bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of the coupled Z mode at Arecibo
Authors: Muldrew D. B.
Published: February 2008

For propagation in the magnetic meridian plane at two particular angles of incidence near the vertical, the ordinary (O) electromagnetic mode couples into what Budden [1961] calls the extraordinary (X) mode and what more recently has been called the Z mode. One of the angles is northward of zenith and one is southward. These angles form the transition between O mode reflections at a “Spitze” where the wave frequency ω matches the plasma frequency ωp and reflection below the height where ω = ωp. If the O mode propagates southward from Arecibo, the coupled Z mode is reflected up to a few kilometers above the height of the Spitze; it then propagates downward through the Spitze height to a height where the group path is horizontal. Assuming a horizontal, plane‐stratified uniformly varying ionosphere and no nonlinear effects, the refractive index and wavenormal direction approach constant finite values at this height and the wave remains electromagnetic in character; this is a new result which has not been previously reported. The group velocity is small, and the wave becomes heavily damped due to electron‐ion collisions after several milliseconds. If the O wave propagates northward, the coupled Z mode is reflected a couple of hundred meters or less above the Spitze height; it then propagates downward through the Spitze height and approaches horizontally the height at which the Appleton‐Hartree refractive index becomes infinite. For the same above mentioned assumptions, the Z mode converts gradually from electromagnetic to electrostatic in nature. The electrostatic or Langmuir mode attains a small downward component of group velocity and propagates downward for a few tens of meters while being heavily damped by electron‐ion collisions. Neglecting damping and nonlinear effects, the intensity of the Z mode varies approximately inversely with group velocity. If the HF array near the Arecibo Observatory were modified to place the main or secondary beams in the coupling directions, the electric field due to the coupled Z wave could be enormous. Even weak transmissions from the array should produce a nonlinear region. It is thus difficult to say how much of the linear mode coupling description is valid before nonlinear effects dominate. The nonlinear effects might generate Langmuir waves of a similar frequency to the HF which could be detected by the Arecibo 430‐MHz radar. Exciting new plasma line observations should thus be possible.
Transient scattering from dielectric cylinders: E‐field, H‐field, and combined field solutions
Authors: Vechinski Douglas A. , Rao Sadasiva M.
Published: February 2008

In this work, the problem of transient scattering by arbitrarily shaped two‐dimensional dielectric cylinders is solved using the marching‐on‐in‐time technique. The dielectric problem is approached via the equivalence principle. Three different formulations, namely, the electric field integral equation formulation, the magnetic field integral equation formulation, and the combined field integral equation formulation are considered. Numerical results are presented for two cross sections, namely, a circle and a square, and compared with inverse discrete Fourier transform (IDFT) techniques. In each case, good agreement is obtained with the IDFT solution.
Accuracy of time comparison derived from reception of LORAN‐C and Global Positioning System time signals
Authors: Horiai Koji
Published: February 2008

The accuracy of time comparison by means of the reception of common time signals, namely, LORAN‐C and Global Positioning System (GPS), is examined. Differences of UTC from the emission times of these two radio wave signals measured at four Japanese stations and one U.S. station are analyzed and compared with the clock comparison reports published by the Bureau International des Poids et Mesures. The accuracy of the time comparison via LORAN‐C signals of the northwest Pacific chain is about 3.61 μs and that via GPS is 0.14 μs. The accuracy analysis reveals the existence of systematic errors at the individual stations. In LORAN‐C, the most serious error comes from those in the delay time calibration of receiving instruments and estimation of the propagation delay over land. Calibration of the clocks by a portable clock improves the accuracy of the GPS method to the accuracy of the GPS signals.
Remote sensing of the atmosphere using a system of synchronously orbiting satellites
Authors: Gorbunov M. E. , Gurvich A. S.
Published: February 2008

The paper contains a description of the numerical simulation of remote sensing of the Earth's atmosphere using a system of synchronously orbiting satellites based upon methods of refractional tomography. Materials of the Global Atmospheric Research Program were used for the simulations. It was shown that a system of 8 or 12 satellites linked to each other with communication lines passing through the atmosphere potentially allows reconstruction of the pressure field with sufficient precision for meteorology.
Theoretical study of the VHF radar echo statistics
Authors: Chu Yen‐Hsyang
Published: February 2008

In this article the statistical characteristics of the VHF radar returns, which are assumed to comprise components generated from the atmospheric isotropic turbulences plus anisotropic irregularities are theoretically studied. By employing a theory of the random variable, the analytic form of the amplitude and phase probability density functions of the VHF radar echoes are derived. After a somewhat tedious and complicated calculation it shows that the conventional Rayleigh distribution, the Rice distribution, and the Hoyt distribution are closely related to the derived generalized probability density function. The Nakagami m parameter corresponding to this generalized probability density function of the VHF radar signal amplitude is derived as well. It indicates that the magnitude of Nakagami m parameter is governed by the radar echo parameters, that is, 2S2, σ2, and μ, where 2S2 is the power of the radar echo component scattered from the isotropic turbulences, μ and σ2 are the mean and variance, respectively, of the radar signal component generated from the anisotropic irregularities. After examining the general behavior of the derived Nakagami m parameter in more detail, it is found that no matter what the S value is, the magnitude of Nakagami m parameter, m, is always in one of the following three categories, depending on the relative changes between μ and σ. Namely, m = 1 if σ2 = (2½ ‐ 1)μ2; 0.5 < m < 1 if σ2 > (2½ ‐ 1)μ2; and m > 1 if σ2 < (2½ ‐ 1)μ2. These results are quite different from those expected with the conventional theories. Therefore great care should be taken when the probability density function of signal amplitude and phase and the Nakagami m parameter are employed to distinguish the echo mechanism of VHF radar.
Multiple scattering of electromagnetic waves from two prolate spheroids with perpendicular axes of revolution
Authors: Dalmas Jeannine , Deleuil Roger
Published: February 2008

A study of multiple scattering from two perfectly conducting prolate spheroids with perpendicular axes of revolution is performed, and new numerical results are given. This study is carried out with rotational‐translational addition theorems established by the authors and R. H. MacPhie. In addition, rotational‐translational addition theorems for the spheroidal vector wave functions Mr and Nr with a sine or cosine φ dependence necessary for this study are also established. The propagation vector of the incident plane wave is in the negative y direction, and consequently, two new expressions of the incident field in terms of series expansions of spherical and spheroidal vector wave functions with respect to the vector r are presented. Finally, multiple scattering polar patterns are shown for two identical prolate spheroids spaced 3.5 times their semimajor axis and this for two values of c, namely c = 2 and c = 5.
A first‐principle derivation of the high‐latitude total electron content distribution
Authors: Crain D. J. , Sojka J. J. , Schunk R. W. , Doherty P. H. , Klobuchar J. A.
Published: February 2008

Calculation of the high‐latitude distribution of the vertical total electron content (TEC) is possible using a three‐dimensional, time‐dependent ionospheric model. Global and local comparisons may be made with observations of TEC. We compare the local diurnal variation of TEC calculated by the model with observations of TEC at Goose Bay, Labrador and Hamilton, Massachusetts. Data from the period of March 1–11, 1989, and monthly averaged data for solar maximum and solar minimum periods are examined. We extend the model to predict diurnal variations of TEC in the polar cap and compare these results with the observed TEC at Thule, Greenland, during an 8‐day campaign from January 28 through February 4,1984. We propose a possible explanation for the large variability observed. We show that the “equivalent vertical content” TEC is very sensitive to horizontal F layer electron density gradients and that such “equivalent vertical” TECs may vary significantly from the true vertical TEC of the ionosphere. By incorporating these results, we calculate the vertical TEC distribution of the high‐latitude ionosphere for a wide range of solar activity, seasons, and Kp variation represented by a recently completed Utah State University time‐dependent ionospheric model data base. Finally, we discuss the possible uses of TEC as a diagnostic tool for testing ionospheric models.
A time domain model for sea scatter
Authors: Wetzel L. B.
Published: February 2008

With the increasing use of ultra high resolution probes in the investigation of radar sea scatter, it is of interest to consider a time domain formulation of sea scatter that emphasizes the instantaneous response of the surface to impulselike waveforms. In this paper a simple scalar analogue of radar sea scatter in the time domain is presented. An impulse (δ function) is shown to return a signal that is highly sensitive to both the curvature and slope of the scattering surface. Using a simulated gravity wave as a reference scatterer, the response to realizable waveforms based on the Gabor wavelet is examined. It is found that a symmetric wavelet scatters much like the impulse, while the return for an antisymmetric wavelet is considerably weaker. Some implications of causality in ultra high resolution scattering are discussed, along with the similarities and differences between the time and frequency domain formulations of the surface scattering problem.
Application of the contour transformation method to a vertical electric dipole over Earth
Authors: Dvorak Steven L. , Mechaik Mehdi M.
Published: February 2008

A contour transformation method is applied to the computation of the Sommerfeld integral associated with a vertical electric dipole above Earth. In this method the slowly varying part of the transformed Sommerfeld integrand is approximated by a few exponential terms using Prony's method. The resulting integrals are then carried out analytically, thereby, yielding incomplete Lipschitz‐Hankel integrals. Therefore numerical integration of the Sommerfeld integral is unnecessary since the incomplete Lipschitz‐Hankel integrals are computed using efficient Bessel series expansions. This method is compared with a direct numerical integration of the Sommerfeld integral and a contour deformation technique which also utilizes Prony's method. The results demonstrate that the contour transformation method enables the accurate and efficient computation of the Sommerfeld integral for all source and observation locations (i.e., near zone, far zone and even grazing). This technique can also be applied to problems involving multiple layers.
Lithoprobe crustal reflection structure of the Southern Canadian Cordillera 2: Coast mountains transect
Authors: Varsek John L. , Cook Frederick A. , Clowes Ronald M. , Journeay J. Murray , Monger James W. H. , Parrish Randall R. , Kanasewich Ernest R. , Spencer Carl S.
Published: February 2008

The Lithoprobe seismic reflection transect across the southern Coast Mountains of the Canadian Cordillera images fundamental crustal structures presumably related to collision of the Intermontane and Insular composite terranes, and deep levels in the upper plate of the offshore Cascadia subduction belt. The eastern part of the Coast Mountains are characterized by east dipping upper crustal reflectors that project to exposed faults and east dipping lower crustal reflectors; they are truncated by subhorizontal to west dipping middle and upper crustal reflectors. These geometric relationships are interpreted to have formed during an early phase of primarily west directed contraction that created the east dipping structures of the upper and lower crust, and a later phase of east directed shortening caused by wedging of the Intermontane belt into the lower and middle crust of the tectonic stack. Subsequently, the Coast belt may have been displaced eastward on contractional faults that ascend from the lower crust beneath the Intermontane belt and surface in the Omineca and Foreland belts. Extensional faults bounding the east flank of the Coast Mountains and west flank of the central Nicola horst in the Intermontane belt flatten into the middle and lower crust of the intervening region and geometrically outline crustal boudinage. Within the western Coast Mountains, east dipping reflections spanning the middle crust to upper mantle are traced updip to Vancouver Island and the underlying Cascadia subduction zone. The C reflector on Vancouver Island is believed to separate Wrangellia from underlying accreted terranes and is correlated to the mainland where it forms the upper boundary of a reflective lower crustal wedge that flattens into the Moho. If the Moho is not a young feature, then some accreted material appears to have wedged into the continental framework above the crust‐mantle boundary, possibly causing shortening in the overlying crust and creating midcrustal ramps observed on the reflection data. The structurally lower E reflections, interpreted as shear zones, originate at the subduction contact offshore and project landward into sub‐Moho reflections within the upper plate on the Mainland. The region between the E reflector and the descending oceanic plate is interpreted to be subducted lower continental crust and mantle.
Global geodesy using Doris data on SPOT‐2
Authors: Soudarin L. , Cazenave A.
Published: February 2008

The DORIS system developed for precise orbitography and precise positioning has been operational since the launch of the SPOT‐2 satellite in January 1990. Doppler DORIS data have been currently analysed since the beginning of the mission for geodetic objectives. Absolute positioning results based on a semi‐dynamical orbital analysis approach have been derived with the 2 years of DORIS data available. Cartesian coordinates of the global DORIS network (43 beacons) derived on a monthly basis show a month‐to‐month repeatability of 5–7 cm rms. Comparison between DORIS station coordinates and those determined by VLBI or SLR collocated with DORIS beacons indicates an accuracy of 5–7 cm rms in the 3 coordinates. Earth pole positions are determined at 5‐day intervals with a standard deviation of 1–2 mas. The comparison of the pole positions estimated from the DORIS data with a homogeneous series provided by the International Earth Rotation Service shows differences with an amplitude of a few mas.
Excitation of Earth’s polar motion by atmospheric angular momentum variations, 1980–1990
Authors: Fong Chao Benjamin
Published: February 2008

We compute the polar‐motion excitation function due to the atmospheric angular momentum (AAM) for both IB (inverted‐barometer) and non‐IB cases, as well as the excitation function from geodetically observed Earth orientation data for the period 1980–1990. The two are then compared in studying the AAM contribution to the polar motion excitation. The polar drifts with periods longer than ∼2 years have similar characteristics, but the comparison is inconclusive because of data uncertainties. For the seasonal wobble excitation, the agreement is poor except for the prograde annual wobble, indicating the influence of other geophysical excitations than AAM. For the Chandler wobble excitation, a correlation coefficient of 0.53 for non‐IB and 0.58 for IB are found for 1986–1990. Together with a coherence spectral analysis, they clearly demonstrate a strong contribution of AAM to the Chandler wobble excitation.
Reassessment of Crete (Greenland) ice core acidity/volcanism link to climate change
Authors: Crowley Thomas J. , Criste Tamara A. , Smith Neil R.
Published: February 2008

Previous comparisons of the Crête (Greenland) ice core acidity record with climate variations of the last 1400 years suggested that changes in volcanism may have significantly influenced climate on this time scale. However, the ice core acidity record consists of volcanically‐induced spikes superimposed on a background acidity of nonvolcanic origin that varied significantly in amplitude. Herein we produce a record of Crête volcanism based solely on an objective definition of individual volcanic events in the ice core record. There are 92 acidity peaks in the 1420‐year record. Since at least 26% of the post‐1600 eruptions are of local (Icelandic) origin, we estimate a mean recurrence interval of 20.8 years for hemispheric‐scale eruptions rich in sulphate. On decadal time scales, volcanism has varied by a factor of three‐four over the last 1400 years. However, the climate‐volcanism correlation is considerably less impressive (r = −0.23) than previously concluded (r = −0.52). The good correspondence between volcanism and climate previously reported are due to background acidity levels that show a significant Little Ice Age increase. The background increase may reflect changes in ocean productivity.
The first negative bands of N2+ in the dayglow from the ATLAS‐1 shuttle mission
Authors: Torr Marsha R. , Torr D. G. , Chang T. , Richards P. G. , Baldridge T. W. , Owens J. K. , Dougani H. , Fellows C. , Swift W. , Yung S. , Hladky J.
Published: February 2008

During November–December 1983 the first spectral images of the N2+ first negative bands in the dayglow were measured by the Imaging Spectrometric Observatory on the Spacelab 1 shuttle mission. These data contained two unexpected characteristics: the intensities were considerably higher than current photochemistry predicts (by factors of 3–5), and the bands showed larger than expected populations in the higher vibrational levels. Both of these characteristics persisted throughout the mission and were independent of vehicle attitude. The spectra were imaged for the second time in the dayglow by the same instrument from the ATLAS‐1 shuttle mission in March 1992, providing an opportunity to re‐examine these issues. The vibrational distributions measured from ATLAS‐1 are found to be rather similar to those measured from Spacelab 1, but with somewhat lower populations in levels, ν′= 2 and 3. The Spacelab 1 and the ATLAS‐1 missions were the first opportunities to image the Δν = +1 progression at 3584 Å, allowing the first determinations of the populations in levels higher than 2, which earlier studies were not able to address. The integrated column intensities of the 0–0 band emission at 3914 Å as measured from ATLAS‐1 are found to be in good agreement with model values, while the Spacelab 1 intensities appear to have been significantly affected by vehicle‐induced effects. It would appear that the Spacelab 1 mission was highly anomalous in this regard, and the emission spectra from that mission are contaminated by non‐ambient features, many of which are from the same species as are found in the thermosphere. The ion environment, in particular, appears to have been very perturbed on that mission. By contrast, the ATLAS‐1 mission spectra appear to be very clean and do not show obvious evidence of vehicle effects. It appears that the absence of the large pressurized double‐Spacelab module that occupied much of the payload bay for Spacelab 1, and the revised payload and orbiter processing procedures, have resulted in an environment that is substantially improved for remote sensing purposes. Studies of natural emissions, such as this one of the N2+ bands, are feasible and provide good data for modeling of the region.
Triggering the HF breakdown of the atmosphere by barium release
Authors: Papadopoulos K. , Milikh G. M. , Sprangle P.
Published: February 2008

RF ionization rates for mixtures of air with barium are computed using a Fokker‐Planck code. It is shown that there is an optimum mixing ratio of barium to air, significantly lower than unity, which maximizes the ionization rate for a given value of incident RF power density and frequency. Rocket injection of barium at a selected height reduces significantly the RF breakdown threshold for the mixture, and allows atmospheric and ionospheric breakdown at the selected heights using the radiation from the powerful HF radio facilities. The possibility of field experiments using currently available or projected HF heaters is discussed.
Thermospheric airglow emissions: A comparison of measurements from ATLAS‐1 and theory
Authors: Torr Douglas G. , Torr Marsha R. , Richards P. G.
Published: February 2008

The Imaging Spectrometric Observatory flown on the ATLAS‐1 shuttle mission was designed to measure the dayglow and nightglow emissions of the thermosphere and mesosphere. During this mission the ISO obtained the first detailed spectral atlas of the dayglow over a broad wavelength range (600 Å to 8400 Å). Spectral emissions over this wavelength range were obtained as a function of altitude, allowing comparisons to be made with current thermospheric photochemistry models. Much of the present understanding of thermospheric photochemistry is based on the work done using the multi‐instrument complement onboard the Atmosphere Explorer satellites flown in the 1970's. It is therefore of considerable interest to answer the question of how well that basic photochemistry predicts a large number of different airglow emissions measured almost 20 years later. In this paper we run our comprehensive thermospheric model for conditions appropriate to the time of the ATLAS‐1 mission and compare the slant path intensities thus computed (as a function of altitude, latitude, longitude, and local time) with a dozen major emissions measured in the course of a particular observing sequence. Bearing in mind that the model has been run in a predictive mode, and that no attempt has yet been made to iterate the fit to the data, it is found that the agreement is reasonably good, indicating that the major processes controlling the thermospheric airglow are relatively well understood.
Mesospheric nightglow spectral survey taken by the ISO Spectral Spatial Imager on ATLAS 1
Authors: Owens J. K. , Torr D. G. , Torr M. R. , Chang T. , Fennelly J. A. , Richards P. G. , Morgan M. F. , Baldridge T. W. , Fellows C. W. , Dougani H. , Swift W. , Tejada A. , Orme T. , Germany G. A. , Yung S.
Published: February 2008

This paper reports the first comprehensive spectral survey of the mesospheric airglow between 260 and 832 nm taken by the Imaging Spectrometric Observatory (ISO) on the ATLAS 1 mission. We select data taken in the spectral window between 275 and 300 nm to determine the variation with altitude of the Herzberg I bands originating from the vibrational levels v′ = 3 to 8. These data provide the first spatially resolved spectral measurements of the system. The data are used to demonstrate that to within an uncertainty of ± 10%, the vibrational distribution remains invariant with altitude. The deficit reported previously for the v′ = 5 level is not observed although there is a suggestion of depletion in v′ = 6. The data could be used to place tight constraints on the vibrational dependence of quenching rate coefficients, and on the abundance of atomic oxygen.
Southern surface rupture associated with the 1992 M7.4 Landers Earthquake: Did it all happen during the mainshock?
Authors: Hough S. E. , Mori J. , Sembera E. , Glassmoyer G. , Mueller C. , Lydeen S.
Published: February 2008

Approximately three minutes after the magnitude 7.4 Landers mainshock on 28 June 1992, a M5.7 aftershock occurred south of the mainshock epicenter, with a location of 34° 7.65′N, 116° 23.82′W. This aftershock was recorded on an array of portable digital seismic instruments deployed in Morongo Valley, 21 km southwest of the event. Although peak accelerations are found to differ by approximately 50% at stations with similar general site conditions within 500 m of each other, there is good coherence of arrivals across the array for frequencies ≤1 Hz. We use the recordings to determine the apparent phase velocity and azimuth of propagation across the array, and show that the event clearly ruptured to the south, with a rupture length of ∼11 km and a rupture velocity of approximately 3.0 km/s. Our results suggest that at least some of the mapped surface rupture south of the town of Yucca Valley (∼11 km in extent; maximum displacement of 20 cm) may have been associated with this aftershock. If this is the case, then the fault that produced the southern end of the Landers mainshock (the Johnson Valley fault) need not continue at depth across the active left‐lateral, east‐west trending Pinto Mountain fault.
Paleomagnetism of the Gays River zinc‐lead deposit, Nova Scotia: Pennsylvanian ore genesis
Authors: Pan H. , Symons D. T. A. , Sangster D. F.
Published: February 2008

The Gays River zinc‐lead deposit is the largest known Mississippi Valley‐type deposit in the Mississippian Windsor Group of Atlantic Canada. Thermal and AF demagnetization show that both ore and host rock have very similar magnetic characteristics. Stability tests constrain the magnetization to be mid‐Mississippian to late Pennsylvanian. The pole position from the ore and host rock sites falls next to the Pennsylvanian APW path, suggesting an 8° clockwise rotation of the Meguma platform relative to the craton. Regional thermal history and geochemical evidence suggest that the zinc‐lead ore magnetization and host rock remagnetization are coeval.
A model for tropical‐extratropical transport of volcanic ash in the lower stratosphere
Authors: Rietmeijer Frans J. M.
Published: February 2008

Large nonspherical volcanic ash particles up to 30 micrometer in size were collected between 17–19 km altitude over the northern hemisphere at high latitudes between October 1988 and April 1990. These particles may be derived from minor Plinian eruptions in the tropics rather than from localised volcanic activity close to the collection region. Ash particles were injected into the lower equatorial stratosphere where they entered a regime of efficient transport just above the tropopause from the tropical region towards the northern extratropical region. Transport is enhanced by stable autorotation that generates a sufficient lift force to loft nonspherical ash with a rough surface during transport, and by the gradually decreasing altitude of the tropopause from the tropics to the polar regions.
Springtime stratospheric water vapour in the southern hemisphere as measured by MLS
Authors: Harwood R. S. , Carr E. S. , Froidevaux L. , Jarnot R. F. , Lahoz W. A. , Lau C. L. , Peckham G. E. , Read W. G. , Ricaud P. D. , Suttie R. A. , Waters J. W.
Published: February 2008

The effects of the break‐up of the antarctic vortex on the water vapour distribution are studied using MLS measurements of water vapour made during September 1991 and November 1991. In early November at 22 hPa a moist area is found within the polar vortex, consistent with an observed descent of order 10 km and strong radiative cooling. As the vortex erodes (beginning of November 1991), parcels of moist air become detached from the edge of the vortex and mix rapidly (within 2–3 days) with drier mid‐latitude air. When the vortex breaks up (mid‐November), larger parcels of moist air from both the edge arid the inner vortex migrate to mid‐latitudes. These parcels have a longer lifetime than those produced by vortex erosion, probably because they are correlated with higher potential vorticity gradients. The break‐up of the vortex is accompanied by a mean adiabatic equatorward transport resulting in a significant increase in mid‐stratospheric water vapour values at mid‐latitudes in late spring.
Potential impact of combined NOx and SOx emissions from future high speed civil transport aircraft on stratospheric aerosols and ozone
Authors: Bekki S. , Pyle J. A.
Published: February 2008

A two‐dimensional sulphate aerosol model is used to assess the impact of combined NOx and SOx emissions from future High Speed Civil Transports on stratospheric aerosols and ozone. The model predicts that SOx emitted by this fleet of supersonics may double the aerosol surface area and the number of optically active particles below 20 km in the northern lower stratosphere. When the heterogeneous conversion of N2O5 to HNO3 on sulphate aerosols is taken into account, the predicted ozone changes due to future HSCTs emissions are smaller than those calculated when SOx and the subsequent increase in aerosol loading are neglected. It is worth noting that the doubling of the aerosol surface area may lead not only to a reduction in predicted ozone sensitivity to NOx, but also to an enhancement in ozone sensitivity to chlorine in the lower stratosphere.
Present and past regional ridge segmentation: Evidence in Geoid data
Authors: Calcagno P. , Cazenave A.
Published: February 2008

Global geoid data from the Geosat altimeter satellite and topography data have been analysed in the Pacific and Atlantic oceans to study present (along‐axis) and past (off‐axis) regional mid‐ocean ridge segmentation. Along the Mid‐Atlantic Ridge, East Pacific Rise and Pacific‐Antarctic Ridge, axial geoid and depth variations are positively correlated at length scale 800–1000 km. Respective peak to peak amplitudes are in the range of 0.4–0.8 m and 200–400 m. Axial variations are correlated with the position of large offset transform faults which coincide with geoid and topography lows. Triple junctions are also located in geoid and topography lows. The observed admittance between geoid and depth is estimated to 2 ± 0.5 m/km, a value indicative of a dynamic (convective) origin for the along‐axis regional variability.

Off‐axis analysis shows a regional pattern of geoid (topography) anomalies elongated in the direction of spreading. This pattern has also a length scale of 800–1000 km and possibly represents past regional segmentation. Large offset fracture zones coincide with off‐axis geoid (topography) lows.
Bio‐optical observations of first‐year Arctic sea ice
Authors: Perovich D. K. , Cota G. F. , Maykut G. A. , Grenfell T. C.
Published: February 2008

The interrelationships among snow cover, ice structure, optical properties, and biological activity are of critical importance in understanding the response and behavior of sea ice systems. Of particular concern in this regard are the optical properties of the algae and the effect of snow thickness on biomass accumulation. In this paper we present the first direct in situ measurements of biomass specific diffuse attenuation spectra for arctic ice algae. The data show in situ attenuation values that are about 3 times larger than those obtained from corresponding in vivo absorption measurements, apparently reflecting differences in the geometrical distribution of the algae or the influence of skeletal ice and dissolved organic material. Observations also confirm that maximal algal accumulation occurs when there is a thin layer of snow covering the ice. A new technique to separate the effects of snow and algae in observed transmission spectra is presented. The ratio of transmittance between 600 nm and 450 nm is a sensitive indicator of biomass, while the 700 nm to 600 nm ratio is strongly affected by snow depth.
Observations of the UARS Particle Environment Monitor and computation of ionization rates in the middle and upper atmosphere during a geomagnetic storm
Authors: Sharber J. R. , Frahm R. A. , Winningham J. D. , Biard J. C. , Lummerzheim D. , Rees M. H. , Chenette D. L. , Gaines E. E. , Nightingale R. W. , Imhof W. L.
Published: February 2008

During the geomagnetic storm of 8–9 November 1991, the Upper Atmosphere Research Satellite (UARS), orbiting at 585 km, passed through the expanded auroral zone during portions of several successive orbits. The instruments of the UARS Particle Environment Monitor (PEM) observed particle precipitation, auroral x‐ray emissions, and large‐scale disturbances in the geomagnetic field during this time. In this paper we present observations made by the PEM instruments during this storm and compute ionization and energy deposition rates as functions of altitude in the middle and upper atmosphere by incident electrons and positive ions in the storm interval. The suite of PEM instruments provides a systematic measurement of energetic particles and their associated x‐rays over an energy range not fully covered by previous satellite missions. In this energy range the ionization and dissociation rate in the atmosphere may be inferred from the upper stratosphere to the thermosphere. The impact on the chemistry of the region may be investigated.
Deviatoric stress in a quasi‐hydrostatic diamond anvil cell: Effect on the volume‐based pressure calibration
Authors: Meng Yue , Weidner Donald J. , Fei Yingwei
Published: February 2008

The deviatoric stress in gold as a function of pressure and temperature, in a diamond anvil cell with neon as the pressure medium, is measured based on gold diffraction peaks. We find that the deviatoric stress becomes detectable at a pressure of about 15 GPa and reaches 0.62 GPa by 30 GPa. Upon heating, the deviatoric stress decreases rapidly and disappears at a temperature of about 650 K. The effect of deviatoric stress on the unit cell volume measurement and further on the volume‐based pressure calibration is directly proportional to K/μ of the measured material, and it is also related to the anisotropy, as well as the sign of the deviatoric stress and the orientation of the x‐ray diffraction. We find that the measured unit cell volume of gold is very sensitive to the deviatoric stress due to a high value of K/μ. Although the observed deviatoric stress may be insignificant for most samples, it causes a significant systematic error on the pressure calibration based on the unit cell volume of gold.
Mesospheric water vapor sounding using Earth‐limb pure‐rotational emission in the LWIR
Authors: Adler‐Golden Steven , De Piali , Smith Donald , D'Agati Anthony
Published: February 2008

Limb sounding of mesospheric water vapor using pure rotational emission in the long‐wavelength infrared region has been demonstrated using data from the ELC‐1 rocket experiment, launched in October, 1983. By simultaneously analyzing H2O emission at 23–29 µm and CO2 emission in the ν2 band region, effects due to uncertainties in the atmospheric temperature and instrument calibration are minimized. The H2O profile obtained from ELC‐1 is consistent with other fall to early‐winter measurements. Given accurate line‐of‐sight pointing information, this approach will be feasible for global mesospheric H2O sounding from limb‐viewing satellites.
Dissolution of K in molten iron at high pressure and temperature
Authors: Ito E. , Morooka K. , Ujike O.
Published: February 2008

Partitioning of K between molten iron and silicate melt was examined at about 26 GPa and 2600°C using a mixture of pure iron and natural microcline as the starting material. The dissolution of K in molten iron up to about 0.2 wt % was confirmed. The distribution coefficient of K between molten iron and silicate melt was about 3.8×10−2 (atomic ratio). This value suggests the presence of 5 ppm K in the earth's core, yielding 3×1010 W for the present day heat generation by K.
On the adsorption of NO and NO2 on cold H2O/H2SO4 surfaces
Authors: Saastad Ole W. , Ellermann Thomas , Nielsen Claus J.
Published: February 2008

A static reaction chamber attached to a mass spectrometer was employed to study the adsorption of NO and NO2 onto cold surfaces of pure ice and liquid/solid 70 wt % H2SO4. No significant adsorption could be observed for surface temperatures in the range 193–243 K and NO/NO2 partial pressures of 10−2–10−5 mbar. This sets an upper limit on the uptake coefficients for both NO and NO2 of 5 · 10−5. The possible formation of nitrosyl sulphuric acid by adsorption of NO and NO2 on cold sulphuric acid particles is therefore unlikely to be of importance in the stratosphere.
Does rapid change in ice loading modulate strain accumulation and release in glaciated, tectonically active regions
Authors: Cohen Steven C.
Published: February 2008

There are major glaciated regions of the world that are also seismologically active. Changes in the thickness of ice due to glacier surges, advances, or retreats produce stress changes that may be a significant fraction of the tectonic stress accumulated during an earthquake cycle. The changes in ice loading can affect both the normal and shear stress on a fault with stresses being enhanced or reduced depending on glacier and fault geometry. The stress change has a nearly instantaneous elastic component and a longer time‐scale viscoelastic component. Thus I propose that glacier motion can produce geodetically significant horizontal and vertical crustal displacements and can affect strain, strain rate, and the time of occurrence of earthquakes. In regions that are not tectonically active, rapid ice motion can also produce locally significant and geodetically detectable crustal deformations.
Three dimensional P velocity image of the Oroville Reservoir Area, California, from local earthquake tomography
Authors: Rajendran Kusala , Salvador Mario E. , Owens Thomas J.
Published: February 2008

This study images the P velocity structure of a region in the vicinity of the large artificial reservoir at Oroville, California. The velocity structure of the upper crust (to a depth of 12 km) was obtained by simultaneous inversion of P‐arrivals of 168 aftershocks of the 1975 Oroville earthquake. A decrease in P‐wave velocity by 7 to 8% was observed across a known fault zone. The hypocenters of the 1975 sequence are associated with a southwest dipping structure characterized by low velocity, with most of the deeper activity occurring in adjacent regions of higher velocity. Resolution of the velocity structure was examined through inversions of synthetic travel times using different starting velocity models. Although the role of the reservoir in generating the low velocities remains speculative, the structure is comparable to that of some active segments of the San Andreas fault where fluid pressures are thought to be high.
Fluid‐pressure induced seismicity at regional scales
Authors: Keller Edward A. , Loaiciga Hugo A.
Published: February 2008

The role of high fluid pressure as a seismogenic agent has been the subject of intense study (Hubert and Rubey, 1959; Hanshaw and Bredehoeft, 1968; Healy and Rubey, 1968; Simpson, 1976; Walder and Nur, 1984; Sibson, 1990). Of particular interest is the so‐called fault‐valve mechanism (Sibson, 1976; Sibson, 1990) a hypothesis whereby fluid pressure rises (as a result of tectonic compression and pore volume reduction) until crustal failure occurs, triggering seismic activity and upward fluid discharge. Sealing and healing of the rock matrix (Richter and Simmons, 1977; Sprunt and Nur, 1979; Angevine et al, 1982) following coseismic stress drop facilitates reaccumulation of fluid pressure, initiating another loading cycle. The fault‐valve mechanism is entertained as a plausible explanation for present‐day seismic activity in the western Transverse Ranges of California. We provide a quantitative test of the fault‐valve hypothesis that uses geologic data and rates of active tectonics for a cross‐section through an active fold‐and‐thrust belt on the flank of a developing mountain range. Rates of fluid pressure buildup and average recurrence times of large earthquakes in the fold‐and‐thrust belt are estimated to be on the order of 104Pa/yrand hundreds of years, respectively.
Raman spectroscopy at mantle pressure and temperature conditions experimental set‐up and the example of CaTiO3 perovskite
Authors: Gillet Philippe , Fiquet Guillaume , Daniel Isabelle , Reynard Bruno
Published: February 2008

We present a new experimental set‐up for studying minerals by Raman spectroscopy in‐situ at simultaneously high pressures (up to 35 GPa) and high temperatures (up to 2000 K). High pressures are generated with a diamond anvil cell and local sample heating is obtained by focussing the beam of a CO2 laser on the pressurized sample through a type IIa diamond. The Raman spectrum and the thermal emission of the sample are collected on the same 2 µm‐sized heated area, whereas the pressure can be measured simultaneously anywhere in the pressure chamber. Temperature in the central part of the heated spot is estimated from the thermal emission curves. Pressures are obtained by the classical fluorescence technique. Raman spectra of CaTiO3 perovskite, analogue of MgSiO3‐perovskite, are presented at temperatures up to 1700 K at a pressure of 12 GPa. These data are compared with high temperature Raman data at ambient pressure. The spectral changes upon heating observed in both series of experiments are discussed.
Airborne observations of the composition of the 1992 tropical stratosphere by FTIR solar absorption spectrometry
Authors: Toon G. C. , Blavier J.‐F. , Solario J. N. , Szeto J. T.
Published: February 2008

Vertical column measurements of the gaseous composition of the tropical stratosphere were made from the NASA DC‐8 aircraft early in 1992. As anticipated, the burdens of the stratospheric source gases (e.g. O3, HF, HCl, ClNO3, HNO3) were reduced from their mid‐latitude values due to increased uplift and photolysis. The tracers revealed considerably more uplift near the equator than the sub‐tropics. For example, the HF burdens at ±20° latitude (0.50×1015 molec.cm−2) were nearly double those at 5°N (0.27×1015 molec.cm−2). This, together with results obtained from other long‐lived gases (e.g. N2O, CH4, CF2Cl2) indicates that volume mixing ratios found at 22 km altitude at mid‐latitudes occurred at 26 km in the sub‐tropics and at 30 km in the equatorial zone. This zone of uplift was symmetrical about the equator even though the sun was overhead at 20°S.
Balloon observations of galactic cosmic ray helium before and during a Forbush decrease
Authors: Clem J. M. , Guzik T. G. , Lijowski M. , Wefel J. P. , Beatty J. J. , Ficenec D. J. , Tobias S. , Mitchell J. W. , McKee S. , Nutter S. , Tarle G. , Tomasch A. , Bower C. R. , Heinz R. M. , Mufson S. L. , Musser J. , Pitts J. , Spiczak G. M. , Ahlen S. P. , Zhou B.
Published: February 2008

The energy spectrum of galactic cosmic ray Helium was measured in two different balloon experiments launched four days apart from Canada: SMILI‐I on 1‐Sept‐1989 and MASS on 5‐Sept‐1989. A slow Forbush decrease began on 4‐Sept‐1989 and had not reached its maximum at the time of the MASS flight. Comparison of the balloon measurements shows a fractional decrease of 0.37 to 0.15 in the Helium flux between 200 and 450 MeV/nucleon (1.2–2.0 GV). The rigidity dependence is analyzed in two models and found to be steeper than previous observations. Interplanetary particle data and ground‐based Neutron Monitor results are consistent with the balloon observations. Probable sources for this Forbush decrease are discussed.
Warm O+ polar wind and the De‐1 polar cap electron density profile
Authors: Ho C. Wing , Horwitz J. L.
Published: February 2008

Theoretical steady state semikinetic polar wind density profiles, based on DE1/RIMS polar wind data [Chandler et al., 1991] at low altitudes (up to 3700 km), were obtained which agree very well with the power law (ne = 490 r−3.85 cm−3) electron density profile measured by the DE1/PWI for high altitudes [Persoon et al., 1983] (2–5RE). The polar wind is found to be O+ dominated for the full altitude range considered (up to 8 RE). Multiple solutions are obtained for various combinations of base altitude ion temperatures and electron temperatures, such that the densities fit the Persoon et al. profile. For example, good fits to measured density profile are found for low base ion temperatures (5000 K) and high electron temperatures (9000 K), and also for unheated H+ and O+ (3000 K) with electron temperatures of 11,000 K. Below 2.8 RE the theoretical polar wind density deviates somewhat from the r−3.85 power law. It is concluded that this theoretical polar wind density profile, with a sum of base electron and ion temperatures of 14,000 K, yields a close match with the measured DE‐1 electron density profile.
A nested model study of the Sahelian climate response to sea‐surface temperature anomalies
Authors: Semazzi Fredrick H. M. , Lin Neng‐Huei , Lin Yuh‐Lang , Giorgi Filippo
Published: February 2008

A nested high resolution atmospheric model is used to investigate the sensitivity of the Sahelian climate to large‐scale sea‐surface temperature (SST) anomalies. The nested system has realistic vegetation and detailed bottom orography. Two separate sets of northern hemispheric summer (June, July and August) numerical integrations are performed; one corresponding to the SST anomalies in 1950 when the Sahelian region was relatively much wetter than the long‐term average conditions and a second integration based on 1984 SST anomalies when one of the driest rain seasons in the last few decades was experienced.

Although the low resolution (R15 ≈ 4.5° by 7.5° latitude by longitude) stand‐alone global climate model reasonably simulates the lower rainfall amounts in 1984 compared to 1950, the nested system yields more realistic regional climate because its forcing includes more detailed effects of topography, land‐sea contrasts, and land surface processes. In particular, two distinct rainfall maxima primarily anchored to the regions of highest terrain are simulated by the model. One corresponding to the highlands in Cameroon over the Adamawa Plateau and a second maxima over Guinea and Sierra‐Leone. Inspection of model circulation indicates that the weaker moist cross‐equatorial monsoon flow in the 1984 is responsible for the lower amounts of the Sahelian rainfall compared to 1950. Our results are in agreement with several diagnostic and modeling studies performed in the recent years which show that deficient sub‐Saharan rainy seasons tends to coincide with the southwesterly surface monsoon flow not extending as far north along the West African coast as in the wetter years (Lamb and Peppier, 1990, and others).
The impact of the eruptions of Mount Pinatubo and CERRO Hudson on Antarctic aerosol levels during the 1991 austral spring
Authors: Pitts M. C. , Thomason L. W.
Published: February 2008

At the beginning of the 1991 Austral spring, volcanic aerosols from Mt. Pinatubo and Cerro Hudson were present in the polar stratosphere of the Southern Hemisphere. Satellite observations of aerosol extinction were used to identify and track the movement of these aerosols in the vicinity of the Antarctic vortex during August through November 1991. A layer of mature Mt. Pinatubo aerosols was identified near 21 km and a layer of fresh Cerro Hudson aerosols was identified near 12 km. This altitude separation of the Mt Pinatubo and Cerro Hudson aerosols was observed throughout the period. Below 15 km, the polar stratosphere was subject to episodes of strong wave activity which transported the Cerro Hudson aerosols poleward and, after the middle of September, they became a persistent feature beneath the vortex. Above 15 km, signatures of Mt. Pinatubo aerosols were observed near the vortex boundary, but significant portions of the vortex interior remained free of any detectable intrusions of Mt. Pinatubo aerosols until the final warming in mid‐November.