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721.
We considered the problem dealing with the far field of internal gravity waves generated by the source oscillating in the
vertical. It is shown that, at a fixed observation point, we first record the arrival of the main wave front of a separate
mode followed by the arrival of two fronts of an additional field of this wave mode, which is caused by the oscillations of
the source, the asymptotics near the additional wave front being expressed via Airy function. 相似文献
722.
The composition of suprabenthic crustacean assemblages, their diversity, production (P) and production/biomass (P/B) ratios, were analyzed at species level along two transects situated to the north (N) and south (S) of Mallorca (Balearic Islands, western Mediterranean) at depths between 134 m and 760 m, based on a ca. bi-monthly sampling performed between August 2003 and June 2004. Differences with depth and season in assemblage composition and diversity were analyzed as a function of the contrasting environmental features (e.g. water mass dynamics) of the two areas. We identified 187 species (18 decapods, 5 euphausiids, 16 mysids, 76 gammaridean amphipods, 13 hyperiids, 1 caprellid, 21 isopods and 37 cumaceans). Substantial mesoscale variability in the deep-sea suprabenthic assemblages coupled with diversity trends between the N and S transects were found. Seasonality was the most important gradient influencing the dynamics of suprabenthos over the upper (350 m) and middle (650–750 m) slope in the N area. Conversely, the S area appeared to be more stable temporally with depth as the main gradient inducing assemblage differences. Different depth-related patterns were observed both for diversity and P/B. To the north diversity was very low at the shelf-break, increasing on the upper-slope (H′ > 3.00) and then decreasing again on the middle-slope. To the south diversity increased smoothly downward, reaching the highest values on the middle-slope. Regarding productivity, P/B was highest at intermediate depths to the north (over ca. 450–500 m), while to the south highest P/Bs were found deeper (over ca. 600–650 m). The higher P/B at intermediate depths found along N are likely due to higher % of organic matter (OM) in sediments, a product of oceanographic frontal systems. In particular, P/B was higher along N among omnivores and detritus feeders (e.g. Andaniexis mimonectes, Lepechinella manco and combined cumaceans), coupled to enriched OM in sediments, while along S mesoplanktonic carnivores (Rhachotropis spp.) had higher P/Bs. We conclude that on the north slope the influence of frontal systems and more active flow dynamics of different water masses (WIW and LIW) increases natural disturbance in the area, increasing productivity and diversity of suprabenthic peracarids in the Benthic Boundary Layer. Also, species showed a displacement of their average distributions (their Centres of Gravity, CoG) to shallower depths along N, which is another indicator of more favorable habitat conditions for suprabenthos in the 400–500 m range at N. 相似文献
723.
On the basis of the results of regional reanalysis of the atmospheric circulation presented with a resolution of 9 km, the
process of formation of breezes is studied for the case of weak synoptic background activity in the rectilinear part of the
west coast of the Black Sea for the period 01–04.07.2007. It is shown that the gravitational currents, breeze fronts, and
intense internal waves are formed under these conditions in the troposphere during the daytime. The Hovm?ller diagrams of
the wind velocity and the maps of the vertical sections of potential temperature, vertical velocity of the air masses, and
other parameters are presented. On the basis of these diagrams and maps, we obtain quantitative estimates of the wind velocity
in the breeze and of the velocity of propagation of the breeze front and compare these estimates with the available literature
data. 相似文献
724.
E. G. Lunev V. A. Ivanov A. G. Kirichenko E. M. Lemeshko S. V. Motyzhev 《Physical Oceanography》2011,20(5):366-378
The autonomous drifting buoys equipped with satellite link turn into one of the most important components of the global system
of operative observations of the ocean and the surface layer of the atmosphere. However, on the regional level, the problem
of analysis of the surface circulation of waters in the coastal zone and sea straits remains quite urgent because the available
drifters cannot be used in this case due to their sizes and long intervals between measurements. We present the results of
development and testing of a new drifter system aimed at measuring currents. The system is based on the use of buoys operating
at depths less than 1 m. To improve the space-and-time resolution of measurements, the buoys are equipped with receivers of
the global positioning system (GPS) and GSM modems for the data transfer via cellular communication networks. The drifter system guarantees the possibility of determination
of the coordinates of buoys with a resolution of 3 min in time and 14 m in space. We describe the specific features of the
design of the proposed information-and-measuring drifter system and present the first results of application of new buoys
called “minidrifters” for the pilot monitoring of currents in the Kerch Strait. 相似文献
725.
Short-term wave design approach of marine structures, using nonlinear time domain simulations, is a design procedure that is recognized by various modern standard codes. One of the most challenging points of this approach is the evaluation of the characteristic extreme values for response parameters used in the design check equations. The most straightforward and recommended way to evaluate a response characteristic value is by fitting an extreme value probability distribution to the N-sample of extreme values extracted from N independent time domain simulations with duration equal to the short-term period indicated by the code, which is usually taken as 3 h. However, this procedure would not be practical for some types of marine structures, such as risers and mooring lines, under numerous design load cases and demanding huge finite element models. A more feasible approach would be to assess the response extreme value distribution using only a single short-term time domain simulation with duration shorter than 3 h. But reduced time simulations always introduce some additional statistical uncertainty into the extreme values estimates. This paper discusses a workable way of properly taking into account the statistical uncertainty associated with the simulation length in the assessment of a characteristic short-term extreme response value based on a single time series. 相似文献
726.
I. N. Mordvintsev N. G. Platonov I. V. Alpatsky 《Izvestiya Atmospheric and Oceanic Physics》2011,47(9):1127-1134
The main results of processing the long-term satellite data in different spectral ranges and with different spatial resolutions
used to map Arctic sea ice parameters are presented. The advantages of the methods developed in order to estimate these parameters
on the basis of microwave sensor measurements are indicated. The specific features of the long-term dynamics of the main sea
ice geophysical parameters (the sea ice area and distribution during the summer minimum, ice age structure and thickness,
multiyear ice concentration, times of ice melt and freeze onset, etc.) are presented. The effect of changes in sheet ice on
the status of large Arctic mammals is estimated. 相似文献
727.
V. V. Zuev S. L. Bondarenko N. E. Zueva 《Izvestiya Atmospheric and Oceanic Physics》2011,47(9):1032-1038
The response of the total ozone (TO) at subarctic latitudes to volcanic eruptions, products of which were injected into the
stratosphere, is analyzed. It is established that the behavior of the series of average annual TO values according to the
TOMS, SCIAMACHY, and GOME space equipment data averaged for 55°–65° N latitudes agrees with the activity of explosive volcanic
eruptions. The series of the TO satellite monitoring instrumental data are extended by 200 years into the past using a reconstruction
from the dendro-chronologic data. An analysis of the series of TO reconstructed values indicates that volcanogenic perturbations
of the subarctic ozonosphere initiate long-term negative TO deviations. In this case, the TO negative deviation depth depends
on the frequency of the ozonosphere volcanogenic perturbations and the phase of quasiperiodic oscillation cycles rather than
on the strength of a single volcanic explosion. 相似文献
728.
M. B. Gokhberg G. M. Steblov S. L. Shalimov V. A. Veis E. A. Grekhova 《Izvestiya Atmospheric and Oceanic Physics》2011,47(8):929-940
Using available Russian and international Global Positioning System (GPS) network data, we studied the ionospheric response
to the M = 8.9 submarine earthquake of March 11, 2011, on the northeastern coast of Honshu Island, Japan, both near and far (about
2000 km away) from the epicenter. In the region over the epicenter, 8.7 min after the event, we detected a characteristic
signal of the total electron content (TEC) variations consisting of compression and rarefaction phases and a linear transition
zone in between, i.e., in the form of an N-type wave with a steep leading front indicating a rapid uplift of the water surface and, correspondingly, the bottom of the
ocean. The shape of the signal can be used for early tsunami warning; i.e., it may indicate the tsunamigenic character of
a submarine earthquake. We monitored the subsequent evolution of the ionospheric response as far as 2000 km from the epicenter.
It was shown that, besides the wellknown ionospheric N-type wave response to the earthquake, there is also a response in the form of an inverted N-wave, both nearby and far from the epicenter. We detected two more types of ionospheric responses far from the epicenter:
a solitary-like wave and an internal gravity wave (IGW). The detected signals have been interpreted. 相似文献
729.
We studied the surface perturbations of a two-layer ideal fluid induced by a flow past a submerged obstacle (simulated by
a point dipole) in the vicinity of the density-jump layer. It is shown that the formation of two different types of surface
waves is possible behind the flowed past obstacle in the real conditions of the open sea. The comparison of the amplitudes
of the surface perturbations induced by the obstacle located above and below the density jump revealed their significant differences,
which seems to be important for the use of this effect in practical problems. 相似文献
730.