bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of the antagonistic effects of different angiotensin II receptor blockers in human coronary arteries
Authors: Pantev Emil , Stenman Emelie , Wackenfors Angelica , Edvinsson Lars , Malmsjö Malin
Published: December 2002

Background:

Angiotensin II (Ang II) is a potent vasoconstrictor and a deleterious factor in cardiovascular pathophysiology. Ang II receptor blockers (ARBs) have recently been introduced into clinical practice for treatment of hypertension and congestive heart failure.

Aims:

This study was undertaken to evaluate the inhibitory effects of ARBs on vasoconstriction in humans.

Methods:

Vasomotor tone was analyzed in endothelium denuded, human coronary artery (HCA) segments. Ang II type 1 (AT1) and type 2 (AT2) receptor mRNA expression was examined by reverse transcriptase‐polymerase chain reaction (RT‐PCR).

Results:

Ang II was a potent vasoconstrictor (pEC50=7.7). At 1 nM of the AT1 receptor antagonists, candesartan and valsartan, the maximum contraction was depressed to 57 and 50% of Ang II, respectively, indicating insurmountability. Although generally considered surmountable, the presence of 100 nM losartan elicited a depression of the Ang II response to 32%. Its active metabolite, EXP 3174 (1 nM), abolished the Ang II contraction. The AT1 receptor antagonists had the following order of blocking effect; EXP 3174>candesartan=valsartan>losartan. The AT2 receptor antagonist, PD 123319 (100 nM) significantly attenuated the Ang II contraction (Emax=62% of Ang II). RT‐PCR of HCA smooth muscle cells demonstrated expression of both AT1 and AT2 receptor mRNA.

Conclusions:

Ang II contraction in HCA is mediated mainly by AT1 but also involves AT2 receptors. The active metabolite of losartan, EXP 3174, is the most efficacious AT1 receptor antagonist in HCA.
An evaluation of the statistical significance of the association between northward turnings of the interplanetary magnetic field and substorm expansion onsets
Authors: Hsu Tung‐Shin , McPherron R. L.
Published: December 2002

An outstanding problem in magnetospheric physics is deciding whether substorms are always triggered by external changes in the interplanetary magnetic field (IMF) or solar wind plasma, or whether they sometimes occur spontaneously. Over the past decade, arguments have been made on both sides of this issue. In fact, there is considerable evidence that some substorms are triggered. However, equally persuasive examples of substorms with no obvious trigger have been found. Because of conflicting views on this subject, further work is required to determine whether there is a physical relation between IMF triggers and substorm onset. In the work reported here a list of substorm onsets was created using two independent substorm signatures: sudden changes in the slope of the AL index and the start of a Pi 2 pulsation burst. Possible IMF triggers were determined from ISEE‐2 observations. With the ISEE spacecraft near local noon immediately upstream of the bow shock, there can be little question about propagation delay to the magnetopause or whether a particular IMF feature hits the subsolar magnetopause. Thus it eliminates the objections that the calculated arrival time is subject to a large error or that the solar wind monitor missed a potential trigger incident at the subsolar point. Using a less familiar technique, statistics of point process, we find that the time delay between substorm onsets and the propagated arrival time of IMF triggers are clustered around zero. We estimate for independent processes that the probability of this clustering by chance alone is about 10−11. If we take into account the requirement that the IMF must have been southward prior to the onset, then the probability of clustering is higher, ∼10−5, but still extremely unlikely. Thus it is not possible to ascribe the apparent relation between IMF northward turnings and substorm onset to coincidence.
Slip distribution of the 1997 Umbria‐Marche earthquake sequence: Joint inversion of GPS and synthetic aperture radar interferometry data
Authors: Lundgren Paul , Stramondo Salvatore
Published: December 2002

In September–October 1997 a seismic sequence struck the southern part of the Umbria‐Marche region in central Italy. The three largest earthquakes took place on 26 September (0033 UT, Mw 5.7; 09:40 GU, Mw 6.0) near Colfiorito, and on 14 October (Mw 5.6) near Sellano. We present a slip model for the main sequence over two separate fault planes. We use previously published Global Positioning System (GPS) and differential interferometric synthetic aperture radar (DInSAR) data as well as new DInSAR data covering the Sellano event as input to a simulated annealing solution for the distribution of fault slip. The combination of both types of geodetic data as well as the combination of SAR interferograms from both ascending and descending satellite tracks allows us to make a more complete geodetically based assessment of the fault slip for these earthquakes. For the solutions presented here we required the slip distribution to match the observed surface displacements while maintaining a total scalar seismic moment approximately equal to the seismologically inferred moments for this sequence. We find the slip was concentrated in a zone at 4–5.5 km depth with a shallower tail extending to near the surface at the northern end of the Colfiorito sequence. For both the second Colfiorito event and the Sellano event, individual patches were calculated with maximum slip of 2 m, implying stress drops as high as 20 MPa. Coulomb stress calculations show that the coseismic slip distribution for the Colfiorito events facilitated slip of the adjacent Sellano earthquake.
Spectroscopic study of the Moses Lake dune field, Washington: Determination of compositional distributions and source lithologies
Authors: Bandfield Joshua L. , Edgett Kenneth S. , Christensen Philip R.
Published: December 2002

Source lithologies and transport histories of materials within the Ephrata Fan are investigated. Data were collected using a variety of remote‐sensing, laboratory spectroscopic, and field observations and techniques. Laboratory thermal emission spectra were collected of bedrock within the Grand Coulee, dune samples, and clast deposits. Factor analysis, target transformation, and end‐member recovery techniques were applied to the set of dune samples as well as a set of grain size fractions. The dune sample spectra are composed of three components that represent basalt, granodiorite, and clay compositions. The basalt and granodiorite components are similar to spectra of clast and bedrock samples from the Grand Coulee and the Ephrata Fan. The clay component is similar to weathering surfaces located within the dune field. The same components were recovered from the set of grain size fractions from a single dune sample demonstrating a relatively higher basalt concentration with grain sizes greater than ∼250 μm. Thermal Infrared Multispectral Scanner (TIMS) data display significant intradune compositional variation and no discernable interdune compositional variation, indicating that the basalt and granodiorite components were likely deposited simultaneously and subsequently separated by wind based on grain size. Basalt and granodiorite bedrock units within the Channeled Scablands are source materials for the deposits within the Ephrata Fan and Moses Lake dune field. The Columbia River, located 20 km west of the dune field, is not a likely source of material.
Nitriles produced by ion chemistry in the lower ionosphere of Titan
Authors: Molina‐Cuberos Gregorio J. , Schwingenschuh Konrad , López‐Moreno José J. , Rodrigo Rafael , Lara Luisa M. , Anicich Vincent
Published: December 2002

Titan, the largest satellite of Saturn, possesses a dense N2‐CH4 atmosphere rich in organics with a complex chemistry that could be similar to Earth's primordial atmosphere. Due to its massive atmosphere and the long distance to the Sun, cosmic rays are the main energetic source of the lower part of the atmosphere. Cosmic radiation can reach Titan's troposphere (z < 40 km) and activate the chemistry at depths where UV light and high‐energy electrons cannot penetrate. The interaction of cosmic rays with the neutral constituents of Titan produces a complex ion chemistry that leads to the formation of a high variety of massive ions and organic molecules. The low temperatures and high pressures prevailing in Titan's atmosphere result in a high efficiency of three‐body reactions and on the formation of ion clusters. Association of neutral molecules with HCNH+, CH3CNH+, and HC3NH+ produces ions containing the CN group, and the electron recombination of these clusters can produce a high variety of N‐containing compounds. Here we propose schemes to synthesize nitrile‐type molecules from the dissociative recombination ion clusters produced by cosmic rays. Our ion chemistry model can explain the existence of some of the nitriles found in laboratory studies, such as propenenitrile, propanenitrile, butanenitrile, pentanenitrile, and 10 more as well as predict the existence of new species. Experimental simulations of Titan's atmosphere yield the formation of a high number of species, which are not considered in the chemical schemes of current photochemical models.
Diurnal cycles and seasonal variation of isoprene and its oxidation products in the tropical savanna atmosphere
Authors: Holzinger R. , Sanhueza E. , von Kuhlmann R. , Kleiss B. , Donoso L. , Crutzen P. J.
Published: December 2002

Using the proton transfer reaction mass spectrometry (PTR‐MS) technique, isoprene and its oxidation products were measured in a productive woodland savanna (Calabozo site, during the wet and dry seasons) and a less productive grassland savanna (La Gran Sabana, Parupa site). The measured protonated masses in the PTR‐MS, postulated compounds, and daytime average volume mixing ratios at the Calabozo site during the wet season are: 69 isoprene (1.62 nmol/mol), 71 methyl vinyl ketone + methacrolein (0.98 nmol/mol), 83 3‐methyl furan + unsaturated C5‐hydroxycarbonyls (0.12 nmol/mol), and 101 isoprene hydroperoxides (0.16 nmol/mol). Significant diurnal cycles of the hydrocarbon concentrations were observed, with distinct characteristics between sites and seasons. Two times lower levels of isoprene were observed during the dry season. At the Parupa site measured concentrations of all masses were about three times lower than at the Calabozo site during the wet season, and significant transport of isoprene from upwind forests was observed. Comparison with a photochemical box model revealed that surface deposition is likely a significant sink for isoprene and its oxidation products. An isoprene source of 2.1–3.2 × 106 molec/cm3/s and an HO concentration of 4.1–6.0 × 105 molec/cm3 averaged over 24 hours were needed to match the observed mixing ratios. Assuming a mixed boundary layer of 1500 m and an isoprene source half the strength during the 5 months dry season, a global emission of isoprene to the atmosphere from tropical savannas between 53 and 79 Tg C/yr can be calculated from our results if the Calabozo site is representative.
Evaluation of terrestrial carbon cycle models with atmospheric CO2 measurements: Results from transient simulations considering increasing CO2, climate, and land‐use effects
Authors: Dargaville R. J. , Heimann M. , McGuire A. D. , Prentice I. C. , Kicklighter D. W. , Joos F. , Clein J. S. , Esser G. , Foley J. , Kaplan J. , Meier R. A. , Melillo J. M. , Moore B. , Ramankutty N. , Reichenau T. , Schloss A. , Sitch S. , Tian H. , Williams L. J. , Wittenberg U.
Published: December 2002

An atmospheric transport model and observations of atmospheric CO2 are used to evaluate the performance of four Terrestrial Carbon Models (TCMs) in simulating the seasonal dynamics and interannual variability of atmospheric CO2 between 1980 and 1991. The TCMs were forced with time varying atmospheric CO2 concentrations, climate, and land use to simulate the net exchange of carbon between the terrestrial biosphere and the atmosphere. The monthly surface CO2 fluxes from the TCMs were used to drive the Model of Atmospheric Transport and Chemistry and the simulated seasonal cycles and concentration anomalies are compared with observations from several stations in the CMDL network. The TCMs underestimate the amplitude of the seasonal cycle and tend to simulate too early an uptake of CO2 during the spring by approximately one to two months. The model fluxes show an increase in amplitude as a result of land‐use change, but that pattern is not so evident in the simulated atmospheric amplitudes, and the different models suggest different causes for the amplitude increase (i.e., CO2 fertilization, climate variability or land use change). The comparison of the modeled concentration anomalies with the observed anomalies indicates that either the TCMs underestimate interannual variability in the exchange of CO2 between the terrestrial biosphere and the atmosphere, or that either the variability in the ocean fluxes or the atmospheric transport may be key factors in the atmospheric interannual variability.
Impact of atmospheric aerosol light scattering and absorption on terrestrial net primary productivity
Authors: Cohan Daniel S. , Xu Jin , Greenwald Roby , Bergin Michael H. , Chameides William L.
Published: December 2002

Scattering and absorption of sunlight by anthropogenic aerosols reduce the photosynthetically active radiation (PAR) incident upon the Earth's surface, but increase the fraction of the PAR that is diffuse. These alterations to irradiance may elicit conflicting responses in terrestrial plants: photosynthesis and net primary productivity (NPP) are slowed by reductions in total PAR, but enhanced by increases in diffuse PAR. In this paper, we use two canopy photosynthesis models to estimate the net effect of aerosols on carbon assimilation by green plants during summertime at midlatitudes. The model calculations indicate that the net effect of PAR scattering and absorption by atmospheric aerosols on NPP can be positive, neutral, or negative. Two parameters that strongly influence the net effect are the aerosol optical depth (integral of light extinction with height) and the cloud cover. On cloudless days NPP peaks under moderately thick aerosol loadings. On overcast days, aerosols slow NPP. The implications of these results for various regions of the globe and possible directions for future studies on the effect of aerosols on plant growth are discussed.
Distribution of anthropogenic CO2 in the Pacific Ocean
Authors: Sabine C. L. , Feely R. A. , Key R. M. , Bullister J. L. , Millero F. J. , Lee K. , Peng T.‐H. , Tilbrook B. , Ono T. , Wong C. S.
Published: December 2002

This work presents an estimate of anthropogenic CO2 in the Pacific Ocean based on measurements from the WOCE/JGOFS/OACES global CO2 survey. These estimates used a modified version of the ΔC* technique. Modifications include a revised preformed alkalinity term, a correction for denitrification, and an evaluation of the disequilibrium terms using an optimum multiparameter analysis. The total anthropogenic CO2 inventory over an area from 120°E to 70°W and 70°S to 65°N (excluding the South China Sea, the Yellow Sea, the Japan/East Sea, and the Sea of Okhotsk) was 44.5 ± 5 Pg C in 1994. Approximately 28 Pg C was located in the Southern Hemisphere and 16.5 Pg C was located north of the equator. The deepest penetration of anthropogenic CO2 is found at about 50°S. The shallowest penetration is found just north of the equator. Very shallow anthropogenic CO2 penetration is also generally observed in the high‐latitude Southern Ocean. One exception to this is found in the far southwestern Pacific where there is evidence of anthropogenic CO2 in the northward moving bottom waters. In the North Pacific a strong zonal gradient is observed in the anthropogenic CO2 penetration depth with the deepest penetration in the western Pacific. The Pacific has the largest total inventory in all of the southern latitudes despite the fact that it generally has the lowest average inventory when normalized to a unit area. The lack of deep and bottom water formation in the North Pacific means that the North Pacific inventories are smaller than the North Atlantic.
Dynamic global patterns of nitrate, phosphate, silicate, and iron availability and phytoplankton community composition from remote sensing data
Authors: Kamykowski Daniel , Zentara Sara‐Joan , Morrison John M. , Switzer Anne C.
Published: December 2002

Satellites routinely provide frequent, large‐scale, near‐surface views of many oceanographic variables pertinent to plankton ecology, but nutrient fertility remains problematic. A recently derived set of nitrate (N), phosphate (P), and silicate (S) nutrient depletion temperatures (NDT) were subtracted from AVHRR‐derived sea surface temperatures for March 1999 through June 2000 to determine eight categories of temporally varying N, P, and S presence/absence in the world ocean. Complementary midmonth, aerosol optical thickness (70°N to 70°S) and precipitation (40°N to 40°S), obtained from the AVHRR Pathfinder effort and the TRMM microwave imager, respectively, represented iron (F) presence (>10%)/absence (<10%) in the world ocean as dry and wet (40°N to 40°S) or just dry (40°N–70°N and 40°S–70°S) deposition of atmospheric dust. The resulting 16 N, P, S, and F presence/absence categories provided a dynamic view of seasonal and interannual nutrient variability in the world ocean. SeaWiFS chlorophyll a maps for April, July, and October 1999 and January 2000 were compared to the N, P, S, and F categories from these months. Phytoplankton cell size and taxonomic composition categories linked to each of the 16 nutrient availability categories translated the nutrient associations with chlorophyll a into an inferred phytoplankton community structure. Consideration of additional bottom‐up (like solar irradiance exposure) and top‐down (like grazing by zooplankton) influences on size and species/class specific net phytoplankton growth can improve the assignment of inferred phytoplankton community structure. The proposed dynamic approach toward monitoring nutrient availability can contribute to refined estimates of biogeochemical fluxes in the world ocean.
Revision of the global carbon budget due to changing air‐sea oxygen fluxes
Authors: Plattner Gian‐Kasper , Joos Fortunat , Stocker Thomas F.
Published: December 2002

Carbon budgets inferred from measurements of the atmospheric oxygen to nitrogen ratio (O2/N2) are revised considering sea‐to‐air fluxes of O2 and N2 in response to global warming and volcanic eruptions. Observational estimates of changes in ocean heat content are combined with a model‐derived relationship between changes in atmospheric O2/N2 due to oceanic outgassing and heat fluxes to estimate ocean O2 outgassing. The inferred terrestrial carbon sink for the 1990s is reduced by a factor of two compared with the most recent estimate by the Intergovernmental Panel on Climate Change (IPCC). This also improves the agreement between calculated ocean carbon uptake rates and estimates from global carbon cycle models, which indicate a higher ocean carbon uptake during the 1990s than the 1980s. The simulated decrease in oceanic O2 concentrations is in qualitative agreement with observed trends in oceanic O2 concentrations.
Global biogeochemical cycle of boron
Authors: Park Haewon , Schlesinger William H.
Published: December 2002

The global Boron (B) cycle is primarily driven by a large flux (1.44 Tg B/yr) through the atmosphere derived from seasalt aerosols. Other significant sources of atmospheric boron include emissions during the combustion of biomass (0.26–0.43 Tg B/yr) and coal, which adds 0.20 Tg B/yr as an anthropogenic contribution. These known inputs to the atmosphere cannot account for the boron removed from the atmosphere during rainfall (3.0 Tg B/yr) and estimated dry deposition (1.3–2.7 Tg B/yr). In addition to atmospheric deposition, rock weathering is a source of boron (0.19 Tg B/yr) for terrestrial ecosystems, and humans mine about 0.31 Tg B/yr from the Earth's crust. More than 4.8 Tg B/yr circulates in the biogeochemical cycle of land plants, and about 0.53–0.63 Tg B/yr is carried from land to sea by rivers. The biogeochemical cycle of boron in the sea includes 4.4 Tg B/yr circulating in the marine biosphere, and an annual loss of 0.47 Tg B/yr to the oceanic crust via a variety of sedimentary processes that collectively remove only a small fraction of the total annual inputs to the oceans. Thus with our current understanding of the global biogeochemistry of B, the atmospheric budget shows outputs > inputs, while the marine compartments show inputs > outputs. Despite these uncertainties, it is clear that the human perturbation of the global B cycle has more than doubled the mobilization of B from the crust and contributes significantly to the B transport in rivers.
Global ocean emission of dimethylsulfide predicted from biogeophysical data
Authors: Simó Rafel , Dachs Jordi
Published: December 2002

Among the biosphere‐atmosphere interactions that influence climate, the emission of dimethylsulfide (DMS) from the ocean plays a prominent role for its high potential in cloud albedo regulation. In order to advance in our understanding and quantification of this coupled ocean‐atmosphere system, both synoptic and predictive capabilities must be largely improved. Hitherto, large‐scale oceanic DMS has eluded being captured from remote sensing, correlated with synoptic variables, or simulated by mechanistic modeling. We have found a simple empirical relationship that permits global‐ocean monthly distributions of DMS concentration to be computed from a combination of remotely sensed biospheric data (chlorophyll a) and climatological geophysical data (mixed layer depth). This relationship allows for the desired synopticity and predictability in the ocean‐to‐atmosphere sulfur flux, which we have globally quantified as 23–35 Tg S yr−1. Also, our algorithm stands in support of a biogenic‐DMS/solar‐radiation negative feedback and opens the door toward quantifying its strength and its response to global warming.
Nitrous oxide and methane fluxes in six different land use systems in the Peruvian Amazon
Authors: Palm C. A. , Alegre J. C. , Arevalo L. , Mutuo P. K. , Mosier A. R. , Coe R.
Published: December 2002

The contribution of different land‐use systems in the humid tropics to increasing atmospheric trace gases has focused on forests, pastures, and crops with few measurements from managed, tree‐based systems that dominate much of the landscape. This study from the Peruvian Amazon includes monthly nitrous oxide and methane fluxes from two cropping systems, three tree‐based systems, and a 23‐year secondary forest control. Average N2O fluxes from the cropping systems were two to three times higher than the secondary forest control (9.1 μg N m−2 h−1), while those of the tree‐based systems were similar to the secondary forest. Increased fluxes in the cropping systems were attributed to N fertilization, while fluxes from the tree‐based systems were related to litterfall N. Average CH4 consumption was reduced by up to half that of the secondary forest (−30.0 μg C m−2 h−1) in the tree‐based and low‐input cropping systems. There was net CH4 production in the high‐input cropping system. This switch to net production was a result of increased bulk density and increased soil respiration resulting in anaerobic conditions. Reduced rates of N2O emissions, similar CH4 consumption, and high C sequestration rates in these tree‐based systems compared with mature forests, coupled with the large area of these systems in the humid tropics, may partially offset the past effects of deforestation on increased atmospheric trace gas concentrations. In contrast, cropping systems with higher N2O emissions, substantially reduced CH4 consumption or even net CH4 emissions, and little C sequestration exacerbate those effects.
O2 volumes at high pressure from KClO4 decomposition: D″ as a siderophile element pump instead of a lid on the core
Authors: Walker D. , Clark S. M. , Cranswick L. M. D. , Johnson M. C. , Jones R. L.
Published: December 2002

New measurements of the high‐pressure volume of oxygen make plausible old, controversial diamond anvil cell (DAC) observations of a high‐pressure reaction between liquid Fe and Fe‐bearing silicate in which FeO dissolved into liquid Fe. If the Earth's D″ layer between core and mantle is the waste product of this reaction proceeding forward with oxygen transfer to the core, then D″ would form an effective lid preventing escape of siderophile elements from the core. On the other hand, it is at least as plausible that the core is now oxygen saturated and that core cooling and internal crystallization drive this reaction backward with transfer of Fe‐ and O‐rich material out of the core into D″. The 186Os anomalies in some plume basalts are more consistent with this D″ as a siderophile element pump scenario than the D″ as‐lid scenario. Contributions of siderophile elements to the mantle from the core could assist in balancing the persistently enigmatic budget of these elements.
The link between volcanism and deglaciation in Iceland
Authors: Maclennan J. , Jull M. , McKenzie D. , Slater L. , Grönvold K.
Published: December 2002

Temporal variation in the eruption rate and lava composition in the rift zones of Iceland is associated with deglaciation. Average eruption rates after the end of the last glacial period, ∼12 kyr BP, were up to 100 times higher than those from both the glacial period and recent times (<5 kyr BP). This peak in volcanic activity finished less than 2 kyr after the end of deglaciation. New geochemical data from ∼80 basalt and picrite samples from the Theistareykir and Krafla volcanic systems show that there is a temporal variation in both the major and trace element composition of the eruptions. Early postglacial eruptions show a greater range in MgO contents than eruptions from other times, and at a fixed MgO content, the concentration of incompatible elements in subglacial eruptions is higher than that in early postglacial eruptions. Recent eruptions from the Krafla system have similar compositions to subglacial eruptions. The high eruption rates and low rare earth element (REE) concentrations in the lava from early postglacial times can be accounted for by increased melt generation rates in the shallow mantle caused by unloading of an ice sheet. Magma chamber processes such as crystallization and assimilation can produce the temporal variation in REE contents if garnet is present. However, garnet is not observed as a phenocryst or xenocryst phase and is not required to match the variation in major element contents observed at Krafla and Theistareykir. If the increase in eruption rates reflects increased melt production rates in the mantle, then the relative timing of deglaciation and the burst in eruption rates can be used to estimate the rate of melt transport in the mantle. The observed duration of enhanced eruption rates after deglaciation can be reproduced if the vertical melt extraction velocity is >50 m yr−1.
Anomalously high δD values in the mantle
Authors: Xia Qun‐Ke , Deloule Etienne , Wu Yuan‐Bao , Chen Dao‐Gong , Cheng Hao
Published: December 2002

Hydrogen isotopic compositions of four amphibole grains from three lherzolite xenoliths hosted in Cenozoic basanites of Nushan, eastern China have been analyzed by ion microprobe. δD values of all analyzed points range from −94 to +46‰. Large heterogeneities of D/H ratios within single grains have been observed with variations of δD up to 80‰ on the scale of less than 400 μm. Neither correlation between δD values and water contents of the analyzed points nor regular variation between δD values and positions of analyzed points within the same grain can be found, implying that the scatter of δD values could not result from a late shallow process such as hydrogen loss or hydrothermal alterations and should be considered as inherited from the source at depth. Chemical compositions of Nushan amphiboles are very homogeneous, excluding the possibility that the scatter of δD values could arise from variable fractionation factors between a single fluid source and minerals. Therefore, metasomatic fluids responsible for the formation of Nushan amphiboles should have variable and unusually high hydrogen isotopic compositions. We suggest that this variation in the metasomatic fluids could be related to melt degassing in the mantle source.
NAO influence on sea ice extent in the Eurasian coastal region
Authors: Hu Aixue , Rooth Claes , Bleck Rainer , Deser Clara
Published: December 2002

Influence of winter pre‐conditioning of Arctic sea ice due to atmospheric forcing associated with the North Atlantic Oscillation (NAO) on the reduction in summer sea ice extent is studied. It is found that winter sea ice is about 50 cm thinner in high‐NAO index years than in low‐NAO index years in the Eurasian coastal region mainly due to stronger wind‐driven ice export. The thinner wintertime ice combined with strengthened southerlies in spring promotes an earlier break‐up of the ice pack in the Eurasian coastal region, resulting in significant sea ice export. The higher ice efflux, in turn, further reduces the ice compactness, thus more solar radiation is absorbed by the oceans which enhances the summer melting process. Thus, winter and spring atmospheric anomalies associated with the positive phase of the NAO may underlie the reduction of summer sea ice extent observed during the 1980s and 1990s.
Harmonic structure of field line eigenmodes generated by ionospheric feedback instability
Authors: Pokhotelov Dimitri , Lotko William , Streltsov Anatoly V.
Published: December 2002

Ionospheric feedback instability generates field line eigenmodes under favorable conditions of low ionospheric conductivity and high electric convection. A numerical study has been performed using a two‐dimensional model in dipole magnetic field geometry that includes active ionospheric feedback and shear Alfvén wave dynamics of the magnetospheric response. Strong parallel inhomogeneities of the magnetospheric parameters included in the numerical model permit the simultaneous development of local ionospheric resonator modes (fast feedback) trapped between the ionosphere and Alfvén speed maximum above it and field line eigenmodes (slow feedback) that stand along the entire magnetic field line between two conjugate ionospheres. Fourier analysis of the numerical solution has been used to investigate the relative contribution of fast and slow feedback in the global dynamics of magnetosphere–ionosphere coupling. While many harmonics of the global magnetospheric resonator can be simultaneously generated by the ionospheric feedback instability, all modes above the fundamental eigenmode are strongly suppressed by Alfvén wave dispersion. The numerical results suggest that ionospheric feedback is a generating mechanism for the formation of narrow field line resonances.
Auroral poleward boundary intensifications and tail bursty flows: A manifestation of a large‐scale ULF oscillation?
Authors: Lyons L. R. , Zesta E. , Xu Y. , Sánchez E. R. , Samson J. C. , Reeves G. D. , Ruohoniemi J. M. , Sigwarth J. B.
Published: December 2002

Auroral zone observations often show significant ULF power. We have analyzed auroral and plasma sheet observations during two prolonged periods of strongly southward and relatively steady interplanetary magnetic field (IMF). We find evidence that auroral poleward boundary intensifications (PBIs), which have large intensity and occur repetitively throughout such periods, may be a manifestation of a large‐scale ULF oscillation mode that strongly perturbs the plasma sheet and the auroral ionosphere. If this is correct, then ULF modes would be a major component of tail dynamics, of magnetosphere coupling to the ionosphere, and of auroral zone disturbances during periods of enhanced convection. They would simultaneously affect a large region of the nightside, extending along auroral zone field lines from the ionosphere to the equatorial plasma sheet and extending from field lines that lie near the magnetic separatrix to, at times, as close to the Earth as synchronous orbit. They would also occasionally have amplitudes as large as the changes that occur in association with other auroral zone disturbances such as substorms. Here we have found peak‐to‐peak amplitudes as high as several hundred nanoteslas in ground X, an order of magnitude in synchronous energetic proton fluxes, ∼20–40 nT in synchronous magnetic field components, ∼20 nT in tail magnetic field components, ∼1000 km/s in tail flow speeds, and ∼400 m/s in ionospheric flow speed. We find evidence for significant power at 0.5–0.7 mHz (∼25–30 min period), significant power at a possible second harmonic (∼1.1–1.3 mHz), and power at frequencies that could be higher harmonics simultaneously within the auroral ionosphere and within the nightside plasma sheet.
Two‐dimensional structure of auroral poleward boundary intensifications
Authors: Zesta E. , Donovan E. , Lyons L. , Enno G. , Murphree J. S. , Cogger L.
Published: December 2002

We investigate the two‐dimensional structure of auroral poleward boundary intensifications (PBIs). PBIs are a nightside auroral intensification that has been studied primarily with ground‐based meridian scanning photometers (MSPs). They have a signature that in the MSP data, appears as an increase in intensity at or near the magnetic separatrix and is often seen to extend equatorward. They are also associated with fast flows in the tail and are thus important to the dynamics of the plasma sheet. MSP data provide information about the temporal evolution of the aurora in one spatial dimension, in this case roughly along a magnetic meridian. This paper is motivated by a desire to determine the physics of PBIs that is revealed by their two‐dimensional structure. To do this, we have identified a number of PBI events in the CANOPUS Rankin Inlet and Gillam MSPs that occurred at times when high‐resolution, two‐dimensional images of the aurora over the same region were also available. The two‐dimensional images used in this study were obtained by the Freja UV imager, from October 1992 to January 1993, and by the CANOPUS Gillam all‐sky imager during the winter viewing season of 1996–1997. We find that PBIs, as observed by the MSPs, are either equatorward extending or non‐equatorward extending. Equatorward extending PBIs are either north‐south aligned structures or east‐west arcs propagating mostly equatorward, but we were not able to determine without doubt which type is the most prevalent. We suggest that equatorward extending PBIs may be the auroral footprint of two major modes of energy transfer in the plasma sheet: multiple, narrow, earthward fast‐flow channels in the plasma sheet and sequences of azimuthally broad and primarily earthward propagating phase fronts initiating near the separatrix. Nonequatorward extending PBIs are found to mostly be a series of multiple bead‐like intensifications along the poleward boundary of the aurora zone. Such PBIs may be evidence for shear instabilities at the separatrix boundary on the flanks of the magnetotail.
Icy particles in the summer mesopause region: Three‐dimensional modeling of their environment and two‐dimensional modeling of their transport
Authors: Berger U. , von Zahn U.
Published: December 2002

In summertime, layers of icy particles form in the high‐latitude mesopause region, causing the phenomena of noctilucent clouds and polar mesosphere summer echoes. We study the formation of these layers by means of a 3‐D general circulation model of the middle atmosphere (COMMA/IAP) including new modules for the mesospheric chemistry and for the microphysics of icy particles. We initialize the mesopause region with an ensemble of two million particles and investigate their time‐dependent transport in a 2‐D Lagrangian way. We use the model to study in considerable detail ice particle formation by heterogeneous nucleation on smoke particles, freeze‐drying of the mesopause region by formation of ice particles, and the influences of tidal waves and particle eddy diffusion on ice particle and noctilucent cloud (NLC) layer behavior. We present model results on the requirements for adequate size of smoke particles to act as condensation nuclei in the mesopause region (directly after initialization > 0.7 nm radius; after 8 hours > 2 nm), the types of ice particle trajectories, the timescale for growth of particles (6 to 8 hours to radii > 20 nm) and sublimation of ice particles (duration of sublimation phase typically 6 hours), the typical altitude range of maximum NLC brightness (82.5–83.0 km), the size distributions of ice particles (closer to Gaussian than lognormal in shape), the importance of the vertical component of the tidal winds on NLC layer behavior, and the dominance of semidiurnal over diurnal tidal effects. Furthermore, the model allows us to make predictions on a number of NLC features that are either currently under study or may become observable in the near future, such as properties of NLC at high arctic latitudes, and the development of layers with strongly enhanced water vapor mixing ratios near the lower border of the NLCs.
Long‐term‐average, solar cycle, and seasonal response of magnetospheric energetic electrons to the solar wind speed
Authors: Vassiliadis D. , Klimas A. J. , Kanekal S. G. , Baker D. N. , Weigel R. S.
Published: December 2002

Among the interplanetary activity parameters the solar wind speed is the one best correlated with the energetic electron fluxes in the inner magnetosphere. We examine the radial and temporal characteristics of the 2–6 MeV electron response, approximating it in this paper with linear filters. The filter response is parameterized by the time delay (τ), measured from the time of solar wind impact, and the L shell (L). We examine solar cycle and seasonal effects using an 8‐year‐long database of Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX)/ Proton Electron Telescope (PET) measurements at the radial range L = 1.1–10. The main peak P1 of the long‐term‐average response is at (τ, L) = (2, 5.3) and has a simultaneous response over a wide range of radial distances, ΔL = 5. The duration of the response after the peak is inversely proportional to the L shell. The central part of the inner magnetosphere (L = 3.7–5.75) has a much more prolonged response (>10 days) than other parts. Prior to the main response, P1, a brief response, P0, of typically lower amplitude appears at (τ, L) = (0, 3), probably as a quasi‐adiabatic response to the compression of the magnetosphere by the solar wind pressure. Over the solar cycle the variation in solar wind input results in a systematic change of the position, amplitude, radial extent, and duration of the two peaks: during solar wind minimum the quasi‐adiabatic peak disappears, and the radial size of the responding region decreases; both are responses to low‐density, high‐speed streams. During solar minimum, the duration is at least 3 days (30%) longer than average, probably due to the sustained solar wind input. Systematic variations appear also as a function of season due to several magnetic and fluid effects. During equinoxes the coupling is stronger, and the duration is longer (by at least 2 days) compared to solstices. Between the two equinoxes the fall response has a significantly higher amplitude and longer duration than the spring equinox response. This is at least partly due to the higher GSE By component during the observation time, which acts to increase the effective GSM Bz component according to the Russell‐McPherron effect. The seasonal modulation of the response is consistent with the variation in the fluxes themselves [Baker et al., 1999]. The modulation is discussed in terms of the equinoctial and axial hypotheses [Boller and Stolov, 1970; Russell and McPherron, 1973; Cliver et al., 2000].
Nonlinear time series analysis of interpeak intervals of AL data
Authors: Choe Wongyu , Kim Hee‐Jeong , Rostoker Gordon , Kamide Yohsuke
Published: December 2002

Earlier studies have found characteristics of self‐similarity and self‐organized criticality in AL time series. In this paper we have investigated various aspects and dynamical consequences of the nonlinear dynamical properties of AL time series. A smoothed time series is created by averaging an AL time series over a neighborhood of size T. The negative peaks are automatically detected as minima of the smoothed time series, and the time intervals between successive peaks, called interpeak intervals (IPI) are computed. The analysis is repeated with different averaging window sizes T to examine timescale dependence. The number of peaks increases with decreasing window size, showing power law scaling behavior with exponent 3/5, due to the self‐similarity of the time series. The distribution function of the IPI is found to be well fitted to an analytic function which arises from the barrier crossing problem in stochastic dynamics. Also, the shape of the distribution function is scale invariant after a suitable time rescaling, which agrees with the scale‐free property of self‐organized criticality. A scale invariant parameter γ which determines the shape of the universal distribution function is identified. Examination of the annual values of γ reveals a good correlation with the solar cycle. However, the peak statistics for storm time and non–storm time data do not exhibit any significant differences.
Four‐point Cluster application of magnetic field analysis tools: The Curlometer
Authors: Dunlop M. W. , Balogh A. , Glassmeier K.‐H. , Robert P.
Published: December 2002

For the first time, the Cluster spacecraft have collected 3‐D information on magnetic field structures at small to medium scales in the Earth's dayside magnetosphere. We focus here on the first application of the Curlometer (direct estimation of the electric current density from curl(B), using measured spatial gradients of the magnetic field) analysis technique. The applicability of this multipoint technique is tested, for selected events within the data set, in the context of various mission constraints (such as position, timing, and experimental accuracy). For the Curlometer, nonconstant spatial gradients over the spacecraft volume, time dependence, and measurement errors can degrade the quality of the estimate. The estimated divergence of the magnetic field can be used to monitor (indirectly) the effect of nonconstant gradients in the case of many magnetic field structures. For others, and at highly distorted spacecraft configurations, this test may not reflect the quality of the Curlometer well. The relative scales and relative geometry between the spacecraft array and the structures present, as well as measurement errors, all are critical to the quality of the calculation. We demonstrate that even when instrumental and other errors are known to contribute to the uncertainty in the estimate of the current, a number of current signatures within the magnetosphere can be plausibly determined in direction, if not absolute size. A number of examples show consistent currents at the magnetopause, both separate from, and nearby or in the cusp region. Field‐aligned currents near the polar cap boundary are also estimated reliably. We also demonstrate one example of an anomalous current arising from the effect of a highly distorted spacecraft configuration.
Auroral kilometric radiation source characteristics using ray tracing techniques
Authors: Schreiber R. , Santolik O. , Parrot M. , Lefeuvre F. , Hanasz J. , Brittnacher M. , Parks G.
Published: December 2002

3‐D ray tracing to the presumed auroral kilometric radiation (AKR) source region has been performed using the input data from wave distribution function (WDF) based on the AKR waveforms recorded on board the Interball 2 satellite by the French wave experiment MEMO. Both the direction of the WDF maximum and the WDF form and angular size have been taken into account. Two instances of AKR emissions were observed on 28 January 1997 at 2037 and 2107 UT. Rays traced in R‐X mode out of the s/c point toward two different active regions on the auroral oval (as seen with Polar UV imager after projection of the source region along the magnetic field lines down to the ionosphere level). Source region apparent angular sizes based on WDF are compatible with sizes estimated from signal modulation produced by electric antenna system rotation.
Proton pitch angle diffusion rate and wave turbulence characteristics in the magnetosheath plasma
Authors: Pudovkin M. I. , Zaitseva S. A. , Besser B. P. , Baumjohann W. , Meister C.‐V. , Maulini A. L.
Published: December 2002

Results of the analysis of variations of the proton temperature anisotropy (A) across the magnetosheath along with some plasma wave turbulence characteristics are discussed. It is shown that the deviation of the observed values of A from the bounded anisotropy model may be explained by a finite value of the temperature isotropization time τ. In turn, the obtained values of τ have a tendency to decrease with the increase of the intensity of the magnetic field oscillations. The discovered dependence of τ on the intensity of mirror‐wave‐like turbulence seems to confirm the supposition by Hill et al. [1995] on a significant role of mirror waves in the pitch angle scattering of protons in the magnetosheath plasma. It is shown that the observed periods of abnormally low values of A in some cases correspond to the periods of relatively high intensive magnetic field oscillations, most probably of an external origin.
Cluster observations of the heliospheric current sheet and an associated magnetic flux rope and comparisons with ACE
Authors: Eastwood J. P. , Balogh A. , Dunlop M. W. , Smith C. W.
Published: December 2002

Cluster and ACE magnetic field measurements from the 13 February 2001 are presented. On this day the four Cluster spacecraft made two crossings of the heliospheric current sheet (HCS) while in the solar wind and observed a large‐scale rotation of the magnetic field in the magnetosheath. These features were also observed by ACE upstream of the Earth at the L1 point. Minimum variance analysis (MVA) is used to show the similarity of the HCS orientation at ACE and Cluster, and Cluster multispacecraft analysis of the timing, orientation, and changes across the reversal is used to show that these results are consistent with crossings of the HCS. The structure of the currents in the HCS is also investigated using the Cluster curlometer technique. The field rotation observed by Cluster in the magnetosheath and ACE in the solar wind is identified as a magnetic flux rope, and MVA shows that although the structure and ordering of the flux rope are unchanged by the bow shock, the orientation of the axis changes. This is most likely caused by the rotation of the interplanetary magnetic field (IMF) as it is processed by the bow shock, augmented by draping effects deeper in the magnetosheath.