bluuebunny/crossref_metadata_2025 huggingface dataset:
Signatures of stirring and mixing in the Japan sea surface temperature patterns in autumn 1993 and spring 1994
Authors: Ostrovskii Alexander G.
Published: February 2004

A wavelet analysis of the NOAA satellite radiometry data shows remarkable difference in the typical patterns of the sea surface temperature (SST) of the Japan Sea in autumn 1993 and spring 1994. The plumes of irregular shapes with characteristic horizontal scale of less than 30 km developed over the SST field at the beginning of the cooling season when the horizontal temperature gradients were essentially eroded. In contrast, very narrow and elongated up to 100 km streaks appeared at the beginning of the heating season when the temperature gradients were sharp. The spectral analysis of SST results in the power law behavior of k−2.0 in October and k−2.8 in May, for the scales ranging from 10 km to 100 km. This research suggests that the surface cooling in the autumn favors the enhancement of three dimensional mixing, while during the onset of heating the horizontal stirring becomes more pronounced at geostrophic turbulence scales.
A note on the sensitivity of mantle convection models to composition‐dependent phase relations
Authors: Bina Craig R. , Liu Mian
Published: February 2004

Numerical simulations of mantle convection are highly sensitive to the dependence of phase relations upon pressure, temperature, and composition. Phase transitions in the (relatively silica‐poor) olivine components of the mantle tend, with increasing iron content, to inhibit convective mass transfer between the upper and lower mantle. Those occurring in the (relatively silica‐rich) non‐olivine components fail to inhibit (and indeed promote) such mass transfer. Behavior in the real mantle must entail an interplay between such competing effects, with the finite width of multivariant phase fields acting to mitigate impediments to flow. Attempts to directly correlate computed flow or temperature fields with models derived from physical observables should be approached with caution, given the sensitivity of the former to compositional heterogeneity and uncertainties in phase relations.
Doppler observations of the impact of comet P/Shoemaker‐Levy/9, fragment A
Authors: Cacciani A. , Moretti P. F. , Dolci M. , Brocato E. , Smith E. J.
Published: February 2004

This paper discusses an attempt to detect the impact of fragment A of the comet Shoemaker‐Levy 9 on Jupiter using the Doppler effect. We give a short description of the technique used to observe the impact, then present the observations along with a tentative theoretical analysis and interpretation. The instrumentation used is an advanced and more sensitive version of the Magneto‐Optical Filter (normally used in Helioseismology to detect global oscillations of the Sun) and a 40 cm aperture telescope. The observed signal in July 16 (fragment A) consists of a pair of transients that, if related to the comet impact, could be interpreted as the signature of an expanding perturbation. We present only the first step of the theoretical analysis simulating a wave pulse expanding radially from the impact site. The result is remarkable in that it reproduces the two peaks although with much lower amplitudes than observed. Furthermore, the inferred particle speed is in the range 5–20 km/s which is more consistent with the plume and debris material expansion speeds derived from the HST observations and/or with shock wave propagation away from the impact site.
Complex refractive indices in the infrared of nitric acid trihydrate aerosols
Authors: Richwine L. J. , Clapp M. L. , Miller R. E. , Worsnop D. R.
Published: February 2004

The refractive indices of nitric acid trihydrate (NAT) have been determined from the infrared spectra of laboratory generated aerosols. The aerosols are formed via homogeneous nucleation in a flow cell with separate regions for nucleation and observation, allowing for independent control of the temperature conditions in these regions. A spectrum of small, non‐scattering particles is recorded to determine the frequency dependent imaginary refractive index, within a scaling factor. A subtractive Kramers‐Kronig routine is then used to calculate the real index. The scaling factor for the imaginary indices is determined by fitting a spectrum associated with larger, scattering particles, which depends on both the real and imaginary portions of the refractive indices. The complex refractive indices of NAT are reported over the range 700 cm−1 to 4000 cm−1. While in good qualitative agreement with previously reported results, there are significant quantitative differences which are discussed.
Interface waves propagating along tensile fractures in dolomite
Authors: Roy Sanjit , Pyrak‐Nolte Laura J.
Published: February 2004

Elastic interface waves have been observed in induced tensile fractures in dolomite rock cores. Multiscaling wavelet analysis distinguishes the interface wave from bulk shear waves, quantifies the interface wave spectral content, and determines the arrival time of the peak energy. The dominant seismic energy is concentrated in the slow interface wave, with little or no detectable energy in the fast wave. As the stress across the fracture increases, the slow interface wave velocity increases, and the frequency of the spectral peak shifts to higher frequencies. The shear dynamic specific stiffness of the fracture was calculated from the peak energy arrival time as a function of stress.
A chemical‐dynamical model of wave‐driven sodium fluctuations
Authors: Hickey Michael P. , Plane John M. C.
Published: February 2004

A comprehensive chemical‐dynamical model is used to investigate the interaction of gravity waves with twenty minor species involved in the atomic sodium chemistry in the mesopause region. We find that chemistry becomes important on the underside of the sodium layer, primarily below 85 km altitude, where the relative importance of chemistry in wave‐driven sodium fluctuations increases with increasing wave period and increasing horizontal wavelength. We also find that for altitudes below 80 km an adequate determination of the effects of chemistry in these fluctuations requires the inclusion of several reactions related to ozone chemistry. However, the atomic Na density is too low this region to be routinely observed by current sodium lidars. Importantly, we find that above 85 km altitude sodium can be treated as a passive tracer of gravity wave motions.
CLAES observations of Mt. Pinatubo stratospheric aerosol
Authors: Mergenthaler J. L. , Kumer J. B. , Roche A. E.
Published: February 2004

The UARS CLAES instrument made extensive measurements of the infrared emission of stratospheric aerosol resulting from the June 15, 1991 eruption of Mount Pinatubo from October, 1991 until May, 1993. The aerosol distribution is shown as a series of daily zonal‐mean latitude cross‐sections of absorption coefficient and stratospheric infrared optical depth with coverage from 80°N to 80°S. Sulfuric acid mass estimates are presented.
On the influence of tropospheric clouds on zenith‐scattered‐light measurements of stratospheric species
Authors: Erle F. , Pfeilsticker K. , Platt U.
Published: February 2004

Examples for the influence of tropospheric clouds on the ground‐based measurement of stratospheric species using the DOAS‐technique (Differential Optical Absorption Spectroscopy) are reported. At Camborne/Great Britain (50.216°N, 5.316°W) on Sept. 11–15, 1994, episodic enhancement of absorption lines of O4, H2O, O3 and NO2 were observed in coincidence with tropospheric clouds being in the instrumental field of view (1.1° full angle). At a solar zenith angle (SZA) of 88°, absorption enhancements up to roughly a factor of 3 were detected for the tropospheric species O4 and H2O and the tropospheric fractions of the total column of O3 and NO2. The additional absorptions in the visible spectral range are probably caused by multiple Mie‐scattering in tropospheric clouds. For our conditions, a tropospheric light path enhancement (TLPE) of 135±40 km can be inferred, being largely independent of SZA. This observation has several important implications for the atmospheric radiative transport, which are briefly discussed.
Dependence of the magnetopause Kelvin‐Helmholtz instability on the orientation of the magnetosheath magnetic field
Authors: Miura Akira
Published: February 2004

It is shown by means of a 2‐D MHD simulation that the observed rotation of the unperturbed magnetic field within the magnetopause (MP), which is assumed to be a tangential discontinuity (TD), leads to a significant dependence of the magnetopause Kelvin‐Helmholtz (K‐H) instability on the orientation of the sheath field. That is, northward sheath Bz is more favorable to the instability than southward Bz and the MP undulates most strongly when the sheath field points due north. When the sheath field does not point due north, a slow rarefaction region is formed in the velocity boundary layer (BL) inside the MP, wherein there are minima of the plasma pressure and temperature accompanied by a maximum of the magnetic pressure.
The QBO modulation of the occurrence of the counter electrojet
Authors: Chen Pei‐Ren , Luo Yi , Ma Jun
Published: February 2004

Continuous hourly measurements of horizontal component of geomagnetic field obtained at Trivandrum, India, have been used to study the occurrence of the Counter Electrojet (CEJ). Because the data cover nearly three solar activity cycles, they can be used to investigate long‐term variations of the CEJ. After the data have been processed and detrented to reduce the influence of solar cycles and annual variations, they reveal a quasi‐biennial oscillation (QBO) of the occurrence of the CEJ. When compared with the QBO wind phase in the stratosphere, the occurrence of the CEJ is found to increase in east phase and to decrease in west one. This relationship suggests a possible mechanism for the production of the CEJ. Under certain conditions the interaction between the upward propagating planetary waves and the solar or lunar semidiurnal tides may cause the semidiurnal tides to be increased in amplitude and shifted in phase, which ultimately results in the occurrence of the CEJ.
Spectral reflectance studies of the Grimaldi Region of the Moon
Authors: Peterson C. A. , Hawke B. R. , Lucey P. G. , Coombs C. R. , Spudis P. D.
Published: February 2004

Near‐infrared reflectance spectra were used to investigate the composition and origin of the various geologic units in the Grimaldi region as well as the stratigraphy of the Grimaldi pre‐impact target site. The results of our spectral analysis indicate that the portions of the Hevelius Formation that occur in the Grimaldi region are composed of noritic anorthosite and anorthositic norite. Gabbroic material was excavated from beneath Orientale‐related units by small impact craters in three areas in the Grimaldi region. The primary ejecta deposits of the Grimaldi basin as well as the pre‐Orientale floor unit are dominated by noritic anorthosite and anorthositic norite. The peak ring of Grimaldi is composed, at least in part, of pure anorthosite. The anorthosites on the inner ring and elsewhere within Grimaldi were derived from a layer of pure anorthosite that exists at depth beneath a more pyroxene‐rich unit.
A positive conglomerate test for the characteristic remanent magnetization (ChRM) of the Emeishan Basalt from southwest China
Authors: Huang K. , Opdyke N. D.
Published: February 2004

A positive conglomerate test has been achieved on ten basalt clasts from a pyroclastic breccia in the Emeishan basaltic sequence from Southwest China. Nine basalt samples collected from a nearby lava flow yield ChRM directions similar to the northeasterly and shallow up directions reported from elsewhere in the basalt province. This effectively refutes the suggestion that this group of directions represents a remagnetization of as late as Jurassic or Triassic age. The difference between different sets of results from the Emeishan Basalt and the non‐antipodality between the northeasterly directions and the reversed southwesterly down directions are likely to be due to a combination of minor structural rotations about vertical axes between the sampled localities, inaccuracy in determination of bedding attitude in massive basaltic rocks, and insufficient paleomagnetic sampling.
Coincident 1.3‐year periodicities in the ap geomagnetic index and the solar wind
Authors: Paularena K. I. , Szabo A. , Richardson J. D.
Published: February 2004

Recent observations show an approximately 1.3‐year period in the speed of the solar wind detected by the IMP 8 and Voyager 2 spacecraft. A similar period is also seen in the north‐south (GSE) component of the magnetic field observed by IMP 8. Since both parameters are commonly used as input to models of geomagnetic activity, the ap index (a measure of geomagnetic disturbance) is examined to look for this periodicity. The Lomb‐Scargle periodogram method is used on the ap, plasma, and magnetic field data during the 1973–1994 time range. A dynamic FFT periodogram method is also used to analyze the ap data during this time, as well as to look for periods present between 1932 and 1972. A clear 1.3‐year periodicity is present in the post‐1986 data when the same period is observed in the plasma and field data. The V2Bzsm and V2Bs proxies for geomagnetic activity also show this periodicity. However, the southward (GSM) component of the magnetic field does not have a 1.3‐year period, and neither do solar wind or ap data from 1973–1985. This demonstrates that the ap geomagnetic index can act as a proxy for solar wind periodicities at this time scale. Historic ap data are examined, and show that a similar periodicity in ap exists around 1942. Since auroral data show a 1.4‐year periodicity, all these similar periods may result from a common underlying solar mechanism.
Richardson number constraints for the Jupiter and outer planet wind regime
Authors: Allison Michael , Del Genio Anthony D. , Zhou Wei
Published: February 2004

Present theories of the dynamics of the outer planet atmospheres are limited by the absence of direct observations of the wind and temperature layering below their visible cloud decks. We show that if the potential vorticity is assumed to be small at low latitudes, then cloud‐tracked wind measurements of the equatorial flow on Jupiter, Saturn, Uranus, and Neptune can be used to constrain their vertical stratification at deeper levels. A Richardson number between 1.2 and 4 is indicated for all the giant planets, which at their rapid rotation implies a much more vertical isentropic structure at these levels than is realized in the terrestrial atmospheres. These conditions signify the likely presence of a unique but as yet unstudied regime for the jovian meteorology, illustrated by a new “Richardson‐Rossby” diagram for comparative planetary circulations. The Jupiter case will be directly tested by the Galileo atmospheric entry probe.
Mechanistic analysis of interhemispheric transport
Authors: Hartley Dana E. , Black Robert X.
Published: February 2004

After a strong interannual modulation in methyl chloroform was observed at Samoa, it was hypothesized that a mechanism other than convection, namely the propagation of Rossby waves through the tropical westerly ducts, may also be responsible for interhemispheric transport. We assess the role of these mechanisms in this exchange using the National Center for Atmospheric Research (NCAR)'s Community Climate Model 2 (CCM2). In our analysis of Northern Hemisphere wintertime transport we find that convective outflow is the dominant mechanism for cross‐equatorial transport. Rossby wave propagation through westerly ducts contributes significantly less. Furthermore, we find that the observed modulation of methyl chloroform mixing ratio at Samoa is due to a shift in the low level convergence pattern during El Nino, resulting in a more southeasterly flow at the surface over Samoa.
Auroral radiation ray distribution in the light of Viking observations of AKR
Authors: De Feraudy H. , Schreiber R.
Published: February 2004

The observations of the Viking satellite have shown that the AKR sources are narrow structures with sharp density edges, filled with hot tenuous plasma, into which the wave fields are trapped over some distance before escaping into free space. We examine the consequences of these features for the free propagation of the waves and for the distribution of their energy through space. The length of the trapping is estimated in a realistic situation corresponding to orbit 237 of Viking. The AKR energy is found to be confined inside an emission cone. It is shown that 60% of the wave energy concentrates at the thin edges of the cone, corresponding to an angular range of wave vectors oriented slightly downward. It is shown that in realistic situations met by Viking, the effect of a broad auroral cavity is to stretch significantly the pattern in longitude.
Aerosol surface areas deduced from early 1993 SAGE II data and comparisons with stratospheric photochemistry, aerosols, and dynamics expedition measurements
Authors: Yue G. K. , Thomason L. W. , Poole L. R. , Wang P.‐H. , Baumgardner D. , Dye J. E.
Published: February 2004

Stratospheric Aerosol and Gas Experiment II (SAGE II) multi‐wavelength stratospheric aerosol extinction measurements are used to estimate near‐global distributions of aerosol surface area density for early months of 1993. A comparison of monthly contour plots shows that the aerosol surface area density above the tropopause gradually decreased from about 15 µm²cm−3 in January 1993 to about 10 µm²cm−3 in May 1993. Aerosol surface area density profiles measured by the Forward Scattering Spectrometer Probe (FSSP‐300) during the Stratospheric Photochemistry, Aerosols and Dynamics Expedition (SPADE) campaign in May 1993 are compared with estimated SAGE II surface area density profiles obtained at nearby locations. FSSP measurements are in general, slightly lower than the SAGE II measurements. The possible sources of this discrepancy are discussed. When 4‐day average FSSP measurements are compared with the SAGE II zonal mean profile for May 1993 and 35°N–40°N at altitudes above 16 km, the agreement is good. In addition, SAGE II aerosol surface area density profiles calculated by assuming a lognormal size distribution and by using principal component analysis are compared, good agreement is shown at high altitudes. However, at low altitudes their differences may be as high as 25%.
Topographically forced planetary wave breaking in the stratosphere
Authors: Li Long , Nathan Terrence R. , Wuebbles Donald J.
Published: February 2004

The effects of topographically forced planetary wave breaking on eddy transport in the stratosphere are examined for zonal wavenumbers 1 and 2. Zonally averaged basic states representative of Northern Hemisphere (NH) and Southern Hemisphere (SH) winter conditions are used. Waves 1 and 2 each have significant wave breaking effects in the extratropical stratosphere during NH winter, whereas only wave 1 is important during SH winter. During NH winter, eddy mixing is dominated by wave 2 in the lower stratosphere and by wave 1 in the upper stratosphere and at the tropopause at low latitudes. The eddy diffusion effects due to the combined influence of waves 1 and 2 are much stronger in NH winter than in SH winter.
Determination of horizontal and vertical structure of an unusual pattern of short period gravity waves imaged during ALOHA‐93
Authors: Taylor M. J. , Fritts D. C. , Isler J. R.
Published: February 2004

An all‐sky CCD imager has been used to measure the properties of short period gravity waves present over the Hawaiian Islands during the ALOHA‐93 campaign. Observations of emissions from four different altitudes provided a capability to describe the vertical as well as the horizontal structure of the wave field. On several occasions during this campaign an unusual morphology wave pattern was detected that consisted of a group of small‐scale waves oriented in the same direction. These were most noticeable in the OI (557.7 nm) emission, altitude ∼96 km, and were usually observed in association with a larger scale gravity wave. This paper presents a preliminary analysis of data recorded on the night of 22 October during which both types of waves were prominent. The small‐scale waves exhibited highly coherent phase structures at each emission altitude, consistent with a ducted wave motion. The spatial intensity and phase modulation of this display is indicative of interference between two waves with similar characteristics and slightly different propagation directions. The larger scale wave motion was observed to propagate perpendicular to the small‐scale waves, and showed evidence of phase progression with altitude, implying upward energy propagation. These data have been interpreted in the context of simultaneous wind measurements from an MF radar.
Tangential discontinuities at high heliographic latitudes (∼−80°)
Authors: Ho C. M. , Tsurutani B. T. , Goldstein B. E. , Phillips J. L. , Balogh A.
Published: February 2004

In this study, tangential discontinuities (TDs) near −80° heliographic latitude have been studied. Based on our quantitative definitions, we find that the TDs may generally be divided into two clear types. There is a distinct population of TDs small (<40°) directional changes. About 19% of all high‐latitude TDs are in this category. These types of TDs are found at the edges of mirror mode structures. The latter are presumed to be locally generated by ion anisotropies, based on examination of the mirror mode instability criteria. Another 50% of high latitude TDs are associated with large field directional changes (>60°). These TDs typically are found at the boundary between two streams. The discontinuities have large normals in the plane perpendicular to the background field, as might be expected for features generated by currents flowing along the field. These discontinuities usually have larger current intensities than those of the mirror‐mode related TDs. The remainder of the discontinuities have angular changes which lie in between the mirror‐mode‐associated and the current‐sheet‐associated TDs.
Io torus EUV emissions during the comet Shoemaker‐Levy/9 impacts
Authors: Hall D. T. , Gladstone G. R. , Herbert F. , Lieu R. , Thomas N.
Published: February 2004

Extreme Ultraviolet Explorer satellite observations of Jupiter's Io plasma torus conducted over a two‐year time period before, during and after the impacts of comet Shoemaker‐Levy/9 reveal that no new spectral features appeared in the 400–715 Å spectral region. Io torus emission line luminosities remained stable to within ±20% and showed no strong coherent increasing or decreasing trend during the weeks preceding or following the impact events. This work supersedes our previous claims of possible luminosity changes to the torus derived from the same data (McGrath et al., Science, 267, 1313, 1995)
“Wasp‐waisted” hysteresis loops from a pyrrhotite and magnetite‐bearing remagnetized Triassic limestone
Authors: Muttoni Giovanni
Published: February 2004

Remagnetized samples of the Triassic Prezzo Limestone from northern Italy contain a mixture of pyrrhotite and magnetite, as deduced by thermal unblocking characteristics of triaxial isothermal remanent magnetizations (IRM's) and low‐temperature cycling of saturation IRM's. Hysteresis loops are commonly “wasp‐waisted” and remanent coercivity curves contain a break in slope, as a result of the contrast in coercivity between remanence‐carrying pyrrhotite and magnetite. The relative proportion of the high to low remanent coercivity fractions, as deduced by the study of the remanent coercivity curves, seems to control the degree of “wasp‐waistedness” of the hysteresis loops. Samples that are dominated by one of the two coercivity end members have lower Bcr/Bc values as well as hysteresis loops that have a less pronounced constricted waist compared to samples with higher Bcr/Bc values. Maximum Bcr/Bc values (and thus maximum degrees of “wasp‐waistedness” in the hysteresis loops) are attained when the low remanent coercivity fraction contributes 15–35% to the bulk remanent coercivity curves.
Electrical conductivity of a natural (Mg,Fe)SiO3 majorite garnet
Authors: Kavner Abby , Li Xiaoyuan , Jeanloz Raymond
Published: February 2004

The electrical conductivity of meteoritic majorite, measured at 10 Hz under a nitrogen atmosphere at ambient pressure, is 3.8 (±1.8) × 10−7 S/m at room temperature and displays an Arrhenius behavior with an activation energy of 0.55 (±0.1) eV over the temperature range 290–370 K. Extrapolating these values to conditions of the Earth's mantle suggests that majorite and spinel can account for the increase in electrical conductivity observed from the upper mantle to the transition zone, where these phases are stable.
Pervasive small‐scale enhancements in mantle and polar rain precipitation
Authors: Veselovsky Igor S. , Newell Patrick T. , Lui Anthony T. Y.
Published: February 2004

Short duration bursts—1–3 s or 0.05–0.15° MLAT—of 32 eV to several hundred eV electrons are regularly observed in the polar rain and mantle precipitation regions by the DMSP satellites. The spacing between bursts is typically 9–12 s (70–90 km) and is sometimes regular but more often irregular. Sometimes quasi‐periodic trains of 4 or 5 evenly spaced bursts occur. Electron spectra in the bursts are variable, but typically represent an enhancement of an order of magnitude in the spectral differential energy flux, but without showing signs of field‐aligned acceleration. Previous reports of bursty polar cap precipitation consisted of precipitation with large scale (hundreds of km) spatial inhomogeneity of plasma sheet origin under northward IMF conditions. The bursts described herein occur for southward as well as northward IMF Bz, and represent fine structure (7.5 km) within regions that are of magnetosheath origin and which are homogenous over larger spatial scales (>∼100 km). We suggest that the observed phenomena may be related to the nonstationary processes in the outer high latitude magnetosphere.
The Ulysses south polar pass: Energetic ion observations
Authors: Sanderson T. R. , Bothmer V. , Marsden R. G. , Trattner K. J. , Wenzel K.‐P. , Balogh A. , Forsyth R. J. , Goldstein B. E.
Published: February 2004

We present here a preliminary analysis of observations of energetic ions during the first polar pass of the Ulysses spacecraft, concentrating mainly on the region where the spacecraft was continually immersed in high speed flow from the polar coronal hole. During the ascent to high latitudes, a single recurrent peak was observed once per solar rotation. From 70°S during ascent to 43°S during descent no major peaks were observed. Thereafter, two peaks per solar rotation were observed.
Total ozone variations in middle Asia and dynamic meteorological processes in the atmosphere
Authors: Henriksen Kjell , Roldugin Valentin
Published: February 2004

The total ozone content over the former Soviet Middle Asia is compared with the heights and the temperatures at the 500 hPa and 100 hPa levels. There is a significant and negative correlation between the heights of the 100 hPa and 500 hPa levels and the total ozone content. The ozone column density is positively correlated with the temperature at 100 hPa and negatively correlated at 500 hPa. No observed time delay between ozone and temperature changes is found, indicating that the correlations are caused by dynamic processes. Ozone changes due to chemistry have time constants at least of the order of days, but correspondingly large time delays are not found. It is concluded that the horizontal advection is connected with ascending and descending air streams, and they are the main causes of decrease and increase of total ozone content with time constants of the order of one day.
Scale effects on dynamic wave propagation in heterogeneous media
Authors: Yin Hezhu , Mavko Gary , Mukerji Tapan , Nur Amos
Published: February 2004

To study scale‐effects on wave propagation in 3‐D heterogeneous media, we conducted dynamic and static laboratory experiments on seven samples of glass beads cast with epoxy. We measured P and S wave velocities and frequency dispersion by the pulse‐transmission method, and static elastic Young's modulus by a uniaxial stress test. We changed the scale of the heterogeneity by varying the diameter of the glass beads in each sample, and obtained wavelength to scale ratios varying from 0.2 to 20. We observed about 22% P‐wave velocity dispsersion and 15% S‐wave velocity dispersion within this range of wavelength to scale ratios. We observed no scale effects on the static Young's modulus of the same seven samples. It is clear that strong wave velocity dispersion in the experiment is due to the dynamic wavelength‐scale effects caused by scattering.
Dual‐frequency radio sounding of the solar corona during the 1995 conjunction of the Ulysses spacecraft
Authors: Pätzold M. , Bird M. K. , Edenhofer P. , Asmar S. W. , McElrath T. P.
Published: February 2004

The Ulysses Solar Corona Experiment was performed during the spacecraft's superior solar conjunction from 22 February to 14 March 1995, shortly before perihelion and the transit through the ecliptic plane. The high inclination of the Ulysses orbit resulted in an unusual occultation geometry for coronal radio sounding with the spacecraft's dual‐frequency downlink signals. Viewed from Earth, the virtual position of Ulysses on the plane of the sky moved diagonally through the southwest quadrant of the corona from the solar South Pole to the heliographic equator. The impact parameter of the ray path (solar offset) varied from 32 solar radii (R⊙) at the beginning and end of the experiment down to a minimum of 21.4 R⊙ at 45°S. The total electron content of the inner heliosphere, computed from measurements of the dual‐frequency ranging propagation delays, is presented as a function of latitude and solar offset. The observations are compared with the coronal structure inferred from synoptic magnetic source surface maps. An increase in electron content by a factor of two is recorded from the center of the southern coronal hole at the pole, to the equator, the northernmost extension of the hole at the time of the observation. A streamer belt, identified by an abrupt rise in electron content, rotated into the radio ray path at southern heliographic latitudes between 16° and 21°.
The chlorine budget of the lower polar stratosphere: Upper limits on ClO, and Implications of new Cl2O2 photolysis cross sections
Authors: Shindell D. T. , de Zafra R. L.
Published: February 2004

Chlorine catalytic chemistry, which destroys ozone while cycling chlorine between Cl, ClO, and Cl2O2, is the primary cause of the springtime Antarctic ozone hole. We have calculated the concentrations of Cl2O2 which are in equilibrium with midday ground‐based, aircraft, and satellite observations of ClO in the Antarctic spring lower stratosphere. Two significant conclusions are presented here: (1) Using the JPL 94 recommended rates and photolysis cross sections, more than ∼2.0 ppbv ClO in the polar lower stratosphere causes inferred total active chlorine to exceed the total chlorine budget. This limit is smaller than some reported ClO measurements. (2) Using smaller cross sections recently measured by Huder and DeMore [1995], the amount of Cl2O2 in midday equilibrium with measured ClO is approximately doubled. Activated chlorine inferred from many measurements then exceeds total chlorine in the lower stratosphere, suggesting these cross sections may be too small.
Remotely triggered seismicity inferred from Taiwan Regional Catalog
Authors: Beresnev Igor A. , Wen Kuo‐Liang
Published: February 2004

The June 1992 Landers (California) earthquake triggered an increase in earthquake activity at distances up to 1250 km. It posed the question whether the remote triggering was really widespread in nature. To check this, we use the regional catalog of seismicity in Taiwan where twelve large 6.0 ≤ MD ≤ 6.5 seismic events took place over the last twenty years. We calculate the number of MD ≥ 2.0 earthquakes, as well as the number of MD ≥ 4.5 earthquakes, starting 15 days prior to and ending 15 days after each MD ≥ 6.0 event. The small‐magnitude activity does not respond to the occurrence of a very large event. However, in 9 out of 12 cases, more MD ≥ 4.5 earthquakes occurred after a large event than in the same time interval before. The number of additional events is proportional to the size of the triggering earthquake. Thus, these extra events are possibly remotely triggered.
Changes in the Earth inertia tensor: The role of boundary conditions at the core‐mantle interface
Authors: Spada Giorgio
Published: February 2004

In the early seventies, a broad scientific debate began upon the nature of the conditions to be applied at the core‐mantle interface in order to study the static deformations of the Earth. This controversy, which first arose in the context of post‐seismic deformations, has also affected later investigations on inertia perturbations driven by surface or internal density contrasts. The aim of this communication is not to readdress the long‐standing question about the appropriate set of boundary conditions to be imposed at the core‐mantle boundary, but rather to show how the choice of these conditions may affect the calculation of inertia changes. When applied to glacially‐induced inertia perturbations, our results demonstrate that the pitfall of the core‐mantle boundary conditions has been acting for a long time after the scientific discussion mentioned above came to an end.
A reappraisal of seafloor spreading lineations in the Gulf of California: Implications for the transfer of Baja California to the Pacific Plate and estimates of Pacific‐North America Motion
Authors: DeMets Charles
Published: February 2004

An analysis of seafloor spreading lineations in the southern Gulf of California demonstrates that divergence of the Baja peninsula from North America since 3.6 Ma has been significantly slower than Pacific‐North America (PA‐NA) motion estimated solely from closures of global plate circuits. This discrepancy remains unchanged or increases with modifications to the plate circuits and kinematic data used to predict PA‐NA motion, suggesting that it arises from the probably‐incorrect assumption that Baja California has been rigidly coupled to the Pacific plate since 3.6 Ma. A ∼15% increase in seafloor spreading rates in the southern Gulf after ∼1 Ma could have been caused by a transfer of motion along faults west of Baja California to the modern‐day plate boundary, or alternatively could indicate a recent speedup in PA‐NA motion. Both interpretations imply that PA‐NA motion is now 4±2 mm yr−1 (2σ) faster than predicted by the 3.16‐Myr‐average NUVEL‐1A model.
Improved stability of a deeply anchored geodetic monument for deformation monitoring
Authors: Langbein John , Wyatt Frank , Johnson Hadley , Hamann Duane , Zimmer Paul
Published: February 2004

A test of two different monument designs used in geodetic networks shows that monuments installed to depths of 5 to 10 meters, and laterally braced, exhibit less environmentally caused displacement than those installed to 2 meters depth. At Parkfield, California, we have been monitoring the lengths of 17 baselines over the past decade with a 2 to 3 day interval between measurements using a two‐color geodimeter with a nominal precision of 0.5 mm over 5 km long baselines. Significant variations are observed on many of these baselines which appear to be related to the seasonally occurring rainfall, with the larger variations approaching 10 mm over the past decade. To test whether we could improve upon the measurements on some of the more susceptible lines, at two sites we installed new monuments within about 30 meters of the original monuments. After 1.5 years of measurements it is evident that the new monuments significantly attenuate the seasonal displacements to less than 1 mm. The use of deeply anchored monuments should improve the ability of fault‐scale geodetic monitoring arrays to detect small tectonic displacements.
Direct inversion of potential fields from an uneven track with application to the Mid‐Atlantic Ridge
Authors: Hussenoeder Stefan A. , Tivey Maurice A. , Schouten Hans
Published: February 2004

Current methods of potential field inversion require measurements to be reduced onto a level plane, resulting in a loss of resolution. This is especially true for draped surveys in areas of extreme topography. We examine a method that bypasses this limiting step by making use of an approximately equivalent geometry from which data are directly inverted. Corrections are applied to an initial solution to account for errors generated by the transformation of geometries. A numerical model and an example data set are used to explore this method's benefits and drawbacks in relation to the conventional approach of data reduction onto a level plane prior to inversion. We show that this direct inversion method is particularly better than the conventional approach at resolving fine‐scale features, such as the narrow zone of crustal emplacement at the Mid‐Atlantic Ridge and adjacent areas of tectonic disruption and magnetic source alteration.
Recurring transitional geomagnetic field geometries: Evidence from sediments and lavas
Authors: Clement B. M. , Rodda P. , Smith E. , Sierra L.
Published: February 2004

Records of the geomagnetic polarity transitions bounding the Nunivak Subchron have been obtained from the Suva Marl, Fiji (18.2°S, 178.5°E). The transitional virtual geomagnetic pole (VGP) positions cluster near southern South America and are remarkably similar to the VGP paths for these same reversals obtained from Sicily. The lower Nunivak VGP path and relative intensity record are also very similar to a lower Pliocene reverse to normal (R to N) polarity transition recorded in lavas on Kauai. The similarities in these transition records from both lava and sediment records suggests that an inclined near‐dipolar state of the transitional field recurred in these back to back reversals.
Lidar observations of stratospheric ozone and aerosol above the Canadian High Arctic during the 1994–95 winter
Authors: Donovan D. P. , Bird J. C. , Whiteway J. A. , Duck T. J. , Pal S. R. , Carswell A. I.
Published: February 2004

This letter reports on lidar observations of arctic stratospheric ozone and aerosol made from late December 1994 to mid‐March 1995. These observations were conducted at Eureka (80°N,86.42°W) in the Canadian arctic. Based on NMC potential vorticity data and aerosol observations, the lower stratosphere over Eureka was seen to be clearly within the Polar Vortex for most of the observation period. The intravortex observations showed that in the stratosphere below the 500 K potential temperature level average ozone mixing ratios decreased on the order of 15% from early January to mid‐February with an additional 15% decrease observed from mid February to mid‐March. These trends are consistent with the Upper Atmospheric Research Satellite (UARS) Microwave Limb Sounder (MLS) measurements of ozone made during the same time periods.
The lidar dark band: An oddity of the radar bright band analogy
Authors: Sassen Kenneth , Chen Tiehan
Published: February 2004

The properties of the melting layer in rain showers were studied using polarization lidar and W‐band Doppler radar systems, and supporting research aircraft. The changes in hydrometeor scattering behavior at wavelengths ranging from 0.532 µm to 3.2 mm during the snowflake‐to‐raindrop transition generally conform with the expected features of the bright band phenomenon, except that a narrow lidar returned signal minimum, or dark band, was observed ∼750 m below the freezing level. This new feature is found where Doppler velocity and depolarization data indicate raindrops, and, ironically, also occurs at the position of the W‐band radar reflectivity bright band. Drawing from laboratory laser scattering studies and Mie theory, we conclude that the particles responsible for the lidar dark band are inhomogeneous ice‐containing raindrops formed by the structural collapse of severely melted snowflakes.
Entry of galactic electrons into the high latitude heliosphere
Authors: Simnett G. M. , Tappin S. J. , Roelof E. C.
Published: February 2004

Evidence is presented for the first detection of galactic cosmic ray electrons in the general energy range 1 to 20 MeV by the HI‐SCALE instrument on Ulysses as it passed over the solar poles. The electrons manifest themselves by a strong latitude dependence of the background counting rates in the HI‐SCALE detectors, in excess of that predicted from the COSPIN measurements. The majority of the detected electrons have penetrated the housing around the detectors; the apparent spectrum of this excess is completely inconsistent with penetrating ions, whatever their spectrum. We have compared the inferred electron flux with an extrapolation of the cosmic ray electron spectrum measured in the ecliptic plane and inferred from radio astronomy at ≳1 GeV and conclude that the galactic spectrum does not continue as a power law down to a few MeV.
A few considerations for ascribing statistical significance to earthquake predictions
Authors: Stark P. B.
Published: February 2004

There are many potential pitfalls in assigning statistical significance to “successful” earthquake predictions, including sensitivity to the stochastic model for earthquake occurrence, dependence among the parameters used to specify an earthquake, and the stochastic alternative model for the predictions. There is no simple resolution to these difficulties, but it is clear that assuming earthquake location and size variables are independent can lead to the erroneous impression that predictions are statistically significant when they are not, and that assuming that main shocks follow a Poisson process in time (and space) can make chance predictions appear statistically significant, and can make sound predictions appear statistically insignificant. It is possible to avoid assuming any probability distribution for the occurrence of earthquakes, treating the seismicity history as fixed (conditioning on the observed seismicity) and testing the performance of the prediction algorithm against various random predictors; this “conditional” approach seems preferable.
Cosmic ray modulation by expanding, high‐latitude streams
Authors: Quenby J. J. , Drolias B. , Keppler E. , Reuss M. K. , Blake J. B.
Published: February 2004

As ‘Ulysses’ moved to latitudes above 45°, the regular, recurring series of mid‐latitude high‐speed streams is no longer observed out to 4 AU. However, the associated, near‐relativistic particle modulation persists to at least 70°. We explain this remote shadowing as due to the spread in latitude of the fast streams beyond the ‘Ulysses’ trajectory and show that an estimate of the particle diffusion coefficient within the stream, based on magnetometer data, yields sufficient modulation to make the model plausible.
Anomalous cosmic ray oxygen and neon (∼2.4 MeV/nucl) at high southern heliolatitudes
Authors: Lanzerotti L. J. , Maclennan C. G.
Published: February 2004

We report measurements of the anomalous oxygen and neon as measured with the HI‐SCALE instrument on Ulysses at high southern heliolatitudes. Using both energy spectral features and C/O ratios, 2.0–2.8 MeV/nucl anomalous O is not distinguishable below a latitude of ∼40°S. The heliolatitude gradient is found to be +0.06±0.50% / degree for the heliolatitude range 40°S to 80°S for an assumed radial gradient of 15% per AU. For the assumption of no radial gradient, the heliolatitude gradient is 0.39±0.42%/degree. The O flux at this energy is ∼2 × 10−8/(cm² sr s MeV/nucl); the Ne flux is ∼5 × 10−9/(cm² sr s MeV/nucl).
Anisotropy in inner core attenuation: A new type of data to constrain the nature of the solid core
Authors: Souriau Annie , Romanowicz Barbara
Published: February 2004

During the last decade, the presence of velocity anisotropy inside the inner core, with a fast axis parallel to the Earth's rotation axis, has been well established. The quantitative analysis of the amplitudes of waves which sample a particular region of the inner core, under Africa, but exhibit various orientations allows us to document and characterize the presence of anisotropy in attenuation. The analysis is based on a comparison of both amplitudes and travel times of the PKP(DF) wave, which samples the inner core, and the PKP(BC) wave, which has nearly the same path but bottoms inside the liquid core. The data reveal that the direction of strong attenuation correlates with that of fast velocity. When referred to the same epicentral distance and focal depth, the PKP(DF)/PKP(BC) amplitude ratio are about five times lower for paths tilted by 25° with respect to the Earth rotation axis, than for nearly equatorial paths. A clear negative correlation is observed between travel time and amplitude residuals, when the angle to Earth rotation axis varies. This first quantitative analysis, combined with experimental results on oriented crystals and mushy media, may bring important constraints on the mechanism responsible for anisotropy in the inner core.
Three‐stage rupture process of the 28 December 1994 Sanriku‐Oki Earthquake
Authors: Sato Tamao , Imanishi Kazutoshi , Kosuga Masahiro
Published: February 2004

We investigated the rupture process of the 28 December 1994 Sanriku‐Oki earthquake (Mw = 7.7) using broadband seismograms recorded at local distances. The earthquake rupture nucleated at the eastern end of the aftershock area. As it propagated towards the west, a major subevent occurred near the center of the aftershock area about 26 s after the initial rupture, releasing most of the seismic energy of this earthquake. About 24 s later, another subevent followed at the western end of the aftershock area, emitting large high‐frequency waves. The whole rupture time is about 55 sec. The three‐stage rupture process is very similar to the earlier‐stage rupture process of the 1968 Tokachi‐Oki earthquake (Mw = 8.2). The difference is that the rupture of the Tokachi‐Oki earthquake further propagated towards the north in the following stage instead of terminating at the western end. The occurrence of the Sanriku‐Oki earthquake is critical to the validity of the characteristic earthquake so far believed to exist in this part of the plate boundary.
High velocity zone beneath the Southern Tibetan Plateau from P‐wave differential travel‐time data
Authors: Zhou Ran , Grand Stephen P. , Tajima Fumiko , Ding Xiao‐Yang
Published: February 2004

We analyzed P‐wave travel‐time data of earthquakes along a north‐south vertical cross section in the central Tibetan plateau to search for high velocity zones related to downwellings in the upper mantle. Differential travel‐time residuals of an event in southern Tibet vs. north central and Himalayan events show relatively fast arrivals at stations in the northwest ‐ southeast direction. Results of numerical simulation with simple velocity anomaly models suggest that a narrow, nearly vertical, high velocity zone extending to at least 400 km beneath the southern plateau can account for the observed fast arrivals. This high velocity zone may result from cold downwellings predicted by the delamination model for continental convergence.