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101.
102.
On a relativistic geodesy 总被引:3,自引:1,他引:3
Arne Bjerhammar 《Journal of Geodesy》1985,59(3):207-220
Theoretical formulas for relativistic estimation of geopotential differences are given. The relativistic geoid is defined.
A technique for measuring potential differences with high precision clocks (masers or equivalent) is described. The method
can operate over arbitrary terrestrial distances. Two clocks are used. The drift between the clocks is estimated by using
closed loops. The clocks are used in an operational mode during the whole measuring interval. No satellite links are necessary
but VLBI, GPS and ANIK-links can be used in combination with the method. 相似文献
103.
The main results of Whitham's averaged Lagrangian method for the treatment of linear wave-trains in a weakly inhomogeneous, moving medium are presented briefly. This method is then applied to an ideal, isotropic, one-fluid plasma which can be taken for the lowest order approximation for the interplanetary solar wind expansion. 相似文献
104.
Guy Schurgers Uwe Mikolajewicz Matthias Gröger Ernst Maier-Reimer Miren Vizcaíno Arne Winguth 《Climate Dynamics》2007,29(4):357-373
Transient experiments for the Eemian (128–113 ky BP) were performed with a complex, coupled earth system model, including
atmosphere, ocean, terrestrial biosphere and marine biogeochemistry. In order to investigate the effect of land surface parameters
(background albedo, vegetation and tree fraction and roughness length) on the simulated changes during the Eemian, simulations
with interactive coupling between climate and vegetation were compared with additional experiments in which these feedbacks
were suppressed. The experiments show that the influence of land surface on climate is mainly caused by changes in the albedo.
For the northern hemisphere high latitudes, land surface albedo is changed partially due to the direct albedo effect of the
conversion of grasses into forest, but the indirect effect of forests on snow albedo appears to be the major factor influencing
the total absorption of solar radiation. The Western Sahara region experiences large changes in land surface albedo due to
the appearance of vegetation between 128 and 120 ky BP. These local land surface albedo changes can be as much as 20%, thereby
affecting the local as well as the global energy balance. On a global scale, latent heat loss over land increases more than
10% for 126 ky BP compared to present-day. 相似文献
105.
106.
Daniela Müller Rik Tjallingii Mateusz Płóciennik Tomi P. Luoto Bartosz Kotrys Birgit Plessen Arne Ramisch Markus J. Schwab Mirosław Błaszkiewicz Michał Słowiński Achim Brauer 《Boreas: An International Journal of Quaternary Research》2021,50(2):535-555
The sediment profile from Lake Gościąż in central Poland comprises a continuous, seasonally resolved and exceptionally well-preserved archive of the Younger Dryas (YD) climate variation. This provides a unique opportunity for detailed investigation of lake system responses during periods of rapid climate cooling (YD onset) and warming (YD termination). The new varve record of Lake Gościąż presented here spans 1662 years from the late Allerød (AL) to the early Preboreal (PB). Microscopic varve counting provides an independent chronology with a YD duration of 1149+14/–22 years, which confirms previous results of 1140±40 years. We link stable oxygen isotopes and chironomid-based air temperature reconstructions with the response of various geochemical and varve microfacies proxies especially focusing on the onset and termination of the YD. Cooling at the YD onset lasted ~180 years, which is about a century longer than the terminal warming that was completed in ~70 years. During the AL/YD transition, environmental proxy data lagged the onset of cooling by ~90 years and revealed an increase of lake productivity and internal lake re-suspension as well as slightly higher detrital sediment input. In contrast, rapid warming and environmental changes during the YD/PB transition occurred simultaneously. However, initial changes such as declining diatom deposition and detrital input occurred already a few centuries before the rapid warming at the YD/PB transition. These environmental changes likely reflect a gradual increase in summer air temperatures already during the YD. Our data indicate complex and differing environmental responses to the major climate changes related to the YD, which involve different proxy sensitivities and threshold processes. 相似文献
107.
108.
The contribution of urban runoff to organic contaminant levels in harbour sediments near two Norwegian cities 总被引:1,自引:0,他引:1
Cornelissen G Pettersen A Nesse E Eek E Helland A Breedveld GD 《Marine pollution bulletin》2008,56(3):565-573
The main aim of the present study was to compare the quality of particle emissions (urban runoff and settling particles in rivers and harbours) to the quality of top-layer bed sediments, for two Norwegian harbours (Oslo and Drammen). A sub-aim was to investigate whether non-industrial urban runoff contributed to the organotin load of sediments, apart from leaching from ship hulls. Time-integrated samples of stormwater runoff were obtained in an innovative manner, by sampling man-holes in the stormwater system. Settling particles were sampled with sediment traps. The study focused on PAHs, PCBs and organotin compounds. Contaminant levels were generally a factor of 2-10 (PAHs) and 3-30 (TBT) lower in emitted riverine and runoff particles than in top-layer bed sediments, except for PCBs in Oslo harbour (only 20-30% lower). Significant levels of tributyltin (TBT; median 140mug/kg) were shown in runoff particles, showing that TBT can also be emitted via urban sources, since the sampled man-holes were not in areas where dry-docking activities take place. Possible land-based TBT sources include long-lasting house paint and use of TBT as PVC stabilizer and timber preservative. Since there are ongoing emissions into the two studied harbour areas, it is concluded that the addition of an actively sorbing capping material such as activated carbon might be the best remediation alternative. 相似文献
109.
Heidi Moe Odd Sture Hopperstad Anna Olsen Østen Jensen Arne Fredheim 《Ocean Engineering》2009,36(12-13):992-1002
Creep in materials and structures may lead to increasing strains, permanent deformations, change in mechanical properties and rupture at loads significantly smaller than the breaking strength. In this paper, we present data on temporary-creep properties, recovery of strain post creep and post-creep tensile properties of a selection of Raschel knitted netting materials. Creep strain in wet netting materials subjected to a creep target load of 10–90% of average force at break for 30 min varied from 1.6% to 3.5%. The rate of creep decreased with time and decreased target load. The recovery of strain post creep was relatively fast and approximately half of the creep strain was elastic. Post-creep tensile testing showed that the length and force at break were not significantly affected by the creep load history. However, due to permanent deformations of the specimens from the creep test, the nominal breaking strain decreased and the stiffness increased with increased creep target load. 相似文献
110.
Yvan J. Orsolini Retish Senan Rasmus E. Benestad Arne Melsom 《Climate Dynamics》2012,38(11-12):2437-2448
The autumn and early winter atmospheric response to the record-low Arctic sea ice extent at the end of summer 2007 is examined in ensemble hindcasts with prescribed sea ice extent, made with the European Centre for Medium-Range Weather Forecasts state-of-the-art coupled ocean–atmosphere seasonal forecast model. Robust, warm anomalies over the Pacific and Siberian sectors of the Arctic, as high as 10°C at the surface, are found in October and November. A regime change occurs by December, characterized by weaker temperatures anomalies extending through the troposphere. Geopotential anomalies extend from the surface up to the stratosphere, associated to deeper Aleutian and Icelandic Lows. While the upper-level jet is weakened and shifted southward over the continents, it is intensified over both oceanic sectors, especially over the Pacific Ocean. On the American and Eurasian continents, intensified surface Highs are associated with anomalous advection of cold (warm) polar air on their eastern (western) sides, bringing cooler temperatures along the Pacific coast of Asia and Northeastern North America. Transient eddy activity is reduced over Eurasia, intensified over the entrance and exit regions of the Pacific and Atlantic storm tracks, in broad qualitative agreement with the upper-level wind anomalies. Potential predictability calculations indicate a strong influence of sea ice upon surface temperatures over the Arctic in autumn, but also along the Pacific coast of Asia in December. When the observed sea ice extent from 2007 is prescribed throughout the autumn, a higher correlation of surface temperatures with meteorological re-analyses is found at high latitudes from October until mid-November. This further emphasises the relevance of sea ice for seasonal forecasting in the Arctic region, in the autumn. 相似文献