bluuebunny/crossref_metadata_2025 huggingface dataset:
Temporal increases of phosphate and apparent oxygen utilization in the subsurface waters of western subarctic Pacific from 1968 to 1998
Authors: Ono T. , Midorikawa T. , Watanabe Y. W. , Tadokoro K. , Saino T.
Published: February 2004

30‐years time series of AOU and phosphate in the Oyashio sub‐surface domain showed an increasing trend superimposed on bidecadal oscillation. AOU and phosphate trend on isopycnals between 26.7 and 27.2 σθ increased by an average of 0.9±0.5 and 0.005±0.003 µmol/kg/y, respectively. Salinity on these isopycnals also showed an average linear increase of 0.0008 psu/y. Salinity and density of winter mixed layer, on the other hand, was found to have decreased during the observation period. Observed bidecadal oscillation (average period 20±1 y) in subsurface AOU negatively correlated with that of North Pacific Index (r=−0.88±0.06). As the cause of the linear increase of subsurface phosphate and AOU, we speculated that vertical water exchange in the upper layers of the subarctic North Pacific might have been diminished during this period. A decreasing trend of salinity and density of winter mixed layer in Oyashio that was observed during the same period supported this speculation.
Majoritic garnets in Hawaiian Xenoliths: Preliminary results
Authors: Keshav Shantanu , Sen Gautam
Published: February 2004

In this report we present chemical, textural, and spectroscopic information on some mantle garnets from Oahu, Hawaii that have recorded the pyroxene ⇔ garnet transformation. Their textural and compositional characteristics indicate a high pressure origin, consistent with a depth range of 180–270 km, which is much deeper than previously thought (<100 km). One eclogitic xenolith is particularly interesting because its textural and compositional characteristics suggest an origin in the deep upper mantle or the transition zone.
Experimental evidence of inertial waves in a precessing spheroidal cavity
Authors: Noir Jérôme , Brito Daniel , Aldridge Keith , Cardin Philippe
Published: February 2004

We have demonstrated experimentally the existence of inertial waves in a slowly precessing spheroid of fluid. Although such oscillatory internal shear layers have been predicted theoretically and numerically, previous precession experiments had shown no evidence of their presence. Using an ultrasonic Doppler velocimetry technique, profiles of radial velocity have been measured in our precession experiment. Comparison of these profiles with their synthetic counterparts obtained numerically, proves the presence of the predicted internal shear layers. They are emitted from the breakdown of the Ekman layer at the two critical latitudes of the fluid (around 30° and −30°) and propagate through the entire volume on conical surfaces. The asymptotic laws for these oscillatory layers, confirmed experimentally and numerically, lead us to predict an oscillatory flow of 10−6 m/s along such characteristic cones in the Earth's fluid outer core.
Generation of kinetic Alfvén waves by mirror instability
Authors: Wu B. H. , Wang J. M. , Lee L. C.
Published: February 2004

The perturbed velocity δV and δB of mirror waves are usually coplanar with the wave vector k and background magnetic field B0. However, recent satellite observations and hybrid simulations show the presence of extra non‐coplanar components in δV and δB associated with mirror waves. In this paper, we show from hybrid simulations that in the nonlinear stage of mirror instability, the non‐coplanar perturbations in δV and δB of high wavenumber modes can be decoupled from mirror waves and generate a pair of kinetic Alfvén waves propagating in opposite direction. The Hall effect can explain the excitation of non‐coplanar components in mirror waves. These kinetic Alfvén waves can be generated in the day side magnetosheath, propagate tailward along the magnetic field lines draped around the magnetopause, and contribute to the plasma transport into magnetosphere.
Wide‐angle reflectivity across the Torngat Orogen, NE Canada
Authors: Funck Thomas , Louden Keith E. , Hall Jeremy
Published: February 2004

Data from a Lithoprobe refraction/wide‐angle reflection seismic transect across the Torngat Orogen in NE Canada were depth‐migrated to produce a record section similar to near‐vertical incidence seismic data. Densely spaced airgun shots and a station spacing between 9 and 25 km were able to produce a low‐frequency image of the lower crustal reflectivity for most of the transect. Over the western end of the profile, a series of east‐dipping lower crustal reflectors continue down to the Moho, which is clearly defined at a depth of 36 to 38 km. The lower crustal reflectors can be correlated laterally for up to 80 km. This reflection fabric is interpreted as evidence for thick‐skinned deformation caused by convergence of the Nain and Superior provinces. Over the eastern end of the line, reflectors in the Nain Province are less continuous and may indicate steeply dipping faults, which have not been modified during formation of the orogen.
Evidence for rapid thinning of sea ice in the western Arctic Ocean at the end of the 1980s
Authors: Tucker Walter B. , Weatherly John W. , Eppler Duane T. , Farmer L. Dennis , Bentley Diane L.
Published: February 2004

Examination of springtime ice drafts obtained from submarine profiles in a narrow band of the western Arctic Ocean from offshore Alaska to 89°N indicates that the mean ice draft decreased 1.5 m between the mid‐1980s and early 1990s. No similar trend was evident in ice drafts near the North Pole. The 1980s drafts were composed largely of ice exceeding 3.5 m, while the early 1990s drafts contained more ice in thinner categories. The differences in drafts between the two periods appear to be related largely to ice dynamics effects associated with the presence and strength of the Beaufort Gyre, which weakened considerably in the early 1990s.
A unique stratospheric warming event in November 2000
Authors: Manney Gloria L. , Sabutis Joseph L. , Swinbank Richard
Published: February 2004

Stratospheric sudden warmings frequently influence temperatures and circulation in the Arctic winter stratosphere. A unique stratospheric warming in Nov 2000 was characterized by wave 1 amplification with little phase tilt with height, a large displacement of the vortex off the pole, a warm pool at high latitudes, and a modest polar temperature increase, all of which are characteristic of early winter “Canadian” warmings. Unlike most Canadian warmings, the Nov 2000 event led to a strong zonal mean wind reversal for ∼9 days in the mid and lower stratosphere. Wind reversals during Canadian warmings occurred only three times before in the last 23 years. Midstratospheric minimum temperatures continued to decrease during the warming, but lower stratospheric temperatures increased substantially. The Nov 2000 warming was unique in its timing, intensity and duration, and in its impact on the development of the polar vortex, especially in the lower stratosphere.
Evidence of El Niño and the Indian Ocean dipole from Sr/Ca derived SSTs for modern corals at Christmas Island, eastern Indian Ocean
Authors: Marshall John F. , McCulloch Malcolm T.
Published: February 2004

While the El Niño/Southern Oscillation (ENSO) has been regarded as an almost exclusively Pacific Ocean phenomenon, there is a growing amount of evidence that there are interannual events in other ocean basins which are possibly related to ENSO. Here we describe results from Sr/Ca analysis of a 24 year coral record from Christmas Island in the tropical eastern Indian Ocean. The Sr/Ca data was matched with blended ship and satellite data from the region to produce the Sr/Ca‐SST calibration. There is evidence of both warm and cool SST anomalies in the Sr/Ca derived SSTs, with an extreme cooling event of 1994 relating to the unusual oceanographic conditions set up by the Indian Ocean Dipole (IOD) and warmer than normal SSTs corresponding with ENSO events in the Pacific.
Upper mantle conductivity structure of the back‐arc region beneath northeastern China
Authors: Ichiki Masahiro , Uyeshima Makoto , Utada Hisashi , Guoze Zhao , Ji Tang , Mingzhi Ma
Published: February 2004

The upper mantle electrical conductivity structure of the pacific back‐arc beneath northeastern China was investigated through long‐period magnetotelluric (MT) and geomagnetic depth sounding (GDS) experiments. MT and GDS responses were obtained up to periods of 105 ∼ 106 seconds, and were inverted to one‐dimensional (1‐D) models with minimum and smooth structure constraints, respectively. The resulting conductivity model was compared with past models and the mantle transition zone beneath northeastern China is more conductive than those of other tectonic settings by almost one order of magnitude in the depth range of 400∼600 km. This feature may correspond to the presence of a stagnant slab beneath this region. In the mantle at a depth of less than 400 km, the conductivity profile has a similar feature to that in the thermal and extensional tectonic region in the southwestern United States.
Modeling the effect of an inhomogeneous surface albedo on incident UV radiation in mountainous terrain: Determination of an effective surface albedo
Authors: Weihs P. , Lenoble J. , Blumthaler M. , Martin T. , Seckmeyer G. , Philipona R. , De la Casiniere A. , Sergent C. , Gröbner J. , Cabot T. , Masserot D. , Pichler T. , Pougatch E. , Rengarajan G. , Schmucki D. , Simic S.
Published: February 2004

We compare three different methods for determining an average ‘effective‧ UV albedo. These methods are applied to spectral irradiance data from a measurement campaign held in the German Alps during the spring of 1999. The first method is based on the comparison of measurements of absolute levels of UV irradiance with model calculations. The second method takes advantage of changes in the spectral slope of spectral UV irradiance, which is a function of the surface albedo. In the third method, the surrounding area is partitioned into snow‐covered and snow‐free regions, and the effective albedo estimated by applying a higher or lower reflectivity to each facet before integrating over the surroundings. We present the differences and the correlations between the various methods as well as the results for the different locations.
Accurate estimation of transport properties from microtomographic images
Authors: Arns Christoph H. , Knackstedt Mark A. , Pinczewski M. Val , Lindquist W. B.
Published: February 2004

Estimating and minimizing several sources of numerical error result in very accurate predictions of transport properties directly from digitized images. Simulation of electrical conductivity on microtomographic images of Fontainebleau sandstone are in excellent agreement with experimental measurements over a wide range of porosity. The results show the feasibility of combining digitized images with transport calculations to accurately predict petrophysical properties of individual rock morphologies.
Enhancement of cloud‐to‐ground lightning over Houston, Texas
Authors: Orville Richard E. , Huffines Gary , Nielsen‐Gammon John , Zhang Renyi , Ely Brandon , Steiger Scott , Phillips Stephen , Allen Steve , Read William
Published: February 2004

Cloud‐to‐ground lightning flash data have been analyzed for the twelve‐year period 1989–2000, for a geographical area centered on Houston, Texas. Of the 1.6 million cloud‐to‐ground flashes in this area of study, approximately 752,000 flashes occurred in the summer months of June, July, and August, and 119,000 flashes in the months of December, January, and February. The highest flash densities, greater than 4 flashes km−2 in the summer and 0.7 flashes/km−2 in the winter, are near the urban areas of Houston. We suggest that the elevated flash densities could result from several factors, including, 1) the convergence due to the urban heat island effect, and 2) the increasing levels of air pollution from anthropogenic sources producing numerous small droplets and thereby suppressing mean droplet size. The latter effect would enable more cloud water to reach the mixed phase region where it is involved in the formation of precipitation and the separation of electric charge, leading to an enhancement of lightning.
A new peroxycarboxylic nitric anhydride identified in the atmosphere: CH2=CHC(O)OONO2 (APAN)
Authors: Tanimoto Hiroshi , Akimoto Hajime
Published: February 2004

We detected a peroxyacyl nitrate (PAN)‐type compound, peroxyacryloyl nitrate (CH2=CHC(O)OONO2, APAN) which has not previously been reported in the atmosphere. Identification of APAN was made from negative ion chemical ionization (NICI) mass spectra of a cryogenically concentrated ambient air sample by comparison with a synthesized standard. The thermally fragile nature of the compound, and the retention time of the synthesized standard provide additional evidence for the existence of APAN in ambient air. Observations made at a suburban site in Tokyo, and at Rishiri Island, a remote site in northern Japan, suggest the ubiquitous presence of APAN in the global atmosphere. While its mixing ratio was usually low (<1% of PAN), high‐APAN episodes (∼4% of PAN) were observed at Rishiri Island. APAN can be formed from acrolein, which is directly emitted from vehicle exhaust, and may be produced by oxidation of 1,3‐butadiene and aromatics. Further measurements of APAN along with acrolein and other NMHCs are required to understand its distribution, behavior, and sources in the atmosphere.
Is the climate sensitivity to ozone perturbations enhanced by stratospheric water vapor feedback?
Authors: Stuber Nicola , Ponater Michael , Sausen Robert
Published: February 2004

The climate response to a set of idealized ozone perturbations is investigated by integrations with a coupled atmosphere‐ocean model. Although all perturbations, including a homogeneous CO2 increase, induce the same stratosphere adjusted, tropopause radiative forcing, the climate response is quite variable within the set of experiments. Except for an upper tropospheric ozone increase, our model is more sensitive to ozone perturbations than to an equivalent CO2 perturbation. This applies in particular to a lower stratospheric ozone increase. The accompanying changes in the stratospheric water vapor (SWV) distribution are found to impose additional forcings on climate that may well exceed the forcings due to the original perturbations. Without SWV feedback on radiation the climate sensitivity to a lower stratospheric ozone increase draws remarkably near the respective value for equivalent CO2. This emphasizes the crucial role SWV may have in the forcing‐response relationship.
The Karnataka Late Cretaceous Dykes as products of the Marion Hot Spot at the Madagascar ‐ India Breakup Event: Evidence from40Ar‐39Ar geochronology and geochemistry
Authors: Kumar Anil , Pande K. , Venkatesan T. R. , Rao Y. J. Bhaskar
Published: February 2004

Two late Cretaceous mafic dykes with an ENE strike that is orthogonal to the west coast of India and located nearly 200 km inland around Huliyardurga, Karnataka state, yield40Ar‐39Ar plateau ages of 90.0±1.0 and 87.5±0.9 Ma. These Fe‐Ti‐enriched tholeiites are essentially co‐eval with at least four other igneous suites widely scattered in southern India, namely; the south and north Kerala dykes, the Agali‐Anaikatti dykes of central Kerala‐Tamil Nadu and lavas of St Mary islands off the west coast of India. The Karnataka Cretaceous dykes are also co‐eval and compositionally very similar to the Fe‐Ti‐enriched tholeiitic lavas and dykes around Mananjary, a major phase of Late Cretaceous magmatism along the eastern rifted margin of Madagascar which are believed to be products of the Marion hot spot that extruded at ∼88 Ma, synchronous with the India‐Madagascar break up event. The age and compositional similarities between these Late Cretaceous magmatic rocks from India and Madagascar constitute a clear evidence for extension of the thermal manifestations deep into the Indian peninsula.
Parameterizations of oxygen photolysis and energy deposition rates due to solar energy absorption in the Schumann‐Runge Continuum
Authors: DeMajistre R. , Yee Jeng‐Hwa , Zhu Xun
Published: February 2004

Parameterizations of the photolysis of molecular oxygen and corresponding energy deposition rates by solar radiation in the Schumann‐Runge continuum are presented. This parameterization is based on UARS/SOLSTICE version 9 daily solar irradiance and accounts for solar activity using 10.7 cm solar flux as a proxy. The error in the parameterization is 2% and the uncertainty introduced by using the 10.7 cm solar flux as a proxy is 5–10%. The parameterization is of suitable accuracy and efficiency to be used as part of multidimensional models.
Equation of state of Al‐bearing perovskite to lower mantle pressure conditions
Authors: Daniel Isabelle , Cardon Hervé , Fiquet Guillaume , Guyot François , Mezouar Mohamed
Published: February 2004

Al2O3 is estimated to total 4 to 5 mol% in all mantle compositional models, and is believed to be incorporated into (Mg,Fe)SiO3‐perovskite at lower mantle conditions. Using synchrotron X‐ray diffraction, we have measured the 300 K equation of state of a perovskite with XAl=Al/(Al+Mg+Si)=.077, up to 32 GPa. A least squares refinement of two independent data sets yields the following equation of state parameters V0=163.52(3) Å³, K0=229(4) GPa, and K0=2.5(4). These values allow us to assess the most probable substitution mechanism for aluminium into perovskite at pressure conditions of the shallow lower mantle. Al3+ is likely to be incorporated in place of Si4+ in the octahedral site of perovskite, hence requiring the creation of oxygen vacancies for charge balance. As a consequence, aluminous perovskites may have a high affinity for water. The enhanced compressibility of aluminous perovskite certainly has also strong geophysical and geochemical implications, as it may revive perovskite‐rich lower mantle models.
Electric field and plasma flow: What drives what?
Authors: Vasyliūnas Vytenis M.
Published: February 2004

The MHD approximation connects the plasma bulk flow velocity and the electric field, but it does not say whether one of them can be considered as causing or producing the other, and if so, which one. This question is often viewed as one having no unambiguous answer and possibly no physical meaning. However, a definite answer can be obtained by solving the basic equations with appropriate initial values, with the result that, for the commonly considered case where the Alfvén speed is small compared to the speed of light, (1) a given plasma bulk flow produces an electric field, (2) a given electric field does not produce a plasma bulk flow. The general result can also be derived as a simple consequence of conserving the total (plasma plus electromagnetic field) linear momentum.
Seismic facies characterization by monoscale analysis
Authors: Herrmann Felix J. , Lyons William J. , Stark Colin P.
Published: February 2004

Relating sedimentary records to seismic data is a major challenge. By shifting focus to a scale‐invariant sharpness characterization for the reflectors, we develop an attribute that can capture and categorize the main reflector features, without being sensitive to amplitudes. Sharpness is defined by a scale exponent, which expresses singularity order and determines the reflection signature/waveform. Local scale exponent estimates are obtained with a new monoscale method. Compared to multiscale wavelet analysis, our method has the advantage of measuring transition exponents at a single fixed scale using a simple on‐off criterion. The exponents contain amplitude variation information and describe lithological onsets. We create an image of the earth's local singularity structure by applying our method to seismic traces and well‐log data. The singularity map facilitates interpretation, facies characterization, and integration of well and seismic data.
Accelerating seismicity and stress accumulation before large earthquakes
Authors: Bowman David D. , King Geoffrey C. P.
Published: February 2004

The stress field that existed before a large earthquake can be calculated based on the known source parameters of the event. This stress field can be used to define a region that shows greater seismic moment rate changes prior to the event than arbitrarily shaped regions, allowing us to link two previously unrelated subjects: Coulomb stress interactions and accelerating seismicity before large earthquakes. As an example, we have examined all M ≥ 6.5 earthquakes in California since 1950. While we illustrate the model using seismicity in California, the technique is general and can be applied to any tectonically active region. We show that where sufficient knowledge of the regional tectonics exists, this method can be used to augment current techniques for seismic hazard estimation.
Electron phase‐space holes and the VLF saucer source region
Authors: Ergun R. E. , Carlson C. W. , McFadden J. P. , Strangeway R. J. , Goldman M. V. , Newman D. L.
Published: February 2004

The Fast Auroral SnapshoT (FAST) satellite has identified new properties of VLF saucers that are important to understanding their generation and the physical processes in the source region. The most significant finding is a frequent occurrence (∼79%) of electron phase‐space holes on flux tubes of the VLF saucer source in the downward current region. This finding implies either a common energy source or a direct association between the two phenomenon. FAST observations also demonstrate that VLF saucer vertices are strongly correlated with up‐going electron fluxes associated with diverging DC electric field structures. These observations imply parallel electric fields along the source flux tube of VLF saucers.
Comparative study of dynamical critical scaling in the auroral electrojet index versus solar wind fluctuations
Authors: Uritsky Vadim M. , Klimas Alex J. , Vassiliadis Dimitris
Published: February 2004

Based on an analysis of auroral electrojet (AE) index data, we demonstrate that the temporal evolution of magnetospheric perturbations exhibits non‐trivial power‐law relations consistent with the behavior of a general class of statistical physical models in the vicinity of a stationary critical point. We show that the ensemble average dynamics of the activity bursts in the AE index is essentially scale‐free and can be characterized in terms of spreading critical exponents η and δ. The lifetime T and the size S of the bursts show strong algebraic correlation that is approximated by the dependence S ∼ T1+η+δ. For times shorter than 3.5 hours, we find scaling features in the AE index that are independent of the solar wind input, thus indicating the internal magnetospheric origin of the revealed effects.
Return stroke transmission line model for stroke speed near and equal that of light
Authors: Thottappillil R. , Schoene J. , Uman M. A.
Published: February 2004

Assuming that the lightning return stroke transmission‐line model is applicable, we derive an expression for the return‐stroke magnetic field for an arbitrary return stroke speed and from that expression show that for a return stroke speed equal to the speed of light c the electric and magnetic field waveforms at all points in space and the current waveform are identical. Recent measurements indicate that the electric field and current waveforms are similar for about 100 ns for triggered lightning return strokes, potentially implying that the initial return stroke speed is actually near c for that time, that is, for the bottom 30 m or so of the triggered lightning channel. While for the transmission‐line model the current waveform and the total electric field waveform are identical for a return stroke speed of c, we show that each of the three individual components (electrostatic, induction, and radiation) that comprise the total field varies significantly with distance.
The death of an altocumulus cloud
Authors: Larson Vincent E. , Fleishauer Robert P. , Kankiewicz J. Adam , Reinke Donald L. , Vonder Haar Thomas H.
Published: February 2004

What causes altocumulus clouds to decay? To address this question, the authors examine an observational case study of a mid‐level cloud that was measured during the Complex Layered Cloud Experiments (CLEX). The budget of liquid water reveals that the cloud was not dissipated by fallout of precipitation. Rather, the largest contributor to decay of liquid water was subsidence drying. The strong link between subsidence and cloud lifetime is an important difference between altocumuli and boundary layer clouds. The net effect of radiative transfer on our cloud is unclear: liquid water was directly increased by radiative cooling, but this was offset by radiatively induced entrainment drying.
Distant plasma sheet ion distributions during reconnection
Authors: Owen C. J. , Mist R. T.
Published: February 2004

Previous models of the plasma sheet following reconnection and current sheet acceleration predict ‧lima‐bean‧ ion distributions. These are inconsistent with observational constraints. We postulate that following initial interaction with the current sheet, a fraction of outflow ions are backscattered and re‐encounter the current sheet. Fermi acceleration processes then generate an additional high‐energy outflow population. In the backscatter region these ions form a complete shell in velocity space, providing sufficient pressure to support weak fields. Further from the current sheet, where backscatter is less efficient, a hemispherical shell of ions moves away from the current sheet, and field strengths are nearer the external lobe value. The fastest ions stream ahead of the bulk population to form the plasma sheet boundary layer. This model predicts a multi‐layered plasma sheet structure, consistent with recent GEOTAIL observations.
Ultraviolet radiation in partly snow covered terrain: Observations and three‐dimensional simulations
Authors: Kylling Arve , Mayer Bernhard
Published: February 2004

Coastal regions with fiords and mountains with seasonally varying snowcover form complex environments for ultraviolet radiative transfer. The presence of snow causes enhanced levels of UV radiation, the quantitative interpretation of which is only possible with detailed three‐dimensional radiative transfer simulations. Such calculations of the irradiance at 340 nm have been performed for the location of Tromsø, Norway, under cloudless and overcast conditions, moving the snowline from 0 to 1000 m.a.s.l. and finally for snow free conditions. The evolution of the radiation enhancement as the snowline moves up is compared with measurements made by a narrow bandwidth multichannel filter instrument. For a cloudless sky the simulations and measurements exhibit a similar radiation enhancement of 23–27%. For the investigated overcast situation the radiation enhancement is about 40–60%.
Global observation of anthropogenic aerosols from satellite
Authors: Tanré D. , Bréon F. M. , Deuzé J. L. , Herman M. , Goloub P. , Nadal F. , Marchand A.
Published: February 2004

This paper provides the first climatology from satellite of aerosol loading, both over land and oceanic surfaces. Over land, aerosol loading is retrieved using a new remote sensing technique based on the polarization signature of scattered solar radiances. The product is sensitive to particles that are within the accumulation mode, smaller than ≈0.5µm. Those are mainly produced by anthropogenic sources, like smoke and urban/industrial aerosols. A rough identification of aerosol origin is obtained from the concomitant detection of fires from spaceborne observations. The combination of aerosol load and fire identification suggests that biomass burning is the main source of small particles in the atmosphere and that, at the regional scale, other anthropogenic activities have a significant impact limited to China and India.
Anthropogenic signals recorded in an ice core from Eclipse Icefield, Yukon Territory, Canada
Authors: Yalcin Kaplan , Wake Cameron P.
Published: February 2004

Trends in the annual flux of sulfate and nitrate in a new ice core collected at an elevation of 3017 m on Eclipse Icefield, 45 km northeast of Mt. Logan were examined to determine the effect of anthropogenic activity on precipitation chemistry in the remote northwest North America mid‐troposphere. The annual flux of both sulfate and nitrate at Eclipse began increasing in the 1940s, demonstrating, for the first time, the anthropogenic sulfate and nitrate pollution of the northwest North American Arctic in an ice core from this region. Comparison of the Eclipse record with regional emission estimates for total sulfur and nitrogen oxides suggests that Eurasia is the dominant source of pollutants reaching Eclipse. The available data does not permit a confident assessment of the relative importance of European versus Soviet emissions in producing the observed trends in sulfate and nitrate at Eclipse.
Sources of geomagnetic storms for solar minimum and maximum conditions during 1972–2000
Authors: Richardson I. G. , Cliver E. W. , Cane H. V.
Published: February 2004

We determine the solar wind structures (coronal mass ejection (CME)‐related, corotating high‐speed streams, and slow solar wind) driving geomagnetic storms of various strength over nearly three solar cycles (1972–2000). The most intense storms (defined by Kp) at both solar minimum and solar maximum are almost all (∼97%) generated by transient structures associated with CMEs. Weaker storms are preferentially associated with streams at solar minimum and with CMEs at solar maximum, reflecting the change in the structure of the solar wind between these phases of the solar cycle. Slow solar wind generates a small fraction of the weaker storms at solar minimum and maximum. We also determine the size distributions of Kp for each solar wind component.
The July–August 2000 seismic swarms at Campi Flegrei Volcanic Complex, Italy
Authors: Saccorotti Gilberto , Bianco Francesca , Castellano Mario , Del Pezzo Edoardo
Published: February 2004

Two swarms of microearthquakes (ML ≤ 2.2), occurred on July 2–7 and August 22, 2000 at Campi Flegrei, accompained by a ground uplift episode (4 cm) which interrupted on early March 2000 the descending trend started on 1985. Spectral analysis indicates a direct involvement of magmatic/hydrothermal fluids in the source process of the July swarm, while the August events are typical of shear failure, similar to most of the earthquakes that occurred during the last (1982–1984) bradyseismic crisis. Precise 3‐D relative location applied to similar earthquakes allows for the recognition of two parallel alignments trending NE‐SW at depths of 1.7 and 3.2 Km. This trend is consistent with the direction of the main focal plane obtained from fault plane solutions and evidences tensile failure in close proximity to the zone of maximum uplift as depicted by geodetic measurements. A fault weakening mechanism triggered by increasing pore pressure is invoked as the cause of these earthquakes.
Vector empirical orthogonal function modes of the ocean surface wind variability derived from satellite scatterometer data
Authors: Pan Jiayi , Yan Xiao‐Hai , Zheng Quanan , Liu W. Timothy
Published: February 2004

Ocean surface winds derived from NSCAT, QuikSCAT and ERS‐1/2 scatterometer observations during a period from January 1992 to April 2000 were analyzed using the vector empirical orthogonal function (VEOF) method. With the boreal winter and summer oscillation, the first VEOF is dominated by the Indian and East Asian monsoons and also shows an annual cycle of the trade winds. The second VEOF represents the boreal autumn and spring oscillation, and reveals a transition state between winter and summer. The third VEOF indicates the wind variability associated with El Niño Southern Oscillation (ENSO) events, because the temporal mode has a high correlation coefficient of 0.8 with the Southern Oscillation Index (SOI). Furthermore, the third mode reveals the teleconnection of the Indian monsoon and wind variability over high latitude oceans, such as the Aleutian Low system, with ENSO events.
Magnetic local time dependency on cusp ion velocity dispersions in the mid‐altitude cusp
Authors: Krauklis I. , Coates A. J. , Peterson W. K.
Published: February 2004

Observations of cusp ion velocity dispersions made by the TIMAS instrument on the Polar spacecraft in the mid‐altitude cusp during intervals of northward interplanetary magnetic field (IMF) reveal a clear ordering with magnetic local time (MLT). Between 1100 and 1300 MLT the injected ion velocity increased with invariant latitude for 78% of the cusp crossings, between 0900 and 1100 MLT this percentage reduced to 35% and between 1300 and 1500 MLT the percentage reduced to 57%. In contrast similar observations made during intervals of southward IMF revealed no MLT dependency. Between 0900 and 1500 MLT the injected ion velocity increased with invariant latitude for only 17% of the observed cusp crossings. We suggest that the difference in the MLT dependency between northward and southward IMF can be best explained by the different characteristics of polar convection patterns for sub‐solar and lobe reconnection.
Active chlorine in the remote marine boundary layer: Modeling anomalous measurements of δ13C in methane
Authors: Allan W. , Lowe D. C. , Cainey J. M.
Published: February 2004

Measurements of δ13C in methane in the marine boundary layer (MBL) of the extratropical Southern Hemisphere imply a kinetic isotope fractionation much larger than would be expected if the hydroxyl radical were the only tropospheric methane sink. We use a simple chemical box model to show that the assumption of a MBL active chlorine (Cl•) sink can explain these anomalous observations provided there is a seasonal cycle in the Cl• sink with a summer‐winter concentration difference ∼ 6 · 10³ cm−3. The required summer maximum and yearly mean Cl• concentrations are plausible, and imply a global Cl• sink strength for methane of < 5 Tg yr−1. Choice of a Cl• sink seasonal cycle linked to the nonsinusoidal dimethyl sulfide seasonal cycle gives the observed fractionation with a smaller yearly mean Cl• concentration than equivalent sinusoidal Cl• cycles.
Warming and structural changes in the east (Japan) Sea: A clue to future changes in global oceans?
Authors: Kim Kuh , Kim Kyung‐Ryul , Min Dong‐Ha , Volkov Yuri , Yoon Jong‐Hwan , Takematsu Masaki
Published: February 2004

The East (Japan) Sea has been in a warming trend during the last more than 40 years: a 0.1–0.5 degree of warming in the upper 1000 meters. The warming is accompanied by the deepening of the oxygen minimum layer by more than 1000 meters. The analysis of chemical tracers such as dissolved oxygen and CFCs clearly implies that the warming is associated with changes in deep water structures in the area, resulted from a replacement of the past bottom‐water formation with an intermediate water formation in recent time. This shift has a remarkable resemblance to that anticipated to the ocean conveyor‐belt system in coming century associated with recent global warming. In considering a rapid turn‐over time of time scale less than 100 years, the East Sea may serve as a natural laboratory for global changes in the future.
Electromagnetic heterogeneity of the seismogenic region of 1962 M6.5 Northern Miyagi Earthquake, northeastern Japan
Authors: Mitsuhata Yuji , Ogawa Yasuo , Mishina Masaaki , Kono Toshio , Yokokura Takanobu , Uchida Toshihiro
Published: February 2004

Magnetotelluric surveys were carried out to investigate the electrical resistivity structure of the seismogenic region of the 1962 Northern Miyagi Earthquake (M6.5) in Miyagi Prefecture, northeastern Japan. A 2‐D inversion reveals the existence of a deep conductive zone and overlying resistive zone in the upper crust. A positive aeromagnetic anomaly is also recognized above the resistive zone, which is interpreted as a buried Kitakami granitoid pluton. By comparison with the seismicity, we found that the microearthquakes occur just above the deep conductor and in the resistive zone, and that several S‐wave reflectors are just above the deep conductor. Since the S‐wave reflectors suggest the existence of fluid beneath them, the deep conductor can be interpreted as a fluid‐filled zone. Moreover, we suggest that the seepage of the fluid from the conductive fluid‐filled zone to the resistive granitoid pluton can become a trigger of the earthquakes.
Arctic Oscillation signature in a Red Sea coral
Authors: Rimbu Norel , Lohmann Gerrit , Felis Thomas , Pätzold Jürgen
Published: February 2004

We show that the winter time series of the Ras Umm Sidd coral oxygen isotope record from the northern Red Sea (approximately 28°N) is linked to the Arctic Oscillation phenomenon, the Northern Hemisphere's dominant mode of atmospheric variability. Until now, the detection of this mode, which is most prominent in winter, in proxy climate records was difficult due to the lack of a clear seasonality in most paleoclimatic archives. The results suggest that northern Red Sea corals can provide information about the low‐frequency variability of the Northern Hemisphere winter circulation during the pre‐instrumental period.
Latitude variations in light scattered from polar mesospheric clouds
Authors: Carbary J. F. , Morrison D. , Romick G. J.
Published: February 2004

A middle ultraviolet imager over the northern and southern polar regions has measured the scattered intensities of polar mesospheric clouds (PMC) during the austral summer of 1997–98 and the arctic summer of 1999. The intensities, corrected for solar zenith angle, are those at the peak in the PMC radiance profiles for a waveband of 235–263 nm. The peak radiance averaged 12.0±11.0 mega‐Rayleighs (MR) for 13 passes over the south polar region, where the scattering angle was ∼111°. The peak radiance averaged 11.4±7.6 MR for 12 passes over the north polar region, where the scattering angle was ∼48°. The PMC intensities increased with increasing latitude in both the north and the south, but the rate of increase was twice as fast in the south (0.60 MR/° latitude) as in the north (0.32 MR/° latitude).
Extreme water mass anomaly observed in the Hawaii ocean time‐series
Authors: Lukas Roger , Santiago‐Mandujano Fernando
Published: February 2004

Extremely anomalous water mass properties, with deviations as high as 35σ, were observed in the thermocline during January 2001 at the Hawaii Ocean Time‐series site north of Oahu. The spatial distribution of the anomalous waters is consistent with a submesoscale vortex with radius ∼15 km, possibly a remnant of a mesoscale eddy. The most plausible source location of the anomalous waters is offshore of Mexico near Baja California. Given the southwestward subtropical gyre circulation, it is unlikely that these waters were transported directly westward to Hawaii. Unusual northward transport of Equatorial Waters along the North American coast during the 1997–98 El Niño event, and subsequent transport southwestward in the core of a California Undercurrent eddy is more plausible. El Niño modulation of eddy transport and diffusion of water mass properties may substantially impact the mean distribution of properties in the North Pacific subtropical gyre.
Does apparent stress vary with earthquake size?
Authors: Ide Satoshi , Beroza Gregory C.
Published: February 2004

Seismic energy is distributed across a wide frequency band so that limited bandwidth recording can lead to substantial underestimates of the radiated seismic energy or introduce an artificial upper bound of radiated energy. We estimate an adjustment factor to account for the probable missing energy and apply it to three previously studied data sets with limited recording bandwidth. We find that this adjustment, together with accounting for possibly missing events, eliminates much of the moment dependence of radiated energy found previously. We obtain a nearly constant ratio of radiated energy to seismic moment, 3 × 10−5, or 1 MPa of apparent stress drop, over 17 orders of seismic moment. This suggests that deviation from similarity of the energy radiation for seismic events essentially the entire observable range of earthquake size may not yet be resolved.
Cumbre Vieja Volcano—Potential collapse and tsunami at La Palma, Canary Islands
Authors: Ward Steven N. , Day Simon
Published: February 2004

Geological evidence suggests that during a future eruption, Cumbre Vieja Volcano on the Island of La Palma may experience a catastrophic failure of its west flank, dropping 150 to 500 km³ of rock into the sea. Using a geologically reasonable estimate of landslide motion, we model tsunami waves produced by such a collapse. Waves generated by the run‐out of a 500 km³ (150 km³) slide block at 100 m/s could transit the entire Atlantic Basin and arrive on the coasts of the Americas with 10–25 m (3–8 m) height.
An analytical relationship between scattering attenuation and porosity in oceanic crust
Authors: Sun Y. F. , Goldberg D.
Published: February 2004

We present a theoretical derivation of the relationship between scattering attenuation and porosity based on a multiple back‐scattering model. Two parameters, a heterogeneity parameter γ and a formation parameter β0, are introduced to characterize this relationship:
, where ϕ is porosity, Qs0 is a measured value at ϕ=0. The formation parameter β0 describes the micro‐scale formation properties such as rock and pore fluid properties and cracks. The heterogeneity parameter γ represents the effects of local/regional‐scale heterogeneities on scattering attenuation, such as layers and fractures. The relative importance of these two parameters depends on the propagating wavelength. This analytical form fits empirical results in oceanic crust that have been previously reported. Numerical analysis shows that the local/regional‐scale heterogeneity, γ, plays a more dominant role than the microscale properties, β0, on scattering attenuation at seismic and sonic wavelengths in the oceanic crust.
How fast is rupture during an earthquake? New insights from the 1999 Turkey Earthquakes
Authors: Bouchon Michel , Bouin Marie‐Paule , Karabulut Hayrullah , Toksöz M. Nafi , Dietrich Michel , Rosakis Ares J.
Published: February 2004

We report that during the two devastating 1999 earthquakes in Turkey, rupture propagated over a large part of the nearly 200km long fault zone at supershear speed approaching 5km/s. We present observations and modeling which confirm the original inference of supershear rupture during the Izmit earthquake and we show that supershear rupture also occurred during the Düzce earthquake. We show that the rupture velocity measured—about
times the shear wave velocity—is the value predicted by theoretical studies in fracture dynamics. We look for clues to explain these observations.
Some analytical calculations on the effect of turbulence on the settling and growth of cloud droplets
Authors: Ghosh S. , Jonas P. R.
Published: February 2004

Recent research on the interaction of inertial particles with turbulent vortices show that inertial bias causes particles to settle faster in turbulence than in still air as a consequence of particle accumulation in downward fluid velocity regions [Hainaux et al., 2000; Davila and Hunt 2001; Fevrier et al., 2000]. To date, these effects have not been included in models of droplet collection growth. In addition earlier models have also neglected the dependence of the collection growth on the radius of the smaller collected drops assuming that the collected drops are stationary. We have considered all these effects and have still been able to solve the collection equation analytically and the earlier Baker[1993] results are retrievable as a special case when these effects are turned off. The results presented in this study are in closed form and are therefore extremely attractive for precipitation parametrizations in large scale models.
Freshening of the upper thermocline in the North Pacific Subtropical Gyre associated with decadal changes of rainfall
Authors: Lukas Roger
Published: February 2004

Repeated observations in the North Pacific subtropical gyre near Hawaii reveal pronounced freshening (∼0.15 psu) and cooling (∼0.5°C) of the upper thermocline from 1991 through 1997. The freshening appears progressively later on deeper isopycnals consistent with subduction of surface salinity anomalies at higher latitudes and subsequent southward advection. Winter rainfall anomalies in the central North Pacific are dominated by the El Niño/Southern Oscillation (ENSO) phenomenon and by the Pacific Decadal Oscillation (PDO), with the wet phase of the PDO leading the observed freshening. The reversal of the freshening trend in the upper thermocline is related both to extreme drought near Hawaii during the 1997–98 ENSO, and to protracted drought associated with the PDO. The density compensation of decadal thermal anomalies by salinity anomalies means that they do not disperse dynamically, and that the hydrological cycle is an active component of decadal climate variability in the North Pacific.
A negative test of orbital control of geomagnetic reversals and excursions
Authors: Kent Dennis V. , Carlut Julie
Published: February 2004

A ∼41 Kyr periodic component has been reported in some sedimentary paleointensity records, allowing speculation that there may be some component of orbital control of geomagnetic field generation such as by obliquity modulation. However, no discernable tendency is found for astronomically‐dated geomagnetic reversals in the Plio‐Pleistocene (0 to 5.3 Ma) or excursions in the Brunhes (0 to 0.78 Ma) to occur at a consistent amplitude or phase of obliquity cyclicity, nor of orbital eccentricity. An implication is that paleointensity lows which are characteristically associated with these features are not distributed in a systematic way relative to obliquity and eccentricity, supporting the idea that orbital forcing does not power the geodynamo.
The size effect of hematite and corundum inclusions on the efflorescence relative humidities of aqueous ammonium sulfate particles
Authors: Martin Scot T. , Han Jeong‐Ho , Hung Hui‐Ming
Published: February 2004

Mineral dusts inside aqueous atmospheric particles provide surfaces that induce crystallization during episodes of decreasing relative humidity (RH). Submicron aqueous ammonium sulfate particles containing hematite (α‐Fe2O3) and corundum (α‐Al2O3) inclusions are investigated in an aerosol flow tube at 298 K. As compared to 35% RH where homogeneous nucleation is rapid, the heterogeneous nuclei regulate the RH from 35% up to 60% RH as the inclusion size varies from 50 to 450 nm. The strong size dependence can be rationalized by an active site model. Model optimization yields 1010.4 sites cm−2 and m < 0 for α‐Al2O3 and 109 sites cm−2 and m=0.04 for α‐Fe2O3 particles.
Multidomain hematite: A source of planetary magnetic anomalies?
Authors: Dunlop David J. , Kletetschka Gunther
Published: February 2004

Thermoremanent magnetization (TRM) in hematite is larger than TRM in magnetite for grain sizes ≥10 µm. We show that hematite's weak spontaneous magnetization Ms causes its strong TRM, since the self‐demagnetizing field Hd opposing large domain wall displacements is proportional to Ms. In hematite, Hd is comparable to the Earth's magnetic field but in magnetite, Hd is 1000 times larger. As a result, Earth's field TRM of MD hematite (≈ 0.3 Am²/kg) outweighs TRM and induced magnetization of MD magnetite (≈0.01–0.02 Am²/kg and rivals TRM of single‐domain and PSD magnetite as a source of magnetic anomalies on Earth and perhaps on Mars.