bluuebunny/crossref_metadata_2025 huggingface dataset:
Coronagraph observations of inflows during high solar activity
Authors: Wang Y.‐M. , Sheeley N. R. , Howard R. A. , Cyr O. C. St. , Simnett G. M.
Published: September 2002

Since the start of the SOHO mission three years ago, the Large Angle Spectrometric Coronagraph (LASCO) has recorded numerous examples of small, faint features moving inward through the corona. The inflows are observed at heliocentric distances of 2–4 Rs and became increasingly common during 1998, as solar and coronal mass ejection (CME) activity increased. The inward‐moving structures, which are most easily detected in running difference movies, often have a cusplike appearance and tend to leave a density depletion in their wake; the downward velocities range from less than 20 km s−1 to over 100 km s−1. The downflows are observed typically ∼1 day after the passage of a CME, and coexist side by side with continuing outflows of streamer material. We interpret these small‐scale events as observational signatures of the gradual closing‐down of magnetic flux dragged outward by CMEs or other transient outflows.
Two‐dimensional structure of the co‐planar and non‐coplanar magnetopause during reconnection
Authors: Krauss‐Varban D. , Karimabadi H. , Omidi N.
Published: September 2002

The two‐dimensional (2‐D) magnetopause transition during reconnection is investigated with large‐scale hybrid simulations. Contrary to previous studies, but in agreement with observations, the two discontinuities that form are not an intermediate shock or a slow shock. A 2‐D reconnection configuration develops with jumps that do not satisfy Rankine‐Hugoniot conditions of known discontinuities. All plasma quantities are fairly constant between the discontinuities. This region is characterized by a nearly unchanged sheath density, slight temperature enhancement, and significant magnetic field depression and thus resembles the “Sheath Transition Layer” of Song et al. [1989]. For a non‐coplanar magnetic field Bzo, the plasma β attains very high values on the outflow side where Bzo and the Hall‐generated field cancel, and the jet becomes unstable. In this case, the magnetosheath‐side discontinuity resembles the often‐observed rotational discontinuity.
Pacific thermocline bridge revisited
Authors: Schneider Niklas , Venzke Stephan , Miller Arthur J. , Pierce David W. , Barnett Tim P. , Deser Clara , Latif Mojib
Published: September 2002

The coupling on decadal time scales of the mid‐latitude and tropical Pacific via an oceanic ‘bridge’ in the thermocline is investigated using ocean general circulation model hindcasts and a coupled ocean atmosphere model. Results indicate that in the tropics decadal anomalies of isopycnal depth are forced by Ekman pumping and are largely independent of the arrival of subducted anomalies in the thermocline that originate in the mid‐latitudes of either hemisphere. In the coupled model, temperature anomalies on isopycnals show little coupling from the tropics to the northern hemisphere, but are lag correlated between southern hemisphere mid‐ and low‐latitudes. However, anomaly magnitudes on the equator are small. These results suggest that the oceanic ‘bridge’ to the northern hemisphere explains only a small part of the observed decadal variance in the equatorial Pacific. Coupling to the southern mid‐latitudes via temperature anomalies on isopycnals remains an intriguing possibility.
Solar‐terrestrial coupling: Solar soft X‐rays and thermospheric nitric oxide
Authors: Barth Charles A. , Bailey Scott M. , Solomon Stanley C.
Published: September 2002

Simultaneous measurements were made of the solar soft x‐ray irradiances and the thermospheric nitric oxide density in the tropics from the Student Nitric Oxide Explorer (SNOE) satellite. The analysis of these observations for 44 days of low geomagnetic activity in the spring of 1998 show that there is a correlation between the solar soft x‐ray irradiances and thermospheric nitric oxide densities in the tropics. Photochemical model calculations that used the measured solar soft x‐ray irradiances as input parameters adequately reproduce the magnitude of the time‐varying component of the thermospheric nitric oxide in the tropics. An additional amount of nitric oxide is present in the tropics that does not vary with the time period of the solar rotation. The conclusion of this analysis is that solar soft x‐rays are the primary cause of the variation in the thermospheric nitric oxide densities in the tropics during times of low geomagnetic activity.
Salinity signature of the Pacific Decadal Oscillation
Authors: Overland James E. , Salo Sigrid , Adams Jennifer Miletta
Published: September 2002

Three sites in the North Pacific have temperature and salinity observations in most months for several years before and after 1977. The Gulf of Alaska station (57°N, 148°W) showed a 2°C warming and a 0.6 freshening in salinity at 10 m depth in the 1980s compared to the 1970s. OWS PAPA (50°N, 145°W) and PAPA line station 7 (49.1°N, 132.4°W) show warming of 0.6°C and 0.9°C, with no major salinity change. The decrease in density and increase in stratification in the Gulf of Alaska after 1977 corresponds primarily to a decrease in salinity in the upper 150 m. We propose that while the Pacific Decadal Oscillation has an east/west character in temperature, the salinity signature will have a NNW/SSE character, similar to the pattern of interannual variability in precipitation.
36Cl in modern atmospheric precipitation
Authors: Scheffel C. , Blinov A. , Massonet S. , Sachsenhauser H. , Stan‐Sion C. , Beer J. , Synal H. A. , Kubik P. W. , Kaba M. , Nolte E.
Published: September 2002

The 36Cl/Cl ratios of annual precipitation samples, collected at 28 meteorological stations over the globe were measured with accelerator mass spectrometry. Local 36Cl fallout rates were obtained from the experimental data and compared with theoretical fluxes deduced from atmospheric cosmogenic production and an atmospheric transport model. Most of the measured fluxes were found to be larger than the predicted cosmogenic ones, up to about one order of magnitude. The deviations are largest in the northern hemisphere and for low latitudes. Recycling of 36Cl from nuclear weapon tests from the biosphere into the troposphere as CH3Cl is proposed as a possible source of the observed difference and can explain the measurements as simulation calculations showed.
O2‐O2 absorption band identification based on optical depth spectra of the visible and near‐infrared
Authors: Michalsky J. , Beauharnois M. , Berndt J. , Harrison L. , Kiedron P. , Min Q.
Published: September 2002

The first implementation of the rotating shadowband spectroradiometer allows the routine collection of direct normal solar spectral irradiance data at 512 wavelengths. These data are used on clear days to calculate spectra in optical depth. A persistent absorption band near 477 nm in the first optical depth spectra collected led to the eventual identification of six bands in the 400 to 1080 nm range resulting from absorption by O2 collision pairs. All of these O2‐O2 bands were discovered earlier using atmospheric long pathlength or laboratory high pressure techniques, however, it is notable that this method's sensitivity permitted their detection at one air mass. These data suggest that there are no unexplained narrowband absorption features in the visible/near‐infrared, that excess optical depth measured near 1000 nm may now have an explanation, and that the linearity of the O2‐O2 absorption may be exploited to investigate mean pathlengths in the atmosphere.
A comparison of geodetic and seismic estimates of inner‐core rotation
Authors: Buffett Bruce A. , Creager Kenneth C.
Published: September 2002

Seismological observations suggest the inner core has been rotating faster than the mantle during the past 30–50 years. Differential rotation can produce large gravitational torques on the mantle which, if not balanced by other torques, would be detectable as changes in the rotation rate of the mantle (Length of Day or LOD). We compare seismological estimates of inner core rotation with estimates derived by inverting LOD observations using models of gravitational coupling. Model predictions depend on several parameters, but for the expected range of parameter values, the seismological estimates of relative rotation are at least an order of magnitude larger than those predicted by the LOD data. Furthermore, the LOD data predict oscillation in the angular alignment of the inner core and mantle during the past 30–50 years, while the seismological data seem to require a component of steady rotation. We show that steady rotation of the inner core implies a steady torque on the mantle. This torque is not accelerating the rotation rate of the mantle, so it must be opposed by another torque. The required torque is consistent with a frictional electromagnetic stress on the base of the mantle due to a westward flow at the top of the core.
Spacebased observations of the seasonal changes of south Asian monsoons and oceanic responses
Authors: Liu W. Timothy , Xie Xiaosu
Published: September 2002

The seasonal changes of monsoons in the South China Sea and the Arabian Sea are compared, using observations by spaceborne microwave scatterometers and radiometers. The oceanic responses to the forcing of wind stress and latent heat flux resulting from the monsoon changes are identified through surface temperature tendency and sea level changes.
How well does a coarse‐resolution circulation model simulate observed interannual variability in the upper Indian Ocean?
Authors: Schiller Andreas
Published: September 2002

A global ocean general circulation model (OGCM) simulated interannual variability in the upper Indian Ocean between January 1982 and December 1997. The model is forced by NCEP wind stresses and the surface fluxes are provided by coupling the OGCM to an atmospheric boundary‐layer model. The simulated interannual variability along two hydrographic lines in the Indian Ocean was compared to observations from expendable bathythermograph (XBT) data and satellite altimetry data. In both space‐ and timescales they were in good agreement. However, averaged correlation coefficients along the XBT lines for simulated and observed anomalies of sea‐surface height (
=0.52) are higher than those for anomalies of sea‐surface temperature (
=0.38). Possibly this is because the temperature anomalies are determined by interior ocean dynamics plus ocean‐atmosphere heat fluxes (which have observational and parameterization errors), whereas the height anomalies represent a vertically integrated property of the ocean in which surface heat fluxes are less important. The results demonstrate that our model is currently better at representing the subsurface thermal structure than it is at modelling sea‐surface temperature. It emphasizes the need for improved heat flux products.
Large airglow enhancements produced via wave‐plasma interactions in sporadic E
Authors: Djuth F. T. , Bernhardt P. A. , Tepley C. A. , Gardner J. A. , Kelley M. C. , Broadfoot A. L. , Kagan L. M. , Sulzer M. P. , Elder J. H. , Selcher C. , Isham B. , Brown C. , Carlson H. C.
Published: September 2002

In the past there has been great interest in monitoring enhanced 557.7 nm O(¹S) emissions from the thermosphere in connection with high‐power, high‐frequency (HF) radio wave modification of the F region ionosphere. These emissions are considered to be evidence that the HF‐modified electron distribution function is non‐Maxwellian because a significant flux of ∼5–6 eV electrons is required to produce the airglow. The suprathermal tail is believed to develop as a result of nonlinear plasma processes. Past F region observations of 557.7 nm airglow at Arecibo Observatory, Puerto Rico have yielded only a few Rayleighs of enhanced emissions. Recently, airglow enhancements were monitored in sporadic E above Arecibo. Surprisingly, these experiments yielded ∼55 Rayleighs of enhanced 557.7 nm airglow and the first observations of emissions from the N2 first positive molecular bands. The observations imply that a large flux of energetic (5–10 eV) electrons is generated as part of the wave‐plasma interaction in sporadic E.
Detection of massive negative chemiions in the exhaust plume of a jet aircraft in flight
Authors: Arnold F. , Curtius J. , Sierau B. , Bürger V. , Busen R. , Schumann U.
Published: September 2002

Gaseous negative ions were mass spectrometrically measured in the exhaust plume of a jet aircraft in flight. Using a quadrupole mass spectrometer operated in a high‐pass mode, it was found that by far most of the ions had mass numbers > 450 amu (atomic mass units) and number densities which markedly exceeded the number densities of ambient atmospheric ions. The latter were observed outside the exhaust plume and had mostly mass numbers < 200 amu. Both their large numbers and large concentrations strongly suggest that the massive ions observed inside the plume are chemiions which were produced by the jet engines. The low fuel sulfur content (22 µg/g) suggests that the massive ions consist at least partly of species other than sulfuric acid. By interaction with exhaust gases these chemiions experienced rapid chemical transformation and growth in the early exhaust plume already at plume ages < 0.4 s.
An improved precipitation climatology for the Arctic Ocean
Authors: Yang Daqing
Published: September 2002

Bias correction methods from the World Meteorological Organization Solid Precipitation Measurement Intercomparison Project are applied to 31 years of the Arctic Ocean drifting station records. Observation biases of wind‐induced gauge undercatch and trace amount of precipitation are corrected on a daily basis. Gauge‐measured mean annual precipitation is increased significantly from 150mm to 260mm due to the bias corrections. The seasonal cycle of bias corrected precipitation over the Arctic Ocean is characterized by a minimum in April and a maximum in September; this regime is consistent with other precipitation climatologies for the Arctic Ocean and is also in general agreement with several climate model simulations. The results of this work will have a significant impact on the Arctic fresh water budget, and they will also be useful for validation of global and regional climate models.
Fire or ice: anticorrelation of volcanism and glaciation in California over the past 800,000 years
Authors: Glazner Allen F. , Manley Curtis R. , Marron J. S. , Rojstaczer Stuart
Published: September 2002

Compilation of published ages of Quaternary volcanism in eastern California indicates that volcanism was episodic, with maxima occurring during interglacial periods. The smoothed age distribution shows peaks at 10, 100, 185, 320, and 690 kyr, corresponding to interglacial cycles 1, 5, 7, 9, and 17. This implies that volcanism was modulated by changes in climate, although the processes that link the two are not well understood. Several factors, including transient loads imposed across rugged topography by ice and water and changes in groundwater regime, may provide the link. Although climatic modulation of volcanism is generally tied to changes in sea level, these data indicate that even volcanoes far from the coast can be affected by climatic change.
Implications of temperature‐dependent near‐IR spectral properties of common minerals and meteorites for remote sensing of asteroids
Authors: Hinrichs J. L. , Lucey P. G. , Robinson M. S. , Meibom A. , Krot A. N.
Published: September 2002

Remote sensing analysis of common mafic silicates on bodies like asteroid 433 Eros may be in error unless temperature effects are considered. In this paper, spectral sensitivity to temperature as a function of wavelength from 0.4 to 2.5 microns is quantified using new measurements of reflectance spectra of olivine and two ordinary chondrites. The new data were obtained at higher temperature resolution and with greater accuracy than previous measurements. We use a simple thermal model to show that the temperature difference between terrestrial ambient conditions and those prevailing on main belt asteroids, as well as the temperature variations expected on the surfaces of individual asteroids during observations by spacecraft, are large enough to cause easily detectable spectral differences. Therefore, interpretations of asteroid spectra using spectra of minerals and meteorites obtained at terrestrial ambient conditions are suspect.
First simultaneous in situ measurement of electron density and electric field fluctuations during spread F in the Indian Zone
Authors: Sinha H. S. S. , Raizada Shikha , Misra R. N.
Published: September 2002

The paper presents results of in situ measurements of electron density and electric field fluctuations (δne, δE'v and δE'H) during a strong spread F event from the SHAR rocket range in India. Intermediate scale ne irregularities were observed in the F region valley over SHAR, which was earlier found to be free from irregularities. Experimental evidence of the validity of the image striation theory is provided through first simultaneous spectral measurement of electron density and electric field in the valley region. Correlation analysis of δne, δE'v and δE'H suggests the existence of a sheared flow of current below the F‐peak. A new type of irregularity in the intermediate scale having a steep spectrum (n = −3.1) has also been detected in the valley region. A very sharp layer of ionization wherein the electron density increased by a factor of 50 in 10 km vertical extent was detected at 105 km.
The source population for the cusp and cleft/LLBL for southward IMF
Authors: Fuselier S. A. , Lockwood M. , Onsager T. G. , Peterson W. K.
Published: September 2002

The distinction between plasma properties in different dayside regions in the Earth's magnetosphere is of strong interest as it is often indicative of specific physical processes. This is certainly true for the distinction between low latitude boundary layer (LLBL) and cusp plasma, which has been attributed to the effects of plasma diffusion across the magnetopause (LLBL) versus a more direct entry of magnetosheath plasma (cusp). It is also the case, however, that quite different plasma regions can result more simply from a common source plasma, and from different stages of temporal evolution of the plasma associated with magnetospheric convection. In this paper, we show that, for southward interplanetary magnetic field (IMF) conditions, the distinction between the cusp and cleft/LLBL at low altitudes may result from the single process of magnetosheath plasma entry into the magnetosphere on reconnected field lines. The different plasma characteristics of the two regions result from the properties of the source magnetosheath ion distribution and the effects of magnetic reconnection. Using well known properties of the magnetosheath, several predictions concerning the cusp and cleft/LLBL precipitation are readily derived.
Comparison of aerosol extinction measurements by ILAS and SAGE II
Authors: Burton S. P. , Thomason L. W. , Sasano Y. , Hayashida S.
Published: September 2002

Seventy‐three pairs of nearly coincident profiles of aerosol extinction at visible wavelengths from the Improved Limb Atmospheric Spectrometer (Version 3.1) and the Stratospheric Aerosol and Gas Experiment (SAGE) II (Version 5.931) are compared for a week in January and February 1997. The comparisons require an interpolation of SAGE II multi‐wavelength aerosol extinction profiles to compensate for the difference between the measurement wavelengths of the two instruments. The profiles are shown to agree within ten percent for the altitude range from approximately 15 to 24 km, with a small systematic bias that requires further study.
A cubic relationship between air‐sea CO2 exchange and wind speed
Authors: Wanninkhof Rik , McGillis Wade R.
Published: September 2002

Using recent laboratory and field results we explore the possibility of a cubic relationship between gas exchange and instantaneous (or short‐term) wind speed, and its impact on global air‐sea fluxes. The theoretical foundation for such a dependency is based on retardation of gas transfer at low to intermediate winds by surfactants, which are ubiquitous in the world's oceans, and bubble‐enhanced transfer at higher winds. The proposed cubic relationship shows a weaker dependence of gas transfer at low wind speed and a significantly stronger dependence at high wind speed than previous relationships. A long‐term relationship derived from such a dependence, combined with the monthly CO2 climatology of Takahashi [1997], leads to an increase in the global annual oceanic CO2 uptake from 1.4 Gigaton C yr−1 to 2.2 Gigaton C yr−1. Although a cubic relationship fits within global bomb‐14C oceanic uptake constraints, additional checks are warranted, particularly at high wind speeds where the enhancement is most pronounced.
New kinematic models for Pacific‐North America motion from 3 Ma to present, I: Evidence for steady motion and biases in the NUVEL‐1A Model
Authors: DeMets Charles , Dixon Timothy H.
Published: September 2002

We use velocities derived from 2–4.5 years of continuous GPS observations at 21 sites on the Pacific and North American plates along with a subset of the NUVEL‐1A data to examine the steadiness of Pacific‐North America motion since 3.16 Ma, the transfer of Baja California to the Pacific plate, and the magnitude of biases in the NUVEL‐1A estimate of Pacific‐North America motion. We find that Pacific‐North America motion has remained steady since 3.16 Ma, but at rates significantly faster than predicted by NUVEL‐1A. In the vicinity of Baja California, our GPS‐derived model and recent seafloor spreading rates in the southern Gulf of California both indicate that the NUVEL‐1A model underestimates Pacific‐North America rates by 4±2 mm yr−1. Steady Pacific‐North America motion since 3.16 Myr and increasing seafloor spreading rates since 3.58 Myr in the Gulf of California imply that Pacific‐North America motion was partitioned between seafloor spreading in the Gulf of California and decelerating slip along faults in or offshore from the Baja peninsula.
Buckling versus folding: Importance of viscoelasticity
Authors: Schmalholz S. M. , Podladchikov Yu.
Published: September 2002

We present a dominant wavelength solution for a viscoelastic layer embedded in a low viscosity matrix under layer‐parallel compression based on the thin‐plate approximation. We show that the deformation mode approximates the elastic or viscous limits depending on a parameter, R, which is the ratio of dominant wavelength predicted by pure viscous theory to the one predicted by pure elastic theory. In contrast, conventional analyses based on the Deborah number incorrectly predict the deformation mode. The dominant viscoelastic wavelength closely follows the minimum out of viscous and elastic dominant wavelengths. The viscoelastic thin‐plate theory is verified by two‐dimensional modeling of large strain viscoelastic folding, for which we develop a new numerical algorithm based on a combined spectral/finite‐difference method. The robustness of the numerical code is demonstrated by calculation, for the first time, of the pressure field evolution during folding of a viscoelastic layer with up to 100% strain.
On the record reduction in 1998 western Arctic Sea‐ice cover
Authors: Maslanik James A. , Serreze Mark C. , Agnew Thomas
Published: September 2002

During summer 1998, record reductions in ice cover occurred in the Beaufort and Chukchi seas. Open water formed earlier than in prior years, and September ice extent in this region was 25 percent less than the previous minimum for 1953–1997. Seven percent of the Arctic Basin that had been perennially ice covered was ice‐free in 1998. This reduction in western Arctic ice extent can be attributed in part to preconditioning by light‐ice cover in autumn 1997 and to atmospheric circulation patterns during the following winter through autumn that favored southerly and easterly winds. Such decreases in northerly winds, and the associated weakening or displacement of the Beaufort Gyre, is found to be typical of winters that precede years with below‐normal ice extent in the western Arctic.
OIO and the atmospheric cycle of iodine
Authors: Cox R. A. , Bloss W. J. , Jones R. L. , Rowley D. M.
Published: September 2002

IO and BrO radicals are intermediates in the atmospheric photo‐oxidation of iodo‐ and bromocarbons and can act as catalysts for ozone loss. We have studied the kinetics and mechanisms of the reactions of IO with itself and with BrO to establish their role in the atmospheric chemistry of iodine. We have found that iodine dioxide, OIO, is produced in these reactions. The results of these and other experimental observations together with a recent computational study suggest an unexpectedly high photochemical stability for OIO. It is shown that OIO formation and its attachment to particles could account for the high enrichment of iodine in the small size fraction of marine aerosol, which is important for the transport of iodine from the sea to the continents. OIO may be a route to the formation of iodate, which is present in atmospheric precipitation. OIO formation also implies a reduced efficiency for iodine catalysed ozone loss.
Source process of the 1997 Yamaguchi, Japan, earthquake analyzed in different frequency bands
Authors: Ide Satoshi
Published: September 2002

A set of source rupture models for the 1997 Yamaguchi, Japan, earthquake are constructed using an inversion analysis of strong‐motion data. Synthetic Green functions and empirical Green functions (EGF) are adopted for a low‐frequency band and a high‐frequency band, respectively. Slip zones in the high‐frequency models correspond to the edge of the large slip zones of low‐frequency models in space and to the rupture onset in time. The calculated slip‐stress relations show that the stress decrease rate is more rapid in the high‐frequency models and that there is little slip at a constant stress level in all the models.
Effect of rising Asian emissions on surface ozone in the United States
Authors: Jacob Daniel J. , Logan Jennifer A. , Murti Prashant P.
Published: September 2002

The effect of increasing fossil fuel combustion in eastern Asia on surface O3 air pollution in the United States is examined with a global three‐dimensional tropospheric chemistry model. Tripling of Asian anthropogenic emissions from 1985 to 2010 is expected to increase monthly mean O3 concentrations by 2–6 ppbv in the western United States and by 1–3 ppbv in the eastern United States, the maximum effect being in April–June. This increase would more than offset the benefits of 25% domestic reductions in anthropogenic emissions of NOx and hydrocarbons in the western United States. Asian influence may be less under the stagnant conditions leading to violations of the U.S. air quality standard. Nevertheless, our results suggest that a global perspective is necessary when designing a strategy to meet regional O3 air quality objectives.
Identifying seismicity patterns leading flank eruptions at Mt. Etna Volcano during 1981–1996
Authors: Latora Vito , Vinciguerra Sergio , Bicciato Silvio , Kamimura Roy T.
Published: September 2002

Seismicity time properties of the Etna Volcano (Italy) are investigated through a systematic pattern recognition analysis. Mean Hypothesis Testing (MHT) has been applied to a long time database of instrumental data recorded from 1981 to 1996 to identify relevant correlation among seismic patterns, main seismogenic volumes and the eight flank eruptions occured in the same period. Time evolution of the test statistic (T‐Ratio), calculated on a temporal window starting 75 days prior to a volcanic eruption and extending 25 days after, reveals that there is a pattern of seismic activity prior to the eruptions that can be used as a diagnostic tool as well as a physical modeling support in eruption forecasting.
Differences in the temporal variations of galactic cosmic ray electrons and protons: Implications from Ulysses at solar minimum
Authors: Heber B. , Ferrando P. , Raviart A. , Wibberenz G. , Müller‐Mellin R. , Kunow H. , Sierks H. , Bothmer V. , Posner A. , Paizis C. , Potgieter M. S.
Published: September 2002

According to standard drift dominated modulation models the intensity variations of galactic cosmic ray protons and electrons respond differently to the latitudinal extension of the heliospheric current sheet α. In an A>0 solar cycle intensities of protons should vary weakly with the latitudinal extension, whereas electrons should show a strong response. We investigate this charge dependent variation in the 1990s (A>0) using Ulysses Kiel Electron Telescope (KET) measurements. Proton measurements at 2.5 GV corrected for latitudinal variations show the same time profile as electrons from mid 1994 until the beginning of 1996, and later from September 1997 to the end of 1997. In 1996 and 1997, when α was below ∼25°, two long lasting time periods were found when electrons had a ∼5–10% higher level. These variations are in agreement with our computations indicating that drift effects play an important role in determining the temporal variation of electrons close to solar minimum.
Plasma sheet dynamics in the Jovian magnetotail: Signatures For substorm‐like processes ?
Authors: Woch J. , Krupp N. , Khurana K. K. , Kivelson M. G. , Roux A. , Perraut S. , Louarn P. , Lagg A. , Williams D. J. , Livi S. , Wilken B.
Published: September 2002

During Galileo's orbit G2 in 1996 the Energetic Particles Detector (EPD) onboard the spacecraft detected a number of particle bursts with large radial/antisunward anisotropies in the distant Jovian magnetotail [Krupp et al., 1998]. In this letter we focus on a detailed analysis of one of the bursts. Prior to the onset of the burst, particle intensities at low energies increase over several hours. This phase can be interpreted as a plasma loading phase. It ends after the onset of strong distortions in the magnetic field with a bipolar excursion of the north‐south component being the most prominent feature. The subsequent plasma sheet encounters show that the plasma sheet has thinned considerably. Accelerated/heated ion beams first from the Jovian direction and then later from the tail direction are seen at the plasma sheet and lobe interfaces and intense radio and plasma wave emissions are detected. The event is tentatively interpreted as a dynamical process, where the Jovian magnetotail is internally driven unstable by mass loading of magnetic flux tubes.
Reactive nitrogen budget during the NASA SONEX Mission
Authors: Talbot R. W. , Dibb J. E. , Scheuer E. M. , Kondo Y. , Koike M. , Singh H. B. , Salas L. B. , Fukui Y. , Ballenthin J. O. , Meads R. F. , Miller T. M. , Hunton D. E. , Viggiano A. A. , Blake D. R. , Blake N. J. , Atlas E. , Flocke F. , Jacob D. J. , Jaegle L.
Published: September 2002

The SASS Ozone and Nitrogen Oxides Experiment (SONEX) over the North Atlantic during October/November 1997 offered an excellent opportunity to examine the budget of reactive nitrogen in the upper troposphere (8–12 km altitude). The median measured total reactive nitrogen (NOy) mixing ratio was 425 parts per trillion by volume (pptv). A data set merged to the HNO3 measurement time resolution was used to calculate NOy (NOy sum) by summing the reactive nitrogen species (a combination of measured plus modeled results) and comparing it to measured NOy (NOy meas.). Comparisons were done for tropospheric air (O3 <100 parts per billion by volume (ppbv)) and stratospherically influenced air (O3 > 100 ppbv) with both showing good agreement between NOy sum and NOy meas. (slope >0.9 and r² ≈ 0.9). The total reactive nitrogen budget in the upper troposphere over the North Atlantic appears to be dominated by a mixture of NOx (NO + NO2), HNO3, and PAN. In tropospheric air median values of NOx/NOy were ≈ 0.25, HNO3/NOy ≈ 0.35 and PAN/NOy ≈ 0.17. Particulate NO3− and alkyl nitrates together composed <10% of NOy, while model estimated HNO4 averaged 12%. For the air parcels sampled during SONEX, there does not appear to be a large reservoir of unidentified NOy compounds.
Highly structured tropical airglow and TEC signatures during strong geomagnetic activity
Authors: Kelley M. C. , Garcia F. , Makela J. , Fan T. , Mak E. , Sia C. , Alcocer D.
Published: September 2002

A remarkable set of all‐sky images using the 630 nm airglow emission has been taken over the Arecibo Observatory in Puerto Rico. Wave‐like structures at a height of about 250 km are commonly found to travel in the southwest direction at speeds ranging from 20–120 m/s. Most surprising is that geomagnetic activity seems to greatly amplify them, forming very intricate patterns of light and dark. Simultaneous observations using GPS satellite transmissions on one night reveal that dark regions are severely plasma depleted while bright regions have nighttime content as large as the full noontime ionosphere. This unexpected geomagnetic effect at mid‐latitudes has implications for trans‐ionospheric radiowave propagation and Space Weather.
Variability of an additional layer in the equatorial ionosphere over Fortaleza
Authors: Balan N. , Batista I. S. , Abdu M. A. , Bailey G. J. , Watanabe S. , MacDougall J. , Sobral J. H. A.
Published: September 2002

The day‐to‐day variations (or the weather) of an additional layer, called the F3 layer, that has been predicted to exist at altitudes above the F2 peak in the equatorial ionosphere are studied through ionosonde observations and theoretical modeling. The ionograms recorded in 1995 at the equatorial station Fortaleza (4°S, 38°W; dip angle 9°S) in Brazil show the occurrence of the F3 layer during daytime from 0800 to 1630 LT, with the duration of occurrence ranging from 15 min to 6 hours. Although the layer occurs most frequently (75% of the days) in local summer as previously predicted, there are consecutive and individual magnetically quiet and disturbed days when the layer does not occur. There are also days when the layer reoccurs. The model results, obtained using the Sheffield University plasmasphere‐ionosphere model, show that the day‐to‐day variations of the F3 layer arise from the corresponding variations of the vertical plasma velocity. The layer occurs when the time‐cumulative vertical velocity displaces the daytime F2 peak to high altitudes, to form the F3 layer, while the normal F2 layer develops at low altitudes. Sudden displacements result in more distinct F3 layers than gradual displacements. Model results also show that the plasma temperature within the F3 layer decreases as the plasma density increases, and, like the plasma density, the plasma temperature also undergoes large day‐to‐day variations.
On space weather consequences and predictions
Authors: Feynman Joan , Gabriel S. B.
Published: September 2002

This paper focuses on the question of what needs to be predicted and what processes need to be understood to predict and forecast space weather conditions that are hazardous to current technology. The paper's aim is to see if we are working on the correct space parameters to permit prediction of those quantities that actually present hazards to current space technology. The paper is not intended to be encyclopedic. We conclude that although the sunspot number is a general proxy for many space hazards, there is surprisingly little direct need for its accurate prediction or for the prediction of solar flares as such. We also find that knowledge of Kp and other geomagnetic indices are rarely directly required. Important gaps in our knowledge exist concerning the variations of storm time electron, proton, and ion populations within the magnetosphere. Work is also required in predicting fast coronal mass ejections (CMEs) and in understanding the processes of CME initiation and acceleration within the corona and high energy solar particle acceleration and propagation.
The nature of reflection and mode conversion of MHD waves in the inductive ionosphere: Multistep mode conversion between divergent and rotational electric fields
Authors: Yoshikawa A. , Itonaga M.
Published: September 2002

The nature of reflection and mode conversion of MHD waves at the high‐latitudinal inductive ionosphere is analyzed, based on the current conservation law of wave modes. The term “inductive ionosphere” refers to the nonzero rotational electric field or nonzero compressional magnetic field in the reflection process of shear Alfvén waves on the ionosphere. The finite rotational electric field causes mutual induction between the divergent and rotational current systems at the ionosphere. The one‐step Hall effect for the divergent electric field of the shear Alfvén wave produces a rotational Hall current and excites the ionospheric surface compressional wave. The Hall effect for the rotational electric field of an ionospheric surface compressional wave produces a divergent Hall current (two‐step Hall effect), which feeds back the compressional magnetic energy to the reflected field‐aligned current. We find that the renormalization of the ionospheric rotational electric field to the reflection process of the shear Alfvén wave causes some peculiarities in the distribution of ionospheric currents and mode‐converted wave magnetic fields. Such peculiarities become particularly obvious in the high‐conducting ionosphere. For example, in the ionospheric current distributions, a considerable component of the ionospheric divergent current is accounted for by the divergent Hall current. The rotational Hall and Pedersen currents cancel each other out and lead to zero total ionospheric rotational current. The amplitude of the poloidal magnetic field transmitted from the toroidal magnetic field of the incident shear Alfvén wave shows a nonlinear dependence on ΣH/Σp. It also shows a new type of effective ionospheric shielding effect in the Σp/ΣA parameter space for a fixed ΣH/Σp condition. We assert that the inductive response of the ionosphere should become an indispensable concept for reflection, mode conversion, transmission, and generation of various phenomena relating to the field‐aligned current system.
Evolution of thin current sheet with a southward interplanetary magnetic field studied by a three‐dimensional electromagnetic particle code
Authors: Nishikawa K.‐I. , Ohtani S.
Published: September 2002

This paper reports the spatial and temporal development of sheet current intensification in the near‐Earth tail using our three‐dimensional global electromagnetic particle simulation with a southward turning interplanetary magnetic field (IMF) in a context of the substorm onset. As the solar wind with the southward IMF advances through the Earth, the near‐Earth tail thins and the sheet current intensifies. The peak of the current density moves toward the Earth. Before its peak becomes maximum the reconnection takes place. The earthward flows are generated by the reconnection, which coincides with the earthward expansion of the intensified sheet current. Because of the pileup of the earthward plasma flows, the dawnward current is generated near the Earth. This dawnward current dissipates rapidly with the sheet current because of the opposite current direction, which coincides with the dipolarization in the near‐Earth tail. This simulation study shows the sequence of the substorm dynamics in the near‐Earth tail, which is similar to the features obtained by the multisatellite observations. The identification of the timing and mechanism of triggering substorm onset requires further studies in conjunction with observations.
Interaction between an interplanetary magnetic cloud and the Earth's magnetosphere: Motions of the bow shock
Authors: Wu D. J. , Chao J. K. , Lepping R. P.
Published: September 2002

An interplanetary magnetic cloud (IMC) is an important solar‐terrestrial connection event. It is an ideal object for the study of solar‐terrestrial relations and space weather because the Earth's space environment can be affected considerably during an IMC passage. An IMC was observed to pass the Earth during October 18–20, 1995. Wind recorded its interplanetary characteristics at ∼ 175 RE upstream of the Earth's bow shock, and ∼ 45 min later, Geotail, being near the nominal location of the dawn bow shock, detected IMC‐related multiple bow shock crossings. Using simultaneous measurements from Wind and Geotail, we analyzed, with a semiempirical bow shock model with two parameters, the bow shock motion caused by the interaction of the IMC with the magnetosphere during the passage. We also compared the bow shock motion predicted by the model, and hence the predicted Geotail bow shock crossings, with Geotail observations of the actual crossings. The results showed that the observed multiple bow shock crossings, which were obviously due to temporal variations of the upstream solar wind, can be well explained by the model‐predicted bow shock motion.
Deflected magnetosheath flow at the high‐latitude magnetopause
Authors: Siscoe G. L. , Erickson G. M. , Sonnerup B. U. Ö , Maynard N. C. , Siebert K. D. , Weimer D. R. , White W. W.
Published: September 2002

This paper presents results of a study that uses the output of a global MHD simulation to investigate the geometry and dynamics of solar wind deflection from tangential magnetic force acting at the magnetopause. Tangential magnetic force at the magnetopause is a consequence of merging between the geomagnetic field and the interplanetary magnetic field at the dayside magnetopause. This is the first study explicitly to show deflection of magnetosheath flow at the magnetopause and to compute deflection phenomenon quantitatively using self‐consistent MHD. The presentation connects magnetopause deflection with polarcap magnetic perturbations called the Svalgaard‐Mansurov effect.
Self‐consistent acceleration of multiply reflected pickup ions at a quasi‐perpendicular solar wind termination shock: a fluid approach
Authors: le Roux J. A. , Fichtner H. , Zank G. P. , Ptuskin V. S.
Published: September 2002

The purpose of this paper is to report about a self‐consistent study of acceleration of multiply reflected pickup protons at a quasi‐perpendicular solar wind termination shock and the influence of these protons on the shock's structure. A time‐dependent formulation is developed by treating the solar wind and low‐energy pickup protons as one fluid under the influence of the accelerated pickup protons as a second fluid. The results suggest that the termination shock would experience significant mediation by such accelerated pickup protons if the width of the termination shock's (sub)ramp would be smaller than four times the thermal electron inertial length Le. There are examples in observations of the Earth's bow shock with a width close to such values. For a shock width of 2Le and a multiply reflected ion (MRI) distribution function fMRI ∝ v−a with a = 4, the shock compression ratio is reduced to ∼2.4 compared with the initial value of ∼3.1 and the fraction of reflected pickup protons is ∼11%. For this width the accelerated pickup protons reach a maximum energy of up to ∼ 51 keV, if a ε [3,4]. Such extended MRI spectra for pickup protons, if realistic, might enable a direct injection of these particles into the process of diffusive shock acceleration at the termination shock. Therefore the model also provides a theoretical basis for a study of the formation of anomalous cosmic rays.
Ion acoustic damping effects on parametric decays of Alfvén waves
Authors: Gomberoff L.
Published: September 2002

It is well known that in plasmas with β = (υs/υA)2 < 1 (υs is the ion acoustic velocity and υA is the Alfvén velocity), Alfvén waves propagating along an external magnetic field can have three kinds of parametric instabilities: ordinary decay instability, beat wave instability, and modulational instability. However, when β ≥ 1, there is only a beat wave instability, although decay and modulational instabilities are also possible from the point of view of the resonance conditions. When β ≤ 1, there is, in general, a beat wave instability, but a modulational and a decay instability can also occur for some values of the pump wave amplitude. It is shown here that damping effects can destabilize regions that are stable under nondissipative fluid theory. This is done by using only fluid theory. Landau damping effects on the ion acoustic modes are simulated by a collisional‐like term in the longitudinal component of the fluid equations. It is shown that when there is only a beat wave instability, damping effects can destabilize modulational‐ and decay‐type instabilities. When there is a beat wave and a modulational instability, damping effects destabilize the region where one could expect a decay instability. The modulational‐like instability is shown to trigger a forward propagating Alfvén wave. On the other hand, the decay‐like instability generates backward propagating Alfvén waves. These results are in agreement with hybrid kinetic‐fluid approaches and hybrid simulation codes.
Precipitation of relativistic electrons by interaction with electromagnetic ion cyclotron waves
Authors: Lorentzen K. R. , McCarthy M. P. , Parks G. K. , Foat J. E. , Millan R. M. , Smith D. M. , Lin R. P. , Treilhou J. P.
Published: September 2002

On August 20, 1996, balloon‐borne X‐ray detectors observed an intense X‐ray event as part of a French balloon campaign near Kiruna, Sweden, at 1532 UT (1835 magnetic local time), on an L shell of 5.8. The energy spectrum of this event shows the presence of X rays with energies > 1 MeV, which are best accounted for by atmospheric bremsstrahlung from monoenergetic ∼1.7 MeV precipitating electrons. Ultraviolet images from the Polar satellite and energetic particle data from the Los Alamos geosynchronous satellites show the onset of a small magnetospheric substorm 24 min before the start of the relativistic electron precipitation event. Since the balloon was south of the auroral oval and there was no associated increase in relativistic electron flux at geosynchronous altitude, the event is interpreted as the result of selective precipitation of ambient relativistic electrons from the radiation belts. Pitch angle scattering caused by resonance with electromagnetic ion cyclotron mode waves is the most likely mechanism for selective precipitation of MeV electrons. A model is presented in which wave growth is driven by temperature anisotropies in the drifting substorm‐injected proton population. The model predicts that this wave growth and resonance with ∼1.7 MeV electrons will occur preferentially in regions of density >10 cm−3, such as inside the duskside plasmapause bulge or detached plasma regions. The model predictions are consistent with the location of the balloon, the observed energies, and the timing with respect to the substorm energetic particle injection.
The solar magnetic field and the solar wind: Existence of preferred longitudes
Authors: Neugebauer M. , Smith E. J. , Ruzmaikin A. , Feynman J. , Vaughan A. H.
Published: September 2002

Direct measurements of the solar wind speed and the radial component of the interplanetary magnetic field acquired over more than three solar cycles are used to search for signatures of a persistent dependence of solar wind properties on solar longitude. Two methods of analysis are used. One finds the rotation period that maximizes the amplitude of longitudinal variations of both interplanetary and near‐Earth data mapped to the Sun. The other is based on power spectra of near‐Earth and near‐Venus data. The two methods give the same result. Preferred‐longitude effects are found for a synodic solar rotation period of 27.03 ± 0.02 days. Such high precision is attained by using several hundred thousand hourly averages of the solar wind speed and magnetic field. The 27.03‐day periodicity is dominant only over long periods of time; other periodicities are often more prominent for shorter intervals such as a single solar cycle or less. The 27.03‐day signal is stronger and more consistent in the magnetic field than in the solar wind speed and is stronger for intervals of high and declining solar activity than for intervals of low or rising activity. On average, solar magnetic field lines in the ecliptic plane point outward on one side of the Sun and inward on the other, reversing direction approximately every 11 years while maintaining the same phase. The data are consistent with a model in which the solar magnetic dipole returns to the same longitude after each reversal.