bluuebunny/crossref_metadata_2025 huggingface dataset:
A case study of atmospheric boundary layer mean structure for flow parallel to the ice edge: Aircraft observations from CEAREX
Authors: Shaw William J. , Pauley Randal L. , Gobel Teresa M. , Radke Lawrence F.
Published: February 2008

This paper describes a case study of the mean structure of the atmospheric boundary layer (ABL) in the marginal ice zone of the Barents Sea for flow nearly parallel to the ice edge. Data were collected by the NOAA P‐3 Orion research aircraft on March 24, 1989. The geostrophic wind above the boundary layer was oriented approximately 15° off‐ice with a speed of 12 m s−1, and the atmosphere above the ABL showed little cross‐ice‐edge variability. A lidar on the aircraft revealed (over the water) the downward slope of a stratocumulus deck toward the ice edge. The associated inversion continued to slope downward over the ice, creating large thermal wind effects within the boundary layer. The inversion slope, combined with horizontal boundary layer temperature gradients, produced a factor‐of‐2 decrease in surface geostrophic wind from water to ice. Below the inversion the data revealed an ABL that remained well mixed for 100 km into the ice. A gust probe system on the aircraft provided a mapping of low‐level fluxes from a 200‐km leg perpendicular to the ice edge.
Studies of the Arctic ice cover and upper ocean with a coupled ice‐ocean model
Authors: Piacsek Steve , Allard Richard , Warn‐Varnas Alex
Published: February 2008

An ice‐ocean model has been developed by coupling the Hibler ice model to a three‐dimensional ocean model that consists of a turbulent mixed layer model and an inverse geostrophic model. The coupled model has a horizontal grid spacing of 127 km and has 17 vertical levels extending to the ocean bottom. The model is forced with 12‐hourly general circulation model‐derived atmospheric fluxes for the year 1986, for which good quality ice edge analyses and buoy tracks were available for comparisons. The results are presented for the fifth year of a repetitive simulation with the 1986 fluxes, at which time the system has reached a statistical equilibrium. The seasonal and geographical variations of the ice cover and the upper few hundred meters of the ocean have been examined, including the heat and salt budgets. The computed heat fluxes and mixed layer depths (MLDs) fall in the observed seasonal ranges, with winter heat fluxes ranging from 15 W m−2 in the central Arctic to about 500 W m−2 in the Barents Sea area, and summer fluxes from about 5 W m−2 under the ice to about 30 W m−2 in the various marginal ice zone (MIZ) edge areas. The corresponding winter MLDs are found to be about 25–75 m in the central Arctic to a deep 800 m in the Greenland Sea; typical summer MLDs are between 5 and 30 m. In all seasons, the MIZ was found to be the center of flux activity for both heat and salt, with the processes of advection, diffusion, atmospheric forcing, and vertical oceanic fluxes having their largest values here, and of comparable magnitudes. Values of the heat flux components in the MIZ exceed those found under the ice by an order of magnitude or more, and those in the open water region by a factor of 2. For salt, the situation is similar except in the summer (June through September), when a lot of salt flux activity takes place under the ice. Comparisons are made with Naval Polar Oceanography Center (NPOC) analyses for ice concentration and ice edge, and with observed Arctic buoy tracks, in the same 1986 time period. The computed ice edge positions have comparable accuracy to previous three‐dimensional coupled ice‐ocean studies, with too much ice growth during the winter in the Barents Sea and too little ice east of Greenland. The ice thickness distributions, however, are much better, with a monotonic increase of the ice thickness from the Siberian coast east toward the Canadian archipelago with maximum winter values of about 5–6 m.
A note on the generation and narrowness of periodic rip currents
Authors: Hammack Joe , Scheffner Norman , Segur Harvey
Published: February 2008

Periodic rip currents on a wide planar beach are generated in the laboratory by shoaling water waves that are periodic in time and in two spatial directions: one normal (x direction) and one parallel (y direction) to the shoreline. These short‐crested waves propagate in water of uniform depth with nearly permanent form. They are described analytically by a family of solutions of the Kadomtsev‐Petviashvili (KP) equation (KP solutions of genus 2). During shoaling, genus 2 waves retain their spatial pattern past breaking, and they quickly generate periodic rip currents along the beach with a spacing of one‐half the y wavelength of the incident waves. KP theory also provides a plausible explanation and prediction for the narrow widths, relative to their longshore spacing, of rip currents generated in this manner. An estimate of their widths is one‐half the x wavelength of the incident waves.
Introduction: Third Marginal Ice Zone research collection
Authors: Muench Robin D. , Jezek Ken , Kantha Lakshmi
Published: February 2008

The decade of the 1980s might well have been designated “The Decade for Marginal Ice Zone (MIZ) Research.” These highly energetic regions where air, ice, and water intermingle and interact thermodynamically and dynamically have undergone an unprecedented amount of study during this past decade. Relevant major programs have included the Office of Naval Research‐sponsored Marginal Ice Zone Experiment (MIZEX) West and East experiments, the Coordinated Eastern Arctic Experiment (CEAREX) in the Arctic, and the National Science Foundation‐sponsored Antarctic Marine Ecosystem Research in the Ice Edge Zone (AMERIEZ) program in the Antarctic. There have been a host of smaller experiments as well.
Top/bottom multisensor remote sensing of Arctic sea ice
Authors: Comiso J. C. , Wadhams P. , Krabill W. B. , Swift R. N. , Crawford J. P. , Tucker W. B.
Published: February 2008

The Arctic sea ice cover has been studied using near simultaneous observations by passive and active (synthetic aperture radar, SAR) microwave sensors, upward looking and sidescan sonars, a lidar profilometer, and an infrared sensor. Data from two aircraft and a submarine over an approximately 100 km track of central Arctic sea ice were registered and analyzed to evaluate the characteristics of the ice cover and the utility of each sensor in ice studies. The results of comparative and correlation analyses are as follows. The probability density functions of ice draft from sonar and elevation from lidar were found to be almost identical when isostasy is taken into account. This result suggests that the basic ice thickness distribution can be derived from the surface topography measurements alone. Reasonable correlation was found between SAR backscatter and ice draft (or elevation) especially when scales were adjusted such that 15–20 SAR pixels were averaged. However, surface roughness derived directly from standard deviations in the lidar elevation data was found to be poorly correlated to the SAR backscatter. These results indicate that the SAR values are affected more by scattering from the ice than from the snow‐covered surface. The active and passive microwave sensors are shown to generally complement each other as the two sensors are especially sensitive to different physical properties of the sea ice. Undeformed first‐year ice showed low backscatter values but high brightness temperatures while some multiyear ice showed high backscatter values and low brightness temperature. However, surfaces identified as multiyear ice by the passive system have a large spread in the unaveraged SAR backscatter, indicating limitations when using a one‐channel SAR for ice type identification at the highest resolution. Also, ridged ice identified by sonar and SAR data covers a large range of passive microwave emissivity, suggesting considerable variability in the age and salinity of this type of ice. Significant variations (about 0.11) in the minimum emissivity of consolidated multiyear ice are observed in different regions of the Arctic using the high‐resolution (30 m) passive microwave data. This suggests that regional variations in texture and scattering characteristics of multiyear ice in the Arctic are present, likely influenced by different histories of formation of the ice in different regions.
A zonal‐averaged model of the ocean's response to climatic change
Authors: Rahmstorf Stefan
Published: February 2008

A new vertical mixing model is described. It combines a box‐advection‐diffusion model with a bulk mixed layer model, which simulates wind mixing and penetrative convection. It is shown that mixed layer models can have steady periodic solutions if either the mixing decays to zero at depth or vertical advection is included. The latter approach is adopted. This mixing model is applied to a series of latitude bands between 50°N and 50°S. It successfully simulates present‐day seasonal cycles of temperature and mixed layer depth. It is then subjected to an additional heat flux resulting from an increase in greenhouse gases. For an equilibrium warming of 3°C for CO2 doubling, the model predicts the following transient response: a 0.5–0.8°C temperature rise from 1850 to 1990, and a 1.5–2.0°C rise from 1850 to 2050. The ocean acts as a thermal buffer, so that the actual warming lags the equilibrium warming by 25–50 years. Mixed layer and deep ocean contribute about equally to this lag. The seasonal cycle of mixed layer depth pumps more heat down to deeper waters, compared to a fixed mixed layer depth model. The heat uptake depends strongly on possible changes in the global thermohaline circulation, which could therefore affect sea level predictions. The climatic warming also leads to a reduction in winter mixing depth in the higher latitudes, whereas the mixing depth in other seasons and latitudes would be mainly affected by wind changes. A scenario for reduced CO2 emissions shows that the surface warming can be slowed dramatically but that a long‐term sea level rise from thermal expansion may be inevitable.
Frequency spectra of vertical velocity from Flatland VHF radar data
Authors: VanZandt T. E. , Nastrom G. D. , Green J. L.
Published: February 2008

The vertical wind velocity over very flat terrain was observed every 153 s in the troposphere and lower stratosphere by the Flatland radar, near Champaign‐Urbana, Illinois. Several hundred frequency spectra were calculated from all accepted 6‐hour time series from March through May 1987. By stratifying the spectra in various ways we find the following: (1) The spectra were independent of altitude within the troposphere or lower stratosphere, but the spectra in the two regions differed in amplitude and frequency; (2) At a given altitude the spectra were independent of the wind shear dū/dz, the buoyancy frequency N, and the maximum wind speed below 16 km; (3) The change of spectral shape and amplitude with increasing background wind speed ū was much less than at stations near mountains. The variance of the spectra, equal to twice the vertical kinetic energy per unit mass, roughly doubled as ū increased by 10 m s−1; (4) The spectra were consistent with being due to a spectrum of gravity waves, as indicated by the sharp drop in spectral amplitude near N at small ū and by the fact that the observed change of shape with increasing ū was quite consistent with the change of shape of model Doppler‐shifted gravity wave spectra; (5) The results of comparison between the observed and model spectra are consistent with an intrinsic gravity wave spectrum that is invariant with ū, dū/dz, etc., contrary to expectations from gravity wave theory; (6) The results are insensitive to the azimuthal distribution of gravity wave energy, as long as the distribution is roughly symmetrical relative to the mean flow; (7) The resulting characteristic horizontal phase velocity c* of the intrinsic frequency spectrum was about 6 m s−1 in both the troposphere and the stratosphere. The corresponding characteristic vertical wavelengths were about 3300 and 1800 m, respectively, consistent with previous estimates.
Review and revision of measurements of stratospheric N2O5
Authors: Roscoe H. K.
Published: February 2008

Measurements of N2O5 in the stratosphere and of its spectrum at 1240 cm−1 in the laboratory are reviewed. Errors in previous publications about N2O5 are discussed briefly. The earliest stratospheric measurement is significantly revised in the light of new measurements of band strength. All the measured profiles are tabulated using a standard value for the band strength; they can be linearly scaled if future, more accurate, measurements suggest that a different value should be used.
Comment on “Southward magnetic field in the neutral sheet produced by wavy motions Propagating in the dawn‐dusk direction”
Authors: Uberoi C.
Published: February 2008

In a recent paper Nakagawa and Nishida [1989] have suggested that wavy motions of the neutral sheet can be generated by the Kelvin‐Helmholtz instability if the dawn‐dusk flow of only several tens of km/s is present. However, their mathematical analysis is based on the choice of particular magnetic field directions in the three regions consisting of north, south lobes and the neutral sheet. In an earlier paper Uberoi [1986] discussed the Kelvin‐Helmholtz instability of a similar structured plasma layer without any assumptions either on velocity field directions or on the magnetic field directions, thus pointing out the angle effect due to variation in magnetic field directions on the instability criterion. The relevance of these results to the problem of wavy motions of the neutral sheet are pointed out. In particular it is found that when the y‐component of the magnetic field in each lobe is taken into consideration the Kelvin‐Helmholtz instability can be exicted only when the dawn‐dusk flow is of several hundreds of km/s a order of ten higher than that arrived in the analysis by Nakagawa and Nishida [1989].
Role of ion temperature anisotropy in multistage refilling of the outer plasmasphere
Authors: Singh Nagendra
Published: February 2008

Plasmaspheric refilling after geomagnetic storms is studied using a model in which the ion temperature anisotropy (TAN) is allowed to evolve self‐consistently with the interhemispheric plasma flow. The refilling processes predicted from this TAN model and those from a model based on the assumption of temperature isotropy (TISO) are compared. TISO model predicts that a flux tube with L=4 undergoes a substantial refilling in about 12 hours after a severe depletion and during this time the flows from the conjugate ionospheres remain supersonic with a flux ∼2 × 108cm−2 s−1. The above refilling time is too short compared to observed refilling times. The TAN model predicts much longer refilling time divided in two stages; during the early stage, the flows from the conjugate ionospheres are supersonic, and it is characterized by interhemispheric plasma exchange, shock formations and their propagations like in the TISO model. But in the TAN model, the supersonic flows last only over a few hours (<5 hours) and the plasma in the flux tube develops a temperature anisotropy such that T| > T⟂. This anisotropy causes a downward force, which balances the upward electric and pressure forces on ions keeping the flux tube depleted. The ensuing second stage starts when the temperature anisotropy begins to relax due to Coulomb collisions at high latitudes. In this stage the flow is generally subsonic and in the late stage of the refilling the equatorial density is seen to increase at a rate < 15 cm−3/day.
Ion cyclotron harmonics in auroral radar echoes: Real effect or analysis artifact?
Authors: Farley D. T. , Sahr J. D. , Providakes J. F.
Published: February 2008

Certain analyses of Canadian radar studies of auroral electrojet echoes have apparently shown spectra with multiple ion cyclotron harmonic peaks. On the basis of these, it has been argued that ion cyclotron effects must be important for all echo types seen by VHF radars, not just type 3. We reject this conclusion for two reasons: (1) at the altitude of auroral backscatter (∼ 100–120 km) the ion‐neutral collision frequency is much higher than the gyro frequency—ions are essentially unmagnetized; (2) we show that the “high resolution” signal processing algorithm employed does not distinguish between echoes with and without harmonic structure. With a simulation, we show that the algorithm itself can impose apparent quasi harmonic structure onto the spectrum of random noise.
Visible and near IR albedo measurements of ice/dust mixtures
Authors: Oehler A. , Neukum G.
Published: February 2008

The surface energy budget is an important input parameter for modelling the dynamical processes of the KOSI samples. In order to calculate the absorbed fraction of the irradiation the directional‐hemispherical albedo of the samples must be known. The albedo is calculated from the spectral radiance factor in the wavelength range from .36 μm to 2.5 μm. All samples were analysed before and after the experiments. The spectra of the experiments KOSI 3,4 and 6 have been measured under three different illumination geometries.

During the KOSI sublimation experiments a dust mantle 1 to 5 millimeter thick formes on top of the samples. This changes the spectrophotometric properties of the sample surfaces in terms of scattering characteristics and water ice absorptions at 1.5 μm. and 2.0 μm. Water ice absorptions observed after the experiment may be partly due to frost contamination.
Performance test on long‐period moment tensor determination for near earthquakes by a sparse local network
Authors: Nakanishi Ichiro , Hanakago Yasushi , Moriya Takeo , Kasahara Minoru
Published: February 2008

We have investigated the accuracy of long‐period moment tensor determination for local to regional earthquakes by a sparse local network consisting of three stations equipped with a very‐broad‐band, three‐component seismometer. We present the analysis results for 15 events with seismic moments of 3 × 1017 to 9 × 1019 Nm, which occurred in and near the Japanese region during the period from January to December of 1989. The moment tensor solutions obtained for the events are compared with the solutions retrieved from global networks and reported in PDE (Preliminary Determination of Epicenters). The comparison shows that a sparse local network of three‐component, very‐broad‐band seismometers can reliably determine the moment tensors of near‐distance, moderate to large events.
The problem of machine stiffness revisited
Authors: Labuz Joseph F.
Published: February 2008

The notion of “size effect” is introduced into the problem of machine stiffness by assuming that the rock specimen fails according to the slip‐weakening fracture model. Consequently, when the strain energy (stored per unit volume) in the machine and specimen is greater than the fracture energy (dissipated per unit area) of the rock, an unstable response is observed. Theory and experiments demonstrate that machine stiffness is not the sole factor in determining stability of a compression element, once the deformation has localized. In fact, the softening behavior of a rock tested under the same conditions is due to geometry and size. This means that the experimentalist may be able to design compression tests to achieve a stable post‐peak response.
Ozone profiles at McMurdo Station, Antarctica, The austral spring of 1990
Authors: Deshler T. , Hofmann D. J.
Published: February 2008

Vertical profiles of ozone and temperature were measured on 40 occasions during the austral spring of 1990 at McMurdo Station, Antarctica, and once again near record levels of ozone depletion were observed. Total ozone decreased from 260 DU in late August to its minimum value of 145 DU on 9 October, when the ozonesonde was at it's lower detection limit from 15 to 16.5 km. Ozone reductions were observed almost exclusively between 12 and 20 km, with a half life of 20 days. This is similar to previous years. Although McMurdo was within the polar vortex for most of the period, there were several occasions when the edge of the vortex was over McMurdo. During these periods, ozone above 20 km approximately doubled, but below 20 km remained relatively unchanged.
Paleontology of the Toa Baja #1 Well, Puerto Rico
Authors: Montgomery Homer , Robinson Edward , Saunders John , Van den Bold Willem
Published: February 2008

The Toa Baja well penetrated 585.2 m of fossiliferous Oligocene and Miocene limestone, sandstone, and shale above 2119 m of Eocene, dominantly volcaniclastic strata. Oligocene and Miocene rocks were deposited on a broad, shallow shelf. The unconformity between Eocene and Oligocene strata spans at least the Late Eocene, and probably part of the Early Oligocene at Toa Baja. Below the unconformity, unfossiliferous volcaniclastic and igneous rocks are interstratified with fossiliferous limestone beds containing Middle and possibly late Early Eocene planktic foraminifera probably deposited in deep water. No Paleocene or Cretaceous fossils were recovered.
Fractal dimension of mesospheric radar backscatter at 2.75 MHz
Authors: Hall Chris , Armstrong Richard J. , La Hoz César
Published: February 2008

We have identified the fractal dimension of radar returns from the mesopause region at 2.75MHz. The input dataset was a time series of echo amplitude at a discrete height obtained from a partial reflection radar operating at Ramfjordmoen in northern Norway. Two different algorithms both of which yield approximations to the fractal dimension have been employed and give almost identical results. The radar echo dataset in question exhibits a dimension of between 7 and 8.
Heterogeneous reactions with NaCl in the El Chichon volcanic aerosols
Authors: Michelangeli Diane V. , Allen Mark , Yung Yuk. L.
Published: February 2008

Previous investigations of the effects of the 1982 eruption of the El Chichon volcano could not explain all the observations of changes in O3, HCl, NO and NO2 simultaneously without proposing unproven chemical reactions. Since reactions between solid NaCl and gaseous ClNO3 and N2O5 rapidly produce photochemically active chlorine species and solid NaNO3 in laboratory experiments, we suggest that these reactions could have occurred with the NaCl observed to be present in the El Chichon sulfuric acid aerosols. As a consequence, we predict that HCl should increase substantially, while NOx should decrease, in agreement with the measurements after the eruption. Ozone should only be slightly affected by these reactions. Reactions between solid NaCl and the acids H2SO4 and HNO3 might prove to be important, but we lack sufficient evidence regarding their efficiency and the presence of HNO3 in the aerosols to be more conclusive.
Laboratory‐determined permeability of cores from the Kola Superdeep Well, USSR
Authors: Lockner D. , Hickman S. , Kuksenko V. , Ponomarev A. , Sidorin A. , Byerlee J. , Khakaev B.
Published: February 2008

We have conducted constant flow‐rate permeability measurements on three core samples taken from the 12‐km‐deep well on the Kola Peninsula, USSR. All cores are from 11.4– 2.0 km depth. Pore pressures, Pp, used in these permeability measurements ranged from 112–117 MPa. Measurements were performed at effective confining pressures (Peff=pc‐Pp) ranging from 10 to 400 MPa. The resulting permeabilities varied from approximately 2.5 × 10−17 m2 (25 μDa) at a Peff of 10 MPa to 1 × 10−22 m2 (0.1 nDa) at a Peff of 300 MPa. The unusual sensitivity of permeability to Peff exhibited by these samples is most likely the result of severe stress‐relief crack damage that occurred during coring and sample retrieval. This strong pressure dependence underscores the importance of measuring permeability at in situ pressures to obtain meaningful bounds on in situ matrix permeabilities in this well. In an attempt to infer closure pressure of these stress‐relief cracks, and provide estimates of in situ Peff, we have analyzed the pressure dependence of permeability, resistivity and crack porosity. By applying an equivalent‐channel‐model analysis, these data appear consistent with either an in situ pore pressure exceeding the hydrostat by as much as 100 MPa or a hydrostatic Pp and sub‐lithostatic in situ vertical stress. In either case, if this closure pressure accurately reflects the in situ confining pressure, then an upper bound on in situ matrix permeabilities would be 1 × 10−20 to 2 × 10−19 m2 for the samples studied.
Increased mean depth of earthquakes at Parkfield
Authors: Wyss Max
Published: February 2008

The mean focal depth of earthquakes in the northern and southern parts of the Parkfield segment of the San Andreas fault was greater than long term average by 1km during the last 4 years approximately. It is proposed that this is a precursor to the next characteristic Parkfield earthquake, because the same phenomenon occurred before at least three other mainshocks along the San Andreas fault. In the northern segment the increase in mean depth is mostly due to reduction of shallow activity, in the southern segment deeper than usual activity seems to have increased. Within about 8 km from the 1966 epicenter no significant increase of mean depth is observed, but seismic quiescence [Wyss et al., 1990a] and a decrease in deformation rate [Wyss et al., 1990b] was documented. These observations are interpreted to suggest that the precursory process at Parkfield varies along strike, and that the next rupture may extend further north than the last one.
CH4 AND N2O photochemical lifetimes in the upper stratosphere: In situ estimates using SAMS data
Authors: Stanford J. L. , Ziemke J. R.
Published: February 2008

Upper stratospheric photochemical lifetimes are estimated in situ for CH4 and N2O for the first time, based on an analysis technique using 3 years of satellite measurements from the Stratospheric And Mesospheric Sounder (SAMS) instrument. The technique involves investigation of the time dependence of tracers injected into high Northern latitudes in late winter and their subsequent photochemical decay during the dynamically quiescent summer stratosphere. Dynamical corrections are made for mean meridional circulation contributions. The lifetimes for N2O at 2 and 7 hPa (∼ 43 and ∼ 35 km altitude) are found to be 1.7 and 8.3 months, respectively. For CH4, 0.6 (∼ 52 km altitude) and 2 hPa lifetimes are 3.3 and 3.4 months, respectively. These observed values are in good agreement with model calculations by Solomon et al. [1986].
Linear prediction filters for linear and nonlinear modeled geomagnetic activity
Authors: Klimas A. J. , Baker D. N. , Roberts D. A.
Published: February 2008

It is shown that the Faraday loop analogue model of geomagnetic activity exhibits both the directly driven and loading‐unloading magnetospheric responses to solar wind input. It is further shown that the directly driven component is a linear response to loading while the loading‐unloading response is nonlinear. Linear prediction filters which relate model input to output are discussed. By either allowing or suppressing the loading‐unloading model response, filters that relate to nonlinear or linear dynamics, respectively, have been computed. Filters that describe the directly driven response are finite ranged; they asymptote to zero with increasing lag on a time scale that is fixed by the dissipation rate of the model. Filters that describe the nonlinear total response are infinite ranged; they asymptote with increasing lag to large amplitude periodic oscillations. Some implications of these infinite ranged filters are discussed.
Quasi‐Biennial Oscillation above 10 MB
Authors: Baldwin Mark P. , Dunkerton Timothy J.
Published: February 2008

It is shown that the quasi‐biennial oscillation of the equatorial lower stratosphere was correlated with mean zonal wind in the upper stratosphere, 1979–90. Correlations were positive near 60°N and 30°S during northern hemisphere (NH) winter and negative in the equatorial upper stratosphere during all seasons. Spatial autocorrelation of mean zonal wind during NH winter was actually largest in the upper stratosphere, between 10°S and 62°N, due to strong coupling between tropical and extratropical flow at upper levels.
Intermittent upwelling of asthenosphere beneath the Gregory Rift, Kenya
Authors: Tatsumi Yoshiyuki , Kimura Nobukazu , Itaya Tetsumaru , Koyaguchi Takehiro , Suwa Kanenori
Published: February 2008

K‐Ar dates and chemical compositions of basalts in the Gregory Rift, Kenya, demonstrate marked secular variation of lava chemistry. Two magmatic cycles characterized by incompatible element relative depletion are recognized; both occurring immediately after the peak of basaltic volcanism and coeval with both trachyte/phonolite volcanism and domal uplift of the region. These cycles may be attributed to increasing degree of partial melting of mantle source material in association with thinning of the lithosphere by thermal erosion through contact with hot upwelling asthenospheric mantle. Cyclic variation in asthenosphere upwelling may be considered an important controlling process in the evolution of the Gregory Rift.
Pyroxene/melt trace element behavior: A study of pyroxenes from the Valley of Ten Thousand Smokes, Alaska
Authors: Shearer C. K. , Papike J. J. , Spilde M. N. , Shimizu N.
Published: February 2008

An initial trace element study of selected pyroxenes from the 1912 Katmai volcanics was conducted using combined electron microprobe and secondary ion mass spectrometry techniques. Trace element distribution between pyroxene and melt over a wide range of melt composition (58.5–77 wt.% SiO2) is dominantly controlled by pyroxene crystal chemistry. Most other factors (melt structure, temperature) appear to be minor. In addition, major and trace element zoning patterns suggest an episode(s) of magma replenishment of the volcanic sub‐system with more “primitive” magmas. This may correspond to events within the complex Novarupta‐Trident‐Mount Katmai magma plumbing system.
Normal fault earthquake off the northern Mozambique: A possible isotropic source
Authors: Honda Satoru , Yomogida Kiyoshi
Published: February 2008

An earthquake which occurred off the northern Mozambique gives a peculiar feature of P‐waves recorded by WWSSN long period instruments. All the P‐waveforms can be divided into two parts: the amplitude of the first arriving phase varies from station to station, which is consistent with the normal fault type solution of the Harvard CMT solution determined by the long period GDSN data. The amplitude of the second phase, in contrast, is fairly constant over all the stations, inconsistent with the normal fault solution. From these observations and data analyses, we propose that the source process of this event is a combination of a normal fault and a subsequent isotropic source starting with an explosion followed by a contraction or a corruption with each net moment of 2 ∼ 3 × 1025 dyne.cm at the assumed depth of 7.5 km. Our image of these source mechanisms is consistent with the known geological setting around the epicenter: grabens with many dikes or intrusions.
Observations of short period mesospheric wave patterns: In situ or tropospheric wave generation?
Authors: Taylor M. J. , Edwards R.
Published: February 2008

Near infrared images showing wave structure in the hydroxyl (OH) nightglow emission have been obtained from Maui, Hawaii during the ALOHA‐90 campaign. Analysis of two nights during this campaign (25 and 31 March) indicate extensive, highly coherent, linear wave patterns of very short apparent period (∼5 and 10 min respectively). Both displays exhibited several features characteristic of the in situ breakdown of a large scale, long period, upper atmospheric wave disturbance. Data in support of this mechanism was found by other ALOHA instruments which detected concurrent long period (1–2 hour) mesospheric wave disturbances on both occasions. However, a tropospheric source for these waves cannot be ruled out. At least on 25 March a weather front occurred at ∼1400 km range with a favourable orientation and location. Although its range was relatively large, background winds may have substantially increased the path length of the waves through the intervening atmosphere.
A 2D numerical study of recurrent driven reconnection processes at the magnetopause
Authors: Ip W.‐H. , Jin S.‐P.
Published: February 2008

Two‐dimensional (2D) compressible MHD simulations are performed to explore the time‐dependence of driven reconnection process in the vicinity of the magnetopause. It is found that recurrent formation of magnetic islands/plasmoids occurs when the magnetic Reynolds number is sufficiently large (Rm=4000). This result is in line with the bursty reconnection model for the flux transfer events (FTEs) as advocated by Scholer (1988) and Southwood et al. (1988). Furthermore, the formation of magnetic islands in a multiple X‐line configuration is also consistent with the Lee‐Fu model (1985). In other words, the present results represent a new class of hybrid FTE model. With appropriate scalings, the characteristic time interval between the formation of magnetic islands is estimated to be on the order of 8 min. This time scale is compatible with the quasi‐periodicity sometimes found in optical and/or radar ionospheric signatures which might be associated with FTEs.
Petrogenesis of high‐silica rhyolite on the Alaska Peninsula
Authors: Lowenstern Jacob B. , Mahood Gail A.
Published: February 2008

The chemical and isotopic compositions of sills at West Mageik Lake are contrasted with high‐silica rhyolite erupted in 1912 at the nearby Valley of Ten Thousand Smokes to gain insight into the petrogenesis of evolved magmas in the Aleutian arc. A high‐silica rhyolitic sill has an εNd value (+8.8) similar to an adjacent dacite porphyry stock, but the elevated Al, Sr, and 87Sr/86Sr of the rhyolite suggest that fractionation of a parental dacite magma was accompanied by significant contamination by Sr‐rich sediments, probably of Paleozoic age. The chemical and isotopic character of the West Mageik Lake rhyolite suggest that the system was of small volume, making it easily affected by crustal contamination. The fact that the 8 km³ of high‐silica rhyolite erupted at the Valley of Ten Thousand Smokes shows only a slight Sr isotopic shift from associated dacite and andesite suggests it was part of a larger system that could assimilate small masses of crust without having its composition significantly affected.
A scheme for reducing the effect of selective availability on precise geodetic measurements from the Global Positioning System
Authors: Feigl Kurt L. , King Robert W. , Herring Thomas A. , Rothacher Markus
Published: February 2008

From March to August 1990, the signals transmitted by the Block II satellites of the Global Positioning System (GPS) were dithered under a policy of “Selective Availability” (SA). The dithering appears as a ∼10−10 deviation of the satellite oscillator frequency, which, when accumulated over several minutes, can produce an error of ∼100 cycles (∼20 m) in the model for carrier beat phase. Differencing between simultaneously sampling receivers minimizes the error. If, however, the receivers do not sample simultaneously, it is necessary to model the frequency deviation, which we estimate from the phase observed at a station with a stable local oscillator. We apply such a model to data collected in March 1990 by TI4100 and Minimac receivers sampling at times separated by 0.92 s. Applying the algorithm significantly improves the root mean square (RMS) scatter of the estimated relative position vectors. The RMS scatter from a data set including dithered satellites is similar for both simultaneously and non‐simultaneously sampling receivers, a result which indicates that SA can be adequately modeled.
Emission of formic and acetic acids from tropical Savanna soils
Authors: Sanhueza Eugenio , Andreae Meinrat O.
Published: February 2008

Fluxes of formic (HCOOH) and acetic (CH3COOH) acids between soils and the atmosphere were measured in a scrub‐grass savanna and a semideciduous forest of Venezuela. High emissions of both acids were observed from savanna soils during daytime, with a daily contribution to the atmospheric boundary layer of about 0.15 ppb HCOOH and 0.07 ppb CH3COOH. Soil watering, simulating rainfall, produces a significant increase in CH3COOH emissions. Forest soils consumed these acids, with deposition velocities of 0.21 and 0.16 cm s−1. Savanna soils appear to be a significant source of HCOOH and CH3COOH to the tropical savanna atmosphere.
The Fe‐FeO buffer at lower mantle pressures and temperatures
Authors: Hirsch L. M.
Published: February 2008

As a constraint on oxygen fugacity of the lower mantle, the iron‐wüstite (IW) oxygen buffer has been calculated for temperatures to 3000 K and pressures to 135 GPa using available thermochemical and thermophysical data for Fe, FeO, and O2. At conditions corresponding to the coremantle boundary and 670 km depth, respectively, the oxygen fugacity of this buffer is 1020 and 10³ Pa; oxygen activities referenced to these conditions are 10−9 and 10−13.
A general circulation model study of the solar and QBO modulation of the stratospheric circulation during the northern hemisphere winter
Authors: Kodera Kunihiko , Chiba Masaru , Shibata Kiyotaka
Published: February 2008

A general circulation model has been used to study the modulation of north‐polar temperatures during winter by both solar activity and the equatorial quasi‐biennial oscillation (QBO). The variation of solar activity was simulated by changing the heating rate due to the absorption of ultraviolet (UV) radiation by ozone, while the QBO zonal wind fields were reproduced by incorporating zonal‐momentum sources in the equatorial stratosphere. A total of 10 experiments were conducted by changing the heating rate from 70 to 110% for each of the simulated QBO easterly and westerly cases. The results of the numerical experiments show modulation effects similar to those found by Labitzke [1987] in the 30‐mb temperatures at the North Pole.
Analysis of seismic SV waves in the core's penumbra
Authors: Lay Thorne , Young Christopher J.
Published: February 2008

Vertically‐polarized S‐waves (SV) attenuate rapidly as they diffract around the Earth's core, whereas horizontally‐polarized S‐waves (SH) propagate to large distances in the core shadow zone. The amplitude decay of diffracted SV signals is so strong that few studies have been made of these phases, despite their acute sensitivity to velocity structure just above the core‐mantle boundary. We analyze SV signals in the penumbra of the core's shadow, finding systematic waveform complexities indicative of local stratification and apparent anisotropy at the base of the mantle, with implications for the dynamic processes in this internal boundary layer.
Depth dependance of Q beneath the Baltic Shield inferred from modeling of short period seismograms
Authors: Pedersen H. , Campillo M.
Published: February 2008

We use Rg waves (fundamental Rayleigh wave) to measure shear wave velocity and attenuation in the crust in central Finland. We used seismograms from quarry blasts in USSR recorded during the LITHOSCOPE‐SVEKA 89 experiment. We deduced from dispersion curves a shear wave velocity model for the upper crust. From the attenuation of Rg waves as a function of frequency, we found the quality factor Qs in the uppermost crust as a function of depth. The quality factor appears to be low (about 100) in the shallow crust and to increase rapidly at depth (to about 1000). In order to test this result we calculated complete synthetic seismograms for this velocity‐attenuation model. We were able to simulate accurately the arrival times and the relative amplitudes of all the major phases present in the actual seismograms (including Pg and Lg waves). This comparison supports the presence of a very attenuative surface layer with a thickness of about 1 km beneath the Baltic shield while the deep crust presents a very weak attenuation. This relatively thick attenuative superficial layer plays an important part in the overall attenuation observed in shield areas.
The vent of the 1912 Katmai Eruption: Gravity and magnetic measurements
Authors: Goodliffe Andrew M. , Stone David B. , Kienle Jürgen , Kasameyer Paul
Published: February 2008

This study is aimed at defining the boundary and internal structure of the Novarupta vent area, the source of the 1912 Katmai eruption. A geodetic grid consisting of 145 stations was occupied for gravity and magnetic measurements and an aeromagnetic survey was flown at 1100 m above sea level. The combined gravity and magnetic data indicate that there are probably two intrusive bodies within the vent, not just one at Novarupta, as was previously thought. The outline of the overall vent at the surface is well defined by the aeromagnetic survey, and the vent appears to dip inwards indicating that it flares from depth. This is in contrast to the piston‐like collapse thought to have taken place at Mt. Katmai in 1912.
Effects of phase transions and possible compositional changes on the seismological structure near 650 km depth
Authors: Jeanloz Raymond
Published: February 2008

If the lower mantle is enriched in Fe ± Si relative to the upper mantle, the compositional boundary is expected to be an interface with a density jump of ∼5 (±2)% and with depth varying laterally by >100–300 km, but with changes in seismic velocities that are nearly unobservable: ∼0 to −1.0 (± 2.5)% discontinuities in compressional (VP) and shear (VS) wave velocities. In contrast, the polymorphic transformation of transition‐zone minerals to the perovskite‐bearing assemblage of the lower mantle is estimated to produce a jump of ∼5–10 percent in density, VP and VS near 650 km depth, and the depth of the seismological discontinuity due to the phase transition is relatively independent (<50–150 km variation) of temperature or horizontal position. If present, a compositional boundary is not in general expected to occur at the identical depth (∼650 km) as the phase transition to the perovskitebearing assemblage, although the depths of the two may be linked.
Correlation‐modulated chaotic scattering in the Earth's magnetosphere
Authors: Büchner J.
Published: February 2008

We show that due to correlations between subsequent separatrix traversals the chaotic scattering of thermal ions and energetic electrons in the plasma sheet of the Earth's magnetotail is modulated, oscillating in dependence on the strength of the magnetic field inhomogeneity and particle energy. Correlation‐modulated chaotic scattering creates non‐Maxwellian features of the magnetotail ion distribution both in the CPS and the PSBL. It also causes an oscillating latitudinal variation of the auroral ion precipitation.
Equilibrium profiles of atomic 7Be and 10Be in the atmosphere above 100 km
Authors: Petty G. W.
Published: February 2008

Theoretical profiles of cosmogenic 7Be in the atmosphere above 100 km were computed in an effort to explain unexpectedly high accumulations of this radionuclide found on the leading surfaces of the Long Duration Exposure Facility (LDEF) spacecraft. Our diffusion calculations suggest that gravitational fractionation is sufficient to explain most, and possibly all, of the observed 7Be enrichment at the recovery altitude of the spacecraft, provided only that the nuclide exists at and above the turbopause predominantly in the form of free atoms. Upward diffusion of 7Be atoms through the turbopause appears to occur rapidly enough to largely offset losses at higher altitudes due to radioactive decay. The same model is used to compute cosmogenic 10Be profiles in order to predict the probable outcome of planned measurements of 10Be accumulations on LDEF surfaces.
A computational evaluation of the gas‐phase ClO dimerization thermodynamics
Authors: Slanina Zdeněk , Uhlík Filip
Published: February 2008

The equilibrium constant KP and the standard enthalpy, entropy and heat capacity at constant pressure changes for the ClO(g) dimerization are calculated from partition functions. The Cl2O2 partition functions are constructed using recent quantum‐chemical data while in the ClO case spectroscopic information is applied. A due attention is given to the Cl2O2 isomerism, viz. to the individual species ClOOCl (C2 symmetry), ClClO2 (C3), and ClOClO (C1). The available observed standard thermodynamic terms are reproduced within their estimated experimental errors, entropy terms yielding a better theory‐experiment agreement (comparing to enthalpy case). The thermodynamic terms are evaluated in a wide temperature interval, pointing out some features not amenable from the observations. The data can be useful in concentration evaluations as an intermediate for elucidating ozone‐depleting mechanisms.
Dehydration of brucite (Mg(OH)2) at high pressures detected by differential thermal analysis
Authors: Kanzaki Masami
Published: February 2008

The differential thermal analysis (DTA) technique has been applied in a multi‐anvil high‐pressure apparatus to study the dehydration reaction of brucite (Mg(OH)2) to periclase (MgO) plus H2O at 4 to 6 GPa. At 4 GPa and 1030°C, endothermic and exothermic peaks due to dehydration and rehydration were observed during heating and cooling cycles, respectively. These peaks were shifted to higher temperature with increasing pressure (1080°C at 5 GPa; 1120°C at 6 GPa), suggesting that the reaction has a positive dT/dP slope within this pressure range. The stability of brucite under deep mantle condition is discussed.
Two‐dimensional model of a slow‐mode expansion fan at Io
Authors: Krisko P. H. , Hill T. W.
Published: February 2008

We develop a 2‐D model for the standing slow‐mode expansion fan that is expected to exist downstream of the Jovian moon Io. The leading edge of the expansion fan makes an angle of 45° with the upstream magnetic field direction, and the fan width is about 114°. The plasma flow returns to its upstream direction by way of a slow‐mode shock behind Io where the MHD parameters return asymptotically to their upstream conditions. The magnetic field perturbation within the fan is much smaller than that associated with the Alfvén wing, which lies farther upstream.
Infrared reflectance spectra (4–12 µm) of typical lunar samples
Authors: Nash Douglas B.
Published: February 2008

A laboratory study of the mid‐infrared spectral reflectance properties of typical Apollo lunar rock and soil samples was conducted using a modern interferometric spectrometer. The results show that characteristic spectral features exist in the 4–12 micrometer range that are diagnostic of rock composition and mineralogy, especially for the plagioclase‐rich rocks and soils. This is the first phase of a comprehensive infrared reflectance study underway to better understand the use of infrared emission spectroscopy for mapping the surface composition of the Moon and other silicate bodies.
Observations of a 12 H wave in the mesopause region at the South Pole
Authors: Collins Richard L. , Senft Daniel C. , Gardner Chester S.
Published: February 2008

In December 1989 a Na lidar was installed at the Amundsen‐Scott South Pole Station and was used to measure aerosol, stratospheric temperature and mesospheric Na profiles through October 1990. The mesospheric Na data are used to characterize the gravity wave field in the mesopause region. These first lidar observations of Na layer dynamics at the South Pole show strong wave activity during the Antarctic winter. Data for 25 June and 19 August 1990 UT are presented here. The total wave induced variances in atmospheric density are respectively 29 and 35 (%)2. The Na layer centroid height is very low during both observation periods. On 25 June a strong 12 h oscillation is observed in the bottomside of the Na layer which extends to altitudes as low as 74 km. The vertical displacement and temperature amplitudes associated with the 12 h oscillation are respectively 1.9 km and 19 K. The characteristics of the 12 h wave are similar to the pseudotide observed at Svalbard by Walterscheid et al. [1986].