bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ground‐based FTIR measurements of vertical column densities of several trace gases above Spitsbergen
Authors: Notholt J. , Schrems O. 
Published: February 2004

During the EASOE campaign ground‐based FTIR measurements have been performed in March 1992 at Ny‐Ålesund (Spitsbergen, 79°N, 12°E) to derive column amounts of several trace gases. For the first part of the measurement campaign Ny‐Ålesund was situated inside the polar vortex.The obtained concentrations of N2O, CH4 and HF inside the vortex are consistent with subsidence. The ratio of HClstrat/HF varied from about 2.0 inside to about 2.8 outside the vortex. Inside the vortex low values for NO2 and high values for HNO3 were found. The O3 concentrations inside the vortex are slightly lower than what was observed outside the vortex.
Magnetic interpretation along the Sudbury Structure Lithoprobe Transect
Authors: Hearst Robert , Morris William , Thomas Michael 
Published: February 2004

Magnetic modelling of the Sudbury Structure (SS) has been undertaken using the geometrical and lithological framework provided by high‐resolution seismic reflection data. This initial constraint was required because of the complex magnetic properties exhibited by rock units of the SS. Locally remanent magnetisation (NRM) dominates over induced magnetisation, and the orientation and amplitude of the NRM vector varies both between and within individual rock units. The use of measured magnetic susceptibility and NRM values afforded an important constraint in the modelling process, and provided a valuable insight into the genesis of the various magnetic anomalies.The magnetic anomaly profile along the Lithoprobe Transect across the SS appears to arise from three main sources: a) a broad regional magnetic anomaly ascribed to a more magnetic layer of the Levack Gneiss Complex subjacent to the base of the Sudbury Igneous Complex (SIC); b) a prominent magnetic high associated with the southern contact between the Onwatin and Onaping Formations, believed to reflect a zone of hydrothermal mineralisation; and c) a magnetic high associated with the southern contact between the SIC and the Huronian mafics is related to the juxtaposition of rock units produced by northward directed thrusting and an enhanced NRM signature in the basal unit of the South Range Norite.
Correlation between stratospheric temperature, total ozone, and tropospheric weather systems
Authors: Petzoldt K. , Naujokat B. , Neugebohren K. 
Published: February 2004

The unusual dynamical situation over Europe in the winter 1991/92 caused an unusual behaviour of the total ozone. The strongest negative deviations from the long‐term monthly means occured in January. A very cold middle stratosphere developed at the edge of the polar vortex above a warm anticyclonic block in the troposphere. The corresponding low temperature in the tropopause region was located just beneath the coldest air in the stratosphere.A high positive correlation between the temperature and ozone partial pressure was derived at the edge of the polar stratospheric vortex for the tropopause region and for the middle stratosphere. The physical background was vertical motions changing temperature as well as the ozone content. That means unusually low ozone values can be expected when an elevated tropopause is combined with the adiabatically cooled end of the upwelling branch of an enhanced planetary wave in the middle stratosphere. It is shown that in February 1990, when extremely low total ozone was also observed over Scandinavia during a short anticyclonic blocking, this event was caused by the same process. However, during transient events the tropopause temperature is often anticorrelated with the middle stratospheric temperature (a tropospheric ridge reaching into the stratosphere has a cold high tropopause, but a warm middle stratosphere). The forced vertical motions result in extreme ozone columns only when they are in the same direction in both layers.The enhanced wave activity was connected with a strong polar warming in the upper stratosphere in both winters. At 30 hPa in the middle stratosphere the warm center was situated over Eastern Siberia and the coldest part shifted towards Northern Europe.The same situation was available in 11 cases during the fourteen years series of TOMS data (1979–1992), when total ozone reached values below 225 DU at the edge of the stratospheric polar vortex: enhanced wave activity in the middle stratosphere, polar warming in the upper stratosphere, shift of the coldest part of the polar vortex towards northern Europe over a cold high tropopause of a tropospheric anticyclone.
Constraints on North Atlantic upper mantle anisotropy from S and SS phases
Authors: Yang Xiaoping , Fischer Karen M. 
Published: February 2004

Several analyses of SSH‐SH differential travel‐times disagree on whether these data contain evidence for azimuthal anisotropy in the North Atlantic upper mantle. To explore possible explanations for these discrepant results, we calculated the azimuthal variation in SSH‐SH travel‐times predicted by an anisotropic upper mantle model. Theoretical travel‐times were obtained by cross‐correlating S and SS phases on transverse‐component reflectivity synthetic seismograms. We determined that predicted azimuthal travel‐time patterns are sensitive to the relative amplitudes of radial and transverse particle motions incident on the anisotropic medium. If a large variation in the relative incident amplitudes exists in a dataset, the overlap of different azimuthal travel‐time patterns may obscure anisotropic signatures.We analyzed shear‐wave splitting in a dataset of 12 SS and 10 S phase observations to constrain the presence of anisotropy in the North Atlantic upper mantle. A comparison of SS splitting parameters with S and SKS particle motions suggests that shear wave splitting apparent in the SS phases is at least partially due to anisotropy in the vicinity of their bounce‐points, although contributions from anisotropy in the source and station regions cannot be ruled out. Observed SS splitting is consistent with an olivine model in which horizontal a‐axes are aligned at an average of N24°W in the central North Atlantic (15°–40°N), and at an average of N23°E in the northern North Atlantic (40°–50°N).
Late Quaternary paleoceanography of the Eurasian Basin, Arctic Ocean
Authors: Cronin T. M. , Holtz T. R. , Stein R. , Spielhagen R. , Fütterer D. , Wollenburg J. 
Published: February 2004

We reconstructed late Quaternary deep (3000–4100 m) and intermediate depth (1000–2500 m) paleoceanographic history of the Eurasian Basin, Arctic Ocean from ostracode assemblages in cores from the Lomonosov Ridge, Gakkel Ridge, Yermak Plateau, Morris Jesup Rise, and Amundsen and Makarov Basins obtained during the 1991 Polarstern cruise. Modern assemblages on ridges and plateaus between 1000 and 1500 m are characterized by abundant, relatively species‐rich benthic ostracode assemblages, in part, reflecting the influence of high organic productivity and inflowing Atlantic water. In contrast, deep Arctic Eurasian basin assemblages have low abundance and low diversity and are dominated by Krithe and Cytheropteron reflecting faunal exchange with the Greenland Sea via the Fram Strait. Major faunal changes occurred in the Arctic during the last glacial/interglacial transition and the Holocene. Low‐abundance, low‐diversity assemblages from the Lomonosov and Gakkel Ridges in the Eurasian Basin from the last glacial period have modern analogs in cold, low‐salinity, low‐nutrient Greenland Sea deep water; glacial assemblages from the deep Nansen and Amundsen Basins have modern analogs in the deep Canada Basin. During Termination 1 at intermediate depths, diversity and abundance increased coincident with increased biogenic sediment, reflecting increased organic productivity, reduced sea‐ice, and enhanced inflowing North Atlantic water. During deglaciation deep Nansen Basin assemblages were similar to those living today in the deep Greenland Sea, perhaps reflecting deepwater exchange via the Fram Strait. In the central Arctic, early Holocene faunas indicate weaker North Atlantic water inflow at middepths immediately following Termination 1, about 8500–7000 year B.P., followed by a period of strong Canada Basin water overflow across the Lomonosov Ridge into the Morris Jesup Rise area and central Arctic Ocean. Modern perennial sea‐ice cover evolved over the last 4000–5000 years. Late Quaternary faunal changes reflect benthic habitat changes most likely caused by changes in the import of cold, deepwater of Greenland Sea origin and warmer and middepth Atlantic water to the Eurasian Basin through the Fram Strait, and export of Arctic Ocean deepwater.Appendix Tables Al‐A4 are available on microfiche. Orderfrom the American Geophysical Union, 2000 Florida Avenue,N.W., Washington, DC 20009. Document P94‐002; $2.50.Payment must accompany order.
The low radio frequency limit of solar type III bursts: Ulysses observations in and out of the ecliptic
Authors: Leblanc Y. , Dulk G. A. , Hoang S. 
Published: February 2004

We measure the low frequency limit flo of 1028 type III bursts and compare it with the observed plasma frequency at the spacecraft fp. We consider three periods: when Ulysses was in the ecliptic plane near the Sun, far from the Sun, and out of the ecliptic; the average plasma frequency was 20, 10, and 5 kHz respectively. The major results are: 1) During the entire period of Ulysses flight November 1990 to March 1995, 9 kHz is the lowest frequency at which type III electromagnetic radiation was ever seen, even though fp was often 3–4 kHz. 2) The distribution of cutoffs is independent of ecliptic latitude, and of fp at the spacecraft (excepting of course that flo ≥ fp) and is broadly spread between 17 and 300 kHz. 3) When fp is about 20, 10 and 5 kHz, only 15, 5 and 0% respectively of type III burst radiation approaches within a factor of two of fp.We develop three hypotheses to explain these results: 1) that the low‐frequency cutoff of type III bursts is intrinsic to the radiation mechanism, 2) that it is due to directivity of the radiation, and 3) that it is due to propagation conditions between the burst source and the spacecraft. The evidence for intrinsic cutoffs is strong, but propagation effects play a role in some cases.
Convectively induced mesoscale weather systems in the tropical and warm‐season midlatitude atmosphere
Authors: Smull Bradley F. 
Published: February 2004

As anticipated by Nelson [1991] in the last U.S. National Report, mesoscale meteorology has continued to be an area of vigorous research activity. Progress is evinced by a growing number of process‐oriented studies capitalizing on expanded observational capabilities, as well as more theoretical treatments employing numerical simulations of increasing sophistication. While the majority of papers within the scope of this review fall into the category of basic research, the field's maturation is evident in the emergence of a growing number of applications to operational weather forecasting.Even as our ability to anticipate shifts in synoptic scale upper‐air patterns and associated baroclinic developments has steadily improved, lagging skill with regard to quantitative forecasts of precipitation—particularly in situations where deep moist convection is prevalent—has sustained research in warm‐season mesoscale meteorology. Each spring and summer midlatitude populations are exposed to life‐threatening natural weather phenomena in the form of lightning, tornadoes, straight‐line winds, hail, and flash floods. This point was driven home during the summer of 1993, when an extraordinarily persistent series of mesoscale convective systems (MCSs) led to unusually severe and widespread flooding throughout the Mississippi and Missouri river basins. In addition to this obvious impact on regional climate, the 1990's have brought an increased appreciation for the less direct yet potentially significant role that tropical convection may play in shaping global climate through phenomena such as the El Niño‐Southern Oscillation (ENSO).
Western boundary currents
Authors: Hogg Nelson G. , Johns William E. 
Published: February 2004

The past decade has seen considerable progress toward clarifying the mean circulation of the World's oceans. At the same time we have come to realize that the specification of a mean circulation is difficult as there is energy at all time scales which are quantifiable and the spectrum is usually red.The western boundary currents (WBCs) of the oceans are the principal conduits for communication between the equatorial regions, where heat is added to the oceans and the polar regions where it is removed. Understanding how these current systems work is fundamental to understanding the earth's global climate engine. Several substantial observational programs focussed on WBCs have been undertaken in recent years especially within the North and South Atlantic. These include studies of the Brazil‐Malvinas Confluence and the South Atlantic Ventilation Experiment (SAVE) within the South Atlantic, the Western Tropical Atlantic Experiment (WESTRAX) in the tropics, and the Subtropical Atlantic Climate Study (STACS) and Synoptic Ocean Prediction experiment (SYNOP) in the subtropics. We shall concentrate in this review with a summary of the results from these programs but will also briefly cover new findings from other parts of the globe. Efforts connected with programs of the World Ocean Circulation Experiment in the Pacific and the South Atlantic (particularly the Deep Basin Experiment) are still underway and can be expected to make substantial contributions to the knowledge of WBCs in the future. The nature of this review also compells us to emphasize recent U.S. research but we will incorporate results from the international community, as well, especially in regions of the globe where the U.S. has done little. The reader may also wish to consult recent reviews by Ierley [1990] and Huang [1991], which discuss many issues relevant to WBCs in subtropical gyres.
The Australia‐Pacific boundary and Cenozoic plate motions in the SW Pacific: Some constraints from Geosat data
Authors: Sutherland Rupert 
Published: February 2004

Finite poles of Australia‐Pacific rotation are calculated using a three‐plate (Australia‐Antarctica‐Pacific) model and published Geosat data analyses of the Indian and Pacific Oceans (GEOS‐3P solution). Features identified on maps of Geosat data from SW of New Zealand are used to determine a new best fit finite pole for the prerift (mid Eocene; ∼45 Ma) configuration of the Australia‐Pacific plate boundary and to refine Eocene‐Miocene motions on the plate boundary (∼45–20 Ma; GEOS‐NZ results).Inverting the Australia‐Pacific best fit finite rotation to find relative displacements between east and west Antarctica since the Eocene implies dextral oblique extension in the Ross Embayment and almost pure dextral movement in the Queen Maud Range. Early‐mid Eocene convergence predicted through Antarctica conflicts with geological evidence and remains an unresolved problem.
Emulation of the results from a coupled general circulation model using a simple climate model
Authors: Raper S. C. B. , Cubasch U. 
Published: February 2004

An upwelling diffusion (UD) model has been fitted to the results of a globally coupled ocean atmosphere general circulation model (O/AGCM). In order to adequately simulate the results of the O/AGCM, the differential heating over land and ocean, the change of the upwelling rate with rising mixed‐layer temperature and the climate adjustment of the O/AGCM evident in the control simulation had to be taken into account.Comparisons using the results of four O/AGCM perturbation experiments show that the timing of the adjustment in the O/AGCM control run differs from that in the perturbed runs. The UD model simulates the global mean temperature evolution, as calculated by the O/AGCM reasonably well. However, when time dependent upwelling is included, the UD model substantially overestimates the thermal expansion compared to this O/AGCM. Possible reasons for this overestimation have been identified.
Ground‐based measurements of OClO and HCl in austral spring 1993 at Arrival Heights, Antarctica
Authors: Kreher K. , Keys J. G. , Johnston P. V. , Platt U. , Liu X. 
Published: February 2004

Ground‐based measurements of stratospheric OClO and HCl total columns are reported. The data were obtained during the spring season of 1993 at Arrival Heights (77.8°S/166.7°E), Antarctica, using zenith sky and direct sun absorption spectroscopy in the visible and infrared spectral regions. Together these data sets represent complementary measurements of chlorine species in Antarctica over an extended period in spring. To illustrate aspects of Antarctic stratospheric chemistry and dynamics that are significant in current studies of ozone depletion, the OClO and HCl data are supplemented by simultaneously measured NO2 data as well as ancillary data from other sources.Observations of OClO, HCl and NO2 provide an indication of the degree of the perturbed chemistry that is operating in the spring stratosphere. The measurements illustrate the repartitioning of active chlorine into the less reactive HCl reservoir as spring progresses. Comparison of the data with total ozone and stratospheric temperature records shows that the springtime chlorine variations are in agreement with currently accepted models of Antarctic ozone depletion chemistry.
A discussion on “The 410‐km‐depth discontinuity: A sharpness estimate from near‐critical reflections” by Vidale et al.
Authors: Krishna V. G. , Ramesh D. S. 
Published: February 2004

Vidale et al. [1995] presented a convincing evidence of a fairly sharp ‘410‐km’ seismic discontinuity uncjer the western United States by examining clear noise‐free reflected arrivals from this discontinuity in the near‐critical distance range of 11.5° to 14° (Fig. Ia). They reconstructed the P velocity‐depth model from the arrival times of the 410‐km reflection and initial P waves across the distance range 8°–14°. The prominent features of the upper mantle P velocity model given by them include; a low velocity layer (LVL) in the depth range of about 110–200 km with a broad transitional bottom, a fairly large velocity gradient (0.4 km/s velocity increase from 200 to 410 km depth) above the 410‐km discontinuity which is sharp and associated with a 5.5% velocity increase.Seismic estimates of sharpness as well as velocity contrast at the ‘410‐km’ and ‘660‐km’ discontinuities in the mantle transition zone provide important constraints to plausible models of composition, temperature and convective processes in the deep earth. The rapid increases of seismic wave velocities inferred in the transition zone, at depths of 410‐Km and 660‐km, are classically associated [Ringwood, 1975] with the pressure‐induced phase transitions in Olivine which is considered to be the predominant mineral in the upper mantle. Recent observations of high quality coherent seismic reflections from the transition zone [Benz and Vidale, 1993; Vidale et al., 1995] conclusively reveal that the 410‐km discontinuity is fairly sharp. Contrastingly the experimental results from mineral physics [Akaogi et al., 1989; Bina and Wood, 1987; Katsura and Ito, 1989] predict a substantially larger transition width, on the order of 6–19 km for the olivine‐beta spinel phase transition at pressures corresponding to 410‐km‐depth discontinuity. Similar inconsistencies in the magnitude of velocity contrast at the 410‐km discontinuity are also found [Duffy et al., 1995; Jeanloz, 1995] by comparison of results from modern seismic measurements and the new experimental models of the olivine‐beta spinel phase transition, the latter revealing a relatively large contrast. In view of these apparently contradicting results it is certainly critical to evaluate the high quality seismic data [Vidale et al., 1995] for reliable estimates of both sharpness and velocity contrast of the 410‐km discontinuity in order to consider its traditional association with the simple phase transition in the olivine dominated compositional model.
Messinian deep‐water turbidites and glacioeustatic sea‐level changes in the North Atlantic: Linkage to the Mediterranean salinity crisis
Authors: Zhang Jijun , Scott David B. 
Published: February 2004

Our benthic foraminiferal data clearly indicate eight layers of deep‐water turbidites during the Messinian (MTL 1‐8) and one in the early Pliocene (PTL 1) in Ocean Drilling Program Leg 105, Site 646B. These deep‐water tuibidite deposits are characterized by highly concentrated agglutinated marsh benthic foraminifera (e.g., Trochammina cf. squamata, Ammotium sp. A, Miliammina fusca), rounded quartz, polished thick‐walled benthic foraminifera, wood fragments, plant seeds, plant fruit, and highly concentrated mica and are interbedded with sediments containing deep‐water benthic faunas. We suggest these turbidites deposited during sea‐level low stands (∼80–100 m below sea level), and their ages are tentatively correlated to 6.59, 6.22, 6.01, 5.89, 5.75, 5.7, 5.65, 5.60, and 5.55 Ma, respectively, based on the Messinian oxygen isotope enrichments at Site 552A of Deep Sea Drilling Project Leg 81. The turbidites layers during the late Messinian, coeval with frequent climate changes suggested by six oxygen enrichment excursions of Site 552A, may have been in part linked to the late Messinian evaporite deposits in the Mediterranean Basin. The most profound climate changes at 5.75 and 5.55 Ma may have been related to the Lower and Upper Evaporites in the Mediterranean Basin.An electronic supplement of this material may be obtained on adiskette or Anonymous FTP from KOSMOS .AGU.ORG, (LOGIN toAGU's FTP account using ANONYMOUS as the username and GUESTas the password. Go to the right directory by typing CD APEND. TypeLS to see what files are available. Type GET and the name of the file toget it. Finally, type EXIT to leave the system. (Paper 96PA00572,Messinian deep‐water turbidites and glacioeustatic sea‐level changes inthe North Atlantic: Linkage to the Mediterranean Salinity Crisis, JijunZhang and David B. Scott). Diskette may be ordered from AmericanGeophysical Union, 2000 Florida Avenue, N.W., Washington, D.C.20009; $15.00. Payment must accompany order.