bluuebunny/crossref_metadata_2025 huggingface dataset:
Dual‐polarization airborne lidar observations of polar stratospheric cloud evolution
Authors: Poole L. R. , Kent G. S. , McCormick M. P. , Hunt W. H. , Osborn M. T. , Schaffner S. , Pitts M. C.
Published: February 2008

Dual‐polarization λ=0.532 μm lidar data show systematic polar stratospheric cloud (PSC) evolution along a portion of the Airborne Arctic Stratospheric Expedition DC‐8 flight of January 31, 1989. This flight leg was roughly aligned with air parcel motion on isentropic surfaces from 400–500K, where the local adiabatic cooling rate was ≈20 K/day. Type 1 PSCs show low depolarization ratios and scattering ratios which approach intermediate limiting values as ambient temperature decreases. These data suggest that Type 1 particles formed by rapid cooling may be nearly spherical and are restricted in size by partitioning of a limited HNO3 vapor supply among many competing growth sites. Type 2 PSCs appear at temperatures below estimated local frost points with increases in depolarization and scattering typical of larger ice crystals.
Denitrification mechanisms in the polar stratospheres
Authors: Toon Owen B. , Turco R. P. , Hamill P.
Published: February 2008

Microphysical simulations suggest that the time required for nitric acid particles to sediment from the stratosphere is comparable to the time required for falling ice particles to incorporate nitric acid vapor from the vapor phase. Since nitric acid particles form earlier in the winter than ice particles these simulations favor denitrification being a separate process from dehydration, with denitrification being due to nitric acid particles and dehydration due to ice particles. In our simulations, the column abundance of nitric acid is only depleted if temperatures low enough for nitric acid particles to exist extend to the altitude above which the column is measured. Such low temperatures are infrequent in the Arctic lower stratosphere, which may be the main reason that the Arctic stratospheric column shows little loss of nitric acid dining winter, while the colder Antarctic stratospheric column shows a substantial loss of nitric acid. In order to learn more about denitrification mechanisms further observational and laboratory studies are needed.
The January 30, 1989 Arctic polar stratospheric clouds (PSC) event: Evidence for a mechanism of dehydration
Authors: Gandrud B. W. , Dye J. E. , Baumgardner D. , Ferry G. V. , Loewenstein M. , Chan K. R. , Sanford L. , Gary B. , Kelly K.
Published: February 2008

In‐situ particle measurements made aboard the NASA ER‐2 in the Arctic on 890130 (YYMMDD) show Type 1 PSC particles over much of the flight, with instances of embedded Type 2 PSCs. The Type 2 particles were observed at temperatures warmer than the local frost‐point temperature of water; extended up to the upper size cutoff of the instrument (∼ 24 μm diameter); and are shown to contain too large a volume to be primarily NAT. Based on measured vertical temperature profiles, we conclude that the Type 2 particles observed on this day were formed above the aircraft in a region where saturation with respect to ice was achieved and were sufficiently large to have fallen into the path of the ER‐2. Although, the amount of material in the particles, expressed as water, is small by comparison to the total (vapor + aerosol) water concentration, the flux of water from the falling particles is of sufficient magnitude, if sustained, to lead to dehydration of the source region. These observations verify the mechanism for dehydration of polar vortex air masses by precipitation of ice particles.
Nitric oxide measurements in the Arctic winter stratosphere
Authors: Fahey D. W. , Kawa S. R. , Chan K. R.
Published: February 2008

Measurements of nitric oxide (NO) from five flights of the NASA ER‐2 aircraft during the Airborne Arctic Stratospheric Expedition (AASE) are presented. The NO values and vertical gradient near 60°N latitude are similar to previous measurements near 50°N in winter [Ridley et al, 1984; 1987]. The NO latitudinal gradient is distinctly negative outside of the polar vortex, approaching zero at the boundary of the vortex, and remaining below the 20 pptv detection limit inside the vortex. The low NO values in the vortex occur at solar zenith angles as low as 82° indicating that NO2 values in the vortex are also low. Steady state NO2 and NOx (NO+NO2) are calculated from measured NO, O3, and ClO, and modeled photodissociation rates. NOx outside the vortex shows a negative dependence on latitude and solar zenith angle. The average ratio of NOx to NOy (at the same relative latitudes from different flight days) shows a strong latitude gradient with values near 0.08 at 12° equatorward of the vortex edge, decreasing to less than 0.02 at the vortex boundary. Low NOx and NOx/NOy inside and near the vortex boundary may be indications of heterogeneous removal of CIONO2 and N2O5.
Near UV atmospheric absorption measurements of column abundances during Airborne Arctic Stratospheric Expedition, January – February 1989: 2. OClO observations
Authors: Schiller Cornelius , Wahner Andreas , Platt Ulrich , Dorn Hans‐Peter , Callies Jörg , Ehhalt Dieter H.
Published: February 2008

Column abundances of OClO were measured during the Airborne Arctic Stratospheric Expedition from January 6 to February 9,1989 by near UV absorption spectroscopy. OClO was detected during AASE inside the vortex and at the edge of the vortex with column abundances of 3 – 10 × 1012 cm−2 under twilight conditions and up to 1 × 1014 cm−2 during the night. For comparison, in the Antarctic winter nighttime column abundances of OClO ranged from 1 – 2.5 × 1014 cm−2, while those at mid‐latitudes were below the detection limit, i.e. by at least a factor of 10 lower (Solomon et al., 1988). The measurements are broadly consistent with observed BrO column abundances and chemical model calculations.
Simulating the evolution of the chemical composition of the 1988/89 Winter vortex
Authors: Jones R. L. , McKenna D. S. , Poole L. R. , Solomon S.
Published: February 2008

During the 1988/89 Airborne Arctic Stratospheric Expedition (AASE) observations of the chemical composition and aerosol characteristics of the winter vortex were obtained from a NASA ER‐2 aircraft. In this paper we present interpretations of observations obtained on three ER‐2 flights using a Lagrangian coupled photochemical‐microphysical model. It is argued that observations obtained on January 16 and 19, and February 10, represent different stages of the chemical evolution of the vortex, from the early stages of chlorine release, the onset of denitrification and the intensively processed state.
Model test of CCN‐cloud albedo climate forcing
Authors: Ghan S. J. , Taylor K. E. , Penner J. E. , Erickson D. J.
Published: February 2008

Cloud condensation nuclei (CCN) influence cloud albedo through their effect on the cloud droplet size distribution. A number of studies have evaluated the climatic impact of the CCN‐cloud albedo feedback, but all have assumed that cloud distributions, cloud thicknesses, and cloud liquid water contents would remain constant as the climate adjusted. We have tested this assumption using the Livermore version of the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM1). Our results indicate that there are no significant compensating changes in cloud properties that would counteract the 1.7% global albedo increase resulting from a fourfold increase in marine CCN concentration. Furthermore, when ocean surface temperatures are decreased 4° C in a manner broadly consistent with the enhanced cloud albedos, we predict an increase in cloud fraction of 3.5% and a reduction in cloud altitude, leading to a positive feedback from clouds that would imply a climate impact roughly double that calculated from cloud droplet size distribution change alone.
Measurements of nitrogen oxides in the Arctic
Authors: Honrath R. E. , Jaffe D. A.
Published: February 2008

Nitric oxide (NO) and total reactive nitrogen (NOy) were measured at the NOAA Geophysical Monitoring for Climatic Change baseline site near Barrow, Alaska, during July–August 1988. Concentrations of NOy in air from the clean‐air sector (45° to 130°) ranged from non‐detectable to 300 ppt (hourly‐average), with a median value of 100 ppt. NO concentrations were generally less than the detection limit of 50 ppt and reached a maximum of 100 ppt. These levels are similar to those observed at other remote sites, and are lower than the two previous measurements of NOy and peroxyacetyl nitrate (PAN) in the Arctic during spring. A diurnal cycle in NOy concentrations was also observed, with maximum levels near local solar noon, and minima near midnight. The cause of this cycle is not known, but it may be due to (1) daytime ventilation of NOy‐rich air to the surface each day combined with fog scrubbing or dry deposition at night or (2) biological production of NO.
CASA UNO GPS orbit and baseline experiments
Authors: Schutz B. E. , Ho C. S. , Abusali P. A. M. , Tapley B. D.
Published: February 2008

CASA UNO data from sites distributed in longitude from Australia to Europe have been used to determine orbits of the GPS satellites. The characteristics of the orbits determined from double difference phase have been evaluated through comparisons of two‐week solutions with one‐week solutions and by comparisons of predicted and estimated orbits. Evidence of unmodeled effects is demonstrated, particularly associated with the orbit planes that experience solar eclipse. The orbit accuracy has been assessed through the repeatability of unconstrained estimated baseline vectors ranging from 245 km to 5400 km. Both the baseline repeatability and the comparison with independent space geodetic methods give results at the level of 1–2 parts in 108. In addition, the Mojave/Owens Valley (245 km) and Kokee Park/Ft. Davis (5409 km) estimates agree with VLBI and SLR to better than 1 part in 108.
Controls on groundwater Rn‐222 concentrations in fractured rock
Authors: Torgersen Thomas , Benoit Janina , Mackie David
Published: February 2008

Approximately 150 Rn‐222 analyses from groundwater wells in fractured lithologies of eastern Connecticut were made to evaluate the intralithologic and interlithologic variability. Although there is a control of Rn‐222 activity in porefluids by uranium (radium) concentration in the host rock, the variability of local Rn‐222 is dominated by site‐specific rock properties. These are (with their contribution to the variability); (i) the specific fracture surface area (>103x), which is functionally dependent on crack width, (ii) the emission efficiency (>102x) which is functionally related to the fracture spacing and (iii) the enrichment of uranium (Ra‐226) on the fracture surface (>102x). Thus, the activity of radon in fractured lithologies is difficult to predict and the measurement of radon activity does not uniquely constrain the geometry of the rock or the chemical inhomogeneity.
Aspera/Phobos measurements of the ion outflow from the MARTIAN ionosphere
Authors: Lundin R. , Zakharov A. , Pellinen R. , Barabasj S. W. , Borg H. , Dubinin E. M. , Hultqvist B. , Koskinen H. , Liede I. , Pissarenko N.
Published: February 2008

This report reviews the first results on the ionospheric ion outflow in the Martian magnetosphere by the ion composition experiment ASPERA on Phobos‐2. The measurements show that Mars is characterized by a strong loss of plasma from its topside ionosphere. This loss results from both ion pick‐up due to mass‐loading of the solar wind in the Martian boundary layer and an acceleration mechanism, quite similar to that observed above the Earth's auroral oval, providing intense ionospheric O+ beams of energies up to several keV.

A preliminary estimate of the ionospheric outflow from Mars indicates that the planet at present is losing oxygen at a rate of ≈3·1025 ions/s. This corresponds to an evacuation of its present total atmospheric oxygen content (contained in CO2 and O2) in less than 100 million years.
igneous origin for the Na in the cloud of Io
Authors: Johnson Mary L. , Burnett D. S.
Published: February 2008

We heated mixtures of sulfur and Na‐bearing silicates in evacuated silica glass capsules to temperatures between 600°C and 950°C. At or above 850°C, Na‐silicate glass reacts with elemental S to form a (Na,K) sulfide. Mobilization of this phase may account for the presence of Na and K on the surface of Io, and hence in the material sputtered into the Jovian magnetosphere.
The 23 May 1989 MacQuarie Ridge Earthquake: A very broad band analysis
Authors: Ekström Göran , Romanowicz Barbara
Published: February 2008

We use data from the GEOSCOPE global seismograph network to determine source parameters for the 23 May 1989 Macquarie Ridge earthquake. By moment tensor inversion of long‐period surface waves we obtain a seismic moment of 1.8–2.4 × 1021 N m, which makes this the largest seismic event to have occurred worldwide since the 1977 Sumba earthquake. The focal mechanism shows pure right‐lateral strike‐slip motion on a plane parallel with Macquarie Ridge and the Pacific‐Australian plate boundary. The mechanism is consistent with the strike‐slip motion predicted for this area from relative plate motion models. We invert broad band teleseismic P and SH waveforms to determine source complexity, using the results from the long‐period analysis as a priori soft constraints. The broad band waveforms show that the release of seismic energy was concentrated in the first 30 s of seismic rupture, but fault slip continued for more than 60 s. Lack of directivity in the long‐period and broad band waveforms indicates that the rupture propagated bilaterally or vertically from the nucleation point.
Rupture process of the MacQuarie Ridge Earthquake of May 23, 1989
Authors: Braunmiller Jochen , Nábělek John
Published: February 2008

Broadband body waves recorded at 15 digital seismic stations worldwide are used to study the rupture process of the May 23, 1989 Macquarie Ridge earthquake. The centroidal solution (strike 211°, dip 86°, rake 180°, and depth of 10 km below the seafloor) indicates shallow rupture with pure right‐lateral strike‐slip motion along the Pacific‐Australia plate boundary, in agreement with motion predicted by plate tectonic models. The total seismic moment is 13.4×1020 Nm, 80% of which was released in the first 24 s of the rupture process. Modeling favors a bilaterally propagating rupture with slightly different dip and rake for the northward and southward fault segments and similar moment release along both directions. The estimated fault length is quite short, about 90 km, and the derived stress drop of 180 bar and average displacement of 17 m are unusually high. The bathymetry in the epicentral region shows topographic segmentation of the ridge, possibly indicating fault segmentation which confines ruptures to short segments.
Constraints on lower mantle composition and temperature from density and bulk sound velocity profiles
Authors: Bina Craig R. , Silver Paul G.
Published: February 2008

Recent studies comparing density (ρ) from the seismological model PREM to that predicted for various perovskite and magnesiowüstite phase assemblages under lower mantle conditions suggest that the lower mantle is a few percent denser than reasonable candidates for upper mantle composition such as pyrolite. This has been interpreted as evidence for an iron‐enriched lower mantle. In addition to density, bulk sound velocity (
) provides an important constraint upon proposed lower mantle compositions. Being independent of the shear modulus,
has several desirable characteristics. Experimentally, it can be determined in the laboratory by density measurements under static compression; seismologically, it is not affected by attenuative dispersion and is expected to be much less laterally heterogeneous than P‐ or S‐wave velocities. We have calculated ρ and
along lower mantle adiabats, as functions of iron‐magnesium content (XMg ) and silica content (XPv ), and compared them to values obtained from PREM. For a reasonable temperature estimate at the top of the lower mantle ( Tlm ) of 2000 K, we find that the ρ data are most compatible with a lower mantle enriched in Fe, in agreement with previous studies. In addition, the
data require that silica enrichment accompany this Fe enrichment. Furthermore, increasing Tlm increases both the required Fe and Si content. With a high assumed Tlm (>2700 K), the ρ data can be satisfied by low XMg values, but even a pure perovskite lower mantle is too slow compared to
. Thus, assuming no free SiO2 in the lower mantle, this provides an upper bound on Tlm of approximately 2700 K. Finally, conclusions regarding the composition and temperature of the lower mantle are strongly dependent upon uncertainties in estimated thermoelastic parameters and upon choice of a seismological model. Most importantly, neither Fe nor Si enrichment is required if the zero‐pressure volume coefficient of thermal expansion of perovskite is about 2.5×10−5K−1, rather than 4.0×10−5K−1, at high temperatures. Alternatively, but less probably, Fe and Si enrichment are not required if the average ρ of the lower mantle is 1.0% less than given by PREM. The Si enrichment is not required if the average
of the lower mantle is 0.5% slower than PKEM, closer to the value given by the body‐wave model derived from the Jeffreys‐Bullen tables, or if the lower mantle is anomalously cold, with Tlm ≈ 1700 K.
Source parameters of the 1989 Loma Prieta Earthquake determined from long‐period Rayleigh waves
Authors: Zhang Jiajun , Lay Thorne
Published: February 2008

The source parameters of the Loma Prieta earthquake are determined using long‐period Rayleigh waves recorded by USGS/ERIS, IDA/IRIS, and GEOSCOPE stations. The source mechanism is well‐constrained by the Rayleigh wave radiation pattern, with a dip = 70 (±5)°, strike = 130 (±5)°, rake = 135 (±5)°, and moment = 3.4 (±0.5) × 1019 Nm (Mw = 7.0). This mechanism is generally consistent with independent body wave determinations. The most stable long‐period waves, with periods from 200 to 275 s, indicate that the source process has a centroid time of about 10 s, somewhat longer than that indicated by body waves (about 5–6 s). This discrepancy cannot be uniquely attributed to source effects because of uncertainties in the propagation corrections. The importance of using surface waves with short propagation paths for analysis of moderate size earthquakes such as the Loma Prieta event is demonstrated by the unreasonably long source durations inferred from R3 arrivals.
A possible geodetic anomaly observed prior to the Loma Prieta, California, Earthquake
Authors: Lisowski M. , Prescott W. H. , Savage J. C. , Svarc J. L.
Published: February 2008

Monthly measurements since mid‐1981 of distance from a geodetic station located 11 km from the epicenter of the Loma Prieta earthquake (Ms = 7.1; October 17, 1989) to three stations 30 to 40 km distant provides an unusually complete record of deformation in the epicentral region in the years prior to an earthquake. Roughly 1.3 years before the earthquake, at about the time of the first magnitude‐5 foreshock, the rate of change in line length for two of the lines appears to change; the rate for the third line does not change. Other similar, though smaller, changes in rate are apparent in the eight‐year record. Thus, there is marginal evidence for a change in deformation rate about one year before the Loma Prieta earthquake, but that change need not be a precursor.
Post‐seismic slip on the San Andreas Fault at the northwestern end of the 1989 Loma Prieta Earthquake rupture zone
Authors: Langbein John O.
Published: February 2008

A small geodetic network spanning the San Andreas fault was measured 7, 77, 157, and 200 days following the October 17, 1989 Loma Prieta M7.1 earthquake. This network is located at the northwestern end of the rupture plane defined by the locations of numerous aftershocks. In the initial 70‐day interval, the measured line‐length changes revealed that 5.4 ± 0.4 mm of right‐lateral slip occurred within the network. However, during the later 4 month interval only a marginally significant rate, 3.2 ± 1.4 mm/yr, of right‐lateral slip could be detected. Thus, it appears that the measured slip is a typical response of the fault following a major shock in that the rate of slip decreases rapidly with time. However, the magnitude of the post‐seismic slip is less than 0.5% of the inferred co‐seismic slip at depth.
Downward propagation of upper stratospheric mean zonal wind perturbation to the troposphere
Authors: Kodera Kunihiko , Yamazaki Koji , Chiba Masaru , Shibata Kiyotaka
Published: February 2008

An investigation is conducted to determine the influence of changes in the upper stratospheric mean zonal wind on the circulation of the lower atmosphere. In addition to observed data, results of numerical experiments with a general circulation model are used, in which the solar ultraviolet heating rate is varied to force changes in the mean zonal wind in the upper stratosphere.

It is found that when the upper stratospheric mid‐latitude westerlies are strong during December, lower stratospheric polar night jet is persistent and the westerlies in the polar region of the troposphere become stronger in the following February. These results are common to both the observations and the numerical experiments.
the 1989 Antarctic Ozone Hole as observed by TOMS
Authors: Stolarski Richard S. , Schoeberl Mark R. , Newman Paul A. , McPeters Richard D. , Krueger Arlin J.
Published: February 2008

In 1989 the Total Ozone Mapping Spectrometer (TOMS) aboard the Nimbus 7 satellite observed the springtime decrease in Antarctic total ozone for the 11th consecutive year. The 1989 minimum values of total ozone measured by TOMS declined throughout the month of September at a rate nearly identical to 1987. The National Meteorological Center analysis of lower stratospheric temperatures in August and September 1989 also showed conditions similar to those observed in 1987. A minimum in total ozone of 111 DU was reached on October 7, 1989. Within uncertainties this is the same as the previously observed minimum on October 5, 1987. The area of the ozone hole as defined by the 220 DU contour grew rapidly during early September. It reached a mid‐September peak of 7.5% of the southern hemisphere or 19 million square kilometers, essentially the same as observed in 1987. From mid October through November 1989, minimum polar total ozone values increased and the area within the 220 DU contour decreased more rapidly than during the comparable period of 1987. The more rapid erosion of the 1989 ozone hole resulted from strong wave number one perturbations of the vortex dynamics in late October.
Formation of nitric acid hydrates ‐ A chemical equilibrium approach
Authors: Smith Roland H.
Published: February 2008

Published data are used to calculate equilibrium constants for the reactions

 

over the temperature range 190 to 205 K. Standard enthalpies of formation and standard entropies are calculated for the tri‐ and mono‐hydrates. These are shown to be in reasonable agreement with earlier calorimetric measurements. The formation of nitric acid trihydrate in the polar stratosphere is discussed in terms of these equilibrium constants.
Effect of iron on the crystal structure of (Mg,Fe)SiO3 perovskite
Authors: Kudoh Y. , Prewitt C. T. , Finger L. W. , Darovskikh A. , Ito E.
Published: February 2008

The perovskite form of Mg0.981, Fe0.028Cr0.011 Si0.979 O3, quenched from 26 GPa and 2173 K in a uniaxial split‐sphere‐type high‐pressure apparatus, was studied at the SUNY X3A beamline at the National Synchrotron Light Source. With a Si (111) double‐crystal monochromator and a single crystal of perovskite measuring 29×29×43 μm, intensities of 127 independent reflections were collected with sin θ/λ < 0.60 Å−1 and I0 > 3.5σI. This is the first‐reported single‐crystal diffraction study of a Mg‐silicate perovskite containing a significant amount of Fe or other cations. The unit cell parameters obtained through the refinement of 30 reflections are: a = 4.7823(3), b = 4.9331(3), c = 6.9026(8) Å, V = 162.84(2) Å3. The result of structural refinement in space group Pbnm indicates that Fe and a small amount of Cr substitute for Mg rather than for Si, contrary to the result of Jackson et al. (1987) who reported Fe in the octahedral site of a perovskite synthesized at 50 GPa and 2000 K in a diamond‐anvil cell with laser heating.
Venus: A total mass estimate
Authors: Sjogren W. L. , Trager G. B. , Roldan G. R.
Published: February 2008

Reductions of four independent blocks of Pioneer Venus Orbiter Doppler radio tracking data have produced very consistent determinations of the GM of Venus (the product of the universal gravitational constant and total mass of Venus). These estimates have uncertainties that are significantly smaller than any values published to date. The value of GM is also consistent with previously published results in that it falls within their one‐sigma uncertainties. The value of 324858.60 ±0.05 km3/sec2 is our best estimate.
Effect of a global plume distribution on Earth normal modes
Authors: Lognonne Philippe , Romanowicz Barbara
Published: February 2008

We show that a global distribution of small scale heterogeneities in the lower mantle induces both frequency splitting and amplitude scatter of low angular order modes. These effects can be used in order to map the global distribution of small scale structures in the mantle, such as plumes. Two independent datasets, consisting respectively of lower mantle modes interaction coefficients and of observed amplitudes of core modes, can then be used to constrain the low angular degrees of the spatial distribution and the mean size of heterogeneities, allowing us to constrain the mantle structure at different scales. If these heterogeneities are assumed to be plumes associated with hotspot activity, the mean size of plumes obtained using the two datasets is then in good agreement with that obtained from geodetical or numerical convection studies.
Fast dual tomography
Authors: Carrion Philip M.
Published: February 2008

This paper can be considered as a continuation of the work by Carrion and Carneiro (1989), where a generalized approach to linearized inversion of geophysical data was developed. Their method allows one to incorporate virtually any constraints in the inversion and reformulate the problem in the dual space of Langrangian multipliers (see also Carrion, 1989a). The constrained tomography makes traveltime inversion robust: it automatically rejects “bad data” which correspond to solutions beyond the chosen constraints and allows one to start inversion with an arbitrary chosen initial model.

In this paper, I will derive basic formulas for constrained tomographic imaging that can be used in such areas of geophysics as global mapping of the earth interior, exploration geophysics, etc. The method is fast: an example that will be shown in the paper took only 6 min. of VAX CPU time. Had the conventional least‐squares matrix inversion been used it would have taken more than 10 hours of the CPU time to solve the same problem.
A self‐exciting process of acoustic emission occurrence in steady creep of granite under uniaxial stress
Authors: Nishizawa Osamu , Noro Harufumi
Published: February 2008

Clustering of acoustic emissions (AE) in space and time was found in a laboratory experiment. To investigate the stochastic process of AE occurrence, event times of AE were measured during steady creep phases under different stress levels. Oshima granite was continuously subjected to constant uniaxial stress of different intensity. The occurrence time of AE event was analyzed as a combination of a Poisson process and a self‐exciting part; in the latter, events are excited by preceding events. The self‐exciting character was more enhanced under higher crack density, in accordance with a stronger concentration in hypocenter distribution at higher stress.
Seafloor topography: A record of a chaotic dynamical system?
Authors: Smith Deborah K. , Shaw Peter R.
Published: February 2008

We suggest that limits on the number of independent variables that play a role in controlling the shape of the seafloor can be obtained directly from bathymetry data. To obtain this information, seafloor topography is considered as a product of a larger system that produces the oceanic lithosphere. We hypothesize that this dynamical system is chaotic, and use bathymetric depth values to search for evidence of a strange attractor, the dimension of which approximates the number of degrees of freedom in the system. An analysis of Sea Beam multibeam data collected along a flow line of seafloor spreading in the Northeast Pacific Ocean indicates that the dynamical system that forms the topography (on the length scale of 100'S of meters) has an underlying structure indicative of a high‐order attractor.
Distortion of gravity wave spectra measured from ground‐based stations
Authors: Lefrère J. , Sidi C.
Published: February 2008

The attenuation induced by time averaging of ground based measurements of internal gravity waves is made scale dependent by the Doppler shifts resulting from mean atmospheric motions, leading to some distortion of the experimental spectra versus vertical wavenumber. This spectral distortion mainly affects the large wavenumber range where the spectral level may be strongly underestimated, even for a few minutes averaging time in the case of vertical velocity measurements. Numerical evaluations of the spectral attenuation are presented, assuming a standard model of the random internal wave field.
Hot flow anomaly formation by magnetic deflection
Authors: Onsager T. G. , Thomsen M. F. , Winske D.
Published: February 2008

Hot Flow Anomalies (HFAs) are localized plasma structures observed in the solar wind and magnetosheath near the Earth's quasi‐parallel bow shock. We present 1‐D hybrid computer simulations illustrating a formation mechanism for HFAs in which the single, hot, ion population results from a spatial separation of two counterstreaming ion beams. The higher‐density, cooler regions are dominated by the background (solar wind) ions, and the lower‐density, hotter, internal regions are dominated by the beam ions. The spatial separation of the beam and background is caused by the deflection of the ions in large amplitude magnetic fields which are generated by ion/ion streaming instabilities.
Low‐frequency radio emissions at Neptune
Authors: Kurth W. S. , Barbosa D. D. , Gurnett D. A. , Poynter R. L. , Cairns I. H.
Published: February 2008

The Voyager 2 plasma wave receiver detected weak radio emissions from Neptune's magnetosphere in the frequency range of 3 – 60 kHz. The emissions occurred in bursts lasting for typically 1.5 hours, often occurring twice per planetary rotation. Most of these radio bursts were detected within several degrees of the magnetic equatorial plane. During the passage through the magnetosphere, electrostatic upper hybrid resonance bands were observed close to the magnetic equator in conjunction with intensifications of the radio emissions at frequencies close to and above the upper hybrid bands. Further, near closest approach, the radio emissions were observed to cross the right‐hand cutoff frequency with no apparent attenuation. We conclude that the Neptunian radio emissions below about 60 kHz are produced by mode conversion from the upper hybrid waves and propagate in the ordinary mode into beams within about 12° of the magnetic equator. There is also evidence of an extraordinary mode emission at about 60 kHz which is apparently generated by an entirely different source from the escaping continuum radiation.
The magnetosphere of Neptune: Its response to daily rotation
Authors: Voigt Gerd‐Hannes , Ness Norman F.
Published: February 2008

The Neptunian magnetosphere periodically changes every eight hours between a “pole‐on” magnetosphere with only one polar cusp and an “Earth‐type” magnetosphere with two polar cusps. In the “pole‐on” configuration, the tail current sheet has an almost circular shape with plasma currents closing entirely within the magnetosphere. Eight hours later the tail current sheet assumes an atmost flat shape with plasma currents touching the magnetotail boundary and closing over the tail magnetopause.

We have calculated magnetic field and tail current sheet configurations in a three‐dimensional model, but have investigated the plasma‐ and thermodynamic conditions in a simplified two‐dimensional MHD equilibrium magnetosphere. By matching the asymptotic plasma sheet β = 2μ0P/B2 values in the two models, we found to our surprise that the free energy F in the tail region of the two‐dimensional model becomes independent of the dipole tilt angle. We conjecture that the Neptunian magnetotail might assume quasi‐static equilibrium states that make the free energy of the system independent of its daily rotation.
He 584 Å dayglow at Neptune
Authors: Parkinson Christopher D. , McConnell John C. , Sandel Bill R. , Yelle Roger V. , Broadfoot A. Lyle
Published: February 2008

The Voyager 2 Ultraviolet Spectrometer measured the emission intensity of the He resonance line at 584 Å to be
R on the day side of Neptune. Our calculations of the He 584 Å intensity at Neptune using partial frequency redistribution and inhomogeneous atmospheric models show that the product of the volume mixing ratio (mole fraction), fHe, and the eddy diffusion coefficient at the homopause, Kh, is fHeKh = 107 cm2 s−1 with upper and lower bounds to the uncertainty of about a factor of 3 and 9, respectively. If fHe is taken as the current Infrared Interferometer Spectrometer working value, fHe = 0.19, then Kh = 5×107 cm2 s−1 with a similar uncertainty. This range of K overlaps that obtained from analysis of the hydrocarbon distributions on Neptune (Broadfoot et al., 1989).
Rheology of solid methane and nitrogen: applications to TRITON
Authors: Eluszkiewicz Janusz , Stevenson David J.
Published: February 2008

The existing information about the rheological properties of solid methane and nitrogen is reviewed. The main limitation is the absence of creep data for solid nitrogen, but estimated properties are derived on the basis of simple scaling arguments for van der Waals bonded materials. On Triton solid methane and most likely nitrogen are too soft to support any topography over billions of years. Topographic support by water ice‐rich materials seems almost certain. Nitrogen and methane do not intermix by solid‐state diffusion. The weakness (absence?) of the opposition effect on Triton can be explained by annealing of nitrogen grains, provided the latter have sizes characteristic of freshly deposited frost.
Zonally averaged thermal balance and stability models for nitrogen polar caps on Triton
Authors: Stansberry John A. , Lunine J. I. , Porco C. C. , McEwen A. S.
Published: February 2008

We have analyzed Voyager four color imaging data of Triton to calculate the bolometric hemispheric as a function of latitude and longitude. Zonal averages of these data have been incorporated into a thermal balance model involving insolation, reradiatation and latent heat of sublimation of N2 ice for the surface. The current average bolometric albedo of Triton's polar is 0.8, implying an effective temperature of 34.2K and a surface pressure of N2 of 1.6 μb for unit emissivity. This pressure is an order of magnitude lower than the surface pressure of 18 μb inferred from Voyager data [Broadfoot et al., 1989; Conrath et al., 1989], a discrepancy that can be reconciled if the emissivity of the N2 on Triton's surface is 0.66. The model predicts that Triton's surface north of 15° N latitude is experiencing deposition of N2 frosts, as are the bright portions of the south polar cap near the equator. This result explains why the south cap covers the entire southern hemisphere of Triton. Initial results from a seasonal model are also described briefly, although they do not agree with the Voyager observations.
Ultra‐low‐frequency wave power in the magnetotail lobes 1. Relation to substorm Onsets and the auroral electrojet index
Authors: Smith R. A. , Goldstein M. L. , Sands M. R. , Lepping R. P. , Goertz C. K. , Harrold B. G. , Fitch C. A. , Shan L.‐H.
Published: February 2008

Time series observations of the magnetotail lobe magnetic field have been Fourier analyzed to compute the frequency‐weighted energy density Pfz in the range 1–30 mHz. Pfz is generally observed in the range 10−4 – 10−2 γ2 – Hz, with a mean value of 1.2 × 10−3 γ2 – Hz during substorm phases and 1.0 × 10−3 γ2 – Hz in the comparison intervals. No strong correlation of Pfz is found with AE in set of intervals, but during substorm growth phases Pfz may vary by an order of magnitude over time scales of 30 min, with a tendency for higher power levels to occur later in the growth phase. Increases in Pfz are seen to precede by ∼ 10 min localized expansive phase activity observed in individual magnetograms. The observed levels of Pfz during growth phase are in general accord with the requirements of the thermal catastrophe substorm model.
ARe droughts becoming more frequent or severe in the United States?
Authors: Karl Thomas R. , Heim Richard R.
Published: February 2008

The frequency of droughts, their areal extent, and the quantity of precipitation received over the United States is highlighted by considerable decadal variability. At this time, there is no evidence to support a Twentieth Century drying trend in the United States precipitation and/or drought climatology. The considerable decadal variability however, suggests that major biophysical and socio‐economic impacts are likely to accompany convincing evidence of a change in drought climatology.
ISEE observations of low frequency waves and ion distribution function evolution in the plasma sheet boundary layer
Authors: Elphic R. C. , Gary S. P.
Published: February 2008

This paper describes ISEE plasma and magnetic fluctuation observations during two crossings of the plasma sheet boundary layer in the Earth's magnetotail. Distribution function observations show that the counterstreaming ion components undergo pitch‐angle scattering and evolve into a shell distribution in velocity space. This evolution is correlated with the development of low frequency, low amplitude magnetic fluctuations. However, the measured wave amplitudes are insufficient to accomplish the observed degree of ion pitch‐angle scattering locally; the near‐Earth distributions may be the result of processes occurring much farther down the magnetotail. Our results show a clear correlation between the ion component beta and the relative streaming speed of the two components, suggesting that electromagnetic ion/ion instabilities do play an important role in the scattering of PSBL ions.
Blob tectonics: A prediction for Western Aphrodite Terra, Venus
Authors: Heirick Robert R. , Phillips Roger J.
Published: February 2008

It is proposed that the Western Aphrodite Terra region of Venus was formed by four diapirs of heated mantle material, or blobs, rising to the surface in a region of convective upwelling. The four blobs are in different stages of evolution, producing different topography, gravity anomalies, and morphology. We show that this model is consistent with available data and make specific predictions that can be tested with Magellan radar data.
Enhanced ultraviolet transmission of Antarctic sea ice during the austral spring
Authors: Trodahl H. J. , Buckley R. G.
Published: February 2008

In determining the effect of the recent enhanced UV levels on Antarctic life it is important to know UV radiance under the vast sea ice cover surrounding the continent. This radiance is influenced by the transmission of the ice, and in this paper we report the first UV measurements on this turbid medium. The transmission is found to be largest in the Spring, so that life under the ice has always experienced its major UV irradiation dose in October. Dose enhancements by as much as an order of magnitude will have been experienced under the ozone holes of recent years.
Flux transfer events at the magnetopause and in the ionosphere
Authors: Elphic R. C. , Lockwood M. , Cowley S. W. H. , Sandholt P. E.
Published: February 2008

On December 1, 1986 the ISEE 1 and 2 spacecraft pair passed through the dayside magnetopause at a location which mapped approximately to ionospheric field‐line foot‐points near the fields of view of the EISCAT radar and photometers and an all‐sky camera on Svalbard. The magnetosheath magnetic field was southward and duskward at the time, and flux transfer events (FTEs) were observed at the ISEE location. At the same time, the EISCAT radar observed ionospheric flow bursts of up to 1 km s−1. The peak of each burst followed an FTE observation at ISEE by a few minutes. The bursts, each lasting ten or fifteen minutes, were comprised of first a westward then a poleward flow. An all‐sky camera at Ny Ålesund observed dayside auroral breakup forms during or shortly after the flow bursts, moving westward then poleward. While these flow bursts and associated dayside auroral forms have been previously reported in association with southward IMF orientations, this is the first observation of a direct link to FTEs at the magnetopause. On this occasion, the lower limit on the inferred potential associated with the FTEs is roughly 10 kV. Their inferred east‐west extent in the ionosphere ranges between 700 and 1000 km, corresponding to a 3 – 5 RE local time extent at the average magnetopause.
A two‐dimensional kinematic dynamo model of the ionospheric magnetic field at Venus
Authors: Cravens T. E. , Wu D. , Shinagawa H.
Published: February 2008

The ionosphere of Venus was observed by the magnetometer on the Pioneer Venus Orbiter (PVO) to be permeated by a large‐scale magnetic field for conditions of high solar wind dynamic pressure. The ionospheric conductivity is very high above 170 km and magnetic flux is carried by the plasma flow both vertically downward and in an antisunward direction. Ohmic dissipation of the electric current allows the magnetic field to diffuse for altitudes below 150–170 km. A number of one‐dimensional kinematic dynamo and MHD models have been developed to explain the observed vertical magnetic field profiles, but did not include the effects of horizontal transport. We have constructed a two‐dimensional kinematic dynamo model of the dayside ionospheric magnetic field at Venus in which the 2‐D magnetic induction equation (i.e., magnetic diffusion‐convection equation) is numerically solved using specified plasma velocities. The vertical velocity profile is taken from the one‐dimensional MHD model of Shinagawa and Cravens [1988] and the horizontal velocities are adapted from published PVO retarding potential analyzer results [Knudsen et al., 1982]. We demonstrate that the basic features of the vertical magnetic field profile, such as the presence of a magnetic layer at 170 km, remain unaltered by horizontal flow effects. However, we also show that horizontal plasma flow can strongly affect the magnetic field for altitudes above 300 km.
CRIT II electric, magnetic, and density measurements within an ionizing neutral stream
Authors: Swenson C. M. , Kelley M. C. , Primdahl F. , Baker K. D.
Published: February 2008

Measurements from rocket borne sensors inside a high velocity neutral barium beam show a factor of six increase in plasma density in a moving ionizing front. This region was co‐located with intense fluctuating electric fields (δE ≈ 300 mV/m) at frequencies well under the lower hybrid frequency for a barium plasma. Large quasi‐DC electric and magnetic field fluctuations were also detected with a large component of the current and the electric field parallel to Bo. An Alfvén wave with a finite electric field component parallel to the geomagnetic field was observed to propagate along Bo, where it was detected by an instrumented sub‐payload.
Heating of the ambient ionosphere by an artificially injected electron beam
Authors: Cartwright D. G. , Monson S. J. , Kellogg P. J.
Published: February 2008

An electrostatic analyzer on the electron accelerator of the Electron Echo 2 experiment showed that the electrons of the background plasma were heated to 10,000°K or more within 8 ms of the start of gun pulses. The degree of heating was dependent on the orientation of the rocket with respect to the magnetic field but was not measurably dependent on ambient electron density or neutral atmosphere density or on the pitch angle at which the 40‐keV electron beam was injected. This heating was also accompanied by an increase of plasma density. No evidence was found for an ion‐free region around the rocket during gun pulses. These observations show that significant amounts of ionization are taking place around the rocket. During part of the flight a two‐temperature electron distribution was found. It is believed that the high‐temperature part of these distributions represents secondaries produced by the beam.
Whistlers and VLF noises propagating just outside the plasmapause
Authors: Carpenter D. L.
Published: February 2008

Ground‐based recordings of broad‐band whistler mode signals propagating along the outer ‘surface’ of the plasmasphere, just beyond the region of steep plasmapause density gradients, exhibit a number of features that have not been observed in other field line regions. The features include extension of signal frequencies into the range ≃0.5–0.8 fHeq, where fHeq is the equatorial electron gyrofrequency of the path, and echoing or repeated propagation over the path at frequencies above 0.5 fHeq. The effects are frequently exhibited by tne ‘knee trace,’ the whistler component propagating just beyond the plasma‐pause in the low‐density or plasma trough region.The unusual features include VLF noise bands and bursts that are frequently triggered or ‘activated’ by knee whistler traces or echoes of knee traces. The noise bands and bursts tend to occur within the frequency range 0.4–0.8 fHeq and near the frequency of an amplitude peak in knee whistler trace activity. The wave activity is documented in VLF data from Eights, Antarctica (L≃4), for 1963 and 1965 and from Siple, Antarctica (L≃4.2), for 1973 through 1975. Certain features of the whistler and noise activity and of equatorial electron densities deduced from whistlers support earlier findings that the plasmapause equatorial radius may on occasion be irregular, varying by up to 1 RE within the longitudinal viewing range (≃30°) of a whistler receiver. Propagation effects such as guidance along the outer plasmapause surface and coupling of wave energy into and out of the ionosphere are not yet well understood. The VLF noise effects are of a kind recently found to be associated with detectable bursts of electron precipitation into the nighttime lower ionosphere. Because of the special propagation and warm plasma effects associated with the plasmapause, that region appears to offer advantages for experiments on magnetospheric wave injection both from the ground and from satellites.
The altitude profile of the N2+ first negative rotational temperature in an auroral arc
Authors: Romick G. J. , Degen V. , Stringer W. J. , Henriksen K.
Published: February 2008

Data from scanning photometers equipped with fixed interference filters selecting the P and R branches of the N2+ first negative (0–1) band were used to derive the temperature height profile through an auroral arc. The height of the arc was determined by two‐station triangulation techniques. The accuracy of the temperature determination is related to the relative intensity of the background aurora compared to the intensity of the arc. The need for a critical selection of the appropriate event to be analyzed and of the background to be subtracted is an important consideration in the analysis. In this particular example the most reliable part of the derived temperature profile lies between 105 and 140 km, and in this interval the temperatures agree well with the atmospheric temperature profile given by the U.S. Standard Atmosphere (1966) at 800°K exospheric temperature. No heating of the neutral atmosphere within the auroral arc was found.