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991.
V.V. Gopalakrishna F. Durand K. Nisha M. Lengaigne T.P. Boyer J. Costa R.R. Rao M. Ravichandran S. Amrithash L. John K. Girish C. Ravichandran V. Suneel 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(6):739-754
The southeastern Arabian Sea (SEAS), located in the Indian Ocean warm pool, is a key-region of the regional climate system. It is suspected to play an important role in the dynamics of the Asian summer monsoon system. The present study reports the salient features derived from a newly harvested observational dataset consisting of repeated fortnightly XBT transects in the SEAS over the period 2002–2008. The fortnightly resolution of such a multi-year record duration is unprecedented in this part of the world ocean and provides a unique opportunity to examine the observed variability of the near-surface thermal structure over a wide spectrum, from intra-seasonal to interannual timescales. We find that most of the variability is trapped in the thermocline, taking the form of upwelling and downwelling motions of the thermal stratification. The seasonal variations are consistent with past studies and confirm the role of the monsoonal wind forcing through linear baroclinic waves (coastally-trapped Kelvin and planetary Rossby waves). Sub-seasonal variability takes the form of anomalous events lasting a few weeks to a few months and occurs at two preferred timescales: in the 30–110 day band, within the frequency domain of the Madden–Julian oscillation and in the 120–180 day band. While this sub-seasonal variability appears fairly barotropic in the offshore region, the sign of the anomaly in the upper thermocline is opposite to that in its lower part on many occasions along the coast. Our dataset also reveals relatively large interannual temperature variations of about 1 °C from 50 to 200 m depth that reflect a considerable year-to-year variability of the magnitude of both upwelling and downwelling events. This study clearly demonstrates the necessity for sustained long-term temperature measurements in the SEAS. 相似文献
992.
993.
John R. Mattox 《Experimental Astronomy》1991,2(2):75-84
A Monte Carlo simulation shows that the EGRET gamma-ray telescope aboard the GRO satellite does not have sufficient sensitivity to detect linear polarization, even for 100% polarized gamma-ray sources. This is confirmed by analysis of calibration data. Several data selection techniques suggested to enhance polarization sensitivity have been evaluated and found to not significantly improve sensitivity.NRC/NAS RESEARCH ASSOCIATE 相似文献
994.
995.
John Seimenis 《Astrophysics and Space Science》1991,180(2):325-331
We present the generalization of the method of rational Fourier-series approximations for nonlinear ordinary differential equations in galactic dynamics. In previous papers we presented the formulae which describe simple families of periodic orbits with very good accuracy. In this Letter we generalize our formulae to describe periodic orbits of any resonancem:n. 相似文献
996.
997.
Roger K. Ulrich Larry Webster John E. Boyden Nick Magnone Richard S. Bogart 《Solar physics》1991,135(2):211-241
We describe enhancements to the hardware and software for the 150-foot tower system on Mt. Wilson which make possible the acquisition of high precision line profile measurements. This system utilizes the 75-foot pit spectrograph with a photomultiplier detector system to scan line profiles repeatedly in order to study variations induced by the passage of waves vertically through the solar atmosphere. Oscillations of line profile parameters with an amplitude as low as 1.7 m s–1 have been detected with this system using integrated sunlight. Phase relations between oscillations of different parts of the line profile are appropriate to upward energy transport. Consistent with the previous conclusion by Mein and Schmieder (1981), we find that the magnitude of the energy transport is compatible with the 5-min oscillations making an important contribution to the heating of the low chromosphere.The Mount Wilson Observatory is operated by the Mount Wilson Institute under agreement with the Carnegie Institution of Washington. 相似文献
998.
John D. Bunton 《Experimental Astronomy》2001,11(1):193-206
Future radiotelescopes need ever increasing sensitivity. With the limits of receiver sensitivity being reached this can only
be achieved by increasing collecting area. The increase in antenna numbers and the multi-resolution capabilities of these
telescopes, such as the SKA, means a significant departure from existing designs is needed. In this article, some fundamental
designs for antenna arrays that uniformly sample the UV plane are presented. The SKA is used to provide target specifications.
The designs presented allow asymmetric configurations providing more freedom for site selection. They also allow a direct
tradeoff between field of view and correlator complexity.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
999.
John J. Matese Patrick G. Whitman Daniel P. Whitmire 《Celestial Mechanics and Dynamical Astronomy》1997,69(1-2):77-87
We investigate the distribution of Oort cloud comet perihelia. The data considered includes comets having orbital elements
of the two highest quality classes with original energies designated as new or young. Perihelion directions are determined
in galactic, ecliptic and geocentric equatorial coordinates. Asymmetries are detected in the scatter and are studied statistically
for evidence of adiabatic galactic tidal dynamics, an impulse-induced shower and observational bias. The only bias detected
is the well-known deficiency of observations with perihelion distances q > 2.5 AU. There is no significant evidence of a seasonal
dependence. Nor is there a substantive hemispherical bias in either ecliptic or equatorial coordinates. There is evidence
for a weak stellar shower previously detected by Biermann which accounts for ≈ 10% of the total observations. Both the q bias
and the Biermann star track serve to weaken the evidence for a galactic tidal imprint. Nevertheless, statistically significant
asymmetries in galactic latitude and longitude of perihelia remain. A latitude asymmetry is produced by a dominant tidal component
perpendicular to the galactic disk. The longitude signal implies that ≈ 20% of new comets need an additional dynamical mechanism.
Known disk non-uniformities and an hypothetical bound perturber are discussed as potential explanations. We conclude that
the detected dynamical signature of the galactic tide is real and is not an artifact of observational bias, impulsive showers
or poor data.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
1000.
Anthony M. Spencer Per Ivar Briskeby Lone Dyrmose Christensen Rune Foyn Marie KjФlleberg Erling Kvadsheim Ian Knight Morten Rye-Larsen John Williams 《《幕》》2008,31(1):115-124
Offshore exploration in Norway and Denmark-in the North Sea, the Norwegian Sea and the Barents Sea-has involved drilling about 850 wildcat wells, resulting in about 300 oil and gas finds, of which 84 are fields with production. The recoverable resources of all these finds total about 65 billion barrels of oil equivalent. Almost all these hydrocarbons come from a Jurassic source and the main reservoirs and traps are Jurassic sandstones in fault blocks and Paleocene sandstones or Cretaceous chalks in gentle domes. The article describes four major fields-Ekofisk, Gullfaks, Ormen Lange and SnФhvitto illustrate some of the many challenges in developing and producing the hydrocarbons.
Elsewhere in Norden, there has been much less exploration. Drilling results have mostly been negative in mainland Sweden, onshore Denmark, onshore Svalbard and on- and offshore West Greenland. Minor oil finds have been made in Palaeozoic rocks in the Baltic Sea. The first wells have recently been drilled off the Faroe Islands, resulting in one discovery. No drilling has taken place on- or offshore East Greenland.
As a result of the hydrocarbon activities in Norway and Denmark, petroleum geoscience there has flourished, with 2000 geoscientists currently employed in the industry, many technical innovations made, a wealth of publically available information and a great increase in the understanding of the geology. 相似文献
Elsewhere in Norden, there has been much less exploration. Drilling results have mostly been negative in mainland Sweden, onshore Denmark, onshore Svalbard and on- and offshore West Greenland. Minor oil finds have been made in Palaeozoic rocks in the Baltic Sea. The first wells have recently been drilled off the Faroe Islands, resulting in one discovery. No drilling has taken place on- or offshore East Greenland.
As a result of the hydrocarbon activities in Norway and Denmark, petroleum geoscience there has flourished, with 2000 geoscientists currently employed in the industry, many technical innovations made, a wealth of publically available information and a great increase in the understanding of the geology. 相似文献