bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimation of the aerosol perturbation to the Earth's Radiative Budget over oceans using POLDER satellite aerosol retrievals
Authors: Boucher O. , Tanré D.
Published: September 2002

POLDER satellite retrievals of aerosol properties over oceans are used to estimate a global‐mean clear‐sky aerosol shortwave flux perturbation of order −5 to −6 Wm−2. Uncertainties due to aerosol absorption and POLDER cloud screening algorithm are quantified. In order to bound the radiative forcing by anthropogenic aerosols, we attempt to remove the contribution of background aerosols from these estimates and present all‐sky aerosol radiative effects for three regions and two methods. The results are sensitive to the thresholds used to define the background conditions.
Direct retrieval of line‐of‐sight atmospheric structure from limb sounding observations
Authors: Livesey Nathaniel J. , Read William G.
Published: September 2002

Optimal estimation of atmospheric temperature and composition from limb sounding observations is extended to the direct retrieval of line‐of‐sight atmospheric structure that can be obtained in certain limb viewing geometries. The approach is to divide the dataset into slightly overlapping chunks of several atmospheric profiles and retrieve estimates for all profiles concurrently. The method is made efficient due to the sparse nature of the matrices involved. In the case where the number of radiance measurements is significantly larger than the length of the state vector, the computational effort scales linearly with the number of profiles in the chunk. Prototype simulations, done for the EOS MLS experiment, show that application of this method can give significant improvements in accuracy.
The effect of particle size and nitric acid uptake on the homogeneous freezing of aqueous sulfuric acid particles
Authors: Tabazadeh Azadeh , Martin Scot T. , Lin Jin‐Sheng
Published: September 2002

Recent laboratory data on ice freezing from aqueous H2SO4 solutions are used to update our homogeneous ice freezing nucleation algorithm. The effect of particle size on the ice freezing process is demonstrated by calculating and comparing ice freezing curves for different size particles ranging from 0.2 to 4 micron in radius. Using the ice nucleation model we show that liquid water saturation is required above −44°C to activate submicron H2SO4 particles into cloud droplets. A thermodynamic model is used to show that the available laboratory data on ice freezing from ternary H2SO4/HNO3/H2O solutions are insufficient to adequately address the effect of HNO3 uptake on the homogeneous freezing of aqueous H2SO4 particles into ice.
Sources of microphysical variation in marine stratiform clouds in the North Atlantic
Authors: Lowenthal Douglas H. , Borys Randolph D.
Published: September 2002

In a study of marine stratiform clouds on Tenerife in the Canary Islands, droplet concentrations were highly correlated with clear‐air equivalent cloud water concentrations of non‐sea salt sulfate (NSS), nitrate, and pollution‐derived trace elements. Lower correlations with sea salt sodium and crustal aluminum indicated that these sources did not contribute to high concentrations of cloud condensation nuclei. High correlations of NSS and droplet number concentrations with those of pollution‐derived trace elements (non‐crustal V, Sb, Se) suggest that emissions from oil and coal combustion and other industrial sources in Europe controlled cloud microphysical variations in the southeastern North Atlantic.
Seismic quiescence as an indicator for large earthquakes in a system of self‐organized criticality
Authors: Hainzl Sebastian , Zöller Gert , Kurths Jürgen , Zschau Jochen
Published: September 2002

Seismically active fault systems may be in a state of self‐organized criticality (SOC). Investigations of simple SOC models have suggested that earthquakes might be inherently unpredictable. In this paper, we analyze the question of predictability in a more complex and realistic SOC model, which consists of a spring‐block system with transient creep characteristics. Additionally to the power law distribution of earthquake sizes, this model reproduces also foreshock and aftershock sequences. Aside from a short‐term increase of seismicity immediately prior to large model earthquakes, these events are preceded on average by an intermediate‐term period of reduced seismicity. The stronger and the longer the duration of this period, the larger on average is the subsequent mainshock. We find that the detection of seismic quiescence can improve the time—independent hazard assessment. The improvement is most significant for the largest target events.
A study of methyl bromide emissions from automobiles burning leaded gasoline using standardized vehicle testing procedures
Authors: Bertram Frank J. , Kolowich J. Bruce
Published: September 2002

This study measured CH3Br emissions directly from vehicular exhaust while operating under standardized dynamometer conditions, and generated response curves to see if the bromine content of the fuel could be correlated to and used as a predictor for tailpipe emissions. Four lead and bromine fuel concentrations were run in two non‐catalyst automobiles using the standard Federal Test Procedure (FTP) driving cycle and exhaust samples were analyzed for CH3Br using Gas Chromatography‐Electron Capture Detection (GC‐ECD). Total FTP exhaust emissions of CH3Br produced a range of average values from below detection to 26 mg (kg fuel burned)−1. Total FTP Emission Rates were plotted and response curves demonstrated that fuel bromine content was indeed predictive of CH3Br emission rates. Overall average CH3Br mass emission factor was 2.4% (2.1 – 2.7%) which was lower than previous work. Emission results of this study were found to be about 10‐fold lower than indirect methods.
Satellite microwave SST observations of transequatorial tropical instability waves
Authors: Chelton Dudley B. , Wentz Frank J. , Gentemann Chelle L. , de Szoeke Roland A. , Schlax Michael G.
Published: September 2002

Satellite measurements of sea‐surface temperature (SST) by the TRMM Microwave Imager reveal previously unreported features of tropical instability waves (TIWs). In the Pacific, TIW‐related variability is observed from the eastern boundary to at least 160°E. Cusp‐shaped distortions of SST fronts and associated trains of anticyclonic vortices both north and south of the equator propagate westward at ∼0.5 m s−1 with approximately 50% larger meridional displacements in the north. In the Atlantic, TIWs and associated anticyclonic vortices are clearly observed only on the north side of the equator where they propagate from the eastern boundary to the western boundary at ∼0.3 m s−1.
Measurements of lightning rod responses to nearby strikes
Authors: Moore C. B. , Aulich G. D. , Rison W.
Published: September 2002

Following Benjamin Franklin's invention of the lightning rod, based on his discovery that electrified objects could be discharged by approaching them with a metal needle in hand, conventional lightning rods in the U.S. have had sharp tips. In recent years, the role of the sharp tip in causing a lightning rod to act as a strike receptor has been questioned leading to experiments in which pairs of various sharp‐tipped and blunt rods have been exposed beneath thunderclouds to determine the better strike receptor. After seven years of tests, none of the sharp Franklin rods or of the so‐called “early streamer emitters” has been struck, but 12 blunt rods with tip diameters ranging from 12.7 mm to 25.4 mm have taken strikes. Our field experiments and our analyses indicate that the strike‐reception probabilities of Franklin's rods are greatly increased when their tips are made moderately blunt.
40Ar/39Ar evidence for early deglaciation of the central Chilean Andes
Authors: Singer Brad , Hildreth Wes , Vincze Yann
Published: September 2002

Spatial variability of deglaciation and warming since the last glacial maximum is critical for relating hemispheric or regional climate‐forcing mechanisms to global orbitally‐induced insolation changes. Radiocarbon ages of moraines, ice cores, and deep sea sediments from the southern hemisphere suggest that initial warming and glacial recession began before 23,000 years ago, but that in latitudinal belts of concentrated precipitation, glaciers readvanced 18,000 and 13,000 years ago. 40Ar/39Ar dating of glaciated and unglaciated lava flows 2200 m in elevation at Laguna del Maule, central Chilean Andes, implies that at 36° S, the southern Andean ice cap retreated between 25,600±1,200 and 23,300±600 years ago and did not expand afterwards. These ages are reconciled if increased insolation ablated sea‐ice cover and mountain glaciers in the southern hemisphere 5,000 years before the northern, and if subsequently Laguna del Maule lay north of the westerly winds delivering moisture to more southerly (39–52° S) portions of the ice cap.
Denitrification and nitrification in the Arctic stratosphere during the winter of 1996–1997
Authors: Kondo Y. , Irie H. , Koike M. , Bodeker G. E.
Published: September 2002

The concentrations of HNO3, N2O, ozone, and aerosol in the lower stratosphere inside the Arctic vortex were observed by the Improved Limb Atmospheric Spectrometer (ILAS) in the winter of 1996–1997. These data demonstrate that irreversible loss of reactive nitrogen by sedimentation of HNO3 containing particles (denitrification) at 18–23 km occurred in mid‐late February soon after the Arctic vortex cooled below ice saturation temperature (TICE). Denitrification exceeding 40% was observed only in air masses which experienced temperature below TICE. It occurred within 2 days in some of these air masses. Increases in HNO3 by evaporation of the particles (nitrification) at 13–15 km occurred 0–3 days after denitrification was observed, indicating particle radii of 5–10 µm or larger. It is likely that these particles were composed of nitric acid trihydrate (NAT) or NAT‐coated ice particles, given that the temperatures below 16 km were higher than TICE. Continued exposure of air masses below NAT saturation temperature for 1–4 days did not lead to any significant denitrification as long as the temperature did not fall below TICE, indicating that possible nucleation of NAT at these temperatures within 4 days did not play a significant role in causing denitrification. There was little change in the average HNO3 column from February 11 to 28 since HNO3 decreases at 18–23 km were almost completely offset by increases at 12–17 km.
POAM III measurements of dehydration in the Antarctic lower stratosphere
Authors: Nedoluha G. E. , Bevilacqua R. M. , Hoppel K. W. , Daehler M. , Shettle E. P. , Hornstein J. H. , Fromm M. D. , Lumpe J. D. , Rosenfield J. E.
Published: September 2002

We present measurements of stratospheric water vapor and aerosols in the Antarctic from the POAM III instrument during the period April through December 1998. The measured variations in water vapor enable us to study both descent in the vortex and the effect of dehydration that occurs in the lower stratosphere below ∼23 km when the temperature drops below the frost point in July. There is a temporal correlation between the dehydration that occurs in July and an increase in high aerosol optical depth events in the lower stratosphere, suggesting that these events are due to the presence of ice PSC's. When temperatures warm up there is some rehydration at the highest altitudes of the dehydrated region (∼20–23 km), probably resulting from descent within the vortex. At ∼12 km rehydration is probably the result of mixing in of air from outside the vortex. The temperature increase in October produces little rehydration at 17 km and no clear rehydration at 14 km, suggesting that the water has precipitated out of these layers.
Variability on the century time scale and regime changes in a stochastically forced zonally averaged ocean‐atmosphere model
Authors: Aeberhardt Michael , Blatter Marc , Stocker Thomas F.
Published: September 2002

The response of a zonally averaged climate model of the atmosphere‐ocean system to a stochastic freshwater forcing depends on its strength. Three regimes are found: For small perturbations of the system, the ocean responds with irregular oscillations around a state which is characterized by a strong Atlantic overturning circulation. For intermediate to large amplitude forcing the thermohaline circulation in the Atlantic ocean exhibits pronounced regular overturning (flushing) events. The third regime is a complete collapse of the Atlantic overturning. Transitions can be induced between the three regimes. While for moderate values the transitions are reversible, for large forcing amplitudes the Atlantic overturning circulation collapses irreversibly to the third regime.
Self‐limiting geothermal convection in marine carbonate platforms
Authors: Jean‐Baptiste P. , Leclerc A. M.
Published: September 2002

Large scale inward and upward density‐driven convective circulations occur in the porous structure of many marine carbonate platforms. Their geochemical implications are of prime importance for a variety of problems where a substantial transport of chemical species is required. In the present study we show, using simple thermal and hydraulic arguments, that there is a negative feedback between convective flow and heat transfer. This results in an upper limit on geothermally‐driven vertical fluxes, irrespective of the hydraulic conductivity of the medium. This concept is potentially applicable to a variety of problems. Taking the example of two on‐going debated questions in the reef scientific community, i.e., diagenesis and nutrient cycling, we show unambiguously that whereas convective circulations in coral reefs are compatible with dolomitization models, they are too low by at least one to two orders of magnitude to be a significant process in the nutrient budget of coral reefs.
The potential hazard from tsunami and Seiche waves generated by large earthquakes within Lake Tahoe, California‐Nevada
Authors: Ichinose Gene A. , Anderson John G. , Satake Kenji , Schweickert Rich A. , Lahren Mary M.
Published: September 2002

We investigate the potential of local earthquakes to generate tsunamis and seiches within Lake Tahoe. We calculated the long wavelength oscillations generated by 3 hypotheticalMw>7 earthquake scenarios for faults with normal slip directly under and outside the lake basin. The scenarios involving fault slip under the lake are the North Tahoe‐Incline Village and West Tahoe‐Dollar Point scenarios. The Genoa scenario involves a fault that crops out 10 km east of the lake. Faulting beneath the lake generates a tsunami followed by a seiche that continues for hours with waves as high as 3 to 10 m. The seiche potentially threatens low lying lakeside communities and lifelines. We also compare the spectral characteristics of synthetic tide gauge records with wind swell observations. The fundamental mode calculated for a seiche is consistent with the wind swell observations.
Transport and structure within the Antarctic Circumpolar Current to the north of south Georgia
Authors: Trathan P. N. , Brandon M. A. , Murphy E. J. , Thorpe S. E.
Published: September 2002

The Antarctic Circumpolar Current (ACC) crosses rugged topography to the north of South Georgia. In this region the subsurface expression of the Polar Front (PF) is generally thought to occur north of the Maurice Ewing Bank (MEB) close to the Subantarctic Front (SAF). However, in January 1996 the PF was south of the bank, separate from the SAF, in a position where it was most likely constrained by local bathymetry. High rates of transport (25 Sv eastward) were present at the PF, consistent with previous estimates for this current core. High transport rates (20 Sv westward) were also present along the northern shelf of South Georgia close to where the southern ACC Front (sACCF) has previously been reported. During our occupation, the sACCF was not encountered as it probably lay outside the survey area. Comparisons with recent circumpolar analyses emphasise the potential for variability in the region.
Measurement of the isotopic fractionation of 15N14N16O, 14N15N16O and 14N14N18O in the UV photolysis of nitrous oxide
Authors: Röckmann Thomas , Brenninkmeijer Carl A. M. , Wollenhaupt Matthias , Crowley John N. , Crutzen Paul J.
Published: September 2002

The isotopic analysis of atmospheric nitrous oxide (N2O) has become a valuable tool in the investigation of its sources, sinks, and its atmospheric cycle. In particular the considerable isotopic enrichment accompanying stratospheric photolysis of N2O, its dominant atmospheric sink process, provides a key isotope signal in the construction of a global N2O isotope budget. Here we present the first measurements of the individual fractionation constants for 15N14NO, 15ε1 = 10.9±1.7‰ and 14N15NO, 15ε2 = 35.7±0.5‰ during ultraviolet photolysis at 193 nm, along with the 18O fractionation constant, 18ε = 17.3±0.5‰. Consistent results were obtained over a wide range of experimental conditions. The observed position‐dependent 15N fractionation confirms theoretical predictions and provides a unique signature of N2O that has been processed in the stratosphere, adding a new dimension to an isotope‐based description of the atmospheric N2O budget.
Global patterns of ENSO‐induced precipitation
Authors: Dai Aiguo , Wigley T. M. L.
Published: September 2002

Although there have been many analyses of El Niño/Southern Oscillation (ENSO) induced precipitation anomalies, global patterns from these analyses remain incomplete. Here we combine recent satellite estimates of oceanic precipitation and historical rain‐gauge records to derive a global climatology of ENSO‐induced precipitation anomalies using empirical orthogonal function (EOF) analyses. The patterns suggest that the re‐arrangement of convection centers of the Walker circulation during ENSO events induces large precipitation anomalies in the tropics, while associated changes in the monsoon systems (through the Hadley cell) over the Pacific, Indian and Atlantic Oceans, and their interactions with midlatitude westerlies generate coherent anomaly patterns over the extratropics. Our results can be used to evaluate climate models and forecast ENSO‐induced precipitation anomalies.
Experimentally determined kinetic isotope effects in the reaction of CH4 with Cl: Implications for atmospheric CH4
Authors: Tyler Stanley C. , Ajie Henry O. , Rice Andrew L. , Cicerone Ralph J. , Tuazon Ernesto C.
Published: September 2002

We report experimental values for the carbon and hydrogen kinetic isotope effects (KIEs) in the reaction of CH4 with Cl at temperatures between 273 and 350 K. Isotope ratio mass spectrometry was utilized to measure 13CH4/12CH4 and CH3D/CH4 ratios on samples taken from a 5870‐ L reaction chamber. At 299 K, kc12/kc13 = 1.0621±0.0001 (2σ) and kh/kd = 1.474±0.020 (2σ). For both KIEs, the ratio decreased with increasing temperature over the range studied. These results agree well with experimental studies using tunable diode laser absorption spectroscopy and FTIR absorption spectroscopy and with a recent theoretically‐calculated set of values.
Observations of boreal forest fire smoke in the stratosphere by POAM III, SAGE II, and lidar in 1998
Authors: Fromm Michael , Alfred Jerome , Hoppel Karl , Hornstein John , Bevilacqua Richard , Shettle Eric , Servranckx René , Li Zhanqing , Stocks Brian
Published: September 2002

A substantial increase in stratospheric aerosol was recorded between May and October 1998 between 55° and 70°N. This phenomenon was recorded in the absence of reported volcanic eruptions with stratospheric impact potential. The POAM III and SAGE II instruments made numerous measurements of layers of enhanced aerosol extinction substantially higher than typical values 3 to 5 km above the tropopause. A comparison of these observations with lidar profiles, TOMS aerosol index data, and forest fire statistics reveals a strong link between stratospheric aerosol and forest fire smoke. Our analysis strongly suggests that smoke from boreal forest fires was lofted across the tropopause in substantial amounts in several episodes occurring in Canada and eastern Russia. Observations reveal a broad zonal increase in stratospheric aerosol that persisted for at least three months.
What causes long‐term temporal changes in the south Atlantic?
Authors: Holfort Jürgen , Vanicek Michael , Siedler Gerold
Published: September 2002

Two zonal sections at 11°S in the South Atlantic, separated in time by 11 years, provide temperature differences in the deep ocean. The aim of this case study is to check whether intrinsic temperature changes are sufficiently large to identify long‐term water mass property variations which could be related to climate change. Potential temperature differences on isobaric surfaces in the deep ocean here reach several tenths of °C. They can be caused by vertical (cross‐isopycnal) or horizontal (isopycnal) advection and mixing, or by intrinsic water mass changes. The effect of vertical transport is removed by using neutral (density) surfaces. The effect of horizontal transport is determined by using a mixing parameterization for temperature and silica on neutral surfaces. The residual intrinsic temperature changes are, with a few local exceptions, within the range of the ±0.05°C uncertainty, and the temperature changes can thus be explained by advection and mixing alone.
Salinity variability in the equatorial Pacific Ocean during the 1993–98 period
Authors: Maes Christophe
Published: September 2002

The salinity variability during the 1993–98 period in the equatorial Pacific Ocean is estimated by an indirect method based on statistical modes which are fitted to the TAO temperature profiles and the T/P sea level observations. The maximum variability in salinity occurs primarily in the fresh warm pool of the western Pacific. The nature of the variability is consistent with different mechanisms recently proposed. From mid‐95 to the end of 1996, positive anomalies of salinity in the upper layers near the eastern edge of the warm pool lead to a negative steric height anomaly which represent up to 30–40% of the thermal counterpart. As a consequence, the heat storage is significantly greater than the one would have inferred from observed sea level fluctuations only. The potential impact of the salinity field during the 1997–98 El Niño event is also discussed.
Kinematics of lava flows based on fold analysis
Authors: Iezzi Gianluca , Ventura Guido
Published: September 2002

A kinematic analysis of the mingling‐folding structures occurring in a lava flow from Porri volcano (Southern Tyrrhenian Sea) has been performed in order to estimate the flow kinematic parameters. Folds have resulted from the deformation of enclaves and banding structures, and consist of a single layer of a crystal‐rich andesitic magma hosted in a less competent basaltic magma. Results of the analysis indicate that the flow kinematic vorticity increases with the distance from the vent, whereas the ratio between pure shear and simple shear strain decreases following a power law. Quantitative estimates of the kinematic parameters provide an opportunity to examine the deformation behaviour of the lava flow. Near the vent, the lava is a non‐ideal shear flow; away from the vent, the lava is an ideal shear flow. Gravity‐driven mechanisms control the relative contribution of pure and simple shear to the bulk deformation.
Microbial degradation is a key elimination pathway of hexachlorocyclohexanes from the Arctic Ocean
Authors: Harner Tom , Jantunen Liisa M. M. , Bidleman Terry F. , Barrie Leonard A. , Kylin Henrik , Strachan William M. J. , Macdonald Robie W.
Published: September 2002

Hexachlorocyclohexanes (HCHs) are the most abundant pesticides in arctic air and water. We have calculated in situ microbial degradation rates of α‐ and γ‐HCH for the Arctic Ocean using enantiomer ratio (ER) data and concentrations in water at the surface and after it has subducted to depth. The ERs of α‐HCH, which provide the first direct evidence of microbial degradation, allow rates to be estimated. The half‐lives due to microbial activity for (+)‐α‐HCH, (−)‐α‐HCH and γ‐HCH (respectively 5.9 ± 1.2, 22.8 ± 4.7 and 18.8 ± 10.1 years) are 3–10 times faster than removal by the only other known breakdown mechanism, hydrolysis (Harner et al., 1999). Microbial degradation is highlighted as an important elimination process in a revised HCH loss budget for the Arctic Ocean, removing 204 t y−1, α‐HCH and 23 t y−1, γ‐HCH. These tonnages represent 29–37% of the annual HCH removal from the Arctic Ocean.
Almost monoenergetic ions near the Earth's magnetosphere boundaries
Authors: Lutsenko Volt N. , Kudela Karel
Published: September 2002

More than 200 cases of energetic ion beams with an energy spectrum consisting of 1–3 narrow lines were observed during a period from August 1995 to August 1998 in the Earth's magnetosheath and in the region upstream of the Earth's bow shock. The observations are from the DOK‐2 experiment on board of the Interball‐1 spacecraft. Because the relative width at half maximum of these lines is of only 15–30%, we use the term “Almost Monoenergetic Ions” (AMI) for these events. Ion energy values varied for different events from 30 to 600 keV but were almost unchanged during each event. In two peak spectra the energy values ratio was 1:2 and in three peak spectra the ratios were 1:2:(5–6). Such line spectra cannot be explained by current models of particle acceleration or escape from the magnetosphere. We propose a hypothesis explaining the origin and main features of AMI as solar wind ions acceleration in a strong electrostatic field burst in a small region, possibly on the magnetopause or on the bow shock.
Generation mechanism of ESW based on GEOTAIL plasma wave observation, plasma observation and particle simulation
Authors: Matsumoto H. , Frank L. A. , Omura Y. , Kojima H. , Paterson W. R. , Tsutsui M. , Anderson R. R. , Horiyama S. , Kokubun S. , Yamamoto T.
Published: September 2002

Data of electrostatic waves and plasma particles in the deep magnetotail (X ∼ −209RE) respectively obtained by Plasma Wave Instrument and Comprehensive Plasma Instrument onboard the GEOTAIL spacecraft are presented. When the GEOTAIL spacecraft experienced multiple crossings of the plasma sheet boundary layer, broadband electrostatic noise (BEN) and Langmuir wave were observed alternatively. The dynamic frequency spectra of BEN are very bursty in time, and their waveforms are a series of electrostatic solitary waves (ESW). The LW is observed when an enhancement of an electron flux is found on a high‐energy tail of a relatively cold velocity distribution function of the major thermal electrons. The ESW, on the other hand, are observed in the presence of a hot thermal electron distribution function, in which electrons responsible for the ESW are embedded. These plasma conditions are in agreement with the ESW generation model based on particle simulations.
Nilometers, El Niño, and climate variability
Authors: Eltahir Elfatih A. B. , Wang Guiling
Published: September 2002

Nilometers have been used for gauging the level of water in the Nile river for more than five millennia. The written records describing some of these measurements represent the longest written records for any hydrological phenomenon. They describe interannual fluctuations in the Nile river flow which are closely associated with El Niño phenomenon. Here, we use information about long‐term variability in El Niño occurrences that has been extracted from the Nilometers records to test the significance of the recent trend in the frequency of El Niño years. We show that the observed frequency of El Niño years during the last two decades is rather high compared to the long‐term statistics that are computed from about a thousand years of Nilometers data; however similar levels of activity have been observed during the first millennium.
Relationship between the equatorial and meridional modes of climatic variability in the tropical Atlantic
Authors: Servain Jacques , Wainer Ilana , McCreary Julian P. , Dessier Alain
Published: September 2002

The tropical Atlantic Ocean exhibits two primary modes of interannual climate variability: an equatorial mode analogous to, but weaker than, the Pacific El Niño phenomenon, and a meridional mode that does not have a Pacific counterpart. The equatorial mode is responsible for warm (and cold) sea surface temperature (SST) events, mainly in the Gulf of Guinea, and is identifiable by abnormal changes in the equatorial thermocline slope resulting from zonal‐wind anomalies in the western tropical Atlantic. The meridional mode is characterized by a north‐south interhemispheric gradient of SST anomalies. Here it is shown, using observed surface and subsurface oceanic temperatures, that the meridional mode is linked to the equatorial mode, at both decadal and short‐interannual (1–2 years) time scales. Both modes involve north‐south displacements of the ITCZ, as in the annual response.
A dayside ionospheric absorption perturbation in response to a large deformation of the magnetopause
Authors: Weatherwax A. T. , Vo H. B. , Rosenberg T. J. , Mende S. B. , Frey H. U. , Lanzerotti L. J. , Maclennan C. G.
Published: September 2002

A large deformation of the dayside magnetopause was observed by Interball‐1 from 1132 to 1139 UT on July 24, 1996. The spacecraft, near 0800 LT at the time, transited the magnetosheath twice within 7 minutes. In response to these boundary perturbations, the antarctic stations South Pole and AGO‐P3, located at about the same local time as Interball‐1, observed impulsive magnetic variations. These variations were similar to previously reported magnetic variations observed in the northern hemisphere conjugate region during this event and may be related to discrete field‐aligned currents linking the ionosphere to the perturbed outer magnetosphere. Westward propagation of the magnetic signatures in both ionospheric regions is consistent with a travelling convection vortex event; however, the speed is significantly higher in the north (∼10 km/s) than in the south (∼3 km/s). A localized intensification of energetic electron precipitation (427.8 nm auroral emission and riometer absorption) was observed at South Pole station, but not at AGO‐P3 or at the nominally conjugate locations in Greenland and Canada. The complex, Z‐component variation of the magnetic pulse accompanying the particle precipitation at South Pole may be evidence of a localized ionospheric conductivity enhancement, as proposed in a recent model study of travelling convection vortices.
Geomagnetic excursions recorded in Chinese Loess in the last 70,000 years
Authors: Zhu Rixiang , Pan Yongxin , Liu Qingsong
Published: September 2002

Detailed paleomagnetic investigations conducted on the Malan loess (L1) at a well‐dated section (Weinan) in the Chinese Loess Plateau revealed two distinct anomalous directional intervals (ADI) accompanied by lower relative paleointensity. Rock magnetic properties and anisotropy of magnetic susceptibility (AMS) of samples taken from sedimentary horizons carrying the anomalous directions are similar to those taken from outside the anomalous directional intervals. Thus, the anomalous directions are interpreted as geomagnetic excursions. Based on 14C and TL data, the excursions occurred at 27.1–26.0 and 46.8–37.4 kyr B.P; the ages are consistent with the ages assigned to the Mono Lake excursion (MLE) and Laschamp excursion (LE), respectively. The result indicates that the MLE and LE were independent geomagnetic excursions. The morphology of LE at this section suggests that the LE might be an aborted geomagnetic reversal.
Effect of horizontal displacements due to ocean tide loading on the determination of polar motion and UT1
Authors: Scherneck Hans‐Georg , Haas Rüdiger
Published: September 2002

We show the influence of horizontal displacements due to ocean tide loading on the determination of polar motion and UT1 (PMU) on the daily and subdaily timescale. So called ‘virtual PMU variations’ due to modelling errors of ocean tide loading are predicted for geodetic Very Long Baseline Interferometry (VLBI) networks. This leads to errors of subdaily determination of PMU. The predicted effects are confirmed by the analysis of geodetic VLBI observations.
Radon‐220 calibration of Near‐surface turbulent gas transport
Authors: Lehmann Bernhard E. , Lehmann Martin , Neftel Albrecht , Gut Andreas , Tarakanov Sergei V.
Published: September 2002

Activity concentration profiles of the short‐lived radon isotope 220Rn (half‐life 56 seconds) in the lowest 50 cm above the soil are used to study near‐surface gas transport processes. The experimental data are compared to profiles calculated by solving the one‐dimensional diffusion equation for radioactive atoms with a linear increase of the eddy diffusion coefficient K with altitude according to K(z) = K0 + Kz.Z. The slope KZ in this model and the radon flux from the surface are continuously calculated from the activity measurements in time steps of one hour. Transport times for Rn atoms from an altitude Z1 = 5 cm to an altitude Z2 = 20 cm are typically between one and two minutes in stable meteorological conditions when the friction velocity u* is below 0.1 m/s.
Late Cretaceous paleomagnetic results from northeast Asian continental margin: The Sikhote Alin Mountain Range, eastern Russia
Authors: Uno Koji , Otofuji Yo‐ichiro , Matsuda Takaaki , Kuniko Yoshiki , Enami Ryo , Kulinich Ruslan G. , Zimin Petr S. , Matunin Anatoly P. , Sakhno Vladimir G.
Published: September 2002

Welded tuffs in the Upper Cretaceous Kisin Group have been collected for paleomagnetic study from 24 sites in Sikhote Alin, eastern Russia. Normal paleomagnetic directions from 11 sites are regarded as primary directions, whereas reversed paleomagnetic directions from 13 sites are ascribed to secondary origin. The normal directions of the Kisin Group together with the characteristic directions of the Sijanov Group yield the Late Cretaceous characteristic direction of Sikhote Alin (D = 355.0°, I = 59.8° with α95 = 7.2°). A significant separation (15.4°±11.9°) of pole positions is observed between Sikhote Alin (85.9°N, 11.3°E with A95 = 10.1°) and the North China Block. Sikhote Alin has been subjected to counterclockwise rotation through 20.5°±17.7° with respect to North China Block. The rotation occurred during 66–51 Ma, and is ascribed to sinistral motion along the central Sikhote Alin fault.
How accurate are the 234Th based particulate residence times in the ocean?
Authors: Kim Guebuem , Hussain Najid , Church Thomas M.
Published: September 2002

The residence times of colloidal and particulate matter have been estimated often by using naturally occurring 234Th‐238U disequilibria in the surface ocean. However, we show that the conventional 234Th multiple‐box models underestimate the actual residence time. Using a one‐box 234Th model approach, we calculate about a factor of two to four longer residence times for both colloidal and particulate thorium in the open ocean. This approach also yields very similar residence times between particulate thorium (box model based) and particulate organic carbon (sediment trap based) even with the same data sets previously used for showing a large discrepancy. Our results suggest significant corrections in the application of 234Th based residence times of the colloids and particulate matter to gauge the removal rates of reactive trace elements and organic carbon in the surface ocean.
Interdecadal interactions between the tropics and midlatitudes in the Pacific Basin
Authors: Barnett Tim P. , Pierce David W. , Latif Mojib , Dommenget Dietmar , Saravanan R.
Published: September 2002

Analysis of global climate model simulations and observations suggest decadal, midlatitude changes in and over the North Pacific cause decadal modulation of the El Niño‐Southern Oscillation. This coupling between the two geographic regions is via atmospheric, not oceanographic, teleconnections. In essence, large scale changes in the circulation of the atmosphere over the Pacific Basin, while largest in midlatitudes, have a significant projection onto the wind field overlying the equatorial regions. These low frequency wind changes precondition the mean state of the thermocline in the equatorial ocean to produce prolonged periods of enhanced or reduced ENSO activity. The midlatitude variability that drives equatorial impacts is of stochastic origin and, although the magnitude of the signal is enhanced by ocean processes, likely unpredictable.
Interhemispheric transport of relativistic electron beams
Authors: Khazanov G. V. , Liemohn M. W. , Krivorutsky E. N. , Kozyra J. U. , Gilchrist B. E.
Published: September 2002

Relativistic electron beam injection simulation results are presented from a new interhemispheric transport model, with a spatial domain reaching from 90 km to 90 km in the conjugate ionospheres. A single beam pulse is injected upward at 700 km during the first time step (10−4 s) and allowed to scatter and decay through collisional interactions with neutral particles and the core plasma. The maximum pulse duration for collisional processes to prevail over the wave‐beam instabilities is estimated, and the assumed pulse length is well within this limit. For an L=2 field line, the e‐folding time of a 5 MeV beam is 265 s, which is much bigger than the bounce period (0.19 s) and comparable to drift period around the Earth.
Opening of an eruptive fissure and seaward displacement at Piton De La Fournaise Volcano measured by RADARSAT satellite radar interferometry
Authors: Sigmundsson Freysteinn , Durand Philippe , Massonnet Didier
Published: September 2002

Interferometric analysis of Synthetic Aperture Radar images acquired by the RADARSAT‐1 satellite of Piton de la Fournaise volcano, show that an eruptive fissure which opened on 9th of March 1998 caused asymmetric deformation, with displacement and bulging of the volcanic edifice on the seaward side of the fissure. Up to 50 cm ground‐to‐satellite range change occurred in a 3‐km wide area, in response to a shallow (< 1‐km‐deep) inclined dike that opened by up to 60 cm. The erupted magma was transported from more than 7‐km‐depth below sea level, causing no observable volcano‐wide co‐eruptive deflation. A series of pre‐eruption interferograms show also that no significant inflation occurred prior to the eruption. The dike injection slightly reduced the stability of the volcano seaward flank.
Is ozone pollution affecting crop yields in China?
Authors: Chameides W. L. , Xingsheng Li , Xiaoyan Tang , Xiuji Zhou , Luo Chao , Kiang C. S. , St. John J. , Saylor R. D. , Liu S. C. , Lam K. S. , Wang T. , Giorgi F.
Published: September 2002

Newly available data from non‐urban locations in China along with regional model simulations suggest that ground‐level ozone may be sufficiently high to affect China's winter wheat production. As non‐urban ozone increases with industrialization, its effects on crops could hinder efforts to meet increasing food demands in the coming decades, in China.
Mechanisms for the Indian Ocean warming during the 1997–98 El Niño
Authors: Yu Lisan , Rienecker Michele M.
Published: September 2002

This study examines primary mechanisms that gave rise to the basin‐wide variations of the sea surface temperature (SST) in the Indian Ocean during the 1997–98 El Niño by using multi‐source data sets. The evolution of some key atmosphere‐ocean variables indicated that the SST variability in the Indian Ocean was largely attributable to the ENSO impact on the large‐scale atmospheric circulation. During June‐December 1997, when the El Niño in the Pacific was maturing, the Indian Ocean experienced the reversal of the Walker Circulation and the prolonged equatorward displacement of the southeast trades. The resultant changes in surface wind influenced the SST through the following means. In the equatorial region, the easterly winds associated with the reversed Walker Circulation forced equatorial Kelvin/Rossby waves, which then affected the equatorial ocean heat balance (mainly through upwelling/downwelling) and led to the reversal of the zonal SST gradient in the fall of 1997. The negative SST anomalies in the east and positive anomalies in the west in turn helped maintain and prolong the equatorial easterlies, a clear indication of coupled atmosphere‐ocean interactions in operation. Outside of the equatorial waveguide, changes of latent heat flux induced by wind speed variations played a major role in the broad‐scale warming. The effect was most significant during the summer/fall of 1997 when the southeasterly trade winds weakened considerably, leading to a dramatic reduction of latent heat release and subsequently a rapid surface warming in the southern ocean.
Twentieth century trends in droughts in southern Switzerland
Authors: Rebetez Martine
Published: September 2002

An investigation is made of the change in frequency of drought episodes in southern Switzerland. Episodes of drought are shown to have increased in frequency and persistence during the 20th century. They have been particularly frequent and long during the 1940s as well as since 1981. As these two periods have also been particularly warm, the results are discussed in relation to the increase in global atmospheric temperatures observed this century.
Evidence of NOx production within or upon ice particles in the Greenland snowpack
Authors: Honrath R. E. , Peterson M. C. , Guo S. , Dibb J. E. , Shepson P. B. , Campbell B.
Published: September 2002

NOx and NOy were determined in the interstitial air of surface snow and in ambient air at Summit, Greenland. NOx levels in interstitial air were 3 to >10 times those in ambient air, and were generally greater than ambient NOy levels. [NOy] in interstitial air varied diurnally in a manner consistent with photochemical generation within the snowpack. These observations imply that photochemical reactions occurring within or upon the ice crystals of surface snow produced NOx from a N‐reservoir compound within the snow. Average [NOx]:[HNO3] and [NOx]:[NOy] ratios in ambient air above the snow were elevated relative to other remote sites, indicating that NOx release within the snowpack may have altered NOx levels in the overlying atmospheric boundary layer. We suggest that the observed release of NOx may have been initiated by photolysis of nitrate, present in relative abundance in surface snow at Summit. Such a process may affect levels of nitrate and other compounds in surface snow, the overlying atmosphere, and glacial ice, and its potential role in cirrus cloud chemistry should be investigated.
Nitric acid adsorption on ice: Surface diffusion
Authors: Laird S. Kay , Buttry D. A. , Sommerfeld R. A.
Published: September 2002

Knowledge of the behavior of nitric acid on the surface of ice is important to predicting nitrate loads from snowpacks and determining paleoclimates from ice cores. Our experiments have shown that HNO3 will diffuse across the ice driven by concentration gradients. A diffusion constant, D, for this process was determined from Fick's first law to be 3.5(±1.0)×10−7 cm²/sec between −20° and −25° C.
Variation of the infrared spectra of nitric acid hydrates with formation conditions: Impact on PSC identification
Authors: Tisdale Robert T. , Prenni Anthony J. , Iraci Laura T. , Tolbert Margaret A. , Toon O. B.
Published: September 2002

Despite years of effort, the composition of polar stratospheric clouds (PSCs) is still uncertain. Future studies may be able to use FTIR extinction measurements to determine PSC composition. These studies require accurate optical constants for PSC materials. It has been suggested that accurate infrared (IR) optical constants for aerosols can only be derived from aerosol spectra. We have examined the IR spectra of nitric acid trihydrate (NAT) and nitric acid dihydrate (NAD) films and aerosols formed using a variety of experimental conditions. We conclude that several spectroscopically different types of NAD and NAT may exist. Alternatively, NAT could be birefringent and its spectra depend strongly on crystallographic orientation. The important causes for the different types or orientations seem to be the formation conditions and temperature, rather than whether the material is a film or aerosol.
Effect of near‐ridge thermal anomalies on the subsidence of the oceanic lithosphere: Constraints from a 2‐D dynamic model
Authors: Chiao Ling‐Yun , Wang Chi‐Wei
Published: September 2002

A 2‐D dynamic cooling model with temperature‐dependent asthenosphere viscosity is devised to examine the impact of near‐ridge thermal anomalies on the subsidence of the oceanic lithosphere. In this model, mid‐ocean ridge segments with cooler than ambient mantle temperatures have calculated subsidence rates that cannot be differentiated from normal ridge segments. This occurs because the cooler thermal anomaly cannot be sustained, nor can it spread off‐axis, due to thermally driven near‐ridge buoyant flow. When the cooler anomaly is deeply rooted, this buoyant flow can be inhibited only when the asthenosphere viscosity is as high as 3×1020 Pa‐s. On the other hand, ridge segments with warmer mantle temperatures have significantly higher subsidence rates than those predicted from standard conductive cooling models. Simply varying the injection temperature invalidates the 1‐D simplification usually invoked implicitly in models of the cooling process of the oceanic lithosphere.
Transport of Asian air pollution to North America
Authors: Jaffe Dan , Anderson Theodore , Covert Dave , Kotchenruther Robert , Trost Barbara , Danielson Jen , Simpson William , Berntsen Terje , Karlsdottir Sigrun , Blake Donald , Harris Joyce , Carmichael Greg , Uno Itsushi
Published: September 2002

Using observations from the Cheeka Peak Observatory in northwestern Washington State during March‐April, 1997, we show that Asian anthropogenic emissions significantly impact the concentrations of a large number of atmospheric species in the air arriving to North America during spring. Isentropic back‐trajectories can be used to identify possible times when this impact will be felt, however trajectories alone are not sufficient to indicate the presence of Asian pollutants. Detailed chemical and meteorological data from one of these periods (March 29th, 1997) indicates that the surface emissions were lifted into the free troposphere over Asia and then transported to North America in ∼6 days.
Elastic‐wave velocities in sandstones with non‐load‐bearing clay
Authors: Gal Doron , Dvorkin Jack , Nur Amos
Published: September 2002

The elastic moduli (and acoustic velocities) of shaley sandstones strongly depend on the amount of clay as well as on its position among sand grains. In many cases clay may fill pores without noticeably affecting the stiffness of the rock. Such clays are non‐load‐bearing. Here, the stiffness of the rock is determined primarily by the load‐bearing quartz frame. We examine several data sets and show that in this case a simple unique relation exists between the acoustic velocity and the porosity of the load‐bearing frame of the rock. This porosity can be calculated as the sum of the effective porosity (total porosity minus microporosity inside clay) and the volumetric fraction of clay in the rock. Also, it is the sum of the total porosity and the volumetric fraction of solid clay particles in the rock.