摘要:

A data base of ice draft and roughness parameters has been constructed for selected portions of the Arctic Ocean based upon analysis of under‐ice draft distribution data acquired by inverted echo sounder systems on submarines. From the voyages of 12 submarines which traversed the Alaskan, Canadian, and central Arctic regions of the Arctic Ocean during the summer and winter seasons, a series of mean ice draft and deep‐draft keel statistics was calculated for 50‐km segments along each submarine track. Contour maps of the mean ice draft, its standard deviation, the mean keel draft, and the spatial frequency of ice keels were constructed. They show that the greatest ice drafts, the roughest ice, and the greatest number of deep‐draft keels are found off the north coasts of the Canadian Archipelago and Greenland due to ice convergence on these land b

ISSN:0148-0227    

DOI:10.1029/92JC01857

年代:1992

数据来源: WILEY

摘要:

A coupled sea ice‐ocean numerical model has been developed that addresses the role of floe geometry during summertime melting. The model contains a diagnostic equation for average floe diameter in addition to the usual prognostic equations for ice volume per unit area and ice concentration. The partition between melting on the top, bottom, and lateral (side) surfaces of floes is examined using time‐dependent simulations with differing initial average floe diameters. The different parameterizations for bottom and lateral melting in the literature are also compared and found to vary significantly. The results show that lateral melting is important only for floes with diameters less thanO(30 m), given atmospheric thermal forcing typical of the central Arctic in summer. This means that the decrease in ice concentration over the summer is a strong function of floe diameter, in keeping with simple geometrical arguments. In all cases, about 80% of the net thermal energy that enters the ocean through leads goes toward melting ice, while the rest warms the oc

ISSN:0148-0227    

DOI:10.1029/92JC01755

年代:1992

数据来源: WILEY

摘要:

A hypothesis that large‐scale fracture of sea ice plates in the Arctic could be caused by the release of energy of thermal bending moments due to major temperature changes is advanced and examined. Bending propagation of a through‐the‐thickness crack along the floating plate, with negligible inertial forces, is analyzed, assuming the moment field in the plate near the traveling crack front and the fracture process zone to be in a steady state. The analysis uses the plate‐bending theory, and the second‐order geometric effects of the in‐plane normal forces are taken into account. Quasi‐elastic behavior is assumed, and creep is treated approximately according to the effective modulus method. The calculated temperature difference between the top and bottom of the plate required to produce this kind of fracture is found to be well within the range that actually occurs in the Arctic, but this cannot be regarded as a proof of the hypothesis because of the simplifying assumptions made as well as uncertainties about large‐scale fracture properties of sea ice. Further, it is shown that this type of fracture must exhibit a size effect, such that the critical temperature difference decreases in proportion to (plate thickness)−⅜. This might explain why large fractures often form in an intact thick plate rather than only in a thin plate and along lines of weakness. For the case that the in‐plane forces are significant, it is shown that beyond a certain critical crack length the thermally driven bending fracture (if it exists) must transit to a planar (nonflexural) fracture driven by the release of the energy of the in‐plane forces generated by wind and ocean currents. The effect of creep is to increase the required critical temperature difference, as well as the critical crack length for the aforementioned transition. For thermal bending fracture, the minimum possible spacing of parallel cracks increases with the plate thickness and is independent of the crack length, while after transition to planar fracture it increases in proportion to the crack length. The hypothesis of thermal bending fracture cannot be proven or disproven without new types of experiments and measurements in the Arctic, and

ISSN:0148-0227    

DOI:10.1029/92JC00816

年代:1992

数据来源: WILEY

摘要:

The Tatarskiy Strait is the northernmost region of the Japan Sea, with an ice‐covered area in winter of about 4 × 104km2. This study uses the daily passive microwave images of the region from the special sensor microwave imager (SSM/I), which was launched in 1987, to estimate the production of ice and Japan Sea bottom water. In winter, the prevailing winds in the strait are northerly and cold; these conditions create a region of reduced ice concentration in the northern strait, which leads to an enhanced ice production throughout the season. In addition to these prevailing winds, each winter one or two severe storms generate very strong northerly winds and cold temperatures in the strait. These storms create a large transient polynya in the strait at a time simultaneous with the greatest heat flux out of the open water. Calculation of the ice growth from open water in the northern strait yields about 25 km3of ice per season, of which severe storms provide about 25%. The total ice production is sufficient to form about 5–12 × 102km3of the Japan Sea bottom water, which is about 50–100% of the renewal rate required from14C data. Because the oxygen bottom layer thickness decreased between 1969 and 1984, the study also investigates the frequency of the severe storms in the northern strait during 1966–1990 and finds that these storms are about 3 times as frequent at the beginning of this period than at the end. This suggests the storms may play a role in the generation of the Japan Sea bot

ISSN:0148-0227    

DOI:10.1029/92JC01587

年代:1992

数据来源: WILEY

摘要:

A wind‐driven, nonlinear, reduced gravity, primitive equation model is used to simulate the circulation of the northeast Pacific Ocean including the northeast Gulf of Alaska. The model includes the affects of bottom topography. Model geometry encompasses the entire Gulf of Alaska region from Vancouver Island to west of Kodiak Island. This region is traditionally beyond the latitude limits of the reduced gravity model imposed by a weakening thermocline away from the equator. The model resolution, 0.025° in latitude and longitude, is very fine. This is the first time that a model of this type and resolution has been successfully run at these latitudes. Although we expected that such resolution would allow the mesoscale eddy field to develop, it did not. One reason may be the coarse spatial and temporal winds. Twenty year of Comprehensive Ocean‐Atmosphere Data Set pseudo wind stress data used to drive the model are statistically analyzed to obtain a wind stress climatology. After model spin‐up, the monthly stresses for 1986–1989 are used to drive the model. The model reproduces many of the regional oceanographic features such as the Alaskan Gyre, the Alaska Current, the Alaska Coastal Current, the Sitka eddy, and an intense, cyclonic eddy (that has not yet been reported in the literature) northwest of the Queen Charlotte Island in the spring. In addition, the model displays seasonal and interannual variability. Model results are validated through comparisons with National Ocean Service coastal sea level records and a multilayer, oceanic basin scale model being run at the Institute for Naval Ocea

ISSN:0148-0227    

DOI:10.1029/92JC01260

年代:1992

数据来源: WILEY

摘要:

Several advanced very high resolution radiometer (AVHRR) images with spatial resolution of 1.1–3.3 km, together with several concurrent aircraft‐deployed expendable bathythermograph (AXBT) surveys and conductivity‐temperature‐depth (CTD) stations, from spring 1989 are used to describe the Iceland‐Faeroe sea surface temperature (SST) front. In the AVHRR images, SST fronts are located by maximizing |∇SST|. Single, large gradient segments of the SST front do exist, with some exceeding 100 km in length, indicating a multiple frontal structure. These single frontal lines are also segments where |∇2SST| is small, and they can be followed uniquely by a single isotherm eastward from Iceland for a distance of 300 km. With a 35‐km sampled AXBT survey, two small subsurface cold eddies were located south of the surface front in an area 170 km × 270 km east of Iceland. From a May 1987 AVHRR image on 1.1‐km resolution, a population of seven such cold eddies are found between Iceland and the Faroes. They appear to be generated along the surface expression of the Iceland Faroes front and populate the northern slope of the Iceland‐Faroes Ridge. Historical data from towed high‐resolution instruments suggest that the cold eddies are ∼30–50 km in size and uplift the

ISSN:0148-0227    

DOI:10.1029/92JC01341

年代:1992

数据来源: WILEY

摘要:

During two cruises to the Greenland Sea in 1988 and 1989 a total of 690 on‐board aluminium (Al) determinations were performed on samples collected from profiles located along four transects in the Greenland Sea, as part of the Greenland Sea Project. Al concentrations range from extremely low values (0.4 nM) in the Polar waters of the East Greenland Current draining the Arctic Ocean, to 17.9 nM in the newly formed Norwegian Sea Deep Water (NSDW) at the periphery of the Greenland gyre. The Al content in the component water masses serves to constrain the make‐up of these water masses from the various mixing products of the region. The enrichment of Al in the NSDW both at its site of formation within the Greenland Sea (up to 17.9 nM) and in the Lofoten Basin of the Norwegian Sea (up to 40.3 nM) leads to the conclusion that there must be an additional, external, source of Al to these water masses. The apparent inability of water column or sedimentary diagenetic processes to provide this enrichment and the observation of enriched Al values associated with a high‐salinity shelf brine leads us to the conclusion that these brines may be responsible for the observed enrichments. The high concentration of Al in the Greenland Sea Deep Water compared with the water masses that produce it, suggests that Al may be acting as an inverse tracer of the processes that ventilate this basin by convective overturn, i.e. the Al concentration which increases with time, as a result of continuous brine or other external inputs, is reduced during convective events. It is also argued that this flushing of elevated Al water during convective events may have a similar counterpart in the Iceland Sea and that this mechanism could go some way toward solving the Al deficit that exists between the enriched North Atlantic Deep Water and its depleted precursor water masses observed in the intermediate waters of the Greenland and Iceland

ISSN:0148-0227    

DOI:10.1029/92JC01798

年代:1992

数据来源: WILEY

摘要:

Surface height fluctuations across an eastward flowing boundary current, such as the Gulf Stream and the Kuroshio, can be caused by changes both in the upstream inflow and in the neighboring recirculation gyres. Clarifying these causes is important in understanding the time‐dependent nature of the boundary currents and their relationship to the surface wind and buoyancy forcing. Using satellite altimetry data to identify these causes, however, requires mean surface height field information, which is not readily available from the altimetry observation owing to lack of accurate geoid data. The present study presents a method to estimate the mean surface height profile across a boundary current system (including recirculation gyres) by combining altimetrically measured residual height data and historical hydrographic data. Applying this method to the Kuroshio revealed that the absolute surface height profiles thus estimated agree well with the results from quarterly, in‐situ hydrographic observations. By separating the signals of the surface height fluctuations into those of the eastward flowing jet and the recirculation gyres, we found that the seasonal cycle in the surface transport of the Kuroshio, which has a maximum in July and August, is primarily due to the seasonal change in the intensity of the recirculation gyre south of the Kuros

ISSN:0148-0227    

DOI:10.1029/92JC01792

年代:1992

数据来源: WILEY

摘要:

The global structure of the annual and semiannual sea surface height variability is constructed from the first 2 years of the Geosat Exact Repeat Mission (ERM) altimeter data. The GEM‐T2 orbits available for the first 2 years of the ERM have an accuracy of 40 cm RMS. Residual orbit error is modeled as one cycle per orbital revolution and is removed from collinear differences of arcs made of data from one full orbital revolution of the satellite. The error in the Schwiderski M2 tidal model must be estimated due to the fact that the tidal variability aliases to 1.15 cycles per year (cpy), and this frequency is not separable from 1 cpy with the 2 years of data. An estimate of the M2 tidal error is made based on the particular temporal and spatial aliasing of the tide. With this error removed, a least squares fit of sine and cosine waves with annual and semiannual frequencies is made to the time series at every point along the ground track of the satellite. This produces sine and cosine coefficients at the ground track points which are interpolated to a regularly spaced ½° grid over the globe. From the sine and cosine maps, amplitude and phase may be obtained. Interpolation of the sine and cosine coefficients using different spatial scales is done to better observe the large‐scale phase changes and to remove small‐scale noise. Results show the phase relationships between major current systems, large‐scale variations near the equator in the Intertropical Convergence Zone (ITCZ), a 180° phase difference between the northern and southern hemispheres for the annual variability, large‐scale westward propagating waves, and other large‐scale

ISSN:0148-0227    

DOI:10.1029/92JC01708

年代:1992

数据来源: WILEY

摘要:

In this paper, Geosat altimetry data from the northeast Pacific are examined. The data are (1) binned data on 1° latitude by 2° longitude blocks and (2) collinear track data. The binned data cover the region from 20°N to 60°N from the North American coast westward to 150°W and span from December 15, 1986, to June 1, 1989. To examine the data for evidence of westward propagation of sea level anomalies, three zonal transects (45°N, 49°N, and 57°N) are made. Complex empirical orthogonal function analysis of the data transects at these latitudes reveals phase speed and amplitude information. The first eigenmode at each latitude has a very strong annual signal. Two‐dimensional spectral analysis of the first eigenmode at 45°N and 57°N shows westward propagation of sea level anomalies at 45°N only. The propagating features are annual in period and of order 1000 km in length. At 57°N, westward propagation is evident (as at 45°N), but there is also an eastward component. To examine the variability of the coastal sea level signal, collinear track data from three ascending tracks crossing the Gulf of Alaska are analyzed revealing mesoscale features of the order of 100 km that parallel the Canadian and Alaskan coast. The most notable feature is the Sitka eddy. Westward propagation of several of these features is observed. The results from the analysis of both types of Geosat data are compared with other obse

ISSN:0148-0227    

DOI:10.1029/92JC01691

年代:1992

数据来源: WILEY