bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal variation of CO2 and nutrients in the high‐latitude surface oceans: A comparative study
Authors: Takahashi Taro , Olafsson Jon , Goddard John G. , Chipman David W. , Sutherland S. C.
Published: February 2008

Seasonal data for pCO2 and the concentrations of CO2 and nutrients in high‐latitude surface oceans obtained by the Lamont‐Doherty CO2 group and Marine Research Institute, Reykjavik, are presented and analyzed. The seasonal progression and relationships between these properties are described, and their inter‐ocean variation is compared. Spring phytoplankton blooms in the surface water of the North Atlantic Ocean and Iceland Sea caused a precipitous reduction of surface water pCO2 and the concentrations of CO2 and nutrients within two weeks, and proceeded until the nutrient salts were exhausted. This type of seasonal behavior is limited to the high‐latitude (north of approximately 40°N) North Atlantic Ocean and adjoining seas. In contrast, seasonal changes in CO2 and nutrients were more gradual in the North Pacific and the nutrients were only partially consumed in the surface waters of the subarctic North Pacific Ocean and Southern Ocean. The magnitude of seasonal changes in nutrient concentrations in the North Pacific and Southern Oceans was similar to that observed in the North Atlantic and adjoining seas. In the subpolar and polar waters of the North and South Atlantic and North Pacific Oceans, pCO2 and the concentrations Of CO2 and nutrients were much higher during winter than summer. During winter, the high latitude areas of the North Atlantic, North Pacific, and Weddell Sea were sources for atmospheric CO2; during summer, they became CO2 sinks. This is attributed to the upwelling of deep waters rich in CO2 and nutrients during winter, and the intense photosynthesis occurring in strongly stratified upper layers during summer. On the other hand, subtropical waters were a CO2 source in summer and a sink in winter. Since these waters were depleted of nutrients and could only sustain low levels of primary production, the seasonal variation of pCO2 in subtropical waters and the CO2 sink/source condition were governed primarily by temperature. An intense CO2 sink zone was found along the confluence of the subtropical and subpolar waters (or the subtropical convergence). Its formation is attributed to the combined effects of cooling in subtropical waters and photosynthetic drawdown of CO2 in subpolar waters.
An empirical static model of low energy ring current ions
Authors: Collin H. L. , Quinn J. M. , Cladis J. B.
Published: February 2008

The empirical model consists of a set of average equatorial energy and pitch‐angle distributions of fluxes of H+ and O+ in the energy range 110 eV to 35 keV for a number of local time and L ranges. It was constructed from data acquired by the Lockheed IMS‐LO ion mass spectrometer on CRRES (apogee 6.3 RE, inclination 18°) which sampled a substantial portion of the ring current region. Equatorial distributions were constructed by mapping the ion data adiabatically from the satellite location to the equatorial plane, which was taken to be the minimum B surface. There the data were binned by their energy and equatorial pitch angle and sorted into ranges of L and local time. Equatorial distributions from many orbits were accumulated and averaged to construct the average equatorial distributions. This static model represents the average magnetosphere during the CRRES mission, August 1990 through October 1991, regardless of magnetic activity. In the absense of parallel electric fields and wave‐particle interactions, the model may be used to estimate the ion distributions at non‐equatorial magnetic latitudes by adiabatic mapping.
A method of comparison of two close batches data: Application to analysis of fog formation causes
Authors: Boreux J. J. , Guiot J.
Published: February 2008

Given suitable conditions of air temperature and humidity, the density of a fog and its microphysical properties depend mainly on the availability of cloud condensation nuclei (CCN) and their nature. Fogs become particularly dense near certain industrial plants because of high concentration of hygroscopic combustion particles in the air. Their role in dense fog formation is estimated by comparing the local climates and CCN concentrations at two similar sites, the first being more subject to air pollution and dense fogs than the second. Orthogonal regression is applied to three meteorological variables (air temperature, relative humidity, wind speed) and CCN concentration. As we compare very close variables, bootstrap provides precise confidence intervals independent of Gaussian assumptions. Two sites are compared: they are located in the Meuse valley (Belgium) at a distance of about 15 km. We found that the local climate of the polluted site is not only colder and wetter but also richer in CCN that the control site. These results suggest interactions of natural and anthropogenic causes in dense fog formation at industrial site. This method is useful in various domains of geophysics when correlated time series have to be compared.
Laboratory simulations of PSC particle formation
Authors: Marti James , Mauersberger Konrad
Published: February 2008

Recent observations of type I polar stratospheric cloud particles (PSC I) reveal some discrepancies with data on nitric acid trihydrate (NAT) obtained in laboratory studies. To better understand the in situ growth of PSC I particles, this experiment condensed mixtures of water and nitric acid vapor at temperatures and pressures which approximated those of the polar stratosphere more closely than in prior studies. Mono‐, di‐, and trihydrates of nitric acid were observed in solids condensed from vapor mixtures relatively rich in HNO3. Solids formed under conditions that approached stratospheric contained significantly less HNO3 than the 25 mol% expected of NAT; the composition appeared to slowly change toward that of NAT over about ten hours. Solids with low HNO3 content showed HNO3 vapor pressures that were often highly supersaturated with respect to NAT. These results may help explain recent arctic PSC observations as those of relatively young clouds whose condensed materials have not yet reached equilibrium.
Toroidal‐poloidal partitioning of plate motions since 120 MA
Authors: Lithgow‐Bertelloni C. , Richards Mark A. , Ricard Yanick , O'Connell Richard J. , Engebretson Dave C.
Published: February 2008

Changes in plate motions and plate configurations during the Cenozoic and Mesozoic have been investigated extensively, but most geodynamical models have concentrated on present‐day plate motions. We have investigated the recent evolution of plate tectonics by examining the history of toroidal‐poloidal partitioning of plate motions. Taking into account estimated errors, our results suggest a significant increase in the ratio of toroidal to poloidal motions postdating the Hawaiian‐Emperor (H‐E) bend at 43 Ma, corresponding to an overall decrease in global plate motions. These changes may reflect greater mantle plume activity in the Mesozoic, but a causal mechanism is not obvious. In general, observed Cenozoic and Mesozoic plate motions do not appear to be random, which implies that they are correlated. We also find perhaps three significant changes in net rotation of the lithosphere with respect to hotspots since 120 Ma.
Comparison of stratospheric warming following Agung, El Chichon and Pinatubo volcanic eruptions
Authors: Angell J. K.
Published: February 2008

Based on a 63‐station radiosonde network and using 9‐season‐average temperatures to minimize the influence of the quasi‐biennial oscillation, the low‐stratospheric (16–20 km) warming following Agung and El Chichon was greatest in the equatorial zone and least in polar zones. The warming was not symmetric with respect to the equator, however, with greater warming south than north of the equator. The warming following El Chichon was slightly greater than following Agung in all climatic zones except the south polar zone. Results for Pinatubo are preliminary because of the recency of the eruption, but in north extratropics and tropics the warming following this eruption is indicated to be comparable to the warming following Agung and El Chichon. However, in south temperate and polar zones the warming is considerably greater following Pinatubo, perhaps reflecting a contribution from the eruption of Cerro Hudson in Chile. Globally, therefore, the low‐stratospheric warming following Pinatubo is greater than following Agung or El Chichon. Based on a 10‐station tropical radiosonde network with data to greater heights, the warming following El Chichon exceeded the warming following Agung to a height of at least 31 km, the difference in warming increasing with height. The warming following Pinatubo is similar to that following Agung to a height of 24 km, but thereafter is indicated to become less, an unexpected result to be reexamined as more data become available.
Non‐similar frequency‐magnitude distribution for M < 1 Seismicity
Authors: Trifu Cezar‐Ioan , Urbancic Theodore I. , Young R. Paul
Published: February 2008

A series of 1503 induced seismic events ranging in magnitude from −2 to 1 as computed based on a locally calibrated seismic moment scale were located within a well‐defined volume at depth. The seismicity analysis was carried out over 2 months and included events recorded before, during, and following the after‐shock period of a mN 2.6 rockburst. A non‐similar pattern was clearly apparent for both cumulative and non‐cumulative frequency‐magnitude distributions, showing a relative enhancement of seismicity between magnitudes −0.5 and 0. This supports the existence of non‐similar scaling at these magnitudes. The time variation of the b‐value, as computed for a limited self‐similar magnitude domain (−1.1 to −0.4), did not appear to be related to the rockburst. Instead, it is suggested that the rockburst perturbed the local stress field and consequently the distribution of the very small events. No correlations were found between b and space clustering.
Pick‐up ions at Pluto
Authors: Kecskeméty K. , Cravens T. E.
Published: February 2008

Methane molecules escaping from Pluto's atmosphere are ionized, and the resulting ions are picked up by the solar wind. The mass loading associated with this ion pick‐up can produce a comet‐like interaction of the solar wind with Pluto. Heavy ion gyroradii are as large as a half million km in the weak interplanetary magnetic field that exists at 30 AU, which is about an order of magnitude larger than the size of the “interaction region.” We have calculated velocity space distributions of pick‐up ions using numerically determined ion trajectories. The predicted pick‐up ion fluxes are high enough to be detectable by standard charged particle detectors as far upstream of Pluto as 106 km.
Fluctuations in column ozone during the total solar eclipse of July 11, 1991
Authors: Mims Forrest M. , Mims Eric R.
Published: February 2008

A statistical analysis of total column ozone observations during the total eclipse of July 11, 1991, disclosed a series of fluctuations in the ozonosphere following totality. The principle fluctuation, which began 700 seconds after third contact, has an unsmoothed, peak‐to‐peak amplitude of 5 m‐atm‐cm. This amounts to 1.7% of the total ozone column 2000 seconds after third contact. This fluctuation was preceded by one and followed by two fluctuations with reduced amplitude.
Model of magnetosheath plasma in the magnetosphere: Cusp and mantle particles at low‐altitudes
Authors: Onsager T. G. , Kletzing C. A. , Austin J. B. , MacKiernan H.
Published: February 2008

A model of plasma transport in the open magnetic field region of the dayside magnetosphere has been used to investigate the source regions and the distribution of solar wind plasma in the magnetospheric cusp and mantle. This model includes the variation in the magnetosheath properties as the plasma accelerates away from the subsolar point, the variation in the transport of magnetosheath plasma across the magnetopause as the orientation of the magnetic field line evolves following reconnection, and the transport of the magnetosheath plasma within the magnetosphere. Our model results are compared with low‐altitude spacecraft data from a crossing of the cusp and mantle. We find qualitative and quantitative agreement between the model results and the data. This agreement suggests that the zeroth‐order processes included in the model are sufficient to reproduce the commonly observed particle distributions in the low‐altitude cusp and mantle regions.
Near‐axis heat flow measurements on the northern Juan De Fuca Ridge: Implications for fluid circulation in oceanic crust
Authors: Johnson H. Paul , Becker Keir , Von Herzen Richard
Published: February 2008

Present models of the cooling of oceanic crust suggest that convection of hydrothermal fluid is a major component of the process. In axial regions, abundant faults and open fissures are associated with the venting of high temperature hydrothermal fluid. In older crust, where the insulating sediment cover is thick, previous studies have shown that basement topography is the dominant forcing factor for within‐crust fluid circulation. In the intermediate region, where young crust is lightly sedimented, heat flow data are difficult to obtain with traditional techniques. To determine whether topography or permeability is the dominant process controlling fluid circulation in the near‐axis region, we conducted a profile of heat flow measurements using the submersible ALVIN, on the Endeavour Segment of the Juan de Fuca Ridge. Our data indicate that topographic forcing is responsible for the long wavelength variations, with high heat flow at the ridge summits, and low values in the inter‐ridge valleys. The locations of the extreme values of heat flow taken within the context of subsurface faulting are consistent with a model where a ridge‐valley topographic pair comprises a single circulation cell. This model predicts that the source area for the high temperature axial vents may be in the flanking inter‐ridge valleys.
Lava flow topographic measurements for radar data interpretation
Authors: Campbell Bruce A. , Garvin James B.
Published: February 2008

Surface topography is of great importance in radar backscattering, but the quantitative interpretation of data collected in the field is still a difficult problem. We present topographic profiles at 25‐cm and 5‐cm horizontal resolution for three sites along a lava flow on Kilauea Volcano, and use these data to illustrate techniques for surface roughness analysis. Height and slope distributions and the height autocorrelation function are evaluated as a function of varying lowpass filter wavelength for the 25‐cm data. Rms slopes are found to increase rapidly with decreasing topographic scale and are typically much higher than those found by modeling of Magellan altimeter data for Venus. A more robust description of the surface roughness appears to be the ratio of rms height to surface height correlation length. For all three sites this parameter falls within the range of values typically found from model fits to Magellan altimeter waveforms. The 5‐cm profile data are used to estimate the effect of small‐scale roughness on quasi‐specular scattering.
The accuracy of traveltime perturbations from isotropic to anisotropic medium
Authors: de Araújo Simões‐Filho Ivan
Published: February 2008

The accuracy of perturbation methods for traveltime computations in anisotropic media is investigated as a function of the medium deviation from isotropy. The traveltime perturbation equations are briefly reviewed and a method for the choice of the isotropic background is proposed. The perturbed traveltimes are then compared with results of exact ray tracing for four different anisotropic models with orthorhombic symmetry and increasing anisotropy. The accuracy of the perturbed traveltimes is very good for media with small perturbations and decreases rapidly for perturbations larger than 15%.
Stability of the Io plasma torus/atmosphere interaction
Authors: Johnson R. E. , McGrath Melissa
Published: February 2008

The stability of the Io plasma torus‐atmosphere interaction is examined. A simple plasma deflection model describes how transients in the plasma flux and the content of the atmosphere affect the ionospheric conductance, limiting the plasma bombardment and, hence, the supply of atmospheric species to the torus. The supply of the torus is seen to be determined by the thermal structure of the plasma, namely, the amount of low energy plasma producing atmospheric erosion vs. that which produces ionization, so that the torus supply rate is not simply proportional to the torus ion density.
The non‐linear response of the magnetosphere: 30 October 1978
Authors: Price C. P. , Prichard D.
Published: February 2008

Previous efforts to find evidence of deterministic nonlinear dynamics in the global geomagnetic system have treated the geomagnetic system as autonomous. However, the geomagnetic system is strongly driven by the stochastic solar wind. We consider the response of the magnetosphere, as given by the AE index, for one day when the IMF had a nearly constant southward value. Using both a series of non‐linear statistics and non‐linear prediction of the response to the input signal υBs, we find that there is some evidence for deterministic non‐linear response of the Earth's magnetosphere on that day.
High‐time resolution measurements of upstream magnetic field and plasma conditions during flux transfer events at the Earth's dayside magnetopause
Authors: Jacob Jamey D. , Cattell Cynthia
Published: February 2008

We present preliminary results of a study of upstream magnetic field and plasma conditions measured by IRM during flux transfer events observed at the Earth's magnetopause by CCE. This study was designed to determine the importance of various upstream factors in the formation of bipolar magnetic field signatures called flux transfer events (FTEs). Six FTE encounters were examined. Three cases were when the two satellites were on similar magnetic field lines. Preliminary investigation showed that fluctuations occurred in the Bz component of the interplanetary magnetic field (IMF) resulting in a southward field preceding the FTE in all three of these cases. In two of these cases, the changes were characterized by a distinct rotation from a strong southward to a strong northward field. There were also accompanying changes in the dynamic and thermal pressure in the solar wind immediately before the FTE was encountered. Examination of the 3d plasma distributions showed that these pulses were due to the addition of energetic upstreaming foreshock particles, There were no consistent changes in either Bz or the plasma pressure at IRM for the three events when the satellites were not connected by the IMF.
Paleomagnetic record over the past 35,000 years of a sediment core from off Shikoku, southwest Japan
Authors: Ohno Masao , Hamano Yozo , Murayama Masafumi , Matsumoto Eiji , Iwakura Hirokazu , Nakamura Toshio , Taira Asahiko
Published: February 2008

The paleomagnetism of a sediment core (KT89‐18, P4), recovered from the sea floor off Southwest Japan, was studied to investigate geomagnetic field variation over the past 35,000 years. Alternating fields demagnetization revealed that the remanent magnetization of the unconsolidated sediments was stable and not affected by any secondary overprints. 14C datings were made on 21 horizons, using a Tandetron accelerator mass spectrometer, providing a detailed time scale to the core. The inclination record agrees with that from Lake Biwa [Kawai et al., 1975], and supports the existence of the geomagnetic excursions which had been found in the Lake Biwa core. The ages of the excursions are estimated to be during ca. 32 ky.B.P. ∼ ca. 28 ky.B.P. and ca. 26 ky.B.P. ∼ ca. 24 ky.B.P.
Upper limits to the nightside ionosphere of Mars
Authors: Fox J. L. , Brannon J. F. , Porter H. S.
Published: February 2008

The nightside ionosphere of Mars could be produced by electron precipitation or by plasma transport from the dayside, by analogy to the Venus, but few measurements are available. We report here model calculations of upper limits to the nightside ion densities on Mars that would be produced by both mechanisms. For the auroral model, we have adopted the downward traveling portions of the electron spectra measured by the HARP instrument on the Soviet Phobos spacecraft in the Martian plasma sheet and in the magnetotail lobes. For the plasma transport case, we have imposed on a model of the nightside thermosphere, downward fluxes of O+, C+, N+, NO+ and O+2 that are near the maximum upward fluxes that can be sustained by the dayside ionosphere. The computed electron density peaks are in the range (1.3–1.9) × 104 cm−3 at altitudes of 159 to 179 km. The major ion for all the models is O+2, but significant differences in the composition of the minor ions are found for the ionospheres produced by auroral precipitation and by plasma transport. The calculations reported here provide a guide to the data that should be acquired during a future aeronomy mission to Mars, in order to determine the sources of the nightside ionosphere.
An empirical model relating the auroral geomagnetic activity to the interplanetary magnetic field
Authors: Vassiliadis D. , Sharma A. S. , Papadopoulos K.
Published: February 2008

A damped linear oscillator (LRC circuit) predicts a significant amount of the AL index variations when it is driven by the IMF's BSouth component. The model parameters are determined from fitting the AL time series and show a small, apparently nonsystematic variation with the activity level. Following an isolated external disturbance the LRC model's response peaks at 15 min ‐ 0.5 h and decays after 1–2 more hours. The time scales and the correlation between observed AL and the circuit output (60–80%) are in good agreement with earlier linear prediction filter results. The results support the modeling of the global magnetospheric behavior with dynamical systems of a few degrees of freedom.
Estimate of the tsunami source of the 1992 Nicaraguan Earthquake from tsunami data
Authors: Imamura Fumihiko , Shuto Nobuo , Ide Satoshi , Yoshida Yasuhiro , Abe Katsuyuki
Published: February 2008

The Nicaraguan earthquake of September 2, 1992 excited large tsunamis which caused significant damage along the Nicaraguan coasts. Some of the inhabitants felt only minimal shock before the tsunami arrived, indicating that excitation of short‐period seismic waves was very small. Numerical simulation with the initial tsunami source estimated by the seismic data is carried out to study the characteristics of the tsunami source by comparing the calculated data with the measured data along the Nicaraguan coast. Finding of the comparison shows that the dislocation of the fault estimated from the measured data is 5.6 to 10.0 times larger than that from seismic data. The tsunami source area, which is 200km in length × 100km in width, is used to explain the distribution of measured tsunami heights along the coast and the wave period as shown in the tide record at Corinto. The effect of rise time on tsunami excitation indicates a slow process, which corresponds with the seismic waves. This event falls under the tsunami earthquake category to produces anomalously large tsunamis relative to earthquake magnitude.
Geologic methane as a source for post‐glacial CO2 increases: The Hydrocarbon Pump Hypothesis
Authors: Loehle Craig
Published: February 2008

This paper evaluates the hypothesis that historical CO2 levels could have been governed by releases of geologic methane. Methane clathrates and natural gas could have contributed to CO2 increases at the ends of the last two glacial periods. Computations indicate that oxidation of CH4 to CO2 could have rapidly provided enough CO2 to cause historical CO2 changes. A simple dynamic model, the hydrocarbon pump, for methane as the source term for changes in CO2 over the glacial cycles matches several features of the historical record. If methane clathrates were the source of CO2, then CO2 at the interglacial transitions should be depleted in 14C because of the low 14C levels in C from this source. Evidence is presented that this is the case. 13C data are also evaluated. Overall, CH4 is a credible source for CO2, but definitive conclusions await further data.
Rapid source mechanism determination of large (Mw≥5) earthquakes in the western United States
Authors: Ritsema Jeroen , Lay Thorne
Published: February 2008

Inversion of complete long‐period ground motions is used for rapid determination of source mechanisms of Mw ≥ 5 earthquakes in the western United States. The first few minutes of ground motions on local and regional distance waveforms are inverted for point‐source centroid moment tensors. Waveforms recorded at regional distances (300–1500 km) can be adequately modeled at periods longer than 50 s using the laterally homogeneous PREM model [Dziewonski and Anderson, 1981]; at closer distances (<300 km) waves with periods as short as 35 s can be analyzed using PREM. Best double‐couple focal mechanisms for 18 recent large western U.S. earthquakes compare very well with those obtained by other methods. Our procedure, interfaced with automated data retrieval and source location methods, is a viable tool for reliable determination of seismic moment and fault mechanism within 30 minutes after an earthquake.
Eastward‐moving 2–4 day waves in the winter Antarctic mesosphere
Authors: Fraser G. J. , Hernandez G. , Smith R. W.
Published: February 2008

The structure of short period (2–4 days) planetary waves in the Antarctic mesosphere has been determined from ground based wind measurements. At the South Pole observations are made with a Fabry‐Perot spectrometer (FPS) to determine the meridional wind component of OH tracer molecules. Azimuth scanning of the FPS shows that the observed modes are of zonal wavenumber one, as expected at the rotation pole in the neutral atmosphere. At Scott Base (78°S) observations are made with an MF spaced‐antenna mode mesospheric wind‐profiler radar. The vertical structure of the waves at altitudes of 80–100 km shows a phase variation corresponding to a vertical wavelength of more than 100 km. The observed periods support previous interpretations, based on satellite observations and barotropic instability models, of modes associated with the ‘4‐day’ wave.
Importance of anelasticity in the interpretation of seismic tomography
Authors: Karato Shun‐ichiro
Published: February 2008

Temperature dependence of seismic wave velocities comes both from anharmonicity and anelasticity. The contribution from anelasticity is shown to be important in the Earth's mantle particularly for shear waves. In the low Q (Qµ∼100) regions in the upper mantle, the correction due to anelasticity will roughly double the temperature derivatives due to anharmonicity alone. The correction for anelasticity will also be important in the deep mantle where Q is larger, if temperature derivatives due to anharmonicity will decrease significantly with pressure. These results imply that the temperature anomalies associated with low velocity anomalies in the mantle will be significantly smaller than previously considered on the basis of anharmonic effect alone and that the amplitude of velocity anomalies will be significantly larger for shear waves than for compressional waves.
Decrease of stratospheric NO2 at 44°N caused by Pinatubo volcanic aerosols
Authors: Koike M. , Kondo Y. , Matthews W. A. , Johnston P. V. , Yamazaki K.
Published: February 2008

Following the arrival of Pinatubo volcanic aerosols, significant decreases in NO2 column amount were observed at Moshiri, Japan (44°N, 142°E). A slight decrease started in September 1991 and reductions of more than 20 % have been seen since January 1992. The reduction was largest in April 1992 when NO2 amounts were about 50 % lower than observed in April 1991. Between May 1992 and January 1993, the reduction has been getting smaller, however until October 1992, about 35 to 20 % lower NO2 amounts were observed. At southern mid‐latitudes, a clear decrease in NO2 started in August 1991 [Johnston et al., 1992]. Aerosol data obtained from lidar measurements and the SAGE II satellite instrument show that the observed major reductions in NO2 in the both hemispheres generally correspond to the arrival of volcanic aerosols above 25 km.
Multi‐scale roughness spectra of Mount St. Helens debris flows
Authors: Austin Richard T. , England Anthony W.
Published: February 2008

A roughness spectrum allows surface structure to be interpreted as a sum of sinusoidal components with differing wavelengths. Knowledge of the roughness spectrum gives insight into the mechanisms responsible for electromagnetic scattering at a given wavelength. Measured spectra from 10‐year‐old primary debris flow surfaces at Mount St. Helens conform to a power‐law spectral model, suggesting that these surfaces are scaling over the measured range of spatial frequencies. Measured spectra from water‐deposited surfaces deviate from this model.
An estimate of the anthropogenic contribution to atmospheric methyl bromide
Authors: Reeves C. E. , Penkett S. A.
Published: February 2008

A global, 2‐D, atmospheric chemistry model of latitude versus altitude, employing a prescribed hydroxyl field, is used to estimate the anthropogenic contribution to atmospheric CH3Br. An even spatial distribution is applied to natural emissions, whilst an anthropogenic source is assumed for the northern hemispheric mid‐latitudes. Model calculations, constrained by observed concentrations of CH3Br and its interhemispheric ratio, lead to the conclusion that the total emission source of CH3Br has a strength of 75–105 ktonnes yr−1, with a 33–74% anthropogenic contribution of 25–80 ktonnes yr−1. The best estimate is a total strength of 91 ktonnes yr−1, with a 54% anthropogenic contribution of 49 ktonnes yr−1. The sensitivity of these results are discussed with respect to OH concentration, transport, seasonality, altitude, and the representative nature of the latitudinal spread of data and spatial distribution of emissions.
Constraining proposed combinations of ice history and Earth rheology using VLBI determined baseline length rates in North America
Authors: Mitrovica J. X. , Davis J. L. , Shapiro I. I.
Published: February 2008

We predict the present‐day rates of change of the lengths of 19 North American baselines due to the glacial isostatic adjustment process. Contrary to previously published research, we find that the three‐dimensional motion of each of the sites defining a baseline, rather than only the radial motions of these sites, needs to be considered to obtain an accurate estimate of the rate of change of the baseline length. Predictions are generated using a suite of Earth models and late Pleistocene ice histories; these include specific combinations of the two which have been proposed in the literature as satisfying a variety of rebound related geophysical observations from the North American region. A number of these published models are shown to predict rates which differ significantly from the VLBI observations.
Molecular dynamics simulations of periclase crystallization
Authors: Lee W. ‐J. , Kubicki J. D.
Published: February 2008

Molecular dynamics simulations of MgO based on interionic potentials derived from modified electron‐gas calculations have been used to model crystallization of periclase from a supercooled liquid. The phase transition between supercooled liquid and crystal is signaled by a large decrease in the enthalpy of the system, a decrease in calculated pressure, and a [4]Mg → [6]Mg coordination change. Nucleation is nearly instantaneous above a critical density corresponding to the transformation to octahedral coordination in the supercooled liquid. Crystal growth enhances diffusion during the simulation as ions in the liquid move in a direction consistent with the crystal orientation at the liquid‐solid interface. Ions do not detach from the crystal surface once they are bonded to the growing crystal, suggesting that growth is in the diffusion‐limited regime.
Seasonal cycle of sea surface temperature and mixed layer heat budget in the tropical Pacific Ocean
Authors: Chang Ping
Published: February 2008

Climatological data derived from the Comprehensive Ocean‐Atmosphere Data Set (COADS) combined with the climatological temperature fields from XBT observations in the tropical Pacific Ocean are used to assess the importance of various oceanic and atmospheric processes in the seasonal variation of the mixed layer temperature. The analyses indicate that in most areas of the extra‐equatorial oceans, where the mixed layer is deep and oceanic mixing is weak, the seasonal change in SSTs can be attributed to the net local heating received by the mixed layer. However, in other parts of the equatorial oceans, oceanic processes are found to play an important role in determining the seasonal fluctuations of the SST. In particular, in the eastern equatorial Pacific Ocean where the mixed layer is shallow, the thermal‐inertia of the upper ocean is reduced significantly by the intense vertical mixing so that the response of the SST is nearly in phase with the surface heating. Using the Kraus‐Turner type of entrainment parameterization, the analyses further demonstrate that the vertical heat flux induced by the mean entrainment velocity contributes significantly to the mixed layer heat budget.
Atmospheric methane, record from a Greenland Ice Core over the last 1000 year
Authors: Blunier T. , Chappellaz J. A. , Schwander J. , Barnola J. ‐M. , Desperts T. , Stauffer B. , Raynaud D.
Published: February 2008

The atmospheric methane concentration in ancient times can be reconstructed by analysing air entrapped in bubbles of polar ice sheets. We present results from an ice core from Central Greenland (Eurocore) covering the last 1000 years. We observe variations of about 70 ppbv around the mean pre‐industrial level, which is confirmed at about 700 ppbv on a global average. According to our data, the beginning of the anthropogenic methane increase can be set between 1750 and 1800. Changes in the oxidizing capacity of the atmosphere may contribute significantly to the pre‐industrial methane concentration variations, but changes in methane emissions probably play a dominant role. Since methane release depends on a host of influences it is difficult to specify clearly the reasons for these emission changes. Methane concentrations correlate only partially with proxy‐data of climatic factors which influence the wetland release (the main source in pre‐industrial times). A good correlation between our data and a population record from China suggests that man may already have influenced the CH4‐cycle significantly before industrialisation.
A mechanism for the multiple brightenings of dayside poleward‐moving auroral forms
Authors: Fasel G. J. , Lee L. C. , Smith R. W.
Published: February 2008

Magnetic reconnection plays an important role in the magnetosphere‐ionosphere coupling and may lead to the formation of the dayside auroras. Observations of the dayside auroras may provide clues to the reconnection process at the magnetopause. Recently Fasel et al. [1992] observed poleward‐moving dayside auroral forms that rebrighten during their lifetimes. Lee et. al. [1993] examined the topology of magnetic flux ropes formed by the patchy multiple X‐line reconnection (PMXR), in which a magnetic flux tube reconnects with other flux tubes at multiple sites of limited extent. This paper develops the connection between the evolution of the magnetic flux ropes and the multiple brightenings of poleward‐moving dayside auroral forms.
The return of the anomalous cosmic rays to 1 AU in 1992
Authors: Mewaldt R. A. , Cummings A. C. , Cummings J. R. , Stone E. C. , Klecker B. , Hovestadt D. , Scholer M. , Mason G. M. , Mazur J. E. , Hamilton D. C. , von Rosenvinge T. T. , Blake J. B.
Published: February 2008

New observations of low energy (∼1 to 200 MeV/nuc) cosmic rays measured by three newly launched experiments on SAMPEX during 1992 and 1993 show the strong presence of anomalous cosmic ray (ACR) nitrogen and oxygen, well before the approaching solar minimum. When compared with ACR temporal variations over the past two solar cycles we find that the 1992–1993 fluxes are ∼5 to 10 times their level at corresponding neutron monitor counting rates in 1969–1970 and 1985.
First observation of the upper stratospheric vertical wind velocities using the Jicamarca VHF radar
Authors: Maekawa Yasuyuki , Fukao Shoichiro , Yamamoto Mamoru , Yamanaka Manabu D. , Tsuda Toshitaka , Kato Susumu , Woodman Ronald F.
Published: February 2008

The Jicamarca VHF radar (50 MHz) has detected atmospheric echoes in the so‐called ”gap region” from 30 to 60 km heights. These echoes are, for the first time, discriminated from clutter echoes, using both co‐polarized (co‐pol) and cross‐polarized (x‐pol) arrays to monitor the clutter component which may enter the antenna sidelobes. The atmospheric scatterings in this region are shown to be composed of refractivity layers with thickness as of 1–2 km as in other middle atmospheric height ranges, suggesting that these scatterings are caused by thin turbulent layers. The height profile of inferred vertical wind velocities indicates a wavy structure. The wave amplitude, as a whole, increases with height, suggesting the activity of upward‐propagating gravity waves.
Disappearance of the heliospheric sector structure at Ulysses
Authors: Smith E. J. , Neugebauer M. , Balogh A. , Bame S. J. , Erdös G. , Forsyth R. J. , Goldstein B. E. , Phillips J. L. , Tsurutani B. T.
Published: February 2008

In May, 1993, the heliospheric current sheet (HCS) ceased to be seen by the Ulysses spacecraft at a heliocentric latitude of ∼30° S and distance of 4.7 AU. The disappearance of the HCS coincided with the solar wind speed remaining >560 km/s and with the disappearance of one of four interaction regions previously seen on each solar rotation. The heliographic latitude of the disappearance of the HCS at Ulysses was 11° equatorward of the latitude of the magnetic neutral sheet computed at the source surface at 2.5 solar radii, and it occurred a half year earlier than predicted on the basis of the persistence of the time profile of the neutral sheet tilt from one solar cycle to the next.
Simulation of the prompt energization and transport of radiation belt particles during the March 24, 1991 SSC
Authors: Li Xinlin , Roth I. , Temerin M. , Wygant J. R. , Hudson M. K. , Blake J. B.
Published: February 2008

We model the rapid (∼ 1 min) formation of a new electron radiation belt at L ≃ 2.5 that resulted from the Storm Sudden Commencement (SSC) of March 24, 1991 as observed by the CRRES satellite. Guided by the observed electric and magnetic fields, we represent the time‐dependent magnetospheric electric field during the SSC by an asymmetric bipolar pulse that is associated with the compression and relaxation of the Earth's magnetic field. We follow the electrons using a relativistic guiding center code. The test‐particle simulations show that electrons with energies of a few MeV at L > 6 were energized up to 40 MeV and transported to L ≃ 2.5 during a fraction of their drift period. The energization process conserves the first adiabatic invariant and is enhanced due to resonance of the electron drift motion with the time‐varying electric field. Our simulation results, with an initial W−8 energy flux spectra, reproduce the observed electron drift echoes and show that the interplanetary shock impacted the magnetosphere between 1500 and 1800 MLT.
Scaling law of volcanic explosion earthquake
Authors: Nishimura Takeshi , Hamaguchi Hiroyuki
Published: February 2008

The aim of the present study is to clarify a scaling law for volcanic explosion earthquakes excited by a counter force of eruption. Based on the data of explosion earthquakes at three volcanoes, we derived the following results: The peak amplitude of the single force is proportional to the square of the pulse width of source time function. The initial pressure stored in a shallow region beneath a volcano before eruption is 1 MPa with a perturbation of one order. The kinetic energy of explosion earthquake is proportional to the cube of crater radius. The scaling law of the explosion earthquake is quite similar to that of the earthquake caused by a faulting. It is possible to predict the strength of explosion earthquake by measuring the crater radius beforehand.
First paleomagnetism of eocene rocks from Gargano: Widespread overprint or non rotation?
Authors: Speranza F. , Kissel C.
Published: February 2008

A paleomagnetic study was carried out in the Gargano Peninsula on 37 sites (500 cores) of mainly Eocene age. Eight normal polarity directions can be interpreted either in terms of remagnetization, or of a small post Middle‐Eocene counterclockwise rotation of Adriatic foreland with respect to stable Africa. The reverse directions seem to result from a widespread remagnetization.
Observations of upper atmospheric optical flashes recorded from an aircraft
Authors: Sentman D. D. , Wescott E. M.
Published: February 2008

Short‐duration upper atmospheric optical flashes were recorded on the night of 8 July, 1993 (9 July UT) from the NASA DC‐8 Airborne Laboratory flying over the American Midwest. All‐sky video images from an intensified silicon intensified target (ISIT) camera revealed 19 upper atmospheric flashes occurring over a period of ∼100 min. The flashes were similar in appearance to previously reported ground and shuttle‐based video observations. Detailed analysis of 12 of the events yielded these parameters: (1) duration ≤17 ms; (2) brightness 10–50 kR, roughly that of bright aurorae; (3) terminal heights 30–100 km, with a mean of ∼60 km; (4) horizontal extent 10–50 km; (5) emission volume >1000 km³. The relative frequency of the optical flashes was (6) 1:200–1:400 compared to negative cloud‐to‐ground discharges and 1:20–1:40 compared to positive cloud‐to‐ground discharges.
An extension of the geomagnetic activity index series aa for two solar cycles (1844–1868)
Authors: Nevanlinna Heikki , Kataja Eero
Published: February 2008

This paper deals with an extension of Mayaud's aa‐index series (from 1868 to the present) for two solar cycles 1844–1868. The magnetic data sources are hourly declination readings at the Helsinki magnetic‐meteorological observatory carried out in 1844–1880. The new data set provides a reliable and homogeneous series of declination for computations of equivalent aa–indices. For the time period 1868–1880 the linear correlation coefficient between the two indices was 0.96 on the monthly basis. Behaviour of the geomagnetic activity during the course of the sunspot cycles 9–12 revealed similar periodicities and linear dependencies (Ohl's and Feynman's relationships) as later activity data analysis has shown.
The Pioneer Venus Orbiter entry phase
Authors: Strangeway R. J.
Published: February 2008

In October, 1992 the Pioneer Venus Orbiter entered the atmosphere of Venus, ending nearly 14 years of observations at Venus. Prior to the entry into the atmosphere and subsequent loss of the spacecraft careful management of spacecraft resources had allowed the acquisition of much low altitude data over the nightside of the planet. The long duration of the Pioneer Venus mission has enabled us to study the ionosphere and atmosphere of Venus under different levels of solar activity.
Interplanetary transport of solar electrons and protons: Effect of dissipative processes in the magnetic field power spectrum
Authors: Achatz U. , Dröge W. , Schlickeiser R. , Wibberenz G.
Published: February 2008

Quasi‐linear theory describing charged particle transport in interplanetary space within the framework of a slab turbulence picture was for a long time confronted with the problem that the theoretically predicted mean free path for scattering at magnetic field fluctuations was too small when compared with the corresponding parameter derived from fits to observed intensity and anisotropy profiles of solar energetic particles. The theory up to now has neglected the dispersiveness of some of the scattering plasma waves and the effects resulting from the finite temperature of the plasma through which the particles propagate. We have therefore attempted to give a more realistic model of an observed interplanetary turbulence spectrum. The most simple picture we find requires the dissipation range to be constituted by parallel dispersive whistler, electron and ion cyclotron waves in a warm plasma (β ≈ 1). The dispersion relation of heavily thermally affected ion cyclotron waves needed in this model is calculated for the first time. The model is fitted to the turbulence spectrum measured on June 7, 1980, by ISEE 3 (ICE). The derived model parameters are used in a quasi‐linear calculation of both proton and electron mean free paths. As a first step resonance broadening due to wave damping is neglected. The results are compared with typical empirical proton mean free paths and with electron mean free paths obtained from fits to electron intensity and anisotropy profiles observed simultaneously by the same satellite. In both cases the theoretical values seem to be systematically larger than the empirical ones. Thus scattering enhancements by nonlinear or thermal resonance broadening or oblique waves now bear the hope to remove the discrepancy between theory and observation.
Modeling the magnetic effects of field‐aligned currents
Authors: Donovan E. F.
Published: February 2008

In this paper, I present a newly developed model of the magnetic effects of field‐aligned currents. The magnetic field of a large‐scale field‐aligned current system is obtained by summing the magnetic fields of a large number of finite length cylindrical current elements. The resulting magnetic field is valid inside of, near and far away from the model field‐aligned currents, both near the ionosphere and in the magnetosphere. The modeling technique allows for the closure of the field‐aligned currents along any specified path. In order to investigate the effects of field‐aligned currents on the nightside magnetospheric magnetic field and on mapping between the night‐side magnetosphere and ionosphere, I add the effects of region I and II field‐aligned currents to an empirical magnetic field model. Using this model, I demonstrate the following three things: (1) reasonable amounts of field‐aligned current can cause the ionospheric footprint of a point at geosynchronous orbit to shift in local time by one hour or more; (2) depending on how they are closed, field‐aligned currents can cause Bz in the equatorial plane, near midnight, either to increase or to decrease; (3) CPS field lines can cross the equatorial plane 10 RE or more further from the noon‐midnight meridian than they would if field‐aligned current effects were not included, a result that also depends on how the currents are closed.