bluuebunny/crossref_metadata_2025 huggingface dataset:
Bathymetry and gravity data across a mid‐Cretaceous triple junction trace in the southwest Pacific basin
Authors: Pockalny Robert A. , Larson Roger L. , Viso Richard F. , Abrams Lewis J.
Published: October 2002

Bathymetry and gravity profiles from the southwest Pacific have been used to locate and characterize the trace of a ridge‐ridge‐ridge triple junction created between ∼84 and ∼120 Ma. In areas free of subsequent volcanism, the triple junction trace is identified by a 1 km‐deep bathymetric trough bordered by seafloor spreading fabric with distinctly different trends. Crustal thickness estimates obtained with gravity models indicate the triple junction trace is often characterized by anomalously thin crust, which may result from relatively low melt production at a triple junction. Crustal thickness estimates follow previously identified spreading rate‐related trends.
An improved ELF/VLF method for globally geolocating sprite‐producing lightning
Authors: Price Colin , Asfur Mustafa , Lyons Walter , Nelson Thomas
Published: October 2002

The majority of sprites, the most common of transient luminous events (TLEs) in the upper atmosphere, are associated with a sub‐class of positive cloud‐to‐ground lightning flashes (+CGs) whose characteristics are slowly being revealed. These +CGs produce extremely low frequency (ELF) and very low frequency (VLF) radiation detectable at great distances from the parent thunderstorm. During the STEPS field program in the United States, ELF/VLF transients associated with sprites were detected in the Negev Desert, Israel, some 11,000 km away. Within a two‐hour period on 4 July 2000, all of the sprites detected optically in the United States produced detectable ELF/VLF transients in Israel. All of these transients were of positive polarity (representing positive lightning). Using the VLF data to obtain the azimuth of the transients, and the ELF data to calculate the distance between the source and receiver, we remotely determined the position of the sprite‐forming lightning with an average locational error of 184 km (error of 1.6%).
Salinity records for the 1997–98 El Niño from Western Pacific corals
Authors: Morimoto Maki , Abe Osamu , Kayanne Hajime , Kurita Naoyuki , Matsumoto Eiji , Yoshida Naohiro
Published: October 2002

Seasonal sea surface salinity (SSS) records can be of great value in reconstructing El Niño/Southern Oscillation (ENSO) variability in the equatorial Western and Central Pacific, a region where ENSO‐related evaporation and precipitation (E‐P) changes are dramatic. The δ18O values of coral skeleton (δ18Ocoral) reflect seawater δ18O (δ18Oseawater) changes, which in tropical oceans are also generally influenced by E‐P changes. Therefore, δ18Ocoral is a good indicator of rainfall and ENSO variability. We present biweekly data from Palau, in the northern part of the Western Pacific Warm Pool, for the period 1998–2000, which indicate a strong quantitative relationship between δ18Ocoral, sea surface temperature, δ18Oseawater and SSS. The coral skeletal δ18O values documented the SSS changes after the 1997–98 El Niño; therefore, δ18Ocoral can be used to estimate paleosalinity changes. However, the slope of the δ18Oseawater ‐ SSS relationship cannot be assumed to be constant throughout the tropics, making site‐specific calibrations is essential.
On the structure and compressibility of CaSiO3 perovskite
Authors: Akber‐Knutson Sofia , Bukowinski Mark S. T. , Matas Jan
Published: October 2002

The equation of state and structure of CaSiO3 perovskite are determined at high pressures using the density‐functional‐based Variationally Induced Breathing (VIB) method, modified with a small, parameterized covalent correction to the short‐range Si‐O interaction. Our thermally corrected room temperature equation of state parameters (V0 = 45.90 ± 0.02 Å, K0 = 228 ± 2 GPa, K′ = 4.3 ± 0.1) are in very good agreement with near‐hydrostatic compression data as well as recent calculations based on first‐principles methods. We examined the tetragonal, orthorhombic, and triclinic structures, and compared their stabilities relative to the cubic structure at lower mantle pressures. We found that the orthorhombic perovskite structure of CaSiO3 is the thermodynamically stable phase at all mantle pressures. The structural and energy differences between the orthorhombic and cubic lattices under static conditions are small, and increase only slightly with pressure. Consequently, the cubic structure may be thermodynamically stable at lower mantle temperatures.
Fault slip‐rate variations during crustal‐scale strain localisation, central Italy
Authors: Roberts Gerald P. , Michetti Alessandro M. , Cowie Patience , Morewood Nigel C. , Papanikolaou Ioannis
Published: October 2002

Rates of plate motion are generally uniform over 10–102 Myrs timescales. Faults between tectonic plates might, therefore, be expected to show temporally‐uniform slip‐rates if the same number of faults remain active. For an extending region of the Eurasia‐Africa plate boundary, Italy, finite throw values (vertical component of the slip) for seismogenic normal faults are less than that predicted when recent throw‐rates are extrapolated over the fault lifetimes. The effect correlates with distance from the fault system tips and demonstrates that the slip‐rates on centrally‐located faults have increased with time. Neighbouring normal faults were active in the Quaternary but show no signs of surface faulting during the latest Pleistocene to Holocene. Death of these faults has provided the extra strain per unit time to drive the increased slip‐rates measured on other faults. Thus, fault interaction and death modify slip‐rates and seismic hazards associated with plate tectonics.
An event‐driven phytoplankton bloom in southern Lake Michigan observed by satellite
Authors: Lesht B. M. , Stroud J. R. , McCormick M. J. , Fahnenstiel G. L. , Stein M. L. , Welty L. J. , Leshkevich G. A.
Published: October 2002

Sea‐viewing Wide Field‐of‐View Sensor (SeaWiFS) images from June 1998 show a surprising early summer phytoplankton bloom in southern Lake Michigan that accounted for approximately 25% of the lake's annual gross offshore algal primary production. By combining the satellite imagery with in situ measurements of water temperature and wind velocity we show that the bloom was triggered by a brief wind event that was sufficient to cause substantial vertical mixing even though the lake was already stratified. We conclude that episodic events can have significant effects on the biological state of large lakes and should be included in biogeochemical process models.
Flow‐through magnetic reconnection
Authors: Siscoe G. L. , Erickson G. M. , Sonnerup B. U. Ö. , Maynard N. C. , Schoendorf J. A. , Siebert K. D. , Weimer D. R. , White W. W. , Wilson G. R.
Published: October 2002

This note reports properties of a little‐studied but possibly common mode of magnetic reconnection—“flow‐through reconnection” or “FTR”—characterized by plasma flowing at high speed right through a stationary reconnection site. FTR is readily identified in global MHD simulations by the following diagnostic properties, which affect slab‐like portions (tongues) of the magnetopause, usually at high latitudes and along the flanks. 1. A magnetic null point lies near the downwind extreme of an FTR tongue. 2. Elsewhere within the tongue the magnetic field is also weak. 3. Electric current density is strong. 4. “J‐dot‐E” dissipation is strong. 5. Most remarkable, the electric field is antiparallel to and stronger than −V × B, the motional electric field. This last property implies that plasma and magnetic field flow in opposite directions—plasma downwind, magnetic field upwind. Here we discuss FTR for strictly northward interplanetary magnetic field, which manifests FTR properties in idealized geometry.
Subsidence monitoring using SAR interferometry: Reduction of the atmospheric effects using stochastic filtering
Authors: Crosetto Michele , Tscherning Carl Christian , Crippa Bruno , Castillo Manuel
Published: October 2002

The atmospheric effects represent one of the major limits of SAR interferometry as a quantitative technique to monitor subsidences. In this work, which focuses on subsidences of small spatial extent, a procedure to reduce these effects is described. The atmospheric component of the interferometric phase is estimated adopting a filtering and prediction procedure, which exploits the phase over stable areas identified in the vicinity of the analysed subsidence area. The procedure was validated on a suitable test site located in North‐eastern Spain. Furthermore, it was employed in the study of a small‐scale subsidence, where the interferometric results were validated using precise geodetic observations.
Coupling between cycles of phytoplankton biomass and aerosol optical depth as derived from SeaWiFS time series in the Subantarctic Southern Ocean
Authors: Gabric Albert J. , Cropp Roger , Ayers Gregory P. , McTainsh Grant , Braddock Roger
Published: October 2002

The Subantarctic Southern Ocean is a high‐nutrient low‐chlorophyll region, and it has been suggested that primary production is limited by deep mixing and the availability of iron. Australian dust is high in iron content and can be transported over the Subantarctic Southern Ocean, particularly during the austral spring and summer when dust storm frequency in southern Australia is maximal. We present evidence for a coupling between satellite‐derived (SeaWiFS) aerosol optical thickness and chlorophyll concentration in the upper ocean. The coupling is evident at monthly, weekly and daily timescales. Although the monthly coherence is likely to be due to other covarying factors, the coupling at weekly and daily timescales supports the hypothesis that the episodic atmospheric delivery of iron is stimulating phytoplankton growth. We also discuss the impact of oceanic dimethylsulfide production on aerosol concentration in the study region.
The paradoxical increase of Mediterranean extreme daily rainfall in spite of decrease in total values
Authors: Alpert P. , Ben‐Gai T. , Baharad A. , Benjamini Y. , Yekutieli D. , Colacino M. , Diodato L. , Ramis C. , Homar V. , Romero R. , Michaelides S. , Manes A.
Published: October 2002

Earlier reports indicated some specific isolated regions exhibiting a paradoxical increase of extreme rainfall in spite of decrease in the totals. Here, we conduct a coherent study of the full‐scale of daily rainfall categories over a relatively large subtropical region‐ the Mediterranean‐ in order to assess whether this paradoxical behavior is real and its extent. We show that the torrential rainfall in Italy exceeding 128 mm/d has increased percentage‐wise by a factor of 4 during 1951–1995 with strong peaks in El‐Nino years. In Spain, extreme categories at both tails of the distribution (light: 0‐4 mm/d and heavy/torrential: 64 mm/d and up) increased significantly. No significant trends were found in Israel and Cyprus. The consequent redistribution of the daily rainfall categories ‐torrential/heavy against the moderate/light intensities ‐ is of utmost interest particularly in the semi‐arid sub‐tropical regions for purposes of water management, soil erosion and flash floods impacts.
Modelling nutrient cycling during the eastern Mediterranean transient event 1987–1995 and beyond
Authors: Stratford Kevin , Haines Keith
Published: October 2002

Recent observations in the eastern Mediterranean have revealed not only significant changes to the temperature and salinity structure of the deep waters, but an uplifting of the thermocline which has been accompanied by altered distributions of biogeochemical species such as dissolved nutrients and oxygen. This letter presents results from a fully coupled high resolution physical and biogeochemical cycling model which reproduces the eastern Mediterranean transient event. The impact of the event on both biogeochemical tracer distributions and modelled export production between 1987 and 1995 is investigated and compared with available observations. When run on with climatological conditions after 1995, the model suggests the transient event has little impact on export production in the basin.
Impact of some land hydrological phenomena on GOCE mission
Authors: Moreaux Guilhem , Balmino Georges
Published: October 2002

The GOCE (Global Ocean Circulation Explorer) satellite mission, scheduled for launch in 2005, is designed to map out the Earth's gravity field to high accuracy on a global scale over a nominal lifetime of 2 years. Changes in the gravity field are caused by the redistribution of mass within the Earth and on or above its surface. Since GOCE will fly at a low orbit (250 km), it will be under influence of mass redistribution. Therefore, in this paper, based on Global Soil Wetness Project data, we both estimate the impact of some land hydroligical phenomena (evapotranspiration, runoff, snow cover, and soil moisture) in terms of orbit perturbation and gravity gradient at GOCE altitude on a global scale. Compared with the expected GOCE error characteristics, that study shows that only annual signals up to degree and order 20 should be recovered by GOCE mission.
Interannual variability in the global uptake of CO2
Authors: Bates Nicholas R.
Published: October 2002

A major uncertainty are the causes for interannual variability of the global ocean uptake of CO2. Existing estimates, based on atmospheric CO2 data, indicate that peak‐to‐peak interannual variability in ocean uptake of CO2 is up to 2–4 Pg C year−1 (Pg = 1015 g), while those estimates based on ocean observations and models suggest that year‐to‐year variability is much smaller (∼0.4–0.8 Pg C year−1). Here, it is shown that these differences can be partly reconciled if global air‐sea CO2 flux estimates include the CO2 flux associated with tropical cyclones (TC), extra‐tropical cyclones (ETC), and new air‐sea CO2 gas exchange relationships. The impact of storm events on air‐sea CO2 flux is influenced by climate variability such as the El Niño/Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO), contributing to an interannual peak‐to‐peak variability in global ocean uptake of CO2 of up to ∼1.8 Pg C year−1.
Satellite‐derived increases in net primary productivity across North America, 1982–1998
Authors: Hicke Jeffrey A. , Asner Gregory P. , Randerson James T. , Tucker Compton , Los Sietse , Birdsey Richard , Jenkins Jennifer C. , Field Christopher , Holland Elisabeth
Published: October 2002

We used a new 17‐year, high spatial resolution satellite record and a carbon cycle model to explore how changing net primary productivity (NPP) contributed to a proposed carbon (C) sink in North America. We found a small but significant increase in NPP, 0.03 Pg C yr−2 or 8% over 17 years, that could explain a substantial fraction of the C sink. The largest increases occurred in the central and southeastern United States, eastern Canada, and northwestern North America, and were consistent with NPP trends derived from forest inventories and crop yields. Interannual NPP variability was small, implying that the large interannual variability in the C sink found in previous studies were driven by changes in heterotrophic respiration.
Remote sensing of subpixel snow cover using 0.66 and 2.1 μm channels
Authors: Kaufman Yoram J. , Kleidman Richard G. , Hall Dorothy K. , Martins J. Vanderlei , Barton Jonathan S.
Published: October 2002

Hydrologic models increasingly require knowledge of the amount of snow cover within a pixel in order to provide accurate estimates of snow covered area. Present methods for remote sensing of subpixel snow cover require knowledge of the spectral reflectance properties of the snow as well as the background material, making these methods difficult to apply globally. Similar problems were encountered in global remote sensing of aerosol particles over varying land terrain. Since both aerosol and snow are dark at 2.1 μm, we suggest a method for sub‐pixel snow mapping based on experience with remote sensing of aerosols. Here the pixel reflectance at 2.1 μm is used to estimate the reflectance of the non‐snow regions in the pixel at 0.66 μm. The difference between the total pixel brightness at 0.66 μm and the derived brightness of the same pixel without the snow is used to estimate the sub‐pixel snow cover with an error usually < ±0.05.
Paleomagnetic inclinations in DSDP Hole 417D reconsidered: Secular variation or variable tilting?
Authors: Schouten Hans
Published: October 2002

In Deep Sea Drilling Program (DSDP) Hole 417D in the western central North Atlantic, dips of pillow margins measured in the upper and lower part of basement correlate with tilts predicted from paleomagnetic inclinations in the corresponding parts of the hole. A ∼40° westward dip of the seafloor around 417D matches the tilt predicted from inclinations and pillow margin dips in the uppermost lavas. The correlation suggests that most of the large long‐wavelength inclination variation in Hole 417D is caused by variable tilting about an axis more or less parallel to the paleo rift rather than by secular variation. The variable tilt in Hole 417D is interpreted as the sum of rotation due to lava loading along the Mesozoic paleo rift and a later block rotation of ∼40° in the rift valley walls. This interpretation allows a reconstruction of the paleo rift environment in which the 417D upper crust formed.
A multi‐instrument approach for characterizing the atmospheric aerosol optical thickness during the STAAARTE/DAISEX‐99 campaign
Authors: Martínez‐Lozano José A. , Pedrós Roberto , Flamant Cyrille , Utrillas María P. , Tena Fernando , Moreno José , Pelon Jacques , Cisneros Juan M. , González‐Frias Carlos
Published: October 2002

This work deals with the retrieval of the aerosol optical thickness (AOT) needed to carry out the atmospheric correction of remote sensing data measured in Barrax (Spain) on 4 June 1999 in the framework of 1999 Digital Airbone Imaging Spectrometer Experiment (DAISEX'99). The AOT was estimated through three approaches based on: spectral extinction of direct solar irradiance at ground level, airborne nephelometer measurements at different altitudes, and backscatter lidar in the lower troposphere. We found extremely low AOT values due to a cold Atlantic front that swept across the Iberian Peninsula from west to east producing light rain over the test area on 2 June 1999. The results were solar irradiance extinction: 0.085±0.018; nephelometer: 0.063±0.020; lidar: 0.083±0.030. Nephelometer‐ and lidar‐derived values account for both extinction and absorption, assuming a single scattering albedo value of 0.90. Errors values include measurements and retrieval uncertainties as well as statistical variability.
Relationship between CME Speed and Geomagnetic Storm Intensity
Authors: Srivastava Nandita , Venkatakrishnan P.
Published: October 2002

In this paper, we discuss the solar origin and interplanetary consequences of the coronal mass ejection of March 29, 2001 that was responsible for the most intense geomagnetic storm (DST ∼ −377 nT) of the current solar cycle to date. A comparison of the CME of March 29, 2001, with a set of geo‐effective halo CMEs associated with X‐class flares showed that the strength of the geomagnetic storm at the earth is well correlated with the speed of the halo. Our study shows that the fast ejection is responsible for building up the ram pressure at the earth's magnetosphere. This may serve as a useful tool in the forecasting of intense geomagnetic storms.
Interplanetary radio emission due to interaction between two coronal mass ejections
Authors: Gopalswamy Nat , Yashiro Seiji , Kaiser Michael L. , Howard Russell A. , Bougeret J.‐L.
Published: October 2002

We report on the detection of a new class of nonthermal radio emission due to the interaction between two coronal mass ejections (CMEs). The radio emission was detected by the Radio and Plasma Wave Experiment (WAVES) on board the Wind satellite, while the CMEs were observed by the white‐light coronagraphs of the Solar and Heliospheric Observatory (SOHO) mission. There was no type II radio burst (metric or interplanetary) preceding the nonthermal emission. The radio emission occurred at a distance beyond 10 Rs from the Sun, where the two CMEs came in contact. Using H‐alpha and EUV images, we found that the two CMEs were ejected roughly along the same path. We argue that the nonthermal electrons responsible for the new type of radio emission were accelerated due to reconnection between the two CMEs and/or due to the formation of a new shock at the time of the collision between the two CMEs.
Long‐term variations of climate and carbon fluxes over the Amazon basin
Authors: Botta Aurélie , Ramankutty Navin , Foley Jonathan A.
Published: October 2002

The Amazon basin contains some of the most productive ecosystems on the planet, yet we have little understanding of the long‐term behavior. By examining historical climate records over the Amazon, we identify several modes of climatic variability—including previously undocumented long‐term modes. Furthermore, using a process‐based ecosystem model, we show that these variations in climate generate variations in terrestrial carbon fluxes on short (3–4 year), intermediate (8–9 year), and long (24–28 year) time scales. The long‐term cycles in terrestrial carbon balance have not been previously suggested. Finally, we find that time‐lags between productivity and decomposition enhance the short‐term variations in net carbon balance, while slightly dampening the long‐term variations. Given the worldwide attention on terrestrial carbon cycling, and the potential for “carbon sinks”, we suggest that an improved understanding of long‐term climatic and ecosystem processes is crucial. Other regions should be examined for potential long‐term carbon cycle variations.
Migration of the Mendocino triple junction and ephemeral crustal deformation: Implications for California Coast range heat flow
Authors: Guzofski Chris A. , Furlong Kevin P.
Published: October 2002

Thermal models have been constructed to demonstrate how regional crustal deformation and subsequent asthenospheric upwelling associated with the migration of the Mendocino triple junction affect the thermal regime of the northern California Coast Ranges. Ephemeral crustal thickening caused by the migration of the triple junction, coupled with the thermal effects of inflow of asthenosphere into the slab window, produces a heat flow signature that is consistent with the observed surface heat flow in the region. In addition the thermal models provide evidence that slab window temperatures are lower than previously assumed following the passage of the triple junction.
Epicenter location by abnormal ULF electromagnetic emissions
Authors: Du Aimin , Huang Qinghua , Yang Shaofeng
Published: October 2002

The epicenter location before earthquake is very important. We investigated the characteristics of the ULF electromagnetic emissions, which were observed by an east‐west chain at Kashi, Anxi, and Beijing stations before the ML = 7.1 Hetian earthquake, Xingjiang, China, on November 19, 1996. We define the polarization angle as the angle between the east direction of the geomagnetic field and the major axis of the polarization ellipse, which is obtained by the filtered data of two horizontal components. The source of ULF electromagnetic emissions before earthquake is probably coming from the direction perpendicularly to the polarization major axis of earthquake related emissions. We located the source as the cross of two source directions that were obtained at Kashi and Anxi station on November 18, 1996. The estimated source is consistent with the epicenter of the Hetian event.
Past and future sensitivity of primary production to human modification of the landscape
Authors: DeFries R.
Published: October 2002

Primary production is the basis of the food chain for humans and all other animal species on Earth. This study estimates the sensitivity of global terrestrial net primary production (NPP) to both past and future human modifications of the landscape in comparison with decadal‐scale interannual variability in NPP. Landscape modification in the past has had spatially varying effects on NPP, generally within the range of interannual variability. In the future, landscape modification is likely to occur predominantly in the humid tropics with large NPP reductions outside the range of interannual variability. Future landscape modification, in the absence of improved land management, is likely to be a more significant negative influence on NPP than in the past, which should be considered in studies investigating the biospheric response to climate change, enhanced atmospheric carbon dioxide, nutrient deposition, and other forcing factors for NPP.
Relationship between discontinuities, magnetic holes, magnetic decreases, and nonlinear Alfvén waves: Ulysses observations over the solar poles
Authors: Tsurutani B. T. , Galvan C. , Arballo J. K. , Winterhalter D. , Sakurai R. , Smith E. J. , Buti B. , Lakhina G. S. , Balogh A.
Published: October 2002

Ulysses magnetic field data are used to study magnetic field microstructure over the solar poles. Magnetic holes (MHs) and magnetic decreases (MDs) are found to be located at the phase‐steepened edges of nonlinear Alfvén waves. The phase‐steepened edges (directional discontinuities) occur in time‐coincidence with MHs, one edge of an MD, or throughout the whole MD. These MH‐ and MD‐related discontinuities have both rotational and compressive properties, perhaps explaining why many directional discontinuities detected in interplanetary space have non‐MHD properties. The dispersive, dissipative and compressive features of nonlinear Alfvén waves may be important for the heating of the solar corona.
Transition zone thickness beneath Indonesia as inferred using the receiver function method for data from the JISNET regional broadband seismic network
Authors: Saita Tomoharu , Suetsugu Daisuke , Ohtaki Toshiki , Takenaka Hiroshi , Kanjo Kenji , Purwana Ibnu
Published: October 2002

We analyzed broadband waveforms recorded by the newly deployed Japan‐Indonesia Seismic Network to determine the depths of the 410 km and 660 km discontinuities and thickness of the mantle transition zone beneath Indonesia by the receiver function method. The discontinuities have an undulation with a maximum difference of 40 km with respect to the Iasp91 model. The thickness of the transition zone is well correlated with seismicity and seismic velocity anomalies, suggesting that the topography is caused by temperature anomalies associated with the subducted slabs beneath Indonesia.
The southern edge of cratonic North America: Evidence from new satellite magnetometer observations
Authors: Purucker Michael , Langlais Benoit , Olsen Nils , Hulot Gauthier , Mandea Mioara
Published: October 2002

A global model is developed for both induced and remanent magnetizations in the terrestrial lithosphere. The model is compared with, and well‐described by, Ørsted satellite observations. Interpretation of the observations over North America suggests that the large total field anomalies, associated with spherical harmonic degrees 15–26 and centered over Kentucky and the south‐central United States, are the manifestations of the magnetic edges of the southern boundaries of cratonic North America. The techniques and models developed here may be of use in defining other cratonic boundaries.
Applying artificial neural network to the short‐term prediction of electron density structure using GPS occultation data
Authors: Zeng Zhen , Hu Xiong , Zhang Xunjie
Published: October 2002

Artificial neural network (ANN) is used for assimilating of GPS ionospheric occulted data in order to take full advantage of the abundant GPS occulted data. A feedforward, full‐connected network is chosen based on the back‐propagation algorithm. Universal time, latitude, longitude, height, Kp index, and F10.7 solar flux are chosen as the input vectors of the network while the electron density as the output vectors. The GPS occultation data on May 24th, 1996 were taken as training samples to train an ANN, and then the well‐trained ANN was used to predict the electron density on 25th. Comparison of the predicted results and observed data demonstrated that ANN is a promising method in assimilating the GPS occulted data to establish the ionospheric weather prediction model. Furthermore, the accurate and abundant observations are essential for ensuring the good performance of ANN.
Fast acceleration of a CME‐related X‐ray structure in the low solar corona
Authors: Alexander David , Metcalf Thomas R. , Nitta Nariaki V.
Published: October 2002

We report on a unique observation of the early and rapid acceleration of a fast CME in the low solar corona. The coronal disturbance associated with a LASCO CME and concurrent X1.2 flare on 1998 April 23 was well‐observed by the Yohkoh Soft X‐ray Telescope. The X‐ray observations clearly show an accelerating structure, reaching 800–1100 km/s in ∼500s at a de‐projected height of only 280 Mm, indicating an acceleration well in excess of 1700 m/s2. The soft X‐ray observations are coincident with the onset of the CME, which ultimately attained a velocity of 1390 km/s and generated a number of interplanetary radio signatures, frequently associated with fast events. Assuming a constant acceleration, a0, throughout the duration of the X‐ray observations, we determine a best‐fit value of a0 = 1756 m/s2, while application of a power‐law acceleration model yields a better fit to the data with a peak acceleration of ∼4865 m/s2 within the first 280 Mm of the solar corona.
Effect of global warming on the length‐of‐day
Authors: de Viron Olivier , Dehant Véronique , Goosse Hugues , Crucifix Michel ,   Participating CMIP Modeling Groups
Published: October 2002

The anthropogenic increase in greenhouse gas concentrations in the Earth atmosphere will probably induce important modifications of the global circulation in the atmosphere and ocean. Due to the angular momentum conservation of the Earth‐atmosphere‐ocean system, variation of the length‐of‐day (LOD) can be expected. By using the outputs of the models participating to the Coupled Model Intercomparison Project (CMIP‐2), we reach the following conclusions: (1) the models globally agree to an increase of the LOD of the order of 1 μs/year, (2) the effect is mostly associated with an increase of the mean zonal wind, of which about one third is compensated by a change in mass repartition.
Magnetoclimatology and paleoprecipitation: evidence from a north‐south transect through the Chinese Loess Plateau
Authors: Evans M. E. , Rokosh C. D. , Rutter N. W.
Published: October 2002

Magnetic measurements and grain‐size analyses are reported for eight sites along a 420‐km north‐south transect across the Chinese Loess Plateau with the goal of assessing the quantitative estimation of paleoprecipitation during the last interglacial (oxygen isotope stage 5, ∼130 kyr B.P.). The climofunction of Maher et al. [1994] suggests that precipitation was generally elevated by about 150 mm/yr over today's values, but with the same north‐south gradient. However, in one area, low precipitation values are found that suggest no significant increase.
The uppermost mantle beneath the Kenya dome and relation to melting, rifting and uplift in East Africa
Authors: Davis Paul M. , Slack Philip D.
Published: October 2002

We compare new results on S‐wave delays and P wave tomography to characterize the rising limb and melt zone of an inferred mantle convection cell beneath the Kenya dome. These results are extended to the Nyiragongo and Ethiopia domes using long wavelength gravity and topography. We suggest that the east African rift results from separation of deeper mantle upwelling into three currents that impinge on and erode the base of the lithosphere. Their thermal buoyancy drives the domal uplift, whereas brittle failure of the upper lithosphere forms the rift grabens.
Ocean fertilization experiments may initiate a large scale phytoplankton bloom
Authors: Neufeld Zoltán , Haynes Peter H. , Garçon Véronique , Sudre Joël
Published: October 2002

Oceanic plankton plays an important role in the marine food chain and through its significant contribution to the global carbon cycle can also influence the climate. Plankton bloom is a sudden rapid increase of the population. It occurs naturally in the North Atlantic as a result of seasonal changes. Ocean fertilization experiments have shown that supply of iron, an important trace element, can trigger a phytoplankton bloom in oceanic regions with low natural phytoplankton density. Here we use a simple mathematical model of the combined effects of stirring by ocean eddies and plankton evolution to consider the impact of a transient local perturbation, e.g. in the form of iron enrichment as in recent ‘ocean fertilization’ experiments. The model not only explains aspects of the bloom observed in such experiments but predicts the unexpected outcome of a large scale bloom that in its extent could be comparable to the spring bloom in the North Atlantic.
First scalar magnetic anomaly map from CHAMP satellite data indicates weak lithospheric field
Authors: Maus S. , Rother M. , Holme R. , Lühr H. , Olsen N. , Haak V.
Published: October 2002

Satellite magnetic anomaly maps derived by different techniques from Magsat/POGO data vary by more than a factor of 2 in the deduced strength of the lithospheric magnetic field. Here, we present a first anomaly map from new CHAMP scalar magnetic field data. After subtracting a recent Ørsted main and external field model, we remove remaining unmodeled large‐scale external contributions from 120° track segments by subtracting a best‐fitting uniform field. In order to preserve N/S trending features, the data are not filtered along‐track. Direct integration of the spherically gridded data yields the final degree 14–65 spherical harmonic expansion of the total intensity anomaly at the mean satellite altitude of 438 km. Apart from enhanced long wavelength features and a smoother general appearance, our initial map is strikingly similar to one of the lower strength Magsat/POGO maps.
Analyses of in‐situ airborne volcanic ash from the February 2000 eruption of Hekla Volcano, Iceland
Authors: Pieri D. , Ma C. , Simpson J. J. , Hufford G. , Grindle T. , Grove C.
Published: October 2002

A McDonnell‐Douglas DC‐8 NASA research aircraft inadvertently flew into an airborne volcanic ash plume from the 26 February 2000 eruption of Hekla Volcano. Filter samples from the aircraft were compared with “normal use” and “pristine clean” filters using SEM, energy‐dispersive x‐ray spectrometer, and Nicolet FTIR spectrophotometer analyses. These analyses confirm that the DC‐8 encountered airborne volcanic ash from Hekla Volcano. This result is supported by independent onboard heated aerosol observations at the time of the encounter. The analyses further demonstrate the ambiguous nature of the dual band thermal IR (“split window”) method for detecting volcanic ash from the point of view of aviation safety. They also highlight the utility of in situ aircraft filter‐based observations of volcanic aerosols for scientific purposes.
Observatory crustal magnetic biases during MAGSAT and Ørsted satellite missions
Authors: Mandea Mioara , Langlais Benoit
Published: October 2002

Computing main‐field models derived from MAGSAT and Ørsted satellite magnetic measurements, the crustal influence on satellite data can be treated as random noise. Satellite data can thus be used in conjunction with magnetic observatory measurements to isolate the non‐core field at the observatory locations. Crustal biases for the horizontal northward X, eastward Y and vertical downward Z components are computed for all magnetic observatories where data are available for MAGSAT (1979–1980) and Ørsted (1999–2000) epochs, to study their correlation over twenty years. For a set of observatories installed after 1979 new crustal biases are computed.
Wind‐shear‐driven, closed‐current dynamos in midlatitude sporadic E
Authors: Cosgrove Russell B. , Tsunoda Roland T.
Published: October 2002

Rocket and radar experiments have found anomalously large electric fields associated with midlatitude sporadic E (Es). In Cosgrove and Tsunoda [2001], a neutral wind source mechanism for the electric fields was proposed, by way of a simple model involving two idealized Es patch dynamos closing current with one another. Below, we show that this source mechanism can operate in generic distortions or fragmentations of an Es layer. The result is a closed‐current dynamo phenomenon that occurs whenever a Es layer is distorted against a wind shear background. Either modulation of the Es layer altitude by a gravity wave, or Kelvin‐Helmholtz billows, could produce large electric fields.
Upper mantle structure of the Kaapvaal craton from surface wave analysis—a second look
Authors: Saltzer Rebecca L.
Published: October 2002

Surface waves from earthquakes recorded during the two‐year Southern Africa Seismic Experiment have been used to estimate the average velocity structure beneath the Kaapvaal craton. By cross‐correlating the data with synthetics derived using mode summation techniques, I measure frequency‐dependent phase delays for Love and Rayleigh waves, as well as higher modes, for 12 events ranging in epicentral distance between 12° and 91°. I simultaneously invert the traveltime delays for structure beneath the array and outside of the array. In this way, heterogeneity along the path lying outside of the array is not mapped erroneously into structure beneath the array. The differential dispersion between the Love and Rayleigh waves require some anisotropy in the upper mantle; however, models with a range of anisotropic depths (as shallow as 150 km and as deep as 220 km) can equally well fit the data. The sensitivity of the fundamental mode surface waves used in this study begins to decline significantly below ∼200 km depth limiting interpretation of deeper structure. Nonetheless, this range of anisotropic depths is significantly different than the 100 km depth proposed in a recent study by Freybourger et al. [2001] using a similar technique and different data from the same array. I attribute the difference in their dispersion measurements and modeling to the improper use of a phaseless (i.e. frequency‐dependent) filter on the data, which systematically biased their measurements at lower frequencies. In addition, I find no evidence of a low‐velocity layer as proposed by Qui et al. [1996] and Priestley [1996].
Real‐time forecasting of biological and physical dynamics at the Iceland‐Faeroes Front in June 2001
Authors: Popova Ekaterina E. , Srokosz Meric A. , Smeed David A.
Published: October 2002

Real‐time physical and biological forecasting was carried out at sea in June 2001 at the Iceland‐Faeroes Front using a 3D coupled physical and biological model. Data collected during three repeated mesoscale surveys were used for model initialisation, data assimilation and forecast verification. The forecast successfully predicted the evolution of an anticyclonic meander and associated deep mixed layer leading to severe light limitation of phytoplankton production.
The influence of continental surface area on the assembly time for supercontinents
Authors: Tao Winston , Jarvis Gary T.
Published: October 2002

We employ a kinematic numerical model of circular continental blocks moving about randomly on a two‐dimensional periodic model of the Earth's surface and monitor the time required for all of the blocks to assemble into a single model supercontinent. We examine the sensitivity of the assembly times of our model supercontinents to the size of individual continental blocks, the fraction of the model Earth=s surface covered by the continents and the degree of continental deformation that occurs upon collision. Assembly times are found to be most sensitive to the total continental surface area. We show that in the absence of any dynamic effects due to deep mantle flow, continents of present‐day scale moving randomly about the Earth's surface would naturally aggregate into a single mass in approximately 0.4 Gy.
Detection of earth‐origin electric pulses
Authors: Tsutsui M.
Published: October 2002

Using a newly developed system for measuring the electromagnetic (EM) environment in the earth, we detected electric pulses originating from the ground. The intensity of the electric pulses detected above the ground was weaker than those in the earth. There were clear lower frequency cutoffs in the spectra suggesting the existence of a kind of horizontal wave‐guide in the earth and the propagation of EM waves there. The estimated scale depth of the bottom conductive boundary of the wave‐guide is consistent with the result obtained from geomagnetic field investigations. The detected electric pulse swarms provided important images of EM wave behavior in the earth.
Observations of the flow in the Mozambique Channel
Authors: de Ruijter Wilhelmus P. M. , Ridderinkhof Herman , Lutjeharms Johann R. E. , Schouten Mathijs W. , Veth Cornelis
Published: October 2002

During a recent research cruise to investigate the nature and continuity of the Mozambique Current, we observed that the flow in the Mozambique Channel is dominated by a train of large anti‐cyclonic eddies (diameters >300 km) that reach to the channel bottom and propagate southward. At a frequency of 4 per year they cause a net poleward transport of about 15 Sv (1 Sv = 106 m3/s). In the deep sea, a Mozambique Undercurrent flows equatorward along the continental slope. Using a lowered acoustic Doppler current profiler maximum observed velocities are about 0.2 m/s around 2400 m with another current core around 1000 m. It carries about 5 Sv of intermediate (AAIW) and deep waters (NADW) of Atlantic origin into the Channel. Subsequently, the equatorward flowing AAIW is largely entrained by the eddies and, while mixing with intermediate water from the North Indian Ocean in the eddy core, returned to the Agulhas Retroflection region.
Partial melting in the deepest mantle
Authors: Simmons N. A. , Grand S. P.
Published: October 2002

We have compared the travel times of direct (P, S) and core‐reflected (PcP, ScS) phases recorded in southern Africa from earthquakes occurring in the Scotia Arc region. The low‐velocity region beneath the south Atlantic is explored by calculating ScS‐S and PcP‐P travel‐time residuals to determine the correlation and magnitude of Vs and Vp reductions in the deepest mantle. Residual calculations yield extraordinary results as PcP‐P is about 1 second larger than expected while ScS‐S is >7 seconds larger for a great circle arc distance of 54°. We investigate models of P and S velocity reductions in the deepest mantle that may explain these residuals to provide constraints on the velocity structure of the D” region in this extremely slow zone. The reductions in P and S velocity needed to match the data are consistent with partial melting in the deepest mantle for a wide range of 1D models.
Decadal variations in the subtropical cells and equatorial pacific SST
Authors: Nonaka Masami , Xie Shang‐Ping , McCreary Julian P.
Published: October 2002

A mechanism for generating decadal sea surface temperature (SST) variability in the equatorial Pacific is investigated using an ocean general circulation model forced by observed wind stress. Equatorial SST variability is governed by different ocean dynamics on interannual and decadal time scales. At interannual time scales, equatorial SST anomalies are mainly driven by equatorial winds. At decadal time scales, on the other hand, they are forced both by equatorial winds and by off‐equatorial winds in the tropics, while the contribution from midlatitude winds poleward of 25° is negligible. Trade‐wind variations in the off‐equatorial tropics force equatorial SST variability by spinning up and down the subtropical cells that transport cold water into the equatorial upwelling zone. Equatorial SST anomalies induced by this mechanism lag behind the response to local equatorial winds by about two years.
Modulation of auroral field‐aligned electron fluxes under two inverted‐V structures at different altitudes
Authors: Tung Y.‐K. , Delory G. T. , Carlson C. W.
Published: October 2002

This paper presents observations of field‐aligned electron flux bursts from the auroral sounding rocket flight, Alaska 2000, launched February 25, 2000 from Poker Flat, Alaska. In one particular energetic electron burst, the field‐aligned electron flux is observed to be modulated at 22–30 Hz at energies up to 30 keV. By assuming that the observed energy dispersion in the bursts is caused by time‐of‐flight effects, we obtain characteristic source altitudes of 87 dispersive electron bursts, and find that the average characteristic source altitude of the bursts is 4015 ± 684 km in the first inverted‐V and 5411 ± 972 km in the second inverted‐V. This result implies that the electron‐wave or other interaction depends more strongly on which arc it occurs in, rather than another factor such as energy of the electrons, since dispersive bursts at a wide range of energies and durations were used to arrive at the result.
Regional Wavefield reconstruction for teleseismic P‐waves and Surface waves
Authors: Sheldrake K. Prindle , Marcinkovich C. , Tanimoto T.
Published: October 2002

With the recent availability of dense seismological array data there is the opportunity to reconstruct 2D wavefields of propagating seismic energy. Such a reconstruction allows seismic data to be viewed as wavefields rather than as single station traces. Reconstruction of such wavefields within an array will improve our understanding of complex wave propagation effects and, hence, the underlying Earth structure beneath the array. We propose an algorithm applicable for teleseismic waves that is based on wavefield expansion by cubic B‐splines. Application to the high‐density array in Southern California shows that we can identify basin resonances and wavefront shifts; such wavefield shifts could be caused by local structure or travel path structure, as waves pass through major structural contrasts.
Plasma density enhancements in the high‐altitude polar cap region observed on Akebono
Authors: Ichikawa Yoh‐ichi , Abe Takumi , Yau Andrew W.
Published: October 2002

The plasma density in the polar cap ionosphere is generally low (<103 cm−3 above 3000 km), mainly because of plasma escape from the ionosphere along open magnetic‐field lines. The Akebono satellite occasionally encounters regions of unusually high plasma density (≥103 cm−3) above 4000 km altitude, in which the thermal plasma exhibits a distinctively low electron temperature (<3000 K) and low parallel ion drift velocity (≤1 km/s). Such events are almost always observed on the dusk side. The occurrence of low electron temperature and ion drift velocity appears to suggest the antisunward convection of high‐density plasma into the polar cap, and the decrease in electron temperature due to the disruption of field‐aligned heat flux in the high‐altitude polar cap.
A global diagnostic of interior ocean ventilation
Authors: Blanke Bruno , Speich Sabrina , Madec Gurvan , Maugé Rudy
Published: October 2002

Ventilation is the process by which water is transferred from the surface mixed layer to the interior ocean. Ventilation anomalies as the result of climate variability may impact the atmosphere in remote regions where the flow returns to the mixed layer. From the Lagrangian analysis of monthly‐mean ocean fields of a numerical model constrained by observed climatologies, we show that 324 Sv of mixed layer water travel throughout the interior ocean for periods longer than 12 months, leading to an average volume replacement time of roughly 125 yr. We evaluate the connections established on a global scale, with an appropriate mapping of the ventilation and corresponding obduction regions, and highlight the role of the Antarctic Circumpolar Current as a main receptacle of the water masses formed throughout the world ocean.