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111.
Monthly mean surface pressure patterns in the European area are reconstructed for those winter and summer seasons of the 16th century with outstanding climatic anomalies being either widespread over Europe or remarkably intensive in some European regions. From the available documentary information about weather characteristics and their sequences, it proved possible to infer prevalent processes of lower tropospheric advection of typical air masses and to assess the position and strength of major surface pressure centres on a monthly scale. For comparison with modern pressure patterns, monthly mean sea level pressure (SLP) grids from the 20th century have been selected for seasons with similar climatic anomalies. There are broad coincidences between these pressure patterns of the 16th and the 20th centuries except for cold summer seasons. Finally, results from the 16th century are discussed in terms of circulation dynamics (different phases of the North Atlantic Oscillation (NAO) in winter, decreasing frequency of anticyclonic ridging in summer). 相似文献
112.
W. Baumjohann R. A. Treumann E. Georgescu G. Haerendel K.-H. Fornacon U. Auster 《Annales Geophysicae》1999,17(12):1528-1534
The Equator-S magnetometer is very sensitive and has a sampling rate of normally 128 Hz. The high sampling rate allows for the first time fluxgate magnetometer measurements of ELF waves between the ion cyclotron and the lower hybrid frequencies in the equatorial dayside magnetosheath. The so-called lion roars, typically seen by the Equator-S magnetometer at the bottom of the magnetic troughs of magnetosheath mirror waves, are near-monochromatic packets of electron whistler waves lasting for a few wave cycles only, typically 0.25 s. They are right-hand circularly polarized waves with typical amplitudes of 0.5–1 nT at around one tenth of the electron gyrofrequency. The cone angle between wave vector and ambient field is usually smaller than 1.5°. 相似文献
113.
L. M. Kistler B. Klecker V. K. Jordanova E. Möbius M. A. Popecki D. Patel J. A. Sauvaud H. Rème A. M. Di Lellis A. Korth M. McCarthy R. Cerulli M. B. Bavassano Cattaneo L. Eliasson C. W. Carlson G. K. Parks G. Paschmann W. Baumjohann G. Haerendel 《Annales Geophysicae》1999,17(12):1611-1621
During the main and early recovery phase of a geomagnetic storm on February 18, 1998, the Equator-S ion composition instrument (ESIC) observed spectral features which typically represent the differences in loss along the drift path in the energy range (5–15 keV/e) where the drift changes from being E × B dominated to being gradient and curvature drift dominated. We compare the expected energy spectra modeled using a Volland-Stern electric field and a Weimer electric field, assuming charge exchange along the drift path, with the observed energy spectra for H+ and O+. We find that using the Weimer electric field gives much better agreement with the spectral features, and with the observed losses. Neither model, however, accurately predicts the energies of the observed minima. 相似文献
114.
Internal morphology, habit and U-Th-Pb microanalysis of amphibolite-to-granulite facies zircons: geochronology of the Ivrea Zone (Southern Alps) 总被引:52,自引:2,他引:50
Gerhard Vavra Rolf Schmid Dieter Gebauer 《Contributions to Mineralogy and Petrology》1999,134(4):380-404
Several types of growth morphologies and alteration mechanisms of zircon crystals in the high-grade metamorphic Ivrea Zone
(IZ) are distinguished and attributed to magmatic, metamorphic and fluid-related events. Anatexis of pelitic metasediments
in the IZ produced prograde zircon overgrowths on detrital cores in the restites and new crystallization of magmatic zircons
in the associated leucosomes. The primary morphology and Th-U chemistry of the zircon overgrowth in the restites show a systematic
variation apparently corresponding to the metamorphic grade: prismatic (prism-blocked) low-Th/U types in the upper amphibolite
facies, stubby (fir-tree zoned) medium-Th/U types in the transitional facies and isometric (roundly zoned) high-Th/U types
in the granulite facies. The primary crystallization ages of prograde zircons in the restites and magmatic zircons in the
leucosomes cannot be resolved from each other, indicating that anatexis in large parts of the IZ was a single and short lived
event at 299 ± 5 Ma (95% c. l.). Identical U/Pb ages of magmatic zircons from a metagabbro (293 ± 6 Ma) and a metaperidotite
(300 ± 6 Ma) from the Mafic Formation confirm the genetic context of magmatic underplating and granulite facies anatexis in
the IZ. The U-Pb age of 299 ± 5 Ma from prograde zircon overgrowths in the metasediments also shows that high-grade metamorphic
(anatectic) conditions in the IZ did not start earlier than 20 Ma after the Variscan amphibolite facies metamorphism in the
adjacent Strona–Ceneri Zone (SCZ). This makes it clear that the SCZ cannot represent the middle to upper crustal continuation
of the IZ. Most parts of zircon crystals that have grown during the granulite facies metamorphism became affected by alteration
and Pb-loss. Two types of alteration and Pb-loss mechanisms can be distinguished by cathodoluminescence imaging: zoning-controlled
alteration (ZCA) and surface-controlled alteration (SCA). The ZCA is attributed to thermal and/or decompression pulses during
extensional unroofing in the Permian, at or earlier than 249 ± 7 Ma. The SCA is attributed to the ingression of fluids at
210 ± 12 Ma, related to hydrothermal activity during the breakup of the Pangaea supercontinent in the Upper Triassic/Lower
Jurassic.
Received: 7 July 1998 / Accepted: 4 November 1998 相似文献
115.
R. Nakamura G. Haerendel W. Baumjohann A. Vaivads H. Kucharek B. Klecker E. Georgescu J. Birn L. M. Kistler T. Mukai S. Kokubun P. Eglitis L. A. Frank J. B. Sigwarth 《Annales Geophysicae》1999,17(12):1602-1610
Data from Equator-S and Geotail are used to study the dynamics of the plasma sheet observed during a substorm with multiple intensifications on 25 April 1998, when both spacecraft were located in the early morning sector (03–04 MLT) at a radial distance of 10–11 RE. In association with the onset of a poleward expansion of the aurora and the westward electrojet in the premidnight and midnight sector, both satellites in the morning sector observed plasma sheet thinning and changes toward a more tail-like field configuration. During the subsequent poleward expansion in a wider local time sector (20−04 MLT), on the other hand, the magnetic field configuration at both satellites changed into a more dipolar configuration and both satellites encountered again the hot plasma sheet. High-speed plasma flows with velocities of up to 600 km/s and lasting 2–5 min were observed in the plasma sheet and near its boundary during this plasma sheet expansion. These high-speed flows included significant dawn-dusk flows and had a shear structure. They may have been produced by an induced electric field at the local dipolarization region and/or by an enhanced pressure gradient associated with the injection in the midnight plasma sheet. 相似文献
116.
Knittel Lukas Wichtmann Torsten Niemunis Andrzej Huber Gerhard Espino Edgar Triantafyllidis Theodoros 《Acta Geotechnica》2020,15(8):2075-2088
Acta Geotechnica - The elastic stiffness of a fine sand at small to moderate strains ( $$\varepsilon \le 2 \times 10^{-4}$$ ) has been studied based on cyclic triaxial tests on cube-shaped samples... 相似文献
117.
A hydrogeological study was completed within a sub-catchment of the Zerka River drainage basin, in western Jordan. The system
is characterized by anticlinal bending with an axis trending SSW–NNE and plunging a few degrees in the SSW direction. The
anticlinal structure diverts groundwater flow towards the SSW while the strike-slipe faults cause the groundwater to diverge
where the fault is perpendicular to the groundwater flow lines, and to converge where the fault is parallel to the groundwater
flow lines. A direct relationship was found between the location of springs and the type of groundwater flow with regard to
the amount of discharge wherein large spring discharges are located in zones of converging groundwater flow lines. In areas
where faults are not abundant, the groundwater retention time in the aquifers is long and a zonation of the electrical conductivity
was detected due to mineral dissolution. By controlling groundwater flow, the anticlinal setting produces three genetic groups
of groundwater flow systems: (1) alkaline–earth alkaline water which is predominately a bicarbonate-type composition, (2)
alkaline–earth alkaline water which is predominately bicarbonate–sulfate, and (3) alkaline–earth alkaline water with a high
alkaline component. 相似文献
118.
Laboratory experiments show that dusty bodies in a gaseous environment eject dust particles if they are illuminated. We find that even more intense dust eruptions occur when the light source is turned off. We attribute this to a compression of gas by thermal creep in response to the changing temperature gradients in the top dust layers. The effect is studied at a light flux of 13 kW/m2 and 1 mbar ambient pressure. The effect is applicable to protoplanetary disks and Mars. In the inner part of protoplanetary disks, planetesimals can be eroded especially at the terminator of a rotating body. This leads to the production of dust which can then be transported towards the disk edge or the outer disk regions. The generated dust might constitute a significant fraction of the warm dust observed in extrasolar protoplanetary disks. We estimate erosion rates of about 1 kg s?1 for 100 m parent bodies. The dust might also contribute to subsequent planetary growth in different locations or on existing protoplanets which are large enough not to be susceptible to particle loss by light induced ejection. Due to the ejections, planetesimals and smaller bodies will be accelerated or decelerated and drift outward or inward, respectively. The effect might also explain the entrainment of dust in dust devils on Mars, especially at high altitudes where gas drag alone might not be sufficient. 相似文献
119.
Impact of loading displacements on SLR-derived parameters and on the consistency between GNSS and SLR results 总被引:5,自引:4,他引:1
Krzysztof Sośnica Daniela Thaller Rolf Dach Adrian Jäggi Gerhard Beutler 《Journal of Geodesy》2013,87(8):751-769
Displacements of the Earth’s surface caused by tidal and non-tidal loading forces are relevant in high-precision space geodesy. Some of the corrections are recommended by the international scientific community to be applied at the observation level, e.g., ocean tidal loading (OTL) and atmospheric tidal loading (ATL). Non-tidal displacement corrections are in general recommended not to be applied in the products of the International Earth Rotation and Reference Systems Service, in particular atmospheric non-tidal loading (ANTL), oceanic and hydrological non-tidal corrections. We assess and compare the impact of OTL, ATL and ANTL on SLR-derived parameters by reprocessing 12 years of SLR data considering and ignoring individual corrections. We show that loading displacements have an influence not only on station long-term stability, but also on geocenter coordinates, Earth Rotation Parameters, and satellite orbits. Applying the loading corrections reduces the amplitudes of annual signals in the time series of geocenter and station coordinates. The general improvement of the SLR station 3D coordinate repeatability when applying OTL, ATL and ANTL corrections are 19.5 %, 0.2 % and 3.3 % respectively, w.r.t. the solutions without loading corrections. ANTL corrections play a crucial role in the combination of optical (SLR) and microwave (GNSS, VLBI, DORIS) space geodetic observation techniques, because of the so-called Blue-Sky effect: SLR measurements can be carried out only under cloudless sky conditions—typically during high air pressure conditions, when the Earth’s crust is deformed, whereas microwave observations are weather-independent. Thus, applying the loading corrections at the observation level improves SLR-derived products as well as the consistency with microwave-based results. We assess the Blue-Sky effect on SLR stations and the consistency improvement between GNSS and SLR solutions when ANTL corrections are included. The omission of ANTL corrections may lead to inconsistencies between SLR and GNSS solutions of up to 2.5 mm for inland stations. As a result, the estimated GNSS–SLR coordinate differences correspond better to the local ties at the co-located stations when applying ANTL corrections. 相似文献
120.
Christian Hirt Martin Schmitz Uwe Feldmann-Westendorff Gerhard Wübbena Cord-Hinrich Jahn Günter Seeber 《GPS Solutions》2011,15(2):149-159
The method of geometric-astronomical leveling is presented as a suited technique for the validation of GNSS (Global Navigation
Satellite System) heights. In geometric-astronomical leveling, the ellipsoidal height differences are obtained by combining
conventional spirit leveling and astronomical leveling. Astronomical leveling with recently developed digital zenith camera
systems is capable of providing the geometry of equipotential surfaces of the gravity field accurate to a few 0.1 mm per km.
This is comparable to the accuracy of spirit leveling. Consequently, geometric-astronomical leveling yields accurate ellipsoidal
height differences that may serve as an independent check on GNSS height measurements at local scales. A test was performed
in a local geodetic network near Hanover. GPS observations were simultaneously carried out at five stations over a time span
of 48 h and processed considering state-of-the-art techniques and sophisticated new approaches to reduce station-dependent
errors. The comparison of GPS height differences with those from geometric-astronomical leveling shows a promising agreement
of some millimeters. The experiment indicates the currently achievable accuracy level of GPS height measurements and demonstrates
the practical applicability of the proposed approach for the validation of GNSS height measurements as well as the evaluation
of GNSS height processing strategies. 相似文献