bluuebunny/crossref_metadata_2025 huggingface dataset:
The warm Cretaceous climate: Role of the long‐term carbon cycle
Authors: Gérard Jean‐Claude , Dols Vincent
Published: February 2008

An annual energy‐balance model is coupled to a steady state formulation of the long‐term CO2 cycle to investigate the possible sources of the global warming at the Cretaceous. It is found that paleogeography solely is an insufficient factor but that the different latitudinal distribution of continental masses 100 My ago influenced the CO2 cycle and favored a larger content of the atmospheric CO2 level. A larger rate of tectonic activity and the possible influence of the vegetation in a CO2 richer atmosphere provide further sources of atmospheric carbon dioxide increase.

The combination of these factors, together with a more vigorous poleward heat transport, provides CO2 levels 5 to 15 times larger than today and a global surface warming within the 6–1°C estimated from paleoindicators.
A signature of auroral precipitation in the nightside ionosphere of Venus
Authors: Fox J. L. , Taylor H. A.
Published: February 2008

We show here that the densities of mass‐28 ions measured by the Pioneer Venus Orbiter ion mass spectrometer (OIMS) on the nightside of Venus are highly variable and show little correlation with the values of the O+ densities. We have determined the total production rates of mass‐28 ions in the chemical equilibrium region and find that this production rate cannot be explained by known chemical production reactions. We propose that the “excess” production is due to precipitation of electrons into the nightside thermosphere.
Sputter‐produced plasma as a measure of satellite surface composition: The CASSINI mission
Authors: Johnson R. E. , Sittler E. C.
Published: February 2008

Measurements of the co‐orbiting neutral cloud or the plasma produced by sputtering of the icy Saturnian satellites can be used to determine the relative abundance of a minority surface species which would be difficult to determine from reflectance spectra. This is due to the fact that the sputter source rates, hence the plasma supply rates, are directly proportional to the bulk concentrations of mixed solids or clathrates, although the surface grains may be depleted in the most volatile species.
Heliospheric shocks and catastrophe theory
Authors: Burlaga L. F.
Published: February 2008

Various configurations of forward and reverse shocks that occur in the outer heliosphere can be classified using catastrophe theory. The existence of a forward shock is associated with a local maximum of a polynomial, and the existence of a reverse shock is associated with a local minimum of a polynomial. A configuration with N forward shocks and N reverse shocks corresponds to a polynomial with N maxima and N minima. The formation of forward and reverse shocks corresponds to the creation of maxima and minima of a polynomial, which is described by the separatrices of the catastrophes AK. The coalescence of two forward (reverse) shocks corresponds to the situation when two maxima (minima) of a polynomial have equal values, and the interaction of a forward shock with a reverse shock corresponds to a polynomial with a local maximum equal to a local minimum; these situations are described by the Maxwell sets of the appropriate catastrophes.
The Triton torus revisited
Authors: Richardson John D. , Eviatar A. , Delitsky M. L.
Published: February 2008

Prior to the Voyager encounter with Neptune, Delitsky et al. [1989] predicted that a torus of ions emanating from Triton would be discovered. We revisit those predictions in light of the Voyager results. Sputtering of Triton's atmosphere can produce the heavy ion densities inferred at Triton's orbit by the Voyager plasma experiment if the ion residence time is about 30 days. The torus is found to be longitudinally asymmetric near Triton, with peak densities at longitudes of 170° and 350°. The total nitrogen flux due to sputtering is about 2×1021 s−1. The consequences of larger escape fluxes of both N2 and H2 (suggested by Broadfoot et al. [1989]) are investigated; it is difficult to reconcile large escape fluxes with the plasma and ultraviolet spectrometer observations.
Hot plasma parameters in Neptune's magnetosphere
Authors: Krimigis S. M. , Mauk B. H. , Cheng A. F. , Keath E. P. , Kane M. , Armstrong T. P. , Gloeckler G. , Lanzerotti L. J.
Published: February 2008

Energy spectra of energetic protons and electrons (Ep ≳ 28 keV, Ee ≳ 22 keV, respectively) obtained with the Low Energy Charged Particle (LECP) instrument during the Voyager 2 encounter with Neptune on August 24–25, 1989 are presented. The proton spectral form was a power law (dj/dE = KE−γ), outside the orbit of Triton ( ∼ 14.3 RN); inside that distance, it was found to be a hot (kT ≃ 60 keV) Maxwellian distribution. Such distributions, observed in other planets as well, have yet to be explained theoretically. Similarly, the electron spectral form changed from a simple power law outside Triton to a two‐slope power law with a high energy tail inside. Intensity and spectral features in both proton and electron fluxes were identified in association with the crossings of the Triton and 1989 N1 L‐shells, but these features do not occur simultaneously in both species. Such signatures were manifested by relative peaks in both kT and γ spectral indices. Peak proton pressures of ∼2 × 10−9 dynes cm−2, and β ∼ 0.2 were measured at successive magnetic equatorial crossings, both inbound and outbound. These parameters show Neptune's magnetosphere to be relatively undistorted by hot plasma loading, similar to that of Uranus and unlike those of Saturn and Jupiter. Trapped electron fluxes at Neptune, as at Uranus, exceed the whistler mode stably trapped flux limit. Whistler‐induced pitch angle scattering of energetic electrons in the radiation belts can yield a precipitating energy flux sufficient to drive Neptune's aurora.
Low‐energy plasma in Neptune's magnetosphere
Authors: Richardson John D. , McNutt Ralph L.
Published: February 2008

Plasma data from the region of Neptune's magnetosphere between L=6.5 and L= 13.5 are analyzed. Selecting only spectra where both light and heavy ions are present, we derive density and temperature profiles under the assumption that the ions are H+ and N+. These results are used to calculate the total flux shell content (for a shell of unit width in L), N, of each km in this region. Values of N derived from inbound and outbound data are similar, indicating the plasma distribution functions are isotropic. Average values of NL2 are 3×1032 for H+ and 1×1032 for N+. Profiles of NL2 for both H+ and N+ increase outwards, suggesting that Triton is the probable source of both these components. Evidence is presented for significant inbound‐outbound asymmetries in the plasma morphology.
The ionosphere of Triton
Authors: Majeed T. , McConnell J. C. , Strobel D. P. , Summers M. E.
Published: February 2008

We have used a model of the atmospheric temperature structure and composition inferred from the Voyager UVS solar occultations together with a 1‐D chemical diffusive model to interpret the Voyager RSS ingress measurements of Triton's electron density. Although N+2 is the major ion created, N+ produced by dissociative ionization is the dominant ion. Reaction of thermospheric H2, produced by Lyman‐α dissociation of CH4 in the lower atmosphere, is the major loss for N+ ions and maintains these ions in PCSS below 600 km. Solar EUV ionisation cannot generate electron densities at the magnitude measured by the RSS experiment and an additional ionosphere source ∼ 3 × 108 ions cm−2 s−1 is required. The ionosphere may undergo a transition from PCSS to diffusive control if the N+ ion production rates were greater than the H2 flax derived from CH4. In this case the upward flowing H2 is totally converted to H by reaction with N+ and the remaining N+ ions recombine radiatively to create an ionosphere under diffusive control above the peak.
Nitrogen ion clusters in Triton's atmosphere
Authors: Delitsky Mona L. , Turco Richard P. , Jacobson Mark Z.
Published: February 2008

The formation of nitrogen cluster ions [N2+(N2)n, N+(N2)n] should occur easily in Triton's thin cold nitrogen atmosphere. These ions are formed stepwise as: At low altitudes, thermodynamics (temperature and pressure) favour cluster sizes up to and including N2+(N2)40. Such ions are close to the threshold (critical size) to nucleate, forming a stable nitrogen ice aerosol seen as extended hazes in Voyager images of Triton's limb. The critical ion radius for nucleation is about 8.3 Å. As temperature increases and pressure decreases with altitude, cluster ion formation becomes less favorable and small cluster sizes predominate. At altitudes >200 km, clusters are thermodynamically unstable and only N2+ and N+ are present. Because electron recombination with atomic (N+) is very slow, a dense ionosphere should form where N+ recombination via N+ clustering with N2 is unfavorable. Model calculations yield peak electron concentrations above 200 km, as detected by Voyager radio occultation measurements. The sharp ledge at the bottom of the ionosphere is caused by the onset of rapid electron‐ion recombination associated with duster ion formation.
Near‐fault measurement of postseismic slip associated with the 1989 Loma Prieta, California, Earthquake
Authors: Rymer Michael J.
Published: February 2008

Five small‐aperture (0.5 to 7.7 m) quadrilaterals were installed across the San Andreas fault and newly formed extensional cracks shortly after the October 17, 1989 Loma Prieta M7.1 earthquake. Two quadrilaterals were installed across the San Andreas fault near the southeast and northwest ends of the 1989 rupture, and three were installed across dominantly extensional cracks in the Summit Road area near the main‐shock epicenter and off the San Andreas fault. Measurements of line‐length changes from as early as 4 d up to 184 d after the earthquake in the nail quadrilaterals indicate a small amount of right‐lateral postseismic slip on the San Andreas fault. The site near the southeast end of the 1989 afterstock zone on the San Andreas fault showed about 5±2 mm of postseismic right‐lateral component of slip in addition to 23 mm of right‐lateral coseismic movement. The site near the northwest end of aftershocks likewise showed about 5±2 mm of postseismic slip, but after only 5 mm of coseismic slip. Measurements at sites across extensional cracks indicate possible minor left‐lateral postseismic slips, and possible extensional/contractional motion. No measurements were made of possible vertical movements. Sites on extensional cracks showed similarly small amounts of possible postscismic lateral slip, from ∼2 to 10 mm, even though coseismic lateral slips were much greater (up to 410 mm) than on the surface trace of the San Andreas fault. The small slip values, in spite of uncertainties, clearly show that the lack of coseismic surface slip associated with the earthquake was not followed by large postseismic slip.
Equatorial gyroresonance between electrons and magnetospherically reflected whistlers
Authors: Jasna D. , Inan U. S. , Bell T. F.
Published: February 2008

Magnetosphericaily reflected whistlers resonantly interact with energetic (of order 100 keV) electrons in a relatively narrow energy range during multiple equatorial crossings over a wide range of L‐shells (1.5 < L < 4). Results indicate that wave energy that enters the magnetosphere at a fixed location can potentially contribute to the loss of particles over a wide range of latitudes.
Laboratory investigation of shuttle glow mechanisms
Authors: Caledonia G. E. , Holtzclaw K. W. , Green B. D. , Krech R. H. , Leone A. , Swenson G.
Published: February 2008

A fast oxygen atom source was used to investigate the Shuttle glow phenomena in the laboratory. Both room temperature and cooled targets were dosed with NO and then irradiated by 8 km/s oxygen atoms. The observed fluorescence is spectrally similar to that seen on the Shuttle supporting previous suggestions that recombination of O with surface bound NO is the responsible mechanism for the visible Shuttle glow.
Frequency spectra of mesospheric wind fluctuations observed with the MU radar
Authors: Muraoka Yoshikazu , Fukao Shoichiro , Sugiyama Takuya , Yamamoto Mamoru , Nakamura Takuji , Tsuda Toshitaka , Kato Susumu
Published: February 2008

Spectral analysis was made for mesospheric radial wind velocities estimated from the measurement of Doppler‐shifted echo power by the MU radar at Shigaraki (34.9°N, 136.1°E), Japan. In this paper we give an overview of the data and present the frequency spectra of the radial winds at altitudes of 74 to 77 km. Under quiet wind conditions, the frequency spectra for the vertical winds show an almost flat response in between the inertial and Brunt‐Väisälä (fB) frequencies with the peak at a frequency a little lower than fB. The frequency spectra for the other oblique winds have an approximate f−2 spectral slope with a weak peak at the same frequency as the vertical one. These features are consistent with the results given by a theoretical spectral model of gravity waves and suggest that the observed wind fluctuations are caused by gravity waves.
Atmospheric carbon monoxide: Latitudinal distribution of sources
Authors: Khalil M. A. K. , Rasmussen R. A.
Published: February 2008

Based on our global measurements of CO, taken over 2–8 years at 16 sites, we have estimated the latitudinal and seasonal distributions of the sources. We find that the most concentrated sources of CO, amounting to some 30% of the global production, are in the industrialized regions bounded by 30° N and 50° N. About 47% of CO comes from the whole of the mid‐northern latitudes and another 40% comes from the tropics. Our calculations show that the production of CO is significantly higher during spring and summer, particularly in the industrialized middle northern latitudes. From these results it is apparent that the observed seasonal cycle of CO concentrations cannot be explained by the seasonal variation of OH alone.
Can existing climate models be used to study anthropogenic changes in tropical cyclone climate?
Authors: Broccoli A. J. , Manabe S.
Published: February 2008

The utility of current generation climate models for studying the influence of greenhouse warming on the tropical storm climatology is examined. A method developed to identify tropical cyclones is applied to a series of model integrations. The global distribution of tropical storms is simulated by these models in a generally realistic manner. While the model resolution is insufficient to reproduce the fine structure of tropical cyclones, the simulated storms become more realistic as resolution is increased. To obtain a preliminary estimate of the response of the tropical cyclone climatology, CO2 was doubled using models with varying cloud treatments and different horizontal resolutions. In the experiment with prescribed cloudiness, the number of storm‐days, a combined measure of the number and duration of tropical storms, undergoes a statistically significant increase in the doubled‐CO2 climate. In contrast, a smaller but significant reduction of the number of storm‐days is indicated in the experiment with cloud feedback. In both cases the response is independent of horizontal resolution. While the inconclusive nature of these experimeital results highlights the uncertainties that remain in examining the details of greenhouse gas induced climate change, the ability of the models to qualitatively simulate the tropical storm climatology suggests that they are appropriate tools for this problem.
A simple method to estimate the fractal dimension of a self‐affine series
Authors: Malinverno Alberto
Published: February 2008

Time/space series of natural variables (e.g., surface topography) are often self‐affine, i.e., measurements taken at different resolutions have the same statistical characteristics when rescaled by factors that are generally different for the horizontal and vertical coordinates. Self‐affinity implies that the standard deviation measured on a sample spanning a length w is proportional to wH = w2 − D, where H is the Hurst exponent and D is the fractal dimension (1 ≤ D ≤2 for a fractal series). In this paper, a “roughness‐length” method based on this property of self‐affine series is presented. In practice, the root‐mean‐square roughness is computed in a number of windows of varying length w, and H is measured from the slope of a log‐log plot of roughness versus w. Montecarlo simulations show that the fractal dimension as measured by the roughness‐length method is approximately the same as that defined by the power spectrum. The roughness‐length method is closely related to the grid fractal dimension, is simple to implement, and can be applied to non‐uniformly spaced series.
Multi‐satellite measurements of the substorm injection region
Authors: Reeves G. D. , Fritz T. A. , Cayton T. E. , Belian R. D.
Published: February 2008

Measurements of energetic particles obtained with a set of three geosynchronous satellites (1977‐007, 1981‐025, and 1982‐019) are used to investigate the substorm injection region and particle drifts for an event on Feb. 3, 1983. A technique has been developed which allows remote sensing of the boundaries of the substorm injection region and the injection time by using measured energy dispersion and modeling particle drifts within the semi‐empirical magnetospheric field model of Tsyganenko and Usmanov [1982]. The injection region for this event was found to span 90° around local midnight. The presence of spacecraft on either side of the injection region limit possible errors. Good agreement between long and short drift paths is found for ions while electron measurements give less reliable results.
Magnetic reconnection in the magnetotail current sheet for varying cross‐tail magnetic field
Authors: Hesse Michael , Birn Joachim
Published: February 2008

Three‐dimensional magnetic reconnection is investigated by means of resistive MHD simulations on the basis of magnetotail models with various magnitudes of the average net cross‐tail magnetic field component. Typical quantities such as parallel electric fields, reconnected flux and flow velocities are studied to determine the influence of increasing By values on the fast dynamical evolution of the magnetotail. We find that a cross‐tail magnetic field of less than about 10% of the maximum lobe field strength, as typically observed, has little influence on the dynamic evolution. The dynamic growth becomes considerably suppressed for a cross‐tail field of about 25% of the lobe field strength, which is in the maximum observed range.
Ion composition in and near the frontside boundary layer
Authors: Eastman T. E. , Greene E. A. , Christon S. P. , Gloeckler G. , Hamilton D. C. , Ipavich F. M. , Kremser G. , Wilken B.
Published: February 2008

A key problem in unfolding the physics of magnetospheric boundary layers is that of clearly identifying ion source and transport characteristics. Direct measurements of ion composition near the magnetopause have recently demonstrated the existence of the ionospheric species O+ and He+ as well as the solar wind species He++ within the magnetospheric boundary layer. Based on a select group of 13 boundary layer crossings by the AMPTE/CCE spacecraft and using the Charge‐Energy‐Mass Spectrometer (CHEM) of the University of Maryland and Max‐Planck‐Institut für Aeronomie/Lindau, we have clearly identified several additional ion species that overlap the boundary layer. Ion species of ionospheric origin such as O+, N+, He+, and the molecules NO++O2+, as well as solar wind ions such as He++ and the high charge‐state groups of CNO, Si, and Fe, are found in the frontside, low‐latitude boundary layer. By comparing ratios of ion number densities observed in each of the 13 crossings, we find that ion densities in the boundary layer are roughly one‐half those observed in the respective source regions. On average, only 1 to 9% of ions are found in the region on the other side of the boundary layer away from their respective source region. Our observations indicate that such transport across the boundary layer is a one‐way process with dawn‐dusk asymmetry. Individual ion density ratios from which these various averages are obtained cover a very wide range of values indicating large spatial or time variability. These results are not consistent with any simple steady state process for producing the boundary layer; however, our analysis to date cannot distinguish between possible non‐steady state processes such as impulsive penetration or non‐steady reconnection. In summary, the boundary layer is a region of overlap of ions of both solar wind and magnetospheric origin with high variability in ratios of ion densities.
Biologically effective ultraviolet radiation, total ozone abundance, and cloud optical depth at McMUrdo Station, Antarctica September 15 1988 through April 15 1989
Authors: Stamnes Knut , Slusser James , Bowen Melissa , Booth Charles , Lucas Timothy
Published: February 2008

Spectral measurements of solar ultraviolet (UV) radiation taken at McMurdo Station, Antarctica arc used to determine biologically effective UV dose, ozone column content, and effective cloud optical depth. The seasonal variation in these parameters from September 15, 1988 through April 15, 1989 is presented and discussed. Although no days from September 15 through October experienced UV dose exceeding that occurring at summer solstice, the temporal variation in the level of UV radiation is markedly asymmetric with respect to summer solstice. A general enhancement by about 20% in biologically effective UV dose in October, 1988 compared to March, 1989 is clearly evident. The main cause of this asymmetry appears to be the coincident deficiency in ozone abundance by about 8% in spring compared to fall. The percent increase in UV dose per percent decrease in ozone abundance is about 2.5 in agreement with theoretical predictions. The total ozone amount is generally depleted (to about 250 DU) during October 1988, but there are large day‐to‐day fluctuations. Presumably these fluctuations are caused primarily by the motion of the polar vortex. After summer solstice UV radiation levels and ozone amounts exhibit much less pronounced day‐to‐day fluctuations. No spring/fall asymmetry in cloudiness, as it affects the surface ultraviolet radiation budget, is discernible from the measurements if the surface albedo is assumed to vary symmetrically around solstice.
Role of carbon dioxide in cooling planetary thermospheres
Authors: Sharma Ramesh D. , Wintersteiner Peter P.
Published: February 2008

A new value of the rate coefficient for the deactivation of the bending mode of carbon dioxide by atomic oxygen at low temperatures is derived from the observation of 15 μm emission from the atmosphere of the Earth. This new value gives a cooling rate for the lower thermosphere that is two to three times the rate previously calculated, and it may resolve a long‐standing problem in the Mars‐Venus aeronomy.
Terrestrial cometary tail and lunar corona induced by small comets: Predictions for Galileo
Authors: Dessler A. J. , Sandel B. R. , Vasyliunas V. M.
Published: February 2008

A search for small comets near 1 AU is an objective of the Galileo mission. If small comets are as numerous and behave as has been proposed, two near‐Earth signatures of small comets should be observable by the UVS experiment on the Earth flybys of Galileo: ( 1 ) a comet‐like tail of Earth created by small comets that come close to Earth, break up and vaporize, but just miss the atmosphere and proceed back into interplanetary space, and (2) a corona surrounding the Moon induced by lunar impact of small comets.
Status of the OH contribution to the surface glow detected from the Dynamics Explorer satellite
Authors: Copeland Richard A. , Slanger Tom G.
Published: February 2008

A Fabry‐Perot interferometer on the DE‐2 satellite measured a surface glow near 732 nm at an altitude of 250 km. By comparison with the mesospheric nightglow, the hydroxyl radical (OH) was implicated as the fluorescing species. Unfortunately, the identification was not clear cut, since the spectrum showed an additional feature not observed in the nightglow. Calculations indicated that this feature could originate from ground state OH vibrational levels well above die energetic limit of v = 9 for the reaction of H + 03. Until recently, existing spectroscopic data were inadequate for a positive identification of all the features in the Fabry‐Perot spectrum. New laboratory data coupled with accurate spectroscopic fitting indicate that the position of the additional feature is consistent with its identification as the P2(5) doublet of the (11,5) vibrational band of OH.
A mechanism for crustal thinning without lateral extension
Authors: Schmeling Harro , Marguart Gabriele
Published: February 2008

In some continental regions thin crust is found without observing significant indications of extensional tectonics. We argue that in such regions upwelling mantle flows may give rise to sublithospheric loading stresses which may be able to squeeze out the ductile lower crust, but leave the upper crust and sub‐crustal lithosphere essentially unstretched. This model allows us to constrain the viscosity of the lower crust if the amount and time scale of crustal thinning is observed in any subsidence basin. We applied our model to the Pannonian Basin (Hungary) and found lower crustal viscosities between 1020 and 1021 Pa s. Comparing this viscosity with laboratory data of crustal rocks results in lower crustal temperatures of about 600 to 800°C, which are in good agreement with geothermal models. Our model might also help to understand the appearance of a very thick crust and lithosphere without any pronounced topography as it is found in Fennoscandia.
Approach to the volcanic tremor by covariance analysis: Application to the 1989 eruption of Mt. Etna (Sicily)
Authors: Ferrucci F. , Godano C. , Pino N. A.
Published: February 2008

Polarization of the tremor wavefield, recorded during three periods of the 1989 eruption of Mt. Etna at a temporary array of three‐component stations, is analyzed by use of a polarization filter. The tremor shows steady horizontal, near‐linear, west‐east polarization at all stations. Such a behaviour, which could be coherent with a P‐wavefield radiated by a vertical extended source with overall north‐south alignment, excludes confinement of the source to the only active vent and is tentatively linked to activity of the main dyke‐system of Mt. Etna.
Elastic properties of the pyrope‐majorite solid solution series
Authors: Yeganeh‐Haeri Amir , Weidner Donald J. , Ito Eiji
Published: February 2008

The adiabatic elastic properties of two synthetic polycrystalline garnets, with an average grain size of 0.8 micron, and with compositions of 67% pyrope‐33% majorite and 66% majorite‐34% pyrope, have been measured at ambient conditions by Brillouin spectroscopy. Within the experimental uncertainties the measured bulk and shear moduli of the two majorites are comparable to those of pyrope. The dissolution of pyroxene in the garnet structure therefore, does not significantly affect the elastic properties in the pyrope‐majorite solid solution series.
Acceleration of solar wind He++3. Effects of resonant and nonresonant interactions with transverse waves
Authors: Hollweg Joseph V. , Turner James M.
Published: February 2008

Simple models are described which investigate the combined effects on solar wind He++ of resonant and nonresonant acceleration by left‐hand transverse waves. The principal points are the following. (1) For a wide range of parameters, (υα – υp) at 1 AU is close to the effective phase speed of the left‐hand waves. (2) The most important factor in determining υα/υp at 1 AU is whether the high‐frequency left‐hand waves are predominantly outward propagating, inward propagating, or a mix of both. The resonant acceleration may be more important than the effects of heating or stream‐stream interactions. (3) Reasonable values of υα/υp at the sun (and of nα/np at 1 AU) are obtained for a power law index α ≅ 1.5 in the wave power spectrum if the effective phase speed of the resonant waves near the sun is not small in comparison to the Alfvén speed there. This requires a substantial level of high‐frequency power in outward going waves at the sun, which cannot come from heat‐conduction‐driven instabilities. (4) The present models do not allow one to decide whether the coronal He++ abundance is greater or less than that at 1 AU. (5) Some of the models show a positive correlation between nα/np and υp at 1 AU, roughly as has been observed. (6) The models suggest that variations in nα/np at 1 AU can result from variations in the wave properties near the sun and not necessarily from variations in the coronal abundance. (7) Some models indicate that (υα/υp) may decrease with increasing r in the vicinity of 1 AU. (8) The resonant acceleration is more efficient than Coulomb friction in the sense that it does not exhibit a runaway effect. (9) Observations of minor species may be used to deduce wave properties and plasma processes in the solar wind.
Stormtime Pc 5 magnetic pulsations observed at synchronous orbit and their correlation with the partial ring current
Authors: Barfield Joseph N. , McPherron Robert L.
Published: February 2008

Stormtime Pc 5 pulsations are a class of magnetic pulsations observed at synchronous orbit most frequently during the main phase of magnetic storms. The waves are linearly polarized in a meridian plane with nearly equal compressional and transverse components. The waves usually accompany a depression in local field magnitude associated with the onset of a magnetospheric substorm. In this paper, we use local time‐universal time maps of mid‐latitude magnetic perturbations to study the association of these waves with the development of the partial ring current. We find that these waves occur at the local time of maximum development of the partial ring current, at or shortly after the onset of a magnetospheric substorm. These results confirm our earlier speculation based on satellite data alone that the waves are associated with substorm enhancement of the partial ring current.
Electron cooling by excitation of carbon dioxide
Authors: Morrison Michael A. , Greene Arthur E.
Published: February 2008

The cooling of a heated electron gas by electron impact excitation of CO2 is believed to be an important process in the neutral atmospheres of Mars and Venus. Electron energy loss rates are calculated for a variety of excitation processes as a function of electron temperature at a CO2 gas temperature of 200 K. Vibrational excitation is found to be the most efficient cooling mechanism for the range of electron temperatures studied. The contributions of various vibrational energy loss processes to electron cooling are discussed.
Small‐scale transverse magnetic disturbances in the polar regions observed by Triad
Authors: Saflekos N. A. , Potemra T. A. , Iijima T.
Published: February 2008

Small‐scale transverse magnetic field disturbances are often observed with the magnetometer experiment on board the Triad satellite at latitudes poleward of the large‐scale field‐aligned current regions associated with auroral phenomena (Iijima and Potemra, 1976b). In contrast with the magnetic variations associated with the large‐scale auroral field‐aligned currents the polar cap magnetic variations are smaller in amplitude (∼100 γ) and show variations over smaller latitude ranges (∼0.2°). The small‐scale variations are transverse to the main geomagnetic field and therefore explainable by field‐aligned currents, but these currents are not necessarily sheets aligned in the geomagnetic east‐west direction as the auroral field‐aligned currents often are. The small‐scale disturbances occur most frequently in the morning sector (between approximately 0300 and 0900 MLT) up to ∼82° invariant latitude during a wide range of Kp. The amplitudes of the polar magnetic variations show little correlation with Kp, but they are observed more frequently at lower invariant latitudes during disturbed geomagnetic conditions. The frequency of occurrence of the small‐scale magnetic variations is correlated with the azimuthal direction of the interplanetary magnetic field (IMF). They are observed in the north polar cap twice as often during periods when the IMF is directed away from the sun than when it is directed toward the sun. The situation is reversed in the southern hemisphere, where the small‐scale variations are observed more than twice as often during periods when the IMF direction is toward the sun compared with periods when the IMF is away from the sun. There is no obvious dawn‐dusk asymmetry of the occurrence distribution of the polar magnetic variations which is related to the IMF. These observations contribute to the mounting evidence for the direct connnection of earth magnetic field lines to those of the solar wind and the ready access of charged particles to the polar regions.
A note on lunar tides in the ionosphere
Authors: Evans J. V.
Published: February 2008

Considerable progress has been made recently in elucidating the importance of various solar tides in generating winds, electric currents, and polarization fields in the ionosphere. From incoherent scatter radar observations at Arecibo, St. Santin, and Millstone Hill it appears that high‐order (2, 4) and (2, 5) semidiurnal tides dominate in the height interval 105–125 km and contribute significantly to the generation of the solar quiet (Sq) dynamo current. These tides are thought to be excited by energy coupled out of the fundamental (2, 2) semidiurnal mode in the mesosphere through the presence of background winds. This paper suggests that by analogy with the behavior of the solar thermal tides the lunar gravitational (2, 2) tide also may generate higher‐order modes. In this event, lunar tidal influences on the ionosphere, which invariably have been attributed to the (2, 2) mode, should be reexamined. It appears that phenomena such as the lunar height variations of the E layer might better be explained as arising from the lunar (2, 4) rather than the fundamental (2, 2) mode.
Rigidity‐independent propagation of cosmic rays in the solar corona
Authors: Newkirk Gordon , Wentzel Donat G.
Published: February 2008

The delay in arrival times at the earth of solar cosmic rays has traditionally been explained in terms of diffusive transport within the corona to locations distant from the flare site and subsequent escape followed by interplanetary propagation more or less along the spiral field. The mechanism of such diffusive coronal transport has often been thought to be pitch angle scattering by irregularities in the coronal magnetic field. Recently, Ma‐Sung et al. have noted that the time delays attributed to the coronal portion of the propagation for electrons between 0.5 and 12 MeV and protons between 4 and 100 MeV are independent of rigidity and energy. It is demonstrated that the observed delays, their independence of rigidity over 2 orders of magnitude, and the absence of significant losses of particles in traveling large distances in the corona are inconsistent with propagation by continuous diffusion by pitch angle scattering for any reasonable topology of the coronal magnetic field. We propose an alternate mechanism for the coronal transport of solar cosmic rays: the bird cage model, in which particles are normally transferred between adjacent flux tubes by field line reconnection produced by the rearrangement of the field in the supergranulation network. The observed size of coronal flux loops and the rate of reorganization of flux in the supergranulation network lead to ‘diffusion’ rates which are both independent of rigidity and energy and consistent with the observed propagation rates.
Global morphology of nitric oxide in the lower E region
Authors: Cravens T. E. , Stewart A. I.
Published: February 2008

Measurements of nitric oxide at 105 km by the ultraviolet nitric oxide experiment on Atmosphere Explorer C are presented. The amount of nitric oxide in the lower E region is shown to depend on latitude, longitude, and magnetic activity. Near the equator the density at the peak of the NO layer is typically about 2 × 107 cm−3 and varies little with longitude or magnetic activity, except during major storms. At high latitudes (up to 68° geographic latitude), peak densities are typically 2 or 3 times larger and much more variable. A longitudinal dependence is found in both geographic and geomagnetic coordinates, with minimum densities found near 45°E geomagnetic longitude and maxima near 135°W geomagnetic longitude. At 40° dip latitude the half amplitude is about 30%.
Simultaneous observations of the Na 5893‐Å nightglow and the distribution of sodium atoms in the mesosphere
Authors: Clemesha B. R. , Kirchhoff V. W. J. H. , Simonich D. M.
Published: February 2008

Simultaneous laser radar observations of the vertical distribution of sodium in the mesosphere and the intensity of the sodium nightglow show that variations in the glow are well correlated with perturbations in the sodium density. These perturbations have a wavelike structure, with a vertical wavelength of about 10 km, and show downward phase propagation. On most occasions the airglow is best correlated with the density at 88 km, which is about 4 km below the average height of maximum sodium concentration. It is shown that, on the average, a layer 10 km wide centered on 89 km best explains the observed variations. By using current models for atomic oxygen and ozone it is shown that such a distribution is in good agreement with the Chapman mechanism for the sodium nightglow with respect to its height and width but that the calculated emission is about 50 times too small.
Nighttime dynamics of the F region near Arecibo as mapped by airglow features
Authors: Sobral J. H. A. , Carlson H. C. , Farley D. T. , Swartz W. E.
Published: February 2008

Red line (6300 Å) airglow measurements have been made at Arecibo (29°N geomagnetic latitude) by using a scanning photometer in order to determine the direction and phase velocity of propagation of major airglow enhancements, which incoherent scatter and ionosonde measurements have shown are in turn associated with pronounced descents of the F region. The scans were made in the N‐S direction on 13 nights and in the E‐W direction on five nights. The most common type of descent is observed first to the south and then progresses northward, with an apparent phase velocity of the order of 300 m/s. Neutral winds are apparently the cause of this type of descent, and future models of upper atmospheric diurnal pressure patterns should be consistent with this large‐scale regular nighttime feature. Descents of the equatorial ionosphere were observed from ionogram data to occur 2–3 hours earlier than this type of airglow enhancement at Arecibo. The equatorial descents are caused by electric fields and do not directly drive the descent at Arecibo, but both are ultimately driven by the global neutral pressure gradients and resulting winds. A second type of enhancement, seen on occasion and probably due to traveling ionospheric disturbances, was observed to travel from north to south with comparable velocities. A third type does not seem to correspond to anything previously reported in the literature. Sudden descents lasting an hour or so sometimes occurred nearly simultaneously over regions extending at least 1000 km in the N‐S or E‐W direction.
On the role of the ionosphere in substorms: Generation of field‐aligned currents
Authors: Goldstein H. , Schindler K.
Published: February 2008

The onset of a substorm is widely understood as an instability of the magnetosphere‐ionosphere system. A promising candidate for the instability is the ion‐tearing mode (Schindler, 1974). The treatment of Galeev and Zelenyi (1976) shows that during the expansion phase, electric potentials may arise in the plasma sheet if the magnetosphere is regarded as an isolated system. In the present approach we consider the influence of ionospheric conductivity. We find that the occurrence of several neutral lines in the tail, created by the tearing mode, would generate a series of sheets of Birkeland currents. In the present highly simplified picture these sheets are aligned in the east‐west direction; adjacent sheets carry currents of opposite signs. The results are shown to be in agreement with the observed multiple‐sheet structure. The total current per sheet is estimated to be of the order of 106 A.
Adiabatic modulation of equatorial pitch angle anisotropy
Authors: Kaye S. M. , Lin C. S. , Parks G. K. , Winckler J. R.
Published: February 2008

Particle measurements from the University of Minnesota detector aboard the geostationary ATS 6 satellite reveal striking equatorial pitch angle anisotropies. A study of 7 days of data shows a diurnal variation in anisotropy with J(α=40°) > J(α=90°) during times of low |B| on the nightside and J(α=90°) > J(α=40°) during times of high |B| on the dayside. Six representative anisotropy events are studied in finer detail. The 32‐ to 51‐keV electron anisotropies increase and decrease with the total magnetic field intensity. The proton and higher energy electron anisotropies do not show as much variation. The particle anisotropies are studied in light of adiabatic and cyclotron resonance theory; the results indicate that adiabatic effects are the dominant modulation mechanism of particle pitch angle distributions in the outer radiation belt.
Detached auroral arcs in the trough region
Authors: Anger C. D. , Moshupi M. C. , Wallis D. D. , Murphree J. S. , Brace L. H. , Shepherd G. G.
Published: February 2008

The region of auroral emissions is normally terminated on its equatorward side by a regular and well‐defined boundary of diffuse aurora. We report here the observation of arclike auroral emissions in the northern hemisphere equatorward of this boundary, apparently in the ionospheric trough region. These ‘detached arcs’ always have a pronounced drop in intensity at their eastern extremity, equatorward of the diffuse aurora. The arcs show a pronounced local time and longitude dependence which yields an observing probability (for the Isis 2 satellite scanning photometer) in excess of 25% in the vicinity of 270° corrected geomagnetic longitude at 1800 hours corrected geomagnetic time. The arcs are not correlated in any obvious way with Kp or Dst, and they do not show any enhancement in 6300‐Å emission or electron temperature relative to normal aurora findings, leading to the conclusion that they are probably not related to stable auroral red arcs.
Group velocity of whistlers in a two‐ion plasma
Authors: Leer Egil , Johansen K. M. , Albrigtsen R.
Published: February 2008

Computations of the group velocity of whistlers in a two‐ion plasma show that a quasi‐longitudinal (QL) right‐handed polarized wave (electron wave) has a minimum group velocity at the so‐called crossover frequency; a QL left‐handed polarized wave has a maximum group velocity at the same frequency. A quasi‐transverse (QT) electron wave has a minimum group velocity at the ion hybrid frequency. In an oxygen/hydrogen plasma this minimum occurs only for almost perpendicular waves, whereas in a helium/hydrogen plasma it occurs also for waves propagating off perpendicular to the magnetic field. We also find that a small concentration of helium in a hydrogen plasma introduces a ‘stop band’ for quasi‐transverse waves with frequencies just above the helium gyrofrequency. The theoretical results are used to interpret satellite observations of quasi‐transverse low‐frequency whistlers.
Spread F bubbles: Nonlinear Rayleigh‐Taylor mode in two dimensions
Authors: Hudson Mary K.
Published: February 2008

Analytic results on the nonlinear evolution of the Rayleigh‐Taylor instability into equatorial spread F bubbles are presented. The nonlinear saturation amplitude and k spectrum of the inertia‐dominated Rayleigh‐Taylor instability is computed in two dimensions (east‐west and vertical). Analogous to the collisional case, the dominant nonlinearity is found to be two dimensional. The linearly most unstable modes which are primarily horizontal (kx < ky) saturate by nonlinear generation of vertical spatial harmonics which may be damped by either recombination or diffusion. The resulting 1/kx amplitude spectrum is consistent with observations and suggests that bubbles will be vertically elongated in the inertial as well as collisional regimes.
Dynamic MHD modeling of solar wind corotating stream interaction regions observed by Pioneer 10 and 11
Authors: Dryer M. , Smith Z. K. , Smith E. J. , Mihalov J. D. , Wolfe J. H. , Steinolfson R. S. , Wu S. T.
Published: February 2008

An opportunity to test an MHD one‐dimensional time‐dependent model of corotating solar wind streams presented itself during the period from September 30 to November 25, 1973, when Pioneer 11 and Pioneer 10 were near radial alignment with the sun. This observational period was characterized by five or six corotating interaction regions which streamed past the two spacecraft. Conditions were well suited for a comparison with the one‐dimensional MHD model because of the presence of two prerequisites: (1) multiple‐spacecraft radial alignment and (2) temporally varying conditions at the solar wind source. Plasma and magnetic field observations at Pioneer 11, located at approximately 2.8 AU, are used as the input (or forcing functions) for the model of Steinolfson et al. (1975a, b). The outputs, consisting of the solar wind velocity, density, proton temperature, azimuthal magnetic field, and the various energy and mass fluxes, are directly compared with the observations by Pioneer 10, which was located at approximately 4.9 AU. The test of the theoretical model was successful in the sense that both the phasing of the streams and the various solar wind properties were satisfactorily reproduced. The amplitudes of the radial velocity, density, and azimuthal magnetic field were also reasonably well predicted; the proton temperature, however, generally peaked at values about twice those observed. A limitation of the model, the neglect of thermal energy exchange, was thereby revealed. One of the streams was also analyzed in greater detail. The MHD simulation satisfactorily predicted features such as the development of the forward and reverse shocks as well as the interface between them, the increasing displacement between these shocks with heliocentric distance, and the local magnetic field maxima between the shocks. Generally, our results lead us to suggest that future study should be directed to the roles of collective proton‐electron interactions and thermal conduction within one‐ and two‐dimensional time‐dependent MHD flows.
Ultraviolet extinction measurements of molecular oxygen density
Authors: Carver J. H. , Davis L. A. , Horton B. H. , Ilyas M.
Published: February 2008

Observations of the atmospheric extinction of solar ultraviolet radiation in the 142‐ to 149‐nm and 155‐ to 168‐nm bands have been used to determine molecular oxygen densities over the 100‐ to 160‐km altitude range in a series of rocket flights from Woomera, Australia (31°S, 136.5°E). Comparison of data from morning and evening flights made on the same day (October 2, 1974) indicates that the evening density in the 107–118 km region was approximately 1.5 times that observed in the morning. With the exception of the sole evening flight, all the measurements in the 100‐ to 120‐km region are significantly below the mean Cira (1972) model. Observations made following a period of magnetic disturbance with Kp = 4+ indicate that the molecular oxygen density near 150 km was enhanced by a factor of about 1.5 compared with similar observations made under quiet conditions with Kp = 1−.