bluuebunny/crossref_metadata_2025 huggingface dataset:
Coronal dimmings and energetic CMEs in April‐May 1998
Authors: Thompson B. J. , Cliver E. W. , Nitta N. , Delannée C. , Delaboudinière J. ‐P.
Published: September 2002

We have analyzed the coronal dimmings for seven fast (> 600 km/s) coronal mass ejections (CMEs) occurring between 23 April and 9 May which were associated with flares from NOAA active region (AR) 8210. Each of these CMEs had at least one group of interplanetary radio bursts associated with them. These dimming regions were identified by their strong depletion in coronal EUV emission within a half hour of the estimated time of CME lift‐off. They included areas which were as dark as quiescent coronal holes as well as other regions with weaker brightness depletions. While the location of the active region and the associated flare did not correspond well with the coronagraph observations, we found that the extended dimming areas in these events generally mapped out the apparent “footprint” of the CME as observed by white‐light coronagraph. We briefly discuss the implications of these results on models of CME topology.
Diffraction model of ionospheric irregularity‐induced heater‐wave pattern detected on the WIND satellite
Authors: Guzdar P. N. , Gondarenko N. A. , Papadopoulos K. , Milikh G. M. , Sharma A. S. , Rodriguez P. , Tokarev Yu. V. , Belov Yu. I. , Ossakow S. L.
Published: September 2002

High frequency (HF) radiation from the HAARP and SURA ionospheric heaters transmitted through the underdense ionosphere and received by the WIND satellite show the presence of strong spatial structure in the radiation pattern. A simple model based on the combination of ionospheric irregularities and interference effects has been developed to account for the observations. The analysis demonstrates the utility of satellite receptions as probes of ionospheric irregularities created or enhanced by powerful HF radio waves.
Triggering of whistler mode emissions by the band‐limited impulse (BLI) Associated with amplified Vlf signals from Siple Station, Antarctica
Authors: Helliwell Robert A.
Published: September 2002

At termination of an amplified and saturated (Bsat) Vlf pulse from Siple Station, Antarctica, a band‐limited (50–500 Hz range) impulse (BLI) is generated which in turn triggers a narrowband emission, of about the same amplitude, that starts at about 50–150 Hz above the frequency of Bsat, called the positive frequency offset (PFO). The BLI creates the PFO by reducing the parallel velocities of existing phase‐bunched cyclotron resonant electrons that form the source currents (J⟂) of the stimulated radiation. The PFO is proportional to the magnetic field intensity BBLI of the BLI. Since BBLI ≈ Bsat the PFO then becomes a measure of the saturated field Bsat. An example for L = 4 and a pitch angle of 60°, gives Bsat ≅ 5pT, in good agreement with previous estimates of Bsat.
Mass‐dependent effects in ion conic production: The role of parallel electric fields
Authors: Lund E. J. , Möbius E. , Ergun R. E. , Carlson C. W.
Published: September 2002

Previous observational studies indicate that the energies of different ion species in ion conics produced by broad‐band extremely low frequency (BBELF) waves are nearly equal. In contrast, theoretical studies predict a definite preferential acceleration for heavy ions over lighter ions. We show that this discrepancy can be resolved if a downward parallel electric field is present in the heating region: for a sufficiently strong electric field ions of different masses acquire approximately the same energy in escaping the trapping region.
SuperDARN observations of medium‐scale gravity wave pairs generated by Joule heating in the auroral zone
Authors: Sofko George J. , Huang Chao‐Song
Published: September 2002

It is known that Joule heating caused by currents associated with enhanced electric fields in the auroral ionosphere can generate gravity waves. Some modeling studies found that each short‐lived (∼10 min) electric field enhancement in the ionosphere leads to the generation of a single gravity wave pulse. Observational evidence of such single wave pulses has been reported in the ground‐scatter echoes seen by the SuperDARN HF radars. In this paper, we present new SuperDARN observations which show that, under certain conditions, each electric field enhancement can generate a pair of gravity waves. On December 2, 1998, the IMF Bz had a perturbation with a period of ∼100 min and caused oscillations in the ionospheric electric field at the same period. Each positive or negative half‐cycle of the oscillating electric field gave rise to one Joule heating enhancement which, in turn, generated a pair of gravity waves (two wave pulses). Six successive gravity wave pairs were observed. We suggest that the reason for two gravity wave pulses was that the Joule heating events in the present case were of longer duration than those in the previous events. We also show that the periodic velocities seen in the far‐range ionospheric echoes are due to the direct auroral electric field modulation and not to indirect modulation caused by the equatorward‐moving gravity waves.
A novel on‐line method for single station prediction and forecasting of the ionospheric critical frequency foF2 1 hour ahead
Authors: Bilge Ayşe H. , Tulunay Yurdanur
Published: September 2002

The unpredictable variability of the ionospheric F region greatly limits the efficiency of communications, radar and navigation systems which employ high frequency (HF) radiowaves. The objective of this work is to forecast the ionospheric critical frequency values (foF2) one hour in advance. For this a novel method has been developed for 1‐hour ahead forecasting of the critical frequency of the F2 layer (foF2) based on applying feedback on predicted monthly median values of foF2 for each hour. The basic model for the prediction of the monthly medians consists of a parabolic dependency on R12 superimposed by a trigonometric expansion in terms of the harmonics of yearly variation, linearly modulated by R12. The monthly medians for each hour are predicted by applying the basic model over a sliding data window.
Electron holes as a common feature of double‐layer‐Driven plasma waves
Authors: Singh Nagendra
Published: September 2002

Using a Vlasov code for simulating fully nonlinear behavior of a plasma driven by an applied potential drop, it is shown that fast solitary potential pulses in the form of electron holes are a common feature of the high potential side of a strong double layer. Temporal and spatial features of the electron holes seen in the simulations are compared against the measurements from FAST. The evolution of the electron beam accelerated by a double layer and that of the plasma on its high potential side generate the suitable conditions for nearly continuously creating fast moving electron holes.
Detached vortices in equivalent ionospheric currents in the winter dayside ionosphere
Authors: Benkevich Leonid , Lyatsky Wladislaw
Published: September 2002

The high‐latitude ionosphere is not homogeneous, especially for winter conditions. In the winter dayside high‐latitude ionosphere the terminator often appears equatorward of the cusp region where sources of geomagnetic disturbances are thought to be located. In these cases, when the cusp region appears in darkness, secondary field‐aligned currents arise on the terminator because of the redistribution of ionospheric currents in the conjugate summer sunlit ionosphere where the conductivity is significantly higher. This work presents results of calculations using a numeric model that was elaborated for the study of the potential and 3D currents in two hemispheres with different ionospheric conductivities. The interhemispheric field‐aligned currents are shown to arise near the terminator position, leading to the formation of vortices in equivalent ionospheric currents, which can be detached from sources of the electric potential and lie several degrees equatorward of the potential sources.
Monitoring solar activity on the far side of the sun from sky reflected Lyman α radiation
Authors: Bertaux Jean‐Loup , Quemerais Eric , Lallement Rosine , Lamassoure Elisabeth , Schmidt Walter , Kyrölä Erkki
Published: September 2002

Solar active regions are known to be brighter in Lyman α radiation than the quiet sun. Accordingly, they illuminate more H atoms in interplanetary space through resonance scattering. As we show here, this excess of illumination related to active regions is clearly seen in full‐sky Lyman α maps recorded by the SWAN instrument on board SOHO, including those excesses resulting from active regions which are on the far side of the Sun. Since solar activity is most often connected to solar active regions, this technique could be used in the future to improve the quality of Space Weather forecast, by earlier detection of the birth of a new active region on the far side of the sun, before it comes into Earth's view at the East limb.
Quasi‐periodic ionospheric disturbances with a 40‐min period during prolonged northward interplanetary magnetic field
Authors: Huang Chao‐Song , Sofko G. J. , Kustov A. V. , MacDougall J. W. , Andre D. A. , Hughes W. J. , Papitashvili V. O.
Published: September 2002

It has been observed that quasi‐periodic oscillations in the solar wind and interplanetary magnetic field (IMF) can result in the generation of auroral electrojet bursts and gravity waves with a similar period. In this paper, we present radar and magnetometer observations of quasi‐periodic ionospheric disturbances during stable, northward IMF. Magnetic deviations of ∼10 nT with a 40‐min periodicity were registered with ground magnetometers between magnetic latitudes 75° and 80° over an extended region along the longitudinal direction in the morning sector. A sequence of gravity waves were observed by HF radars at lower latitudes and appeared to be closely related to the high‐latitude 40‐min current disturbances. There were no obvious source perturbations in the upstream solar wind for the ionospheric disturbances. We suggest that field line resonances could be excited in a closed magnetosphere during prolonged northward IMF and result in the generation of the ionospheric current disturbances and gravity waves.
Average profile of ion flow and convection electric field in the near‐Earth plasma sheet
Authors: Hori T. , Maezawa K. , Saito Y. , Mukai T.
Published: September 2002

Two‐dimensional distribution of ion flow and convection electric field in the near‐Earth plasma sheet (9 < R < 30 RE) is investigated on the basis of GEOTAIL measurements. Our statistics confirms that the observed ion flow in the plasma sheet is generally earthward, being accompanied by a significant dawn‐to‐dusk component which is distributed asymmetrically about the noon‐midnight meridian. On the other hand, the convection electric field deduced from the V×B term after excluding the effects of ion pressure gradient drift shows much better symmetry about the noon‐midnight meridian. Existence of significant difference between the ion and magnetic flux convection patterns suggests that the frozen‐in condition does not hold in the near‐Earth plasma sheet.
Seismicity and average velocities beneath the Argentine Puna Plateau
Authors: Schurr B. , Asch G. , Rietbrock A. , Kind R. , Pardo M. , Heit B. , Monfret T.
Published: September 2002

A network of 60 seismographs was deployed across the Andes at ∼23.5°S. The array was centered in the backarc, atop the Puna high plateau in NW Argentina. P and S arrival times of 426 intermediate depth earthquakes were inverted for 1‐D velocity structure and hypocentral coordinates. Average velocities and υp/υs in the crust are low. Average mantle velocities are high but difficult to interpret because of the presence of a fast velocity slab at depth. Although the hypocenters sharply define a 35° dipping Benioff zone, seismicity in the slab is not continuous. The spatial clustering of earthquakes is thought to reflect inherited heterogeneties of the subducted oceanic lithosphere. Additionally, 57 crustal earthquakes were located. Seismicity concentrates in the fold and thrust belt of the foreland and Eastern Cordillera, and along and south of the El Toro‐Olacapato‐Calama Lineament (TOCL). Focal mechanisms of two earthquakes at this structure exhibit left lateral strike‐slip mechanisms similar to the suggested kinematics of the TOCL. We believe that the Puna north of the TOCL behaves like a rigid block with little internal deformation, whereas the area south of the TOCL is weaker and currently deforming.
Shear wave attenuation profile from sonic dipole well‐log data
Authors: Sun Xinhua , Frazer L. Neil
Published: September 2002

A shear wave attenuation profile is extracted from dipole waveform well‐log data. The method is demonstrated by applying it to synthetic data, and then to monopole and dipole field data for a hard formation. The attenuation profiles for the two types of field data agree remarkably well.
Percolation in the crust derived from distortion of electric fields
Authors: Bahr Karsten
Published: September 2002

Fractal crack distributions in the crust have been discussed in the context of earthquake cycles, fluid percolation, and the electrical conduction mechanism. With the impedance matrix rotation analysis in magnetotellurics (MT), a special type of apparent amplification of variational electric fields in one horizontal direction was detected. Here a possible link between crustal fracture networks and MT distortion is suggested. It is shown that the strong electric field amplification can be explained with a very heterogeneous crack network which in one direction stays in the vicinity of the percolation threshold. The apparent similarity to fluid percolation models does not automatically support the fluids paradigm, but rather allows for a choice between present fluid percolation and ‘paleopercolation’ to be the origin of the conductivity structure. In the latter model, the fluid caused the precipitation of graphite which now forms a partly interconnected network.
ULF electromagnetic precursors for an earthquake at Biak, Indonesia on February 17, 1996
Authors: Hayakawa Masashi , Itoh Tetsuya , Hattori Katsumi , Yumoto Kiyohumi
Published: September 2002

ULF electromagnetic emissions associated with a large earthquake occurred at Biak Island, Indonesia at 5h 59m UT on February 17, 1996 (magnitude (Mw) = 8.2 and depth = 20 km from USGS catalog), have been investigated on the basis of ULF magnetic observations at two stations, Biak and Darwin in Australia (about 1,200 km apart). Though a simple analysis of magnetic field intensity (horizontal and vertical magnetic field components) at both stations was found to be closely correlated with geomagnetic ΣKp activity, a detailed analysis of the difference of H and Z components at the two stations, the polarization analysis (Z/H) and fractal analysis (frequency spectrum slope) at these two stations has yielded that the ULF emissions (in the frequency range from 5 mHz to 30 mHz) about 1.5–1.0 months before the quake are likely to be a precursory signature of the quake with its intensity on the order of 0.2–0.3 nT.
TRMM observed first direct evidence of smoke from forest fires inhibiting rainfall
Authors: Rosenfeld Daniel
Published: September 2002

Although it has been known that smoke from biomass burning suppresses warm rain processes, it was not known to what extent this occurs. The satellite observations of the Tropical‐Rainfall‐Measuring‐Mission (TRMM), presented here, show that warm rain processes in convective tropical clouds infected by heavy smoke from forest fires are practically shut off. The tops of the smoke‐infected clouds must exceed the freezing level, i.e., grow to altitudes colder than about −10°C, for the clouds to start precipitating. In contrast, adjacent tropical clouds in the cleaner air precipitate most of their water before ever freezing. There are indications that rain suppression due to air pollution prevails also in the extra‐tropics.
Sea level drop in the Mediterranean Sea: An indicator of deep water salinity and temperature changes?
Authors: Tsimplis Michael N. , Baker Trevor F.
Published: September 2002

Coastal sea level data from seven tide gauges in the Western Mediterranean and the Adriatic show decreasing sea levels after 1960. Control stations in the Black Sea and in the northeastern Atlantic indicate sea levels still rising after 1960. The sea level trend in the Mediterranean before 1960 was between 1.2 and 1.5 mm yr−1, while in the Atlantic and the Black Sea stations it was between 1.8 and 2.2 mm yr−1. After 1960 the sea level in the Mediterranean is decreasing with rates up to −1.3 mm yr−1, while in the Black Sea the sea level trend remains unaltered and at the Atlantic stations sea level keeps rising with reduced rates of 1.0–1.2 mm yr−1. The change of the Mediterranean sea level trends, which is in excess of the sea level trend reduction at the Atlantic sites, is consistent with increases in temperature and salinity of the Mediterranean Deep Water. The reduction of sea level trends at the Atlantic sites is probably related to the North Atlantic Oscillation.
PKP(BC‐DF) Travel time residuals and short scale heterogeneity in the deep Earth
Authors: Bréger Ludovic , Romanowicz Barbara , Tkalčić Hrvoje
Published: September 2002

Differential PKP(BC)‐PKP(DF) travel time residuals for quasi‐polar paths in the earth present large excursions from the trends predicted by simple models of inner core anisotropy. We analyze a set of such paths classified according to specific source and station regions, and show that observations are compatible with a constant anisotropy model of at most 1.5% in the outer 400 km of the inner core. To explain local departures of up to 3 sec from the predictions of such a model, strong lateral variations on scale lengths shorter than a few hundred km need to be invoked, either in the core or in the mantle. Independent results of D' modelling argue in favor of an important contribution from the latter.
Geochemical constraints on the origin of thrust fault fluids
Authors: Dworkin S. I.
Published: September 2002

The character and origin of Sevier Cordilleran thrust fault fluids was investigated through the analysis of Sr, O, and C isotope ratios in thrust fault breccia matrix. Breccia matrix has depleted oxygen, depleted carbon and more radiogenic strontium when compared to undeformed rocks. This isotope chemistry indicates that meteoric waters descended below the horizon of thrusting and interacted with rocks that released radiogenic Sr to the fluid. The fluids subsequently ascended into the thrust faults where they imparted their unique isotopic signature to the matrix of the recrystallizing thrust fault breccia. The similar trends in isotope chemistry of thrust fault breccias along geographically far‐spaced locations of the Cordilleran thrust belt indicates that a common hydrologic regime was operating during Sevier deformation.
Anomalous temperatures in central Scotia Sea sediments – Bottom water variation or pore water circulation in old ocean crust
Authors: Barker Peter F. , Lawver Lawrence A.
Published: September 2002

We report low temperature gradients (from 60% to 12% of geothermal), and extrapolated temperatures offset from modern bottom water temperatures, in sediments from the central Scotia Sea. We examine possible causes, bearing in mind similar anomalous measurements 18 years previously, attributed at the time to instrumental error. Small temperature offsets (±0.1°C) may reflect short‐term bottom temperature variation within eddies of the Antarctic Circumpolar Current. Low sediment temperature gradients may be caused by horizontal advection of cold water within the upper oceanic basaltic layer (documented in younger ocean floor elsewhere), or by northward encroachment of colder bottom waters (from the Antarctic Peninsula shelf or Weddell Sea) for several years prior to measurement.
Sound wave velocities and elastic constants for Magnesiowüstite using gigahertz interferometry
Authors: Reichmann H. J. , Jacobsen S. D. , Mackwell S. J. , McCammon C. A.
Published: September 2002

Ultrasonic interferometry at near‐gigahertz frequencies is used to investigate longitudinal sound wave velocities parallel to [100] and [111] and the elastic constant c11 for high quality single crystals of magnesiowüstite (Mg,Fe)O. The measurements were made at room pressure and temperature on samples spanning the full compositional range from periclase (MgO) to wüstite (Fe1‐xO). A strong P‐wave anisotropy of ∼10% was measured for periclase, increasing about 1% for Mg0.94Fe0.06O then decreasing linearly to ∼0% for wüstite. The elastic modulus c11 of magnesiowüstite decreases linearly with iron content by −0.72(3) GPa/mol% FeO with the exception of a sharp increase for pure periclase. Thus, the addition of a small amount of iron to periclase has a major effect on its elastic behavior. This observation indicates that the use of a simple interpolation of elastic constant data between periclase and wüstite [Jackson, 1998] may yield erroneous predictions for lower mantle compositions based on seismic data.
Magnetic characterization of reduction in Mount Fuji basaltic tree‐mold
Authors: Wasilewski Peter , Kletetschka Günther , Dickinson Tamara
Published: September 2002

A Mount Fuji basaltic tree‐mold presents the mineralogical record associated with a large oxygen fugacity gradient during the cooling of the basalt. Magnetic exchange anisotropy is postulated to be characteristic of cation excess in some spinel titanomagnetites. The exchange anisotropy is characterized by loop shifting along the field and magnetization axes when cooled in a magnetic field, large coercivity increase, and magnetic viscosity which has discrete activation fields and logarithmic to linear decay characteristics. The cryogenic loop characteristics attributable to exchange anisotropy are not found in the tree‐mold where iron and ilmenite are the main phases. The coupling has been created in the laboratory with ordinary basalt artificially reduced in Hydrogen gas. The coupling is not found in spinel oxidation non‐stoichiometry. These results imply that we are able to identify the presence of spinels that have equilibrated in the low oxygen fugacity range of the spinel stability field where cation excess is characteristic.
A model for propagation and concentration of microcracks
Authors: Wackertapp J. , Hergarten S. , Neugebauer H. J.
Published: September 2002

We present a model for mode I propagation and concentration of microcracks in brittle solids driven by remote stresses or volumetric changes, e.g., due to thermal contraction or desiccation. Using a crack density integral, we obtain an effective elastic tensor; the dynamics of the crack density integral is described by an additional differential equation assuming subcritical microcrack growth. Numerical simulations allow the investigation of the physical background of pattern evolution and provide some hints that the pattern formed by the concentration of microcracks may have a significant influence on the macroscopic crack pattern which finally occurs.
Accurate transfer function determination for superconducting gravimeters
Authors: Van Camp Michel , Wenzel H. ‐G. , Schott P. , Vauterin P. , Francis O.
Published: September 2002

The transfer function for the cryogenic gravimeter GWR‐C021 operating at Membach (Belgium) has been experimentally determined by injecting known voltages into the control electronics of the system. The output of the gravimeter to the injected sine waves and step functions has been observed. This give a precise knowledge of the transfer function of the gravimeter. It allows one to reach a precision of better than 0.01 second in the phase response of the instrument, in agreement with the Global Geodynamics Project (GGP) requirements.
Bottom water circulation in the western equatorial Pacific as inferred from carbon tetrachloride observations
Authors: Klatt Olaf , Holfort Jürgen
Published: September 2002

Hydrographic and tracer data from the western equatorial Pacific, collected during cruise 113 of R/V Sonne in October–November 1996, are discussed in the context of spreading of lower Circumpolar Deep Water (lCDW). The horizontal distribution of CCl4 and other properties indicate a deep western boundary current north of the Caroline Seamounts. Elevated concentrations of CCl4 at the bottom show that a small fraction of lCDW in this region is younger than about 70 years. This age is used to infer a minimum spreading rate of about 0.8 cm/s for the young components of this water mass. The current appears to bifurcate at about 143°E into topographically guided northward and westward currents.
Shelf break upwelling driven by Brazil Current Cyclonic Meanders
Authors: Campos Edmo J. D. , Velhote Denise , da Silveira Ilson C. A.
Published: September 2002

Analysis of hydrographic data and results of numerical modeling show the occurrence of upwelling associated with the cyclonic meanders of the Brazil Current, in the region known as the Southeast Brazil Bight or Santos Bight. The temperature and salinity distributions collected during summer and winter confirm the idea that meander‐induced shelf break upwelling plays an important role in the pumping of South Atlantic Central Water from the slope region onto the continental shelf.
High speed video of initial sprite development
Authors: Stanley Mark , Krehbiel Paul , Brook Marx , Moore Charles , Rison William , Abrahams Bill
Published: September 2002

High speed video of sprites show that they are typically initiated at an altitude of about 75 km and usually develop simultaneously upwards and downwards from the point of origin with an initial columniform shape. The initial development of sprites appears to be dominated by corona streamers with velocities in excess of 107 m/s. Many of the observed characteristics are consistent with a conventional breakdown mechanism for both sprite initiation and initial sprite development.
Kinetic evolution and acceleration of the solar wind
Authors: Tam Sunny W. Y. , Chang Tom
Published: September 2002

We investigate the effects of kinetic wave‐particle interactions on the solar wind using a global hybrid model. The model follows the evolution of the particle distributions along an inhomogeneous field line under the influence of wave‐particle interactions, an am‐bipolar electric field that is consistent with the particle distributions themselves, and Coulomb collisions. This represents the “first results” of global evolutionary study of the solar wind that take into account these kinetic effects. The model can account for the bulk acceleration of the solar wind, the preferential heating of the helium ions over the protons, as well as the occasionally observed double‐peaked proton velocity distributions.
Solar wind control of polar chorus
Authors: Salvati M. A. , Inan U. S. , Rosenberg T. J. , Weatherwax A. T.
Published: September 2002

The intensity of chorus as observed at several high latitude ground stations in the Antarctic is highly correlated with the solar wind dynamic pressure exerted on the magnetopause boundary. In two different cases, intense chorus and associated precipitation measured as riometer absorption were abruptly interrupted by several minutes of deep quieting. Satellite measurements of solar wind dynamic pressure showed the intensity of chorus to rapidly respond to magnetospheric compression and relaxation over an extended region as evidenced by the fact the effect was observed at multiple sites.
The solar wind interaction with Mars: Locations and shapes of the bow shock and the magnetic pile‐up boundary from the observations of the MAG/ER Experiment onboard Mars Global Surveyor
Authors: Vignes D. , Mazelle C. , Rme H. , Acuña M. H. , Connerney J. E. P. , Lin R. P. , Mitchell D. L. , Cloutier P. , Crider D. H. , Ness N. F.
Published: September 2002

The Mars Global Surveyor spacecraft was inserted into an elliptical orbit around Mars on September 12, 1997. It includes the MAG/ER instrument with two magnetometers providing in‐situ sensing of the ambient magnetic field and an electron reflectometer measuring the local distribution function of the electrons in the energy range of 10 eV to 20 keV. This statistical study deals with the identification and the position of the Bow Shock (BS) and of another plasma boundary, the Magnetic Pile‐up Boundary (MPB), proved as permanent by MAG/ER. During the first year of the MGS mission, a total of 290 orbits have been considered to fit the geometric characteristics of these boundaries. The position and shape of these boundaries are compared with previous studies. Good agreement is found with the Phobos 2 observations, suggesting than the mean bow shock and MPB locations are independent of solar cycle phase. The great number of crossings shows that the Bow Shock position and nightside MPB position are highly variable.
Ion injection and shock acceleration in the outer heliosphere
Authors: Rice W. K. M. , Zank G. P. , Richardson J. D. , Decker R. B.
Published: September 2002

Voyager 2 data from 47 AU shows a delay of about 6 days between the arrival of interplanetary shock fronts and the peaks in the 0.52–1.45 MeV energetic proton flux. Similar data recorded when Voyager 2 was at 5 AU shows that the shock fronts and the peaks in the energetic proton flux are virtually coincident. If injection and acceleration is taking place at the shock fronts one would expect the peaks in the energetic proton flux and the shocks to coincide. We show that the delay observed at 47 AU can be understood if the injection and acceleration of energetic protons becomes negligibly small some time before the shocks are observed.
First observations of coherent scatter from the mid‐latitude F‐region in the Caribbean
Authors: Swartz Wesley E. , Makela Jonathan J. , Kelley Michael C.
Published: September 2002

The Cornell University Portable Radar Interferometer (CUPRI) started a new series of measurements of the mid‐latitude ionosphere from Puerto Rico in July 1997. On the first day of operation, coherent echoes were obtained from the F region. This was the first detection of such echoes in this longitude sector. This is surprising since the MU radar has seen similar eches over Japan and the presence of related phenomena in the Caribbean suggested they should have been seen in other VHF studies. A number of F‐region events were subsequently observed. Some echoes were characterized with very narrow spectra and small mean Doppler shifts. Two events had echoes whose range changed rapidly with time, but only one of these had comparable Doppler velocities. Such differences suggest that we caught the events in different stages of development. In addition to presenting samples of the data, we outline the reasons why these structures were anticipated.
Dynamic spectra of the Stokes parameters for the dayside and nightside auroral kilometric radiation
Authors: Hanasz J. , Boudjada M. Y. , Schreiber R. , Krawczyk Z. , Malycha M. , Mogilevsky M. M. , Rucker H. O. , Romantsova T. V.
Published: September 2002

First determination of dynamic spectra of the Stokes parameters for the AKR are reported. Frequent appearance of the L‐O mode of AKR sometimes as intense as the R‐X one, and sporadically even more intense than that was observed in the dayside magnetosphere. Existence of dayside sources of AKR is inferred from discussion of their visibility from the s/c orbiting on the dayside, taking into account a limited opening angle of the AKR emission cone. The domination of the R‐X wave mode is confirmed for the nightside observations.
New method for inferring total ozone and aerosol optical thickness from multispectral extinction measurements using eigenvalue analysis
Authors: Taha Ghassan , Box Gail P.
Published: September 2002

Eigenvalue analysis provides a way of predicting the measurement value at a particular wavelength from measurements made at other wavelengths. It was applied to MFRSR data to find the aerosol contribution made to the measured total optical thickness at the Chappuis band centered near 0.614 µm, within the measurement accuracy. This was used to calculate the total ozone column. The estimated total ozone columns using this technique are compared with the ozone determined using the method described by (King and Byrne, 1976), both were compared with ADEOS and EP total ozone mapping spectroradiometer (TOMS) measurements. The new method gave an excellent agreement with the satellite measurements. The weekly mean percentage difference between the total ozone and both ADEOS and EP/TOMS was 1% and 2% respectively.
A 22° long seismic profile for the study of the top of D'
Authors: Freybourger Marion , Krüger Frank , Achauer Ulrich
Published: September 2002

We present a collection of 100 vertical component seismograms of a Kuril Islands earthquake recorded by stations in western Europe (between 73 and 95° of epicentral distance) which shows evidence of a PdP wave reflected on top of D' beneath northern Siberia. The PdP travel time curve varies rapidly, suggesting the existence of sharp lateral variations (scale length smaller than 1°). The first onset times observed at distances larger than 85° are compatible with a D' velocity about 1% larger than standard models along these paths, up to a depth of 2850 km. By one dimensional forward modeling we find one model with a 2.8% discontinuity at 2605 km depth, another with a 7 km thick 3% low velocity lamella at 2607 km depth. They both generate waveforms which fit the data similarly.
Contribution to the climatological study of lightning
Authors: Michalon N. , Nassif A. , Saouri T. , Royer J. F. , Pontikis C. A.
Published: September 2002

In this work, a new parameterization of the thunderstorm cloud electrical flash frequency is obtained on the basis of simple dimensional arguments. The flash frequency is expressed as a power function of both the cloud top height and the cloud droplet concentration, thus partly taking into account the role of the microphysical cloud characteristics. Since droplet concentrations are not predicted by General Circulation Models (GCMs) and further show great variability, two different “standard” droplet concentrations, respectively valid for continental and maritime thunderstorms, are used. A numerical experiment has been made by using the METEO‐France GCM “ARPEGE” in relation to both, this new parameterization and the Price and Rind (1992) parameterization, in order to determine the global characteristics of electrical flashes. The analysis of the results reveals that the mean annual global flash frequency as well as the total number of flashes that strike annually the globe are higher when the new parameterization is used but are in better agreement with the Optical Transient Detector (OTD) (Christian et al., 1996) observations, thus indirectly attesting for its validity. Further, the good agreement between monthly and diurnal global flash numbers and the corresponding OTD observations confirms the ability of “ARPEGE” of correctly representing the global thunderstorm development. Finally, the new parameterization has been used in a second numerical experiment in order to infer the role of a doubling of CO2 on the global distribution of electrical flashes. A 10% increase of the mean global annual flash frequency is obtained for a surface warming of roughly 2°C.
The Pacific decadal oscillation, air‐sea interaction and central north Pacific winter atmospheric regimes
Authors: Bond Nicholas A. , Harrison D. E.
Published: September 2002

Prominent and persistent anomalies in the atmospheric flow (troughs and ridges) occur sporadically over the central North Pacific, and can have profound consequences for the weather of North America. We have examined how these events are associated with large scale central North Pacific sea surface temperature (SST) anomalies, using an index for the Pacific Decadal Oscillation (PDO). The anomalies in turbulent air‐sea heat fluxes and low‐level baroclinity associated with the PDO are manifested differently during troughs than during ridges in their effects on the transient eddies (storms). These effects may help explain why prominent troughs (ridges) occur about 3 (2.5) times more frequently during periods when the PDO is significantly positive (negative) than of opposite sign. Our results suggest that the state of the mid‐latitude Pacific Ocean more fundamentally affects the atmosphere than has been thought.
Cloud‐resolving and single‐column simulations of a warm‐frontal cloud system: Implications for the parameterization of layered clouds in GCMs
Authors: Szeto Kit K. , Lohmann Urike
Published: September 2002

A winter oceanic cyclonic cloud system was simulated by using both a cloud‐resolving model (CRM) and two single‐column models (SCMs) utilizing different approaches to parameterize layer clouds. When driven with advective forcing derived from the CRM, the SCMs can capture the general developments of the large‐scale cloud field during the warm‐frontal passage. However, the vertical cloud structures differed significantly among the models. Some of the differences in the model cloud structures can be attributed to the lack of, or inappropriateness of the parameterizations of some cloud microphysical processes and subgrid cloudiness in current GCM prognostic cloud schemes. The high resolution CRM results will be valuable in identifying such deficiencies in current GCM cloud schemes and in the future developments and calibrations of these schemes.
Multi‐scale dynamics of soil moisture variability observed during SGP'97
Authors: Crow Wade T. , Wood Eric F.
Published: September 2002

Data sets produced by the 1997 Southern Great Plains Field Experiment (SGP'97) provide information about surface soil moisture dynamics across a range of scales. A multi‐scale analysis of the data reveals a qualitatively different relationship between soil moisture means and soil moisture spatial variances when variability is sampled at fine (<1 km) versus coarse (>10 km) spatial scales.
Uptake of nitric acid by sub‐micron‐sized ice particles
Authors: Arora O. P. , Cziczo D. J. , Morgan A. M. , Abbatt J. P. D. , Niedziela R. F.
Published: September 2002

The uptake of gas phase nitric acid by half‐micron‐diameter ice crystals has been studied at 230 K by measuring the nitrate content of ice particles which have been exposed to 5 × 10−6 torr of nitric acid in a low temperature flow tube. A cold NaOH‐coated denuder is used to distinguish gas‐phase nitric acid from adsorbed nitric acid. Ice particle diameters were determined by fitting measured aerosol infrared extinction spectra to spectra calculated via Mie theory, and their number density is measured directly with a CN counter. Under conditions in which the surface is saturated and not all the gas‐phase nitric acid adsorbs, the measured uptakes are 1.2 × 1014 molecules/cm² where the surface area is the geometric area of the particles. Within experimental uncertainties, this surface coverage is the same as that measured on thin films of ice formed by freezing liquid water. These results are the first quantitative study of the nitric acid uptake capacity of ice particles, and they provide additional support to the suggestion that ice and snow provide a route for the efficient scavenging of nitric acid from the atmosphere.
The reflectance of rough snow surfaces in Antarctica from POLDER/ADEOS remote sensing data
Authors: Mondet Jean , Fily Michel
Published: September 2002

The POLDER (POLarization and Directionality of the Earth's Reflectances) sensor was launched onboard the Japanese ADEOS satellite in August 1996. It measured the energy reflected by the Earth in the solar spectrum at 8 wavelengths. From this sensor, an Earth target could be seen up to 14 times along a single path providing a good characterization of the BRDF (Bidirectional Reflectance Distribution Function) from space. A set of one month of POLDER data over east Antarctica was analyzed. After cloud masking and atmospheric corrections, mean BRDFs were derived for different areas. In some parts of the ice sheet the BRDF is assymetric with a strong reflectance peak in the half space oriented towards the sun (backscatter). This peak is due to the anisotropic roughness of the surface (sastrugi) and its position depends on the sastrugi direction.
Warming and circulation change in the eastern South Pacific Ocean
Authors: Schaffer G. , Leth O. , Ulloa O. , Bendtsen J. , Daneri G. , Dellarossa V. , Hormazabal S. , Sehlstedt P. ‐I.
Published: September 2002

Deep‐ocean temperature, salinity and dissolved oxygen observations in the eastern South Pacific Ocean collected during the late austral fall in 1995 are compared with observations made there 28 years earlier during the same season and similar El Niño‐Southern Oscillation phase. Warming observed above 800 m at 43°S reflects the production of warmer Subantarctic Mode Water in recent decades. Warming observed above 1600 m at 28°S is due to downward isotherm displacement and southward movement of water masses by 100–200 km, as revealed by joint analysis of temperature and oxygen data. Such changes would be expected for a weaker subtropical gyre in the South Pacific. An observed oxygen decrease between about 1800 m and 2900 m at 28°S may indicate enhanced southward, boundary current flow at mid‐depths off Chile.
The influence of El Niño‐Southern Oscillation events on the northern hemisphere 500 hPa circumpolar vortex
Authors: Frauenfeld Oliver W. , Davis Robert E.
Published: September 2002

The relationship between El Niño, the Southern Oscillation, and their joint effect (ENSO), and Northern Hemisphere 500 hPa midlatitude circulation for the 1946–1994 observational record is determined. Seasonally standardized vortex positions at a spatial resolution of 5° longitude are correlated with an equatorial Pacific sea surface temperature anomaly index and the Southern Oscillation Index (SOI). The 500 hPa circumpolar vortex is consistently expanded over the central Pacific during and for the entire year following warm ENSO periods. The vortex is contracted over North America concurrently with warm ENSO and to a lesser degree during the following season. Expansion/contraction variability is also evident over east Asia, although the linkages to warm or cold ENSO are weak. Sea surface temperatures have a stronger association with the vortex than does the SOI.
Modeling mineral reactions in compacting sedimentary basins
Authors: Yang Xin‐She
Published: September 2002

Smectite‐illite reaction of sediment minerals in sedimentary basins is modelled as a one‐step dehydration reaction. The water released from the mineral reaction can affect compaction process so as to retard porosity reduction and thus may cause overpressuring, especially in the reaction region. The coupled nonlinear model equations have been solved numerically, and the asymptotic analysis has been used to get the analytical solutions of the nonlinear model equations in some regions of most practical interests. The comparison of the obtained asymptotical solutions with the numerical results and real data shows very good agreement.
A simple model of mantle convection including a past history of yielding
Authors: Honda Satoru , Nakakuki Tomoeki , Tatsumi Yoshiyuki , Eguchi Takao
Published: September 2002

A two‐dimensional dynamic model of mantle convection, showing plate‐like behavior, is constructed by considering the effects of the previously yielded segments. Only within an uppermost thin layer is the material assumed to yield at a constant stress. The advection of the segments affected by yielding is calculated. The area covered by these segments continues to yield until it reaches a certain depth. The resultant flow shows movement of the top layer in the parameter range in which, without yielding, it becomes sluggish. A comparison of the results with and without historical effects shows the enhancement of the plate‐like behavior. We consider the horizontal variation of the yield stress, which may be caused by the difference in the amount of H2O in the crust. The place of sinking is controlled by the lateral change in the yield stress and the flow behavior becomes different from the case with uniform yield stress.
The waveguide effect of metastable olivine in slabs
Authors: Koper Keith D. , Wiens Douglas A.
Published: September 2002

We use a finite difference algorithm to compute P‐SV synthetic seismograms for deep earthquakes recorded at regional seismic stations located above a subducting slab. We calculate synthetics for 2‐D slab models in which the 410 km‐discontinuity is uplifted, owing to the exothermic nature of the α → β transition (the equilibrium model), and models in which the 410 km‐discontinuity is depressed, owing to inhibited kinetics of the α → β olivine transition (the metastable model). In the latter case the existence of the low‐velocity wedge of metastable olivine has a profound influence on the waveforms of deep‐focus earthquakes. The wedge acts as a geometrical waveguide, with the energy‐focusing effect apparent even after the wavefront has traveled the several hundred kilometers from the wedge boundary to the Earth's surface. The guided energy is most pronounced for receivers located near the surface projection of the deep slab but is observable over a range of 300 km and so may provide a valuable diagnostic for discriminating between equilibrium and metastable models of subduction. A recent search for such guided energy, using regionally recorded P and S waves from deep events in Tonga, yielded negative results.
Characterization of North American land cover from NOAA‐AVHRR data using the EOS MODIS Land Cover Classification Algorithm
Authors: Friedl M. A. , Muchoney D. , McIver D. , Gao F. , Hodges J. C. F. , Strahler A. H.
Published: September 2002

Land cover is a key boundary condition in weather, climate, and terrestrial biogeochemical models. Until recently, such models have used maps depicting potential vegetation, which are known to be of relatively poor quality, to parameterize land surface properties. In this paper we describe the compilation and assessment of a new map of North American land cover produced through the application of advanced pattern recognition techniques to multitemporal satellite data. This map was produced in a fully automated fashion using supervised classification methods that are robust, fully automated, and repeatable. The processing flow described in this paper is a prototype of the algorithm to be used to generate maps of global land cover using data from EOS MODIS. The superior quality and timeliness of these maps should be very useful for a wide array of sub‐continental to global‐scale modeling and analysis activities.
Evaluating uncertainties in the prediction of regional climate change
Authors: Giorgi Filippo , Francisco Raquel
Published: September 2002

Uncertainties in regional climate change simulations for the 21st century by five coupled atmosphere‐ocean General Circulation Models (AOGCMs) (two of them including ensembles of simulations), for different anthropogenic forcing scenarios and 23 regions in the World, are examined. Seasonally and regionally averaged precipitation and surface air temperature for the future period of [2070–2099] as compared to the period of [1961–1990] are considered. The dominant source of uncertainty in the simulation of average regional climate change is due to inter‐model variability with inter‐scenario and internal model variability playing secondary roles. The range of predicted climate changes by different realizations of the same ensemble is small, and simulated changes exhibit a high level of coherency among different forcing scenarios. Uncertainties in regional changes are 3 K or greater for temperature and 25% of present day values or greater for precipitation. The model biases in reproducing present day climate are ≤1 K to over 5 K for temperature and ≤10% to over 100% for precipitation.