bluuebunny/crossref_metadata_2025 huggingface dataset:
Forecast of an exceptionally large even‐numbered solar cycle
Authors: Schatten Kenneth H. , Sofia Sabatino
Published: February 2008

Using the "dynamo theory" method to predict solar activity, an accurate prediction was made for solar cycle 21 by Schatten, Scherrer, Svalgaard, and Wilcox [1978]. The method had been first tested with data from 8 solar cycles. Using the same dynamo technique for solar cycle 22, a value for the smoothed sunspot number of 170 ± 25 is obtained. This large sunspot number is expected to peak in 1990 ± 1 year. The F10.7 radio flux is expected to reach a smoothed value of 210 ± 25 flux units. Since this value is larger than values obtained with prediction schemes based upon "statistical" and "periodicity" methods, it provides a useful test for the current methodology, based upon the strength of the Sun's polar field near solar minimum. The predicted degree of solar activity is expected to enhance the density and temperature of the earth's thermosphere to values somewhat larger than those found in solar cycle 21. This will have an impact on the orbital lifetime of low altitude satellites.
Horizontal gravity gradient: An aid to the definition of crustal structure in North America
Authors: Sharpton V. L. , Grieve R. A. F. , Thomas M. D. , Halpenny J. F.
Published: February 2008

A map of the magnitude of the horizontal Bouguer gravity gradient over the North American continent is used to delineate lateral discontinuities in upper crustal density and/or thickness associated with such processes as suturing and rifting. The usefulness of gradient trends in mapping major structural boundaries, which are sometimes poorly exposed or completely buried, is demonstrated by examples such as the buried southward extension of the Grenville Front and buried boundaries of the Superior Province. Gradient trends also draw attention to poorly known structures, which may have major tectonic significance, and to a continent‐wide structural fabric, which may provide a record of the tectonic growth of the North American continent.
Determination of O2 (a¹Δg) and O2 (b¹Σ+g) yields in the reaction O + ClO → Cl + O2 : Implications for photochemistry in the atmosphere of Venus
Authors: Leu Ming‐Taun , Yung Yuk L.
Published: February 2008

A discharge flow apparatus with chemiluminescence detector has been used to study the reaction O + ClO → Cl + O2*, where O2* = O2(a¹Δg) or O2(b¹Σ+g). The measured quantum yields for producing O2(a¹Δg) and O2(b¹Σ+g) in the above reaction are less than 2.5 × 10−2 and equal to (4.4 ± 1.1) × 10−4, respectively. The observed O2(a¹Δg) airglow of Venus cannot be explained in the context of standard photochemistry using our experimental results and those reported in recent literature. The possibility of an alternative source of O atoms derived from SO2 photolysis in the mesosphere of Venus is suggested.
Disruption of the magnetotail current sheet observed by AMPTE/CCE
Authors: Takahashi K. , Zanetti L. J. , Lopez R. E. , McEntire R. W. , Potemra T. A. , Yumoto K.
Published: February 2008

The Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer (AMPTE/CCE), with a small inclination of 4.8° and an apogee of ∼8.8 RE, is capable of exploring the dynamical behavior of the near‐earth magnetotail current sheet during substorms. At ∼1153 UT on day 240 (August 28), 1986, the spacecraft was on the midplane of the magnetotail near midnight (∼23.4 h LT) at a radial distance of ∼8 RE, when the onset of a substorm took place. The magnetic field data for the ∼3.5‐min interval following the onset indicated a variation of the magnetic field that has not been observed by geostationary satellites or by other spacecraft flown in the near‐earth tail (r ≲ 20 RE). The variation was characterized by a large‐amplitude (from less than 10 nT to greater than 40 nT) oscillation of the total field with a period of ∼13 s and also by southward turning of the field during most cycles of the oscillation. At times the magnetic field became strongly southward, and in a few measurements the magnitude of the southward component exceeded 20 nT. The level of high‐frequency perturbations (periods shorter than ∼10 s) was also enchanced during the event. The observations may be due to the formation of an X‐type neutral line and its motion near the spacecraft.
Southern hemsiphere temperature trends: A possible greenhouse gas effect?
Authors: Karoly David J.
Published: February 2008

Experiments with atmospheric general circulation models indicate that increased concentrations of carbon dioxide in the atmosphere may lead to reduced temperatures in the lower stratosphere as well as increased temperatures in the troposphere. An index designed to identify this signal in atmospheric observations has been computed from annual radiosonde temperature data for 19 stations in the Southern Hemisphere for the period 1964‐85. This index has a trend of the same sign, consistent with the impact of increased concentrations of greenhouse gases, at all stations. This trend is significant at most of the stations.
Melt migration beneath mid‐ocean spreading centers
Authors: Morgan Jason Phipps
Published: February 2008

Mid‐ocean ridge volcanism is largely concentrated within a few kilometers of the spreading axis. Geophysical models of upwelling induced melting beneath a ridge axis predict significant melting within a ∼100 kilometer wide region beneath a ridge axis. This provides a strong constraint for testing models of melt migration beneath a spreading center since a successful melt migration mechanism must be able to focus melt from a broad region of melt production to the narrow emplacement zone at the ridge axis. Tensile dike propagation transport of melt within the mantle would move melt away from the ridge axis and thus does not satisfy this constraint. However, porous flow of melt within a viscously deforming asthenosphere is a viable possibility. Models of porous flow are constructed which consider the effects of mantle flow‐induced pressure gradients and strain‐induced anisotropic permeability on porous melt migration. In order for flow‐induced pressure gradients to shape melt migration the sub‐ridge asthenospheric viscosity must be 1021 Pa‐s, two orders of magnitude larger than currently accepted values. Mantle strain‐induced anisotropic permeability variations can explain the focussing of melt towards the ridge axis if the ratio of the directional anisotropic permeabilities is as small as 3. Furthermore, mantle strain‐induced anisotropy in rock permeability may be an important mechanism shaping melt migration within the mantle.
Airborne lidar observations of Arctic polar stratospheric clouds: Indications of two distinct growth stages
Authors: Poole Lamont R. , McCormick M. Patrick
Published: February 2008

Airborne lidar observations of Arctic polar stratospheric clouds (PSCs) during January 1984 and January 1986 show constrast suggestive of two distinct PSC growth stages delineated by the frost‐point temperature. Results obtained at temperatures 2–6K above the frost point indicate a stage of significant, but limited, particle growth such as proposed in recent models of PSC formation by co‐deposition of HNO3 and H2O vapors. Results obtained at a temperature near the frost point indicate the formation of somewhat larger crystalline particles.
First observations of summer polar mesospheric backscatter with a 224 MHz radar
Authors: Hoppe Ulf‐Peter , Hall Chris , Röttger Jürgen
Published: February 2008

Exceptionally strong echoes from the mesopause region have been observed with the EISCAT 224 MHz radar during the summer of 1987. The echoes are so strong that they cannot be explained by incoherent scatter theory but may instead be associated with neutral air turbulence. We discuss the variability of these echoes in terms of time and height distribution, and outline some characteristics of vertical velocity oscillations observed at the echo height.
Remanent magnetization of the oceanic upper mantle
Authors: Arkani‐Hamed Jafar
Published: February 2008

Skewnesses of the marine and MAGSAT magnetic anomalies of the Atlantic ocean are explained in terms of the remanent magnetization gradually acquired by the oceanic lithosphere during its cooling. Magnetizations of the lower crust and the upper mantle are about 20–50 and 10–30 percent of the magnetization of the oceanic basaltic layer 2A, respectively. The oceanic upper mantle controls the skewness of the MAGSAT anomalies, whereas the skewness of the marine anomalies arise primarily from the oceanic lower crust.
Radar observations of the onset of current driven instabilities in the topside ionosphere
Authors: Foster J. C. , del Pozo C. , Groves K. , St. Maurice J.‐P.
Published: February 2008

Millstone Hill radar spectra exhibit pronounced spectral asymmetries in the presence of field‐aligned currents in the topside ionosphere. The enhanced, often intense, returns associated with the current‐driven growth of the ion acoustic mode exhibit the characteristics of hard‐target backscatter suggesting that many “satellite echoes” observed by UHF radars at high latitudes might be caused by this mechanism. A large current density (>100 µamp/m²) is calculated for the conditions observed, consistent with that seen in intense earthward‐directed current filaments. Our observations indicate that the ion acoustic mode grows toward instability with increasing altitude. Backscatter observed from the unstable region at higher altitudes is characteristically at the ion plasma frequency consistent with the unstable growth of the acoustic mode for large ratios of electron to ion temperature.
Large impact basins and the mega‐impact origin for the crustal dichotomy on Mars
Authors: Frey Herbert , Schultz Richard A.
Published: February 2008

The origin of the fundamental crustal dichotomy on Mars remains the outstanding unsolved problem in martian geologic evolution. The hypothesis that this dichotomy is due to a single giant (mega) impact early in martian history is tested by comparing the observed number of large impact basins on Mars with the number expected from a D−2 distribution. This test is based on the assumption that the mega‐impact Borealis Basin is the largest member of such a distribution. The difference between observed and “expected” basins is the number of “missing” basins that might have been obscured by subsequent geologic events. If the Borealis Basin were the largest member of a D−2 impact population, there would be a very large number of “missing” basins on Mars: 1 larger than 5000 km, 10 larger than 2000 km and 40‐50 larger than about 1000 km diameter. The area occupied by these “missing” basins (allowing for overlap) is too large to be hidden by the younger surface units. A large population of presently unrecognized large impact basins would have to be located in the well preserved cratered highlands. By contrast, if Chryse is the largest member of a D−2 impact population, the more modest number of “missing” basins could in principle be confined to areas of Mars that have been resurfaced or reworked by subsequent geologic processes. A possible alternative to the mega‐impact hypothesis is that the crustal dichotomy is due to the cumulative effects of multiple overlapping large (but not giant) impacts.
Acid rain: Simultaneous observations of a natural marine background and its acidic sulfate aerosol precursor
Authors: Vong R. J. , Hansson H.‐C. , Covert D. S. , Charlson R. J.
Published: February 2008

Rainwater samples collected on the northwestern coast of Washington State have excess sulfate concentrations which are similar to other remote marine sites. Simultaneous sampling of submicrometer aerosol particles and rainwater in meteorologically selected marine air masses shows that the sulfuric acid component of these particles is sufficient to account for the observed rainwater sulfate via the process of nucleation scavenging based on an effective liquid water content (Leff); its small range and realistic magnitude support this conclusion. Equilibrium modeling based on aerosol sulfate and Leff predicts a rainwater pH of 5.2 compared to the measured pH of 5.1.
NRM: IRM(S) demagnetization plots; An aid to the interpretation of natural remanent magnetization
Authors: Fuller M. , Cisowski S. , Hart M. , Haston R. , Schmidtke E. , Jarrard R.
Published: February 2008

AF demagnetization of thermoremanent magnetization (TRM) and saturation isothermal remanent magnetization (IRM(s)) are used to establish diagnostic criteria for primary TRM and for secondary magnetization in igneous rocks. In applying the approach to the interpretation of natural remanent magnetization (NRM), the demagnetization of IRM(s) documents the nature of the magnetic phases in the rock, while the demagnetization of the NRM gives information about the process of magnetization. The ratio of NRM : IRM (s) measures the efficiency of the magnetization process.
Ray tracing of electrostatic waves in a hot plasma and its application to the generation of terrestrial myriametric radiation
Authors: Horne R. B.
Published: February 2008

The first results from the program HOTRAY for ray tracing electrostatic and electromagnetic waves in a hot plasma are presented. The calculations are applied to the linear mode‐conversion window theory for the generation of Terrestrial Myriametric Radiation corresponding to a specific event observed by the DE‐1 satellite. Results show that backward propagating electrostatic waves can refract in a density gradient normal to the magnetic field to become Z‐mode waves and can have access to the radio window. During propagation the waves remain minimally damped. Variations of approximately 0.01° in the initial wave normal angle ψ can result in a large difference in the transmitted wave intensities. However, if such variations do occur, waves from different locations can still access the radio window so that energy transfer to the conversion point remains efficient. Strong refraction of electrostatic waves at latitudes > 1° show that the magnetic equator is the preferred location for mode conversion to take place.
Large‐scale topography of Io: Implications for internal structure and heat transfer
Authors: Gaskell Robert W. , Synnott Stephen P. , McEwen Alfred S. , Schaber Gerald G.
Published: February 2008

New stereographic techniques were applied to Voyager 1 images to determine the shape and large‐scale topography of Io. The best‐fit triaxial figure has semiaxes of 1830.0, 1818.7 and 1815.3 kilometers with random errors of about 200 meters. Systematic navigation and optical system errors are comparable. The resulting figure is consistent with a differentiated satellite in hydrostatic equilibrium. The deviation from homogeneity could be explained by the presence of an iron core with a radius of about 800 km. Most elevations over areas larger than ≈500 km diameter deviate from the triaxial figure by no more than ±1 km; we suggest that many of these broad topographic swells and basins may be due to isostatic responses to thermal changes in the lithosphere ‐ asthenosphere system. In the simplest picture, increasing the heat flow converts the basal lithosphere into lower‐density asthenosphere, resulting in isostatic uplift. Lithospheric thicknesses ranging from 5 to 100 km may result in elevation variations of up to 1 km. If the large‐scale topography is positively correlated with heat flow, then the global pattern of basins and swells suggests tidal dissipation in a molten or partially molten asthenosphere rather than in the mantle. Areas higher than 1 km may consist of low‐density crustal materials. Media Regio, the largest such region, is centered near the equator at longitude 70°.
Pressure dependence of the elastic wave velocities for Mg2GeO4 spinel to 3 Gpa
Authors: Rigden S. M. , Jackson I. , Niesler H. , Ringwood A. E. , Liebermann R. C.
Published: February 2008

New measurements of compressional and shear wave velocities on polycrystalline Mg2GeO4 spinel (γ) to 3 GPa have yielded the first reported data on pressure derivatives of bulk and shear moduli for this material. The measured values (dK/dP = 4.1 and dG/dP = 1.2) are compared with pressure derivatives for MgAl2O4 spinel. Although dK/dP is comparable for the two materials, dG/dP is much higher for the germanate. Pressure derivatives of elastic properties of mantle spinels cannot be simply predicted from the data on the two analogue materials presently available although single crystal measurements of elastic moduli of magnesium germanate and magnesium silicate spinels at atmospheric pressure by Weidner and co‐workers lend support to the use of magnesium germanate as an elastic analogue for silicate spinels of the Earth's mantle.
Gravity‐driven deformation of the crust on Venus
Authors: Smrekar Suzanne , Phillips Roger J.
Published: February 2008

Intense horizontal deformation features are observed on the surface of Venus despite the apparent absence of terrestrial‐style plate tectonics. High surface temperature, low erosion rate, and regions of elevated terrain suggest that gravity spreading may be responsible for some of these features. Gravity spreading on the Earth is known to cause extensive deformation in certain thin‐skinned tectonic regions, where the uppermost layers become detached along a decollement. While the high pore pressures and soft sedimentary rocks frequently observed along decollements on the Earth are not plausible for Venus, temperature induced regions of ductile deformation may exist. Simple viscous models of gravity spreading above a ductile region of the crust are developed to examine the effects of rheology, thermal gradient, surface slope and crustal thickness on deformation. For a reasonable range of parameters, the models show that surface‐slope‐driven ductile deformation at relatively shallow depths in the crust is possible and may be capable of detaching the uppermost rigid portion of the crust, resulting in horizontal translation.
Local magnetic reconnection caused by vortices in the flow field
Authors: Liu Z. X. , Hu Y. D.
Published: February 2008

We suggest that local magnetic field reconnection can be caused by vortices in the flow field. The vortex‐induced reconnection may be an important mechanism of local reconnection in space plasma. MHD simulation is used to investigate the nonlinear evolution of vortex reconnection. We discuss the basic properties of this reconnection model and its application to the magnetosphere.
Lidar observations of Arctic polar stratospheric clouds, 1988: Signature of small, solid particles above the frost point
Authors: Poole L. R. , Osborn M. T. , Hunt W. H.
Published: February 2008

Polar stratospheric clouds (PSC's) in the 21‐24 km altitude range were observed north of Greenland (82‐84°N, 0‐25°W) on January 29, 1988, using an airborne dual‐polarization, 0.532‐µm wavelength lidar. Synoptic analyses at the 30‐mb level (≈22 km) show local temperatures of 191‐193K, which are well above the estimated frost point temperature of 185K and indicate the PSC's were likely of the binary HNO3‐H2O (Type I) class. Peak scattering ratios of 1.1‐1.2 were measured in the PSC layer, compared to values near 1.05 for the ambient (non‐PSC) aerosol over the same altitude range. Profiles of the depolarization ratio distinctly show the PSC layer, but maximum values are 0.06‐0.07, only slightly greater than the value (0.04) measured in cloud‐free regions and well below the values typically found in cirrus clouds (0.2‐0.5). This signature suggests that the Type I PSC's observed during the January flight were composed of small, solid particles having radii on the order of the laser wavelength (≈0.5 µm).
222Rn concentrations in deep formation waters and the geohydrology of the Cajon Pass Borehole
Authors: Hammond D. E. , Leslie B. W. , Ku T. ‐L. , Torgersen T.
Published: February 2008

Measurements of 222Rn, 226Ra, and 238U in formation waters derived from granitic rocks surrounding the Cajon Pass borehole indicate concentrations of about 700, 1, and 0.01 dpm/1, respectively. The radon profile in the borehole indicates that inputs are localized and that several fracture zones must contribute significant amounts of inflow. Radon concentrations in fracture fluids indicate a minimum fracture width of 0.3 µm, and this width may be combined with the measured permeability to show that fracture porosity does not exceed 1.5 × 10−3. It is likely that the calculated fracture width is too small because incongruent weathering enriches fracture walls in 238U and 226Ra relative to the bulk rock. However, radon concentrations are lower than those in formation waters from other crystalline rocks, suggesting that the wall enrichments here are less pronounced and that fractures have experienced relatively limited fluid flow.
An estimate of the long‐term non‐dipole field from marine magnetic anomalies
Authors: Schneider David A.
Published: February 2008

Application of the skewness method to 14 marine magnetic anomaly profiles across the Galapagos ridge provides a precise estimate of the equatorial contribution of the long‐term non‐dipole field. The average inclination anomaly (observed remanent inclination minus dipole inclination) so determined from the central anomaly over the Galapagos ridge is −3.3° ± 0.9°. This result agrees closely with estimates of the non‐dipole field contribution at equatorial latitudes as predicted from prior paleomagnetic studies.
The structure and dynamics of polar mesosphere summer echoes observed with the EISCAT 224 MHz radar
Authors: Röttger Jürgen , La Hoz Cesar , Kelley Michael C. , Hoppe Ulf‐Peter , Hall Chris
Published: February 2008

The EISCAT 224 MHz radar was operated in a high spectral resolution mode to study polar mesosphere summer echoes. Intermittent and localized scattering regions of less than 1 km thickness were observed. Gravity waves were present, which were occasionally steepened. Turbulent velocity fluctuations were not obviously related to certain phases of the observed short‐period gravity waves. We explain the large signal amplitudes of these polar mesosphere summer echoes to result from backscatter due to electron density variations, which extend to scales shorter than the scales of neutral turbulence.
In‐situ detection of OH in the lower stratosphere with a balloon borne high repetition rate laser system
Authors: Stimpfle R. M. , Anderson J. G.
Published: February 2008

Midday stratospheric OH density measurements have been carried out within the altitude interval of 31 to 24 km using the laser induced fluorescence technique deployed on a balloon‐borne gondola launched from Palestine, Texas on July 15, 1987. Laser output at 282 nm is produced with a pulsed, 17 kHz repetition rate, copper vapor laser pumped tunable dye laser. The OH mixing ratio ranged from 16±5 ppt at 31 km to 4±3 ppt in the 27 to 24 km region. Simultaneous ozone and water vapor measurements were also obtained with separate instruments.
Solar cycle dependence of the radial gradient of cosmic ray intensity
Authors: Van Allen James A.
Published: February 2008

Observation of the interplanetary intensity of cosmic rays (Ep > 80 MeV) by Pioneers 10 and 11 now spans a sixteen‐year time period 1972–1988 and heliocentric radial distances, r10 and r11, out to 43.7 AU for Pioneer 10 and 25.8 AU for Pioneer 11. Solar modulation continues to be present at the current distances of both spacecraft. The radial gradient of intensity is measured continuously over the slowly varying, outward moving radial segment Δr = r10 − r11. The 50‐day mean values of the gradient G vary systematically and cyclically in phase with solar activity as measured by sunspot number, with a maximum value of about 2.1 percent (AU)−1 at sunspot maximum and a minimum value of about 1.2 percent (AU)−1 at sunspot minimum. Thus, the apparent scale size of the heliospheric modulation region as measured by 1/G is about 48 AU at solar max and about 83 AU at solar min—a result that is the inverse of the conjectural inference of Randall and Van Allen [1986] using most of the same body of data but a different analytical point of view. There is persuasive evidence that G is independent of radial distance over the range 2.5 to 34 AU in the mid‐point of the segment Δr. No dependence of G on heliographic latitude is evident, but this result does not lend itself to a quantitative statement.
Small scale irregularities in comet Halley's plasma mantle: An attempt at self‐consistent analysis of plasma and magnetic field data
Authors: Vaisberg O. L. , Russell C. T. , Luhmann J. G. , Schwingenschuh K.
Published: February 2008

VEGA‐1 measurements of the plasma density and magnetic field in the coma of Comet Halley show characteristic signatures over a significant portion of the outbound pass. It is found that the assumption that there is a balance between the thermal and magnetic pressures in these features can be used to obtain estimates of the plasma temperature as a function of distance from the nucleus. These estimates indicate that the ions cool from ∼1.5 × 106 °K at 105 km to 2 × 105 °K at 5 × 104 km. The technique used here represents a novel approach whereby temperature measurements can be made in situations where only plasma density and magnetic field data are available.
A technique for determining in‐cloud formation of SO4
Authors: Husain Liaquat
Published: February 2008

A technique based on SO4/Se ratio is developed to determine in‐cloud formation of SO4 from the oxidation of SO2. Whereas nucleation scavenging is the only significant source of Se in cloud water, both nucleation scavenging and dissolution of SO2 with subsequent oxidation are significant sources of SO4 in cloud water. Based on the assumption that no fractionation occurs between Se and SO4 aerosols during nucleation scavenging, it is shown that a simultaneous measurement of SO4 and Se in cloud water and ambient air permits a direct determination of in‐cloud SO4 formation. The data to support this assumption are provided. The results from two cloud events during July and August, 1987 show that in‐cloud formation ranged between 8 and 28% in ten hourly samples.
Derivation of return stroke parameters from the electric and magnetic field derivatives
Authors: Cooray Vernon
Published: February 2008

In this paper we discuss the possible errors, caused by the presence of near field components and propagation effects, in the return stroke parameters derived from the transmission line model by using the electric and magnetic field derivatives measured at different distances over ground.
Iron atoms and metallic species in the Earth's upper atmosphere
Authors: Granier C. , Jegou J. P. , Megie G.
Published: February 2008

Resonant lidar detection of iron atoms have been performed at the Observatoire de Haute Provence (France) during 4 nights in november 1986 and in april 1987. The average iron atoms abundance is 3.6 × 109 cm−2 in november, and 2.6 × 109− cm−2 in april. Iron atoms density profiles are compared to the atomic sodium ones, obtained simultaneously by lidar and indicating an average sodium abundance of 4 × 109 cm−2. The relative abundance of the sum of the atomic and ionic forms is compared for several metallic species with their abundance ratios in the incoming meteorites. Finally, similar comparisons using lidar and mass spectrometer data are made for the ratio of the atomic and the ionic forms in the atmosphere.
Seasonal variations of volcanic eruption frequencies
Authors: Stothers Richard B.
Published: February 2008

Do volcanic eruptions have a tendency to occur more frequently in the months of May and June? Some past evidence suggests that they do. The present study, based on the new eruption catalogue of Simkin et al., investigates the monthly statistics of the largest eruptions, grouped according to explosive magnitude, geographical latitude, and year. At the 2σ level, no month‐to‐month variations in eruption frequency are found to be statistically significant. Examination of previously published month‐to‐month variations suggests that they, too, are not statistically significant. It is concluded that volcanism, at least averaged over large portions of the globe, is probably not periodic on a seasonal or annual time scale.
Observing oceanic mesoscale eddies from Geosat altimetry: Preliminary results
Authors: Fu Lee‐Lueng , Zlotnicki Victor
Published: February 2008

Mesoscale eddies constitute the most energetic component of the variability of ocean currents. Sea level variations measured by the Geosat radar altimeter are used to study the spatial and temporal scales of the eddy motion. An attempt is also made to map the temporal evolution of the eddy field in the region of the Agulhas Current south of Africa, where the eddy motions are among the strongest in the world. The results demonstrate that Geosat has provided an unprecedented opportunity to map from space the temporal evolution of sea level variability associated with the energetic eddies in the ocean.
Northern hemisphere temperature trends: A possible greenhouse gas effect?
Authors: Karoly David J.
Published: February 2008

Radiosonde temperature data from 147 stations in the Northern Hemisphere for the period 1964–85 have been used to investigate recent temperature trends in the troposphere and lower stratosphere. Experiments with atmospheric general circulation models indicate that increased concentrations of greenhouse gases in the atmosphere will lead to reduced temperatures in the stratosphere as well as increased temperatures in the troposphere. An index designed to identify this signal has been computed from the station data. This index has positive trend at most of the stations, consistent with the greenhouse effect. Over the hemisphere, the signal is statistically significant. However, opposing temperature variations in the troposphere and stratosphere are associated with many other forcing mechanisms and the results cannot be used to identify a specific mechanism.
Biomass burning in Amazonia: Seasonal effects on atmospheric O3 and CO
Authors: Kirchhoff V. W. J. H. , Setzer A. W. , Pereira M. C.
Published: February 2008

The practice of shifting agriculture and the need for the colonization of new land areas determine each year considerable amounts of biomass burnings in the Brazilian Amazon region. This paper describes new results on the effects of these burnings on the composition of the lower atmosphere. Simultaneous measurements of O3 and CO are described at two sites: one within the burning region of central Brazil, Cuiabá (16°S, 56°W), and another one away from it, Natal (6°S, 35°W). The data obtained so far covers the 1987, 1988 dry season periods, when the burning intensity is maximum (July, August, September), and the wet season period of 1988, when practically no burnings occur. Both sites show minimum concentrations of O3 and CO in the wet season, with monthly averages in March of about 12 and 140 ppbv (parts per billion by volume) for Cuiabá, and about 10 and 80 ppbv, for Natal. While the seasonal increase at Natal is of the order of a factor of 2, the seasonal increase at Cuiabá for 1987 was about a factor of 4, and a factor of 6 for 1988. For the month of September 1987, O3 and CO had concentrations of 23 and 110 ppbv for Natal, whereas at Cuiabá these concentrations were 41 and 470 ppbv. The larger concentrations observed in September correlate well with the larger number of fires detected by the infrared radiometer on the NOAA‐9 satellite.
Slow twists of solar magnetic flux tubes and the polar magnetic field of the Sun
Authors: Hollweg Joseph V. , Lee Martin A.
Published: February 2008

The solar wind model of Weber and Davis (1967) is generalized to compute the heliospheric magnetic field resulting from solar rotation or a steady axisymmetric twist including a geometrical expansion which is more rapid than spherical. The calculated increase in the ratio of the toroidal to poloidal field components with heliocentric radial distance r clarifies an expression derived recently by Jokipii and Kota (1989). Magnetic field components transverse to r do not in general grow to dominate the radial component at large r. Our analysis also yields expressions for the Poynting flux associated with the steady twists. These results are regarded as indicative of the Poynting flux associated with very low frequency Alfven waves, and it is shown how the Poynting flux and the spatial evolution of the wave amplitude differ from the usual WKB result. It is found that the low‐frequency Poynting flux at the base of a coronal hole can be about 50 percent larger than the WKB flux inferred from spectral observations of coronal motions (e.g., Hassler et al., 1988).
Transatlantic Earth Potential Variations During the March 1989 Magnetic Storms
Authors: Medford L. V. , Lanzerotti L. J. , Kraus J. S. , Maclennan C. G.
Published: February 2008

Measurements of the cable power supply voltage at the North American end of the fiber optic transatlantic telecommunications cable TAT‐8 during the March 1989 magnetic storm has provided a measure of the large scale changes in the total Earth potential across the Atlantic during the storm interval. East‐west potential changes as large as 700 volts (∼0.12 volts/km) peak‐to‐peak were observed, with many smaller amplitude variations also seen. The largest variations in Earth potential occurred during an extended interval of a very intense eastward electrojet as measured by a magnetometer at the North American terminus of the cable. The eastward electrojet current probably exceeded 106 amps. The design of the TAT‐8 cable power feed equipment is sufficiently conservative that even such unusually large Earth potentials as those measured during this storm were not a threat to the integrity of the communications system.
Interferometric observations of a single stroke cloud‐to‐ground flash
Authors: Rhodes C. , Krehbiel P. R.
Published: February 2008

VHF radiation source location measurements using an interferometric technique are presented for a single stroke cloud‐to‐ground lightning discharge. The discharge began with 100 ms of preliminary activity during which several horizontal streamers developed inside the cloud, one of which culminated in the development of a negative leader to ground and a return stroke. The return stroke was followed by a 10 ms quiet period in the radiation and by a single, fast ‘k‐type‧ event which appeared to transport negative charge horizontally into the region of initial breakdown, completing the flash.
The structure of rotational discontinuities
Authors: Neugebauer M.
Published: February 2008

This study examines the structures of a set of rotational discontinuities detected in the solar wind by the ISEE‐3 spacecraft. It is found that the complexity of the structure increases as the angle θ between the propagation vector k and the magnetic field decreases. For rotational discontinuities that propagate at a large angle to the field with an ion (left‐hand) sense of rotation, the magnetic hodograms tend to be flattened, in agreement with prior numerical simulations. When θ is large, angular "overshoots" are often observed at one or both ends of the discontinuity. When the propagation is nearly parallel to the field (i.e., when θ is small), many different types of structure are seen, ranging from straight lines, to S‐shaped curves, to complex, disorganized shapes.
Atomic emission in the ultraviolet nightglow
Authors: Sharp W. E. , Siskind D. E.
Published: February 2008

An observation of the ultraviolet nightglow between 2670 Å and 3040 Å was conducted over White Sands Missile Range on October 22, 1984, at 0020 hours LST during the Orionids meteor shower. A 1/4‐meter uv spectrometer operating at 3.5 Å resolution viewed the Earth's limb at tangent heights between 90 km and 110 km for 120 seconds. By inverting the observed limb intensities, a total zenith intensity of 1.4 kR is inferred for the Herzberg I system. Excess emission above the Herzberg I (7,3) band at 2852 Å is identified as the Mg I resonance line. The intensity ratio of the Herzberg I band system to the 2972 Å line from O(¹S) was less than that predicted from the accepted O(¹S) branching ratio and acceptable ratios of Herzberg I to 5577Å emissions. Arguments supporting the identification of the Herzberg III band system are also advanced.
A midlatitude interhemispheric model of the O+(2P) airglow emission at 7320 Å
Authors: Torr Marsha R. , Torr D. G. , Richards P. G.
Published: February 2008

The results are reported of the first interhemispheric model of the 7320 Å airglow covering mid‐ and low latitudes, at all longitudes. A comprehensive model of the ionosphere and thermosphere is used to compute volume emission rates as a function of altitude, latitude, longitude, and local time. Selected results are shown here to illustrate the computational capability. In particular we discuss the diurnal and seasonal variability and interhemispheric coupling of conjugate photoelectrons. The model is particularly well suited for airglow studies, and provides a valuable tool for the comparison, interpretation, and planning of spectroscopic observations made from orbiting platforms for all significant thermospheric emissions.
Modelling of thermal anomalies in the NW border of the Valencia Trough by groundwater convection
Authors: Fernández Manel , Torné Montserrat , Zeyen Hermann
Published: February 2008

A 2D numerical model study of a regional scale thermal anomaly along the north Spanish border of the Mediterranean Sea indicates strong lateral offshore heat transport due to groundwater circulation. Although the area is situated at the western side of the Valencia Trough rift zone, the amplitude and wavelength of this coupled negative‐positive anomaly cannot be explained by conductive heat flow. A strong hydraulic gradient onshore and a thick layer of permeable Mesozoic limestones should permit lateral advection of pore water about 30 km offshore where discharge creates anomalous temperature gradients. This result underscores the importance of deep groundwater flow even in the interpretation of regional scale thermal anomalies in rifting zones.
Ion reflection and dissipation at quasi‐parallel collisionless shocks
Authors: Scholer Manfred , Terasawa Toshio
Published: February 2008

Large scale one‐dimensional hybrid simulations have been performed of a quasi‐parallel (ΘBn = 20°) high Mach number collisionless shock. It is found that backstreaming reflected ions, i.e., upstream ions with velocities exceeding the shock ram velocity, originate from the outer part (v≳ 1.7vth) of the velocity space of the incident distribution. The backstreaming ions produce very low‐frequency magnetosonic waves which propagate upstream with about 1.3VA (Alfvén speed). As the wave crests convect toward the shock, they steepen up and the shock reforms itself. During shock reformation a large part of the incident ions are reflected. This, in turn, slows the incident ions down. The slowed down incident particle distribution and the reflected particle distribution merge and constitute the new thermalized downstream distribution. In the interval of a relatively stationary shock low‐frequency whistler waves stand at the shock front. During these time intervals the whistler waves are probably responsible for dissipation by nonadiabatic compression of the incident ions. The whistler waves are destroyed by the incoming large amplitude wave crest and reemerge at the new shock front. The reapparance seems to be due to the nonlinear steepening of the incoming wave crest at the upstream side.
Decay of correlations and the collisionless conductivity in the geomagnetic tail
Authors: Horton W. , Tajima T.
Published: February 2008

The collisionless electrical conductivity is calculated for the geomagnetic tail from the stochastic orbits in the plasma sheet. The new conductivity formula is important for the stochastic heating of the plasma sheet and modifies the Galeev‐Zelenyi formulas for the collisionless reconnection growth rate for geomagnetic substorms.
First GPS baseline results from the north Andes
Authors: Kellogg James N. , Freymueller Jeffrey T. , Dixon Timothy H. , Neilan Ruth E. , Clemente Ropain U. , Sergio M. Camargo , Benjamin Fernandez Ch. , Stowell James L. , Salazai Anibal , Jaime Mora V. , Espin Luis , Perdue Vernon , Leos Leonard
Published: February 2008

The CASA UNO GPS (Global Positioning System) experiment (January‐February 1988) has provided the first epoch baseline measurements for the study of plate motions and crustal deformation in and around the North Andes. Two dimensional horizontal baseline repeatabilities are as good as 5 parts in 108 for short baselines (100–1000 km), and better than 3 parts in 108 for long baselines (>1000 km). Vertical repeatabilities are typically 4–6 cm, with a weak dependence on baseline length. The expected rate of plate convergence across the Colombia Trench is 6–8 cm/yr, which should be detectable by the repeat experiment planned for 1991. Expected deformation rates within the North Andes are of the order of 1 cm/yr, which may be detectable with the 1991 experiment.
Are earthquakes an example of deterministic chaos?
Authors: Huang Jie , Turcotte Donald L.
Published: February 2008

We use a simple mass‐spring model to systematically examine the dynamical behavior introduced by fault zone heterogeneities. The model consists of two sliding blocks coupled to each other and to a constant velocity driver by elastic springs. The state of this system can be characterized by the positions of the two blocks relative to the driver. A simple static/dynamic friction law is used. When the system is symmetric, we observe cyclic behavior. For an asymmetric system where the fractional forces for the two blocks are not equal, the solutions exhibit deterministic chaos. Chaotic windows occur repeatedly between regions of limit cycles on bifurcation diagrams. Our model behavior is similar to that of the one‐dimensional logistic map. In many examples of deterministic chaos, chaotic behavior of a low order system implies chaos in similar higher order systems. Thus, our results provide substantial evidence that earthquakes are an example of deterministic chaos.
Airborne lidar observations in the wintertime Arctic stratosphere: Ozone
Authors: Browell E. V. , Butler C. F. , Ismail S. , Fenn M. A. , Kooi S. A. , Carter A. F. , Tuck A. F. , Toon O. B. , Proffitt M. H. , Loewenstein M. , Schoeberl M. R. , Isaksen I. , Braathen G.
Published: February 2008

Large‐scale distributions of ozone (O3) were measured with an airborne lidar system as part of the 1989 Airborne Arctic Stratospheric Expedition (AASE). Measurements of O3 distributions were obtained between January 6 and February 15, 1989, on 15 long‐range flights into the polar vortex from the Sola Air Station, Norway. The observed O3 distribution was found to clearly indicate the edge of the polar vortex and to be an effective tracer of dynamical processes in the lower stratosphere. On the last two flights of the expedition, large regions with reduced O3 levels were observed by the lidar inside the polar vortex. Ozone had decreased by as much as 17% in the center of these areas, and using the in situ measurements made on the ER‐2 aircraft, it was concluded that this decline was due to chemical O3 destruction.
Radiative effects of polar stratospheric clouds
Authors: Kinne S. , Toon O. B.
Published: February 2008

Radiative transfer calculations are performed for polar stratospheric clouds (PSCs) using newly acquired PSC properties and polar atmospheric data. PSC radiative effects depend strongly on upwelling thermal radiation and vary from infrared heating over warm polar surfaces, such as oceans, to cooling over cold surfaces, such as the Antarctic plateau. Heating and cooling rates of nitric acid PSCs are smaller than ±0.1K/day. Rates for optically thicker ice PSCs vary from 1.0 to −0.2K/day, those for orographically forced ice PSCs even from 3.0 to −0.5K/day. Frequently observed optically thick cirrus decks near the tropopause provide a very cold radiative surface. These clouds not oily act to prevent heating and enhance cooling in ice PSCs to −0.5K/day and orographic ice PSCs to‐day, but such cirrus cloud decks also cool the entire stratosphere by up to −0.5K/day over warm surfaces, even in the absence of PSCs.
Measurements of stratospheric gaseous nitric acid in the winter Arctic vortex using a novel rocket‐borne mass spectrometric method
Authors: Schlager H. , Arnold F.
Published: February 2008

The altitude distribution of stratospheric gaseous nitric acid was measured on 30 January, 1989 at Esrange (68°N, 20°E; Northern Sweden) in a particularly cold stratosphere (lowest temperature 190 K) using a novel rocket‐borne ACIMS (Active Chemical Ionisation Spectrometry)‐ instrument. Within the coldest layer (18.5–22.6 km) gaseous nitric acid was found to be strongly depleted. Probably this depletion was caused by local nitric acid condensation leading to NAT (Nitric Acid Trihydrate) aerosols, which were still present in the same layer, and/or HNO3‐removal from that layer by sedimentation of HNO3‐containing aerosols. Threshold temperatures for nitric acid condensation of about 195–193 K (18.5 km) and 193 K (22.6 km) can be inferred from the present data being roughly consistent with theoretical model predictions.
Calculations of ozone destruction during the 1988/89 Arctic winter
Authors: McKenna D. S. , Jones R. L. , Poole L. R. , Solomon S. , Fahey D. W. , Kelly K. K. , Proffitt M. H. , Brune W. H. , Loewenstein M. , Chan K. R.
Published: February 2008

Calculations of ozone depletion during the 1988/89 Arctic winter using a Lagrangian coupled photochemical‐microphysical model are presented in this paper. Abundances of ClO in excess of 1 ppbv were observed at the end of the Airborne Arctic Stratospheric Expedition (AASE) on February 10, 1989. These are shown to be consistent with the removal of more than 90% of the reactive nitrogen and the conversion of more than 80% of reservoir chlorine to active forms. This chemical state implies that ozone losses of more than 20 ppbv per day can be sustained in heavily denitrified air throughout much of February according to current photochemistry. As much as 74% of the loss is calculated to be due to ClO dimer photolysis. Following the warming of the vortex in mid February 1989, ozone loss through ClO dimer photolysis becomes less effective as the rate of thermal decomposition of the ClO dimer increases. Thus, model results suggest that thermal decomposition of the dimer plays an important role in limiting ozone loss in the Arctic spring.
Loss of ozone in the Arctic vortex for the winter of 1989
Authors: Salawitch Ross J. , McElroy Michael B. , Yatteau John H. , Wofsy Steven C. , Schoeberl Mark R. , Lait Leslie R. , Newman Paul A. , Chan K. Roland , Loewenstein Max , Podolske James R. , Strahan Susan E. , Proffitt Michael H.
Published: February 2008

Measurements of ClO (Brune et al., 1990) acquired during the Airborne Arctic Stratospheric Expedition are used to infer concentrations of reactive chlorine (ClO+2 × Cl2O2). Observed fields of potential temperature and potential vorticity are used to extrapolate in situ data to larger regions of the vortex. Calculated values of the loss rate of O3, based on estimates of reactive chlorine and measurements of BrO (Toohey et al., 1990), suggest that the loss of O3 was about 12% for levels of the atmosphere with potential temperatures between 440 and 470 K over the 39 day duration of the ER‐2 flights into the polar vortex. Calculated loss rates agree with observed rates of removal of O3, although significant uncertainties exist for each.
Particle acceleration during substorm growth and onset
Authors: Williams D. J. , Mitchell D. G. , Huang C. Y. , Frank L. A. , Russell C. T.
Published: February 2008

We present ISEE‐1 observations of ion and electron energization made at ∼11 RE during a substorm event occurring on 2 April 1978. An analysis of the dominant cross‐tail current systems in this event (Mitchell et al., 1990) has allowed us to uniquely associate particle energization processes with the development and/or disruption of the cross‐tail currents. We find that significant ion acceleration occurs as the ions participate in serpentine cross‐tail motion (Speiser, 1965), establishing the dominant plasma sheet current system just prior to onset. As this current disrupts, the magnetic field configuration dipolarizes and further ion energization and the bulk of the electron energization occurs. During dipolarization energization is due primarily to the inductive electric field, including betatron and Fermi acceleration processes.