bluuebunny/crossref_metadata_2025 huggingface dataset:
Daily maximum and minimum temperature trends in a climate model
Authors: Stone Dáithí A. , Weaver Andrew J.
Published: October 2002

The recent observed global warming trend over land has been characterised by a faster warming at night, leading to a considerable decrease in the diurnal temperature range (DTR). Analysis of simulations of a climate model including observed increases in greenhouse gases and sulphate aerosols reveals a similar trend in the DTR of −0.2°C per century, albeit of smaller magnitude than the observed −0.8°C per century. This trend in the model simulations is related to changes in cloud cover and soil moisture. These results indicate that the observed decrease in the DTR could be a signal of anthropogenic forcing of recent climate change.
Estimating daytime vertical ExB drift velocities in the equatorial F‐region using ground‐based magnetometer observations
Authors: Anderson David , Anghel Adela , Yumoto Kiyohumi , Ishitsuka Mutsumi , Kudeki Erhan
Published: October 2002

The daytime equatorial electrojet is a narrow band of enhanced eastward current flowing in the 100 to 120 km altitude region within ±2° latitude of the dip equator. A unique way of determining the daytime strength of the electrojet is to observe the difference in the magnitudes of the Horizontal (H) component between a magnetometer placed directly on the magnetic equator and one displaced 6 to 9 degrees away. The difference between these measured H values provides a direct measure of the daytime electrojet current, and in turn, the magnitude of the vertical ExB drift velocity in the F region ionosphere. This paper discusses a recent study that has established the quantitative relationship between the vertical ExB drift velocity in the ionospheric F region and the daytime strength of the equatorial electrojet in the South American (west coast) longitude sector.
Ozone production rate and hydrocarbon reactivity in 5 urban areas: A cause of high ozone concentration in Houston
Authors: Kleinman L. I. , Daum P. H. , Imre D. , Lee Y.‐N. , Nunnermacker L. J. , Springston S. R. , Weinstein‐Lloyd J. , Rudolph J.
Published: October 2002

Observations of ozone (O3) and O3 precursors taken from aircraft flights over Houston, TX, Nashville, TN; New York, NY; Phoenix, AZ, and Philadelphia, PA show that high concentrations of reactive volatile organic compounds (VOCs) in the Houston atmosphere lead to calculated O3 production rates that are 2 to 5 times higher than in the other 4 cities even though NOx concentrations are comparable. Within the Houston metropolitan area, concentrations of VOCs and O3 production rates are highest in the Ship Channel region; the location of one of the largest petrochemical complexes in the world. As a consequence the concentration of O3 in the Houston metropolitan area has recently exceeded 250 ppb, the highest value observed in the U.S within the past 5 years.
East‐west asymmetry in type‐2 echoes and enhanced electron drift in the equatorial electrojet
Authors: Tsunoda Roland T. , Ecklund Warner L.
Published: October 2002

Simultaneous measurements of type‐2 echoes in the equatorial electrojet (EEJ) and the 150 km echoes were made with a tri‐beam radar on Pohnpei (Federated States of Micronesia). Using the mean Doppler velocity (〈VD〉) to estimate the line‐of‐sight component of electron drift velocity (), we show that its vertical component (Vez) increases with altitude and exceeds Vez measured at 150 km, between 96 and 103 km. At 103 km, the ratio of vertical 〈VD〉 to Vez at 150 km was five. This enhancement explains the hitherto puzzling east‐west asymmetry in 〈VD〉 of type‐2 echoes. More importantly, we show how the enhanced Vez appears to be associated with the discrepancy in the altitude of peak current density of the EEJ, between measurement and model. We discuss roles played by kilometer‐scale irregularities and close by describing apparent effects by atmospheric gravity waves.
Lightning charge moment changes for the initiation of sprites
Authors: Hu Wenyi , Cummer Steven A. , Lyons Walter A. , Nelson Thomas E.
Published: October 2002

The transient ELF(∼50–5000 Hz) magnetic field radiated by lightning discharges across North America was continuously measured at Duke University during the summer of 2000. In total, 881 sprite‐associated lightning discharges over 17 days were analyzed. We report in detail on 76 sprites for which we could reliably determine the lightning charge moment change from the ELF data at the time of sprite onset. The charge moment change for the initiation of a sprite is found to be as low as 120 C km. By folding together the charge moment distributions of sprite‐producing lightning and all positive lightning, we find that the probability of sprite generation for lightning with >1000 C km charge moment change in <6 ms is >90%, while the sprite probability for lightning with <600 C km charge moment change in <6 ms is <10%.
Improving IR cloud phase determination with 20 microns spectral observations
Authors: Rathke Carsten , Fischer Jürgen , Neshyba Steven , Shupe Matthew
Published: October 2002

Adding 20 μm spectral observations to observations in the 8–12 μm region can significantly improve infrared cloud phase determination from both space and the surface. We demonstrate this with 7–20 μm radiance spectra of Arctic stratus clouds measured by a ship‐based FTIR spectrometer during the SHEBA experiment. Our results are compared with phase classifications obtained from lidar, microwave radiometer, and radar data.
Tide‐induced lateral movement of Brunt Ice Shelf, Antarctica
Authors: Doake C. S. M. , Corr H. F. J. , Nicholls K. W. , Gaffikin A. , Jenkins A. , Bertiger W. I. , King M. A.
Published: October 2002

Accurate position data show that Brunt Ice Shelf has an irregular three‐dimensional motion driven by the ocean tide. A 30‐day GPS record from Halley station shows not only the expected vertical tidal displacement, but also a significant variation in horizontal velocity. The maximum forward velocity occurs about four hours before the maximum tidal height, a phase relationship that suggests ocean currents may be responsible. However, values of ice/water friction coefficients needed to make this explanation plausible appear to be too high to be physically reasonable. Alternative explanations invoke interactions between the ice shelf and a grounded area at the ice front. Our findings suggest that significant errors might result if these motions are ignored when interpreting ‘double difference’ satellite SAR interferograms, where the common assumption is that the horizontal velocity of an ice shelf has no tidal dependence.
Presence of sulfite (SIV) in arc magmas: Implications for volcanic sulfur emissions
Authors: Métrich Nicole , Bonnin‐Mosbah Michelle , Susini Jean , Menez Bénédicte , Galoisy Laurence
Published: October 2002

The outstanding production of sulfur dioxide at arc volcanoes is not satisfactorily explained by most of the geochemical models involving the magmatic redox conditions. It is commonly accepted that sulfur is transported mainly as sulfide (SII−) and/or sulfate (SVI) by mantle‐derived melts, before being released as SO2 and/or H2S in volcanic emissions. We present the first experimental evidence that other S‐species coexist in water‐rich arc basalts, by using X‐ray microspectroscopy of olivine‐hosted melt inclusions. In particular, we propose a new model involving sulfite (SIV) as the intermediate species dissolved in basaltic melts which results in highly efficient partitioning of sulfur into volcanic gas emissions at the origin of excess sulphur degassing observed at arc basaltic volcanoes.
Approximate invariant of electron motion in the field of a whistler propagating along the geomagnetic field
Authors: Krasovsky V. L. , Matsumoto H. , Omura Y.
Published: October 2002

The dynamics of high energy electrons in gyroresonance with a quasi‐monochromatic circularly polarized whistler mode tracing a geomagnetic field line are studied numerically. The wavenumber and amplitude of the whistler wave are assumed to be slowly varying functions due to the weak longitudinal inhomogeneity of the geomagnetic field. The space‐time dependence of the electromagnetic field manifests itself in the existence of an approximate invariant of the electron motion. Under the conditions characteristic of the magnetosphere, this invariant is found to be conserved with very high accuracy even in the process of resonant wave‐particle interaction, whereas the constancy of the electron magnetic moment is strongly violated in the resonance. The availability of the approximate constant of the motion allows one to describe the gyroresonant wave‐particle interaction with the aid of simpler equations averaged over the fast Larmor gyration.
Why were cool SST anomalies absent in the Bay of Bengal during the 1997 Indian Ocean Dipole Event?
Authors: Rao Suryachandra A. , Gopalakrishna Vissa V. , Shetye Satish R. , Yamagata Toshio
Published: October 2002

The most important center of atmospheric convection associated with the Indian summer monsoon is located in the Bay of Bengal. This tendency was enhanced during the 1997 Indian Ocean Dipole (IOD) event and cool SST anomalies due to upwelling in the east were restricted to the south of about 5°N in the bay. However, sea surface height anomalies associated with the upwelling propagated all the way to the north bay. Using XBT data collected in the bay, and a high resolution ocean general circulation model simulation, we propose that the permanent, low‐salinity, highly stratified, near‐surface pool in the bay prevented the IOD‐related upwelling from influencing the SST. The strong near‐surface stratification in the bay cannot be broken down by the observed winds there, therefore it ensures that internal ocean dynamics cannot have an impact on SST. As a result, atmospheric convection over the bay may be decoupled from ocean dynamics.
Radiative transfer model constraints on the shock state of remotely sensed lunar anorthosites
Authors: Lucey Paul G.
Published: October 2002

Near‐IR spectra of some lunar basin rings and crater central peaks exhibit no evidence of absorption due to ferrous iron, unlike all other spectral measurements of lunar soil in the laboratory or obtained remotely. These spectral anomalies have previously been interpreted to indicate the presence of a deposit of essentially pure plagioclase feldspar (anorthosite) which has been shocked above 250 kb. Plagioclase possesses a diagnostic absorption feature near 1250 nm caused by trace ferrous iron that is lost when shocked above 250 kb, whereas ferrous features of pyroxene are robust against shock. However, new methods for computing the optical effects of exposure of lunar materials to the space environment show that these optical effects can obscure the spectral features of plagioclase without resorting to shock modification of the plagioclase structure. Our modeling shows that shock is not necessary to explain the apparent lack of absorption, but is not excluded either. Thus, previous reports that some lunar surface features may have experienced high shock levels are not supported.
Can one hear the shape of a saturation patch?
Authors: Tserkovnyak Yaroslav , Johnson David Linton
Published: October 2002

The theory of the acoustics of patchy‐saturation in porous media is used to analyze experimental data on wave velocity and attenuation in partially water saturated limestones. It is demonstrated that the theory can be used to deduce the value of V/A, the ratio of the volume to area of the water patch, and lf, the Poisson size of the water patch. One can “hear” the shape of a patch if the properties of the rock and the measurement frequencies are such as to satisfy the specific requirements for the validity of the theory.
The structure of the dissipation region for component reconnection: Particle simulations
Authors: Hesse Michael , Kuznetsova Masha , Hoshino Masahiro
Published: October 2002

Results from a kinetic simulation of component reconnection are presented. Reconnection proceeds in a current sheet with 104 degrees magnetic field rotation. As a result, magnetic reconnection forms distinctively different signatures from what was found from kinetic models of anti‐parallel reconnection. In particular, ion and electron flow patterns are substantially distorted, the shear magnetic field component does not exhibit a quadrupolar structure, and electron orbits in the diffusion region are substantially modified. The emphasis of the investigation is on the modifications to the diffusion region, with particular emphasis on the electron diffusion zone. Electron pressure nongyrotropies can support collisionless magnetic reconnection even when electron motion in diffusion region is strongly affected by the guide magnetic field.
Observations of thermal plasmas in Jupiter's magnetotail
Authors: Frank L. A. , Paterson W. R. , Khurana K. K.
Published: October 2002

A survey of thermal plasmas and magnetic fields is presented for the orbit of the Galileo spacecraft around Jupiter that occurred during the period May 4 through June 22, 1997. This orbit traversed the magnetotail out to Jovian radial distances of 100.2 RJ in the magnetotail. Perijove was positioned at 9.3 RJ. Three primary ion populations were detected with the plasma analyzer: cool hydrogen ions with temperatures of 10 eV, hot hydrogen ions with temperatures of ∼10 keV, and a third population of heavy ions such as O++, O+, S++, and S+++ with temperatures in the range of 500 eV. Plasma flows near perijove were in the corotational direction but with speeds ∼60% of those for rigid corotation with the planet out to radial distances of ∼18 RJ. In the radial range of 18–26 RJ there were significant radial components for the bulk flows, and the flow components in the corotational direction reached values expected for rigid corotation when the current sheet was crossed. The transient character of the plasma parameters suggests that strong ion plasma acceleration is occurring in this region. The temperatures of the heavy ions increased from 5 × 106 K at 9.3 RJ to ∼108 K at 26 RJ. At distances <20 RJ there is a strong dependence of ion temperatures on System III longitude. The scalar magnetic field outside of the current sheet in the radial distance range 9.3–20 RJ varied as R−2.78 and similar to that for a dipole field, and at distances >50 RJ it varied as R−1.19. The thermal plasma pressure in the current sheet is a factor of ∼10 less than the magnetic pressure at 9.3 RJ at positions above or below the sheet but becomes equal to this magnetic pressure at radial distances >30 RJ. The corresponding values of the ratio of the plasma to magnetic pressure, β, are in the range of 10–100 in the current sheet. The number densities and temperatures of these plasmas are 0.05–0.1 /cm3 and 0.5–1 × 108 K, respectively. In the magnetotail the bulk flows of the thermal plasmas exhibit substantial components in the corotational and radially outward directions, but the bulk speeds of 50–200 km s−1 are significantly less than those for rigid corotation. For this single orbit the average bulk flows were ∼50 km s−1 in the premidnight sector and 200 km s−1 in the early morning sector at radial distances >∼50 RJ. At apojove of 100 RJ an antisunward flow of ∼200 km s−1 is found that is supportive of the magnetospheric “wind” reported for Voyager measurements of energetic charged particles. The 10‐hour periodicity of the pairs of current sheet crossings at the position of the Galileo spacecraft includes a variety of dynamical signatures, which are suggested to be due to the changes in direction and pressures in the solar wind and due to the transient acceleration of plasmas in the current sheet.
Ion escape from Mars in a quasi‐neutral hybrid model
Authors: Kallio Esa , Janhunen Pekka
Published: October 2002

Ion measurements made by the Phobos 2 spacecraft revealed an extensive, ever‐persisting escape of planetary ions in the Martian tail. Observations indicated that in large regions of the Martian tail, most ions were of planetary origin. The measurements suggested that the solar wind "pickup" of planetary ions is an important factor in the global Mars‐solar wind interaction. However, how in detail the newly formed planetary ions affect the formation of the observed global plasma and field regions remained unanswered. In this paper the escape of Martian ions is studied with a quasi‐neutral hybrid simulation model. The used hybrid model includes two ion species: the solar wind protons and the planetary ions. This approach makes it possible to study the asymmetries associated with the finite ion gyroradius as well as the difference between the motion of the solar wind protons and planetary ions. The source of the escaping ions is studied indirectly by producing planetary ions from two ion sources: the neutral corona (photoionization) and the ionosphere. The simulation is found to reproduce many observed features of the Mars‐solar wind interaction in general and those of the planetary ions in particular. Ion escape within the optical shadow forms an antisunward flowing beam of ∼1 keV planetary ions, much as observed. A total mass loss rate of ∼100–400 g s−1 is found to be large enough to reproduce several plasma and magnetic field features observed by Phobos2 on its circular orbits. Simulations produce a wide region behind the planet where the density and the particle flux of H+ ions are much smaller than their solar wind values, resembling the observed "proton cavity." The work also depicts how the "ionotail," formed mainly by the escaping planetary ions, is embedded in the Martian magnetotail. The runs also result in a notable asymmetry with respect to the direction of the convectice electric field in the solar wind which is caused by the finite ion gyroradius. The magnetopause also demonstrates the asymmetry: the magnetopause is a sharp boundary or a smooth transition layer, depending on the direction of the upstream convective electric field. Overall, the work illustrates the importance of the plasma‐neutral interactions in the global Mars‐solar wind interaction.
A high‐latitude interplanetary magnetic field enhancement at Ulysses
Authors: Jones G. H. , Lucek E. A. , Balogh A. , MacDowall R. J. , McComas D. J. , Smith E. J.
Published: October 2002

An analysis is presented of data returned from the Ulysses spacecraft on 28 July 2000, when it encountered a highly unusual event in the high‐latitude solar wind. The event is identified as a class of structure previously found only near Venus and Earth. The event's characteristics are described, in terms of similarities and differences to previously reported events of this type. Several possible origins for the event are discussed. It is noted that some, but not all, of the behavior of the magnetic field and plasma parameters is consistent with mass loading of the solar wind. Assuming such a cause, an attempt is made to derive constraints on a putative cometary source's orbital parameters using a new technique that could be applied to similar events. The origin of the event, however, remains unidentified.
Interplanetary magnetic field control of the entry of solar energetic particles into the magnetosphere
Authors: Richard R. L. , El‐Alaoui M. , Ashour‐Abdalla M. , Walker R. J.
Published: October 2002

We have investigated the entry of energetic ions of solar origin into the magnetosphere as a function of the interplanetary magnetic field orientation. We have modeled this entry by following high energy particles (protons and 3He ions) ranging from 0.1 to 50 MeV in electric and magnetic fields from a global magnetohydrodynamic (MHD) model of the magnetosphere and its interaction with the solar wind. For the most part these particles entered the magnetosphere on or near open field lines except for some above 10 MeV that could enter directly by crossing field lines due to their large gyroradii. The MHD simulation was driven by a series of idealized solar wind and interplanetary magnetic field (IMF) conditions. It was found that the flux of particles in the magnetosphere and transport into the inner magnetosphere varied widely according to the IMF orientation for a constant upstream particle source, with the most efficient entry occurring under southward IMF conditions. The flux inside the magnetosphere could approach that in the solar wind implying that SEPs can contribute significantly to the magnetospheric energetic particle population during typical SEP events depending on the state of the magnetosphere.
Tracing ions in the cusp and low‐latitude boundary layer using multispacecraft observations and a global MHD simulation
Authors: Fuselier S. A. , Berchem J. , Trattner K. J. , Friedel R.
Published: October 2002

High‐latitude observations from the Polar spacecraft on 21 January 1998 show a region of closed magnetic field lines containing several distinct solar wind ion populations in the energy range from <10 eV to >200 keV e−1. Precipitating ion fluxes in this region are consistent with the low‐latitude boundary layer (LLBL). A global MHD simulation of this event (using input from the Wind spacecraft upstream from the Earth's bow shock) reproduces Geotail and Interball/Tail spacecraft observations in the outer magnetosphere and magnetosheath. These results demonstrate that the simulation faithfully reproduces the global magnetic field configuration of the magnetosheath and magnetosphere and provides confidence for the interpretation of the LLBL observations from Polar. Results from the simulation show that a single evolutionary process of plasma entry into the cusp and evolution to the LLBL can account for the development of a multi‐energy ion population of solar wind origin on closed magnetic field lines in the magnetosphere. Sources with direct access to the ultimately closed LLBL field lines observed by Polar are the dayside magnetosheath (low‐energy ions below 3 keV e−1), the quasi‐parallel bow shock (higher‐energy ions between 3 and 100 keV e−1), and possibly the duskside magnetopause (highest‐energy ions above 100 keV e−1).
A model of odd nitrogen in the aurorally dosed nighttime terrestrial thermosphere
Authors: Dothe H. , Duff J. W. , Sharma R. D. , Wheeler N. B.
Published: October 2002

A model of the production and loss of odd nitrogen species (mainly, N(4S), N(2D), NO, and NO+) and the enhanced vibration‐rotation band emission from NO in the infrared from the aurorally dosed terrestrial nighttime thermosphere is described. This model is assessed by analyzing the observations of the fundamental (Δv = −1, ∼5.3 μm) and overtone (Δv = −2, ∼2.7 μm) NO vibration‐rotation band limb emissions made by a Michelson interferometer and radiometer, respectively, aboard the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS‐1A) experiment on the space shuttle Discovery during an auroral event. The auroral dosing along the line of sight is inferred from the 2.7‐μm radiance profiles using a self‐consistent procedure. The dosing obtained is then used in the model to predict the spectrally resolved emission in the 5.3‐μm region. The calculated overtone radiance profiles agree with the measured ones at lower tangent altitudes, where the signal‐to‐noise ratio is large. The calculation, however, underpredicts the observed radiance, both fundamental and overtone, at higher tangent altitudes by a factor of ∼3 and gives a colder rotational temperature for the rotationally hot component of the spectrally resolved emission from nascent NO. The causes of this discrepancy and its impact on the densities of the odd N species are discussed.
Electron acceleration and heating influenced by whistler wave packets at quasi‐parallel shock waves
Authors: Nishimura Kazumi , Matsumoto Hiroshi , Kojima Hirotsugu
Published: October 2002

The acceleration and heating of electrons at quasi‐parallel shock waves are studied by means of a one‐dimensional full particle computer simulation. Our simulation shows that the ion beam instability due to the anomalous cyclotron resonance excites whistler mode waves in the upstream region. When the Mach number becomes large beyond a critical value, the whistler wave packets do not appear. The electron acceleration parallel to the magnetic field results from the parallel electric fields caused by both the whistler mode waves and the electrostatic shock potential. The potential concerning the parallel electric field increases with Mach number below the critical Mach number but is relatively independent of the Mach number beyond the critical Mach number. This verifies that the contribution of the whistler waves to the parallel acceleration is as important as that of the electrostatic shock potential below the critical Mach number. Also, the spatial profile of the potential concerning the parallel electric field is clearly correlated with the magnetic field profile. Downstream, the electron temperature is anisotropic such that the parallel temperature is larger than the perpendicular temperature. The Mach number dependence of the electron parallel temperature can be evaluated from the viewpoint of a wave‐particle interaction (current‐driven instability).
Long‐wavelength mirror modes in multispecies plasmas with arbitrary distributions
Authors: Gedalin M. , Balikhin M. , Strangeway R. J. , Russell C. T.
Published: October 2002

We perform a general analysis of the long‐wavelength mirror instability in multispecies plasmas with generally non‐Maxwellian distributions. The general dispersion relation depends on several moments of the distribution function, in addition to the perpendicular and parallel temperature. A most general condition of the mirror instability is derived that is valid for any gyrotropic distribution functions of the plasma species and any number of species. Deviations of the bi‐Maxwellian shape may be favorable for the mirror instability but may also suppress it. The resulting effect is rather sensitive to the details of the distribution function.
Magnetic dipolarization with substorm expansion onset
Authors: Liou K. , Meng C.‐I. , Lui A. T. Y. , Newell P. T. , Wing S.
Published: October 2002

We compare the timing and spatial extent of dipolarization with auroral breakup by using magnetic field data (1‐min time resolution) from GOES 8 and GOES 9 and global auroral images (37‐s frame rate) from the Polar ultraviolet imager. We survey the entire year of 1997 data and obtain 32 unambiguous dipolarization events that had ionospheric footprints within 2 hours in magnetic local time (MLT) from their associated auroral breakups. It is found that the auroral breakup preceded the arrival of dipolarization at GOES by an average of 1.7 ± 2.7 min. (1.0 ± 2.1 min for events ±1 hour from the auroral breakup). The delay of geosynchronous dipolarization represents a propagation time, as the substorms rarely initiated at the GOES location. Propagation velocities derived from the propagation time are ∼60 km s−1 eastward, ∼75 km s−1 westward, and ∼270 km s−1 earthward at geosynchronous orbit. We also show for the first time that auroral bulge and dipolarization region closely map; the bulge is the region of currents out of the ionosphere. The eastern edge of the dipolarization region, where field‐aligned currents are flowing into the ionosphere, is, based on the T89 magnetic field model, located at ∼0.5 hour in MLT eastward of the eastern edge of the auroral bulge. Within the initiation site meridian the dipolarization onset was observed ∼1 min prior to the auroral breakup at the GOES altitude. This time is associated with Alfvén transit time and therefore depends on the radial location of the onset. The azimuthal scale of the initiation site is found to be ∼0.5 hour in MLT in the ionosphere or less than ∼1 Earth's radius at 6.6 RE. These results support current diversion into the ionosphere as a critical part of substorms. Finally, a simple timing analysis of specific substorm onset time features suggests that near‐Earth reconnection cannot occur before current disruption and therefore cannot be the cause of substorm.
Temporal versus spatial interpretation of cusp ion structures observed by two spacecraft
Authors: Trattner K. J. , Fuselier S. A. , Peterson W. K. , Boehm M. , Klumpar D. , Carlson C. W. , Yeoman T. K.
Published: October 2002

A series of nearly simultaneous cusp crossings by the Polar and Fast Auroral Snapshot (FAST) spacecraft are used to investigate the development of cusp structures such as sudden changes in the energy of cusp precipitating ions. While such changes are generally interpreted as temporal signatures, recent investigations show evidence that such features can also be interpreted as spatial structures. Our analysis of four events during stable solar wind conditions confirms that cusp structures observed by one satellite are remarkably similar to cusp features observed up to several hours later by a second satellite. Using the spatial separation of the Polar and FAST spacecraft, the cusp features could also be traced over several hours in magnetic local time. These similarities led to the conclusion that large‐scale cusp structures are spatial structures related to global ionospheric convection pattern set up by magnetic merging and not the result of temporal variations in reconnection parameters.
Planetary waves and midlatitude sporadic E layers: Strong experimental evidence for a close relationship
Authors: Haldoupis Christos , Pancheva Dora
Published: October 2002

A large‐amplitude, 7‐day period westward propagating S = 1 planetary wave has been reported from ground radar and satellite wind measurements in the mesosphere lower thermosphere (MLT) during the second half of August and well into September 1993. Following recent suggestions that planetary waves might play a role in the formation of midlatitude sporadic E layers (Es), we have obtained and analyzed, for the period from August 1 to September 30, 1993, the sporadic E critical frequency (foEs) time series from eight midlatitude ionosonde stations covering a large longitudinal zone from ∼58°E to 157°W. The analysis revealed that all eight station foEs data showed a strong 7‐day periodicity, occurring concurrently with the 7‐day planetary wave reported elsewhere. Using independent methods for the analysis of the foEs time series, we computed identical estimates for the propagation direction, zonal wave number, and phase velocity of the 7‐day wave, which are in agreement with those reported from radar and satellite neutral wind MLT measurements. The present findings provide the first direct evidence, proving that planetary waves play an important role in the physics of midlatitude sporadic E region layers. In addition, our results include an important implication, that the Es parameters measured routinely and rather reliably with a dense global network of digital ionosondes, as well as the enormous ionogram databases existing in World Data Centers, may be used as an alternative means of studying large‐scale neutral atmospheric dynamics in the MLT region.
Global impact of ionospheric outflows on the dynamics of the magnetosphere and cross‐polar cap potential
Authors: Winglee R. M. , Chua D. , Brittnacher M. , Parks G. K. , Lu Gang
Published: October 2002

Statistical results for the ionospheric outflows indicate that the ionosphere is an important source of plasma to the magnetosphere. However, the exact consequences on the dynamics of the magnetosphere from this ionospheric outflow have yet to be determined. This issue is taken up in multifluid modeling of the 24–25 September 1998 magnetic cloud event for which strong heavy ionospheric outflows have been previously reported. It is demonstrated that one of the key influences of heavy ionospheric outflows is to lower the cross‐polar cap potential due to the mass loading it produces on the magnetosphere; i.e., the heavy ions provide a major sink for momentum that is transferred from the solar wind to the magnetosphere. The derived values for the cross‐polar cap potential are shown to converge to that attained by assimilated mapping of ionospheric electrodynamics (AMIE) as the O+ concentration at the ionospheric boundary is increased to ∼50% of the H+ concentration. The mass outflows produced in the model are comparable to the reported statistical values for the same level of Kp observed during the event. The position of the open‐closed boundary is shown to be located progressively poleward with increasing O+ concentration, and that the derived position at the higher O+ concentrations best fits the Polar UVI images during the event. In addition, the model results shown that the heavy ionospheric ions provide a substantial sink for the energy input into the auroral oval as calculated by either UVI and AMIE. Thus ionospheric outflows are not just important in determining the source of the plasma in the magnetosphere, but have a clear role in controlling the global dynamics of the magnetosphere and the transport of solar wind energy and momentum through the magnetosphere.
Effects of large horizontal winds on the equatorial electrojet
Authors: Hysell D. L. , Chau J. L. , Fesen C. G.
Published: October 2002

The effects of large winds on the low‐latitudeEregion ionosphere and the equatorial electrojet in particular are analyzed theoretically, computationally, and experimentally. The principles that govern the relationship between electric fields, currents, and winds in steady flows in the ionosphere are reviewed formally. A three‐dimensional numerical model of low‐latitude ionospheric electrostatic potential is then described. Scaled wind profiles generated by the National Center for Atmospheric Research (NCAR) thermosphere/ionosphere/mesosphere electrodynamics general circulation model (TIME‐GCM) are used as inputs for the potential model. The model shows that the horizontal wind component drastically modifies the vertical polarization electric field in the electrojet and drives strong zonal and meridional currents at higher dip latitudes outside the electrojet region. Comparison between the model output and coherent scatter radar observations of plasma irregularities in the electrojet indicate that strong winds and wind shears are present in theEregion over Jicamarca that are roughly consistent with NCAR model wind predictions if the amplitudes of the latter are increased by about 50%.
A model of the near magnetosphere with a dawn‐dusk asymmetry 2. Parameterization and fitting to observations
Authors: Tsyganenko N. A.
Published: October 2002

First results are presented of an empirical modeling of the Earth's inner and near magnetosphere (X ≥ −15 RE), using a new set of data and new methods, described in a companion paper. The modeling database included 5‐min average B field data, taken in a wide range of altitudes and latitudes by the International Solar Terrestrial Physics spacecraft Polar (1996–1999) and Geotail (1994–1999), as well as by earlier missions, ISEE 2 (1984–1987), Active Magnetospheric Particle Tracer Explorers (AMPTE)/CCE (1984–1988), AMPTE/Ion Release Module (1984–1986), CRRES (1990–1991), and DE 1 (1984–1990). To take into account the delayed response of the magnetosphere to the solar wind and interplanetary magnetic field (IMF), each data record in the data set was tagged by a “trail” of 5‐min averages of the IMF, solar wind, and Dst field data, covering the preceding 2‐hour interval. The axisymmetric ring current (SRC) and the partial one (PRC), both parameterized by the corrected Dst* index and the solar wind pressure Pd, were found to vary in strikingly different ways. While under quiet conditions the PRC is much weaker than the SRC, it dramatically grows in magnitude and rotates to the dusk sector with rising |Dst*| and Pd, significantly exceeding the SRC even during moderate storms, in excellent agreement with recent particle simulations. The innermost part of the cross‐tail current is quite sensitive to the southward IMF and yields ∼90% of the tail's contribution to the Dst index, in contrast with the more distant tail current, which responds mainly to the solar wind pressure and provides no appreciable contribution to Dst. In response to southward IMF conditions, Region 1 and 2 Birkeland currents rapidly grow in magnitude and expand to lower latitudes, while their peaks shift slightly in local time toward noon. The coefficient of the IMF penetration inside the magnetosphere was found to dramatically increase with growing IMF clock angle: while quite small (∼0.1) for northward IMF, it rises to ∼0.6 as the IMF turns southward. Priorities and challenges for future data‐based modeling studies are discussed.
The modulation of 4‐ to 16‐MeV electrons in the outer heliosphere: Implications of different local interstellar spectra
Authors: Ferreira S. E. S. , Potgieter M. S.
Published: October 2002

The modulation of low‐energy galactic and Jovian electrons is studied using a fully three‐dimensional, steady state modulation model and a two‐dimensional termination shock model, both based on Parker's transport equation. For this purpose the Jovian electron source and local interstellar electron spectrum (LIS) must be specified. The latter is not well known below ∼100 MeV so that four different local interstellar spectra for electrons are studied and compared to the ∼4‐ and ∼16‐MeV Pioneer 10 observations up to ∼70 AU. Assuring that the model represents these observations contributes to a better understanding of the heliospheric diffusion coefficients applicable to low‐energy electron modulation. These electrons respond directly to the energy dependence of the diffusion coefficients below ∼500 MeV in contrast to protons which experience large adiabatic energy losses. In addition, low‐energy electrons experience progressively less drifts below ∼100 MeV. The study illustrates that the different LIS scenarios require a different radial dependence of the diffusion coefficients throughout the heliosphere. By relating the parallel mean free path observations at Earth to the values needed to compute reasonable electron modulation at 16 MeV, a preferred LIS range could be established with ∼100 and ∼1000 particles m−2 s−1 sr−1 MeV−1, as lower and upper limits, respectively. On the basis of this preferred LIS range and the very small radial dependence observed for these electrons between 20 and 70 AU, the model predicts that very large modulation should occur beyond ∼70–80 AU in the heliosphere. This indicates that what happens in the outer most parts of the heliosphere is very important for cosmic ray modulation.
Electron and proton aurora observed spectroscopically in the far ultraviolet
Authors: Galand M. , Lummerzheim D. , Stephan A. W. , Bush B. C. , Chakrabarti S.
Published: October 2002

The only way to get a global, instantaneous picture of the energetic particle input over the auroral oval is through spectral imaging. The major driver of auroral emissions in the high‐latitude ionosphere is overall electron precipitation. However, for certain locations and times, such as the equatorial edge of the evening auroral oval, proton precipitation can be the major energy source and thus the primary contributor to auroral emissions. Using kinetic transport models to describe the transport of energetic particles in the atmosphere, we analyze UV spectra from the STP78‐1 satellite mission during magnetically disturbed conditions (Kp = 6) in the evening sector of the auroral oval. We discuss the contribution of protons and electrons to the auroral emissions. The energy flux of the incident protons is inferred from the H Lyman α emissions, after removing the H geocoronal background induced by solar radiation. Both the mean energy and energy flux of electron precipitation are inferred from non‐H emissions (N II 108.5 nm, N2 135.4 nm, and O I 135.6 nm), after removing the contribution of proton precipitation. From the latitudinal distribution of the incident energy flux the location of the electron and proton aurorae is discussed. The estimation of the particle characteristics allows one to infer the Pedersen and Hall electrical conductances induced by particle precipitation. For the studied substorm period, energetic protons contribute significantly to the Pedersen conductance, ∼25–30% overall of the total particle‐induced conductances and much more at the equatorward edge of the midnight aurora. Because protons and electrons do not interact in the same way with the atmosphere, our study shows that while analyzing auroral spectra and studying the state of the ionosphere, it is crucial to separate electron and proton components of the precipitation. The method described to disentangle the relative contribution of precipitating electrons and protons may be applicable to the UV data of the upcoming TIMED and DMSP missions.
Structure of the magnetic field fluxes connected with crustal magnetization and topside ionosphere at Mars
Authors: Krymskii A. M. , Breus T. K. , Ness N. F. , Acuña M. H. , Connerney J. E. P. , Crider D. H. , Mitchell D. L. , Bauer S. J.
Published: October 2002

The magnetic fluxes associated with the Martian crustal remanent magnetization have been studied in order to investigate the global structure of the magnetic field in and above the level of the Martian ionosphere. The intensely and nonuniformly magnetized crustal sources generate an effective large‐scale magnetic field. Reconnection with the interplanetary magnetic field can possibly take place in many localized regions. This will permit solar wind (SW) and more energetic particles to precipitate into and heat the neutral atmosphere by impact ionization. This may occur not only in cusp‐like field structures above nearly vertical field anomalies but also in halos extending several hundreds of kilometers from these sources. Numerous cusp‐like regions may exist above the many crustal anomalies in the southern hemisphere. The large‐scale horizontal magnetic fields due to the crustal sources and induced by the SW interaction are responsible for controlling the detailed structure of the Martian ionosphere. Radio occultation observations in the southern hemisphere show relatively constant and low average values of the electron density scale height and zero dependence on zenith angle in contrast to that of nonmagnetic Venus.
Sheared magnetic field structure in Jupiter's dusk magnetosphere: Implications for return currents
Authors: Kivelson Margaret G. , Khurana Krishan K. , Walker Raymond J.
Published: October 2002

The configuration of the magnetic field near 100 RJ in the dusk sector of the Jovian magnetosphere varies with distance from the equatorial current sheet. The changing twist out of meridian planes is consistent with flows that lag corotation near the equator but that may lead corotation at higher latitudes. Although a portion of the field perturbation may be produced by magnetopause currents, we argue that the observed sheared field structure requires field‐aligned current flowing toward Jupiter's ionosphere inside the magnetopause but beyond ∼100 RJ. This current must include a portion of the return current of the system that enforces partial corotation of outward moving magnetospheric plasma and may also be fed by boundary layer currents of the region 1 type. We estimate the total current into the auroral ionosphere as ∼6 MA, and this current would flow into a narrow band of latitude (<2°) poleward of the main auroral oval.
FAST observations of discrete electrostatic waves in association with down‐going ion beams in the auroral zone
Authors: Cattell C. , Johnson L. , Bergmann R. , Klumpar D. , Carlson C. , McFadden J. , Strangeway R. , Ergun R. , Sigsbee K. , Pfaff R.
Published: October 2002

Ion beams flowing downward, into the ionosphere, along the Earth's magnetic field have frequently been observed by the FAST satellite in the auroral zone. These discrete downward moving ion beams (DFI) have been characterized by Klumpar et al. [1999] who interpreted the horseshoe‐shaped distributions as being consistent with acceleration in a parallel potential drop above the satellite, followed by motion into a region of increased magnetic field strength. The down‐flowing ion beams are associated with an intense narrowband electrostatic emission at the lower hybrid frequency, polarized perpendicular to the geomagnetic field. Hydrogen cyclotron harmonics both above and below the lower hybrid frequency are also very common. These are the first observations of down‐flowing ions and associated waves outside of the cusp, and the physical mechanism producing the ions is very different from the one associated with cusp ion injections. The DFI events that had a monotonic increase in energy were associated with a clear field‐aligned current signature. The DFI densities were usually ∼5–10/cc, whereas the background plasma had densities up to 100/cc. The wave and DFI observations are consistent with linear dispersion relation calculations and simulations with ion ring distributions that show that the instability is due to coupling of the ion Bernstein waves to the lower hybrid wave. In addition, for a few events, electrostatic ion cyclotron waves were observed. Such waves are usually associated with up‐going ion beams and have not previously been seen with DFI, which have a very different shape in the distribution.
A model of nitric oxide in the lower thermosphere
Authors: Bailey Scott M. , Barth Charles A. , Solomon Stanley C.
Published: October 2002

A model of NO abundance in the lower thermosphere is described. The model includes time dependence, an energetic electron flux calculation that includes transport, neutral and ion photochemistry, and vertical diffusion. We show that a steady state calculation is inadequate for calculating NO abundance. We examine the relationship between observed NO abundance and the integrated energy input to the lower thermosphere over the previous day. It is shown that the relationship between the energy input and the NO abundance varies with the local time of the NO measurement and with the length of daylight. These dependencies arise due to the role of photodissociation as a loss mechanism for NO. This model is designed for analysis of NO observations and will be used in the analysis of observations by the SNOE spacecraft [Barth et al., 1999].
Spatial features observed in the cusp under steady solar wind conditions
Authors: Trattner K. J. , Fuselier S. A. , Peterson W. K. , Carlson C. W.
Published: October 2002

Multispacecraft studies using Polar, Fast Auroral Snapshot (FAST), and Interball observations revealed that many cusp structures observed during stable solar wind conditions are spatial features. While individual cusp events appear to be very different from each other, multiple observations of the same cusp event during periods of stable solar wind conditions are remarkably similar. These spatial cusp structures have been interpreted as a result of the independent evolution of ion distributions from multiple reconnection sites (X‐lines) in both hemispheres. The location of reconnection sites depends critically on the direction of the interplanetary magnetic field. Thus individual cusp events should have similar cusp structures if they occur in the same magnetic local time sector during comparable solar wind conditions, especially during similar interplanetary magnetic field orientations. Data presented in this paper show just such an effect. For three individual cusp events observed by Polar and FAST, similar stepped ion structures are seen by both satellites passing though these large‐scale spatial structures.