ, the distribution does not show the power law relation. The decay of earthquake frequencies after major mainshocks is not observed.
The electrical properties of a 2D conductive zone under the Juan de Fuca Ridge
Authors: Jegen Marion , Edwards R. N.
Published: February 2004

Vertical gradient electromagnetic sounding (VGS) on the Endeavour segment of Juan de Fuca mid‐ocean ridge reveals the presence of a 2D ridge‐parallel, conductivity anomaly. If the anomaly is caused mainly by melt in a conventional upper mantle upwelling zone alone, then the conductivity of the zone is about 0.6 S/m. The corresponding Archie's law melt fraction exceeds 0.10. A significantly lower melt fraction requires a sheet‐like, well interconnected melt. Upwelling zone conductivity can be reduced by a third if the anomaly is broadened and a crustal conductor is added to the model.
Cusp energetic ions: A bow shock source
Authors: Chang S.‐W. , Scudder J. D. , Fuselier S. A. , Fennell J. F. , Trattner K. J. , Pickett J. S. , Spence H. E. , Menietti J. D. , Peterson W. K. , Lepping R. P. , Friedel R.
Published: February 2004

Recent interpretations of cusp energetic ions observed by the POLAR spacecraft have suggested a new energization process in the cusp [Chen et al., 1997; 1998]. Simultaneous enhancement of H+, He+2, and O>+2 fluxes indicates that they are of solar wind origin. In the present study, we examine H+ and He+2 energy spectra from 20 eV to several 100 keV measured by the Hydra, Toroidal Imaging Mass‐Angle Spectrograph (TIMAS), and Charge and Mass Magnetospheric Ion Composition Experiment (CAMMICE) on POLAR. The combined spectrum for each species is shown to be continuous with a thermal distribution below 10 keV/e and an energetic component above 20 keV/e. Energetic ions with comparable fluxes and a similar spectral shape are commonly observed downstream from the Earth's quasi‐parallel (Q∥) bow shock. In addition to the similarity in the ion spectra, electric and magnetic field noise and turbulence detected in the cusp by the Plasma Wave Instrument (PWI) and Magnetic Field Experiment (MFE) onboard POLAR are similar to the previously reported observations at the bow shock. The waves appear to be coincidental to the cusp energetic ions rather than causal. We suggest that these ions are not accelerated locally in the cusp. Rather, they are accelerated at the Q∥ bow shock and enter the cusp along open magnetic field lines connecting both regions.
Objectively mapped stream function fields on the Texas‐Louisiana shelf based on 32 months of moored current meter data
Authors: Cho Kwangwoo , Reid Robert O. , Nowlin Worth D.
Published: February 2004

On the basis of current measurements observed at 31 moorings during April 1992 through November 1994, as part of the Texas‐Louisiana Shelf Circulation and Transport Processes Study, we describe the horizontally nondivergent part of the near‐surface, shelf‐wide‐scale, low‐frequency circulation and its variability on the Texas‐Louisiana continental shelf by means of objectively fitted stream function fields. The 32‐month mean velocity stream function patterns generally support the Cochrane and Kelly [1986] circulation schema for the shelf circulation, in which an elongated cyclonic gyre exists during the nonsummer period (September through May) but with flow in the summer (June to August) directed upcoast (toward the Mississippi delta) over the entire shelf. There exists significant interannual variability of the stream function fields, especially in the transition period from spring to summer to fall and along the shelf break. Strong upcoast (downcoast) currents dominate at the western shelf break associated with the presence of energetic anticyclones (cyclones). The dominant pattern of stream function variability deduced by empirical orthogonal function (EOF) analysis of 32 individual monthly mean patterns contains about 89% of the variance and shows a simple, shelf‐wide, along‐shelf pattern of circulation. The monthly evolution in amplitude of this dominant EOF pattern clearly mimics the monthly evolution of the along‐shelf component of the wind with squared correlation of 0.83. This provides strong evidence that the seasonal variation of the shelf circulation is wind forced, in support of Cochrane and Kelly. The second and residual EOFs show more complex features near the shelf break that are associated with Loop Current eddies known to impact the continental slope and shelf break.