bluuebunny/crossref_metadata_2025 huggingface dataset:
Dispersion of P waves in subducted lithosphere: Evidence for an eclogite layer
Authors: Gubbins David , Snieder Roel
Published: February 2008

Cold, subducted lithosphere has relatively fast seismic velocity which leads to early arrivals for some event‐station paths. The effect is very large for events in the Tonga‐Kermadec deep seismic zone recorded at certain New Zealand stations. These particular arrivals are very high‐frequency (3 Hz or greater) and sometimes resemble two distinct phases, the later arrival appearing at about the time predicted by Jeffreys‐Bullen tables. Data from the digital station SNZO in Wellington confirm the travel time results of the analog stations and furthermore show frequencies above 5 Hz, much higher than can be seen on analog records, and up to 4% dispersion in the range 1–8 Hz. Energy in the second phase (which is often absent at SNZO) is mainly 1–2 Hz. The digital data support the idea, proposed earlier, that the effect is caused by propagation through a thin slab which passes only short‐wavelength waves. The essential features of the wave propagation are modeled by acoustic waves in a one‐dimensional high‐velocity slab; the waveforms produced by the model are discussed in terms of the leaky modes of the system and calculated by a reflectivity method. A very thin (< 15 km) uniform slab provides the required dispersion, but the waves are heavily attenuated and would never be observed at teleseismic distances; a thicker slab allows the energy through but does not give enough dispersion. Altering the variation of velocity across the slab provides the required dispersion if a thick high‐velocity layer, with wave speed increasing gradually with height, is overlain by a thin lid of even higher velocity. For the models considered the lid thickness must lie in the range 6–15 km and be continuous from a depth of about 50 km to the bottom of the earthquake zone. The thick layer could arise from the thermal anomaly in the subducted lithosphere; the thin lid may be the gabbroic part of the subducted crust that has transformed to eclogite.
Convection in three dimensions with surface plates: Generation of toroidal flow
Authors: Gable Carl W. , O'Connell Richard J. , Travis Bryan J.
Published: February 2008

This work presents numerical calculations of mantle convection that incorporate some of the basic observational constraints imposed by plate tectonics. The model is three‐dimensional and includes surface plates; it allows plate velocity to change dynamically according to the forces which result from convection. We show that plates are an effective means of introducing a toroidal component into the flow field. After initial transients the plate motion is nearly parallel to transform faults and in the direction that tends to minimizes the toroidal flow field. The toroidal field decays with depth from its value at the surface; the poloidal field is relatively constant throughout the layer but falls off slightly at the top and bottom boundaries. Layered viscosity increasing with depth causes the toroidal field to decay more rapidly, effectively confining it to the upper, low‐viscosity layer. The effect of viscosity layering on the poloidal field is relatively small, which we attribute to its generation by temperature variations distributed throughout the system. The generation of toroidal flow by surface plates would seem to account for the observed nearly equal energy of toroidal and poloidal fields of plate motions on the Earth. A low‐viscosity region in the upper mantle will cause the toroidal flow to decay significantly before reaching the lower mantle. The resulting concentration of toroidal flow in the upper mantle may result in more thorough mixing there and account for some of the geochemical and isotopic differences proposed to exist between the upper and lower mantles.
Numerical investigation of depth and current refraction of waves
Authors: Hubbert K. P. , Wolf J.
Published: February 2008

A numerical investigation of depth and current refraction of surface waves for several simple test cases is presented. The refraction scheme is incorporated into a third‐generation wave prediction model. It models the effect upon wave propagation of the temporally and spatially varying sea surface elevations and mean currents associated with tides and storm surges. The scheme solves the transport equation for the wave action spectrum. The magnitude of bathymetric depth refraction is large for the lower frequency swell waves. The accuracy to which the proposed scheme can predict refraction is dependent upon the directional resolution of the spectrum. A directional resolution of at least 15° is required; the use of a higher directional resolution may be limited by computational resource restrictions. Current refraction effects are very significant for wave propagation across a simple current eddy. Refraction effects are not limited to just a turning of the waves, but also involve significant changes in the spectral shape. Some of the test results exhibit excessive numerical dispersion associated with the use of upwind differencing. The magnitude of this dispersion is much reduced by employing a simple hybrid differencing scheme in wave frequency‐direction space. The high degree of numerical dispersion present in the model results is also a result of the nature of the simplified test cases. The magnitude of the numerical dispersion produced by the upwind differencing technique may not be significant when the model is used for storm simulation.
A rate for the scavenging of fine particles by macroaggregates in a deep estuary
Authors: Lavelle J. William , Cudaback Cynthia N. , Paulson Anthony J. , Murray James W.
Published: February 2008

234Th activity profiles in Puget Sound have been studied using a model that incorporates reversible exchanges between dissolved, fine particulate, and macroaggregate Th reservoirs. Macroaggregate settling is made responsible for the downward flux of Th and the vertical gradients of activity in measured profiles. Least squares fits of model to data yield rates/time scales for the exchange processes involved. Fine‐particle scavenging by macroaggregates is found to occur with a time scale of 4–6 days over a large range of macroaggregate settling speeds, ws. Macroaggregate‐disaggregation time scales are 1–4 days when ws is 100 m/d. Rates of sorption and remobilization characterizing the exchange between dissolved and fine‐particulate forms of the isotope cannot be individually identified from these data, but acceptable model values include those measured in the laboratory. Rates of sorption that depend on particulate concentrations which increase to the seafloor result in profiles of dissolved Th having above‐bottom maxima. Based on inferred exchange rates, the residence time for fine particles introduced at the surface of this deep (∼200 m) estuary is estimated to be 11–16 days when ws = 100 m/d.
The Arctic snow and air temperature budget over sea ice during winter
Authors: Overland James E. , Guest Peter S.
Published: February 2008

Arctic cooling through the fall‐winter transition is calculated from a coupled atmosphere‐sea ice thermal model and compared to temperature soundings and surface measurements made north of Svalbard during the Coordinated Eastern Arctic Experiment (CEAREX). A typical winter, clear‐sky vertical temperature structure of the polar air mass is composed of a surface‐based temperature inversion or an inversion above a very shallow (30–180 m) mechanically mixed boundary layer with temperatures −30° to −35°C, a broad temperature maximum layer of −20° to −25°C between 0.5 and 2 km, and a negative lapse rate aloft. Because the emissivity of the temperature maximum layer is less than that of the snow surface, radiative equilibrium maintains this low level temperature inversion structure. A 90‐day simulation shows that heat flux through the ice is insufficient to maintain a local thermal equilibrium. Northward temperature advection by transient storms is required to balance outward longwave radiation to space. Leads and thin ice (<0.8 m) contribute 12% to the winter tropospheric heat balance in the central Arctic. CEAREX temperature soundings and longwave radiation data taken near 81°N show polar air mass characteristics by early November, but numerous storms interrupted this air mass during December. Snow temperature changes of 15°C occurred in response to changes in downward atmospheric longwave radiation of 90 W m−2 between cloud and clear sky. We propose that the strength of boundary layer stability, and thus the degree of air‐ice momentum coupling, is driven by the magnitude of the radiation deficit (downward‐outward longwave) at the surface and the potential temperature of the temperature maximum layer. This concept is of potential benefit in prescribing atmospheric forcing for sea ice models because a surface air temperature‐snow temperature difference field is difficult to obtain and it may be possible to obtain a radiation deficit field via satellite sensors.
Wave propagation in the marginal ice zone: Model predictions and comparisons with buoy and synthetic aperture radar data
Authors: Liu Antony K. , Holt Benjamin , Vachon Paris W.
Published: February 2008

In this paper the ocean wave dispersion relation and viscous attenuation by a sea ice cover are studied for waves propagating into the marginal ice zone (MIZ). The derivation of the dispersion relation and the viscous attenuation by an ice sheet are discussed for waves under flexure and pack compression. In the MIZ, the flexure effect is important for short waves. For a fixed wave period the changes in wavelength and group velocity as a function of ice thickness are significant. In turn, the exponential wave attenuation rate shows a rollover at short wave periods, whereby the rapid increase in wave attenuation rate with decreasing wave period slows down or even turns into a decrease. The Labrador Ice Margin Experiment (LIMEX), conducted on the MIZ off the east coast of Newfoundland, Canada, in March 1987, provides us with aircraft synthetic aperture radar (SAR) imagery, wave buoy, and ice property data. On the basis of the wave number spectrum from the SAR data and the concurrent wave frequency spectrum from the ocean buoy data and accelerometer data on the ice during LIMEX '87, the dispersion relation has been estimated and compared with a model. Wave energy attenuation rates are estimated from SAR data and the ice motion package data which were deployed at the ice edge and into the ice pack, and compared with the model. The model‐data comparisons are reasonably good for the ice conditions observed during LIMEX '87. Some previously reported data of wave attenuation in the MIZ are revisited for model comparison.
Fram Strait satellite image‐derived ice motions
Authors: Emery W. J. , Fowler C. W. , Hawkins J. , Preller R. H.
Published: February 2008

In order to develop an operational method for the U.S. Navy/NOAA Joint Ice Center to extract ice velocity vectors from sequential advanced very high resolution radiometer (AVHRR) imagery, we have combined the maximum cross correlation (MCC) method with a spatial filtering technique on the image inferred ice motion vectors. We compute the cross correlations between images directly from the image brightness values rather than computing FFTs. The direct method allows greater flexibility in computational parameter settings and allows one to compute motion vectors near coastlines where irregular windows are required. By using a combination of statistical and spatial filters we can then retrieve coherent ice motion vectors in the presence of cloud contaminated imagery. A series of six satellite images of the Fram Strait region, from April 1986, was used to compute sea ice motion from pairs of sequential images. The resulting ice motion vectors were taken as a representation of the surface flow field derived objectively from the satellite imagery. Resulting vector motion fields were found to match well with manually tracked vectors for the same images, thus verifying the validity of the objective MCC method of computing ice motion. These techniques were applied to both the visible and infrared AVHRR channels and to images with different spatial resolutions yielding an overall bias accuracy of about 0.5 cm/s and standard deviations of about 0.9 cm/s. The MCC ice motion results were also compared with wind‐driven numerical model simulations of the region. Marked differences between the MCC image‐derived velocities and those from the numerical model were thought to be primarily due to a stronger ocean current than was present in the model.
The effect of the degree of wave development on the sea state bias in radar altimetry measurement
Authors: Fu Lee‐Lueng , Glazman Roman
Published: February 2008

The effect of the degree of wave development on the sea state bias (SSB) in Geosat altimeter height measurement is evaluated. Theoretical considerations suggest that the altimetric SSB is generally not a linear function of significant wave height but depends also on other factors of wave development. Of particular interest is its dependence on wave age, defined as the ratio of the phase speed of the dominant ocean waves to ocean wind speed. We estimate wave age rather crudely, on the basis of the significant wave height (H⅓) and wind speed measured by the altimeter. Under general conditions when the sea is not in equilibrium with the wind, this estimate may not correspond to the wave age in a strict sense and hence is called “pseudo wave age” in this paper. Nevertheless, the pseudo wave age is a rough indicator for the degree of wave development. The general trend in the dependence of the SSB on pseudo wave age, as found by analyzing 2.7 years' worth of Geosat data, agrees well with the theoretical prediction: for a given H⅓, the SSB decreases as the degree of the wave development (measured by the pseudo wave age) increases. This empirical trend is modeled as SSB= A(ξ/ξm)M H⅓, where ξ and ξm are the pseudo wave age and its average value, respectively; A = 0.013 ± 0.005, and M = −0.88 ± 0.37. Statistically, this model performs slightly better than a standard model (i.e., SSB = β H⅓ with β being a constant). In terms of the global rms error the improvement is by 1.6 cm. However, because the degree of wave development varies with the season and geographical location, this small improvement could become important for more accurate altimetric missions in the future when the centimetric, basin‐scale signals are the focus of the study.
Ionospheric variability and the measurement of ocean mesoscale circulation with a spaceborne radar altimeter
Authors: Monaldo Frank
Published: February 2008

The propagation of radio waves broadcast to the Earth by a satellite is slowed by the total electron content (TEC) of the ionosphere. Spaceborne radar altimeters, like those aboard the Seasat and Geosat satellites, rely on the time delay between the transmission of a radar pulse and its reception, after reflection from the ocean surface, to estimate the range to the surface. The slowing of the electromagnetic waves by the ionosphere will increase the apparent distance between the satellite and the surface. Variations of the TEC of the ionosphere on horizontal spatial scales less than 300 km could potentially be confused for or mask the presence of sea surface height changes associated with mesoscale ocean circulation. Using dual‐frequency broadcasts from Global Positioning System (GPS) satellites, the spatial variability of the ionosphere is estimated. It is shown that for altimetric monitoring of mesoscale ocean circulation, ionospheric variability is not a significant problem. For altimetric studies of ocean circulation on ocean basin scales, compensation for ionospheric variability maybe necessary.
Surface wind speeds over the North Sea from special sensor microwave/imager observations
Authors: Schluessel Peter , Luthardt Hans
Published: February 2008

The Special Sensor Microwave/Imager (SSM/I) flying as part of the U.S. Defense Meteorological Satellite Program measures millimeter‐wave radiation emerging from the Earth‐atmosphere system at different directions of polarization that can be used to measure oceanic surface wind speed. The radiative transport within the radiometer channels is studied theoretically for a large set of oceanic/atmospheric situations with respect to surface wind speed variations. Statistical retrieval coefficients for the recoverage of surface wind speeds from the satellite measurements are then derived via regression analysis of the synthetic measurements simulated. The theoretically estimated accuracy for the globally valid passive wind speed retrieval is 1.4 m/s under conditions where no heavy rain hampers the surface‐leaving radiation in reaching the satellite. The technique is validated with in situ wind fields over the North Sea being objectively analyzed from routine wind and pressure observations.
Water mass analysis with three conservative variables
Authors: McDougall Trevor J.
Published: February 2008

With one conservative tracer in addition to salinity and potential temperature it is possible to determine the relative strengths of lateral and vertical mixing processes. This is achieved by first eliminating vertical advection through neutral surfaces and then forming a linear combination of the three conservative tracers so that the epineutral gradient (i.e., the lateral gradient along the neutral surface) of the new variable is zero, thereby eliminating lateral advection. The resulting expression for the ratio of the vertical and lateral diffusivities involves the curvatures of property‐property diagrams formed both from vertical casts and from data measured on a neutral surface. The method requires that the epineutral gradients of potential temperature, salinity, and the third conservative tracer are parallel. This condition is often met in the common situation where water parcels are the result of mixing between just two parent water masses.
Aerosol backscatter measurements at 10.6 micrometers with airborne and ground‐based CO2 Doppler lidars over the Colorado High Plains: 1. Lidar intercomparison
Authors: Bowdle David A. , Rothermel Jeffry , Vaughan J. Michael , Brown Derek W. , Post Madison J.
Published: February 2008

An airborne continuous wave (CW) focused CO2 Doppler lidar and a ground‐based pulsed CO2 Doppler lidar were used to obtain seven pairs of comparative measurements of tropospheric aerosol backscatter profiles at 10.6 μm wavelength, near Denver, Colorado, during a 20‐day period in July 1982. In regions of uniform backscatter the two lidars show good agreement, with differences usually less than ∼50% near 8‐km altitude and less than a factor of 2 or 3 elsewhere but with the pulsed lidar often lower than the CW lidar. Near sharp backscatter gradients the two lidars show poorer agreement, with the pulsed lidar usually higher than the CW lidar. Most discrepancies arise from a combination of atmospheric factors and instrument factors, particularly small‐scale areal and temporal backscatter heterogeneity above the planetary boundary layer, unusual large‐scale vertical backscatter structure in the upper troposphere and lower stratosphere, and differences in the spatial resolution, detection threshold, and noise estimation for the two lidars.
Aerosol size distribution, composition, and CO2 backscatter at Mauna Loa Observatory
Authors: Clarke Antony D. , Porter John N.
Published: February 2008

Continuous measurements of aerosol size distributions were obtained during January–March and November–December periods of 1988 at Mauna Loa Observatory, Hawaii. These periods were chosen in order to characterize aerosol physicochemistry during periods representative of “low‐dust” atmospheric conditions and periods associated with appreciable Asian dust transport to that site. Size distributions for particles with diameters between 0.15 and 7.6 μm were accumulated in 256 size bins of a laser optical particle counter for 3‐hour intervals during most of the period. The aerosol sample stream was heated to selected temperatures in order to provide size‐discriminated measurements of aerosol volatility. Resulting data were used to assess the variability in aerosol concentrations and properties related to aerosol backscatter values at a wavelength of 10.6 μm, βCO2 in the mid‐troposphere. Low aerosol concentrations, considered representative of mid‐tropospheric air, occurred in downslope flow between midnight and sunrise. Our measurements for these time periods suggest that βCO2 varied from a low of about 5×10−12m−1sr−1 to a high of 5×10−8m−1Sr−1. Coarse particles with diameters between 1.0 and 5.0 μm account for most of the derived values of βCO2 at all but the highest and lowest aerosol mass concentrations. Volatile aerosol appears to dominate aerosol mass during the cleanest periods but was a small fraction of the total during dust events. During low‐dust periods the aerosol volatile at 320°C often appears as coatings on refractory (e.g., dust) aerosol and is expected to influence measured βCO2 values. This low dust condition is also expected to be most representative of aerosol at higher altitudes in the free troposphere. We estimate that minimum values for βCO2 at about 8 km should usually fall in the range of 1–3×10−12m−1sr−1 and be dominated by a sulfate aerosol.
Aerosol particle characteristics determined by combined cluster and principal component analysis
Authors: Saucy Daniel A. , Anderson James R. , Buseck Peter R.
Published: February 2008

Cluster and principal component analysis procedures were used to examine compositions and time‐dependent concentrations of aerosol particles collected over a 7‐day period near Phoenix, Arizona. The elemental compositions of 13,026 individual particles have been determined by energy dispersive X ray spectrometry using a scanning electron microscope. Cluster analysis of the individual‐particle data revealed 15 chemically distinct particle types. Principal component analysis of the time‐dependent concentrations of these types indicated five unique concentration versus time patterns. Based on the chemical compositions and size characteristics, as well as on wind patterns during collection, distinct sources for the majority of the particle types can be ascribed. The three major sources are crustal material, copper smelters, and marine air. Two minor types, Ti‐rich and Pb‐rich, appear to be of local origin. This combination of the time‐dependent chemistry and size and wind data leads to improved source attribution.
Inferring the abundances of ClO and HO2 from Spacelab 3 Atmospheric Trace Molecule Spectroscopy observations
Authors: Allen Mark , Delitsky Mona L.
Published: February 2008

The vertical distributions of the important highly reactive stratospheric species, ClO and HO2, have been inferred from Spacelab 3 (May 1985) Atmospheric Trace Molecule Spectroscopy (ATMOS) measurements of more detectable radical and reservoir species. A simple steady state algebraic expression for ClO, utilizing the observed ClONO2/NO2 abundance ratio, approximates the ClO results of a time‐dependent photochemical model at sunset (30°N). Balloon measurements of ClO and comparisons of time‐dependent photochemical model calculations of ClONO2 and HCl with the corresponding ATMOS profiles suggest that the actual ClO values are less than the time‐dependent model profiles for ClO at sunset and sunrise (47°S). Errors in the current model simulation of the partitioning among the principal free chlorine species (HCl, ClONO2, and ClO) are indicated. However, a comparison of model results with observations of HOCl suggests that the calculated ClO abundance is not a significant overestimate of actual values. A similar methodology is applied to inferring the HO2 distribution, either algebraically using the ATMOS‐measured HO2NO2/NO2 abundance ratio or numerically utilizing the time‐dependent model. The algebraic results agree with the time‐dependent model values to better than a factor of 2 at sunrise. The accuracy of the time‐dependent model calculations of HO2 is suggested by the agreement between model results and ATMOS observations for HO2NO2 and balloon measurements Of HO2. This confirms for the first time the procedure suggested previously by a number of authors of deriving HOx abundances from observed fields of O3 and H2O.
Three‐dimensional simulations of wintertime ozone variability in the lower stratosphere
Authors: Rood Richard B. , Douglass Anne R. , Kaye Jack A. , Geller Marvin A. , Yuechen Chi , Allen Dale J. , Larson Edmund M. , Nash Eric R. , Nielsen J. Eric
Published: February 2008

The evolution of ozone has been calculated for the winters of 1979 and 1989 using winds derived from our stratospheric data assimilation system (STRATAN). The ozone fields calculated using this technique are found to compare well with satellite‐measured fields for simulations of 2–3 months. Here we present comparisons of model fields with both satellite and sonde measurements to verify that stratospheric transport processes are properly represented by this modeling technique. Attention is focussed on the northern hemisphere middle and high latitudes at the 10‐hPa level and below, where transport processes are most important to the ozone distribution. First‐order quantities and derived budgets from both the model and satellite data are presented. By sampling the model with a limb‐viewing satellite and then Kalman filtering the “observations” of the model, it is shown that transient subplanetary‐scale features that are essential to the ozone budget are missed by the satellite system.
Analyses of infiltration events in relation to determining soil hydraulic properties by inverse problem methodology
Authors: Russo David , Bresler Eshel , Shani Uri , Parker Jack C.
Published: February 2008

At the field scale, because of the relatively large number of observation points required to estimate the spatial distributions of hydraulic properties, application of inversion procedures must be based on a characteristic of the flow that for a given point in the field can be measured with relative ease, and can be used as input for the inversion procedure. Suggesting the use of infiltration data for this purpose, and recognizing the fact that a basic requirement for the design of a transient flow experiment is that the resulting inverse problem be sufficiently well posed to allow solution, this paper addresses the question under which circumstances the resulting inverse problem is well posed, utilizing the concepts of identifiability, uniqueness, and stability. For this purpose, three different models of the soil hydraulic properties were analyzed. The main conclusion of this study is that when infiltration data measured at the Darcy scale are used as input for the inversion procedure, the inclusion of prior information on a single measurable parameter, the saturated conductivity Ks, in the estimation criterion will enhance the likelihood of uniqueness and stability of the inverse solution provided that the structure of the hydraulic model is sufficiently simple. However, since for a particular situation, it is impossible to determine a priori whether the resultant inverse problem is well posed or not, this must be carried out only a posteriori by solving the problem several times with different initial parameter estimates, accompanied by an analysis of the associated estimation errors.
Photochemical production of carbonyl sulfide in seawater and its emission to the atmosphere
Authors: Andreae Meinrat O. , Ferek Ronald J.
Published: February 2008

Carbonyl sulfide (COS) measurements in the surface waters of the temperate and subtropical North Atlantic and the Gulf of Mexico showed COS to be supersaturated with respect to atmospheric equilibrium at almost all locations and times investigated. Its concentration follows a pronounced diel cycle which can be modeled using a simple equation which includes hydrolysis removal and photo‐chemical production. The concentration and ocean/atmosphere flux of COS depends strongly on marine productivity, the highest levels being found in coastal and shelf waters. Analysis of presently available data yields an estimate of 13 Gmol yr‐1 (0.41 Tg S(COS) yr−1) for the total flux of COS from the oceans to the atmosphere.
Emissions of alkaline elements calcium, magnesium, potassium, and sodium from open sources in the contiguous United States
Authors: Gillette Dale A. , Stensland Gary J. , Williams Allen L. , Barnard William , Gatz Donald , Sinclair Peter C. , Johnson Tezz C.
Published: February 2008

Models of dust emissions by wind erosion (including winds associated with regional activity as well as dust devils) and vehicular disturbances of unpaved roads were developed, calibrated,and used to estimate alkaline dust emissions from elemental soil and road composition data. Emissions from tillage of soils were estimated from the work of previous researchers. The area of maximum dust production by all of those sources is the area of the old “Dust Bowl” of the 1930s (the panhandles of Texas and Oklahoma, eastern New Mexico and Colorado, and western Kansas). The areas of maximum alkaline dust production are the arid southwest, the “Dust Bowl,” and the midwestern‐mideastern states from Iowa to Pennsylvania. Our calculations show that calcium is the dominant alkaline element produced by “open sources” (sources too great in extent to be controlled by enclosure or ducting). Although the largest dust mass source is wind erosion (by winds associated with regional activity and convective activity), the largest producer of the alkaline component is road dust because the abundance of alkaline materials in road coverings (which include crushed limestone) is significantly higher than for soils. Comparing the above estimated sources of alkaline material with inventories of SO2 and NOx emissions by previous investigators gives the rough approximation that alkaline emission rates are of the order of the SO2 + NOx emissions in the western United States and that they are much smaller than SO2 + NOx in the eastern United States. This approximation is substantiated by data on Ca/(SO4 + NO3) for wet deposition for National Atmospheric Deposition Program sites.
Detection of 0.5–15 GEV solar protons on 29 September 1989 at Australian stations
Authors: Humble J. E. , Duldig M. L. , Smart D. F. , Shea M. A.
Published: February 2008

A major cosmic ray ground‐level enhancement, the largest in 33 years, occurred on 29 September 1989 during which intensity enhancements at Australian observatories ranged up to a maximum of 344% at Mt. Wellington. The Darwin neutron monitor (cutoff rigidity 14.1 GV) recorded an ∼13% increase in the five‐minute counting rate indicating that solar particles up to at least 15 GeV must have been present. Surface muon detectors at Hobart and Mawson recorded increased fluxes, but the event was not recorded by underground muon detectors at either station. Preliminary analysis of the solar particle flux during the initial phase of the event shows a hard spectrum approximated equally well by an exponential spectra with a Po of 2.0 GV or by a modified power law spectra of exponent ∼−2.9. Particles arriving at the detectors from non‐vertical directions make a significant contribution to the total increase recorded at mid and low latitude stations.
In situ measurements of carbon dioxide in the winter Arctic vortex and at midlatitudes: An indicator of the ‘age’ of stratopheric air
Authors: Schmidt U. , Khedim A.
Published: February 2008

We report measurements of the vertical distribution of the carbon dioxide mixing ratio in the lower and middle stratosphere. They were performed during a series of balloon flights over midlatitudes (44 °N) during different seasons and over high latitudes (68 °N) during winter in the time period from 1982 until 1990. CO2 was gaschromato‐graphically determined in air samples collected by means of cryogenic whole‐air samplers. The annual increase of the CO2 content of the mid‐stratospheric air is comparable to the temporal CO2 trend in the troposphere. However, the stratospheric concentrations are lagging the tropospheric ones by a mean delay time of 5.6 ± 1.1 years. This delay time may be interpreted as the ‘age’ of stratospheric air masses. It is determined by the efficiency of the transport processes that mix tropospheric air into the stratosphere. Our CO2 observations during the last decade suggest that these processes have varied systematically with a time period of 3 to 5 years. A rather low ‘age’ of 2.3 ± 0.3 years was derived from the most recent observations over midlatitudes in summer 1989 as well as in the Arctic region during the CHEOPS III Campaign in winter 1989/90.
Signatures of solar wind injection and transport in the dayside cusp: EXOS‐D observations
Authors: Mukai T. , Matsuoka A. , Hayakawa H. , Machida S. , Tsuruda K. , Nishida A. , Kaya N.
Published: February 2008

Structure of charged particle precipitation in the polar cusp is studied in comparison with the simultaneously observed electric field. The polar cusp is characterized by precipitation of intense low‐energy (∼100 eV) electrons and energetic (0.1∼a few keV/e) ions which often show an energy dispersion. The precipitation region is sometimes divided into two discrete zones which have different dispersion characteristics, one showing an ion energy dispersion in which the characteristic ion energy falls with increasing latitude, and the other showing either clear dispersion of different form or non‐dispersion. On the other hand, the electric field in the cusp reveals non‐uniform and duskward or dawnward convective flows with velocity shears and intense fluctuations. It is remarkable that, nevertheless, ion precipitation shows a clear energy dispersion. We discuss how various types of energy dispersion can be interpreted in terms of the modified velocity filter effect in spite of complexities in the electric field.
Plasma turbulence disc circulating the equatorial region of the plasmasphere identified by the plasma wave detector (PWS) on board the Akebono (EXOS‐D) satellite
Authors: Oya Hiroshi , Iizima Masahide , Morioka Akira
Published: February 2008

For the observation data of the plasma wave turbulence detected by the PWS (Plasma Wave and Sounder Experiment) on board the EXOS‐D (Akebono) satellite, the enhancements of the upper hybrid wave emission called equatorial enhancement of the plasma wave turbulence (EPWAT) that are characterized by the increasing level of the upper hybrid emissions are studied on their occurrence regions and occurrence conditions. The results show that EPWAT's encircle the magnetic equator forming a disc region that spreads from 1000km to 10,000km altitude without dependence on the local time. The generation of plasma wave turbulences, EPWAT's are possibly controlled by the plasma drift as principal source in the region of the magnetic equator due to existing electric field.
k vector measurements of VLF signals by the satellite EXOS‐D
Authors: Yamamoto Masayuki , Ito Yoshihiko , Kishi Yoji , Sawada Akira , Kimura Iwane , Nagano Isamu , Kennai Eiichi , Okada Toshimi , Hashimoto Kozo
Published: February 2008

On board the EXOS‐D (Akebono) satellite is a five channel PFX subsystem of VLF instruments, working to determine the wave normal or k vector and Poynting vector directions by measuring two components of E and three components of B fields using wire and loop antennas.

In order to confirm the characteristics or capability of determining the k vector and the Poynting vector of a coherent VLF Omega signal transmitted from Australia have been analyzed. The observed Omega signal has been found to be right‐handed polarized with Poynting vector is making a small angle with the geomagnetic field and lies nearly on the plane constructed by the geomagnetic field and k vector. The refractive index deduced from the E and B fields well agrees with that calculated by Appleton Hartree formula.
Small‐scale field‐aligned currents observed by the Akebono (EXOS‐D) satellite
Authors: Fukunishi H. , Fujii R. , Kokubun S. , Tohyama F. , Mukai T. , Oya H.
Published: February 2008

The EXOS‐D fluxgate magnetometer data obtained at 3000–10000 km altitude have shown that small‐scale field‐aligned currents always exist in large‐scale region 1, region 2, cusp and polar cap current systems. Assuming that these small‐scale field‐aligned currents have current sheet structure, the width of current sheet is estimated to be 5–20 km at ionospheric altitude. By comparing the magnetometer data with charged particle and high frequency plasma wave data simultaneously obtained from EXOS‐D, it is found that small‐scale currents have one‐to‐one correspondence with localized electron precipitation events characterized by flux enhancement over a wide energy range from 10 eV to several keV and broadband electrostatic bursts occasionally extending above local plasma frequencies or electron cyclotron frequencies.
EXOS‐D observations of upflowing ion conics with high time resolution
Authors: Miyake W. , Mukai T. , Kaya N. , Fukunishi H.
Published: February 2008

Upflowing ion conics with energies of up to 100 eV and its response to quickly varying electron precipitation are reported from Exos‐D charged particle observation. The field aligned bulk shift of upflowing ions is well correlated to electron precipitation even with a small scale, indicating the bulk shift is caused by the acceleration of parallel electric field around the satellite. On the other hand, the anisotropy (perpendicular heating) of upflowing ions responds to the electron precipitation in a dull way. Only in the large or long‐lived region of electron precipitation, the anisotropy is reduced and the ion distribution in phase space approaches the ion beam. Signature of heating at lower altitude is still found in the phase space distribution of the ion beams. The observation shows a close connection between the elevated (bimodal) conics and upward beams.
ELF emissions observed by the EXOS‐D satellite around the geomagnetic equatorial region
Authors: Sawada Akira , Kasahara Yoshiya , Yamamoto Masayuki , Kimura Iwane , Kokubun Susumu , Hayashi Kanji
Published: February 2008

As was introduced in the paper by Kimura et al. [1990], interesting ELF emissions in the frequency ranges above the cyclotron frequencies of He+ and/or O+ have been detected by ELF subsystem of the EXOS‐D satellite. This paper is to propose that these emissions are ion cyclotron mode emissions trapped along the magnetic field lines around the magnetic equatorial plane, which are very similar phenomena detected in frequencies around the He+ cyclotron frequency, FHe+ by GEOS 1 and 2 nearly the geostationary altitude. The propagation characteristics can be confirmed by ray tracing including the effects of ions.
Electron beam injection and associated LHR wave excitation: Computer experiments of electrodynamic tether system
Authors: Usui Hideyuki , Matsumoto Hiroshi , Omura Yoshiharu
Published: February 2008

To study the nonlinear plasma dynamics associated with electrodynamic tether system, we performed computer experiments using a 2D electromagnetic particle code. In the computer experiments, two conducting bodies, corresponding to the satellite and the orbiter, are placed in the x‐y plane in a vehicle frame. The electrons collected by the tether system are emitted from the orbiter. We focus on the plasma response to the tether system, the electron beam dynamics, and the wave emission. At the satellite region, plasma depletion owing to the electron collection along B0 by the high potential satellite is found as well as a wake structure in the downstream region of the plasma flow. At the orbiter region, an electron beam cloud is clearly created in the downstream region. The local electric field induced by the cloud modifies the beam pitch angle and accelerates some of the beam electrons along B0. Moreover, due to the cross‐field current by the electron E × B drift motion around the cloud, LHR mode waves are enhanced locally. The local LHR wave excitation is quantitatively interpreted by the theory of the lower‐hybrid‐drift instability.
Parametric interaction between upper hybrid and lower hybrid waves in heating experiments
Authors: Leyser T. B.
Published: February 2008

A two‐fluid model of the parametric decay of an upper hybrid wave into an electromagnetic wave and a lower hybrid wave [Murtaza and Shukla, 1984] is applied to conditions in the ionospheric F region. It is found that the instability threshold can be exceeded in ionospheric high frequency heating experiments. Features of the growth rate can explain hitherto unexplained properties of a commonly observed prominent spectral structure of stimulated electromagnetic emission. The stimulated radiation can then be used to determine the magnitude of the geomagnetic field where the upper hybrid frequency matches electron cyclotron harmonics in the ionosphere.
Ground‐based UV‐VIS spectroscopy: Diurnal OCIO‐profiles during January 1990 above Søndre Strømfjord, Greenland
Authors: Perner D. , Klüpfel T. , Parchatka U. , Roth A. , Jørgensen T.
Published: February 2008

Considerable amounts of chlorine dioxide, OClO, were observed from 5 January through 2 February, 1990 in the stratosphere above Søndre Strømfjord showing a highly perturbed chlorine chemistry. Photolysis and simultaneous formation of the OClO leads to a typical concentration minimum at noon. Its changes in concentration indicate the release of the OClO precursors BrO and ClO from their respective reservoir substances in the morning. Two incidences of increased OClO production occur repeatedly at 92° and 89° solar zenith angle (SZA). Furthermore, in the beginning of January OClO morning values exceed those found at dusk for comparable SZA whereas towards the end of the month the morning values become depressed compared to the evening. The twilight vertical column densities of OClO often reach about 1.6 × l013 molec cm−2 and a comparison shows an increase from 1988 to 1990.
KOSI: Gas drag derived from ice/dust‐particle trajectories
Authors: Kochan H. , Markiewicz W. J. , Keller H. U.
Published: February 2008

Trajectories of the emitted ice/dust particles successfully monitored by a high speed shutter video camera during the large scale experiment KOSI‐5 (Nov. 1989) performed in the DLR Space Simulator. These new results complement and quantify the high resolution observations of the surface obtained previously in the small chamber. The particles are coupled rather then loosely deposited on the surface. We conclude that the particle dynamics is dominated by the acceleration during their flight. This acceleration is caused by the momentum transfer from the gas sublimating from the sample. The net observed acceleration in the direction normal to the surface is in the range 10 – 20 m/sec². The ice/dust particles appear to be entrained into the gas flow, rather than ejected from the surface.
Comparison of VLBI and SLR geocentric site coordinates
Authors: Ray J. R. , Ma C. , Ryan J. W. , Clark T. A. , Eanes R. J. , Watkins M. M. , Schutz B. E. , Tapley B. D.
Published: February 2008

The geocentric coordinates for 18 pairs of SLR and VLBI sites are compared. After a seven‐parameter frame adjustment, the two coordinate sets have weighted rms differences of 15, 22, and 22 mm for X, Y, and Z, respectively, consistent with the formal errors being too small by a factor of about two.
Precursory changes in fumarolic gas temperature associated with a recent submarine eruption near Izu‐Oshima Volcano, Japan
Authors: Notsu Kenji , Wakita Hiroshi , Igarashi George
Published: February 2008

Significant temperature changes in a steamrich fumarolic gas from a deep hole in the Izu‐Oshima volcano, Japan, were observed prior to a series of earthquake swarms and submarine volcanic eruptions which occurred off the eastern coast off the Izu Peninsula, about 40 km NE of the Izu‐Oshima volcano, in July 1989. We suggest that temperature changes indicate that the Izu‐Oshima volcano and the submarine volcanic cone, the Teishi knoll, are linked and that upward movement of Teishi magma resulted in a gas pressure decrease of the Izu‐Oshima magma. This new suggestion of a link between two magma systems over such a large distance may be of great significance for understanding arc volcanism. Our observation may be of use in the future prediction of volcanic eruptions in the Izu area.
Solar‐wind krypton and solid/gas fractionation in the Early Solar Nebula
Authors: Wiens Roger C. , Burnett D. S. , Neugebauer M. , Pepin R. O.
Published: February 2008

Krypton is the best candidate for determining limits on solid/gas fractionation in the early sun because of the smoothness of the odd‐mass abundance curve in its mass region, which permits relatively precise interpolations of its abundance assuming no fractionation. Here we calculate the solar‐system Kr abundance from solar‐wind noble‐gas ratios, determined previously by low‐temperature oxidations of lunar ilmenite grains, normalized to Si by spacecraft solar‐wind measurements. The estimated 83Kr abundance of 4.1 ± 1.5 per 106 Si atoms is within uncertainty of estimates assuming no fractionation, determined from CI‐chondrite abundances of surrounding elements. This is significant because it is the first such constraint on solid/gas fractionation, though the large uncertainty only confines it to somewhat less than a factor of two.
Magnetotail reconnection: Current diversion and field‐aligned currents
Authors: Scholer Manfred , Otto Antonius
Published: February 2008

We have used a three‐dimensional resistive and compressible MHD code to study reconnection in a magnetotail configuration. The initial state is a two‐dimensional equilibrium with a northward magnetic field component Bz across the current sheet. Reconnection is initiated by applying a finite resistivity localized in the near‐Earth region with a finite extent in the dawn‐dusk direction. The inflow of plasma in the equatorial plane into the reconnection region from dawn and dusk and the divergence of the fast earthward and tailward flow from the reconnection region toward dawn and dusk leads to a magnetic shear. Both this shear and the dipolarization over a limited dawn‐dusk extent are responsible for region 1 field‐aligned currents earthward and tailward of the neutral line. The occurrence of the shear is independent of a particular initial equilibrium, i.e., region 1 field‐aligned currents will also occur during reconnection in a one‐dimensional current sheet when the reconnection line has a limited extent. We also obtained region 2 field‐aligned currents at lower z values near the earthward boundary.
Origin of reflectors in seismic line 2, Toa Baja, Small gas horizons associated with enhanced reflector amplitudes, and recognizing leaky and sealing faults using gas chromatography data
Authors: Larue D. K. , Anderson R. N. , Goldberg D. , Moos D.
Published: February 2008

Reflectors imaged in a multichannel seismic line at Toa Baja, Puerto Rico, were studied by comparing the positions of reflection events with changes in rock properties determined through analysis of logs and cuttings. Reflectors appear to be associated primarily with changes in rock properties across facies or formation boundaries, and more rarely unconformities and faults. Faults that seal versus faults that leak can be recognized on the basis of gas Chromatograph data. Several laterally discontinuous reflectors characterized by modest amplitude anomalies seem to correlate in depth with minor shows of methane gas, measured by onsite gas chromatography. Gas was not recognizeable using geophysical logs indicating small quantities. The gas is apparently associated with rock types and rock properties which affect reflector amplitude rather than directly enhancing reflector amplitude.