bluuebunny/crossref_metadata_2025 huggingface dataset:
An assessment of ECC ozonesondes operated using 1% and 0.5% KI cathode solutions at Lauder, New Zealand
Authors: Boyd Ian S. , Bodeker Greg E. , Connor Brian J. , Swart Daan P. J. , Brinksma Ellen J.
Published: February 2004

The effects of reducing the concentration of the potassium iodide (KI) cathode electrolyte from 1% to 0.5% in electrochemical concentration cell (ECC) ozonesondes flown at Lauder, New Zealand (45° S, 170° E) have been investigated. Four studies were made to assess these effects: 1% and 0.5% KI ozonesonde performance was compared directly in three dual flights, one year of 1% KI and one year of 0.5% KI ozonesonde profiles were compared with near‐simultaneous lidar profiles, integrated ozonesonde profiles were compared with Dobson spectrophotometer measurements over the same period, and ascent and descent profiles were compared for both KI concentrations. Ozonesondes flown with a 1% KI solution showed positive differences of 3% to 8% in the ozone profile and ∼5% in the ozone column compared with the 0.5% KI ozonesondes, which also showed better agreement in profiles and ozone column compared with the lidar and Dobson spectrophotometer measurements respectively.
Storm track signature in total ozone during northern hemisphere winter
Authors: Orsolini Yvan J. , Stephenson David B. , Doblas‐Reyes Francisco J.
Published: February 2004

Total ozone has long been known to correlate with tropospheric synoptic eddy activity, with low total ozone associated with anticyclonic conditions. Synoptic eddy activity is particularly intense in the storm track regions over the North Atlantic and Pacific oceans during boreal winter. An Eulerian diagnostic was introduced by Blackmon et al. [1977] to investigate storm tracks, based on band‐pass filtering the 500 mb geopotential height for synoptic time scales. Wintertime daily satellite observations of total ozone have been analyzed using a similar Eulerian approach. Storm track signatures in total ozone, referred to as ozone tracks, can be discerned. However, the North Atlantic ozone track is stronger than the North Pacific one, and this asymmetry is in part due to intense ozone mini‐hole events in the Atlantic sector, causing extreme total ozone variations. During winter 1996/97, this asymmetry was particularly marked. Furthermore, the Atlantic storm track and the corresponding ozone track were confined to the western Atlantic, due to persistent anticyclonic conditions over western Europe in late winter and spring. Several intense mini‐hole events occurred in the Atlantic sector, with the strongest event in mid‐March 1997.
The Kyoto Protocol: CO2 CH4 and climate implications
Authors: Wigley T. M. L.
Published: February 2004

Kyoto Protocol implications for CO2, temperature and sea level are examined. Three scenarios for post‐Kyoto emissions reductions are considered. In all cases, the long‐term consequences are small. The limitations specified under the Protocol are interpreted in terms of both CO2 and CH4 emissions reductions and a new emissions comparison index, the Forcing Equivalence Index (FEI), is introduced. The use of GWPs to assess CO2‐equivalence is assessed.
New estimates of radiative forcing due to well mixed greenhouse gases
Authors: Myhre Gunnar , Highwood Eleanor J. , Shine Keith P. , Stordal Frode
Published: February 2004

We have performed new calculations of the radiative forcing due to changes in the concentrations of the most important well mixed greenhouse gases (WMGG) since pre‐industrial time. Three radiative transfer models are used. The radiative forcing due to CO2, including shortwave absorption, is 15% lower than the previous IPCC estimate. The radiative forcing due to all the WMGG is calculated to 2.25 Wm−2, which we estimate to be accurate to within about 5%. The importance of the CFCs is increased by about 20% relative to the total effect of all WMGG compared to previous estimates. We present updates to simple forcing‐concentration relationships previously used by IPCC.
The relationship between the North Atlantic Oscillation and El Niño‐Southern Oscillation
Authors: Huang Jianping , Higuchi Kaz , Shabbar Amir
Published: February 2004

We have applied a multiresolution cross‐spectral analysis technique to resolve the temporal relationship between the NAO and ENSO. The study shows significant coherence between NAO and Niño3 SST in about 70% of the warm ENSO events from 1900 to 1995, of which 33% and 37% are associated with a 5‐ to 6‐year period (E1) and a 2‐ to 4‐year period (E2) oscillation terms in the spectral decomposition, respectively. The dominant teleconnection pattern associated with changes in the mean atmospheric circulation during the initial winter of a typical E1 and E2 events is the positive phase of the Pacific/North American (PNA) pattern. Non‐coherence between the NAO and ENSO occurs during relatively weak Niño3 SST anomaly, with a teleconnection pattern which shows a strong negative phase of the NAO and a pattern which resembles a weak eastward shifted negative phase of the PNA pattern.
A pair of forward and reverse slow‐mode shocks detected by Ulysses at ∼5 AU
Authors: Ho C. M. , Tsurutani B. T. , Lin N. , Lanzerotti L. J. , Smith E. J. , Goldstein B. E. , Buti B. , Lakhina G. S. , Zhou X. Y.
Published: February 2004

We report the first finding of a pair of forward and reverse slow‐mode shocks in the distant heliosphere using plasma and magnetic field data from the Ulysses spacecraft located at 5.3 AU and 9°S heliolatitude. The slow‐mode shocks are found to occur in a compressed magnetic field (low plasma ) region within a co‐rotating interaction region (CIR). We find Mach numbers to be 0.3–0.5 with respect to forward/reverse slow shocks. Across each shock, the solar wind velocities jump by at least 40 km/s. The increases in plasma density and ion temperature accompany a decrease in the magnetic field. The shocks are also found to have velocities of 60 km/s and 115 km/s and thicknesses between 7.5‐12.6×104 km (much larger than the ion inertial length, ∼10³ km). Low frequency plasma waves are detected by the Ulysses URAP instrument at the slow‐mode shock transition regions. However, the waves are not of sufficient amplitude to provide enough anomalous resistivity through wave‐particle interactions for shock dissipation. Low energy (∼30–90 keV) electron enhancements directed along the local magnetic field are also found associated with the slow shocks, indicating the ability of the shocks to accelerate interplanetary particles. This finding imply that more slow shocks might be found in the CIR magnetic compressed regions (where plasma is squeezed out) at large heliospheric distances.
Tropospheric corrections of SAR interferograms with strong topography. Application to Etna
Authors: Delacourt C. , Briole P. , Achache J. A.
Published: February 2004

The accuracy of spaceborne geodetic techniques, including SAR interferometry, is limited by the time and spatial variation and altitude dependance of the propagation delay of electomagnetic waves in the lower troposphere, particularly in mountainous areas. In this paper, we use a 1D model developed for tropospheric corrections of GPS and DORIS measurements to correct SAR data. The differential tropospheric delay is computed at each pixel of the interferogram from ground temperature, humidity and pressure using two empirical parameters calibrated from several radio‐soundings acquired in various latitude and climate conditions. It is shown that with such a model, given the 3300 meters topography of Etna, tropospheric variations can generate up to 4π phase rotations between the top and the bottom of the volcano. In 16 out of the 20 interferograms processed with images acquired between August 1992 and October 1993, correction of the tropospheric effect reduces the number of fringes associated with the 1991–93 eruption from previous estimates. The remaining deformation is consistant with a deforming source located at a depth of 14±1 km. During the second half of the eruption, the subsidence rate at the top of the volcano is roughly stable at 13±3 mm/month. These values are in good agreement with tiltmeter data collected on Etna during the same period and with the estimated volume of erupted material. No significant deformation can be observed during the last month of eruption. Inflation of the volcano seems to resume immediately after the end of the eruption at a rate of 3 mm/month.
Hydrates in binary sulfuric acid‐water vapor: Comparison of CIMS measurements with the Liquid‐Drop Model
Authors: McGraw Robert , Weber Rodney J.
Published: February 2004

We report calculations of the distribution of sulfuric acid‐water hydrates under atmospheric conditions using the liquid‐drop hydrate model. The model‐computed total acid concentrations (free acid plus hydrated acid) are compared with chemical ionization mass spectrometer (CIMS) measurements of total sulfuric acid vapor over solutions of varying concentration [Marti et al, 1997] Results from this first direct comparison with experimental measurement suggest that the liquid‐drop model overestimates the extent of hydrate formation. We explore the consequences of this overestimation on binary sulfuric acid‐water nucleation rates, and on higher‐order multi‐component nucleation rates involving these and additional trace species in the atmosphere. In particular, it is found that over‐estimation of hydrate formation by the model can result in substantial underprediction of sulfuric acid‐water nucleation rates.
Evolution of fault systems at a strike‐slip plate boundary: A viscoelastic model
Authors: Roy Mousumi
Published: February 2004

A viscoelastic model of crustal deformation suggests that the formation and evolution of strike‐slip fault systems are strongly influenced by rheologic contrasts between the upper and lower crust. When deformation is driven by a narrow zone of high shear in the mantle, the presence of a low‐viscosity lower crustal layer underlying a primarily elastic upper crust widens the deformation zone with time and promotes the formation of a broadly distributed network of interacting faults within the upper crust. In contrast, the deformation zone in a primarily elastic crust is narrow, encompassing a single, plate‐bounding fault. Patterns of surface strain rate and seismicity are thus significantly more complex in the presence of a low‐viscosity lower crust, due to interactions between faulting in the upper crust at short time scales and viscous behavior in the lower crust at long time scales.
Differential vertical transport of heat and salt by weak stratified turbulence
Authors: Merryfield William J. , Holloway Greg , Gargett Ann E.
Published: February 2004

Numerical experiments are described in which overturning motions mix temperature and salt across stabilizing vertical gradients. In all instances, mixing of temperature exceeds that of salt. Temperature and salinity fluxes can differ significantly, even when large compared to the thermal conductive flux.
Reducing the Backus Effect given some knowledge of the dip‐equator
Authors: Ultré‐Guérard P. , Hamoudi M. , Hulot G.
Published: February 2004

Geomagnetic field models computed from intensity measurements on or near the Earth's surface are plagued with strong errors known as the “Backus effect”. These errors are related to the mathematical non‐uniqueness of the solution which can be theoretically removed by the knowledge of the dip‐equator location. Here, we present a new method for computing models using intensity data and additional information about the location of the dip‐equator. We first give a numerical validation of this approach in an ideal case in which the dip‐equator can be assumed to be perfectly located. We then show that in practice, updating a good past model of the field with a model of secular variation can constrain the location of the dip‐equator sufficiently for our method to be useful. Implications for the planning of future satellite missions are briefly discussed.
The response of high‐latitude convection to a sudden southward IMF turning
Authors: Ruohoniemi J. M. , Greenwald R. A.
Published: February 2004

We describe the response of the high‐latitude convection to a sudden southward turning of the IMF. In this event BZ recorded at the WIND satellite switched from +6 nT to −6 nT in 2½ minutes and effects in the ionosphere were observed by the SuperDARN HF radars. In the vicinity of noon MLT, the convection switched suddenly (∼2 min) from sunward to antisunward with the velocity change reaching magnitudes as great as 1500 m/s in about 6 minutes. Surprisingly, the responses at the other MLTs distributed from noon to midnight began at virtually the same time. Meridional flows near 22 MLT were observed to reverse direction in about 4 minutes with the velocity change reaching magnitudes as great as 750 m/s in about 8 minutes. This example shows that the convection can respond to a sudden IMF change practically simultaneously (∼2 min) over the entire high‐latitude zone and reconfigure from a pattern characteristic of BZ+ to one characteristic of BZ− in a very short (2–4 min) time.
Decadal periodicities of Nile River historical discharge (A.D. 622–1470) and climatic implications
Authors: De Putter Thierry , Loutre Marie‐France , Wansard Guy
Published: February 2004

The Roda Milometer (Cairo, Egypt) has recorded more than 2,000 gauge readings, i.e. annual low‐water and flood levels, from A.D. 622 to the beginning of this century. Spectral analysis of the A.D 622–1470 data set yields several statistically significant periodicities, for both low‐water (256; 75.9; 52.6; 38; 28.9; 20.9; 18.5 and 13.4 yr) and flood levels (75.9; 33.6; 21.4; 14.7; 13.7; 9.7 and 8.1 yr). Evolutionary Multi Taper Method analysis suggests that shifts or disappearances of spectral peaks occur in sub‐intervals of the studied time span. This is noticeable for the low frequency peaks in the sub‐interval A.D. ∼950 ‐ ∼1250 which corresponds to the Medieval Warm Period in Europe. By contrast, a remarkable time stability is observed for the 5 yr period, that could confirm the existence of a robust ENSO‐like forcing during the studied period.
Subduction in the Indo‐Burma Region: Is it still active?
Authors: Satyabala S. P.
Published: February 2004

The Indo‐Burma region (which includes longitude 92°–96°E, latitude 20°–26°N) is a subduction zone where the Indian plate underthrusts the South‐Eastern Asian plate. But the nature of subduction is complex. I examine here the distribution of the P, T and B axes of 37 earthquakes (the time period 1977–1995, depths 0–153 km and magnitudesmb4.8–6.8) with respect to the geometry of the Wadati‐Benioif Zone. The analysis shows that the T axes are clustered close to the down‐dip direction of the subducting slab implying a predominant down‐dip tensional stress regime within the slab, which is typical of intermediate depth seismicity of active subduction zones. These results suggest that the subduction in the Indo‐Burma region is possibly active.
Generation of large sheet‐like ionospheric plasma irregularities at Arecibo
Authors: Lee M. C. , Riddolls R. J. , Burke W. J. , Sulzer M. P. , Kuo S. P. , Klien E. M. C.
Published: February 2004

Large‐scale ionospheric plasma irregularities, generated by O‐mode heater waves at Arecibo, are shown for the first time to have “sheet‐like” structures. The irregularities are aligned with the magnetic meridional plane and have scale sizes ranging from a few hundred meters to a few kilometers. This interpretation is based on detailed considerations of sequential measurements of radar backscatter power, the controlling magnetic field geometry, and the deduced E × B plasma drift. The alignment of O‐mode‐generated irregularities with the magnetic meridional plane, and their disappearance during X‐mode heating intervals are consistent with predictions of the thermal filamentation instability model.
Storm‐time penetration to low latitudes of magnetospheric‐ionospheric convection and convection‐driven thermospheric winds
Authors: Reddy C. A. , Mayr H. G.
Published: February 2004

From DE‐2 satellite measurements during two magnetic storms, we show that (i) the magnetospheric convection‐driven east‐west ion flows of high velocities (1400 m/s) penetrate to magnetic latitudes as low as 30°, with larger velocities (2000–3000 m/s) appearing at 45°–50° latitudes, and (ii) high velocity (300–640 m/s) thermospheric winds appear in association with the above ion flows. The similarity of the latitude structures and time evolutions of the ion and neutral motions indicates that the zonal winds are driven by magnetospheric‐ionospheric convection through ion drag. These velocities of the convection‐driven ion flows and winds at such low latitudes are much larger than those reported from observations or predicted by current models.
Nitrogen fixation by volcanic lightning in the early Earth
Authors: Navarro‐González Rafael , Molina Mario J. , Molina Luisa T.
Published: February 2004

We examine an unusual mechanism to fix nitrogen in the early Earth by lightning discharges occurring inside explosive volcanic clouds containing gases characteristic of Hawaiian volcanoes as a model of Archean volcanic volatiles. The products are predicted on thermodynamic equilibrium assumptions of the chemical species frozen out as the lightning channel rapidly expands and cools to ∼ 2400°C. Volcanic lightning is simulated in the laboratory by flowing the gas mixture into a microwave discharge cavity where the gases are excited and then the products are analyzed downstream by chemical ionization mass spectrometry. Nitric oxide was found to be the major product formed with an energy yield of ∼1 × 1016 molecule J−1. It is estimated that about 1012−1013 g of NO could have been produced annually by volcanic clouds occurring about 4 Gyr ago.
The Soufriere Hills Eruption, Montserrat, British West Indies: Introduction to Special Section, Part 2
Authors: Young S. R. , Voight B. , Sparks R. S. J. , Rowley K. , Robertson R. E. A. , Lynch L. L. , Aspinall W. P.
Published: February 2004

The special section on the eruption of Soufriere Hills volcano is a collection of 24 papers that summarises the early scientific work of the Montserrat Volcano Observatory. Part 1 of the special section, published in a previous issue of GRL, provided a sampling of the multidisciplinary investigations undertaken at Montserrat. The papers published in Part 1 included an overview of the eruption, investigations on seismicity, ground deformation studies, and petrology.

The papers of this issue comprise Part 2 of the special section. These papers also cover a broad spectrum of topics, including various topics in seismology, petrology, pyroclastic flow models, gas chemistry, hydrothermal systems, and tsunami models. In general, papers in Part 1 may be said to be more observational‐ or data‐orientated, and those of Part 2 more model‐orientated, but indeed there is much overlap of descriptive material, data, and modelling within the individual contributions. Considered in total the collection presents a representative summary of the scientific effort carried out in Montserrat through much of 1997.
An instrumental source for the dark pixel clusters in the Polar VIS and UVI Experiments
Authors: McFadden J. P. , Mozer F. S. , Vernetti J. , Sircar I.
Published: February 2004

The controversy over the observation of dark pixels by the DE‐1 and Polar imagers has centered around the small‐comet theory rather than an instrumental source to account for the dark pixels. To check for instrumental effects, we simulated the Polar VIS and UVI response to uniform illumination and calculated the rate of dark pixel clusters. The simulation includes the finite size and exponential amplitude of light pulses from the experiments' image intensifiers and the removal of contamination by penetrating radiation. The dark pixel cluster size distributions from the computer simulations reproduce the distributions observed in both of the Polar imagers. (The VIS distributions were produced independently from one day of raw data kindly provided by Frank and Sigwarth and from a world‐wide‐web catalog of atmospheric hole events prepared by Frank and Sigwarth from their own Polar data. These two sets of VIS distributions are in agreement with each other and with the computer simulations.) These instrumental effects fully explain the dark pixel clusters without the need for invoking a geophysical phenomena.
GPS meteorology: Reducing systematic errors in geodetic estimates for zenith delay
Authors: Fang Peng , Bevis Michael , Bock Yehuda , Gutman Seth , Wolfe Dan
Published: February 2004

Differences between long term precipitable water (PW) time series derived from radiosondes, microwave water vapor radiometers, and GPS stations reveal offsets that are often as much as 1–2 mm PW. All three techniques are thought to suffer from systematic errors of order 1 mm PW. Standard GPS processing algorithms are known to be sensitive to the choice of elevation cutoff angle at this level. We present a processing protocol that is shown to reduce elevation angle dependence in geodetic estimates of zenith delay and, hence, reduce the systematic errors in derived precipitable water. This protocol includes use of the Niell zenith delay mapping functions and International GPS Service phase center models.
Moment‐tensor inversion for offshore earthquakes east of Taiwan and their implications to regional collision
Authors: Kao Honn , Jian Pei‐Ru , Ma Kuo‐Fong , Huang Bor‐Shouh , Liu Chun‐Chi
Published: February 2004

Reliable determination of source parameters for offshore earthquakes east of Taiwan with mb<5.5 was a difficult task because of the poor azimuthal coverage by local network and the lack of signals at teleseismic distances. We take advantage of the recently established “Broadband Array in Taiwan for Seismology” (BATS) to invert seismic moment tensors for 7 such events occurred in 1996. To cope with different patterns of background noise and unknown structural details, we utilize variable frequency bands in the inversion and adapt a two‐step procedure to select best velocity models for individual epicenter‐station paths. Our results are consistent with the overall patterns of regional collision and indicate that the resulting compressive stress has caused significant intraplate deformation within the Philippine Sea plate. Simulation of the region's geological evolution and orogenic processes should take this factor into account and allow the Philippine Sea plate to deform internally.
Changes in sunshine duration are correlated with changes in daily temperature range this century: An analysis of Swiss climatological data
Authors: Rebetez Martine , Beniston Martin
Published: February 2004

Analyses of the relationship between trends in daily temperature range and those of sunshine duration in the Swiss Alps show a strong correlation at lower elevation sites. The decrease in daily temperature range is associated with a corresponding decrease in sunshine duration. At high elevations, however, this relationship is absent. The decrease in daily temperature range observed this century at lower elevation sites is inferred to be a consequence of an increase in low‐level cloudiness. Higher elevation sites lie above the low‐level cloud layers and the moisture‐laden lower atmospheric boundary layer and as a result do not exhibit the same trends.
Measurement of the rate constant for the association reaction CH + N2 at 53 K and its relevance to Triton's atmosphere
Authors: Le Picard Sébastien D. , Canosa André
Published: February 2004

The pulsed laser photolysis (PLP), time‐resolved laser‐induced fluorescence (LIF) technique has been used to study the association reaction CH + N2 in a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) apparatus at 53 K and in the pressure range 0.46–6 mbar. The third order rate constant was found to be ko = (5.7±0.30) × 10−30cm6s−1. Consequences for the production of HCN in the atmosphere of Triton are discussed in light of this result.
On the generation mechanism of Pi 2 pulsations in the magnetosphere
Authors: Lee Dong‐Hun
Published: February 2004

We present a theoretical study on how Pi 2 pulsations are excited in the magnetosphere. When impulsive disturbances associated with the substorm onset are assumed at the tailward region, their propagation toward the sunward direction is investigated with a wave equation. In order to examine the effect of the plasmapause on the initial disturbances, we analytically solve the wave equation based on the model of a reasonable Alfven speed profile. The exact solution shows that virtual resonant states exist in the plasmasphere and plasmapause. We obtain the result that these unique modes strongly persist for arbitrary incoming impulses from the source in the magnetotail, which corresponds to the signature of Pi 2 pulsations.
Annual variation in near‐Earth solar wind speed: Evidence for persistent north‐south asymmetry related to solar magnetic polarity
Authors: Zieger B. , Mursula K.
Published: February 2004

We study the annual variation in solar wind speed at Earth's orbit and in geomagnetic activity since mid‐1960's. The two parameters depict a very similar annual variation during the whole period. Annual variation has maximum amplitude around sunspot minima. The phase of annual variation reverses soon after solar maxima, following the Sun's polarity reversal and indicating a new type of 22‐year periodicity. Stronger solar wind is found at or close to the Earth's highest northern (southern, resp.) heliographic latitudes during solar minima with a negative (positive) magnetic polarity. This implies an asymmetric SW speed distribution across heliographic equator such that the minimum speed region during solar minimum times is displaced away from heliographic equator towards the northern magnetic hemisphere. This may result e.g. from a systematically larger extension of polar coronal holes from the Sun's magnetic south pole toward solar equator. We exclude the earlier explanations proposed for annual variation, such as accumulation of small comets within 1 AU, or internal solar variation.
Aseismic creep along the San Andreas Fault northwest of Parkfield, CA measured by radar interferometry
Authors: Rosen P. , Werner C. , Fielding E. , Hensley S. , Buckley S. , Vincent P.
Published: February 2004

ERS‐1 radar images acquired 14 months apart studied by differential radar interferometry show the wide‐area distribution of aseismic creep along the fault segment northwest of Parkfield, California. A sharp discontinuity in the interferometric phase of less than 2 cm equivalent line‐of‐sight displacement extends over 80 km in the differential interferogram, coincident with the mapped trace of the active San Andreas fault and consistent with the expected and measured fault motion. Although patterns of strain associated with the transition from locked to creeping are not clearly identifiable, a decrease in creep displacement from northwest to southeast along the fault is visible. The observations are in agreement with a model of elastic deformation constrained by in situ data that supports a maximum expected deformation signature of 10 mm across the image.
Melt flow in a variable viscosity matrix
Authors: Richardson Chris N.
Published: February 2004

It is often assumed that the molten regions of planetary interiors can be modeled as a compacting viscous matrix permeated by a less viscous melt phase. In order to assess the true behaviour, it is important to test as many different aspects of these models as possible. In the calculations presented here, the matrix viscosity is made to decrease as the proportion of melt increases. New results in two dimensions show that if only gravity drives the flow, pockets of melt travel upwards as solitary waves, and the behaviour is similar to the well known constant viscosity case. However, when an external shear strain is applied, an instability occurs and melt flows into elongated pockets, or veins, perpendicular to the least compressive stress. Whilst veins much greater than a compaction length in width are suppressed, their minimum width is not clearly constrained. The growth rate of veins is directly proportional to the applied strain rate, so that their degree of development is proportional to the total strain. It is suggested that under mid‐ocean ridges, the total strain may be enough for such veins to be important.
Measurements of electric potential variation by piezoelectricity of granite
Authors: Sasaoka H. , Yamanaka C. , Ikeya M.
Published: February 2004

From laboratory experiments, we observed that unloading stress on a piece of granite induced a pulsed electric potential variation, which decays exponentially with a time constant ranging from 1.5 to 4.0 s. The electric potential variation depends on the magnitude and the sustaining time of applied stress, indicating that the variation is due to piezoelectricity and migration of bound charges that compensate the piezoelectric polarization. An apparent piezoelectric coefficient of granite was obtained to be about 1.4 × 10−15 C/N, three orders of the magnitude smaller than that of a single crystal of quartz.
Geomagnetic response to magnetic clouds of different polarity
Authors: Fenrich F. R. , Luhmann J. G.
Published: February 2004

The polarity of a magnetic cloud refers to its changing magnetic field direction. It is classified as S‐N polarity when the magnetic field rotates from southward to northward and N‐S polarity when the field is initially northward and rotates southward. A study of 29 magnetic cloud events has found that 40–45% of magnetic clouds, independent of polarity, are followed by a fast solar wind stream which compresses the tail end of the cloud. The compression results in an increase in the solar wind plasma density and in 64% of the cases an increase in the magnetic field strength towards the latter part of the cloud. Such tail end compression can have a significant effect upon geomagnetic storm intensity if the magnetic cloud is of N‐S polarity. This is because only in the N‐S polarity case does the compression coincide with the southward IMF portion of the cloud. To test the “geoeffectiveness” of N‐S versus S‐N magnetic clouds three selected magnetic cloud events, two of S‐N polarity and one of N‐S polarity, are investigated in terms of their geomagnetic response through measured and estimated Dst values. It is found that there is an increased geoeffectiveness of N‐S polarity clouds due to both an increased solar wind dynamic pressure and a compressed southward field associated with a following fast solar wind stream.
A new method to determine the solar cycle length
Authors: Mursula K. , Ulich Th.
Published: February 2004

The length of the solar cycle and its long‐term variation have recently received additional significance due to their suggested connection to global climate. The cycle length is conventionally defined as the time difference between two successive sunspot minima. However, the sunspot minimum times sensitively depend on the way the sunspot numbers are averaged, i.e. whether one uses daily or monthly averaged values and whether and how the data are further smoothed. Using differently processed sunspot data, the sunspot minimum times vary typically by a few months, leading to a corresponding inaccuracy in solar cycle length. Here we propose a new method to define the solar cycle length as a difference between the median activity times of two successive sunspot cycles. The great advantage of this method is that the median times are almost independent of how the sunspot minima are determined. Therefore the method allows the solar cycle lengths to be calculated with a very small inaccuracy of a few days only. We show that the individual cycle lengths calculated from the conventional and the median method may differ by nearly a year. However, the long‐term trend of cycle lengths remains roughly the same during modern times.
Equivalent source magnetic dipoles revisited
Authors: Dyment J. , Arkani‐Hamed J.
Published: February 2004

Equivalent point source inversion in the rectangular coordinate system has been widely used to reduce satellite magnetic data collected at different altitudes to a common elevation over small areas. This method is based on the expression of the magnetic anomaly caused by a magnetic dipole. Such an expression derived in a spherical coordinate system by von Frese et al. [1981] is found erroneous. We point out the errors in von Frese et al.'s [1981] formulas and present the correct expression for the magnetic field of a magnetic dipole in a spherical coordinate system.
Stress/shear correlation: Internal wave/wave interaction and energy flux in the upper ocean
Authors: Duda Timothy F. , Jacobs David C.
Published: February 2004

Profiles of three‐dimensional velocity have been collected at the site of an intentional‐tracer diapycnal diffusion study. The velocities can be broken into long‐wavelength and short‐wavelength (fluctuation) components. The Reynolds stresses of the fluctuations, computed in the direction of the long‐wavelength shear, are significantly anticorrelated with the shear. This is consistent with positive eddy viscosity, and with energy transfer to the fluctuations. The transfer rate is near the dissipation rate required to explain the observed diapycnal diffusivity. The fluctuations and stresses are most likely internal wave signals, so this result is consistent with co‐located growth and decay of small‐scale internal waves. Implications are that the decay rate of small‐scale waves may depend on the local energy flux to those waves in addition to their behavior.
Crustal structure of the flanks of the East Pacific Rise: Implications for overlapping spreading centers
Authors: Bazin Sara , van Avendonk Harm , Harding Alistair J. , Orcutt John A. , Canales J. Pablo , Detrick Robert S.
Published: February 2004

Tomographic inversion of seismic refraction data from the flanks of the East Pacific Rise (EPR), 17°15'S, shows that the thickness of layer 2 varies by as much as 500 meters off axis. A thick layer 2 is found in crust affected by migration paths of overlapping spreading centers (OSC). However, no significant variation in crustal thickness is detected throughout the study area. The crustal structure differences documented in this paper are primarily related to this paleo‐tectonic setting rather than the east‐west asymmetries characteristic of this region of the southern EPR.
Orientation and motion of current layers: minimization of the Faraday residue
Authors: Khrabrov Alexander V. , Sonnerup Bengt U. Ö.
Published: February 2004

A simple analytical solution is presented for a minimization problem encountered by Terasawa et al. [1996] in analyzing electromagnetic (EM) field and plasma data series acquired by a spacecraft traversing a one‐dimensional (1D) current layer. Their analysis was developed to infer the direction of spatial variation, n, and velocity, un, along n of a 1D EM structure such as the bowshock, the magnetopause, or the geotail current sheet. We show that the optimization procedure of Terasawa et al., which involved a numerical search, in fact reduces to solving a 3 × 3 eigen‐problem for a certain matrix Q defined in terms of the data. A step‐by‐step outline is given of the operations needed to predict n and un in this manner from an actual data set. Statistical estimates of uncertainty are given. Two magnetopause crossings by the spacecraft AMPTE/IRM are used to illustrate the procedure and to compare the results with those obtained by other methods.
Radial heliospheric magnetic fields detected by Ulysses
Authors: Jones G. H. , Balogh A. , Forsyth R. J.
Published: February 2004

The magnetometer aboard the Ulysses spacecraft has recorded numerous examples of heliospheric magnetic fields orientated in near‐radial directions for periods of several hours or more. These fields are unusual, as their existence is contrary to the predictions of classical theories concerning solar wind production and propagation. The magnetic field data gathered by Ulysses up to the end of 1997 were searched for all instances of radial fields of significant duration. Here, arising from that study, an overview of the detected radial field periods is given; including their latitudinal occurrence, their coincidence with other solar wind features, and some of their phenomenology. A particularly persistent radial field was recorded in early January 1997; this highly unusual event is described in greater depth. The implications and possible causes of radial field periods are discussed.
High resolution mapping of TEC perturbations with the GSI GPS Network over Japan
Authors: Saito A. , Fukao S. , Miyazaki S.
Published: February 2004

Two‐dimensional total electron content (TEC) perturbations over Japan are mapped with the Geographical Survey Institute (GSI) GPS network, GEONET (GPS Earth Observation Network). Its spatial resolution is 0.15° latitude × 0.15° longitude and temporal resolution is 30 seconds. Two‐dimensional TEC observations with these high resolutions revealed spatial structures and temporal evolutions of traveling ionospheric disturbances (TIDs) in the nighttime mid‐latitude ionosphere on July 03, 1997. A preliminary result of the TEC perturbation mapping indicates that it would be a strong tool to investigate the ionospheric structures in detail. Coordinated observations with other ionospheric observation techniques, such as incoherent scatter (IS) radars, airglow imagers, and ionosondes, are needed to clarify the vertical structure of the ionosphere.
Frictional estuarine flow in Juan de Fuca Strait, with implications for secondary circulation
Authors: Ott Michael W. , Garrett Chris
Published: February 2004

Estuarine flow in Juan de Fuca Strait is highly seasonal in nature and an appreciable along‐channel surface pressure gradient is coincident with the peak Fraser River discharge. An upper layer momentum balance requires the vertical eddy viscosity Av to be of the order of 0.02 m2 s−1, slightly larger than implied by conventional empirical formulae and used in current models. Mixing in an estuarine channel and a large vertical eddy viscosity should lead to significant cross‐channel flows. This secondary circulation, which may resemble internal Ekman layers and intrusions of water mixed at the sloping sides of the strait, is much less understood than the basic along‐channel estuarine exchange. Unfortunately, historical current meter data in Juan de Fuca Strait are of insufficient spatial resolution to show the predicted patterns.
Features of coastal current instabilities in the North Sea: Results of a numerical model
Authors: Langenberg H.
Published: February 2004

Coastal currents that are forced by buoyancy discharges from rivers often show a tendency to become unstable under certain conditions. Two such coastal current systems in the North Sea, the German Bight and the Skagerrak, and their instabilities are investigated and compared here with the help of a fully nonlinear, three‐dimensional, baroclinic circulation model. Differences between the two regions were found with respect to three main aspects. First, in the Skagerrak, instabilities contribute to the kinetic energy on a scale that is comparable to the mean kinetic energy. This does not hold for the German Bight. Second, of the two forms of instabilities fed by baroclinic and barotropic energy conversion, in the Skagerrak, barotropic conversion is as important as baroclinic instability, while in the German Bight, baroclinic conversion clearly dominates. Finally, in the German Bight, instability tends to occur only if supported by wind in a direction that helps establishing a steep front against strong tidal mixing. One explanation for the distinction in the features of the two regions is the water depth (German Bight is <40 m; Skagerrak is ∼300 m) and, consequently, the amount of tidal mixing applied to the near‐surface coastal current front. Several deep and shallow water coastal currents outside the North Sea are found to exhibit features similar to those presented for the Skagerrak and German Bight.
Studying subtropical thermocline ventilation and circulation using tritium and 3He
Authors: Jenkins William J.
Published: February 2004

A 13‐year time series of tritium and 3He in the Sargasso Sea near Bermuda shows the downward penetration of the bomb tritium and excess 3He maxima into the main thermocline at a rate of about 17 m yr−1. A simple box‐mixing model effectively mimics both the evolution of the tracer maxima and their thermocline inventories. The thermocline inventory of ζ (the sum of tritium and 3He) near Bermuda has halved over duration of the time series. This can be used to estimate a regional average nitrate efflux from the main thermocline of 0.7±0.2 mol (N) m−2 yr−1. In the eastern subtropical North Atlantic I combine 3H‐3He age with salinity, oxygen, and geostrophy to compute isopycnal diffusivities, oxygen consumption rates, and absolute velocities. The reference level velocities are determined almost solely by the 3H‐3He age equations and to an accuracy of about 1 mms−1. A classic absolute velocity spiral is seen. The depth variation of computed vertical velocities is consistent with vorticity conservation and extrapolates to within errors of surface Ekman pumping and local subduction rates. Isopycnal diffusivities are largely constrained by the salinity equations and are ∼1200 m2 s−l at a depth of 300 m, decreasing gradually downward. Diffusivities apparently decrease toward the surface, likely an artifact of unsteadiness in the salinity equations. The oxygen utilization rates (OURs) determined by the oxygen equations decrease exponentially with depth. Vertical integration of OUR yields a net water column oxygen demand of 4.1±0.8 mol m−2 yr−1, which corresponds to an export production of 2.5±0.5 mol m−2 yr−1 carbon. I present a simple scheme to show how to relate the vertical profiles of 3H‐3He age to the subduction rate as a function of depth projected back to the surface outcrop. The shallowest horizon has a subduction rate indistinguishable from local climatological Ekman pumping rates but gradually exceeds the projected rates with depth. The difference may be attributed to the increasing importance of buoyancy‐forced subduction at higher latitudes.
An investigation of ocean tides derived from along‐track altimetry
Authors: Tierney Craig C. , Parke Mike E. , Born George H.
Published: February 2004

With the availability of a long data record of accurate sea surface height measurements, it is now possible to estimate the ocean tide along the ground track of TOPEX/POSEIDON (T/P). This has been done from over 4.5 years of data using both response and harmonic analyses. These estimates agree well with each other, and with other gridded models over both long and short wavelengths in deep water, for those tidal components whose alias frequencies are separable by the Rayleigh criterion. Comparisons of along‐track (AT) estimates to current tide models show shorter wavelength features not present in dynamical and empirical global models. AT estimates follow the general trends of empirical models far from sharp topographical changes, but near sharp changes, they tend to follow dynamical model results. Error estimates show that the T/P data are not significantly worse in shallow water than in deep water, suggesting that there is accurate information about tides in shallow water in the T/P data. Tides at crossover locations are improved by computing estimates with both ascending and descending track data. Possible techniques to improve AT tidal estimates between crossover points are discussed. AT tidal estimation can be useful for studying local regions where resolution is more important than regular spacing, for studying tidal interactions over sharp topography, and for extending tidal models from deep to shallow waters through assimilation into a dynamical model.
Mobile layer in oscillatory sheet flow
Authors: Flores Nicolas Zala , Sleath John F. A.
Published: February 2004

Measurements are reported of mobile layer thickness and the velocity and concentration distributions within the mobile layer in oscillatory sheet flow. Tests were carried out with sand, PVC, and acrylic granules in an oscillatory water tunnel. Velocities were measured with a laser Doppler anemometer, and concentrations were measured with conductivity probes. The measurements of mobile layer thickness appear to confirm the importance of the parameter S = (ρU0ω/(ρs−ρ)g). At low values of this parameter the measurements tend toward the unique curve which would be expected if pressure gradient and inertia effects were negligible. On the other hand, the velocity profile measurements show some influence of pressure gradient and inertia even for values of S as low as 0.12. At higher values of S a type of plug flow is observed in which the sediment comes to rest as the flow reverses and then begins to move again as a solid block.
Wind‐wave tank measurements of bound and freely propagating short gravity‐capillary waves
Authors: Gade Martin , Alpers Werner , Ermakov Stanislav A. , Hühnerfuss Heinrich , Lange Philipp A.
Published: February 2004

Measurements of the surface elevation and slope and of the backscattered radar power at X and Ka band were carried out in a wind‐wave tank with mechanically generated gravity waves as well as with wind waves on slick‐free and slick‐covered water surfaces. The measured radar Doppler shifts show that on a slick‐free water surface, bound gravity‐capillary (X and Ka band Bragg) waves are generated at the crests of steep gravity waves with frequencies between 3 and 5 Hz. However, steep gravity waves with a frequency of 2Hz do not generate bound Ka band Bragg waves, and the Ka band backscattering from these waves is associated with wave breaking. In the wind speed range from 1.5 to 10m/s, bound gravity‐capillary waves contribute to the X and Ka band backscatter from slick‐free water surfaces. The fraction of bound to freely propagating Bragg waves depends on, among other things, radar frequency, wind speed, wave amplitude of the dominant water wave, and slick coverage. In particular, the strong damping of the gravity waves by the slick at wind speeds of approximately 8 m/s leads to the disappearance of the bound Bragg waves and therefore to a reduction of the X and Ka band Doppler shifts to values corresponding to freely propagating Bragg waves. It is concluded that the study is pertinent to the understanding of former results of radar backscattering measurements in the presence of oceanic surface films.
Oceanographic conditions east of Iceland
Authors: Perkins H. , Hopkins T. S. , Malmberg S.‐A. , Poulain P.‐M. , Warn‐Varnas A.
Published: February 2004

Circulation and hydrography on the shelf east of Iceland and on the western portion of the Iceland‐Faeroe Ridge is described by a series of surveys using temperature‐salinity profilers, moored current meters and satellite‐tracked drifters. The dominant surface current of the region is the northeastward flow of North Atlantic Water at the shelf break southeast of Iceland as it leaves the shelf to join the Iceland‐Faeroe Front. On the bottom beneath it flowing in the opposite direction is a strong, steady current composed of water from the Nordic Seas that has overflowed the ridge and followed along bathymetric contours. North of the front, three comparatively weak currents are identified, formed by splitting of the North Icelandic Irminger Current after it has rounded the northeast corner of Iceland. One branch, the East Icelandic Current, is confined to the shelf and produces a mean, southward flow until it turns eastward to join the Iceland‐Faeroe Front. Another leaves the shelf to form the shallow, southeastward flowing Icelandic Current. The third follows deeper contours of the continental slope and renews waters on the northern flank of the Iceland‐Faeroe Ridge.