bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental pressure solution of Halite by an indenter technique
Authors: Gratier Jean‐Pierre
Published: February 2008

An indenter technique is used to study pressure solution of halite immersed in brine. Two types of dissolution features are observed involving dissolution around or under the indenter: (1) free‐face pressure solution driven by elastic and plastic strain energy; and (2) water‐film diffusion controlled by normal stress. These different types of dissolution features are related to changes in the initial saturation of the brine. Free‐face pressure solution is only observed at slightly undersaturated initial conditions. Under fully saturated conditions, a linear relation of displacement rate versus stress is obtained confirming that the major driving force is the normal stress. However, both types of pressure solution mechanisms (and the associated pressure solution creep laws) can be expected to occur in natural deformation as various conditions of temperature, pressure and fluid composition change during progressive deformation.
CLAES south‐looking aerosol observations for 1992
Authors: Mergenthaler J. L. , Kumer J. B. , Roche A. E.
Published: February 2008

The Cryogenic Limb Etalon Array Spectrometer (CLAES) aboard the Upper Atmosphere Research Satellite (UARS) has made global observations of stratospheric aerosol during 1992. The instrument and measurement technique are briefly discussed. Samples of CLAES aerosol observations for south‐looking days through the course of the Antarctic winter showing evolution of polar stratospheric clouds (PSCs) and the Pinatubo volcanic veil are shown and discussed.
How active was solar cycle 22?
Authors: Hoegy W. R. , Pesnell W. D. , Woods T. N. , Rottman G. J.
Published: February 2008

Solar EUV observations from the Langmuir probe on Pioneer Venus Orbiter suggest that at EUV wavelengths solar cycle 22 was more active than solar cycle 21. The Langmuir probe, acting as a photodiode, measured the integrated solar EUV flux over a 13 1/2 year period from January 1979 to June 1992, the longest continuous solar EUV measurement. The Ipe EUV flux correlated very well with the SME measurement of Lα during the lifetime of SME and with the UARS SOLSTICE Lα from October 1991 to June 1992 when the Ipe measurement ceased. Starting with the peak of solar cycle 21, there was good general agreement of Ipe EUV with the 10.7 cm, Ca K, and He 10830 solar indices, until the onset of solar cycle 22. From 1989 to the start of 1992, the 10.7 cm flux exhibited a broad maximum consisting of two peaks of nearly equal magnitude, whereas Ipe EUV exhibited a strong increase during this time period making the second peak significantly higher than the first. The only solar index that exhibits the same increase in solar activity as Ipe EUV and Lα during the cycle 22 peak is the total magnetic flux. The case for high activity during this peak is also supported by the presence of very high solar flare intensity.
Comparing stratospheric aerosols from El Chichón and Mount Pinatubo using AVHRR data
Authors: Strong A. E. , Stowe L. L.
Published: February 2008

One of the key factors in assessing the climatic impact of the Mount Pinatubo eruption of June 15, 1991, is the relative size of this eruption as it compares with other eruptions. As a first approximation, the climatic changes observed after those earlier eruptions can be used to predict the changes to be expected from the more recent eruption. Ideally this intercomparison should be done with a common measurement system. Data from the advanced very high resolution radiometer (AVHRR) onboard the NOAA polar orbiting environmental satellite can be used to compare the optical properties of the aerosol layer produced by the two most recent major volcanic eruptions, El Chichón, early‐April 1982, and Mount Pinatubo, mid‐June 1991. In this paper, we use the error introduced into the multi‐channel sea surface temperature (MCSST) fields by the volcanically‐produced stratospheric aerosol layer to make a relative comparison of the size of the two eruptions. We also use aerosol optical thickness (AOT) estimates from the visible reflectance channel of the AVHRR to verify that the MCSST errors are indeed related to aerosol particle concentration in the stratosphere. During the first three months following both eruptions, these comparisons reveal that Mount Pinatubo introduced slightly less than twice (1.6 to 1.9) the amount of aerosol into the stratosphere as El Chichón.
Particle drift in the Earth's plasma sheet
Authors: Wolf R. A. , Pontius D. H.
Published: February 2008

We generalize the derivation of the average gradient/curvature‐drift for a flux tube filled with an isotropic distribution of particles at specified kinetic energy. The present treatment is restricted to a two‐dimensional magnetic field with zero electric field, but it includes all chaotic and Speiser orbits, which do not correspond to the simple picture of gradient/curvature drift. We assume that particles are evenly distributed throughout the regions of phase space allowed by their energy and canonical momentum. This assumption is closely related but not exactly equivalent to the assumption of isotropic pitch‐angle distribution. Our derivation assumes that the maximum Larmor radius is small compared to the scale length for equatorial variations in the flux tube volume, but it does not involve any restrictions on the curvature of the field line. The resulting expression for the drift rate is valid for situations where the particle drift velocity is comparable to the thermal speed in some regions. The apparent implication of this generalized treatment is that the existence of very complex non‐adiabatic particle trajectories in the plasma sheet may not invalidate previous estimates of the average rate of particle drift out the sides of the tail, estimates that were made under the assumption of simple guiding‐center drifts.
Cupri observations of PMSE during Salvo B of NLC‐91: Evidence of both partial reflection and turbulent scatter
Authors: Cho John Y. N. , Swartz Wesley E. , Kelley Michael C. , Miller Clark A.
Published: February 2008

During the first rocket sequence (called Salvo B) of the NLC‐91 campaign, the Cornell University Portable Radar Interferometer (CUPRI) observed two simultaneously occurring layers of Polar Mesosphere Summer Echoes (PMSE). During the time of the Turbo B flight, the high time‐resolution CUPRI Doppler spectra exhibited sawtooth‐like discontinuities in the lower layer which we interpret to be a distorted partial reflection layer which was advected across the radar beam. The upper layer, on the other hand, appeared to be caused by turbulent scatter and we estimate the turbulence energy dissipation rate in the upper layer at the time of the Turbo B flight to have been approximately 0.04 W/kg. Furthermore, a shift in the antenna beam direction from vertical to 8° off zenith revealed an aspect sensitivity of approximately 5 dB in the lower layer but none in the upper layer. We conclude that, at this particular time, turbulent scatter was responsible for the upper layer while some form of partial reflection was dominant in the lower layer.
Sn to Sg conversion and focusing along the Atlantic Margin, Morocco: Implications for earthquake hazard evaluation
Authors: Seber Dogan , Barazangi Muawia , Tadili Ben Aissa , Ramdani Mohamed , Ibenbrahim Aomar , Ben Sari Driss , El Alami Sidi Otman
Published: February 2008

Digital data from a telemetered, short‐period seismic network in Morocco provide a new perspective for understanding the cause of severe shaking and macroseismic reports in Morocco produced by large, offshore earthquakes located along the Azores‐Gibraltar seismic zone. Even though the earthquake epicenters are 500–1000 km away from the Moroccan coast, historical records show that such events are capable of producing considerable damage in inland areas. We analyze 15 earthquakes that occurred in this region. The records show multiple S phases with varying frequencies and amplitudes. The S phase with the largest amplitude, usually misinterpreted as Sn, has a phase velocity of 4.2–4.4 km s−1. We show that these S arrivals can best be explained as Sn to Sg converted phases. Calculated locations of the conversion points for these phases exhibit two distinct zones almost parallel to the Atlantic coastline: one is located along the passive continental margin and the other is located about 100 km inland from the coastline. We interpret these two zones to be regions where a sudden change in crustal thickness occurs. Such zones act to focus and magnify the amplitudes of seismic phases. This interpretation explains the unusually strong felt reports within Morocco from such distant offshore events, and it has a significant effect on earthquake hazard evaluation and mitigation studies.
The evolution of CLO and NO along air parcel trajectories
Authors: Schoeberl M. R. , Douglass A. R. , Stolarski R. S. , Newman P. A. , Lait L. R. , Toohey D. , Avallone L. , Anderson J. G. , Brune W. , Fahey D. W. , Kelly K.
Published: February 2008

Back trajectory analysis of Arctic and Antarctic aircraft data reveals that high ClO concentrations are associated with predicted polar stratospheric cloud (PSCs) encounters. The ClO concentrations within the Arctic and Antarctic polar vortices vary widely but appear to be inversely related to parcel solar exposure since the last PSC interaction. These results imply that production of NOx from HNO3 photolysis and reaction with OH is the mechanism, for the loss of chlorine radicals through the reformation of chlorine nitrate. Highly denitrified air parcels show no change in ClO with solar exposure. The recovery process is quantitatively duplicated using a model of chemistry along trajectories. Although PSC processing is the primary mechanism for producing elevated ClO amounts, back trajectories apparently unperturbed by PSC's also show slightly elevated ClO levels in 1992 compared to Arctic 1989 and Antarctic 1987 measurements presumably due to the presence of Pinatubo aerosol.
In‐situ measurements of changes in stratospheric aerosol and the N2O‐aerosol relationship inside and outside of the polar vortex
Authors: Borrmann S. , Dye J. E. , Baumgardner D. , Wilson J. C. , Jonsson H. H. , Brock C. A. , Loewenstein M. , Podolske J. R. , Ferry G. V. , Barr K. S.
Published: February 2008

Two optical particle counters on the ER‐2, together covering a particle size diameter range from 0.1 μm to 23 μm, were used to measure the aerosol bulk quantities integral number, aerosol surface and volume, as well as detailed size distributions inside and outside of the polar vortex in the lower stratosphere. While AASE I (Arctic Airborne Stratospheric Expedition, (Dec. 88‐Feb. 89) was conducted in a period of relative volcanic quiescence, enhancements in aerosol number, surface and volume of factors around 10, 25 and 100 were observed during AASE II (Aug. 91‐Mar. 92) due to the eruption of Mt. Pinatubo. The changes in these bulk quantities as well as in the size distributions measured both outside and inside the the polar vortex are presented and compared with those obtained in polar stratospheric cloud events (AASE I). Except for a shift towards larger aerosol mixing ratios the general shape of correlograms between the measured N2O and particle mixing ratios remain similar before and after the eruption. Similar correlograms are used to interpret data from vertical profiles inside and outside of the polar vortex.
Interaction with the lower ionosphere of electromagnetic pulses from lightning: Heating, attachment, and ionization
Authors: Taranenko Y. N. , Inan U. S. , Bell T. F.
Published: February 2008

A Boltzmann formulation of the electron distribution function and Maxwell's equations for the electromagnetic (EM) fields are used to simulate the interaction of lightning radiated EM pulses with the lower ionosphere. Ionization and dissociative attachment induced by the heated electrons cause significant changes in the local electron density (Ne). Due to ‘slow’ field changes of typical lightning EM pulses over time scales of tens of µs, the distribution function follows the quasi‐equilibrium solution of the Boltzmann equation in the altitude range of interest (70 to 100 km). The EM pulse is simulated as a planar 100 µs long single period oscillation of a 10 kHz wave injected at 70 km. Under nighttime conditions, individual pulses of intensity 10–20 V/m (normalized to 100 km horizontal distance) produce changes in Ne of 1–30% while a sequence of pulses leads to strong modification of Ne at altitudes <95 km. The Ne changes produce a ‘sharpening’ of the lower ionospheric boundary by causing a reduction in electron density at 75–85 km (due to attachment) and a substantial increase at 85–95 km (due to ionization) (e.g., the scale height decreases by a factor of ∼2 at ∼85 km for a single 20 V/m EM pulse). No substantial Ne changes occur during daytime.
The low‐latitude boundary layer at mid‐altitudes: Relation to large‐scale Birkeland currents
Authors: Woch J. , Yamauchi M. , Lundin R. , Potemra T. A. , Zanetti L. J.
Published: February 2008

Data from the hot plasma instruments and the magnetometer on board Viking (apogee at 13,530 km) acquired in the high latitude pre‐dawn to pre‐noon region are combined to study the relations between the low‐latitude boundary layer (LLBL) projection and large‐scale field‐aligned currents (FAC). The projection of the LLBL is defined as the region with precipitation of ions with magnetosheath origin [Woch and Lundin, 1993]. The cusp and plasma mantle regions are excluded. The study focuses on magnetically quiet to moderately disturbed conditions. On the vast majority of passes the R1 FAC is found to be totally confined within the LLBL projection. This can be regarded as direct evidence of a LLBL source for the dayside R1 FAC. The latitudinal width of the LLBL (and consequently also that of the R1 FAC) decreases considerably going from pre‐dawn to pre‐noon MLT sectors. The current intensity increases only slightly towards pre‐noon. The R1 current density maximum known to exist in the pre‐noon region is thus primarily due to the LLBL projection converging towards local noon.
The density jump across the ICB and constraints on P‐reflector in the D' layer from observation of the 1992 Chinese Nuclear Explosion
Authors: Yamada Akira , Nakanishi Ichiro
Published: February 2008

Seismic waves observed from the Chinese nuclear explosion detonated on May 21, 1992 (mb=6.6) are analyzed to detect PKiKP and PdP, reflected waves from the inner core boundary (ICB) and the D” discontinuity, respectively. A linear stacking method is applied to a large number of digital data recorded in the Japanese Islands to identify the reflected waves. The stacked data indicate a weak signal of PKiKP. PKiKP/PcP amplitude ratio of 0.03 is obtained from the stacked waveforms of PKiKP and PcP, which suggests the density jump across the ICB to be 0.6 g/cm³. This value is in agreement with previous estimates from free oscillations data. No positive evidence for the identification of PdP is suggested from the stacking process. This implies the absence of a significant P wave reflector or, if present, the impedance contrast is less than 2% in the lowermost mantle under East China. Another interpretation in terms of gradient zone thickness or reflector topography is also possible.
A comparison of observed (Haloe) and modeled (CCM2) methane and stratospheric water vapor
Authors: Mote Philip W. , Holton James R. , Russell James M. , Boville Byron A.
Published: February 2008

Recent measurements (21 September–15 October 1992) of methane and water vapor by the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS) are compared with model results for the same season from a troposphere‐middle atmosphere version of the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM2). Several important features of the two constituent fields are well reproduced by the CCM2, despite the use of simplified methane photochemistry in the CCM2 and some notable differences between the model's zonal mean circulation and climatology. Observed features simulated by the model include the following: 1) subsidence over a deep layer in the Southern Hemisphere polar vortex; 2) widespread dehydration in the polar vortex; 3) existence of a region of low water vapor mixing ratios extending from the Antarctic into the Northern Hemisphere tropics, which suggests that Antarctic dehydration contributes to midlatitude and tropical dryness in the stratosphere.
Implications of new gravity data for Baikal rift zone structure
Authors: Ruppel C. , Kogan M. G. , McNutt M. K.
Published: February 2008

Newly available, 2D Bouguer gravity anomaly data from the Baikal Rift zone, Siberia, indicate that this discrete, intracontinental rift system is regionally compensated by an elastic plate ∼50 km thick. However, spectral and spatial domain analyses and isostatic anomaly calculations show that simple elastic plate theory does not offer an adequate explanation for compensation in the rift zone, probably because of significant lateral variations in plate strength and the presence of subsurface loads. Our results and other geophysical observations support the interpretation that the Baikal Rift zone is colder than either the East African or Rio Grande rift.
Rheometry of a dacitic melt: Experimental results and tests of empirical models for viscosity estimation
Authors: Stein Daniel J. , Spera Frank J.
Published: February 2008

Empirical models have long been available for estimating the Newtonian viscosity of single‐phase silicate melts from composition in terms of oxide components [Bottinga and Weill, 1972; Shaw, 1972]. These models are used regularly to estimate or parametrize viscosity in field studies and fluid dynamical calculations of magmatic transport. However, few independent viscosity measurements on multi‐component melts of natural composition have been made to test the accuracy of the empirical estimation models. A series of experimental measurements of viscosity has been performed on a dacitic melt, using the technique of concentric cylinder rheometry. In the ranges of temperature and shear rate examined (1000 to 1150° C and 0.013 to 7.43 s−1, respectively), the melt viscosity is found to be independent of shear rate. When the viscomentric results from the present study and those on a rhyolitic composition [Hochella and Brown, 1984] are compared with the results from the empirical models, the model of Shaw [1972] is found to represent both sets of experimental data better than that of Bottinga and Weill [1972]. This is presumably due to differences in the ranges of temperature and composition represented in the data used to construct the respective models.
Chlorine, fluorine, and sulfur emissions from Mount Erebus, Antarctica and estimated contributions to the Antarctic atmosphere
Authors: Zreda‐Gostynska Grazyna , Kyle Philip R. , Finnegan David L.
Published: February 2008

The discharge rates of halogens in aerosols and gases emitted from Mount Erebus between December 1986 and January 1991 were estimated by combining element‐to‐sulfur ratios on filter samples with SO2 output measured by COSPEC. The halogen and sulfur content of the gas vary in a quasi‐cyclical pattern possibly because of a heterogeneous distribution of volatiles in the Erebus magmatic system. The emission rates of HF and HCl have increased twofold since 1986 reaching 6 and 13.3 Gg yr−1, respectively, in 1991, making Erebus an important contributor of halogens to the Antarctic atmosphere.
The fold test in paleomagnetism as a parameter estimation problem
Authors: Watson Geoffrey S. , Enkin Randolph J.
Published: February 2008

Most proposed fold test formulations use significance tests to try pre‐tilting and post‐tilting remanence hypotheses. We suggest that it is better to consider the fold test as a parameter estimation problem. Making the usual assumption that the distribution of remanence vectors was originally roughly parallel, we propose, using a monte carlo simulation technique, to estimate the amount of tectonic tilting at the time of magnetization along with a 95% confidence interval. If, for example, this confidence interval included 100% then one could not rule out pre‐tilting remanence. In the older terminology, the fold test is positive. The k‐ratio test of McElhinny [1964] is often said to be conservative in that if a study passes the k‐ratio test then it certainly passes a more rigorous test. We show with a typical counter‐example that this assertion is incorrect. Observational uncertainty of bedding directions is easily included in this formulation.
A case study of the Mountain Lee Wave Event of January 6, 1992
Authors: Chan K. R. , Pfister L. , Bui T. P. , Bowen S. W. , Dean‐Day J. , Gary B. L. , Fahey D. W. , Kelly K. K. , Webster C. R. , May R. D.
Published: February 2008

A mountain wave event, observed at the southern tip of Greenland on January 6, 1992, was corroborated by three experiments: the Meteorological Measurement System (MMS), the Microwave Temperature Profiler (MTP), and the Reactive Nitrogen Instrument (NO/NOy). Gravity wave signatures with classical phase relationship between wind and temperature were observed on both the outbound and inbound legs at different altitudes. The waves showed both vertically propagating and evanescent properties. Characteristics of the dominant wave mode are: wavelength ≈ 35 km; vertical displacement ≈ 0.8 km, and peak‐to‐peak vertical wind ≈ 6 ms−1. With the prevailing wind at ≈ 37 ms−1, the stratospheric temperature was reduced by 6K to 195.5K within 8 minutes. The implication and potential impact of mountain lee waves on the formation of polar stratospheric clouds (PSC's) are discussed.
Thermal demagnetization of VRM and pTRM of single domain magnetite: No evidence for anomalously high unblocking temperatures
Authors: Dunlop David J. , Özdemir Özden
Published: February 2008

Stepwise thermal demagnetization of viscous remanent magnetization (VRM) and partial thermoremanent magnetization (pTRM) of single‐domain magnetite with mean grain size 37 nm reveals only minor deviations from the predictions of Néel theory. Three different initial states were used, following (1) alternating field demagnetization to 100 mT, (2) thermal demagnetization to 610°C, and (3) modified thermal demagnetization, consisting of zero‐field heating to 610°C followed by zero‐field cooling to the VRM or pTRM acquisition or blocking temperature, TB. VRMs were produced by applying a 0.1 mT field for 3.5 hr, starting from initial states 2, 3 and 1, in that order, at TB=283°C and from states 3, 2 and 1 at TB=404°C. In a final experiment, pTRM was produced by applying 0.1 mT during cooling from TB1=414°C to TB2=404°C, starting from state 3. In all but one case, VRM began to unblock significantly (90% of initial intensity) ≈15°C below TB, dropped to ≈50% at TB, and then tailed off, dropping below 10% ≈40°C above TB=283°C or ≈25°C above TB=404°C. Partial TRM behaved in the same way, except that demagnetization was essentially complete by TB1=414°C. The maximum unblocking temperatures (TUB) observed are exactly as predicted by the theory of Pullaiah et al. (1975). Although very long acquisition times cannot be tested, we find no evidence for anomalously high TUBs of VRM in single‐domain grains. In previously reported cases of rocks with unexpectedly high TUBs, the VRM was probably carried by multidomain grains.
The heating of suprathermal ions above thunderstorm cells
Authors: Bell T. F. , Helliwell R. A. , Inan U. S. , Lauben D. S.
Published: February 2008

We estimate ion heating in the topside ionosphere directly over thunderstorm cells. The primary heating is due to lower hybird waves excited through linear mode coupling as intense electromagnetic (EM) whistler mode radiation from lightning is scattered from small scale (2 – 20 m) magnetic‐field‐aligned plasma density irregularities in the topside ionosphere. For typical radiated EM fields, we find that suprathermal H+ ions in the ≥ 6 eV energy range can be heated by 20 to 40 eV as a result of a single lightning discharge. We also show how the number density of ≥ 6 eV H+ ions is enhanced by preheating resulting from the absorption of proton whistlers in the 500 – 1000 km altitude range. For lightning discharge rates of one or more per second over a 104 km² area, our model predicts a total energy gain for the H+ ions of 400 eV to 2 KeV and a perpendicular ion flux of j⟂ ∼ 105 to 106cm−2sec−1. These fluxes should be observable on low altitude spacecraft using presently available instrumentation.
Effects of strongly temperature‐dependent viscosity on time‐dependent, three‐dimensional models of mantle convection
Authors: Tackley Paul J.
Published: February 2008

Numerical simulations of thermal convection in a wide (8×8×1) Cartesian box heated from below with temperature‐dependent viscosity contrasts of 1000, and Rayleigh number 105 show that boundary conditions and aspect ratio have an enormous effect on the preferred flow pattern. With rigid upper and lower boundaries, spoke‐pattern flow with small (diameter ∼ 1.5) cells is obtained, consistent with laboratory experiments and previous numerical results. However, with the arguably more realistic stress‐free boundaries, the flow chooses the largest possible wavelength, forming a single square cell of aspect ratio 8, with one huge cylindrical downwelling surrounded by upwelling sheets. The addition of stress‐dependence to the rheology weakens the stiff upper boundary layer, resulting in smaller cells, though still with upwelling sheets and downwelling plumes.
Balloon‐borne measurements of CLO, NO, and O3 in a volcanic cloud: An analysis of heterogeneous chemistry between 20 and 30 km
Authors: Dessler A. E. , Stimpfle R. M. , Daube B. C. , Salawitch R. J. , Weinstock E. M. , Judah D. M. , Burley J. D. , Munger J. W. , Wofsy S. C. , Anderson J. G. , McCormick M. P. , Chu W. P.
Published: February 2008

Balloon profiles of chlorine monoxide (ClO), nitric oxide (NO), and ozone (O3) were measured on March 11, 1992 from 100 to 10 mb over Greenland (67.0°N, 50.6°W). Measurements from SAGE II indicate that the aerosol surface area in the region was enhanced by sulfur from the eruption of Mt. Pinatubo, reaching 50 times background near 20 km. Concentrations of ClO were enhanced and concentrations of NO were suppressed relative to low aerosol conditions consistent with the effects of hydrolysis of N2O5 on the surface of sulfuric acid aerosols. The data are consistent with a value of 2×10−4 for the reaction probability of the heterogeneous hydrolysis of ClONO2, indicating a minor role for this reaction at a temperature of 220 K. At these temperatures, we find no evidence for the catastrophic loss of ozone predicted to occur under conditions of enhanced aerosol surface area.
Evidence for day‐to‐night ion transport at low solar activity in the Venus pre‐dawn ionosphere
Authors: Brannon J. F. , Fox J. L. , Porter H. S.
Published: February 2008

Periapsis of the Pioneer Venus spacecraft dropped below 180 km on August 28, 1992 near midnight, and 42 orbits of low altitude data at moderately low solar activity in the pre‐dawn sector were obtained before contact was lost to the spacecraft in October, 1992. Through a combination of analysis of data from the PV orbiter ion mass spectrometer (OIMS) and modeling, we consider here what can be learned about the relative importance of plasma transport from the dayside and electron precipitation in maintaining the nightside ionosphere during the re‐entry period. In particular, we examine here the atomic ion density profiles. We compute the average peak density of O+ as a function of solar zenith angle and determine what fluxes of atomic ions or precipitating electrons would be necessary to produce those values. We then compare model calculations of the ion densities to those observed during the re‐entry period. We find that the low solar activity nightside ionosphere shows evidence of significant day‐to‐night plasma transport.
Observations of the nightside Venus ionosphere: Final encounter of the Pioneer Venus Orbiter Ion Mass Spectrometer
Authors: Cloutier P. A. , Kramer L. , Taylor H. A.
Published: February 2008

During the last orbital sequences of the Pioneer‐Venus spacecraft prior to final encounter and atmospheric entry, data were obtained by the Orbiter Ion Mass Spectrometer (OIMS) at the lowest periapsis altitudes of the mission. These data verified OIMS observations of the nightside ionospheric peak reported earlier in the mission, and revealed additional details related to composition, energetics and maintenance of the nightside ionosphere. OIMS observations of the ion peak during the final encounter sequence are compared with radio occultation data and OIMS peak observations obtained earlier. OIMS ion density and Orbiter Electron Temperature Probe (OETP) electron density are found to correlate near the peak. Coupling of mass channels 30 and 32 during nightside passes is observed and its interpretation considered. Changes in high altitude composition of the nightside ionosphere, especially the relative changes in O+ and H+, are described.
Origin of magnetic viscosity and estimate of long‐term induced magnetization in coarse‐grained submarine basalts
Authors: Prévot Michel , Bina M. Mansour
Published: February 2008

The characteristics of magnetic viscosity and susceptibility disaccommodation of a submarine basalt containing multidomain (MD) titanium‐rich titanomagnetite are found to be quite dissimilar at room temperature. Thus, the viscous induced magnetization (VIM) of submarine basalts in situ is not due to diffusion but to thermal fluctuations. Experiments above room temperature show that a linear log t extrapolation of laboratory measurements at room temperature yields an underestimate of the Brunhes VIM. A theoretical calculation of this projected VIM is difficult because of the thermal dependence of the activation volume of barriers in MD low‐Curie point minerals.
AASE‐II in‐situ tracer correlations of methane, nitrous oxide, and ozone as observed aboard the DC‐8
Authors: Collins J. E. , Sachse G. W. , Anderson B. E. , Weinheimer A. J. , Walega J. G. , Ridley B. A.
Published: February 2008

We report in situ stratospheric measurements of CH4, N2O, and O3 obtained aboard the NASA DC‐8 during the January‐March 1992 Airborne Arctic Stratospheric Expedition II field campaign. These data demonstrate a strong linear correlation between N2O and CH4 in the lower stratosphere thus indicating that both species are effective tracers of stratospheric air motion. Measurements of both species on constant geometric height surfaces indicate that significant subsidence of the arctic stratospheric air mass occurred at DC‐8 altitudes over the course of the AASE‐II expedition. In addition, a widespread reduction in O3 mixing ratios (up to 20%) relative to these conserved tracers was also observed in the lower stratosphere in March as compared to January and February results.
Borehole inclinometer monument for millimeter horizontal geodetic control accuracy
Authors: Bilham Roger
Published: February 2008

A geodetic monument is described whose horizontal position may be monitored relative to points 30 m deep to an accuracy of 0.5 mm, and to points more than 2 km to a potential accuracy of 2 mm. The monument incorporates a 7 cm diameter borehole lining equipped with orthogonal alignment grooves that guide a portable inclinometer during measurements. The inclinometer is raised incrementally from the base of the hole to measure the tilt of contiguous 0.5‐m‐long segments of the borehole prior to geodetic occupation. Integrating the results yields a measure of the surface monument's position. Random errors increase with the square root of the number of downhole measurements N as 0.03 √N mm (N=2d for d‐m‐deep hole). Systematic errors are approximately 0.02% of the lateral offset of the base of the hole relative to the surface monument. Unlike previous monuments the inclinometer‐based system permits surface and subsurface instability to be characterized, and the effectiveness of the monument to be monitored.
The Beaufort Sea continental shelf as a seasonal source of atmospheric methane
Authors: Kvenvolden Keith A. , Lilley Marvin D. , Lorenson Thomas D. , Barnes Peter W. , McLaughlin Elizabeth
Published: February 2008

Methane concentrations in the Beaufort Sea under the winter ice canopy offshore from northern Alaska are 3 to 28 times greater than they are in late summer when the ice is absent in a similar region offshore from northern Canada where methane is in approximate equilibrium with the atmosphere. These observations suggest that methane concentrates in the water under the sea‐ice cover during winter and ventilates rapidly in late summer as the ice melts and retreats. Conditions similar to those on the Beaufort Sea shelf likely exist on the much larger Siberian shelf, making the Arctic Ocean margin a possible seasonal, high‐latitude, marine source of about 0.1 Tg yr−1 atmospheric methane. The small addition of methane likely contributes to the late‐summer increase in atmospheric methane that is observed each year particularly in the northern hemisphere.
anisotropy of Earth's inner core
Authors: Song Xiaodong , Helmberger Don V.
Published: February 2008

In an effort to confirm inner core anisotropy, we conducted a systematic search for PKP ray paths with various angles from the Earth's spin axis. In particular, we studied paths nearly parallel to the spin axis (polar paths) and those nearly parallel to the equatorial plane (equatorial paths). Data for earthquakes and explosions were collected from Worldwide Standardized Seismograph Network (WWSSN), Long Range Seismic Measurements (LRSM), and Global Digital Seismograph Network (GDSN). Absolute times (DF, BC) and differential times (BC‐DF, AB‐DF) as well as waveform data were examined. For all polar paths, differential times of BC‐DF consistently yield residuals of 1.5 to 3.5s larger than equatorial paths. Absolute DF time residuals exhibit anomalies of the same magnitude (1 to 4s) with DF being early along polar paths while BC residuals have no obvious correlation with the differential time anomalies. DF phases appear multi‐pathed for polar paths and are relatively simple for equatorial paths. These results coupled with previous studies suggest an axisymmetric anisotropy at the top of the inner core.
Constraining outermost core velocity with SmKS waves
Authors: Garnero Edward J. , Helmberger Donald V. , Grand Stephen P.
Published: February 2008

SmKS waves (m=2,3,4), seismic waves that travel as S‐waves in the mantle, P‐waves in the core, and reflect (m‐1) times on the underside of the core‐mantle boundary, are well‐suited for constraining outermost core VP structure. This is due to closeness of the mantle paths and also the shallow depth range these waves travel in the outermost core. High quality digitized WWSSN and Canadian network recordings from a deep focus Java Sea event which sample the outer core beneath the northern Pacific, the Artic, and northwestern North America (roughly ⅛th of the globe), are utilized as an example to show the strength of SmKS waves to resolve outermost core structure. S3KS‐S2KS and S4KS‐S3KS differential travel times were measured and compared to those from reflectivity synthetics created from core models of past studies. Constraints and uncertainties in outer core structure using SmKS are discussed. For the event studied, the PREM core model, with possibly a small VP decrease in the outermost 50 km of the core, provides a good fit to the data.
Neural net forecasting for geomagnetic activity
Authors: Hernandez J. V. , Tajima T. , Horton W.
Published: February 2008

We use neural nets to construct nonlinear models to forecast the AL index given solar wind and interplanetary magnetic field (IMF) data. We follow two approaches: 1) the state space reconstruction approach, which is a nonlinear generalization of autoregressive‐moving average models (ARMA) and 2) the nonlinear filter approach, which reduces to a moving average model (MA) in the linear limit. The database used here is that of Bargatze et al. [1985].
Parameterization of the cloud optical thickness: Influence of clear air entrainment
Authors: Pontikis Constantin
Published: February 2008

The effects of clear air entrainment and mixing on the cloud optical thickness are investigated. Three different approximate expressions of the cloud optical thickness are derived according to the type of mixing and the presence or absence of secondary droplet activation. They depend upon the liquid water path as well as upon the optical thickness and liquid water path of the corresponding adiabatic cloud. The influence of the cloud droplet concentration on the cloud optical thickness values is shown. These expressions are used to deduce a parameterization of the optical thickness, that is further validated with experimental data.
Background levels of formate and other ions in ice cores from inland Greenland
Authors: Osada Kazuo , Langway Chester C.
Published: February 2008

Concentration levels of the organic acids HCOO− and CH3SO3−, inorganic acids NO3− and excess SO42− and ammonium were measured in pre‐1900 AD ice layers from seven geographically dispersed inland sites in Greenland. Average multiple‐year background concentration levels are calculated for each ion at each site from laboratory measurements of continuous core samples representing from 4 to 10 years of snow accumulation (32 to 80 individual measurements) from various time intervals.

The HCOO− concentration level increases from 6 ng/g in the most northern colder site to 36 ng/g in the most southern warmer site; CH3SO3− increases from 0.9 ng/g to 2.8 ng/g; NO3− decreases from 83 ng/g to 37 ng/g; excess SO42− decreases from 43 ng/g to 19 ng/g, all with variability. The distribution of the NH4+ ion shows a nearly constant level at about 6 ng/g for all sites except Dye‐2 where it reaches 10 ng/g. The deposition patterns for HCOO− and NH4+ on the ice sheet suggest major contributions arrive from sources originating from the southwest of Greenland.
The opening of the Andaman Sea: Where is the short‐term displacement being taken up?
Authors: Guzmán‐Speziale Marco , Ni James F.
Published: February 2008

The short‐term spreading velocity in the Andaman Sea, a marginal basin inboard of the Western Sunda Arc, is calculated using the strain rate tensor which, in turn, is obtained from summing seismic moment tensors of normal‐faulting earthquakes. A velocity of displacement is also obtained for the right‐lateral Sagaing Fault, which is the northern continuation of the Andaman spreading system. Using earthquakes in a 22‐year period (1964–1986), the maximum spreading velocity in the Andaman Sea is found to be oriented in a N 19° W direction, with a speed of 0.05 cm/yr. The north‐south relative velocity along the Sagaing Fault is 0.5 cm/yr, for strike‐slip earthquakes between 1971 and 1992. Historical earthquakes in the Andaman Sea do not significantly add to the short‐term spreading velocity because there are no earthquakes with Ms≥6.0. For the Sagaing Fault, however, when moment tensors from earthquakes since 1908 are used, the relative velocity is 5.7 cm/yr, a figure close to the 3.72 cm/yr long‐term (13 ma) rate of opening of the Andaman Sea. These results suggest that strain due to the opening of the Andaman Sea is seismic along the Sagaing Fault and aseismic along the Andaman Sea Spreading System, probably because the spreading centers and transform faults in the Andaman Sea are short and cannot accomodate large earthquakes.
Observations of the loss of stratospheric NO2 following volcanic eruptions
Authors: Coffey M. T. , Mankin William G.
Published: February 2008

Observations of stratospheric column amounts of nitrogen dioxide (NO2), nitric oxide (NO) and nitric acid (HNO3) have been made following major eruptions of the El Chichón and Mt. Pinatubo volcanoes. Midlatitude abundances of NO2 and NO were reduced by as much as 70% in the months following the appearance of the volcanic aerosols as compared to volcanically quite periods. There are heterogeneous reactions which could occur on the volcanic aerosols to convert NO2 into HNO3 but no commensurate increase in HNO3 column amounts was observed at the times of NO2 decrease.
A new scenario for the measurement of the auroral plasma parameters in the non‐Maxwellian state
Authors: Hubert D. , Bonnard N. , Lathuillere Ch. , Kofman W.
Published: February 2008

The O+ and NO+ ion velocity distributions in the presence of a large electric field are analytically calculated for the auroral F region, taking into account the collisions with atomic and molecular neutral constituents. We have found an angle of 21°± 1° with respect to the magnetic field direction where the O+ one‐dimensional line‐of‐sight velocity distributions display a Maxwellian shape while the NO+ distribution function is nearly a Maxwellian. A scenario for the measurement of the auroral plasma parameters is discussed. The radar spectrum obtained for the specific angle of 21° depends on five parameters : electron density, electron temperature, ion composition, and two ion line‐of‐sight temperatures. With this reduced number of plasma parameters the fit from radar spectra is nevertheless ambiguous. To resolve this dilemma it is necessary to get an independent measurement of one of these five parameters. The plasma line observation is shown to provide a simultaneous measurement of the electron temperature. From simultaneous measurements of the ion line‐of‐sight temperatures, made at an angle away from 21° the termodynamical temperature, as well as the ion temperature anisotropies, would be determined.
Spheroidal models of magnetic clouds and their comparison with spacecraft measurements
Authors: Vandas M. , Fischer S. , Pelant P. , Geranios A.
Published: February 2008

We present here magnetic force‐free solutions for spherical, oblate, and prolate clouds and show their magnetic field configurations. It is shown that spheroidal models can fit observed clouds as well as the cylindrical model. The spherical model is free of the limitation of the cylindrical model that allows only reduced increase of the magnetic field to 2x of the boundary value following from properties of the Bessel functions. For the tested cases, the cloud diameters following from the fit are generally larger for the spherical model than for the cylindrical one. An analysis of 14 cases shows that the fit using the spherical model is of a comparable accuracy in comparison with the cylindrical model. Generally, no exact determination of the cloud boundaries has been given up to now. We try to estimate cloud boundaries from the plasma data as an independent check, and compare them with cloud boundaries following from models of magnetic clouds. The boundaries given by the spheroidal models are near irregular temperature increases, and we suggest taking these increases as a possible indicator of the cloud physical boundaries.
On the variation of the Sun's X ray background flux and its relation to the Sun's flaring rate, energetic event rate, and the solar cycle
Authors: Wilson Robert M.
Published: February 2008

Daily averages of the Sun's X ray background flux as measured by the GOES satellite are combined to yield monthly means and "smoothed" monthly means (12‐month moving averages) for the interval January 1986 through May 1992 (minimum, rise, maximum, and initial decline of solar cycle 22). These averages are then compared directly to the Sun's optical flaring rate, energetic event rate, and the usual markers of the solar cycle (e.g., sunspot number, total corrected sunspot area, 10.7‐cm solar radio flux, number of groups, and number of spots). The results of this analysis support previous findings that there exists a remarkably close positive relationship between the optical flaring rate and the X ray background flux rate (the independent variable); that the relationship is best described using a logarithmic fit of the form ŷ = a + blog(1 + x); and that the X ray background flux rate can be used as a proxy for the solar cycle. Additionally, this study has found that a strong positive relationship exists between the energetic event rate and the X ray background flux rate (the independent variable), being best described by a linear fit of the form ŷ = a + bx; that the lag between the maxima of the rates of optical flaring and X ray background flux reported for cycle 21 did not recur for cycle 22; and that the lag for cycle 21 and lack of lag for cycle 22 can easily be explained by the peculiar action of the solar cycle, especially as it relates to the phasing of the “magnetic complexity” of active regions (i.e., the particular phasing of the numbers of groups and spots).
The cosmic radiation in the heliosphere at successive solar minima: Steady state no‐drift solutions of the transport equation
Authors: Reinecke J. P. L. , Moraal H. , McDonald F. B.
Published: February 2008

Cosmic ray intensities and density gradients, as observed by the Pioneer 10 and 11, Voyager 1 and 2, and IMP spacecraft during the 1977 and 1987 solar minimum periods are interpreted. This is done with a two‐dimensional, no‐drift version of the cosmic ray transport equation. While this oversimplified model obviously cannot fit all the observations satisfactorily, it does produce useful insight into spectral shapes in the outer heliosphere, the question of anomalous hydrogen, and the properties of radial gradients. These effects are discussed systematically, and it is shown that many of them are due to adiabatic losses inherent in the modulation process. It is also pointed out which effects need more sophisticated models, including drifts, time‐dependent effects and acceleration at the termination shock. In particular, it is demonstrated that there is probably no physically realistic way to reproduce the observed negative latitudinal gradients without resorting to drift models of the modulation. The best fit to the anomalous oxygen data is achieved with either a charge state of 2+, or with a source function that changes between solar minimum periods with a factor of 2.8.
Diurnal double maxima patterns in the F region ionosphere: Substorm‐related aspects
Authors: Pi Xiaoqing , Mendillo Michael , Fox Matthew W. , Anderson David N.
Published: February 2008

Daytime double maxima (twin peaks or bite‐outs) in the ionospheric total electron content (TEC) at middle and lower latitudes are found to be related to substorm signatures shown in both auroral electrojet and ring current variations. Case studies reveal that during substorm onset and recovery phases, the penetration of magnetospheric convection electric fields and their subsequent “overshielding” effects may be the major dynamical sources of these events. A theoretical low‐latitude ionospheric model is used to simulate the dynamical effects of electric field disturbances on F region electron density and TEC. It is demonstrated that the diurnal double maxima in TEC can be created by a combined effect of E × B drift and altitude‐dependent F region chemical loss. The required zonal electric fields are found to have greater penetration efficiency in the early evening sector and their latitudinal requirements appear to change with local time. The time scales for the modeled penetration and overshielding effects are 2‐3 hours. Modeling results also show that considerable structuring in the local time variation of the ionospheric “equatorial anomaly” can occur due to the interplay of convection electric field penetration and overshielding effects. The possible cause of the midday bite‐out ionospheric disturbances by the meridional winds associated with traveling atmospheric disturbances (TADs) is also addressed in modeling studies, but the specialized nature of the required TADs makes this a less well understood substorm‐related mechanism.