bluuebunny/crossref_metadata_2025 huggingface dataset:
Methyl halides from Antarctic macroalgae
Authors: Laturnus Frank , Adams Freddy C. , Wiencke Christian
Published: February 2004

Various species of Antarctic macroalgae have been found to produce and release methyl halides at mean values of 34.7 pmol g−1 waw (wet algal weight) d−1 (methyl chloride), 1.98 pmol g−1 waw d−1 (methyl bromide) and 1.68 pmol g−1 waw d−1 (methyl iodide) into the seawater. Compared to temperate macroalgae, Antarctic macroalgae showed an approximately 10 to 50‐fold lower release of these compounds. Due to the lower release and the restriction to the Antarctic region, Antarctic macroalgae may play a minor role in the global production of methyl halide, but have to be considered as biogenic contributors for methyl halides to the halocarbon budget in the Antarctic environment. Additional, investigated bromoform release, brominating activity and dimethylsulfoniopropionate (DMSP) concentrations detected in Antarctic macroalgae showed no correlation with methyl halides release rates. Therefore, a formation different to suggested enzymic pathways or origin from DMSP reacting with halides can be assumed.
Dual wavelength lidar observation of tropical high‐altitude cirrus clouds during the ALBATROSS 1996 Campaign
Authors: Beyerle G. , Schäfer H.‐J. , Neuber R. , Schrems O. , McDermid I. S.
Published: February 2004

Dual wavelength aerosol lidar observations of tropical high‐altitude cirrus clouds were performed during the ALBATROSS 1996 campaign aboard the research vessel “POLARSTERN” on the Atlantic ocean in October–November 1996. On the basis of 57 hours of night‐time observations between 23.5°N and 23.5°S we find in 72% of the altitude profiles indications of the presence of cirrus cloud layers. This percentage drops to 32% at subtropical latitudes (23.5°–30°) based on 15 hours of data. About one‐half of the subtropical and tropical cirrus layers are subvisual with an optical depth of less than 0.03 at a wavelength of 532 nm. In general the clouds exhibit high spatial and temporal variability on scales of a few tens of meters vertically and a few hundred meters horizontally. No clouds are observed above the tropopause. An abrupt change in the relation between the color ratios of the parallel and perpendicular backscatter coefficients at about 240 K is interpreted in terms of changes of particle shape and/or size distribution. At temperatures between 195 and 255 K only a small fraction of the observations are consistent with the presence of small particles with dimensions of less than 0.1 µm.
Saharan dust: Clay ratio as a relevant tracer to assess the origin of soil‐derived aerosols
Authors: Caquineau Sandrine , Gaudichet Annie , Gomes Laurent , Magonthier Marie‐Claude , Chatenet Bernadette
Published: February 2004

The aim of this study is to find a tracer allowing retrieval of the regional origin of mineral dust for Saharan aerosols transported over the North Atlantic Ocean. Because of physical and chemical fractionation processes occurring at the soil‐atmosphere interface and during the atmospheric transport of dust, clay mineral species seem to be the best candidate. This study shows that the ratio between relative abundance of illite and kaolinite (I/K ratio) is the parameter that is the most sensitive to the regional origin of Saharan dust collected on Sal Island (Cape Verde). By comparing the I/K ratio measured in dust emitted from the same Saharan source and collected along its transport both on Sal Island and Barbados (Caribbean Sea), we show that this ratio seems to remain unchanged after long‐range transport.
Spatial structure and gradients of ion beams observed by FAST
Authors: McFadden J. P. , Carlson C. W. , Ergun R. E. , Mozer F. S. , Temerin M. , Peria W. , Klumpar D. M. , Shelley E. G. , Peterson W. K. , Moebius E. , Kistler L. , Elphic R. , Strangeway R. , Cattell C. , Pfaff R.
Published: February 2004

High time resolution measurements of ion distributions by the FAST satellite have revealed kilometer scale spatial structure in the low altitude auroral acceleration region. The low altitude edge of the acceleration region appears to contain fingers of potential that extend hundreds of kilometers along B but are only a few to tens of kilometers wide. These fingers of potential do not appear to be strongly correlated with the local current or total potential drop. Gradients in the ion beam energy are found to be consistent with the electric field signatures expected in the quasi‐static potential drop model of auroral acceleration. Typical ion beams show gradients of 0.5–1.0 keV/km, with some events as large a 3 keV/km. Integrations of the electric field along the space‐craft velocity are used to calculate parallel potential below FAST and are found to agree well with the ion beam energy for most events. One event is shown where an apparent temporal change in the auroral configuration occurs at the edge of the ion beam producing a disagreement between the beam energy and inferred potential.
Location of Love‐to‐Rayleigh conversion due to lateral heterogeneity or azimuthal anisotropy in the upper mantle
Authors: Kobayashi Reiji , Nakanishi Ichiro
Published: February 2004

Love waves can be converted to Rayleigh waves, which are sometimes called quasi‐Love waves, in laterally heterogeneous or azimuthally anisotropic mantle. A local four‐station network of broadband seismometers in Hokkaido, Japan, records the quasi‐Love waves from the earthquakes located in and around Oregon and California, USA. We infer that these quasi‐Love waves are generated by lateral heterogeneity or azimuthal anisotropy beneath the Aleutian or Kuril trench. We attempt to locate the Love‐to‐Rayleigh conversion areas for the August 17, 1991, off coast of northern California earthquake by using the group velocities of the observed surface waves. The locations of the Love‐to‐Rayleigh conversion areas concentrate near the Kuril trench. The concentration is the most clear at a low frequency of 8 mHz. This successful location of the conversion areas provides us with an important constraint on the generation of the quasi‐Love waves.
Configuration entropy of fractal landscapes
Authors: Rodríguez‐Iturbe Ignacio , D'Odorico Paolo , Rinaldo Andrea
Published: February 2004

Hydrologic fields like rainfall and river basin topography require the quantitative description of their spatial arrangements. These arrangements can be effectively characterized by the spatial structure of the 2‐dimensional images obtained through the intersection with horizontal planes at different heights. We show that configurational entropy clearly displays fundamental aspects of the responsible dynamics. Topography and rainfall depth over a region are found to lack any characteristic length not only in the size of their features but also in their positional arrangements. The spatial arrangement of two‐dimensional images is found to be an effective way to characterize fractal landscapes and the configurational entropy of these arrangements imposes demanding conditions for models attempting to represent these fields.
DC‐8‐based observations of aircraft CO, CH4, N2O, and H2O(g) emission indices during SUCCESS
Authors: Vay S. A. , Anderson B. E. , Sachse G. W. , Collins J. E. , Podolske J. R. , Twohy C. H. , Gandrud B. , Chan K. R. , Baughcum S. L. , Wallio H. A.
Published: February 2004

We report the first measurements of CO, CH4, N2O, CO2, and H2O(g) in the exhaust trails of T‐39, B‐757, and DC‐8 aircraft at cruise conditions. Emission indices (EI) derived from these in‐situ measurements are presented. Results are in agreement with ground‐based tests indicating aircraft act as a net sink for CH4 and recent airborne in‐situ measurements that N2O is not an important exhaust constituent. Condensation of H2O(g) on exhaust particles resulted in EI(H2O(g)) values less than those expected from the combustion of fuel alone. Observed apparent negative EI(H2O(g)) values suggest that aircraft aerosol emissions, under unique atmospheric conditions, seed cloud formation and lead to dehydration of the exhaust‐influenced air parcel. Such conditions may induce the formation of cirrus clouds from persistent contrails. Comparisons with the Boeing EMIT Code show measurement‐derived CO emission index values consistent with model evaluations.
FAST observations of electron distributions within AKR source regions
Authors: Delory G. T. , Ergun R. E. , Carlson C. W. , Muschietti L. , Chaston C. C. , Peria W. , McFadden J. P. , Strangeway R.
Published: February 2004

Observations of high‐time resolution 3‐D electron distributions within the source regions of Auroral Kilometric Radiation (AKR) are reported. In general, the electron data display a broad plateau over a wide range of pitch angles indicating that these distributions have been rapidly stabilized by AKR wave growth. The source of the electron instability appears to come from several features in the distribution, including an isotropic beam feature and its mirroring components, occasional electrons in the “trapped” region, as well as steep gradients present in the atmospheric loss cone. Taken together these features may provide a nearly continuous region of ∂f/∂v⟂ which could contribute to the relativistic cyclotron maser instability. Computer simulations of the evolution of the electron distribution which assume plasma conditions similar to the parameters measured by FAST show similar results to the observed electron distributions. The FAST observations also show that relativistic corrections to the AKR dispersion relation may enable a small k|| mode with a resonance condition that is able to take maximum advantage of the initial instability in the mono‐energetic electron distributions within the auroral acceleration regions.
Calibration of a superconducting gravimeter by comparison with an absolute gravimeter FG5 in Boulder
Authors: Francis O. , Niebauer T. M. , Sasagawa G. , Klopping F. , Gschwind J.
Published: February 2004

This paper reports the results of a calibration of a superconducting gravimeter using simultaneous measurements of Earth tides with an absolute gravimeter. Nine consecutive days of observations were made with both the C024 superconducting gravimeter and the FG5‐202 absolute gravimeter at the NOAA Table Mountain Gravity Observatory near Boulder, Colorado. The precision of the calibration factor is better than 0.1%. The calibration factor obtained in this fashion agrees well with that obtained from a moving platform. This experiment provides a noise estimate for both the superconducting and absolute gravimeter. In addition, the local air pressure admittances of both instruments compare well with a value close to −0.35 µGal/mbar.
Timing accuracy for the simple planar propagation of magnetic field structures in the solar wind
Authors: Collier Michael R. , Slavin J. A. , Lepping R. P. , Szabo A. , Ogilvie K.
Published: February 2004

Results from a correlation analysis of Wind and IMP 8 magnetometer data for a total of 543 two hour periods covering Jan.–Jul. 1995 were analyzed to determine that: (1) the timing accuracy Δτ for advecting solar wind magnetic field structures goes as (dper/dpar) · τcon where dpar is the spacecraft separation along the Sun‐Earth line, dper is the transverse separation, and τcon is the predicted convection lag time, (2) “good” correlation time periods (peak correlation coefficient >0.80) are about twice as likely at solar maximum than at solar minimum, (3) geometry affects timing accuracy more than any propagation of features with respect to the solar wind, and (4) there is a “high” probability (greater than predicted by a Gaussian distribution) of “very bad” (|dparΔτ/dperτcon| >3) timing agreement due to the long tail on the probability distribution.
Shear‐wave splitting at central Tien Shan: Evidence for rapid variation of anisotropic patterns
Authors: Wolfe Cecily J. , Vernon Frank L.
Published: February 2004

At active collisional belts, the fast polarization axis of shear‐wave splitting is generally aligned parallel to the strike of the belt, which has been proposed to indicate mantle strain that is coherent with crustal deformation. A notable exception is central Tien Shan, where anomalous patterns of splitting have previously been observed. We here analyze shear‐wave splitting of SKS phases across north central Tien Shan using digital data from the Kyrgyzstan Broadband Seismic Network (KNET). We find a pattern of short‐wavelength anisotropic heterogeneity that supports complex mantle flow due to small‐scale convection. The along‐strike variations in mantle structure contrast with the coherent pattern of crustal shortening, and indicate that mantle flow is not directly coupled to crustal deformation in this region.
Long base‐line measurements of short‐period mesospheric gravity waves during the SEEK Campaign
Authors: Taylor M. J. , Seo S. H. , Nakamura T. , Tsuda T. , Fukunishi H. , Takahashi Y.
Published: February 2004

Simultaneous observations of short‐period (<1 hour) mesospheric gravity waves were made over an extended base‐line (∼660 km) from two sites in Japan (at Shigaraki and Yamagawa) during the SEEK (Sporadic‐E Experiment over Kyushu) campaign, 9–23 August, 1996. Coincident image data obtained on four nights provided a rare opportunity to investigate the horizontal spatial extent and propagation characteristics of the waves in detail. Surprisingly, out of a total of 12 events observed from Shigaraki and 10 from Yamagawa at most only three exhibited similar propagation characteristics at each site. The majority of the wave displays (∼70–75%) had quite dissimilar characteristics suggesting a preponderance for localized wave motions of limited lifetimes and geographical extent. A marked preference for wave progression towards the N‐NE indicates that the gravity waves imaged in the near infrared OH and OI (557.7 nm) nightglow emissions were probably not directly associated with the observed E‐region irregularities.
Direct observation of large, quasi‐static, parallel electric fields in the auroral acceleration region
Authors: Mozer F. S. , Kletzing C. A.
Published: February 2004

The three‐axis electric field experiment on the Polar satellite provides direct observations of electric field components parallel and perpendicular to the local magnetic field with no arbitrary adjustment parameters. Approximately 750 perigee passes through each of the two southern auroral zones at a geocentric altitude of about two Earth radii have been computer‐searched for parallel electric fields whose eight point (0.2 or 0.4 second) average exceeded 100 mV/m. After elimination of spurious events due to shadowing, saturation, and ten other effects, four events containing parallel fields of 200–300 mV/m, remain. These four events all occur in upward field aligned current regions, their parallel electric fields are all positive such that . >0, and they occur at boundaries between regions of active and quiet perpendicular electric fields. Up‐going ion beams are observed in the active field regions, and the plasma density is higher in the quiet field regions than in the adjacent active field regions. These boundaries are interpreted in terms of model equipotentials, some of which are below the spacecraft in the large field regions and all of which are above the spacecraft in the quiet field regions. In this model, the expected location of large parallel electric fields is where they are observed. That the potential difference measured by the electric field instrument along the vehicle trajectory and the kinetic energy of the up‐going ions are equal lends further credence to the data and its interpretation.
Height comparison of midlatitude E region field‐aligned irregularities and sporadic E Layer
Authors: Ogawa Tadahiko , Sekito Norihide , Nozaki Kenrou , Yamamoto Mamoru
Published: February 2004

We present for the first time detailed comparison of heights of MU radar field‐aligned echoes and sporadic E (Es) layer by applying an FM‐CW sounding technique for observing Es virtual height with high spatial (750 m) and time (one minute) resolutions. The production of typical, discrete quasi‐periodic (QP) radar echoes appearing after sunset is closely related to the oscillation of Es height, supporting a theory of the QP echo generation. No Es height oscillations, however, were observed for the QP echoes appearing around midnight. Continuous radar echoes appearing after sunrise are located at 90–100 km heights that are lower than the Es heights (≥100 km), suggesting that a new mechanism other than the gradient‐drift plasma instability is necessary for producing these morning continuous echoes.
The Arctic oscillation signature in the wintertime geopotential height and temperature fields
Authors: Thompson David W. J. , Wallace John M.
Published: February 2004

The leading empirical orthogonal function of the wintertime sea‐level pressure field is more strongly coupled to surface air temperature fluctuations over the Eurasian continent than the North Atlantic Oscillation (NAO). It resembles the NAO in many respects; but its primary center of action covers more of the Arctic, giving it a more zonally symmetric appearance. Coupled to strong fluctuations at the 50‐hPa level on the intraseasonal, interannual, and interdecadal time scales, this “Arctic Oscillation” (AO) can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft. It is proposed that the zonally asymmetric surface air temperature and mid‐tropospheric circulation anomalies observed in association with the AO may be secondary baroclinic features induced by the land‐sea contrasts. The same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature, sea‐level pressure, and 50‐hPa height over the past 30 years: parts of Eurasia have warmed by as much as several K, sea‐level pressure over parts of the Arctic has fallen by 4 hPa, and the core of the lower stratospheric polar vortex has cooled by several K. These trends can be interpreted as the development of a systematic bias in one of the atmosphere's dominant, naturally occurring modes of variability.
The SEEK Chemical Release Experiment: Observed neutral wind profile in a region of sporadic E
Authors: Larsen M. F. , Fukao S. , Yamamoto M. , Tsunoda R. , Igarashi K. , Ono T.
Published: February 2004

Wind measurements made with the chemical release technique during a sporadic E layer event are presented. The data were obtained as part of the Sporadic E Experiment over Kyushu (SEEK) sounding rocket campaign. The winds show a strong maximum in the lower E region approaching 150 m s−1 near 105‐km altitude and a large shear below the maximum. The large shear was within a few kilometers altitude of the peak in the electron densities measured on the downleg of the rocket trajectory. Calculations of the Richardson numbers for the wind profile show that the altitude range near the layer was highly unstable.
Geosynchronous spacecraft charging in January 1997
Authors: Lanzerotti L. J. , LaFleur K. , Maclennan C. G. , Maurer D. W.
Published: February 2004

Data are presented from two charge plate sensors on the Loral Telstar4 geosynchronous communications spacecraft during an interplanetary magnetic cloud event that intersected Earth on January 10, 1997. The energy input into Earth's magnetosphere from the solar wind during the event produced enhanced plasma populations that caused the charge plates to attain values more than a factor of two larger than at any other time during the month. The time variation of the charging during the event is found to be similar to the variation in conjugate area ionospheric current systems measured by magnetometers near the footpoints of the magnetic flux tube that passes through the spacecraft.
Potential waves for relativistic electron scattering and stochastic acceleration during magnetic storms
Authors: Horne Richard B. , Thorne Richard M.
Published: February 2004

The possibility of electron stochastic energization to relativisitic energies (≥ 1 MeV) via resonant wave‐particle interactions during a magnetic storm is explored. The minimum electron energy Emin for cyclotron resonant interaction with various electromagnetic waves is calculated for conditions representative of storm‐times. Since Emin > 1 MeV for resonance with L‐mode ion cyclotron waves, intense stormtime EMIC waves could contribute to relativistic electron loss, but not acceleration. Inside the plasmapause whistler mode waves, and highly oblique magnetosonic waves near the lower hybrid frequency, can resonate with electrons over the important energy range from ∼ 100 keV to ∼ 1 MeV. In low density regions outside the plasmapause, the whistler, RX, LO and Z modes can resonate with electrons over a similar energy range. These waves have the potential to contribute to the stochastic acceleration of electrons up to relativistic energies during magnetic storms.
Comparison of E‐region electric fields observed with a sounding rocket and a Doppler radar in the Seek Campaign
Authors: Yamamoto Mamoru , Itsuki Tetsuya , Kishimoto Takeshi , Tsunoda Roland T. , Pfaff Robert F. , Fukao Shoichiro
Published: February 2004

This paper describes results from simultaneous measurements of mid‐latitude irregularities by a sounding rocket and a Doppler radar. The experiment was conducted on August 26, 1996 as part of the SEEK (Sporadic‐E Experiment over Kyushu) campaign in Japan. Electric field observed with a double‐probe sensor on the rocket showed very large fluctuations of ±10 mV/m where irregularity echoes were quite intense. Doppler velocities observed with the radar agreed well with the electric fields. We estimated growth rates of the gradient‐drift instability, which showed positive values around the major sporadic‐E layer. It was found that, within intense irregularity region with quasi‐periodic structures, there were large polarization electric fields that was likely to be associated with spatial structure of the sporadic‐E layer.
The magnetospheric driver of subauroral ion drifts
Authors: De Keyser J. , Roth M. , Lemaire J.
Published: February 2004

Subauroral ion drifts (SAID) are narrow layers of intense westward ionospheric flow observed during substorms. We present numerical simulations showing that the combined effect of thermo‐electric and convection electric fields in a magnetospheric current sheet—when mapped down to the ionosphere—can account for the westward direction of the ion drift, the width and intensity of the drift speed peak, and the lifetime of SAID. The model can also explain why SAID occur mainly in the pre‐midnight sector.
Limiting relations between soil moisture and soil texture with implications for measured, modeled and remotely sensed estimates
Authors: Salvucci G. D.
Published: February 2004

The relation between near surface soil moisture (s) and the similar media scaling factor (α) is shown to follow a power law in four limiting cases: long time flux limited infiltration, short time flux limited infiltration into dry soil, long time soil limited evaporation, and long time soil limited transpiration. The exponents of these relations are derived from dimensional analysis of approximate solutions to the Richards equation. Numerical simulations of moisture fluxes indicate that a power law also describes the relation between s and α at intermediate times, with exponents bounded by the short time flux limited infiltration and the long time transpiration solutions. The relative magnitudes of the derived exponents imply an increasing coefficient of variation of soil moisture during drydowns, consistent with observations from field experiments.
Estimates of the Earth's inner core grain size
Authors: Bergman Michael I.
Published: February 2004

Estimates of the Earth's inner core grain size range from 1200 km to 5 mm. A review of the experimental data shows that the single crystal elastic anisotropy of hexagonal closest‐packed (hcp) titanium and zirconium, thought to be good analogs for high pressure hcp iron, increases continuously with temperature, from 4–5% at 4 K to about 11% at the body‐centered cubic (bcc) transition. Thus, in order to match the seismic elastic anisotropy of about 4%, the inner core cannot behave elastically as a single crystal. Several lines of evidence suggest a 5 mm grain size is unrealistically small. They include that core solidification promotes forming non‐equiaxed grains extrapolated to have a smallest dimension of hundreds of meters, that should deformation result in dynamic recrystallization the minimum steady state grain size is likely to be .1 to 10 meters for geophysically plausible stresses, and that iron meteorites over a meter in extent have typically cooled from single crystals. By assuming the observed seismic attenuation anisotropy is due to scattering off cylindrically radial columnar grain boundaries, the shorter grain dimension is again estimated to be hundreds of meters.
Moment tensor analysis of the Central Italy Earthquake Sequence of September–October 1997
Authors: Ekström Göran , Morelli Andrea , Boschi Enzo , Dziewonski Adam M.
Published: February 2004

The larger earthquakes in the Umbria‐Marche (central Italy) seismic sequence of September–October 1997 are analyzed using long‐period seismograms from the Mediterranean seismographic network (MedNet) and additional data from the global seismographic network (GSN). We modify the Harvard centroid‐moment tensor (CMT) algorithm to allow moment tensor inversion of long‐period waveforms, primarily Rayleigh and Love waves, for small earthquakes at local to regional distances (Δ<15°). For the three largest earthquakes (MW>5.5) in the sequence, moment tensors have previously been determined using teleseismic waveforms and standard methods of analysis; our results agree well with those of earlier studies. We determine additional moment tensors for the largest foreshock and 10 aftershocks with MW>4.2. The earthquakes are characterized by normal faulting mechanisms, with a NE‐SW tension axis, and the presumed fault plane dips towards the SW. Only one of the fourteen events studied has a different faulting geometry, indicating instead right‐lateral strike‐slip faulting on a plane oriented approximately E‐W, or left‐lateral faulting on a plane oriented N‐S. The September 26 mainshock (09:40 UT) accounts for only approximately ∼50% of the total moment release in the sequence.
Monitoring SO2 emission at the Soufriere Hills Volcano: Implications for changes in eruptive conditions
Authors: Young S. R. , Francis P. W. , Barclay J. , Casadevall T. J. , Gardner C. A. , Darroux B. , Davies M. A. , Delmelle P. , Norton G. E. , Maciejewski A. J. H. , Oppenheimer C. M. M. , Stix J. , Watson I. M.
Published: February 2004

Correlation spectrometer measurements of sulfur dioxide (SO2) emission rates during the current eruption of the Soufriere Hills volcano, Montserrat, have contributed towards identifying different phases of volcanic activity. SO2 emission rate has increased from <200 tonnes per day (td−1; <2.3 kgs−1) in the early stages of dome growth to >550 td−1 (>6.4 kgs−1) after July 1996, with the uncertainty associated with any individual measurement ca. 30%. Significantly enhanced SO2 emission rates have been identified in association with early phreatic eruptions (800 td−1 (9.3 kgs−1)) and episodes of vigorous dome collapse and pyroclastic flow generation (900 to 1500 td−1 (10.4 to 17.4 kgs−1)). SO2 emission rate has proved a useful proxy measurement for magma production rate. Observed SO2 emission rates are significantly higher than those inferred from analyses of glass inclusions in phenocrysts, implying the existence of a S‐rich magmatic vapour phase.
An investigation into the source of the springtime tropospheric ozone maximum at Mauna Loa Observatory
Authors: Harris J. M. , Oltmans S. J. , Dlugokencky E. J. , Novelli P. C. , Johnson B. J. , Mefford T.
Published: February 2004

Measurements of CH4, CO, O3, and H2O vapor from Mauna Loa Observatory (MLO) are examined in conjunction with isentropic trajectories to investigate the cause of a maximum in tropospheric O3 consistently observed during spring. CO and O3 have been found to be positively correlated in pollution plumes containing O3 precursors downwind of industrialized regions. However, we report that during continental transport from Asia, O3 is not correlated with either CO or CH4, although CO and CH4 are strongly correlated. The relationship between CO and CH4 suggests common source regions. The lack of correlation between these species and O3 probably indicates an O3 source distinct from that of CO and CH4. While Asian pollution does not appear to be a strong candidate for causing the spring increase in O3, transport characteristics and H2O vapor measurements are consistent with both an upper‐tropospheric/stratospheric contribution and an enhancement from transport across O3 gradients.
The nightside ionospheric response to IMF by changes
Authors: Dudeney J. R. , Rodger A. S. , Freeman M. P. , Pickett J. , Scudder J. , Sofko G. , Lester M.
Published: February 2004

A sharp latitudinal gradient in the Doppler spectral width is often observed in the nightside data from the SuperDARN HF radars. We use an excellent conjunction between the Halley HF radar and the POLAR satellite to demonstrate that this gradient is associated with the boundary between the central plasma sheet and boundary layer plasma precipitation. We then exploit this identification to examine the CPS/BPS response simultaneously near the dawn, dusk and midnight, to a significant change of IMF By during a period when the magnetosphere is otherwise in a quiescent state. We find that the direction of the boundary motions are consistent with those previously determined by Holzworth and Meng, [1984]. In the morning sector, the magnitude is consistent with previous observations but in the evening sector the displacement is about 3 times greater than expected. Also the response appears to be in the order of minutes near dawn and dusk, faster than previously reported responses to IMF changes in this region.
Anisotropic seismic tomography of a potential hot dry rock reservoir before and during induced pressurization
Authors: Vécsey G. , Holliger K. , Pratt R. G. , Dyer B. C. , Green A. G.
Published: February 2004

To assess the effects of changing fluid pressure in a potential hot dry rock reservoir, two cross‐hole seismic surveys were conducted: one at ambient pressures and one with the investigated volume hydraulically overpressured by ∼3.3 MPa. Sources and receivers were located in two straight subvertical boreholes ∼100 m apart. Traveltime data were inverted for velocity information in two phases. During the first phase the seismic velocities were constrained to be isotropic, and during the second they were allowed to be anisotropic. Accounting for anisotropy enhanced greatly the interpretability of the tomograms. Before pressurization, a low‐velocity anomaly at 455–475 m depth correlated with a subhorizontal zone of hydraulically permeable fractures connecting the two boreholes. Although the absolute magnitude of anisotropy is not well constrained, the dominant orientation of the TI‐axes is consistent with the local stress field. Hydraulic over‐pressurization resulted in a pronounced extension of the low‐velocity zone, but had no significant effects on the velocity structure elsewhere. The results of this study suggest that anisotropic seismic tomography may be a key method for characterizing hot dry rock reservoirs.
Oxygen isotopes in fresh water biogenic opal ‐ Northeastern US Alleröd‐Younger Dryas temperature shift
Authors: Shemesh Aldo , Peteet Dorothy
Published: February 2004

The first oxygen isotope analysis of biogenic opal from lake sediments, from the Alleröd/Younger Dryas transition in a core from Linsley Pond, Connecticut, gives an average estimate of a 6°C drop in temperature during the Younger Dryas. This shift represents temperatures during the bloom season, and may be less than the winter temperature drop. The sharp transition itself, with a duration of about 200 years, suggests that the temperature decrease may have been as large as 12°C. Previous estimates of the Alleröd/Younger Dryas temperature shifts are controversial, and range from 3–20°C, suggesting that further interdisciplinary research on the same samples is warranted.
Effects of cloud shape and water vapor distribution on solar absorption in the near infrared
Authors: Podgorny Igor A. , Vogelmann Andrew M. , Ramanathan V.
Published: February 2004

A 3D Monte Carlo radiative transfer model is used to demonstrate the importance of cloud shape and water vapor distribution on narrow‐band solar absorption at 0.93 and 2.0 µm. Diurnally averaged absorption for wavy‐topped broken cloud fields can exceed that based on conventional climate model assumptions (plane‐parallel cloud geometry and an unsaturated water vapor distribution in gaps between cloud elements) by 2–10% of the top‐of‐atmosphere insolation. Plane‐parallel clouds often underestimate the absorption by non‐flat‐top clouds, particularly at 2.0 µm and large solar zenith angles. Ambiguities in assigning the above‐cloud water vapor profile create uncertainties in the absorption comparisons between the plane‐parallel and non‐flat‐top clouds, which increase with solar zenith angle and may be as large as 5 to 8%. A thin saturated water vapor layer (0.4 km) above the cloud top systematically enhances column absorption, the magnitude depends on cloud altitude and wavelength. Thus, realistic 3‐D distributions of cloud shape, brokenness and water vapor are needed to quantify the role of clouds in excess absorption.
Resonant diurnal internal tides in the North Atlantic
Authors: Dushaw Brian D. , Worcester Peter F.
Published: February 2004

Using a large acoustical array located midway between Puerto Rico and Bermuda, we have observed enhanced diurnal tidal signals associated with the lowest internal‐wave mode. These signals result from a diurnal internal wave resonantly trapped between the shelf just north of Puerto Rico and the turning latitude, a distance of about 1100 km. The data obtained using the large acoustical array are consistent with the predicted Airy‐function variation with latitude of diurnal internal waves near the turning latitude. The existence of this wave is a striking demonstration of the long spatial and temporal coherence of oceanic internal tides. In general, the energy radiated by such waves is a loss of energy from the earth‐moon system and a source of energy for mixing in the deep ocean.
Characteristics of electromagnetic noise in the Ioannina Region (Greece); A possible origin for so called “seismic electric signal” (SES)
Authors: Pham V. N. , Boyer D. , Chouliaras G. , Le Mouël J. L. , Rossignol J. C. , Stavrakakis G. N.
Published: February 2004

The study of electromagnetic noise in the Ioannina region (NW Greece) shows the existence of long transient electric signals (duration>10 s) without measurable correlated magnetic signals, as is the case for Seismic Electric Signal (SES) observed in the VAN network of short‐term earthquake prediction. Our signals have an artificial origin and are emitted by different kinds of transmitters implanted in the Ioannina region. This origin can be clearly ascertained from simultaneous observation, at stations in direct sight of the transmitters, of four electromagnetic components (two electric and two magnetic) in a broad band of frequencies (10−3–10³ Hz). Relying on these observations, it is proposed that the April 18 and 19, 1995 electric signals, interpreted by the VAN group as SES precursors to the May 13 Kozani earthquake, are due to some transmitter located far to the North of the IOA station of the VAN network. The transmitters of this area would be of digital type, as is increasingly common in radio‐telecommunication networks. We believe that careful studies of electromagnetic noise in a broad range of frequencies should precede lengthy discussions of the statistical significance of recorded signals.
Quaternary geomagnetic field intensity: Constant periodicity or variable period?
Authors: Sato Takaharu , Kikuchi Hisakazu , Nakashizuka Makoto , Okada Makoto
Published: February 2004

Paleomagnetic results are presented from a core, KH 90‐3‐5, in the Melanesia basin and are correlated with the previously obtained results from two cores, KH 73‐4‐7, KH 73‐4‐8, in the same basin in a period between 0.04 Ma and 1.1 Ma. The sediments in the three cores are composed mostly of calcareous ooze. It has been shown that the variation in the saturation isothermal remanent magnetization (SIRM) in the two cores is caused neither by deposition‐rate variation of magnetic minerals nor by rock‐magnetic inhomogeneity but almost solely by variations in CaCO3 dissolution. A close similarity between the variation in the SIRM in the two cores and the variation in the initial susceptibility (κ) in KH 90‐3‐5 has enabled us to correlate among the cores, and also means negligible rock‐magnetic inhomogeneity in the core. A time versus depth correlation has been established from the δ18O record of KH 90‐3‐5. The relative paleointensity record estimated from the natural remanent magnetization (NRM) normalized by κ in KH 90‐3‐5 and those records in the other two cores are remarkably similar, implying that the records faithfully reflect variations in relative paleointensity of the geomagnetic field for the past 1.1 Ma. We examined on the periodicity of the paleointensity records with wavelets. It is shown that periods of major changes in the records reveal continuous shifts between about 50 Ka and 140 Ka over time. We offer an alternative viewpoint about the periodicity of the paleointensity in which periods of major changes shifted continuously within the time range instead of constant periodicities.
The coherence scale length of band‐limited Pc3 pulsations in the ionosphere
Authors: Baker Kile B. , Engebretson Mark J. , Rodger Alan S. , Arnoldy Roger L.
Published: February 2004

Band‐limited Pc‐3 pulsations were observed on one day with pulsation magnetometers, photometers and in VLF activity at South Pole and simultaneously, electric field pulsations were observed in the ionospheric cusp using the PACE HF‐Radar located at Halley Station, Antarctica. The electric field pulsations were observed by the radar on open magnetic field lines, which were likely to be connected more directly to the source region (upstream of the foreshock) of the activity than the magnetic pulsations, which were observed on closed magnetic field lines. The electric field pulsations were found to have a coherence scale length of around 30–60 km, significantly less than the upper limit that can be determined from magnetometer measurements.
Southern hemisphere circulation anomalies associated with extreme Antarctic peninsula winter temperatures
Authors: Marshall Gareth J. , King John C.
Published: February 2004

The Southern Hemisphere reveals markedly different circulation patterns associated with extreme warm and cold Antarctic Peninsula (AP) winter temperatures. Warm winters are associated with negative 500 hPa height anomalies in the Amundsen Sea‐Bellingshausen Sea (AS‐BS) and positive anomalies in the South Pacific (SP) and Scotia Sea with opposing anomalies existent in cold winters. Furthermore, a switch in the relative strength of the two arms of the New Zealand split jet, the subtropical jet (STJ) and polar front jet (PFJ), occurs with the PFJ (STJ) strengthened and the STJ (PFJ) weakened in warm (cold) years leading to increased cyclonic activity in the AS‐BS (SP) and a corresponding decrease in the SP (AS‐BS). These hemispheric anomaly patterns bear a strong resemblance to those associated with El Niño‐Southern Oscillation (ENSO) events, and their origins can be ascribed to tropical sea surface temperatures (SST) changes. However, the correspondence between warm (cold) ENSO events and cold (warm) winters is not perfect. Potential contributors to this non‐linearity include intraseasonal tropical SST variations (not necessarily represented in the usual filtered ENSO indices) and the persistence of local sea ice anomalies west of the Peninsula.
Remote sensing of discrete stratospheric gravity‐wave structure at 4.3‐µm from the MSX satellite
Authors: Picard R. H. , O'Neil R. R. , Gardiner H. A. , Gibson J. , Winick J. R. , Gallery W. O. , Stair A. T. , Wintersteiner P. P. , Hegblom E. R. , Richards E.
Published: February 2004

Distinctive structure in the 4.3‐µm spectral region has been imaged by the SPIRIT 3 radiometer on the MSX satellite observing the cloud‐free atmosphere. We show nadir, high‐nadir‐angle (NA) sublimb, and limb images which, coupled with radiative transfer analysis, indicate that this structure originates from internal gravity waves (GWs). Such structure occurs in a significant fraction of both below‐the‐horizon (BTH), or sublimb, and above‐the‐horizon (ATH), or limb, observations in both MSX 4.3‐µm channels. The structure has different morphology from clouds and has spatial scales appropriate for atmospheric GWs. Calculation of contribution functions (CFs), or weighting functions, for MSX filters and viewing conditions confirms that the BTH GW structure originates from altitudes near 40 km. We believe this is the first high‐resolution imaging of atmospheric GWs from space in the mid‐wave infrared (MWIR) spectral region. In addition, the technique provides structure imaging capabilities at upper stratospheric altitudes inaccessible to airglow imagery.
The arrival of recently formed Labrador sea water in the Deep Western Boundary Current at 26.5°N
Authors: Molinari Robert L. , Fine Rana A. , Wilson W. Douglas , Curry Ruth G. , Abell Jeff , McCartney Michael S.
Published: February 2004

The Deep Western Boundary Current (DWBC) of the North Atlantic is a principal conduit between the formation region for Labrador Sea Water (LSW) and the oceanic interior to the south. Time series (1985–1997) of hydrographic properties obtained in the DWBC at 26.5°N show that prior to 1994, temperature, salinity, and transient tracer properties within the LSW density range showed little indication of recently formed parcels. Properties characteristic of a newer version of LSW (cooler, fresher, and higher tracer concentrations) were observed beginning in 1994 and continuing through 1997. Longer time series of temperature and salinity, developed from a regional data base, show both the 1994 and a 1980–1981 event in the Abaco region. Both events are consistent with anomalies in the Labrador Sea that occurred some 10 years earlier. The 10‐year transit time from the Labrador Sea to 26.5°N is less than the 18‐year transit time inferred from earlier studies.
Two‐fluid model of magnetosonic solitons and shocks
Authors: Hau L.‐N.
Published: February 2004

A nearly perpendicular shock with a thickness on the order of electron inertial lengths has been reported recently by Newbury and Russell (Geophys. Res. Lett., vol. 23, pp. 781–784, 1996) based on the study of ISEE‐1 and ‐2 crossings of Earth's bow shock. This paper examines the structure of nonlinear solitons and shocks propagating exactly perpendicular to the magnetic field based on the two‐fluid model. It is shown that the characteristics of the solutions are distinct for three parameter regimes of the upstream plasma beta, β1, and magnetosonic number, Mms1. Magnetosonic solitons and purely resistive subcritical shocks with or without downstream magnetosonic wavetrains exist only for low β1 and Mms1. For subcritical shocks with intermediate β1 and Mms1, steady solutions exist only for resistivity greater than certain critical values. For subcritical shocks with smaller resistivity and for supercritical shocks (high β1 and Mms1), resistivity alone is insufficient to yield shock transitions. Including viscosity in the model calculations however leads to solutions of unstable upstream and downstream states. This chaotic nature may account for the highly turbulent structure of the observed thin shock.
First direct simultaneous HCl and ClONO2 profile measurements in the Arctic Vortex
Authors: Payan S. , Camy‐Peyret C. , Jeseck P. , Hawat T. , Durry G. , Lefèvre F.
Published: February 2004

Coincident vertical profiles of HCl and ClONO2 in the Arctic vortex have been retrieved simultaneously in the altitude range 13 to 31km. Solar occultation spectra were recorded, during both ascent and occultation, with a balloon‐borne infrared Fourier transform spectrometer launched on 22 March 1995 from Kiruna (Sweden, 67°N, 22°E). A depleted layer of HCl is observed between 16 and 18 km, whereas ClONO2 is showing values larger than 2 ppbv around 20 km. The impact on the derived total inorganic chlorine of a 20% increase of the current ClONO2 absolute line intensities is discussed. These first direct measurements of the mixing ratio profiles of HCl and ClONO2 are compared with the results of the REPROBUS chemistry transport model and discussed in term of chlorine partitioning.
Extension of the F10.7 Index to 1905 using Mt. Wilson Ca K Spectroheliograms
Authors: Foukal Peter
Published: February 2004

The F10.7 index provides a daily record of solar microwave emissions, which vary in rough proportion to the projected area of bright magnetic structures called plages and network, and also sunspots, on the sun's disk. The daily observations used to form the index only began in 1947. Recently, we digitized the archive of daily Ca K spectroheliograms obtained at Mt. Wilson Observatory between 1905–1984, and measured the area variations of plages and enhanced network, on these photographic plates. We calibrated these variations against the F10.7 index between 1947–1984, so we are able to construct a full‐disk proxy of F10.7 extending back to 1905. The behavior of this extended index indicates that UV irradiance levels achieved near the peaks of sunspot cycles 15, 16, and 17 between 1915–1945, were 25–40% higher than would be estimated from behavior of the Zurich sunspot number, Rz.
Rupture length of the October 9, 1995 Colima‐Jalisco Earthquake (Mw 8) estimated from tsunami data
Authors: Ortiz M. , Singh S. K. , Pacheco J. , Kostoglodov V.
Published: February 2004

We analyze tsunami data of the great 1995 Colima‐Jalisco, Mexico earthquake, recorded in Cabo San Lucas, Baja California Sur, to estimate its rupture length, L. To model the tsunami arrival time, we assume a rectangular source area, oriented parallel to the trench, whose SE limit is fixed at the point of rupture initiation. The NW limit of the source area, i.e., L, is varied between 120 and 200 km. The comparison between synthetic and observed data strongly suggests that L of the earthquake was 160±20 km. This length agrees with those reported in various other studies of the earthquake. It, however, disagrees with a previous study, based on the same tsunami data, which suggested that the rupture may have extended 250 km NW from the epicenter [Tanioka and Ruff, 1996]. The cause of this discrepancy is most likely an error in the timing of the records used by Tanioka and Ruff [1996]. We conclude that the earthquake only partially ruptured the Rivera‐North America plate interface. A 120 km‐long segment in the NW extreme of this interface, which apparently ruptured in 1932, remains presently unbroken.
Secondary circulation associated with a shelfbreak front
Authors: Barth John A. , Bogucki Darek , Pierce Stephen D. , Kosro P. Michael
Published: February 2004

Evidence for secondary circulation associated with a shelfbreak front is obtained from a high‐resolution, cross‐shelf section of hydrographic, optical and velocity fields. Convergence in the bottom boundary layer on the inshore side of the front and subsequent upwelling into the interior is evident by a mid‐water region of suspended bottom material emanating from the foot of the front and extending to within 35 m of the surface, 80 m above bottom. Downwelling on the offshore side of the front in the upper water column is inferred from a 20‐m downward bend of the subsurface phytoplankton layer. These observations are in agreement with recent model predictions for secondary circulation near an idealized shelfbreak front. Convergence in measured cross‐shelf velocity at the foot of the front is consistent with upwelling of bottom material detected there. An estimate of 9±2 m day−1 of upwelling on the inshore side of the shelfbreak front is obtained, implying a transit time from the bottom to the surface of 10–16 days.