bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamical relationship of infrared cloudtop temperatures with occurrence rates of cloud‐to‐ground lightning and sprites
Authors: São Sabbas F. T. , Sentman D. D.
Published: May 2003

We correlated cloudtop temperatures obtained from GOES‐8 infrared images, lightning data from the National Lightning Detection Network, and triangulated nadir positions of sprites from a 22 July 1996 Mesoscale Convective System (MCS) over Kansas. The maximum sprite production of the MCS occurred during the transition between growth and decay phases of the system, and when the occurrence rate of negative cloud‐to‐ground (−CG) flash activity maximized. The −CG flash rate was maximum when the overlying cloudtop temperatures Tc were minimum, −69° to −72°C. During the MCS growth phase, the −CG occurrence rate increased smoothly with decreasing Tc, and declined with increasing Tc during the decay phase. By way of contrast, the +CG rate remained associated with approximately constant Tc (−69° and −72°C) during the growth phase, and then also declined with increasing Tc during the decay phase. The sprite‐generating +CGs occurred in regions with cloudtop temperatures 2–3°C warmer than the rest of the +CG population.
Current switching as the cause of rapid warming at the end of the last Glacial Maximum and Younger Dryas
Authors: Rossby T. , Nilsson Johan
Published: May 2003

The sudden termination of the last Glacial Maximum probably resulted from an intensification of the global thermohaline circulation, but the extraordinary rapidity of warming and increased precipitation over Greenland, O(10) years, has been difficult to explain. Using a simple laboratory model we argue that a salinity‐driven positive feedback that accelerates the production and export of North Atlantic Deep Water, which unlike Intermediate Water is not dynamically blocked to the North Atlantic, will lead to a water mass deficit at high latitudes. This loss is rapidly signaled south in the form of topographic and planetary waves, to which the Gulf Stream responds by sending salty water north along a topographically defined path, thereby reinforcing deep water production; the positive feedback that accelerates the process. The Gulf Stream's rapid switch from its glacial zonal to present meridional course led to the abrupt warming observed in the Greenland ice record.
Testing the Hill model of transpolar potential with Super Dual Auroral Radar Network observations
Authors: Shepherd S. G. , Ruohoniemi J. M. , Greenwald R. A.
Published: May 2003

We use a data set consisting of periods for which the transpolar ionospheric potential (Φ) is well‐determined by Super Dual Auroral Radar Network (SuperDARN) data to test the Hill model. The Hill model, as formulated by Siscoe et al. [2002], specifies Φ as a function of solar wind speed and ram pressure, the interplanetary magnetic field, the reconnection electric field (E), and the ionospheric conductance (Σ). The periods used in our study were identified as times when the interplanetary electric field was quasi‐stable for and SuperDARN coverage was sufficient to determine Φ. SuperDARN‐determined Φ (Φ) is compared to Φ determined using the Hill model (Φ) for 1317 10‐min periods. A minimum in the root‐mean‐square difference between (Φ)(E) and (Φ)(E) is achieved when Σ = 23 S and a constant potential, Φ0 = 17 kV, are used. Some aspects of the data agree very well for these values of Σ and Φ0, including the mean value of Φ(E) and that both data sets clearly indicate saturation at higher values of E. The ram pressure dependence of (Φ), however, is inconsistent with that of (Φ) and suggests that Σ should be lower than 23 S. There is also significantly more variability in (Φ) for all values of E than the Hill model predicts.
Mount Etna: Geochemical signals of magma ascent and unusually extensive plumbing system
Authors: Caracausi A. , Favara R. , Giammanco S. , Italiano F. , Paonita A. , Pecoraino G. , Rizzo A. , Nuccio P. M.
Published: May 2003

Five years of gas monitoring from selected sites suggest that Mt Etna's plumbing system is much more extensive than previously reported. It extends at least 40 km SW from the volcano's boundary along the NE‐SW regional fault, where it discharges about 200 tons/day of gas, containing helium with mantle‐type isotopic composition. Synchronous variations of 3He/4He isotopic ratios in gas sampled at sites located 60 kilometers apart have allowed us to detect pulses of ascending magma in the plumbing system, thus providing a powerful tool for eruption forecasting. Following summer 2001 eruption, the still increasing trend of the 3He/4He ratios indicates that magma storage is even now occurring at a shallow depth. Hence, the volcano maintains a high capacity to re‐erupt within the next few months.
Volcanomagnetic signals associated with the 2001 flank eruption of Mt. Etna (Italy)
Authors: Del Negro Ciro , Currenti Gilda
Published: May 2003

Geomagnetic changes were observed during the 2001 flank eruption at Mt. Etna. After differential magnetic fields were filtered from the seasonal thermic noise by using temperature data, we recognized three stages in the total intensity changes related to different volcanic events: (a) rapid variation of 4 nT associated with July 12 seismic swarm recorded beneath the summit craters, (b) step‐like variation of 7 nT occurring during the quick propagation of fractures in the south flank, which was followed by the off‐set of 2 nT before July 17 when the lava outpoured from fissures, and (c) quick variation of 3 nT coincident with July 19 eruptive fissures opening up in the Valle del Leone. These observations are consistent with those calculated from volcanomagnetic models, in which the magnetic changes are generated by stress redistribution due to magmatic intrusions at different depth and by the thermal demagnetization at a rather shallow depth.
Solar wind drivers of Traveling Convection Vortices
Authors: Murr D. L. , Hughes W. J.
Published: May 2003

We present the first clear and consistent evidence of solar wind drivers of Traveling Convection Vortices (TCVs). Using high time resolution data from GEOTAIL just upstream of the bowshock and within 10 earth radii of the sun‐earth line, we were able to clearly identify solar wind triggers for 30 of 31 large amplitude TCV events during 1995. These data showed that 20 of the 30 solar wind drivers were isolated foreshock cavities of the type that have been previously reported. A further 8 events belong to a similar class which occurred primarily during rapid rotations of the IMF from or to a radial orientation, accompanied by a foreshock cavity‐like region at the edge of the IMF transition. These observations suggest that the vast majority of TCVs are driven by perturbations of the magnetosphere caused by foreshock cavities that are formed in the interaction between the IMF and the bowshock.
Behavior of tungsten and hafnium in silicates: A crystal chemical basis for understanding the early evolution of the terrestrial planets
Authors: Shearer C. K. , Righter K.
Published: May 2003

The short‐lived isotopic system involving the decay of 182Hf to 182W (half life of 9 Ma) has been used to establish a time‐scale for planetary assembly and core formation. The W isotope signature of lunar and martian basalts appears to be correlated to characteristics of their source. On the Moon, the small amount of excess 182W is associated with basalts that may be derived from an ilmenite‐ and clinopyroxene‐bearing mantle that was produced during late‐stages of lunar magma ocean crystallization. On Mars, excess 182W is associated with a depleted mantle source. Our experimental measurements for the partitioning behavior of Hf and W between silicates and melt suggest that the early fractionation of Hf from W by phases such as ilmenite, high‐Ca clinopyroxene, and garnet may be significant enough to account for the generation of all or part of the radiogenic W signatures in the mantle sources for these basalts. The duration and nature of early mantle differentiation events on the Moon and Mars may be calculated by combining Hf‐W fractionation with the extent of radiogenic W enrichment.
In situ X‐ray observation of decomposition of superhydrous phase B at high pressure and temperature
Authors: Ohtani Eiji , Toma Motomasa , Kubo Tomoaki , Kondo Tadashi , Kikegawa Takumi
Published: May 2003

High pressure and high temperature in situ X‐ray diffraction experiments on the stability of superhydrous phase B have been conducted to clarify the host of water in the slabs descending into the lower mantle. We observed the decomposition reaction of superhydrous phase B into phase G (= phase D and F), periclase, and MgSiO3 perovskite at around 700 ∼1100°C and above 30 GPa, and the boundary of the decomposition reaction can be expressed as P(GPa) = −0.0037(±0.0017)T(°C) + 32.2(±0.5). This reaction can occur in slabs descending into the uppermost part of the lower mantle.
The spatial coherence of interannual temperature variations in the Antarctic Peninsula
Authors: King John C. , Comiso Josefino C.
Published: May 2003

The west coast of the Antarctic Peninsula is a region of extreme interannual variability in near‐surface temperatures. Recently the region has also experienced more rapid warming than any other part of the Southern Hemisphere. In this paper we use a new dataset of satellite‐derived surface temperatures to define the extent of the region of extreme variability more clearly than was possible using the sparse station data. The region in which satellite surface temperatures correlate strongly with west Peninsula station temperatures is largely confined to the seas just west of the Peninsula. Correlation of Peninsula surface temperatures with those over the rest of continental Antarctica is poor confirming that the west Peninsula is in a different climate regime. Our analysis suggests that only one of five existing ice cores from the region is likely to provide a proxy climate record that is representative of the west coast.
Evidence of nonlinear dynamics in the eastward shift of the NAO
Authors: Peterson K. Andrew , Lu Jian , Greatbatch Richard J.
Published: May 2003

Hilmer and Jung [2000] have identified an eastward shift in the sea level pressure (SLP) pattern associated with interannual variability of the North Atlantic Oscillation (NAO) that took place around 1980. We investigate the nature of the eastward shift using a primitive equation, dry atmospheric model driven by diabatic forcing diagnosed from observations. The model results reveal the nonlinear dependence of the spatial pattern of the NAO on the NAO index, the pattern being shifted to the east (west) for high (low) NAO index. General agreement is found between the model and observations. We suggest that the eastward shift noted by Hilmer and Jung [2000] is a consequence of the trend towards higher NAO index during the last several decades of the 20th century.
A first estimate of present and preindustrial air‐sea CO2 flux patterns based on ocean interior carbon measurements and models
Authors: Gloor M. , Gruber N. , Sarmiento J. , Sabine C. L. , Feely R. A. , Rödenbeck C.
Published: May 2003

The exchange of CO2 across the air‐sea interface is a main determinant of the distribution of atmospheric CO2 from which major conclusions about the carbon cycle are drawn, yet our knowledge of atmosphere‐ocean fluxes still has major gaps. A new analysis based on recent ocean dissolved inorganic carbon data and on models permits us to separately estimate the preindustrial and present air‐sea CO2 flux distributions without requiring knowledge of the gas exchange coefficient. We find a smaller carbon sink at mid to high latitudes of the southern hemisphere than previous data based estimates and a shift of ocean uptake to lower latitude regions compared to estimates and simulations. The total uptake of anthropogenic CO2 for 1990 is 1.8 (±0.4) Pg C yr−1. Our ocean based results support the interpretation of the latitudinal distribution of atmospheric CO2 data as evidence for a large northern hemisphere land carbon sink.
Storm time equatorial belt – an “image” of RC behavior
Authors: Søraas F. , Oksavik K. , Aarsnes K. , Evans D. S. , Greer M. S.
Published: May 2003

During geomagnetic storms a well defined belt of trapped protons and ENAs (energetic neutral atoms) is observed around geomagnetic equator at low L‐values. Their source is RC (ring current) protons existing at larger L‐values. Through charge exchange with the geocorona RC protons become ENAs and if subjected to a new charge exchange become trapped protons. From low latitude particle observations at four different local times we follow; the RC injection region, the drift of RC‐particles through the evening/afternoon into the morning sector, the RC‐asymmetry and convection loss to the dayside during the storm initial and main phase, and its development into a symmetric RC in the recovery phase of the storm.
The wet Nicaraguan slab
Authors: Abers Geoffrey A. , Plank Terry , Hacker Bradley R.
Published: May 2003

Nicaraguan volcanoes show globally high concentrations of geochemical tracers from dehydration of subducting crust, which may reflect a slab with unusually high amounts of H2O. To test this possibility, we measure seismic velocities at the top of the subducted plate and compare them with predictions for hydrated mafic rocks. Regional seismic P waves for intraslab events at 100–150 km depth show a high‐frequency late arrival, apparently trapped in a low‐velocity waveguide 2.5–6 km thick at the top of the downgoing plate, 14.5 ± 2.2% slower than surrounding mantle. The velocities can be explained by ≥5 wt % H2O in the subducted crust, 2–3 times the hydration inferred for other slabs by similar methods. This interpretation implies extensive hydration of the Cocos Plate off Nicaragua, perhaps enhanced by up‐dip fluid flow within the slab at >100 km depth.
Partitioning between seismogenic and aseismic slip as highlighted from slow slip events in Hyuga‐nada, Japan
Authors: Yagi Yuji , Kikuchi Masayuki
Published: May 2003

We present a numerical method to analyze the GPS data, and examine slow fault‐slips in Hyuga‐nada, a region in western Japan where the Philippine Sea plate subducts under the Eurasian plate and earthquakes of Magnitude 7 class are frequent. We found that, after two large earthquakes in 1996, a slow fault‐slip expanded from the source area to the north and then triggered another slow event with a characteristic source duration of about one year. The aseismic slip has increasingly highlighted a particular site where little slow fault‐slip takes place but where the subducting plate drags the overriding plate. It is noteworthy that the highlighted area is just the site of a past large earthquake. We propose that this area is a possible site for a future large earthquake.
Equatorial currents transport changes for extreme warm and cold events in the Atlantic Ocean
Authors: Góes Marlos , Wainer Ilana
Published: May 2003

In this work the Equatorial Atlantic Ocean circulation dynamics for warm and cold composite events are analyzed. Warm and cold typical years were composited from the respective five warmest and the five coldest years of the available record. Equatorial currents velocity and transport are calculated. During a typical warm event, the circulation decreases in the upper ocean, while during the typical cold event there is intensification. The strengthening (weakening) of the circulation during cold (warm) events increases (decreases) the stress between the Equatorial Undercurrent (EUC) and the South Equatorial Current (SEC), associated with an increase (decrease) in entrainment of cold waters into the surface and their westward transport. The EUC showed striking differences between both composited events. For the cold (warm) event the EUC shows a greater (reduced) transport and core velocity, and a deeper (shallower) structure.
A high‐resolution surface vector wind product for coastal oceans: Blending satellite scatterometer measurements with regional mesoscale atmospheric model simulations
Authors: Chao Yi , Li Zhijin , Kindle John C. , Paduan Jeffrey D. , Chavez Francisco P.
Published: May 2003

A 2‐dimensional variational method is used to blend the satellite scatterometer measured (QuikSCAT) and regional mesoscale atmospheric model simulated (COAMPS) surface vector winds for coastal central California. The approach is distinct from existing methods in that it considers errors from both measurements and models. When compared with independent in situ observations, the blended wind product shows consistently higher correlation and smaller RMS errors than QuikSCAT or COAMPS winds. The proposed algorithm can be implemented over any part of the world ocean. It should be a valuable tool for describing small‐scale atmospheric processes in coastal zones and for forcing high‐resolution coastal ocean models.
An acceleration mechanism for the generation of the main auroral oval on Jupiter
Authors: Saur Joachim , Pouquet Annick , Matthaeus William H.
Published: May 2003

In this paper we argue that the weak turbulence observed in the middle magnetosphere of Jupiter couples with the net electric current system needed to maintain Jupiter's magnetospheric rotation [Hill, 1979, 1980] to create a magnetic field‐aligned potential drop sufficient to accelerate magnetospheric electrons to energies required to produce Jupiter's main auroral oval. Based on arguments regarding overall energy within magnetic flux tubes, we estimate a field‐aligned potential of ∼100 kV. We also show that the intensity of the turbulent fluctuations maximizes on field lines at equatorial distances between 18 and 30 Jovian radii. These distances correspond to the field lines where the main auroral oval is observed. The electrons accelerated on these field lines carry a total energy of ∼6 TW.
Kinetic effects in the acceleration of auroral electrons in small scale Alfven waves: A FAST case study
Authors: Chaston C. C. , Bonnell J. W. , Carlson C. W. , McFadden J. P. , Strangeway R. J. , Ergun R. E.
Published: May 2003

In this report we examine the importance of ion and electron kinetic effects in the acceleration of electrons in small scale Alfven waves above the auroral oval. We implement a 1‐D two‐fluid MHD code approximating the effects of electron inertia and ion and electron temperatures to evaluate their role in accounting for the observed energies of field‐aligned electron bursts found in coincidence with these waves above the auroral oval. FAST spacecraft data for a case study event characterized by large auroral ion energies and a hot plasma sheet is employed to define the plasma through which the wave propagates. It is found that strong kinetic effects at altitudes below 5 Earth radii may significantly reduce the amount of electron acceleration possible in the wave in terms of both energy and flux.
Local and remote sources of tropical atlantic variability as inferred from the results of a hybrid ocean‐atmosphere coupled model
Authors: Nobre Paulo , Zebiak Stephen E. , Kirtman Ben P.
Published: May 2003

A hybrid ocean‐atmosphere coupled model is used to study the interannual variability of sea surface temperature and wind stress over the tropical Atlantic. The coupled model is composed of a statistical atmospheric component model that uses sea surface temperature anomalies (SSTA) over the tropical oceans to forecast wind stress anomalies over the tropical Atlantic, coupled to a general circulation model of the ocean configured over the Atlantic. It is shown that, while the Atlantic‐only hybrid coupled model has damped oscillations of SSTA and wind stress, the inclusion of Pacific SSTA variability in the coupled model resulted in sustained oscillations of wind stress and SSTA over the equatorial Atlantic.
Recent cooling in coastal southern Greenland and relation with the North Atlantic Oscillation
Authors: Hanna Edward , Cappelen John
Published: May 2003

Analysis of new data for eight stations in coastal southern Greenland, 1958–2001, shows a significant cooling (trend‐line change −1.29°C for the 44 years), as do sea‐surface temperatures in the adjacent part of the Labrador Sea, in contrast to global warming (+0.53°C over the same period). The land and sea temperature series follow similar patterns and are strongly correlated but with no obvious lead/lag either way. This cooling is significantly inversely correlated with an increased phase of the North Atlantic Oscillation (NAO) over the past few decades (r = −0.76), and will probably have significantly affected the mass balance of the Greenland Ice Sheet.
Heat transfer and interfacial temperature of two‐layered convection: Implications for the D″‐mantle coupling
Authors: Namiki Atsuko , Kurita Kei
Published: May 2003

We performed laboratory measurements of the heat flux and the interfacial temperature of two‐layered thermal convection. Experiments show that the scaling law of the heat flux (Nu‐Ra relation) can be classified by the buoyancy number B. The heat flux under B > 1 follows the well‐known Nu‐Ra relation. However, under B < 1, undulations develop at the interface, and heat flux is systematically enhanced. The interfacial temperature is determined only by the ratio of physical properties between the upper and lower layers. Our results suggest that the existence of less viscous and slightly denser D″ than the overlying mantle would enhance the heat transfer from the core to the mantle.
The 2001 Skyros, Northern Aegean, Greece, earthquake sequence: off ‐ fault aftershocks, tectonic implications, and seismicity triggering
Authors: Karakostas V. G. , Papadimitriou E. E. , Karakaisis G. F. , Papazachos C. B. , Scordilis E. M. , Vargemezis G. , Aidona E.
Published: May 2003

The Mw = 6.4 July 26, 2001 Skyros (North Aegean, Greece) earthquake struck the submarine western end of Northern Aegean Sea causing damage in the nearby Skyros Island. It occurred on a left‐lateral NW‐SE trending strike slip fault, oriented transverse to the dominant dextral strike‐slip faults that are present in the area, appearing to mark the boundary between them and the E‐W trending normal faults of the Greek mainland. Foreshock activity started 5 days before the mainshock, and intense aftershock activity followed on the main rupture plane and off fault. The seismogenic structure consists of three clusters with different orientation, independent from the known normal and dextral strike‐slip faults. Theoretical static stress changes from the main shock suggests off‐fault aftershock triggering, providing a tool for assessing the seismic hazard ensuing from strong aftershocks far from the main rupture.
Critical comparison of OII(732–733 nm), OI(630 nm), and N2(1PG) emissions in auroral rays
Authors: Semeter Joshua
Published: May 2003

All‐sky spectral imagery has been used to study the altitude distribution of OII(732–733 nm), OI(630 nm), and N2(1PG) emissions in tall auroral rays appearing at the poleward edge of the auroral oval. The OII(732–733 nm) emission layer was consistently higher than the OI(630 nm) emission layer in these structures; the peak emission altitudes were estimated to be ∼380 km and ∼240 km, respectively. Neither the high absolute altitude of the OII(732–733 nm) peak nor its >100 km offset from the OI(630 nm) peak are consistent with published model results, which consider electron impact on atomic oxygen as the sole source of auroral O+(2P). The present results suggest that O+(2P) may also be excited directly from ambient ionospheric O+(4S) atoms. Other contributing factors may include a significant underestimation of the rate coefficients for O+(2P) quenching, or field‐aligned up‐flows of ionospheric O+.
Novel Fabry‐Perot interferometer measurements of F‐region ion temperature
Authors: Cierpka K. , Kosch M. J. , Holma H. , Kavanagh A. J. , Hagfors T.
Published: May 2003

Novel optical measurements of F‐region ion temperatures have been made in conjunction with thermospheric neutral temperatures. A ground‐based Fabry‐Perot interferometer has been used to observe high‐latitude F‐region ion temperatures using the O+(2P) auroral emission at 732 nm, and upper‐thermospheric neutral temperatures using the O(1D) airglow emission at 630 nm. Dual wavelength measurements were made during February 2001 and clearly show that the ion temperature is equal to or greater than the neutral temperature, as expected. EISCAT radar measurements show that there is good agreement between the incoherent scatter and optical Doppler broadening methods of inferring ion temperature.
Atmospheric water cycle and moisture fluxes in the West African monsoon: mean annual cycles and relationship using NCEP/NCAR reanalysis
Authors: Fontaine Bernard , Roucou Pascal , Trzaska Sylwia
Published: May 2003

Atmospheric water (Precipitation minus Evaporation, P‐E) and moisture fluxes from the NCEP/NCAR and observed rainfall data from the Climatic Research Unit are analyzed over the West African Monsoon region (WAM: 5°N–20°N; 18°W–18°E) on the period 1968–1998. The main results show that 1) P‐E averaged over the 15°N–20°N belt in July–September (JAS) is a better proxy of observed rainfall in Sudan‐Sahel (12°N–18°N) than NCEP/NCAR rainfall in this reanalysis; 2) part of the moisture fluxes vertically integrated in the layers 1000–300 hPa or 1000–925 hPa advected into WAM originate from the Mediterranean sea and Central Africa; 3) their interannual March–April and JAS variations, especially north of 20°N, present significant relationship with Sahelian P‐E in JAS; 4) at more local scales moisture advections and convergences are also significantly associated with observed Sudan‐Sahel rainfall and, in wet (dry) situations, with a clear dominance of westerly (easterly) anomalies in the moisture flux south of 15°N.
Stochastic modeling of slip spatial complexities for the 1979 Imperial Valley, California, earthquake
Authors: Lavallée Daniel , Archuleta Ralph J.
Published: May 2003

Finite‐fault source inversions reveal the spatial complexity of earthquake slip or prestress distribution over the fault surface. In this paper we discuss a stochastic model that reproduces the spatial variability and the long‐range spatial correlation of the slip distribution of the 1979 Imperial Valley earthquake. We have found that stochastic models based on non‐Gaussian distributions are better suited to describe the spatial variability of the slip amplitude over the fault. We also show that a stochastic modeling of the slip amplitude based on a Gaussian distribution fails to reproduce the spatial variability observed in the original slip distribution. The stochastic models can be used to deduce ground motion from other earthquakes statistically similar to Imperial Valley.
Seasonal variations along auroral field lines: Measurements from the Polar spacecraft
Authors: Johnson M. T. , Wygant J. R. , Cattell C. A. , Mozer F. S.
Published: May 2003

Measurements from the Polar electric field instrument are used to study large electric fields and the ambient plasma density as a function of altitude (1.8–6.0 RE geocentric). Results from the premidnight sector (1800–2400 MLT) along auroral field lines show roughly a fourfold increase in the occurrence of small scale size, large amplitude electric fields (>100 mV m−1) at altitudes from 1.9 to 2.5 RE for dark compared to sunlit ionospheric conditions. Density values inferred from spacecraft potential measurements show these electric fields to be correlated with low plasma densities (0.2 to 3.0 cm−3). An increase in the average plasma density from 10 to 60 cm−3 is also observed for sunlit compared to dark conditions for the same altitude range. In addition, the distribution of density measurements from 1.9 to 2.2 RE also show evidence for an increase in cold ionospheric plasma (from ∼30 to 60 cm−3) for sunlit compared to dark ionospheric conditions.
The Northeastward current southeast of Okinawa Island observed during November 2000 to August 2001
Authors: Zhu Xiao‐Hua , Han In‐Seong , Park Jae‐Hun , Ichikawa Hiroshi , Murakami Kiyoshi , Kaneko Arata , Ostrovskii Alexander
Published: May 2003

In order to estimate the variability of current structure and mean geostrophic volume transport in the southeast of Okinawa Island, the round‐trip acoustic travel times between sea bottom and surface at nine sites were measured by Inverted Echo Sounder with pressure gauge (PIES) from November 2000 to August 2001. Vertical sections of geostrophic velocity are calculated by using vertical profiles of specific volume anomaly derived by the Gravest Empirical Mode method from the PIES data. In the upper 500 m layer over a slope shallower than 1000 m depth, the northeastward current reached up to 60 cm s−1 during the occupation of an anticyclonic eddy, and decreased to −15 cm s−1 during the occupation of a cyclonic eddy, around the mean of 20 cm s−1. The temporal mean geostrophic volume transport relative to the 2000 dbar level was estimated to be 6.1 Sv (1 Sv ≡ 106 m3 s−1) northeastward in the west of 128.85°E.
Mid‐late Holocene El Niño variability in the equatorial Pacific from coral microatolls
Authors: Woodroffe Colin D. , Beech Matthew R. , Gagan Michael K.
Published: May 2003

Oxygen isotope ratios in Porites microatolls from Christmas Island in the central Pacific provide high‐resolution proxy records of El Niño‐Southern Oscillation (ENSO) variability since 3.8 thousand years ago (ka). Compared with modern microatolls, reconstructions from fossil microatolls imply that interannual variations in ENSO sea‐surface temperature and precipitation were less intense 3.8–2.8 ka, but more pronounced at 1.7 ka. Amplification of ENSO at ∼2 ka is consistent with precessional changes in insolation seasonality, but exceeds model predictions and may reflect stronger rainfall teleconnections through enhanced interaction between the Southern Oscillation and the Pacific Intertropical Convergence Zone.
Multi‐point electric field measurements of Short Large‐Amplitude Magnetic Structures (SLAMS) at the Earth's quasi‐parallel bow shock
Authors: Behlke Rico , André Mats , Buchert Stephan C. , Vaivads Andris , Eriksson Anders I. , Lucek Elizabeth A. , Balogh Andre
Published: May 2003

We present the first direct measurements of the electric field and plasma density with high resolution in Short Large‐Amplitude Magnetic Structures (SLAMS) at a quasi‐parallel shock crossing. Cluster observations at the Earth's bow shock confirm the fast‐mode structure of SLAMS. Using the four Cluster spacecraft, we determine the velocity of the SLAMS vSLAMS and find that E = −vSLAMS × B. This indicates that locally the SLAMS is moving with the same velocity as the plasma, thus indicating trapping of ions. A small‐scale (electron gyroradius) electric field with E ≠ −vSLAMS × B is found at the leading edge of the SLAMS. Downstream of several SLAMS, a wake‐like decrease in the plasma density is observed suggesting the three‐dimensional structure of SLAMS. The scale length of these SLAMS is of the order, or larger, than the satellite separation of 600 km.
Observed saturation of the ionospheric polar cap potential during the 31 March 2001 storm
Authors: Hairston M. R. , Hill T. W. , Heelis R. A.
Published: May 2003

Theoretical arguments and MHD simulations have suggested that the potential drop across the polar‐cap ionosphere approaches a constant value when the IMF is very large and southward. This idea has been difficult to test because the conditions producing this effect are extremely rare. During the 31 March 2001 storm the IMF was directed southward for over 6 hours with a magnitude of ∼36 nT to ∼20 nT while the DMSP‐F13 satellite crossed the polar region, obtaining a good measure of the true polar cap potential drop. The observed potentials are compared with predictions from a theoretical model of the saturation process [Hill et al., 1976; Siscoe et al., 2002]. Clear evidence of a non‐linear response consistent with the model predictions for height‐integrated Pedersen conductivities in the range of 5–10 S are shown.
Numerical simulation of the last flank‐collapse event of Montagne Pelée, Martinique, Lesser Antilles
Authors: Le Friant Anne , Heinrich Philippe , Deplus Christine , Boudon Georges
Published: May 2003

We model the submarine emplacement of a debris avalanche generated by the last flank‐collapse event of Montagne Pelée volcano. We estimate the collapsed volume (1.7 km3) using both the volume of the missing material in the horseshoe‐shaped structure and the volume of submarine deposits. This avalanche is treated as the gravitational flow of a homogeneous continuum. It is simulated by a finite‐difference model, solving mass and momentum conservation equations, that are depth‐averaged over the slide thickness. Numerical simulations show that the emplacement of this debris‐avalanche can be suitably modeled by a Coulomb‐type friction law with a variable friction angle below 10°. We propose that variations of the friction angle are mainly influenced by the thickness of the flowing mass.
Observation and modeling of the suction pump effect during rapid dilatant slip
Authors: Grueschow Eric , Kwon Ohmyoung , Main Ian G. , Rudnicki John W.
Published: May 2003

The temporary pressure drop observed during post‐peak dilatant slip in axi‐symmetric testing of a porous aeolian sandstone is modeled using a simple function of opening caused by sliding along the fault surface. Results suggest dilatancy of 0.02 mm accompanying frictional sliding, less than 10% of the typical grain diameter of 0.25–0.50 mm. The rapid void opening, under nominally undrained conditions at constant upstream flow rate, causes a strong ‘suction pump’ effect. A theoretical maximum pressure drop of 0.09 MPa or more, consistent with the experimentally measured results, can occur without a change in permeability properties.
Tropical ice core isotopes: Do they reflect changes in storm activity?
Authors: Lawrence James Robert , Gedzelman Stanley David
Published: May 2003

The oxygen isotopic composition (H218O/H216O) of water vapor samples over the tropical oceans has been measured at three locations during distinct meteorological regimes. H218O concentrations were lowest in and downwind from the most highly organized precipitation systems and reflect the exposure of the air to extensive areas of rain. The tropical ice core record therefore reflects changes not only of temperature but also of average degree of organization of tropical rain systems during different climate regimes.
Jovian dust streams: Probes of the Io plasma torus
Authors: Krüger Harald , Horányi Mihály , Grün Eberhard
Published: May 2003

Jupiter was discovered to be a source of high speed dust particles by the Ulysses spacecraft in 1992. These dust particles originate from the volcanic plumes on Io. They collect electrostatic charges from the plasma environment, gain energy from the co‐rotating electric field of the magnetosphere, and leave Jupiter with escape speeds over 200 km s−1. The dust streams were also observed by the Galileo and Cassini spacecraft. While Ulysses and Cassini only had a single encounter with Jupiter, Galileo has continuously monitored the dust streams in the Jovian magnetosphere since 1996. The observed dust fluxes exhibit large orbit‐to‐orbit variability due to both systematic and stochastic changes. By combining the entire Galileo dust data set, the variability due to stochatic processes can be approximately removed and a strong variation with Jovian local time is found. This result is consistent with theoretical expectations and confirms that the majority of the Jovian dust stream particles originate from Io rather than other potential sources.
Potential vorticity intrusion index and climate variability of surface temperature
Authors: Cai Ming
Published: May 2003

This paper proposes a potential vorticity intrusion index (denoted as PVI) as an alternative diagnostic tool to study the observed climate variability/trend of the surface temperature. The PVI index measures the percentage area of upper lever PV intrusion in the extratropics at any given time. More (fewer) outbreaks of extreme cold surface air temperature in high latitudes take place when the PVI index is high (low). The interannual variability of the PVI index exhibits a strong QBO‐ like signal. The high (low) PVI index prevails when the equatorial zonal mean zonal wind at 50 hPa is easterly (westerly). The probability distribution map of PV intrusion activities shows a shift of the preferred regions of frontogenesis from the oceans to the continents when the PVI index is high. This explains directly why more extreme cold events are observed over the northern Eurasian and Northern America continents when the PVI index is high, or the QBO is in the easterly phase.
First simultaneous observations of Ca+, K, and electron density using lidar and incoherent scatter radar at Arecibo
Authors: Tepley Craig A. , Raizada Shikha , Zhou Qihou , Friedman Jonathan S.
Published: May 2003

We report the first measurements of Ca+ made from the Arecibo Observatory achieved by using a frequency‐agile resonance fluorescence lidar. Simultaneous observations of the electron concentration of the lower ionosphere using the Arecibo incoherent scatter radar were also made, as well as K lidar observations of the mesospause region. We find excellent agreement in the distribution of ions observed between the lidar and radar for both the thin tidal ion layers and for broader formations of ionization that occasionally occur near 90 km altitude. The concentration of Ca+ within ion layers was found to be slightly less than the relative fraction of calcium in meteors, and generally consistent with previous lidar, rocket, and twilight airglow measurements.
Seismic evidence for a moderately thick lithosphere beneath the Siberian Platform
Authors: Priestley Keith , Debayle Eric
Published: May 2003

We have built a Sv‐wavespeed tomographic model for the upper mantle beneath the Siberian platform and surrounding region derived from the analysis of more than 13,000 fundamental and higher mode regional waveforms. The dense path coverage and rich higher mode content of the data allow building an upper mantle image with an horizontal resolution of a few hundred kilometers extending to ∼400 km depth. The high velocity, upper mantle lid or seismic lithosphere is ∼200 km thick beneath most of the Siberian platform but may extend to ∼250 km depth beneath small areas. A high velocity seismic lid also underlies a large region west of the Siberian platform. Our observation of a ∼200 thick seismic lithosphere beneath the Siberian platform on the slow‐moving Eurasian plate, similar to the thickness of the seismic lithosphere beneath Precambrian terrains on the fast‐moving Australian plate, suggests that a moderately thick seismic lithosphere beneath Precambrian terrains may be more common than previously supposed.
Hydroclimatology of the continental United States
Authors: Sankarasubramanian A. , Vogel Richard M.
Published: May 2003

The overall water balance and the sensitivity of watershed runoff to changes in climate are investigated using national databases of climate and streamflow for 1,337 watersheds in the U.S. We document that 1% changes in precipitation result in 1.5–2.5% changes in watershed runoff, depending upon the degree of buffering by storage processes and other factors. Unlike previous research, our approach to estimating climate sensitivity of streamflow is nonparametric and does not depend on a hydrologic model. The upper bound for precipitation elasticity of streamflow is shown to be the inverse of the runoff ratio. For over a century, investigators [Pike, 1964; Budyko, 1974; Ol'dekop, 1911; and Schreiber, 1904] have suggested that variations in watershed aridity alone are sufficient to predict spatial variations in long‐term watershed runoff. We document that variations in soil moisture holding capacity are just as important as variations in watershed aridity in explaining the mean and variance of annual watershed runoff.
Soils: A global sink of atmospheric carbon tetrachloride
Authors: Happell James D. , Roche Mary P.
Published: May 2003

Analysis of soil gas from the world's major biomes indicates that carbon tetrachloride (CCl4) uptake by soils is a ubiquitous process. The global flux of CCl4 from the atmosphere to soils was estimated to be 27 ± 21 kilotons per year (Kt yr−1), corresponding to a partial atmospheric lifetime of 90 years (yr). The total lifetime of CCl4 in the atmosphere, taking into account the stratospheric, oceanic and soil sinks is estimated to be 20 yr. The recently identified oceanic and soil sinks of atmospheric CCl4 suggest that current emission estimates of CCl4 may be underestimated by ∼60%.
Direct seismic energy modeling and application to the 1979 Imperial Valley earthquake
Authors: Favreau Pascal , Archuleta Ralph J.
Published: May 2003

The seismic energy associated with an earthquake has two representations: the work of the seismic waves done against a distant surface or a fault representation. For a fault subject to slip‐weakening friction, the energy density is the difference between an elastostatic work and a work density spent in fracture and relaxation. We apply this to a dynamic simulation of the 1979 Imperial Valley earthquake, whose initial conditions are inspired by previous kinematic studies. A large area of the fault has a negative energy density, and the emission of energy is roughly confined to small parts of the fault with large positive energy density. We compute the work of the seismic waves against the surface of a sphere enclosing the source, and we find the same amount of energy. We produce a map of energy directivity that shows that 40% of the energy passes through only 6.5% of the sphere.
Changing ozone and changing circulation in northern mid‐latitudes: Possible feedbacks?
Authors: Braesicke P. , Pyle J. A.
Published: May 2003

The Met Office Unified Model including a simplified stratospheric chemistry scheme was used to perform three integrations each of twenty years to study the connection between changes in lower stratospheric ozone and the circulation. The model radiation scheme used 1) the ozone calculated by the model, 2) climatological zonal‐mean ozone derived from 1) and, 3) climatological zonal‐mean ozone with an imposed mid‐latitude ozone loss in the northern hemisphere in spring. Integrations 1) and 2) only differ significantly in the northern hemisphere in January, whereas the spring season is unaffected. The dynamical changes between 1)/2) and 3) are most obvious during March, the time of the strongest imposed loss, but the largest impact, on both dynamics and ozone, is found northwards and upwards from the region of the imposed mid‐latitude anomaly away from middle latitudes. We conclude that in our calculations the imposed (observed) middle latitude loss does not produce a large additional feedback on the ozone distribution.
Large Aerosol Radiative Forcing due to the 1997 Indonesian Forest Fire
Authors: Podgorny I. A. , Li F. , Ramanathan V.
Published: May 2003

During the last decade, the feedback between El Niño and biomass burning caused the Indonesia's forest fire aerosols to be the second most significant source of anthropogenic aerosol over the tropical Indian Ocean after the South Asian Haze. In this paper, the estimates of the radiative forcing during the 1997 Indonesia's forest fire have been obtained by integrating satellite derived aerosol optical depths and cloud cover with in‐situ observations of single scattering albedo and a Monte‐Carlo Aerosol‐Cloud radiation model. The haze reduced the seasonal average solar radiation absorbed by the equatorial Indian ocean by as much as 30 to 60 W m−2 during September to November 1997, and increased the atmospheric solar heating by as much as 50% to 100% within the first 3 kilometers. The radiative forcing at the top of the atmosphere (TOA) was in the range of 5 to 15 W m−2 under cloudy skies. The significance of such large radiative flux changes to the tropical ocean‐atmosphere heat budget and climate needs to be examined with climate models.
Low‐frequency continuous tremor around the Moho discontinuity away from volcanoes in the southwest Japan
Authors: Katsumata Akio , Kamaya Noriko
Published: May 2003

Recent enhancement of seismic networks in the Japan Islands revealed occurrence of low‐frequency continuous tremors of a beltlike distribution in the southwest Japan, where the subducting Philippine Sea plate reaches depths of 30–40 km. Source depth of the tremor is estimated by selecting tremor segments with relatively clear P‐wave onsets. The source region of the tremor is assumed to correspond to lowermost parts of crust close to a triple boundary of the crust, mantle wedge, and the subducting slab. The long duration of the phenomenon indicates existence of fluid relating to the generation of the tremor. The most probable fluid is considered to be water produced by dehydration process of chlorite and amphibole in the slab on the basis of data from high pressure and temperature experiments. The northern border of the beltlike distribution is possibly rimmed by the edge of the mantle wedge because serpentine formation absorbs fluid water.
Multi‐decadal variability of flood risk
Authors: Kiem Anthony S. , Franks Stewart W. , Kuczera George
Published: May 2003

Recent research has highlighted the persistence of multi‐decadal epochs of enhanced/reduced flood risk across New South Wales (NSW), Australia. Recent climatological studies have also revealed multi‐decadal variability in the modulation of the magnitude of El Niño/Southern Oscillation (ENSO) impacts. In this paper, the variability of flood risk across NSW is analysed with respect to the observed modulation of ENSO event magnitude. This is achieved through the use of a simple index of regional flood risk. The results indicate that cold ENSO events (La Niña) are the dominant drivers of elevated flood risk. An analysis of multi‐decadal modulation of flood risk is achieved using the inter‐decadal Pacific Oscillation (IPO) index. The analysis reveals that IPO modulation of ENSO events leads to multi‐decadal epochs of elevated flood risk, however this modulation appears to affect not only the magnitude of individual ENSO events, but also the frequency of their occurrence. This dual modulation of ENSO processes has the effect of reducing and elevating flood risk on multi‐decadal timescales. These results have marked implications for achieving robust flood frequency analysis as well as providing a strong example of the role of natural climate variability.
Extratropical sources of Equatorial Pacific upwelling in an OGCM
Authors: Rodgers Keith B. , Blanke Bruno , Madec Gurvan , Aumont Olivier , Ciais Philippe , Dutay Jean‐Claude
Published: May 2003

The extratropical sources of equatorial undercurrent (EUC) water have been identified for an ocean circulation model using Lagrangian trajectory analysis. It has been found that the EUC waters emenate from a wide range of latitudes in the Pacific basin, with its densest constituent watermass being Subantarctic Mode Water (SAMW) from 50°S. Further analysis of the basin‐scale circulation fields has revealed significant advective diapycnal mass fluxes associated with intergyre exchange. As a result of these diapycnal mass fluxes, the EUC transport as a function of density at 151°W (an Eulerian diagnostic) looks quite different from the original subduction rate as a function of density for the same collection of water particles. This implicates diapycnal vertical mixing as an important player in determining the preferred density horizon of maximum EUC transport along the equator. In summary, these results illustrate an important interdependence between advective and diapycnal mixing processes associated with basin‐scale inter‐gyre and inter‐basin exchange in determining the mean equatorial stratification and EUC structure.