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- Author or Editor: R. D. Pillsbury x
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Abstract
The kinetic energy levels Of horizontal oscillations near and above the inertial frequency are described based on 84 current records made during 5 years at Drake Passage. Instrument depths ranged from 280 to 3600 m. Moorings spanned the passage, though the best depth and time coverage is for a central location. For each variance spectrum of horizontal current, the frequency band above the local inertial and semidiurnal tidal peaks was fitted to the Garrett and Munk internal wave spectrum in the form of
The fit is determined by the log-log decay (p) of energy density (NE 0) with frequency (ω), where E 0 is the energy density at 1 cph (ω0) normalized by stability frequency N. Although these parameters were generally near the “universal” values, there was considerable spatial variability—more than the year-to-year variability. Values of p were found to increase with depth; values of E 0 were larger in the northern passage and at the continental slopes suggesting source regions for wave energy. The fitted relation was integrated between local inertial and the appropriate stability frequency to examine the total kinetic energy of horizontal motions in the internal wave field. This internal wave energy was normalized by stability frequency and plotted versus depth for three distinct bathymetric regimes. Both energy levels and vertical distributions differ, with greater energy and more depth variation over the rugged bathymetry of the northern passage.
The prominent inertial peak was examined on the basis of its frequency, peak height and peak width at 50% of peak values. Values of these parameters fell within the range of values obtained by Fu for the North Atlantic. The time and space variations of inertial oscillations was described based mainly on band-passed records centered at local inertial frequencies. The phase coherence for inertial oscillations decreases with increasing vertical instrument separation with a vertical coherence scale somewhere in the order of 700–1500 m. For horizontal separations of less than 20 km the phase coherence is significant in all cases, and for separations greater than 60 km the inertial waves are not coherent.
The partitioning of kinetic energy of horizontal oscillations between 2 hours and 2 days is examined. We earlier estimated that 49% of this energy is found in narrow pass-bands containing the dominant short period tides. Here we find that additionally 10 and 27% of that fluctuation kinetic energy is accounted for by inertial oscillations and internal waves, respectively.
Abstract
The kinetic energy levels Of horizontal oscillations near and above the inertial frequency are described based on 84 current records made during 5 years at Drake Passage. Instrument depths ranged from 280 to 3600 m. Moorings spanned the passage, though the best depth and time coverage is for a central location. For each variance spectrum of horizontal current, the frequency band above the local inertial and semidiurnal tidal peaks was fitted to the Garrett and Munk internal wave spectrum in the form of
The fit is determined by the log-log decay (p) of energy density (NE 0) with frequency (ω), where E 0 is the energy density at 1 cph (ω0) normalized by stability frequency N. Although these parameters were generally near the “universal” values, there was considerable spatial variability—more than the year-to-year variability. Values of p were found to increase with depth; values of E 0 were larger in the northern passage and at the continental slopes suggesting source regions for wave energy. The fitted relation was integrated between local inertial and the appropriate stability frequency to examine the total kinetic energy of horizontal motions in the internal wave field. This internal wave energy was normalized by stability frequency and plotted versus depth for three distinct bathymetric regimes. Both energy levels and vertical distributions differ, with greater energy and more depth variation over the rugged bathymetry of the northern passage.
The prominent inertial peak was examined on the basis of its frequency, peak height and peak width at 50% of peak values. Values of these parameters fell within the range of values obtained by Fu for the North Atlantic. The time and space variations of inertial oscillations was described based mainly on band-passed records centered at local inertial frequencies. The phase coherence for inertial oscillations decreases with increasing vertical instrument separation with a vertical coherence scale somewhere in the order of 700–1500 m. For horizontal separations of less than 20 km the phase coherence is significant in all cases, and for separations greater than 60 km the inertial waves are not coherent.
The partitioning of kinetic energy of horizontal oscillations between 2 hours and 2 days is examined. We earlier estimated that 49% of this energy is found in narrow pass-bands containing the dominant short period tides. Here we find that additionally 10 and 27% of that fluctuation kinetic energy is accounted for by inertial oscillations and internal waves, respectively.
Abstract
Three-week average speeds from an array of current meter moorings which spanned Drake Passage were used in conjunction with geostrophic calculations to estimate the short-term transport of the Antarctic Circumpolar Current. Closely spaced hydrographic stations show that the current consists of three vertically coherent bands of relatively high speed within the generally eastward flow. These bands separate four water mass regimes which have distinct T-S relationships at depths above the core of the Circumpolar Deep Water. The geostrophic transport relative to 3000 db averaged 95×106 m3 s−1 for five transects of the Passage and is consistent with previous measurements. Referencing the geostrophic transport to the current meter measurements gives an adjusted transport of 124×106 m3 s−1 to the east. This estimate is about midway between values obtained in the two previous attempts to adjust relative transport through Drake Passage to observed velocities. The previous estimates are reconsidered and compared with this latest estimate.
Abstract
Three-week average speeds from an array of current meter moorings which spanned Drake Passage were used in conjunction with geostrophic calculations to estimate the short-term transport of the Antarctic Circumpolar Current. Closely spaced hydrographic stations show that the current consists of three vertically coherent bands of relatively high speed within the generally eastward flow. These bands separate four water mass regimes which have distinct T-S relationships at depths above the core of the Circumpolar Deep Water. The geostrophic transport relative to 3000 db averaged 95×106 m3 s−1 for five transects of the Passage and is consistent with previous measurements. Referencing the geostrophic transport to the current meter measurements gives an adjusted transport of 124×106 m3 s−1 to the east. This estimate is about midway between values obtained in the two previous attempts to adjust relative transport through Drake Passage to observed velocities. The previous estimates are reconsidered and compared with this latest estimate.
Abstract
Current and temperature records from 10 meters on six year-long moorings deployed during February 1975 in Drake Passage are examined and discussed in the context of hydrographic data from that area. The mean flow directions are consistent with those from geopotential anomaly charts, showing a northward flow in the central passage and eastward through-passage flow in the south and north. Directly measured vertical shear below 1000 m is remarkably uniform with depth in the central passage. Periods of high shear correspond to periods of high speed and are associated with lateral shifts in the velocity cores imbedded in the Antarctic Circumpolar Current at Drake Passage. Fluctuations in temperature and current are highly correlated in the vertical. Although meters near 2700 m separated by 80 km or more show only a few significant horizontal correlations for record-length statistics, there appear to be coherent fluctuations in the central passage during winter. Temperature and speed variability suggest that there are distinct thermal and kinematic regimes in Drake Passage.
Abstract
Current and temperature records from 10 meters on six year-long moorings deployed during February 1975 in Drake Passage are examined and discussed in the context of hydrographic data from that area. The mean flow directions are consistent with those from geopotential anomaly charts, showing a northward flow in the central passage and eastward through-passage flow in the south and north. Directly measured vertical shear below 1000 m is remarkably uniform with depth in the central passage. Periods of high shear correspond to periods of high speed and are associated with lateral shifts in the velocity cores imbedded in the Antarctic Circumpolar Current at Drake Passage. Fluctuations in temperature and current are highly correlated in the vertical. Although meters near 2700 m separated by 80 km or more show only a few significant horizontal correlations for record-length statistics, there appear to be coherent fluctuations in the central passage during winter. Temperature and speed variability suggest that there are distinct thermal and kinematic regimes in Drake Passage.
Abstract
During the austral summer of 1974–75 direct measurements of currents in the Drake Passage were made. One data set was collected by the Soviet Arctic and Antarctic Research Institute while another set was collected by Oregon State University as a part of the IDOE/ISOS program. The Soviet data from 61°11′S, 62°31′W beginning on 25 December and ending on 10 January are compared with the U. S. data collected at 60°45′S, 62°15′W. While there is a spatial separation of 44 km and a time separation of 47 days, there are significant similarities in the energy spectra and in the trends of the velocity components. Comparison between moorings at 59°03′S, 63°24′W and 58°46.5′S, 64°24′W yields similar results.
Abstract
During the austral summer of 1974–75 direct measurements of currents in the Drake Passage were made. One data set was collected by the Soviet Arctic and Antarctic Research Institute while another set was collected by Oregon State University as a part of the IDOE/ISOS program. The Soviet data from 61°11′S, 62°31′W beginning on 25 December and ending on 10 January are compared with the U. S. data collected at 60°45′S, 62°15′W. While there is a spatial separation of 44 km and a time separation of 47 days, there are significant similarities in the energy spectra and in the trends of the velocity components. Comparison between moorings at 59°03′S, 63°24′W and 58°46.5′S, 64°24′W yields similar results.