bluuebunny/crossref_metadata_2025 huggingface dataset:
Time‐averaged fluxes of lead and fallout radionuclides to sediments in Florida Bay
Authors: Robbins J. A. , Holmes C. , Halley R. , Bothner M. , Shinn E. , Graney J. , Keeler G. , tenBrink M. , Orlandini K. A. , Rudnick D.
Published: February 2004

Recent, unmixed sediments from mud banks of central Florida Bay were dated using 210Pb/226Ra, and chronologies were verified by comparing sediment lead temporal records with Pb/Ca ratios in annual layers of coral (Montastrea annularis) located on the ocean side of the Florida Keys. Dates of sediment lead peaks (1978±2) accord with prior observations of a 6 year lag between the occurrence of maximum atmospheric lead in 1972 and peak coral lead in 1978. Smaller lags of 1–2 years occur between the maximum atmospheric radionuclide fallout and peaks in sediment temporal records of 137Cs and Pu. Such lags are consequences of system time averaging (STA) in which atmospherically delivered particle‐associated constituents accumulate and mix in a (sedimentary?) reservoir before transferring to permanent sediments and coral. STA model calculations, using time‐dependent atmospheric inputs, produced optimized profiles in excellent accord with measured sediment 137Cs, Pu, lead, and coral lead distributions. Derived residence times of these particle tracers (16±1, 15.7±0.7, 19±3, and 16±2 years, respectively) are comparable despite differences in sampling locations, in accumulating media, and in element loading histories and geochemical properties. For a 16 year weighted mean residence time, STA generates the observed 6 year lead peak lag. Evidently, significant levels of nondegradable, particle‐associated contaminants can persist in Florida Bay for many decades following elimination of external inputs. Present results, in combination with STA model analysis of previously reported radionuclide profiles, suggest that decade‐scale time averaging may occur widely in recent coastal marine sedimentary environments.
Short timescale variations of ƒCO2 in a North Atlantic warm‐core eddy: Results from the Gas‐Ex 98 carbon interface ocean atmosphere (CARIOCA) buoy data
Authors: Hood E. M. , Wanninkhof R. , Merlivat L.
Published: February 2004

During a Lagrangian deliberate tracer study in the North Atlantic, the 1998 Gas Exchange Experiment, hourly measurements of wind speed, sea surface temperature, ƒCO2, and fluorescence were made from two carbon interface ocean atmosphere (CARIOCA) drifting buoys in a warm‐core eddy near 46°N and 21.5°W over a period of approximately 20 days. Shipboard measurements of ƒCO2 near the buoys were used to verify the buoy operation, calibrate the buoy measurements, and assess the performance of the ƒCO2 sensor. The strong air‐sea ƒCO2 gradient in the eddy and intense atmospheric forcing during the experiment provided ideal conditions for demonstrating the potential of autonomous drift buoy measurements for studies of surface ocean biogeochemistry, where changes of ƒCO2 were rapid and large. During the experiment a storm occurred with wind speeds reaching as high as 16–17 m s−1, leading to a sharp decrease in sea surface temperature and an increase in ƒCO2 of ∼30 μatm. The magnitude of this sudden change in ƒCO2 is equal to approximately half of the annual range of ƒCO2 in this area. The air‐sea flux estimate for the ∼20 day experiment using the Wanninkhof [l992] gas transfer velocity formulation was −0.012 mol m−2 d−1 and using the Liss and Merlivat [1986] formulation was −0.007 mol m−2 d−1. The storm event, lasting 3–4 days, accounted for ∼38% of the flux over this period. Approximately 16 hours after the onset of the storm, there was an increase in surface fluorescence coincident with the initial increase in ƒCO2. Nitrate measurements made from the ship in the eddy show a sharp peak in surface concentrations ∼24 hours after the increase in winds and ∼6–8 hours after the increase in surface fluorescence. After the upwelling of the NO3 the fluorescence increases more sharply while the ƒCO2 decreases, consistent with biological productivity. The surface fluorescence measurements remain higher than prestorm conditions for ∼5 days after the NO3 has disappeared.
Crustal helium in deep Pacific waters
Authors: Well Roland , Lupton John , Roether Wolfgang
Published: February 2004

We have analyzed deep helium isotope data from World Ocean Circulation Experiment section P17 along 135°W in the Pacific Ocean. Combining these data with neon data, we have derived the isotopic ratio (Rt) of the nonatmospheric part of helium (terrigenic helium). The calculated Rt values are significantly lower than helium isotope ratios from mid‐ocean ridge (MOR) sources (RMOR ≈ 8Ra; Ra: = (3He/4He)air), which are generally presumed to dominate the isotope characteristics of helium of nonatmospheric origin. For the depths most influenced by the southern East Pacific Rise (EPR) helium plume the isotopic ratio of terrigenic helium is ∼7.4 Ra. However, both the northern EPR plume and the Juan de Fuca Ridge (JdFR) plume show significantly lower Rt values of ∼6.8 Ra. We find minimum Rt values of ∼5.6 Ra at about 20°N to 30°N from 2000 m depth to the ocean floor. We conclude that in addition to the EPR and JdFR helium sources (having MOR isotope characteristics) there is a flux of radiogenic 4He out of deep‐sea sediments and the oceanic crust which causes a significant deviation of Rt toward values lower than RMOR. Using our calculated terrigenic 4He concentrations and isotope ratios Rt and the helium isotope ratios of the two end‐members (MOR helium and crustal helium), we derive concentrations and ocean bottom fluxes of crustal 4He (4Hecrust). Maximum concentrations of 4Hecrust (up to ∼30 pmol kg−1) are found at about 20°N to 30°N between 2000 m and 4000 m along the P17 section. The mean crustal 4He flux is obtained as 1.0 (±0.4) 109 atoms m−2Earth s−1.
On mechanisms of rain‐induced air‐water gas exchange
Authors: Ho David T. , Asher William E. , Bliven Larry F. , Schlosser Peter , Gordan Elizabeth L.
Published: February 2004

Previous studies have shown that rain significantly enhances the rate of air‐water gas exchange. However, even though an empirical correlation between the rain rate or kinetic energy flux (KEF) delivered to the water surface by rain and the gas transfer velocity has been established, the physical mechanisms underlying the gas exchange enhancement remain unexamined. During a series of experiments, the processes behind rain‐induced air‐water gas exchange were examined at NASA's Rain‐Sea Interaction Facility (RSIF). Gas transfer velocities for helium (He), nitrous oxide (N2O), and sulfur hexafluoride (SF6) were determined for 22 rain rates (13.6 to 115.2 mm h−1) and three drop sizes (2.3, 2.8, 4.2 mm). Bubbles generated by the raindrops were characterized using a video‐microscope technique, and surface waves were characterized by a capacitance probe. Additionally, rain‐generated turbulence was inferred from friction velocities u*w calculated from KEF. Together, these data suggest that rain‐induced air‐water gas exchange is mainly caused by turbulence‐driven exchange processes, with bubbles contributing anywhere from 0 to 20%, depending on rain rate, drop size, and the solubility of the gas tracer. Furthermore, the data confirm that the previously selected variable KEF is the best correlate for rain‐induced air‐water gas exchange.
Nitrous oxide cycling in the Arabian Sea
Authors: Bange Hermann W. , Rapsomanikis Spyridon , Andreae Meinrat O.
Published: February 2004

Depth profiles of dissolved nitrous oxide (N2O) were measured in the central and western Arabian Sea during four cruises in May and July‐August 1995 and May‐July 1997 as part of the German contribution to the Arabian Sea Process Study of the Joint Global Ocean Flux Study. The vertical distribution of N2O in the water column on a transect along 65°E showed a characteristic double‐peak structure, indicating production of N2O associated with steep oxygen gradients at the top and bottom of the oxygen minimum zone. We propose a general scheme consisting of four ocean compartments to explain the N2O cycling as a result of nitrification and denitrification processes in the water column of the Arabian Sea. We observed a seasonal N2O accumulation at 600–800 m near the shelf break in the western Arabian Sea. We propose that, in the western Arabian Sea, N2O might also be formed during bacterial oxidation of organic matter by the reduction of IO3− to I−, indicating that the biogeochemical cycling of N2O in the Arabian Sea during the SW monsoon might be more complex than previously thought. A compilation of sources and sinks of N2O in the Arabian Sea suggested that the N2O budget is reasonably balanced.
Two‐phase, near‐field modeling of purposefully released CO2in the ocean
Authors: Alendal Guttorm , Drange Helge
Published: February 2004

Injection of carbon dioxide (CO2) in the ocean has been proposed as an option for accelerating the natural net flux of CO2from the atmosphere into the ocean. Liquid CO2released as droplets at depths <3000 m will create an ascending plume of droplets and entrained water. As the CO2droplets dissolve, carbon is transferred into the plume water, yielding increased density and a lowered pH value of the plume water. As ambient water entrains the CO2‐enriched water by mixing, the density difference disappears and the injected CO2follows the ocean dynamics as a dynamically passive tracer. Here we report on numerical experiments performed with a two‐phase Navier Stokes solver. The effects of different droplets sizes, background currents, and injection rates are examined. The numerical experiments show that the droplet size and the background current are key parameter for predicting the vertical distribution of the plume water, the associated reduction in the pH field, and the increase in the plume water density. If rapid dilution of the CO2‐enriched water is the objective (leading to modest reduction in the pH value), large initial droplets and high background currents are preferable. On the other hand, if the objective is to increase the density of the plume water in order to generate a sinking plume (yielding enhanced residence time of the released CO2), CO2injection with small droplets in a stagnant water column is optimal.
Pulsating midmorning auroral arcs, filamentation of a mixing region in a flank boundary layer, and ULF waves observed during a Polar‐Svalbard conjunction
Authors: Famigia C. J. , Sandholt P. E. , Maynard N. C. , Burke W. J. , Scudder J. D. , Ober D. M. , Moen J. , Russell C. T.
Published: February 2004

Magnetically conjugate observations by the HYDRA and the Magnetic Field Experiment instruments on Polar, meridian‐scanning photometers and all‐sky imagers at Ny‐Ålesund, and International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometers on November 30, 1997, illustrate aspects of magnetosphere‐ionosphere coupling at 0900–1000 magnetic local times (MLT) and 70°–80° magnetic latitudes and their dependence on interplanetary parameters. Initially, Polar crossed a boundary layer on closed field lines where magnetospheric and magnetosheath plasmas are mixed. This region contains filaments where magnetospheric electron and ion fluxes are enhanced. These filaments are associated with field‐aligned current structures embedded within the large‐scale region 1 (R1) current. Ground auroral imagery document the presence at this time of discrete, east–west aligned arcs, which are in one‐to‐one correspondence with the filaments. Temporal variations present in these auroral arcs correlate with Pc 5 pulsations and are probably related to modulations in the interplanetary electric field. The auroral observations indicate that the filamented mixing region persisted for many tens of minutes, suggesting a spatial structuring. The data suggest further that the filamented, mixing region is an important source of the R1 current and the associated midmorning arcs. When the interplanetary magnetic field (IMF) turned strongly north, Polar had entered the dayside extension of the central plasma sheet/region 2 current system where it and the underlying ground magnetometers recorded a clear field line resonance of frequency ∼2.4 mHz (Pc 5 range). The source of these oscillations is most likely the Kelvin‐Helmholtz instability. Subsequent to the IMF northward turning, the multiple arcs were replaced by a single auroral form to the north of Ny‐Ålesund (at 1000 MLT) in the vicinity of the westward edge of the cusp. ULF pulsation activity changed to the Pc 3–4 range in the regime of the pulsating diffuse aurora when the IMF went to an approximately Parker spiral orientation and the ground stations had rotated into the MLT sector of cusp emissions.
Interhemispheric plasma flows in the equatorial topside ionosphere
Authors: Venkatraman Sarita , Heelis Rod
Published: February 2004

Latitudinal, longitudinal, and seasonal variations in the field‐aligned and perpendicular flows measured at an altitude near 830 km, by the Defense Meteorological Satellite Program F10 satellite are examined. These profiles are studied during the nighttime (2100 magnetic local time) for solstice periods in 1991 when the solar activity is high. Latitude and longitude variations show the influence of F region winds in modulating the observed field‐aligned flows. At night, large downward field‐aligned flows of the order 400–600 ms−1 are observed in the winter hemisphere and coincide in longitude with the location of previously identified adiabatic heating effects studied by Venkatraman and Heelis [1999a], Interhemispheric flows at 2100 hours local time are seen to extend up to apex heights of ∼ 1000 km during times of high solar activity. Perpendicular drifts, however are relatively invariant with latitude as expected.
Proton and electron heating by radially propagating fast magnetosonic waves
Authors: Horne Richard B. , Wheeler Gavin V. , Alleyne Hugo St. C. K.
Published: February 2004

We investigate the propagation, growth, and decay of fast magnetosonic waves in the Earth's magnetosphere which are believed to contribute to proton heating up to energies of a few hundred eV near the magnetic equator. We construct a model of the proton and electron distribution functions from spacecraft data and use the HOTRAY code to calculate the path‐integrated growth and decay of the waves over a range of L shells from L = 2 to L = 7. Instability calculations show that the waves are excited at very large angles of propagation with respect to the magnetic field, ψ ≈ 89°, at the harmonics of the proton gyrofrequency ΩH+ up to the lower hybrid resonance frequency ωLHR by a proton ring distribution at energies of the order of 10 keV. As a “rule of thumb”, we find that growth is possible for ω > 30ΩH+ when the ring velocity exceeds the Alfvén speed vR > vA, and for ω < 30ΩH+ when vR > 2vA. For propagation in the meridian plane, waves generated just outside the plasmapause grow with large amplification as they propagate away from the Earth but eventually lose energy to plasma sheet electrons at energies of a few keV by Landau damping. The waves grow to large amplification at frequencies just below ωLHR. For inward propagation we find that waves generated just outside the plasmapause can propagate to L ≈ 2 with very little attenuation, suggesting that waves observed well inside the plasmasphere could originate from a source region just outside the plasmapause. Strong wave growth only occurs for large angles of propagation, and thus the waves are confined to within a few degrees of the magnetic equator. Waves generated near geostationary orbit and which propagate toward the Earth are absorbed by Doppler‐shifted cyclotron resonance when they propagate into a region where vR < vA. Cyclotron resonant absorption causes pitch angle scattering and heating transverse to the ambient magnetic field. The amount of absorption, and hence transverse proton heating, increases significantly as the thermal proton temperature is increased up to 100 eV, suggesting a feedback process. Ray tracing shows that transverse heating of the thermal proton distribution is most likely to occur just outside the plasmapause where vA is large. Since proton ring distributions are formed during magnetic storms at ring current energies, we suggest that fast magnetosonic waves provide an additional energy loss process for ring current decay.
Descending layer variability over Arecibo
Authors: Earle G. D. , Bishop R. L. , Collins S. C. , González S. A. , Sulzer M. P.
Published: February 2004

Descending layers of ionization over Arecibo exhibit very diverse behavior from night to night that does not appear to be strongly correlated to geomagnetic activity, solar forcing, or average semidiurnal tidal winds. On some nights, three or more distinct layers are observed to form near 170 km over timescales of ∼2 hours. Rather than descending smoothly over periods of several hours, these layers stall, abruptly disappear, or even reverse direction in the midst of their descent. The time scales for their disappearance are examined and compared to loss rates arising from diffusion and recombination. Diffusion alone is found to be too slow to account for the observations, but recombination is fast enough provided that the convergent wind shear that forms the layer is relatively weak coincident with their disappearance. The continuity equation is solved in conjunction with a time sequence of radar profiles to estimate the vertical drift and horizontal neutral wind consistent with the observed behavior. The resultant wind field is northward, has an average speed of ∼80 m s−1, and varies significantly near the altitude where the layers are observed. These inferred winds are consistent with the presence of the observed layers, and their magnitudes as obtained from the classical continuity and momentum equations are reasonable for this altitude range.
Sami2 is Another Model of the Ionosphere (SAMI2): A new low‐latitude ionosphere model
Authors: Huba J. D. , Joyce G. , Fedder J. A.
Published: February 2004

A new low‐latitude ionospheric model has been developed at the Naval Research Laboratory: Sami2 is Another Model of the Ionosphere (SAMI2). SAMI2 treats the dynamic plasma and chemical evolution of seven ion species (H+, He+, N+, O+, N2+, NO+, and O2+) in the altitude range ∼ 100 km to several thousand kilometers. The ion continuity and momentum equations are solved for all seven species; the temperature equation is solved for H+, He+, O+, and the electrons. SAMI2 models the plasma along the Earth's dipole field from hemisphere to hemisphere, includes the E × B drift of a flux tube (both in altitude and in longitude), and includes ion inertia in the ion momentum equation for motion along the dipole field line. The final point is relevant for plasma dynamics at very high altitudes where ion inertia can be important. For example, we have found that ion sound waves, which are supported by ion inertia, may be generated in the topside ionosphere (> 1000 km) at sunrise and sunset [Huba et al., 2000b]. The neutral species are specified using the Mass Spectrometer Incoherent Scatter model (MSIS86) and the Horizontal Wind Model (HWM93). In this paper we describe in detail the SAMI2 model and present representative results from the model.
Ion dynamics and tail current intensification prior to dipolarization: The June 1, 1985, event
Authors: Ohtani S. , Lui A. T. Y. , Takahashi K. , Mitchell D. G. , Sarris T.
Published: February 2004

The present study investigates the tail current intensification prior to dipolarization, focusing on the dynamics of energetic ions. The event selected for this study, which was initially reported by Lui et al. [1988], occurred on June 1, 1985. The uniqueness of this event is that the AMPTE/CCE spacecraft remained close to the neutral sheet until the local magnetic field was dipolarized. Energetic (30–200 keV) ion fluxes were larger when the telescope was looking dawnward than when it was looking in the opposite direction. Until several tens of seconds before the (local) onset of dipolarization, this dawn‐dusk flux anisotropy was more manifest for higher‐energy ions, suggesting that the anisotropy was caused by the radial gradient of the energetic particle density. That is, the tail current was driven by radial pressure gradient. However, just prior to the onset, the flux level and the dawn‐dusk anisotropy of the lowest‐energy (31–43 keV) channel increased significantly, causing a further intensification of the tail current. The feature was less obvious in higher‐energy channels. This energy dependence is better explained in terms of ion motion across the magnetic field. The velocity of this motion is a function of the ion energy and is estimated at 4% of the velocity corresponding to a given energy. It is likely that the associated enhancement of the tail current density was comparable to the enhancement during the entire growth phase. A positive feedback process between the unmagnetization of ions and the thinning of the current sheet is proposed for explaining this explosive intensification of the tail current. It is also found that electron pressure anisotropy did not contribute to the tail current intensification in the present event. The present result strongly suggests that the ion kinetics is important in the tail current intensification prior to the local onset of tail current disruption.
Latitudinal density dependence of magnetic field lines inferred from Polar plasma wave data
Authors: Goldstein J. , Denton R. E. , Hudson M. K. , Miftakhova E. G. , Young S. L. , Menietti J. D. , Gallagher D. L.
Published: February 2004

Using observations of the electron density ne based on measurement of the upper hybrid resonance frequency by the Polar spacecraft Plasma Wave Instrument, we have examined the radial density dependence along field lines in the outer plasmasphere and the near plasma trough. Our technique depends on the fact that Polar crosses particular L values at two different points with different radial distance R. Sampled L values range from 2.5 to 6.3. In our plasmaspheric data set (ne ≥ 100 cm−3) we find that, on average, ne is flat along field lines from the equator up to the latitudes sampled by Polar (R ≳ 2 RE). In the plasma trough data set (ne < 100 cm−3) there is, on average, a mild radial dependence ne ∝ R−1.7.
Drift mirror instability revisited, 1, Cold electron temperature limit
Authors: Pokhotelov Oleg A. , Balikhin M. A. , Treumann R. A. , Pavlenko Vladimir P.
Published: February 2004

Linear theory of the drift‐mirror instability in high‐β plasma is reconsidered referring to basic principles for the two cases of a one‐ and a two‐component ion plasma in presence of a cold electron background. In both cases the cold electrons serve to shortcut the parallel electric field component which imposes the condition of vanishing the field‐aligned current. The corresponding low‐frequency dispersion relation is derived in the fluid approximation as well as from kinetic theory including nonvanishing gradients in the density. The free energy of the unstable mode is taken from two sources: the pressure anisotropy and the spatial inhomogeneity of the plasma. The dispersion relation contains a correction which originates from the inclusion of the bending of the magnetic field that is caused by the reaction of the field to the total pressure force. It is shown that the mirror force substantially reduces the phase velocity which is in favour of instability since this requires phase velocities less than the drift speed. The direction of phase velocity becomes antiparallel to that of the pure density‐gradient drift velocity. Even for a mirror‐stable plasma an instability arises which is solely due to inhomogeneity. We analyze the transition to the classical mirror instability. Application to ring current (hot ring current ions plus cold plasmasphere ions) and magnetosheath (hot sheath ions only) conditions is presented and is in agreement with observational indication of the apparent stability of the pure mirror mode in the ring current.
Plasma and magnetic field correlations in the solar wind
Authors: Richardson John D. , Paularena Karolen I.
Published: February 2004

Data from multiple spacecraft are used to determine solar wind plasma and interplanetary magnetic field (IMF) correlation coefficients. These correlation coefficients provide information on solar wind scale lengths and the predictive capability of upstream monitors for space weather purposes. Previous work has looked at plasma and IMF correlation coefficients independently and used much smaller databases than those used in this study. We use data sets from 1977–1984 and 1994–1998 and calculate plasma and IMF correlation coefficients. The IMF correlation coefficients are, on average, slightly higher than those for plasma. Dependence of the correlation coefficients on the spatial separation of the spacecraft is important for placement of upstream monitors; we find a small dependence on the radial separation of the spacecraft but a very strong dependence on spacecraft separation in the YZ (GSE) plane. Scale lengths perpendicular to the flow are about 45 Earth radii (RE) for the IMF components, 70 RE for the speed and IMF magnitude, and over 100 RE for the density. Radial scale lengths are of the order of 400 RE. The plasma and IMF correlation coefficients are larger when values of the density standard deviation are high and when the IMF direction is perpendicular to X (GSE). Front orientations are similar for both plasma and IMF features and are more perpendicular than the average field direction.
The onset of long‐term cosmic ray modulation in cycle 23 coupled with a transient increase of anomalous cosmic rays in the distant heliosphere
Authors: McDonald F. B. , Burlaga L. F. , McGuire R. E. , Ness N. F.
Published: February 2004

The onset of significant solar activity in cycle 23 began in November 1997 with several modest events and was followed by an enhanced period of solar activity in April and May 1998. This latter series of events produced a well‐defined step decrease in the cosmic ray intensity at 1 AU as observed by the Goddard Cosmic Ray Experiment on IMP 8. Over the ensuing 2 years there are further decreases in the IMP 8 data with the cumulative effect being in good agreement with the net decrease in cycle 21 at a similar time in the solar cycle. At Voyager 1 (72 AU, 34°N) and Voyager 2 (56 AU, 24°S) there are transient increases in the intensity of 1.8–2.8 MeV H that mark the passage of a large interplanetary disturbance around 1998.75 that was most probably associated with the April–May activity. However, there was no durable decrease observed at that time in the galactic or anomalous cosmic rays. What is unique about this event at Voyager 2 (V 2) in the outer heliosphere is the precursor increase in the anomalous cosmic ray intensity associated with this interplanetary disturbance as defined by the V 2 magnetic field observations. This enhancement event establishes that reacceleration of anomalous cosmic rays can occur in the outer heliosphere. The onset of durable modulation at V 2 begins around 1999.5, probably in association with the disturbances that produced the second step‐like decrease at 1 AU. At Voyager 1 there is preliminary evidence that the corresponding onset time is 1999.85.
Energy transfer in collisions of oxygen atoms in the terrestrial atmosphere
Authors: Kharchenko V. , Dalgarno A. , Zygelman B. , Yee J.‐H.
Published: February 2004

The total and differential cross sections of elastic O(3P) + O(3P) collisions have been obtained from quantal calculations, and the rate of energy relaxation of fast oxygen atoms in atmospheric oxygen gas has been evaluated using realistic differential cross sections of oxygen‐oxygen collisions. All the electronic energy curves of O2 separating to the atomic ground states have been incorporated in calculations of the scattering phase shifts. The total and differential cross sections averaged over a statistical population of O(3P) fine structure levels have been used for calculations of the self‐diffusion coefficient, the viscosity and thermal conductivity of oxygen gas. The kernel of the Boltzmann equation for the energy relaxation process has been determined. The rate of energy losses of energetic oxygen atoms in the upper terrestrial atmosphere are calculated for typical thermospheric conditions. The energy distribution function of the recoil oxygen atoms is constructed using the computed energy relaxation kernel.
Variation of mesospheric ozone during the highly relativistic electron event in May 1992 as measured by the High Resolution Doppler Imager instrument on UARS
Authors: Pesnell W. Dean , Goldberg Richard A. , Jackman Charles H. , Chenette D. L. , Gaines E. E.
Published: February 2004

Highly relativistic electron precipitation events (HREs) include long‐lived enhancements of the flux of electrons with E > 1 MeV into the Earth's atmosphere. HREs also contain increased fluxes of electrons with energies above 100 keV that have been predicted to cause large depletions of mesospheric ozone. For some of the measured instantaneous values of the electron fluxes during the HRE of May 1992, relative depletions greater than 22% were predicted to occur between altitudes of 55 and 80 km, where HOx reactions cause local minima in both the ozone number density and mixing ratio altitude profiles. These ozone depletions should follow the horizontal distribution of the electron precipitation, having a distinct boundary equatorward of the L = 3 magnetic shell. To search for these effects, we have analyzed ozone data from the High Resolution Doppler Imager (HRDI) instrument on UARS. Owing to the multiple, off‐track viewing angles of HRDI, observations in the region affected by the electrons are taken at similar local solar times before, during, and after the electron flux increase. Our analysis limits the relative ozone depletion to values < 10% during the very intense May 1992 HRE. We do observe decreases in the ozone mixing ratio at several points in the diurnal cycle that may be associated with the transport of water vapor into the mesosphere during May 1992. This masking of the precipitating electron effects by the seasonal variations in water vapor can complicate the detection of those effects.
Charge sign dependence of cosmic ray modulation near a rigidity of 1 GV
Authors: Clem J. M. , Evenson P. , Huber D. , Pyle R. , Lopate C. , Simpson J. A.
Published: February 2004

New observations of electron fluxes made in 1997 and 1998 extend our ongoing investigation of the relative modulation of positively and negatively charged particles. We compare electron fluxes measured on high‐altitude balloon flights with continuing observations of helium fluxes from the IMP 8 spacecraft and present new measurements of the primary cosmic ray positron abundance in 1997 and 1998. Electron fluxes during the 1984–1990 period show a flat topped distribution, whereas the positively charged He fluxes show a peaked distribution, with the peak in 1987. This is expected from modulation theory, including the role of drifts when the northern heliospheric magnetic field is inward, and the southern heliospheric field is outward. From 1990 to 1999, data are consistent with an inverse relationship, but electron data are too sparse to allow a definitive statement. Near a rigidity of 1 GV the relative abundance of electrons and helium nuclei is a weak function of the tilt angle of the heliospheric current sheet.
A history of early work on the heliospheric magnetic field
Authors: Parker E. N.
Published: February 2004

The idea of a magnetic field in space around Earth began 400 years ago with Gilbert's recognition that the magnetic field of Earth extends outward into space to form what we now call the magnetosphere. The concept of the solar wind and the heliosphere had its first glimmerings with the recognition, about 270 years ago, that geomagnetic activity is correlated with solar activity. It was suggested about a 100 years ago that the connection is through solar corpuscular radiation with velocities of the order of 103 km/s. The observed acceleration of comet tails indicated the universal nature of solar corpuscular radiation, giving rise to the first speculation on the existence of the heliosphere. The hydrodynamic expansion of the million degree solar corona was then shown to provide the solar wind (solar corpuscular radiation), stretching out the magnetic fields of the Sun to fill the heliosphere with a spiral magnetic field. The advent of the space age soon verified the solar wind and magnetic field with direct measurements.
Lognormal and multifractal distributions of the heliospheric magnetic field
Authors: Burlaga L. F.
Published: February 2004

The heliospheric magnetic field strengthBfluctuates appreciably over a large range of scales in the region from 1 AU to at least 30 AU and throughout the solar cycle. The fluctuations are often extreme and intermittent. For example, the distributions of hour averages of these parameters are usually lognormal to a good approximation, the long tail representing extreme events. The fluctuations can often be described by a multifractal distribution on scales from approximately 12 hours to 27 days or more, reflecting scaling symmetries of various moments of the fluctuations. Statistical variations, burstiness, extreme values, and clusters on various scales are ubiquitous in the time series describing the magnetic field. These properties can be described quantitatively, although not uniquely. Models of the solar wind should at least be consistent with these results. Ultimately, there is a need for physical models that can explain the statistical properties of the observed large‐scale fluctuations.
Evolution of magnetic field fluctuations in high‐speed solar wind streams: Ulysses and Helios observations
Authors: Horbury T. S. , Balogh A.
Published: February 2004

Ulysses magnetic field measurements in high‐speed streams emanating from the Sun's polar coronal holes reveal a complex combination of fluctuations on different scales. Measurements of the wavenumber dependence of radial and latitudinal power scaling, spectral index, and anisotropy of undisturbed polar magnetic field fluctuations between 1.4 and 4.1 astronomical units (AU) are presented. These results confirm earlier work and reveal the presence of three populations: structures at large scales, Alfvén waves at intermediate scales, and turbulent fluctuations at the smallest scales. A significant decrease in power with latitude, as a result of overexpansion of polar coronal holes, has consequences for energetic particle diffusion coefficients. Other results, in particular those related to field magnitude variations, are not well understood at this time. A similar analysis of magnetic field fluctuations in high‐speed streams at low heliolatitudes between 0.3 and 1 AU, measured by the Helios spacecraft, shows consistency with Ulysses measurements, suggesting a common origin for fluctuations in all high‐speed streams.
Eigenmode approach to coronal magnetic structure with differential solar rotation
Authors: Schulz Michael
Published: February 2004

Diffusion of field line foot points in the photosphere couples with latitude‐dependent solar rotation to define an eigenvalue problem, such that coronal magnetic structures derived from certain specific linear combinations of spherical harmonic functions are found to rotate rigidly about the Sun. Such eigenmodes and their corresponding complex eigenfrequencies are readily identified by diagonalizing progressively larger matrix representations of the eigenvalue problem. For azimuthal harmonic number m = 1, the eigenvalue with the least negative imaginary part (≈ −0.6 year−1 for footpoint diffusion coefficient D⊥ = 600 km2s−1 and otherwise roughly proportional to D⊥1/2) corresponds to an eigenmode whose main component is the dipole (n = 1) moment perpendicular to the Sun's rotation axis. Associated values of Re ω11 correspond to heliomagnetic rotation at 99.4% of the Sun's equatorial rate for D⊥ = 600 km2s−1 and otherwise to a retrograde deviation roughly proportional to D⊥1/2 from the Sun's equatorial rotation rate. This eigenmode corresponds to the almost rigidly rotating coronal structure found by Wang et al. [1988] in their numerical simulations of the coronal magnetic field. The associated heliospheric current sheet rotates almost rigidly about the Sun despite the anchorage of adjacent field lines in a differentially rotating photosphere. This particular eigenmode also corresponds most nearly to the nonaxial part of the tilted dipole in the heliospheric model of Fisk [1996], whereby differential solar rotation leads to a latitudinal circulation of field lines through the heliosphere and thus to large‐scale heliospheric convection.
Latitudinal heliospheric magnetic field: Stochastic and causal components
Authors: Jokipii J. R.
Published: February 2004

The transport of energetic charged particles in the heliosphere depends on the structure of the interplanetary magnetic field. The field has both a stochastic part due to turbulence and a causal part due to the regular motions of the plasma. These give rise to the variety of transport effects observed. The stochastic component affects mostly the random walk or diffusive motion of the particles whereas the regular field affects primarily the various drift motions. Of particular interest is the latitudinal transport, which has been constrained by Ulysses observations to the highest latitudes, and which is related closely to the latitudinal magnetic field, both the causal and stochastic components. The observations of corotating‐interaction‐region‐accelerated, low‐rigidity energetic particles on Ulysses are consistent with propagation in a stochastic field superimposed on a Parker spiral, giving some support to the concept. The observations would require a significant cross‐field diffusion. More‐recent observations of energetic particles from impulsive solar flare events show structure on a fine scale which seems also to reflect the field‐line meandering. Large small‐scale gradients normal to the local magnetic field are shown to be completely consistent with significant cross‐field diffusion on larger timescales. A causal latitudinal magnetic field, such as that proposed by Fisk [1996], will also enhance latitudinal transport. This is briefly discussed.
Charge exchange contribution to the decay of the ring current, measured by energetic neutral atoms (ENAs)
Authors: Jorgensen A. M. , Henderson M. G. , Roelof E. C. , Reeves G. D. , Spence H. E.
Published: February 2004

In this paper we calculate the contribution of charge exchange to the decay of the ring current. Past works have suggested that charge exchange of ring current protons is primarily responsible for the decay of the ring current during the late recovery phase, but there is still much debate about the fast decay of the early recovery phase. We use energetic neutral atom (ENA) measurements from Polar to calculate the total ENA energy escape. To get the total ENA escape we apply a forward modeling technique, and to estimate the total ring current energy escape we use the Dessler‐Parker‐Sckopke relationship. We find that during the late recovery phase of the March 10, 1998 storm ENAs with energies greater than 17.5 keV can account for 75% of the estimated energy loss from the ring current. During the fast recovery the measured ENAs can only account for a small portion of the total energy loss. We also find that the lifetime of the trapped ions is significantly shorter during the fast recovery phase than during the late recovery phase, suggesting that different processes are operating during the two phases.
On the drift‐sausage mode in one‐dimensional current sheet
Authors: Yoon Peter H. , Lui A. T. Y.
Published: February 2004

This article presents a two‐fluid stability analysis of Harris current sheet equilibrium under the assumption of charge quasi‐neutrality. It is found that the charge neutrality condition leads to sausage‐type fluctuations, which propagate along the direction of the cross‐field current flow, hence the drift‐sausage mode. It is also shown that solutions which correspond to kink‐type perturbations do not exist under the present assumption of charge neutrality. In view of the fact that a substantial body of simulation works exist which report predominantly kink‐like perturbations, and that analytical theories which do not assume charge quasi‐neutrality predict that the kink‐type mode is a dominant unstable mode, it is concluded that the assumption of quasi‐neutrality may be a poor choice in describing the stability of Harris current sheet equilibrium.
Electrons in the low‐density solar wind
Authors: Ogilvie Keith W. , Fitzenreiter Richard , Desch Michael
Published: February 2004

The recent occurrence of an interval (May 9–12, 1999) of abnormally low density solar wind has drawn attention to such events. The Solar Wind Experiment (SWE) instrument on the Wind spacecraft observed nine similar events between launch (November 1994) and August 1999: one in 1997, three in 1998, and five in January–August 1999. No such events were observed in 1996, the year of solar minimum. This already suggests a strong dependence upon solar activity. In this paper we discuss observations of the electron strahl, a strong anisotropy in the solar wind electrons above 60 eV directed along the magnetic field and observed continuously during the periods of low density in 1998 and 1999. When the solar wind density was less than 2 cm−3, the angular width of the strahl was below 3.5° and the temperature deduced from the slope of the electron strahl phase density (as a function of energy) in the energy range 200–800 eV was 100–150 eV, equivalent to a typical coronal electron temperature. Three examples of this phenomenon, observed on February 20–22, April 26–27, and May 9–12, 1999, are discussed to show their similarity to one another. These electron observations are interpreted to show that the strahl occurs as a result of the conservation of the first adiabatic invariant, combined with the lack of coulomb collisions as suggested by Fairfield and Scudder [1985].
Quasi‐interchange modes and interchange instability in rotating magnetospheres
Authors: Ferrière K. M. , Zimmer C. , Blanc M.
Published: February 2004

Adopting the widely held view that plasma transport in rotating magnetospheres, like those of Jupiter and Saturn, proceeds through the interchange of magnetic flux tubes, we study the physical characteristics and stability properties of interchange motions. We start by examining a broader category of motions containing all the modes driven by buoyancy forces of gravitational or magnetic nature; these modes, known as quasi‐interchanges, fall into two types: type 1, to which the familiar interchange mode belongs, and type 2, in which the plasma moves essentially along magnetic field lines. In the second part of the paper, we focus on the interchange mode, with the purpose of deriving formal analytical expressions for both its dispersion relation and its stability threshold.
Persistent quasiperiodic precipitation of suprathermal ambient electrons in decaying auroral arcs
Authors: Semeter Joshua , Vogt Joachim , Haerendel Gerhard , Lynch Kristina , Arnoldy Roger
Published: February 2004

An analysis of ground‐based images and rocket‐borne electron data from the Physics of Auroral Zone Electrons II rocket experiment suggests that suprathermal ambient electrons, precipitating in field‐aligned bursts, may play an active role in regulating the decay of auroral potential structures. A set of discrete arcs were observed to form in quasiperiodic succession behind a passing westward traveling surge. The nascent arcs faded rapidly, losing 90% of their luminosity within 15s. The fading then abruptly stopped at a brightness consistent with a peak electron energy of ∼ 1.5 keV. Rocket‐borne measurements of energetic electrons over the residual arcs 2 min later revealed a superposition of hot isotropic and cold ionospheric electrons, the latter precipitated in dispersive periodic (3–5 Hz) bursts from a source altitude of 3000–6000 km. A combined analysis of the optical and particle data showed that the FAB component (1) was present for at least l min, (2) precipitated in spatial scales of ∼10 km and (3) carried a number flux comparable to that of the overlying isotropic population. Bulk plasma parameters calculated in the vicinity of the fading arcs revealed an inverse relationship between parallel potential drop and number flux carried by the field‐aligned population.
Discrete electrostatic eigenmodes associated with ionospheric density structure: Generation of auroral roar fine frequency structure
Authors: Yoon P. H. , Weatherwax A. T. , LaBelle J.
Published: February 2004

Radio emissions emanating from the Earth and other planets are often characterized by discrete frequency structures. For example, recent ground‐based observations of auroral roar, an auroral radio emission which occurs near the second and third harmonic of the electron cyclotron frequency, show that it consists of fine frequency structure similar to that of auroral kilometric radiation and other planetary radio emissions. These auroral roar fine structures, sometimes as narrow as a few hertz, often occur in multiplets separated by the order of ≤ 1 kHz which drift up and down in frequency. Theoretical and experimental efforts to explain the generation of auroral roar suggest that in the source region near the F region peak, the quasi‐electrostatic Z mode (or upper‐hybrid) waves are first excited, partly converted to free‐space radio waves and subsequently observed on the ground. Using WKB‐type calculations of the wave mechanics of upper‐hybrid modes in a cylindrical field‐aligned density structure, we show that discrete frequency eigenmodes are a natural consequence of such density structures. Discrete eigenmodes can exist within density enhancements but not within depletions. Cylindrical field‐aligned structures the order of 100 m to several kilometers diameter result in eigenmodes spaced by a few hundred hertz as observed for auroral roar. Since structure of this scale size often occurs in the Earth's auroral ionosphere at F region altitudes, it seems possible that the observed auroral roar fine structure results from this mechanism.
Evidence for interplanetary magnetic field By controlled large‐scale reconnection at the dayside magnetopause
Authors: Marcucci M. F. , Bavassano Cattaneo M. B. , Di Lellis A. M. , Cerulli Irelli P. , Kistler L. M. , Phan T.‐D. , Haerendel G. , Klecker B. , Paschmann G. , Baumjohann W. , Möbius E. , Popecki M. A. , Sauvaud J. A. , Rème H. , Korth A. , Eliasson L. , Carlson C. W. , McCarthy M. , Parks G. K.
Published: February 2004

We report evidence of a long‐lasting reconnection event during which the accelerated plasma flow direction changes in response to an interplanetary magnetic field (IMF) By reversal, indicating a change in the reconnection site location. The observations were made by Equator‐S on the dawn flank of the magnetopause and consist of a large number of plasma jets detected mostly within magnetospheric flux transfer events. The plasma jets were found in quantitative agreement with the theoretical predictions for reconnection. The reversal of the plasma flow direction in the jets following the reversal of the By component not only confirms that the dayside reconnection configuration is controlled by the IMF, as opposed to local control, but also stresses the importance of the IMF dawn‐dusk component, in addition to the north–south component, in determining the global configuration of the reconnection.