bluuebunny/crossref_metadata_2025 huggingface dataset:
Particle simulation of Langmuir turbulence during ionospheric heating
Authors: Clark K. L. , Payne G. L. , Nicholson D. R.
Published: February 2008

Ionospheric heating leads to strong Langmuir turbulence including modulational instability, soliton formation, and spatial collapse. The Zakharov model usually used to describe these effects contains a low‐frequency ion‐acoustic wave equation which cannot be rigorously justified in the ionosphere where the electron and ion temperatures are comparable. In the present work, the low‐frequency physics is described by a many‐ion computer simulation. While some differences are found, the results for the most part confirm the earlier, much less difficult, Zakharov calculations.
Search for lightning‐induced electron precipitation with rocket‐borne photometers
Authors: Massey R. D. , McCarthy M. P. , Parks G. K.
Published: February 2008

Photometers at 3914Å and 5577Å and an optical imager were part of an experimental package launched on a sounding rocket in the 1987 Wave Induced Particle Precipitation (WIPP) campaign at Wallops Island, Virginia. The objective was to measure lightning‐induced electron precipitation (LEP) by means of its optical signature. This was the first attempt to measure LEP using rocketborne optical instrumentation. Launch criteria included nearby thunderstorm activity and ground‐based observations of Trimpi events. Lightning flashes are clearly discernible in the data. The photometer data was also characterized by large spin and precession modulations in the photon count rate, consistent with elevated steady particle fluxes in the northern portion of the instrument field of view. No evidence of LEP was observed by the photometers or onboard particle detectors [Arnoldy and Kintner, 1989]. Analysis of the data has enabled us to place an upper limit of 8 × 10−4 ergs‐cm−2‐sec−1 on any burst precipitation energy flux that may have occurred during the rocket flight in the regions explored by the photometers.
Intense ionospheric electric and magnetic field pulses generated by lightning
Authors: Kelley M. C. , Ding J. G. , Holzworth R. H.
Published: February 2008

Electric and magnetic field measurements have been made in the ionosphere over an active thunderstorm and an optical detector onboard the same rocket yielded an excellent time base for the study of waves radiated into space from the discharge. In addition to detection of intense, but generally well understood whistler mode waves, very unusual electric and magnetic field pulses preceded the 1–10 kHz component of the radiated signal. These pulses lasted several ms and had a significant electric field component parallel to the magnetic field. No known propagating wave mode has this polarization nor a signal propagation velocity as high as we have measured. We have investigated and rejected an explanation based on an anomalous skin depth effect. Although only a hypothesis at this time, we are pursuing a more promising explanation involving the generation of the pulse via a nonlinear decay of whistler mode waves in the frequency range 10–80 kHz.
Phase delays in transverse disturbances in the Earth's magnetosheath
Authors: Gleaves D. G. , Southwood D. J.
Published: February 2008

We have used ISEE 1 and 2 data to analyse a transverse magnetic disturbance in the afternoon sector of the Earth's magnetosheath. The disturbance, which evolved over a five minute period, had the appearance of a linearly polarised Alfven wave. Its most notable feature was the high level of spatial coherence in the signal at ISEE 1 and 2 which were 890 km apart. Points of common phase arrive at the two spacecraft with a clearly discernible time difference which we determined using a cross‐spectral technique. These estimates are compared to the predicted behaviour of MHD waves with similar polarizations to infer probable wave directions. We find that the observed time delays are consistent with propagation vectors having a substantial component across the ambient field and along the inward shock normal. The waves appear to originate in the vicinity of the quasi‐perpendicular bow shock. The inferred direction of wave propagation has important consequences for the transmission of MHD waves from the bow shock to the magnetopause and places significant constraints on the nature of the wave source. We outline possible conditions which may lead to waves propagating along the shock normal and across the field.
The electron signature of parallel electric fields
Authors: Burch J. L. , Gurgiolo C. , Menietti J. D.
Published: February 2008

Electron distribution functions measured on the Dynamics Explorer 1 spacecraft are shown to have the characteristics expected in a region of parallel electric fields. In a previous study we have shown that the distributions typically observed at altitudes near and above an altitude of one earth radius over the auroral oval are indicative of field‐free regions between regions of parallel acceleration above and below the observation point. Test‐particle simulations show that electron distributions resembling bi‐directional conics are expected to occur in regions of parallel electric fields, and this type of distribution has been observed with the High Altitude Plasma Instrument aboard the Dynamics Explorer 1 spacecraft.
Magnetospheric substorm‐related electric fields in the ionosphere: Discrepancy of an observation with model predictions
Authors: Reddy C. A. , Nishida A. , Fukao S. , Somayajulu V. V.
Published: February 2008

Theoretical models of disturbance electric fields in the middle and low latitude ionosphere have successfully explained several observed characteristics of the above electric fields. The models generally predict a large westward electric field in the 2300 – 0400 LT sector; but a recent study of a major F‐region disturbance at mid‐latitudes revealed a large east‐ward electric field in the midnight‐to‐morning sector, during a magnetospheric substorm. This discrepancy indicates that processes additional to those considered in the models so far are playing an important role during substorms. One possible process is the generation of large, secondary ionospheric electric fields in and around the auroral zone due to the interplay of the spatially varying and time‐varying enhanced conductivities, currents and electric fields during substorms. A second process may be the generation of large secondary electric fields in the inner magnetosphere due to the large spatial gradients of particle drifts during the substorm‐time unsteady convection. During substorms, such secondary electric fields may be dominant, in comparison with the effects of the large scale magnetospheric convection electric field and field‐aligned currents treated successfully in the models.
Seasonal variation of some constituents of Antarctic tropospheric air
Authors: Hogan A. W. , Egan W. G. , Samson J. A. , Barnard S. C. , Riley D. M. , Murphey B. B.
Published: February 2008

The interior of Antarctica is dominated by the continental Antarctic [cA] air mass, which resides entirely on the antarctic ice, and only receives heat, moisture and particles by exchange with surrounding air masses. The concentrations of carbon dioxide, total aerosol, and soot aerosol do not vary coincidentally in this air mass during antarctic spring.

A hypothesis describing the modification of these properties within the cA air mass through exchange with the surrounding air masses and variation of the source strength of marine aerosol in maritime polar air masses is proposed.
A 400 years isotope record of the Antarctic Peninsula climate
Authors: Aristarain Alberto J. , Jouzel Jean , Lorius Claude
Published: February 2008

A 400 year deuterium record has been obtained from a 154.3 m ice core drilled on Dalinger Dome (James Ross Island, Antarctic Peninsula). Based on a comparison between the isotope profile and the temperature data over the recent period (Aristarain et al, 1986), an interpretation is proposed in terms of temperature changes. The “warmest part” of this proxy record occurs around 1850 with, as a salient feature, a temperature decline of ∼ 2°C from that time up until present conditions. This feature, at odds with the long timescale warming trend recorded for both hemispheres over the same period, likely reflects a regional characteristic related to the lack of a high latitude/low latitude link in Southern hemisphere circulation patterns.
Loop current eddy shedding estimated using Geosat altimeter data
Authors: Jacobs Gregg A. , Leben Robert R.
Published: February 2008

A method for extracting periodic signals from altimeter data is applied in the Gulf of Mexico using data from the first two years of the Geosat Exact Repeat Mission. The least squares fitting of selected frequencies of sine and cosine functions to the time series of sea surface height at each point of the Geosat ground track is used to estimate the dominant frequency in the gulf for this time period. Optimal interpolation of the sine and cosine coefficients at the dominant frequency to a uniformly spaced grid allows reconstruction of the time series in the gulf and shows eddies shedding from the Loop Current with a period of approximately 10.5 months, consistent with shedding periods determined from numerical models and analysis of satellite infrared data. This technique is a novel method for investigation of periodic signals in Geosat altimetry and is not severely affected by the data outages present in the time series.
Field‐impressed magnetic anisotropy in rocks
Authors: Potter David K. , Stephenson Alan
Published: February 2008

The application of alternating (AF) or direct (DF) magnetic fields to two weakly anisotropic rock specimens which remain static, significantly alters their measured low‐field anisotropy of magnetic susceptibility (AMS) by superimposing an anisotropy which has the form of an ellipsoid of revolution with its unique axis aligned along the field axis. Previous AF history is also shown to influence the acquisition of isothermal remanent magnetization (IRM). These effects can be quite substantial and thus it is essential that rocks should not be used for low‐field AMS analysis or for IRM anisotropy studies if they have previously been subjected to static AF demagnetization. AMS studies should also not be carried out on rocks which carry a significant remanence (e.g., an IRM acquired in ≥5 mT). The field‐impressed effects were also strongly dependent upon whether the ferrimagnetic particles in the rocks were predominantly multidomain (MD) or uniaxial single‐domain (SD). The results were consistent with our recent work on synthetic specimens (containing magnetite, titanomagnetite or magnemite) and add support to our suggestion that these effects could provide a rapid, nondestructive, means of determining the predominant domain state (MD or uniaxial SD) of ferrimagnetic particles in rocks.
Ion acoustic waves in the solar wind
Authors: Gurnett D. A. , Frank L. A.
Published: February 2008

Plasma wave measurements on the Helios 1 and 2 spacecraft have revealed the occurrence of electric field turbulence in the solar wind at frequencies between the electron and ion plasma frequencies. Wavelength measurements with the Imp 6 spacecraft now provide strong evidence that these waves are short‐wavelength ion acoustic waves which are Doppler‐shifted upward in frequency by the motion of the solar wind. Comparison of the Helios results with measurements from the earth‐orbiting Imp 6 and 8 spacecraft shows that the ion acoustic wave turbulence detected in interplanetary space has characteristics essentially identical to those of bursts of electrostatic turbulence generated by protons streaming into the solar wind from the earth's bow shock. In a few cases, enhanced ion acoustic wave intensities have been observed in direct association with abrupt increases in the anisotropy of the solar wind electron distribution. This relationship strongly suggests that the ion acoustic waves detected by Helios far from the earth are produced by an electron heat flux instability, as was suggested by Forslund. Possible related mechanisms which could explain the generation of ion acoustic waves by protons streaming into the solar wind from the earth's bow shock are also considered.
Five‐station observations of Pc 1 micropulsation propagation
Authors: Althouse Edwin L. , Davis John R.
Published: February 2008

An experimental study has been conducted on the characteristics of the propagation of mid‐latitude Pc 1 micropulsations using a five‐station receiving network stretching from New York to Florida and from Maryland to Illinois. All data were telemetered in real time over telephone data lines for centralized recording and analysis. Cross‐correlation techniques were used to determine group velocity and direction of arrival using three different computational methods. Amplitude, spectral, and polarization characteristics are presented for the data analyzed. It was found that the propagation direction tended to coincide approximately with that of the geomagnetic meridian in the vicinity of the network of sites and that the propagation was characterized better by curved wave fronts than by plane wave fronts. No examples of east–west propagation were observed, but this is to some extent a consequence of the mid‐latitude location of the observation sites. Propagation group velocities ranging from 444 to 1523 km/s were observed. Variation in group velocity for a given event over a period of an hour was typically less than 10%. Attenuation rates ranging from 0 to 13 dB/1000 km, with an average of 6.5 dB/1000 km, were observed.
A high‐altitude rocket measurement of nitric oxide
Authors: Thomas Ronald J.
Published: February 2008

The nitric oxide density was measured from 110 to 300 km by a rocket photometer during the day. The small measured peak density, about 6.2 × 106 cm−3 at 111 km, can probably be attributed to the period of very low solar magnetic activity preceding the rocket flight. This experiment was coordinated with a similar measurement made by the Ultraviolet Nitric Oxide Experiment aboard the Atmosphere Explorer C satellite; the measurements are in good agreement. The altitude resolution (<1 km) and sensitivity (1600 counts R−1 s−1) greatly exceed those of previous measurements. Comparison to a model shows agreement above 200 km but less nitric oxide and more structure below that.
Observations of auroral westward traveling surges and electron precipitations
Authors: Meng C. ‐I. , Snyder A. L. , Kroehl H. W.
Published: February 2008

Precipitations of low‐energy electrons above the auroral westward traveling surge were examined from a number of surges observed by the DMSP 32 satellite in the fall of 1974. From the limited surges observed, differences in precipitations were detected, associated with different auroral forms in the vicinity of a surge. To the west of it, over a bright arc (or arcs), the precipitated energy flux was about 10 ergs/cm² s sr, and the differential energy spectrum was very similar to that of quiet evening arcs, but with an occasional shift of the spectral peak from ∼3.2 keV to the next higher energy channel of ∼8 keV. Along the surge front a band of very bright discrete auroras no longer had the precipitation characteristics of quiet arcs, and the energy flux amounted to tens of ergs/cm² s sr. The differential spectrum was highly variable, but sometimes it may be approximated by a power law with index between 1 and 1.5. The most spectacular precipitation feature was observed inside the main body of a surge; an unusually flat differential spectrum was observed. It was harder than dJ/dE ∝ E−1, with an index of about 0.5 extending from 0.2 keV to at least 20 keV. Thus a substantial precipitation of energetic electrons above 20 keV occurred inside a surge. A spectral peak near 8 keV or higher energies was also occasionally observed on this flat background spectrum. To the east of a surge (i.e., behind a westward surge) in the region of nonuniform diffuse auroras the electron precipitation was characterized by a flat spectrum below 8 keV with a sharp cutoff near 10 keV, similar to that of the equatorward diffuse aurora, superposed by a spectral peak near 3.2 or 8 keV, and the energy flux was approximately 1 erg/cm² s sr.
Auroral electron distribution function
Authors: Kaufmann R. L. , Dusenbery P. B. , Thomas B. J. , Arnoldy R. L.
Published: February 2008

The electron velocity distribution function is presented in the energy range 25 eV < E < 15 keV during a rocket flight over an active aurora. The electron measurements are compared with optical observations by all‐sky cameras and a television system. The most striking feature of the velocity distribution function is a broad plateau produced by downcoming electrons. This plateau is the feature of the electron distribution function that is associated with discrete auroral forms. Plateaus either appear or broaden by extending to higher energies each time a bright form is entered. The plateaus decay by erosion of the highest‐velocity portions when the rocket passes either out of an arc or into weak diffuse auroral structures. The high‐velocity cutoff of the plateau also fluctuates when small field‐aligned rays appear within the arcs. Kilovolt electrons were field aligned during portions of this flight, though such alignment was not as striking as that on previous flights. The field alignment is usually confined to a narrow energy band but extends over a broad range of energies during one interval. Electrons with v < 10 × 108 cm/s (E = 300 eV) are nearly isotropic in pitch angle throughout the flight. Upgoing electrons show almost no pitch angle dependence beyond 120°, and their fluxes decline smoothly as energy increases, with little or no evidence of a plateau. Preliminary results of numerical integrations to study bulk properties and stability of the plasma are presented.
Neutral winds and phase velocity of the instabilities in the equatorial electrojet
Authors: Broche P. , Crochet M. , Gagnepain J.
Published: February 2008

It is shown that a neutral wind in the equatorial electrojet induces variations of the phase velocities of the type I (two stream) and type II (cross field) instabilities, which are related to the local wind velocity and to the mean wind velocity (averaged along the whole magnetic field line), respectively. This difference is discussed, particular attention being devoted to its effects on the evaluation of the primary electric field in the electrojet.
New whistler evidence of a dynamo origin of electric fields in the quiet plasmasphere
Authors: Carpenter D. L.
Published: February 2008

A comparison of whistler data from four consecutive magnetically quiet days July 4–7, 1973, confirms and extends previous whistler results on quiet day cross‐L drift motions in the outer plasmasphere near L = 4. A pattern of morningside outward and afternoonside inward drifts at ≃200 m/s (|Ew| ≃ 0.1 mV/m) was repeated daily. (Ew is the westward component of the magnetospheric electric field at the equator.) Over the four days the onset of the outward drift activity shifted backward in time from ≃1000 MLT to ≃0500 MLT. There was a corresponding shift in the harmonic series representing Ew. On the first day the largest term was semidiurnal; on the fourth day it was diurnal. The data provided an opportunity to investigate in some detail the cross‐L drift velocity at spaced L values. During seven periods of the order of 1‐hour duration, drifts of the order of 200 m/s could be simultaneously measured at points spaced over approximately 1 RE in equatorial radius. The inferred equatorial east‐west electric fields near L = 4 decreased at least as rapidly as L−3/2 with increasing distance. (In a dipole field an equatorial variation as L−3/2 would be expected if an east‐west field that is constant with latitude were present at ionospheric heights.) There is some indication that the faster drop‐offs, with variation roughly as L−4, occurred during the first two days of quieting following disturbance and that the falloff approached L−3/2 on the third and fourth days. It is speculated that day‐to‐day changes in subauroral ionospheric conductivity during the quiet period may have been responsible for the ‘shielding’ of the field from high latitudes. The data strongly support the concept that the observed electric fields originate at middle to low latitudes, apparently in an ionospheric dynamo process. The noon‐midnight asymmetry (or noon bulge) of the plasmasphere reported from spacecraft appears to be a consequence of the quiet day flow pattern.
Energization of polar cusp electrons at the noon meridian
Authors: Craven J. D. , Frank L. A.
Published: February 2008

Observations gained with an electrostatic analyzer on board the low‐altitude satellite Ariel 4 demonstrate that the directional, differential spectra of polar cusp electron intensities are regulated by the sign of the elevation angle of the interplanetary magnetic field, θIMF. The altitude of the nearly circular polar orbit was ∼550 km. In the energy range 200 ≲ E ≲ 700 eV, spectra of polar cusp electron intensities were not observed to respond to changes in the sign of θIMF. At greater energies, spectra were found to be significantly harder when θIMF > 0°, with enhancements of a factor of ∼10 typical for 2‐keV electron intensities. Furthermore, these enhanced intensities appear to be localized within a ∼1‐hour sector of magnetic local time centered on the noon meridian. Enhanced intensities were detected during each sampling of electron intensities at local times MLT = 11.5–12.6 hours when θIMF > 0° but were observed only occasionally at lesser and greater local times. The physical processes responsible for the observed enhancements in electron intensities are unknown. Trapped magnetospheric electrons of sufficient intensities, which are generally present just equatorward of the polar cusp, are ruled out as a possible source.
Plasma flow pulsations in Earth's magnetic tail
Authors: Coroniti F. V. , Frank L. A. , Lepping R. P. , Scarf F. L. , Ackerson K. L.
Published: February 2008

During a 5‐hour interval on November 9, 1972, Imp 7 detected strong earthward plasma flows within the plasma sheet. The plasma flow exhibited a sequence of nine clear temporal pulsations in which the bulk speed varied from zero up to 1000–1500 km/s. The pulsations occurred at 15‐ to 30‐min intervals. These speed variations are shown to be positively correlated with changes in the standard deviation of the magnetic field (15‐s accumulations). During the flow pulsations, ground magnetograms exhibited only weak high‐latitude substorm activity, which is consistent with the Heos 2 detection of low values for the interplanetary field, with only a moderate southward component. Closer to earth, ATS 5 and Imp 6 detected some plasma heating during the period of Imp 7 flow pulsations. However, there was no evident periodicity corresponding to the Imp 7 flow pulsations in any of the other magnetospheric or solar wind data. Integrated over the 5‐hour interval, the strong plasma flows injected roughly 1022 ergs into the inner magnetosphere, yet both the solar wind and the ground magnetogram data are consistent with the magnetosphere having been in a relatively quiet state with only weak substorm activity along a contracted auroral oval. We suggest that the pulsations may be evidence that tail reconnection is inherently unsteady, with 10‐ to 30‐min periods.
Neutral composition measurements between 90‐ and 220‐km altitude by rocket‐borne mass spectrometer
Authors: Trinks H. , Offermann D. , von Zahn U. , Steinhauer C.
Published: February 2008

On June 29, 1974, at 1514 LST a neutral gas mass spectrometer with a cryogenically cooled ion source was flown above Wallops Island as part of the Aladdin 74 program. This paper presents the obtained density height profiles of N2, O2, O, and Ar. The maximum of the atomic oxygen density was 6.5 × 1011 cm−3 at 97.5‐km altitude. The altitude where the n (Ar)/n(N2) ratio reaches the sea level value was found to be about 98 km. Above 104‐km altitude the densities of all constituents showed a more rapid decrease than that predicted by the Jacchia 71 model. At 112.5 km the ratio of the total mass density and the model value reached a minimum of 0.33. This and other measurements suggest a high degree of variability in the lowest part of the thermosphere.
Nightglow emissions of OH(X²π): Comparison of theory and measurements in the (9‐3) band
Authors: Frederick J. E. , Rusch D. W. , Liu S. C.
Published: February 2008

The visible airglow experiments on the Atmosphere Explorer C and E satellites have viewed the (9‐3) band nightglow emission of the excited hydroxyl radical in the lower thermosphere at tropical latitudes. The surface brightnesses observed at similar local times vary by approximately a factor of 2. Comparison of the measurements with time‐dependent photochemical calculations shows reasonable agreement and indicates that temporal changes in atmospheric transport processes are the most likely explanation of the nightglow variations.
Observations of energetic radiation belt helium ions at the geomagnetic equator during quiet conditions
Authors: Fritz Theodore A. , Spjeldvik Walther N.
Published: February 2008

Fluxes of geomagnetically trapped energetic helium ions in the immediate vicinity of the geomagnetic equator have been unambiguously identified and measured with Explorer 45. The observations presented span the L shell range 2.25 ≲ L ≲ 5 and extend the observational coverage of radiation belt helium ions. During geomagnetically quiescent conditions these fluxes are found to peak sharply near L = 3.25 with equatorially mirroring intensities of 80 and 34 ions/cm² s sr keV in the 1.16–1.74 Mev and 1.74–3.15 Mev per particle passbands, respectively. The helium ion fluxes are observed to exhibit a significant B/B0 dependence and indicate that the ion flux pitch angle distribution j(α) is very anisotropic. If j(α) ≃ j⊥ sinm α, then m values of 8 and 10 correspond to the responses of the two passbands within the B/B0 range of 1.0–1.4 observed. When the B/B0 dependence is removed, the fluxes exhibit no detectable decay over a 2‐week period covered by the study.
Plasma sheet pressure anisotropies
Authors: Stiles G. S. , Hones E. W. , Bame S. J. , Asbridge J. R.
Published: February 2008

The ecliptic plane components of the pressure tensors for low‐energy (<30 keV) electrons and protons have been examined for more than 400 hours of quiet time plasma sheet data from Imp 6 and Imp 8. Individual high time resolution (≲100 s) measurements show that while at times the tensors may be clearly anisotropic with the pressure parallel to the magnetic field (P∥) being as much as 1.5–2.0 times the pressure perpendicular (P⊥), the anisotropies are not usually of this magnitude and are typically below the value thought necessary to balance the tension of the magnetic field. One‐hour averages of the particle counts have also been calculated. While these averages mask more rapid changes due to variations in the distributions and the magnetic field and can yield only a lower limit to the true anisotropy, examinations of the individual measurements indicate that they do provide a reasonable summary. On this time scale, the protons are nearly isotropic: the ratio of the maximum ecliptic component of the proton pressure tensor to the minimum is typically ≲1.1, and there is no apparent tendency for the distributions to be field aligned. On the same time scale, the electron distributions do show a tendency to be field aligned with P∥/P⊥ ≥ 1.2 approximately 25% of the time. Due to the low energy density of the electrons, however, this anisotropy is not itself sufficient to balance the tension of the magnetic field.
Recurrent Forbush decreases and the relationship between active regions and M regions
Authors: Shah G. N. , Kaul C. L. , Razdan H. , Bemalkhedkar M. M.
Published: February 2008

Recurrent Forbush decreases and recurrent geomagnetic disturbances have been attributed to the solar M regions, which are sources of high‐velocity solar plasma streams. A study of recurrent Forbush decreases for the period 1966‐1975 has been made to examine any possible relationship of M regions with solar active regions. It is shown that at the onset of the recurrent Forbush decrease at the earth there is a high probability of encountering a class of active regions at the central meridian of the sun which give rise to flares of importance ≥2B/3N. These active regions are found to be long lasting and to have large areas as well as high Hα intensities. Other active regions, producing flares of lower importance, are distributed randomly on the sun with respect to the onset of a recurrent Forbush decrease. By using the quasi‐radial hypervelocity approximation the base of the leading edge of the high‐velocity stream at the onset of a recurrent Forbush decrease at the earth is traced to the solar longitude about 40° west of the central meridian. From these results it is deduced that M regions are located preferentially to the west of long‐lasting magnetically complex active regions. Earlier studies of the identification of the M regions on the sun have been reexamined and shown to conform to this positional relationship. A possible mechanism of the development of an M region to the west of the long‐lasting magnetically complex active region is also discussed.
Gravity wave generation, propagation, and dissipation in the thermosphere
Authors: Richmond A. D.
Published: February 2008

This is the first in a series of papers examining large‐scale gravity waves in the thermosphere and their ability to transfer energy from high to low latitudes during magnetic disturbances. The gravity wave source is assumed to be either the Lorentz force of auroral electrojet currents or else a heat input due to energetic particle precipitation or to Joule heating. It is pointed out that the characteristic vertical width of the gravity wave source should usually lie between 2 and 4 pressure scale heights, placing constraints on the vertical wavelengths and horizontal velocities of the generated waves. A simplified analytic model of small‐amplitude wave generation by a current source shows how wave energy production depends on the temporal and spatial dimensions of the source, on the electric field strength, and on the electron density enhancement. The steep thermospheric temperature gradient in the vicinity of the source altitude strongly influences the properties of upward and downward propagating waves compared with waves generated in an isothermal atmosphere. Waves produced by the Lorentz force of Hall currents, by the Lorentz force of Pedersen currents, and by Joule heating are influenced quite differently by this temperature gradient. Because upgoing waves above the source are combinations of waves originally launched upward and waves originally launched downward but reflected around 110 km altitude, the mean effective source altitude is about 110 km for the far field response in the thermosphere. Large‐scale traveling ionospheric disturbances observable at middle latitudes are most likely produced primarily by Pedersen, rather than Hall, currents. The temperature structure of the thermosphere generally causes gravity wave packets to refract upward; waves traveling with a horizontal component of velocity faster than 250 m/s and with an initial downward component of group velocity will always be reflected upward in the lower thermosphere. The effects of viscosity, heat conduction, and Joule dissipation tend to filter out shorter‐period and slower moving waves from observation points at some distance from the source, so that only long‐period fast moving waves can reach low latitudes from an auroral source. For example, a wave with a 94‐min period moving horizontally at 605 m/s is largely dissipated by the time it has traveled 4000 km from a typical auroral source. A numerical simulation using a fairly realistic thermospheric model illustrates many of the points described from analytic considerations.
The midday, discrete auroral gap
Authors: Dandekar B. S. , Pike C. P.
Published: February 2008

A gap in the midday sector of the auroral oval is examined on the basis of Defense Meteorological Satellite Program (DMSP) satellite auroral photographs. All DMSP photographs recorded in June 1975 over the southern hemisphere were examined, and 38 photographs were found suitable to specify details of auroral features in the midday sector. There is not a single example showing the discrete auroral arcs extending continuously across the noon sector, bridging the morning and afternoon sectors of the auroral oval. Hence a gap, manifested by the absence of extended, discrete auroral arcs, exists in the midday sector of the auroral oval. The gap appears typically to extend over more than 15° of longitude or, correspondingly, more than 1 hour of local time and is centered about the 1000 corrected geomagnetic local time meridian. During an early phase of substorms the gap appears to fill with rays and fragmented arcs and to empty after substorm recovery. Similarly, polar cap arcs appear and disappear at the same times that the gap fills and empties of rays and fragmented arcs. The gap therefore appears to be a semi‐permanent feature of the midday auroral distribution.
Ion convection and the formation of the mid‐latitude F region ionization trough
Authors: Spiro R. W. , Heelis R. A. , Hanson W. B.
Published: February 2008

Measurements of total ion concentration and ion drift velocity from Atmosphere Explorer C have been used to examine the convective flow of plasma in the vicinity of the mid‐latitude F region ionization trough. It is found that the low‐latitude portion of the premidnight trough is a region of slow eastward plasma drift while the poleward portion is characterized by generally westward flow. The reversal from eastward to westward flow typically occurs on the low‐latitude edge of the trough where Ni is observed to vary smoothly. We propose that the plasma flux tubes within the premidnight trough have corotated eastward into the evening local time sector from dusk before stagnating and flowing westward at higher latitudes in the nighttime sector. In the absence of ionization sources, rather deep troughs can be formed by F region recombination during the long time required for the flow to stagnate and reverse. The proposed drift paths can result quite naturally from the combined effects of the corotation and magnetospheric electric fields. Large plasma convection velocities that act to increase the F region decay rate are not required to produce a trough but may cause the plasma composition changes that are occasionally observed within the trough.
Daytime nitric oxide at the base of the thermosphere
Authors: Swider W.
Published: February 2008

Nitric oxide profiles are deduced from the analysis of 10 daytime ion composition experiments performed at various latitudes, seasons, and solar conditions, principally over an altitude region from 85 to 100 km. Within a factor of 3, nitric oxide concentrations are found to vary from 1 × 108 cm−3 at 100 km to 2×106 cm−3 at 85 km for various sunspot numbers and seasons, except winter. This strong gradient suggests a vertical eddy diffusion coefficient on the lower side of those thought to be appropriate. The three winter mid‐latitude data sets, all associated with anomalous D region radio absorption, yield higher NO concentrations, two profiles attaining peak values of 109 cm−3.
Atomic carbon emission from photodissociation of CO2
Authors: Robert Wu C. Y. , Phillips E. , Lee L. C. , Judge D. L.
Published: February 2008

Atomic carbon fluorescence, C I 1561, 1657, and 1931 Å, has been observed from photodissociation of CO2, and the production cross sections have been measured. A line emission source provided the primary photons at wavelengths from threshold to 420 Å. The present results suggest that the excited carbon atoms are produced by total dissociation of CO2 into three atoms. The cross sections for producing the O I 1304‐Å fluorescence through photodissociation of CO2 are found to be less than 10−2 Mb in the wavelength region from 420 to 835 Å. The present data have implications with respect to photochemical processes in the atmospheres of Mars and Venus.
The large‐scale structure of the interplanetary magnetic field between 1 and 0.3 AU during the primary mission of Helios 1
Authors: Mariani F. , Ness N. F. , Burlaga L. F. , Bavassano B. , Villante U.
Published: February 2008

The macroscale and mesoscale structure of the interplanetary magnetic field during the primary mission of Helios 1 is discussed. The radial field component behaves essentially in agreement with Parker's theory. The transverse component shows a larger variability than the radial component; its radial variation is in good agreement with Parker's theory for high speeds, but some deviation is found for low speeds. The radial variation of the field variance is also studied. Its dependence upon the heliocentric distance r is expressed by the law r−3, which is necessary but not sufficient for Alfvén waves. The available data do not allow a unique interpretation of the r−3 dependence. No big differences are observed between low (≤500 km/s) and high (≥600 km/s) solar wind velocity regimes.
The formation of the plasma sheet resulting from plasma mantle dynamics
Authors: Pilipp Werner G. , Morfill Gregor
Published: February 2008

In this paper we investigate the possibility that the recently observed plasma mantle may be the most likely source of the plasma sheet. We do not discuss the origin question of the plasma mantle itself, although we present two rough models which we use mainly for the description of particle transport in the tail lobes and for a semiquantitative calculation of plasma mantle parameters (density, bulk velocity, and temperature distribution) at the plasma sheet boundary. Conservative estimates of the particle supply show that the source is adequate to replenish known losses from the plasma sheet. In addition, it is argued that at least the proton energies expected in the plasma sheet from such a model are in agreement with observations.
Magnetopause characteristics inferred from three‐dimensional energetic particle distributions
Authors: Williams D. J.
Published: February 2008

Three‐dimensional distributions for 24‐ to 44.5 keV protons (ions) are presented from the Isee 1 medium‐energy particles instrument during a magnetopause traversal at ∼0145:00 hours UT on November 20, 1977. The use of these data and simple particle orbit geometry allows us to infer magnetopause boundary location, orientation, and velocity. The results are consistent with both overall boundary motions toward and away from the earth at velocities of 10–20 km/s and the presence of a surface wave on the boundary. For the case analyzed, the boundary appears stable and well defined, being capable of supporting trapped type distributions (conservation of the first and second adiabatic invariants) within a fraction (≲0.3 ρ) of a gyroradius from the magnetosheath field where no trapping is observed.
Charge exchange of metastable ²D oxygen ions with molecular oxygen: A new source of thermospheric O2+ ions
Authors: Torr D. G. , Donahue K. , Rusch D. W. , Torr M. R. , Nier A. O. , Kayser D. , Hanson W. B. , Hoffman J. H.
Published: February 2008

Reactions involving metastable ions are difficult to study in the laboratory. Much new information on these reactions has been derived from satellite measurements of aeronomic parameters. In this paper we use Atmosphere Explorer D data to study charge exchange of metastable O+(²D) ions with O2. Using direct measurements of the O2 at 200 km to compute O2 densities at 300 km and supporting ionic concentrations and temperature observations, we find the rate coefficient for this reaction to be 1±0.6 × 10−9 cm³ s−1. The process constitutes a significant source of O2+ ions in the F2 layer at times when the N2 and O2 densities are enhanced. This finding leads to the conclusion that charge exchange with O2 must be a major sink for O+(²D) and an important source of O2+ ions in the E region, because of the increase in the [O2]/[N2] ratio with decreasing altitude. The results imply that 80% of all O+ ions formed in the E region are converted to O2+ and that only ∼20% of the metastable O+ ions are converted into N2+ through charge exchange with N2.
Diffusion and heat flow equations with allowance for large temperature differences between interacting species
Authors: Conrad James R. , Schunk Robert W.
Published: February 2008

For application to planetary ionospheres we have derived diffusion and heat flow equations for a fully ionized three‐component plasma and for a partially ionized three‐component plasma using a formulation that is valid for arbitrarily large temperature differences between the interacting species. These equations can be applied to ionospheric situations where steady state, collision‐dominated conditions prevail and where the species drift velocities are much less than the species thermal speeds (low Mach numbers). The application of the diffusion and heat flow equations to the F region and topside terrestrial ionosphere indicates that the various transport coefficients can exhibit significant variation with the different species temperature ratios.
Maximum entropy spectral analysis of some artificial samples
Authors: Kane R. P.
Published: February 2008

Using simple sinusoids as inputs, the Burg spectra are studied with a view to deciding the appropriate lengths of the prediction error filter (LPEF). It is observed that the higher the frequency (vis a vis the total data length representing the fundamental period), the lower the LPEF needed. In the case of mixed samples, frequencies exceeding the fifth harmonic are resolved with LPEF of about 50% (half‐data length) and higher LPEF are likely to give spurious peaks. For lower frequencies, higher LPEF may be needed, sometimes even approaching 90% of the data length. Thus a mixed sample needs the study of Burg spectra from low as well as high LPEF simultaneously.
Perturbation magnetic fields and current systems associated with eastward drifting auroral structures
Authors: Kawasaki Koji , Rostoker Gordon
Published: February 2008

Magnetospheric substorms feature the development of distorted discrete auroral forms known as surges and loops. The westward traveling surge is known to expand in discrete steps into the evening sector, the western extremity of the surge acquiring a velocity of upward of 1 km/s in the early stages of its formation. Magnetic perturbations associated with the westward traveling surge are known to reach hundreds of nanotesla in the region below the surge form. In this study we report the existence of eastward traveling regions of large magnetic perturbations, whose velocities of propagation are in the range of 0.8–2 km/s. We find that the basic structures of these propagating perturbation regions are maintained over at least 12° of longitude, although the amplitude of the disturbance may vary considerably over that longitude range. We have modeled the eastward propagating disturbance by a three‐dimensional current system of narrow longitudinal extent in which antiparallel Birkeland current sheets are linked by southward flowing current. We have used coincident riometer data to infer that the electrons responsible for E region ionospheric conductivity enhancements can also cause ionospheric absorption; this permits us to extimate the fluxes of energetic electrons responsible for the eastward propagating disturbance and thus to make a rough estimate of the equatorward electric field in the morning sector auroral oval. In particular, the longitudinal scale size of the eastward propagating structures is ∼5°–10° at 67.5°N.
An additional list of auroras from European sources from 450 to 1466 A.D
Authors: Dall'Olmo U.
Published: February 2008

Fifty‐nine auroral displays which occurred during the Middle Ages and have not been cited in previous catalog are listed. All citations, reported in the original language, are from European sources with the exception of a few which were recorded in the Near Eastern area. All entries are followed by a translation into English. The list is preceded by a short discussion about some problems involved in the material as well as medieval terminology, dating, and identification of the events. For the scholar's convenience the dates of auroral displays cited in Link's (1962) and Newton's (1972) catalogs have been interposed among the new accounts.
The mesospheric sodium layer at 23°S: Nocturnal and seasonal variations
Authors: Simonich D. M. , Clemesha B. R. , Kirchhoff V. W. J. H.
Published: February 2008

The vertical profile of mesospheric sodium has been measured by laser radar at São José dos Campos (23°S, 46°W) on 344 nights since 1972. Large day‐to‐day variations are observed, but averaging over a large number of measurements consistently shows an annual variation by a factor of 2 in the sodium abundance, with maximum in local winter. The average nocturnal variation is consistent with photochemical control of the bottomside of the layer and diffusive control of the topside. Variations observed on individual nights appear to be mainly dynamic in origin. Vertical structure with a characteristic wavelength of the order of 10 km is frequently seen to propagate downward through the layer at rates between 1 and 4 km h−1. Comparison of our results with twilight and daytime absorption abundances suggests a latitudinal asymmetry in the seasonal variation of abundance.
Characteristics of acoustic‐gravity waves in a diffusively separated atmosphere
Authors: Del Genio Anthony D. , Schubert Gerald , Straus Joe M.
Published: February 2008

The propagation characteristics of plane acoustic‐gravity waves in an atmosphere in diffusive equilibrium are studied by using a two‐fluid model which takes into account the collisional transfer of both momentum and energy between species. At wave periods of less than the shortest characteristic diffusion time for the minor gas, significant amplitude and phase differences between the wave‐induced density fluctuations of individual gases occur because of the different scale heights of the gases. At longer periods, diffusion induced by the wave acts to eliminate these amplitude and phase differences and restore the perturbed fluid to diffusive equilibrium. Vertical diffusion is most important at large scale sizes, but horizontal diffusion dominates for horizontal wavelengths of less than several hundred kilometers. As a result of wave‐induced diffusion, AE‐C satellite measurements of neutral density fluctuations of thermospheric constituents at 215‐km altitude are only compatible with internal gravity waves with periods of ∼15–30 min, horizontal wavelengths of ≃150–400 km, and downward phase propagation. Diffusion increases in importance with altitude, but is significant for periods of ≳30 min even at 150‐km altitude. Velocity and temperature differences for acoustic‐gravity waves are greatest at periods near the mean collision time and diffusion time. Vertical velocity differences between species can be as large as 40% in amplitude and 17° in phase at 215‐km altitude. Temperature perturbation differences are much smaller but can reach 17% in amplitude and 6.5° in phase at 300‐km altitude. Two other solutions to the governing equations, which may be called diffusion waves, have properties drastically different from the acoustic‐gravity wave solutions, including order‐of‐magnitude amplitude differences and close to 180° phase differences between the density, velocity, and temperature perturbations of the two species at most periods. Because of the velocity and temperature differences between species, dissipation of wave energy will occur. Damping of acoustic‐gravity waves is most significant at periods comparable to the mean collision and diffusion times and can be as large as 50–60% per wave cycle. This effectively filters out those waves with periods long enough to be affected by diffusion except when the observation is near the wave source. The predictions of the theory are consistent with a high‐latitude, lower‐altitude source like Joule heating or particle precipitation for the medium‐scale waves and a more localized random source for the smaller‐scale waves observed by AE‐C.