bluuebunny/crossref_metadata_2025 huggingface dataset:
Export fluxes of dimethylsulfoniopropionate and its break down gases at the air‐sea interface
Authors: Dileep Kumar M. , Shenoy D. M. , Sarma V. V. S. S. , George M. D. , Dandekar M.
Published: October 2002

Dimethylsulfide (DMS) results from the decomposition of dimethylsulfoniopropionate (DMSP), a biogenic product, in seawater. Diffusive transfer of DMS from sea‐to‐air is known to be the most important source of natural non‐ seasalt sulfur (NSS) in the atmosphere. Here, we report on the wider occurrence of DMSP in marine aerosols for the first time. We found DMSP (to about 4.7 pmol m−3) and DMS (up to 5.8 pmol m−3) in marine aerosols, over the Indian Ocean, wherein DMSP abundance appears to be a function of its concentration in surface seawater and wind speeds. An experiment on board revealed rapid loss (90%) of loaded DMSP from filters exposed to marine atmosphere. Hence, a photochemical or other mode of formation of NSS gases from DMSP in aerosols or in surface microlayer, not considered hitherto, can directly contribute to sulfur efflux. Although our computations suggest the DMSP fluxes from these sources to be much smaller (3.4 × 1010 g S y−1) compared to DMS diffusive flux (16–25 × 1012 g S y−1) the former could be significant in rough weather conditions similar to trends in water export.
Hydrological anomalies associated with crustal deformation before the 2000 eruption of Usu volcano, Japan
Authors: Matsumoto Norio , Sato Tsutomu , Matsushima Nobuo , Akita Fujio , Shibata Tomo , Suzuki Atsuo
Published: October 2002

Abrupt and large rises in well water levels were observed three days before the 2000 eruption of Usu volcano, simultaneously with the increase of seismic activity. After the groundwater level in the DT1 well rose 4.07 m, the groundwater discharged one day before the eruption. The groundwater level rose 0.95 m in the DT2 well before the eruption. These water‐level rises are caused by crustal deformation from magma migration, and enable us to estimate 0.63−11.2 × 10−6 of compressional volumetric strain by applying the wells' responses to earth and ocean tides. These strain changes are explained by a 2.8–16.5 × 106 m3 spherical inflation source model located at the Usu volcano. A 5 × 106 m3 inflation source model is estimated by a horizontal displacement observed by GPS near DT2, which is consistent with the volumetric strain estimated by the water‐level rises in DT2.
Evidence for nonmigrating thermal tides in the Mars upper atmosphere from the Mars Global Surveyor Accelerometer Experiment
Authors: Wilson R. John
Published: October 2002

Mars Global Surveyor Accelerometer Experiment density measurements indicate the presence of planetary‐scale wave structure in the Mars upper atmosphere (∼130 km). In particular, Phase 2 aerobraking observations reveal large amplitude zonal wave 2 and 3 variations in dayside density between ±60° latitude. These spatial variations (in a fixed local solar time reference) can be qualitatively reproduced by a Mars general circulation model and are identified as a manifestation of eastward propagating nonmigrating thermal tides with long vertical wavelengths. The simulated wave 2 variation is dominated by a diurnal period wave 1 Kelvin mode while the principal components of the simulated zonal wave 3 structure are a diurnal period wave 2 Kelvin mode and a wave 1 semidiurnal tide. The characterization of these waves is important for understanding the structure and variability of the martian atmosphere at aerobraking altitudes.
Age dependent porosity of young upper oceanic crust: Insights from seafloor gravity studies of recent volcanic eruptions
Authors: Pruis Matthew J. , Johnson H. Paul
Published: October 2002

An October 1997 ALVIN program collected a series of seafloor gravity stations over the February, 1996, volcanic eruption site on the northern Gorda Ridge (46°41′N, 126°47′W). These measurements yielded estimates of the density and porosity of mid‐ocean ridge crust in the first few decades following formation. The estimated crustal density for this pillow eruption of 2270 ± 260 kg/m3 is very low, but in good agreement with the estimated densities of other recent seafloor volcanic flows. Rock matrix densities, measured from hand samples retrieved from the study area, give a bulk porosity for this flow of 34% ± 16%. This data, when included with similar estimates of upper crustal porosity, argue for a rapid evolution of upper crustal porosities from very high values (≥30%) for recent eruptions to much lower values (∼10–15%) where the seafloor is older than 0.5 million years. These variations of density and porosity are of a magnitude consistent with previously observed changes in seismic compressional wave velocity and permeability of ocean crust.
True versus apparent arctic oscillation
Authors: Itoh Hisanori
Published: October 2002

A key issue about the Arctic Oscillation (AO) is whether variations over the Arctic (N), Atlantic (A), and Pacific (P) regions are truly coherent (true AO), or two independent seesaws cause an apparent seesaw over the three regions (apparent AO). We make data analyses as to which is real. Analyses excluding N show that variations in A and P are independent. With including N in the analysis, the AO and a negative correlation mode between A and P simultaneously emerge. Next, two time series, which vary with the AO pattern in A and P, are produced. The correlation between the two is small, but the sum of the two and the time coefficient of the AO highly correlate. All these results lead to the conclusion that the observed AO is almost apparent. In practice, two almost‐independent seesaws reconstructed from the observed data apparently reproduce the AO.
Is the mean Venusian tropospheric circulation unsteady?
Authors: Joshi Manoj , Young Richard
Published: October 2002

The troposphere of Venus, or that region between the surface and the sulphuric acid cloud layer, is characterised by very low horizontal temperature contrasts of less than 10 K. Such low thermal gradients will have a large impact on the tropospheric mean circulation. Using a simplified atmospheric model, we show that the mean circulation might change in strength, and possibly even reverse in direction, on timescales of decades to centuries. The phenomenon is associated with the high surface pressure, and hence long thermal relaxation time scale of the lower atmosphere. Inertial oscillations appear to play a role in any circulation reversals that occur. We note that wind streak data are consistent with a variable Hadley circulation. Our results imply that the Venusian cloud layer could also exhibit significant variability on the same very long timescales, consistent with some observations.
GPS radio occultation with CHAMP: Atmospheric profiling utilizing the space‐based single difference technique
Authors: Wickert Jens , Beyerle Georg , Hajj George A. , Schwieger Volker , Reigber Christoph
Published: October 2002

The GPS (Global Positioning System) radio occultation experiment onboard the German CHAMP (CHAllenging Minisatellite Payload) satellite was successfully started in February 2001. By the end of July 2001 more than 11,000 globally distributed vertical profiles of atmospheric temperature were derived. Operational data processing is based on the double difference method to correct for satellite clock errors. This technique requires a continuous data stream from a global network of GPS ground stations. Termination of the GPS Selective Availability mode on May 2, 2000 reduced the GPS clock errors by orders of magnitude, thereby rendering space‐based single differencing feasible. First results using this single difference technique without direct use of GPS ground station data are presented. The comparison of two data sets consisting of 436 occultations, one processed with space‐based single differencing, the other with classical double differencing, yields no discernible temperature bias below 30 km altitude, a standard deviation of <0.6 K below 20 km and <1.2 K below 30 km. The comparison of both data sets with corresponding meteorological analyses shows nearly identical results with differences in mean and standard deviation of <0.15 K up to 30 km.
Simulation of sedimentary rock deformation: Lab‐scale model calibration and parameterization
Authors: Boutt David F. , McPherson Brian J. O. L.
Published: October 2002

Understanding the mechanical behavior of rock is critical for researchers and decision‐makers in fields from petroleum recovery to hazardous waste disposal. Traditional continuum‐based numerical models are hampered by inadequate constitutive relationships governing fracture initiation and growth. To overcome limits associated with continuum models we employed a discrete model based on the fundamental laws of contact physics to calibrate triaxial tests. Results from simulations of triaxial compression tests on a suite of sedimentary rocks indicate that the basic physics of rock behavior are clearly captured. Evidence for this conclusion lie in the fact that one set of model parameters describes rock behavior at many confining pressures. The use of both inelastic and elastic parameters for comparison yields insight concerning the uniqueness of these models. These tests will facilitate development and calibration of larger scale discrete element models, which may be applied to a wide range of geological problems.
Solar cycle and geomagnetic N+1/O+1 variation in outer dayside magnetosphere: Possible relation to topside ionosphere
Authors: Christon S. P. , Mall U. , Eastman T. E. , Gloeckler G. , Lui A. T. Y. , McEntire R. W. , Roelof E. C.
Published: October 2002

O+1 and N+1 are important ring current ions in great magnetic storms. We study ∼10–210 keV/e O+1 and N+1 in dayside outer ring current (ORC) at ∼9–15 RE using Geotail's EPIC/STICS ion spectrometer. We find: average N+1/O+1 (ΓN/O) varies by ∼2 over a solar cycle, ∼40% (∼20%) at solar minimum (maximum); individual ΓN/O values range from ∼0.15 (moderate solar maximum storm) to ∼1 (18‐hr solar minimum superquiet interval); and N+1 is third in importance after H+ and O+1 during two moderate storms (Dstmin ∼ −80 nT, ∼25% great storm intensity), one at minimum, one maximum. High‐latitude topside ionospheric AE‐D/MIMS ion composition data form a baseline reference used to argue that ORC ΓN/O variations generally reflect and may be partially explained by topside ionospheric density ΓN/O spatial variations.
Flow structure and transport in the Yucatan Channel
Authors: Sheinbaum Julio , Candela Julio , Badan Antoine , Ochoa José
Published: October 2002

The direct ocean current observations across the Yucatan Channel collected during the Canek program allow the best description to date of the exchange between the Caribbean Sea and the Gulf of Mexico. A net transport of 23.8 ± 1 Sv (1 Sv = 106m3s−1; 95% confidence interval) flowed through the Yucatan Channel from the Caribbean Sea into the Gulf of Mexico, during the period between September 1999 and June 2000. This is about 20 percent less than the 30 Sv accepted as the nominal transport of the Florida Current, and less also than the 28 Sv assumed for Yucatan in closing the transport budgets for Caribbean passages. The discrepancy may be an imbalance due to fluctuations in the transports through other passages of the system, especially the Old Bahama and Northwest Providence Channels, which remain poorly known. Our data corroborate the principal features of the flow through the Yucatan Channel: The northerly surface Yucatan Current and its southerly Under‐current off Mexico, and the southerly surface Cuban Counter‐current near Cuba; but previously unobserved mean currents are found to exist at depth, especially on the eastern side of the channel. Fluctuations seen in the deep flows are related to volume anomalies over the Gulf of Mexico. A transport through the Yucatan Channel smaller than previously thought has significant implications for the dynamics of the Gulf of Mexico and its modeling, since this transport is the principal forcing of its circulation. The circulation budgets in the Western Subtropical Atlantic should be revised considering these new results.
Large density depletions in the nighttime upper ionosphere during the magnetic storm of July 15, 2000
Authors: Lee J. J. , Min K. W. , Kim V. P. , Hegai V. V. , Oyama K.‐I. , Rich F. J. , Kim J.
Published: October 2002

We measured electron density and temperature of the nighttime upper ionosphere for the several key intervals during the progress of the magnetic storm on 15 July 2000 with the Langmuir probe on Korea Multipurpose Satellite‐1 (KOMPSAT‐1). During the main phase of the storm KOMPSAT‐1 detected near 0°E a very deep and extensive trough of electron density centered around the geomagnetic equator. The electron density dropped sharply from ∼4 × 105cm−3 to less than 2 × 104cm−3, with the trough region extended over 1400 km along the satellite track. Later in the recovery phase, KOMPSAT‐1 observed severe distortion still persisted near 230°E, with enhanced density in the southern hemisphere. Together with DMSP observations, we estimate the size of the observed trough to be at least 5500 km in the longitudinal direction. DMSP data indicates that the trough was caused by the enhanced eastward electric field which lifted the equatorial F‐region ionosphere upward.
Temporal and spectral properties of gamma‐ray flashes
Authors: Feng Hua , Li T. P. , Wu Mei , Zha Min , Zhu Q. Q.
Published: October 2002

The temporal and spectral properties of terrestrial gamma‐ray flashes (TGFs) are studied. The delay of low energy photons relative to high energy ones in the γ‐ray variations of the TGFs with high signal to noise ratio has been revealed by an approach of correlation analysis in the time domain on different time scales. The temporal structures of the TGFs in high energy band are usually narrower than that in low energy band. The spectral hardness has a general trend of decreasing with time in a flash. The observed temporal and spectral characteristics give constraints and valuable hints on the flash production mechanism.
Salinity variation and its effect on dynamic height along the 156°E in the Pacific warm pool
Authors: Ueki Iwao , Ando Kentaro , Kuroda Yoshifumi , Kutsuwada Kunio
Published: October 2002

The yearlong mooring data of salinity and temperature along 156°E from 8°N to 5°S in 1999–2000 obtained from TRITON (TRIangle Trans‐Ocean buoy Network) demonstrates that the salinity variation contributed to the variation of surface dynamic height, therefore the geostrophic current. The distribution of the surface dynamic height calculated by observed salinity and temperature reveals a large trough corresponding to the southern edge of the north equatorial countercurrent (NECC), which moved northward from 5°N to 8°N in June–September 1999, while the dynamic height calculated by estimated salinity from climatological temperature‐salinity relationships and observed temperature does not represent the same movement. This difference is caused by anomalous low salinity waters, which dominate above halocline at 5°N. This study highlights that, in the Pacific warm pool, the variation of surface geostrophic currents such as the NECC is also affected by salinity variation.
Observed and calculated mesospheric NO, 1992–1997
Authors: Callis Linwood B. , Natarajan Murali , Lambeth James D.
Published: October 2002

Mesospheric nitric oxide as observed by the Halogen Occultation Experiment (HALOE) and calculated by the Langley Research Center two‐dimensional chemical transport model are compared on a daily and collocated basis for the period 920101 through 971231. Results show excellent agreement when energetic electron precipitation (EEP) from the outer trapping region of the magnetosphere is included. A simulation using only an upper boundary condition derived from the HALOE, but not explicitly including EEP, is deficient in NO at altitudes above 60 km. The contribution to the stratosphere of odd nitrogen formed by EEP in the mesosphere is significant and is approximately three times the contribution due to the HALOE upper boundary condition (HUBC) which approximates auroral electron precipitation, and solar EUV and solar X‐ray effects on NO formation.
Long‐period (12 sec) volcanic tremor observed at Usu 2000 eruption: Seismological detection of a deep magma plumbing system
Authors: Yamamoto Mare , Kawakatsu Hitoshi , Yomogida Kiyoshi , Koyama Junji
Published: October 2002

From a temporal deployment of a broadband seismic network at Usu volcano, Japan, we observed long‐period (12 sec) volcanic tremors during the first few weeks of the eruptive activity which started in the end of March, 2000. The source of these long period tremors are located relatively deep at a depth of 5 km, and their amplitude variation well correlates with the uplift rate of the eruption area. We thus attribute these long period tremors to the flow induced vibration of a magma chamber and its outlet located around the source region of the long period tremors. This may be the first seismological detection of long‐period (>10 sec) vibrations of a deep magma plumbing system.
Current disturbance and the diminishing peatland carbon sink
Authors: Turetsky Merritt , Wieder Kelman , Halsey Linda , Vitt Dale
Published: October 2002

Cumulative impacts of disturbances on peatland carbon must be understood to predict future soil carbon stocks, yet the vulnerability and response of peatlands to disturbance have been neglected. We provide the first regional‐scale assessment of peatland carbon storage across 1.7 million km2 of western boreal land. We estimate that disturbances, mainly fire, release approximately 6460 ± 930 GgCyr−1 to the atmosphere. Concurrently, disturbances reduce carbon uptake in continental peatlands by 85% compared to a no‐disturbance scenario. A 17% increase in the area of peatland burned annually and the intensity of organic matter combustion would convert these peatlands into a regional net source of carbon to the atmosphere. Peatlands widely are considered to represent a northern carbon sink, however, we suggest reevaluation of this paradigm for continental boreal regions.
Carbon dioxide in soil profiles: Production and temperature dependence
Authors: Risk David , Kellman Lisa , Beltrami Hugo
Published: October 2002

The temperature dependance of soil respiration has most commonly been addressed using surface flux data, despite the fact that surface flux measurements implicate CO2 transport and storage effects that may preclude robust assessments of the temperature dependence of soil respiration. Here we examine whether soil respiration might be assessed using soil profile CO2 production inferred from soil CO2 concentration profiles. Over the 9‐month study period, we observed marked similarities in the temperature response of CO2 production across four study sites of contrasting vegetation cover and land use.
Correcting GRACE gravity fields for ocean tide effects
Authors: Knudsen Per , Andersen Ole
Published: October 2002

The GRACE mission will be launch in early 2002 and will map the Earth's gravity fields and its variations with unprecedented accuracy during its 5‐year lifetime. Unless ocean tide signals and their load upon the solid earth are removed from the GRACE data, their long period aliases obscure more subtle climate signals which GRACE aims at. The difference between two existing ocean tide models can be used as an estimate of current tidal model error for the M2, S2, K1, and O1 constituents. When compared with the expected accuracy of the GRACE system, both expressed as spherical harmonic degree variances, we find that the current ocean tide models are not accurate enough to correct GRACE data at harmonic degrees lower that 35. The accumulated tidal errors may affect the GRACE data up to harmonic degree 56. Furthermore, the atmospheric (radiation) tides may cause significant errors in the ocean tide model if altimetry corrected for inverted barometer effects was used in its derivation. To study the temporal characteristics of the ocean tidal constituents when sampled by GRACE, approximate alias frequencies were derived assuming a sampling of half a sidereal day. Those results show that the ocean tide errors will not cancel in the GRACE monthly averaged temporal gravity fields. The S2 and the K2 terms have alias frequencies much longer than 30 days, so they remain almost unreduced in the monthly averages.
Zonal jets in and near the Coral Sea, seen by satellite altimetry
Authors: Hughes C. W.
Published: October 2002

A recent model study predicted the existence of zonal jets to the west of islands in and near the Coral Sea in the southwest Pacific, but found only equivocal support for their existence from past in‐situ data. The jets conform to the pattern which would be expected of an ocean in Sverdrup balance except in western boundary currents, when islands are present. Several techniques are used here to identify these jets in satellite altimeter data. There are differences in detail, particularly in the existence of a westward jet at 16°S which is apparent from the altimetry and from previous in‐situ measurements but absent from OCCAM. However, the general picture of westward jets emanating from the northern and southern tips of island groups, and relatively stagnant regions to the west of islands is confirmed by all three altimetric measures of the circulation.
A polar low over The Labrador Sea: Interactions with topography and an upper‐level potential vorticity anomaly, and an observation by RADARSAT‐1 SAR
Authors: Moore G. W. K. , Vachon P. W.
Published: October 2002

Polar lows, high latitude marine mesoscale cyclones, are an enigmatic atmospheric phenomenon. With their small spatial scales, their short life times, and their tendency to develop in remote data sparse regions; they remain difficult to observe and to model. In this paper we use a variety of data sets to discuss the development of a polar low over the Labrador Sea that is of interest for several reasons. First, it developed out of the remnants of a synoptic‐scale cyclone that underwent a bifurcation due to an interaction with the high topography of southern Greenland. Second, the transformation of the resulting circulation into a polar low was aided by an interaction with an upper‐tropospheric potential vorticity anomaly. Finally, the event was observed by the Synthetic Aperture Radar on the RADARSAT‐1 satellite. The resulting image of the ocean's surface provides a new and provocative view of a most interesting weather system.
Effects of the seasonal asymmetry in ionospheric Pedersen conductance on the appearance of discrete aurora
Authors: Pokhotelov Dimitri , Lotko William , Streltsov Anatoly V.
Published: October 2002

A two‐dimensional numerical two‐fluid MHD model of the coupled magnetosphere‐ionosphere system has been used to examine the effects of seasonal asymmetry in ionospheric conductance on the development of feedback instability and associated energetic electron precipitation. Effects of finite electron inertia and anomalous resistivity in the magnetospheric MHD model lead to the formation of parallel electric fields above the ionosphere as the feedback instability develops. The Fridman‐Lemaire model of energetic electron precipitation has been used to calculate the energy flux carried into the auroral ionosphere by accelerated electrons. The electron energy flux into the lower conductivity winter ionosphere is significantly greater than that into the summer ionosphere due to the asymmetry in ionospheric conductance. The higher energy flux into the winter ionosphere may increase the occurrence of discrete aurora in the winter hemisphere as detected by satellite auroral imaging.
Ocean‐Atmosphere Feedback: Using the non‐stationarity in the climate system
Authors: Topliss B. J.
Published: October 2002

Recent climate studies have debated the issue of whether or how the oceans provide feedback to the atmosphere. Since the oceans store heat and release it on various timescales, defining ocean feedback mechanisms is an important stage in being able to provide climate predictions. Currently model runs are used to determine whether they can simulate either oceanic or atmospheric signals. Some success has been achieved at the interdecadal timescale but often studies still lack independent verification or application to the wider ecosystem. Here it is shown that by use of a simple technique applied to atmospheric data it is possible to derive climate indices that capture the non‐linear feedback response of the ocean‐atmosphere climate system. These indices may provide an independent means to verify feedback in models at the same time as bridging the gap between the fields of atmosphere‐ocean and ecosystem climate modelling.
A mathematical model for voigt poro‐visco‐plastic deformation
Authors: Yang Xin‐She
Published: October 2002

A mathematical model for poro‐visco‐plastic compaction and pressure solution in porous sediments has been formulated using the Voigt‐type rheological constitutive relation as derived from experimental data. The governing equations reduce to a nonlinear hyperbolic heat conduction equation in the case of slow deformation where permeability is relatively high and the pore fluid pressure is nearly hydrostatic, while travelling wave exists in the opposite limit where overpressuring occurs and the pore fluid pressure is almost quasi‐lithostatic. Full numerical simulation using a finite element method agree well with the approximate analytical solutions.
Migration of radar altimeter waveform data
Authors: Nuth Van , Pulliam Jay , Wilson Clark
Published: October 2002

Wingham[1993]demonstrated that migration of radar waveforms appears to improve the images of ice sheet topography. We examine whether this qualitative improvement might lead to quantitative benefits in measuring ice sheet elevation change. We find, instead, that estimates based on migrated waveforms at cross‐over points are degraded relative to unmigrated waveforms. Lack of cross‐track data, which would allow true 3D migration, and migration “noise” related to the Kirchoff algorithm are likely contributors to the degradation. Additionally, lack of phase information in radar waveforms degrades the result. This problem is not encountered in seismic applications of migration and is a limitation of the current generation of radar altimeter data. We have not investigated whether other quantitative benefits may be derived from migrating altimeter waveforms. For example, improved resolution of smaller scale topography in migrated data may lead to better quantitative understanding of ice sheet dynamics.
The energetic storm particle event of October 20, 1989
Authors: Lario D. , Decker R. B.
Published: October 2002

The energetic storm particle event of October 20, 1989 has often been cited as an example of high‐energy (≳500 MeV) proton acceleration by CME‐driven shocks near 1 AU. We examine high‐time resolution solar wind and magnetic field data from the IMP‐8 spacecraft and energetic particle data from the IMP‐8 and GOES‐7 spacecraft. We show that the high‐energy particle population in this event is not a locally shock‐accelerated population, but rather a population of particles confined to a plasma structure with depressed magnetic field and solar wind density. This structure was bounded by enhanced densities and strong magnetic fields. Energetic protons within this structure supplied the pressure needed to prevent the structure from collapsing. The intensity and evolution of this energetic storm particle event were shaped mainly by this spatial structure rather than by the CME‐driven shocks.
Electron energy and electric field estimates in sprites derived from ionized and neutral N2 emissions
Authors: Morrill J. , Bucsela E. , Siefring C. , Heavner M. , Berg S. , Moudry D. , Slinker S. , Fernsler R. , Wescott E. , Sentman D. , Osborne D.
Published: October 2002

During the EXL98 aircraft mission, sprites and blue jets were observed by narrow band cameras that measure the N2+ 1NG (0,1) band at 4278Å and the N2 2PG (0,0) band at 3370Å. We discuss the observations (∼1km resolution), instrumental and atmospheric corrections, and altitude profiles of ionized (1NG) and neutral (2PG) emission observed during a specific sprite. The ratio of ionized‐to‐neutral emission indicates a relative enhancement of ion emission below 55km. Characteristic electron energies (ECh) and electric fields (E) are derived from these emission ratios using excitation rates computed from a model that solves the Boltzmann equation as a function of electric field. Up to 55km E follows the breakdown field (Ek) and ECh is ∼2.2eV. Above 55km E drops below Ek and ECh drops to ∼1.75eV near 60km.
Noctilucent clouds, PMSE and 5‐day planetary waves: A case study
Authors: Kirkwood S. , Barabash V. , Brändström B. U. E. , Moström A. , Stebel K. , Mitchell N. , Hocking W.
Published: October 2002

Analysis of global meteorological assimilations between mid‐July and late‐August 2000 shows strong 5‐day planetary waves in the middle atmosphere. Observations of temperature, zonal wind, noctilucent clouds and polar mesosphere summer echoes (PMSE) near Kiruna, Sweden, all at heights between 80 and 95 km, show variations correlating with the passage of the 5‐day waves. Temperature variations correlated with the 5‐day wave reach 15 K peak‐to‐peak and correspond to modulation of PMSE occurrence by up to 50%. These observations appear to be the first experimental evidence of amplification of 5‐day waves at the summer mesosphere which was predicted theoretically in 1976. A close linear relation is found between mean daily temperature and mean daily occurrence of PMSE. This can be explained if temperature is the primary factor controlling PMSE occurrence and time and height variations within each day between 80 and 90 km altitude reach 30 – 50 K.
Geomagnetic episodes of the last 1.2 Myr recorded in Chinese loess
Authors: Pan Y. X. , Zhu R. X. , Liu Q. S. , Guo B. , Yue L. P. , Wu H. N.
Published: October 2002

The Matuyama‐Brunhes (M/B) boundary, termination of Jaramillo normal subchron (J/M) as well as three young geomagnetic excursions has been revealed in the Weinan loess section [Zhu et al., 1994,1998,1999]. Recently, we carried out further paleomagnetic directional studies on the same section and recovered the onset of the Jaramillo normal subchron (M/J) and four geomagnetic excursions, two in the Brunhes and two in the late Matuyama. The fact that all seven excursions found in this section are in loess units and expected excursions in paleosols are not found suggests that short‐lived geomagnetic signals could be only recorded in loess units, and may have been fully smoothed or wiped out in paleosol units by strong pedogenesis. Constrained by a new astronomical timescale (HLD00), ages of the geomagnetic excursions and reversal boundaries have been estimated. We tentatively correlated these excursions with previous results, indicating that a large lock‐in model may not be correct for the whole loess profile, although some apparently big positive age discrepancies were observed for the main boundaries.
Trends in moments of climatic indices
Authors: Vinnikov Konstantin Y. , Robock Alan
Published: October 2002

We propose a new technique to analyze trends in moments of the statistical distribution of climatic indices. A standard approach (linear regression, polynomial fit, or least squares fit to a specific function) is first used to evaluate the trend in the expected value of an observed climatic index. The innovation here is that after the trend in the expected value is subtracted from the observed time series, we calculate the time series of the squares, cubes, fourth powers, and any other combination of the residuals (anomalies). Then we apply the same standard trend analysis technique to the time series of these new variables. This technique can be used to determine whether the observed climate is getting more or less variable. The observed 1901–2000 New York City sea level variations, U.S. annual average precipitation, U.S. annual averages of the Modified Palmer Drought Severity Index, All‐India Monsoon Rainfall Index, and Southern Oscillation Index are used to illustrate the technique. There are no significant trends in variability of any of these climatic indices for the past 100 years.
Future development of the ozone layer calculated by a general circulation model with fully interactive chemistry
Authors: Nagashima Tatsuya , Takahashi Masaaki , Takigawa Masayuki , Akiyoshi Hideharu
Published: October 2002

The future development of stratospheric ozone is estimated using an atmospheric general circulation model that includes a fully interactive chemistry module. Two transient integrations considering the anthropogenic chlorine emission trend were performed. One calculated with a carbon dioxide increase and a sea surface temperature (SST) variation between 1986 and 2050, and the other without the increase or the variation. In the Southern Hemisphere polar region, a 10 day‐averaged column ozone takes its minimum of 140 Dobson Unit (DU) around 2000 and recovers above 220 DU after the late 2030s. Such temporal evolution of ozone is not greatly influenced by the carbon dioxide increase and SST variation but seems to be maintained by simulated chlorine loading in the lower stratosphere. In the integration with carbon dioxide increase and SST variation, the Northern Hemisphere polar column ozone decreases until 2010, but massive depletion such as that causing the Antarctic ozone‐hole (less than 200 DU) does not occur.
An extremely turbid intermediate water in the Sea of Okhotsk: Implication for the transport of particulate organic matter in a seasonally ice‐bound sea
Authors: Nakatsuka Takeshi , Yoshikawa Chisato , Toda Mari , Kawamura Kimitaka , Wakatsuchi Masaaki
Published: October 2002

We found a water mass characterized with enormous turbidity and very low temperature in the intermediate layer of the Sea of Okhotsk in September 1999. In June 2000 and September 1999, the cold and turbid water mass was also located in bottom boundary layer on the northwestern shelf region, where sea ice had rejected large amounts of brine waters in winter. Cold brine waters settled on the bottom of shelf must have entrained sedimentary particles, including newly produced organic matter, due to strong tidal mixing, and finally flowed out into Okhotsk Sea Intermediate Water (OSIW) by a western boundary current intensified in autumn. Sediment traps moored in the deep basin recorded the outburst of particles in autumn. This mechanism is likely to export the particulate organic matter produced on the shelf efficiently to pelagic intermediate waters.
Temporal change in permeability of the rock estimated from repeated water injection experiments near the Nojima fault in Awaji Island, Japan
Authors: Kitagawa Yuuichi , Fujimori Kunio , Koizumi Naoji
Published: October 2002

Three boreholes with depths of 500, 800, and 1800 m were drilled near the Nojima fault, which is one of the 1995 Hyogoken‐Nanbu earthquake faults. In order to research the structure and its temporal change of the active fault, the water injection experiments were conducted from the 1800‐m borehole in 1997 and 2000. Then, the discharge changes at the 800‐m borehole were observed during the water injections. Considering the permeable zone near the fault as simple two‐dimensional layer with an uniform thickness, we estimated the permeability of the permeable zone near the Nojima fault from the discharge changes associated with the water injections. It is found that the permeability of the permeable zone in 2000 became lower than that in 1997.
Spontaneous formation of current‐driven double layers in density depletions and its relevance to solitary Alfven waves
Authors: Singh Nagendra
Published: October 2002

We demonstrate that when magnetic field‐aligned currents encounter density cavities, double layers (DLs) spontaneously form. The parallel electric field in the double layer (DL) accelerates electrons and ions to maintain the current continuity. However, such double layers are found to be transitory; their growth is initially accompanied by further deepening of a part of the cavity and the decay with subsequent refilling. The bursty acceleration of electrons and ions by the double layer provides a mechanism for the conversion of the electromagnetic energy associated with the currents into kinetic energy of the plasma. Thus the spontaneous double layer formation in plasma density cavities could be an effective dissipation mechanism for Alfven waves which carry substantial currents when they acquire sufficiently short wavelengths perpendicular to the magnetic field.
Subdiffusive transport of charged particles perpendicular to the large scale magnetic field
Authors: Qin G. , Matthaeus W. H. , Bieber J. W.
Published: October 2002

Transport of charged particles across the mean magnetic field due to broad band, powerlaw‐distributed magnetic fluctuations is examined by direct computation of a large number of charged test particle trajectories. Fluctuations consist of a one dimensional slab spectrum with an additional 0.01 percent level of two dimensional fluctuations; the net field has no ignorable directions. We find that, at long times (t), the mean square displacements subdiffusively scale as ∼t1/2. This confirms that perpendicular diffusion is suppressed when turbulence lacks strong three dimensional structure, in agreement with theories of Urch and of Kóta and Jokipii.
Evidence and quantification of the correlation between radar backscatter and ocean colour supported by simultaneously acquired in situ sea truth
Authors: Lin I.‐I. , Wen Liang‐Saw , Liu Kon‐Kee , Tsai Wu‐Ting , Liu Antony K.
Published: October 2002

Near simultaneously (within 2 hours) acquired ERS‐2 Synthetic Aperture Radar (SAR) and Sea‐viewing Wide Field‐of‐view Scanner (SeaWiFS) data over an upwelling region shows remarkable similarity in feature's location, scale, and boundary. Under uniform wind and sea states, reduction of Normalised Radar Cross Section (NRCS) from SAR is found highly correlated with the increase of SeaWiFS Chlorophyll‐a (Chl‐a) concentration. Typically, 1 mg/m3 of chlorophyll‐a is correspondent with a 5 dB reduction of NRCS. This relationship is supported by simultaneously collected in situ sea truth measurements. This work provides a direct evidence and exceptional quantification of the relationship between radar backscatter and ocean colour that has long been speculated.
A measurement of the albedo of thick cirrus clouds at 3.9 μm
Authors: Kidder Stanley Q.
Published: October 2002

Cirrus (ice) clouds are often semitransparent (transmittance greater than zero, but less than one), which makes it difficult to measure fundamental cloud properties, such as albedo. This paper explores a way to measure the albedo of thick cirrus clouds (zero transmittance) at 3.9 μm using GOES Imager data. In brief, the 10.7 μm GOES data are used to separate the cirrus clouds into temperature classes. Then the measured 3.9 μm radiance is plotted against the cosine of the solar zenith angle. A theoretical relationship between radiance and solar zenith angle is used to extract the albedo. The result is that thick cirrus clouds have an albedo of 1.08% ± 0.05% at 3.9 μm. The albedo of thick cirrus is a step toward the measurement of the transmittance of thin cirrus.
NAO and winter temperature variability in southern Europe
Authors: Castro‐Díez Y. , Pozo‐Vázquez D. , Rodrigo F. S. , Esteban‐Parra M. J.
Published: October 2002

Here we explore the relationship between the NAO and the temperatures in southern Europe, using NCEP/NCAR reanalysis data to study the synoptic situations associated with different phases and intensities of the NAO as well as with different temperature anomalies. The results show that temperatures in southern Europe are sensitive not only to the phase of the NAO, but also to the exact location of the NAO centers of action. Opposite temperature anomalies are found to be associated with similar NAO index values, leading to linear correlation coefficients between the index and the temperature series close to zero. This does not necessarily imply a negligible influence of NAO on southern European temperatures, but it may indicate a complex and non‐linear relationship, not adequately represented by a simple NAO index. We conclude that the association between the NAO variability and the temperatures in southern Europe substantially differs with respect to central and northern Europe, where no such sensitivity regarding the location of the NAO action centers is found.
North Atlantic SST Forcing of the NAO and Relationships with Intrinsic Hemispheric Variability
Authors: Peng Shiling , Robinson Walter A. , Li Shuanglin
Published: October 2002

Large (100‐member) ensembles of GCM experiments are conducted to examine the atmospheric response to a North Atlantic SST tripole with warm anomalies off the US Eastcoast and cold anomalies north of 40°N and south of 25°N. The response varies seasonally with the model's intrinsic variability, producing a strong NAO pattern only in February–April, the same months in which the model's internal variability projects strongly on the NAO. The response is significantly different for positive and negative SST tripoles, reproducing nonlinearity present in observational composites. The anomalous surface heat flux associated with the strong late‐winter/spring response implies a significantly reduced damping of the SST anomaly, and in some areas even a positive thermal feedback between the atmosphere and the ocean.
Tomographic evidence for a subducted seamount beneath the Gulf of Nicoya, Costa Rica: The cause of the 1990 Mw = 7.0 Gulf of Nicoya earthquake
Authors: Husen S. , Kissling E. , Quintero R.
Published: October 2002

Tomographic images constrain the existence of a subducted seamount beneath the Gulf of Nicoya, Costa Rica. The subducted seamount is found at a depth of 30 km within the rupture area of the March 25, 1990, Mw = 7.0 Gulf of Nicoya earthquake. The Gulf of Nicoya earthquake was a typical thrust‐type subduction earthquake and occurred on a shallow dipping thrust fault parallel or along the boundary between the subducting Cocos plate and the overriding plate. Precise relocation of the mainshock and its aftershocks in a 3‐D P‐wave velocity model shows that the area of the mainshock rupture is coincident with the imaged subducted seamount. Most of the aftershocks are relocated within or close to the inferred subducted seamount above the subducting oceanic plate. We interpret the subducted seamount as an asperity whose rupture caused the 1990 Gulf of Nicoya earthquake.
Polar observations of solitary waves at the Earth's magnetopause
Authors: Cattell CA , Crumley J. , Dombeck J. , Wygant JR , Mozer F. S.
Published: October 2002

Solitary waves have, for the first time, been identified in 3D electric field data at the subsolar, equatorial magnetopause. These nonlinear, bipolar electric field pulses parallel to the magnetic field occur both as individual spikes and as trains of spikes. The solitary waves have amplitudes up to ∼25 mV/m, and velocities from ∼150 km/s to >2000 km/s, with scale sizes the order of a kilometer (comparable to the Debye length). Almost all the observed solitary waves are positive potential structures with potentials of ∼0.1 to 5 Volts. They are often associated with very large amplitude waves in either or both the electric and magnetic fields. Although most of the observed signatures are consistent with an electron hole mode, the events with very low velocities and the few negative potential structures may be indicative of a second type of solitary wave in the magnetopause current layer. The solitary waves may be an important source of dissipation and diffusion at the magnetopause.
History of sulfate aerosol radiative forcings
Authors: Boucher O. , Pham M.
Published: October 2002

The history of the global sulfur cycle has been simulated using an emission inventory of SO2 for 1990 and previously published historical trends in emission on a per country basis. The global‐ annual‐mean radiative forcings due to sulfate aerosols increase (in absolute values) from near‐zero and −0.17 Wm−2 up to −0.4 and −1 Wm−2 between 1850 and 1990, for the direct and indirect effects, respectively. The forcing efficiency (defined as the ratio of the radiative forcing to the anthropogenic sulfate burden) is fairly constant for the direct effect at −150 W(g sulfate)−1 but decreases significantly for the indirect effect with increasing sulfate burden. The model results are compared with long‐term observations for the period 1980 to 1998 in the U.S. and Europe.
Geological noise in near‐surface electromagnetic induction data
Authors: Everett Mark E. , Weiss Chester J.
Published: October 2002

Controlled‐source electromagnetic induction is a geophysical technique used to identify anthropogenic and natural features, such as unexploded ordnance or fluid pathways, in the shallow subsurface. However, electromagnetic responses are difficult to interpret owing to the complexity of the underlying electrical conductivity structure. We show here that electromagnetic responses are fractal signals, reflecting a very rough distribution of electrical conductivity. Apparent conductivity profiles across a floodplain and a fractured sandstone aquifer both show that the fractal properties of the surface response depend on the complexity of the causative geological structure. Small‐scale fluctuations in the response due to geological noise are inherently reproducible, and are not caused by random instrumental or atmospheric effects as often assumed. New approaches to modeling are required to take full advantage of the rich information content of near‐surface electromagnetic data.
Mechanical behavior of western alpine structures inferred from statistical analysis of seismicity
Authors: Sue Christian , Grasso Jean Robert , Lahaie Franz , Amitrano David
Published: October 2002

Two seismic arcs (150 km and 120 km long) located in the western Alps, 50 km apart from each other, are characterized by different statistical patterns in energy and space domains. For the two arcs, we found power‐law distributions in energy domain with a lower b‐value and fall‐off for large events for the easternmost arc only, and roughly similar spatial damage. By comparing the shape and the statistical parameters of these distributions with those provided by numerical models of rock damage, we suggest a relatively more brittle behavior for one area with respect to the other. We discuss the implications of the observed distributions in terms of tectonics and of mechanics of faulting. We suggest three candidates to drive the relative changes in seismicity distribution between the two arcs: the earthquake depth, the host rock composition, and the inherited fracturing patterns.
The changing relationship between the NAO and northern hemisphere climate variability
Authors: Lu Jian , Greatbatch Richard J.
Published: October 2002

Sea level pressure (SLP) difference across Fram Strait is used as a proxy for ice export through the Strait to verify that a secular change in the link between the NAO and Fram Strait ice export occurred around 1980, and that the change was associated with an eastward shift in the SLP pattern associated with the NAO. Two additional variables, Siberian winter temperature, and an index of North Atlantic storm activity, are also found to switch from being uncorrelated with the ice export proxy in the 1950's and 60's to being strongly correlated in the 1980's and 90's, suggesting the emergence of a new climate regime associated with the NAO. We argue that the establishment of this new climate regime is related to an upward trend throughout the whole of the 20th century in the cross‐correlation between the NAO index and Rogers' first storm activity mode for the North Atlantic.
Measurement of Young's modulus of clay minerals using atomic force acoustic microscopy
Authors: Prasad Manika , Kopycinska Malgorzata , Rabe Ute , Arnold Walter
Published: October 2002

The presence of clay minerals, hydrous aluminosilicates that are smaller than 2 μm can alter the elastic and plastic behavior of materials significantly. We have used Atomic Force Acoustic Microscopy (AFAM) to measure elastic properties of clay minerals. We demonstrate the AFAM technique for measuring elastic properties of soft materials. Using this technique, we present first‐ever quantitative measurements of Young's modulus in clay. The Young's modulus of dickite was measured as 6.2 GPa.