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Stefan Maus Chris M. Green & J. Derek Fairhead 《Geophysical Journal International》1998,134(1):243-253
The ocean geoid can be inferred from the topography of the mean sea surface. Satellite altimeters transmit radar pulses and determine the return traveltime to measure sea-surface height. The ERS-1 altimeter stacks 51 consecutive radar reflections on board the satellite to a single waveform. Tracking the time shift of the waveform gives an estimate of the distance to the sea surface. We retrack the ERS-1 radar traveltimes using a model that is focused on the leading edge of the waveforms. While earlier methods regarded adjacent waveforms as independent statistical events, we invert a whole sequence of waveforms simultaneously for a spline geoid solution. Smoothness is controlled by spectral constraints on the spline coefficients. Our geoid solutions have an average spectral density equal to the expected power spectrum of the true geoid. The coherence of repeat track solutions indicates a spatial resolution of 31 km, as compared to 41 km resolution for the ERS-1 Ocean Product. While the resolution of the latter deteriorates to 47 km for wave heights above 2 m, our geoid solution maintains its resolution of 31 km for rough sea. Retracking altimeter waveform data and constraining the solution by a spectral model leads to a realistic geoid solution with significantly improved along-track resolution. 相似文献
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Flow over surface obstructions can produce significantly large wind shears such that adverse flying conditions can occur for aeronautical systems (helicopters, V/STOL vehicles, etc.). The purpose of this analysis is to determine the kinds of flow fields that can result from surface obstructions in an otherwise horizontally homogeneous statistically stationary flow. The technique is based on the boundary-layer/Boussinesq-approximated equations of motion. The pressure gradient resulting from the surface obstruction is that consistent with a potential flow over a two-dimensional cylinder with elliptical cross-section, an approach commonly used for boundary-layer analyses in the engineering community. The dissipative effects of atmospheric turbulence on the mean flow are represented with eddy-viscosity models of the Reynolds stresses. The upstream flow is a neutral one and is characterized by a logarithmic profile for the mean wind. The following conclusions result from the analysis: (1) localized maxima in wind speed occur at the top of a surface obstruction, which are expected in physically real flow situations, (2) an increase in the elliptical aspect ratio decreases the wind speed within the boundary layer at the top of the ellipse and returns it to the logarithmic distribution characteristic of undisturbed flow, (3) increases in surface roughness affect the flow by decreasing the velocity in the boundary layer, with the most pronounced effect occurring near the surface of the smaller aspect-ratio ellipse, (4) Reynolds number has a negligible effect on the overall flow for the range of Reynolds numbers considered in this study, (5) a decrease in the elliptical aspect ratio and an increase in the surface roughness cause larger separation regions. 相似文献
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Stefan Maus 《Geophysical Journal International》2000,143(1):274-277
On average, traveltimes of PKPDF for equatorial ray paths through the quasieastern hemisphere of the inner core are around 0.5 s faster than equivalent ray paths through its quasiwestern hemisphere. In these observations, the eastern hemisphere is sampled primarily by westward and the western hemisphere by eastwardpropagating waves. Noting that westward propagation is faster than eastward propagation inside a rotating earth, I estimate the expected traveltime difference from Coriolis splitting of the displacement eigenfunctions of the PKPDF equivalent modes. It turns out that Coriolis effects are too small to give rise to residuals of the required magnitude. Thus, the observations must be primarily due to velocity heterogeneities. 相似文献
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Interannual variability of dense shelf water salinities in the north-western Barents Sea 总被引：1，自引：0，他引：1
Sönke Maus 《Polar research》2003,22(1):59-66
The maximum dense shelf water salinity formed during winter in the Svalbard Bank area of the north-western Barents Sea is reconstructed for the period 1952–2000 by analysing the transformation of summer remnants. The variability of 34.7 - 35.4, waters being at the freezing point, is mainly generated by interannual variations in the near surface salinity. On interannual time scales the latter is strongly linked to the sea ice import. In contrast, no correlation of the salinity of the Atlantic Water (AW) throughflow to the Arctic Ocean with the ice import is found. Salinities of both the dense shelf water site in the north-west Barents Sea and the north-eastward AW throughflow show a long term decrease, which can partly be explained by a less saline inflow of AW from the Norwegian Sea. The unusually low dense water salinities in the north-west Barents Sea during the 1990s appear to have a different origin, consistent with a response to oceanic heat advection and decreasing sea ice extent. 相似文献
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A gamma-ray transmission method is discussed for measuring the water content of marine sediment samples during consolidation testing. This method permits obtaining consolidation curves for sediment cores while still in the core liner, thereby eliminating several sources of sample disturbance. A narrow beam of gamma-rays is passed through the sample to a detector and counting equipment. The attenuation of this beam is a function of the sample density and hence water content or void-ratio. Equations are developed for calculating water content from gamma-counts. The results of experiments are presented confirming the validity of these equations. 相似文献