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271.
An analysis previously developed for rough surface scattering with narrow-beam reception is extended to wide-beam or omnidirectional reception. The source is considered to be a pulsed electric dipole. The analysis includes multipathing effects on the received signal. The results are used to develop a model for the backscattered radar cross section of the ocean surface, up to a second-order approximation. 相似文献
272.
273.
S.I. Akasofu 《Planetary and Space Science》1985,33(1):81-87
We examine time variations of the total magnetospheric output UT and the two geomagnetic indices AE and Dst during the magnetospheric storm of 31 December 1967–1 January 1968. A unique feature of this particular storm is that the solar-wind magnetosphere dynamo power ε was nearly constant for about 24 h by maintaining a high value of ~1019 erg s?1. It is found that UT was also nearly constant during that period, indicating that the magnetosphere is primarily a directly driven system. However, during an early epoch of the storm, the electrojet intensity levelled off, while the ring current began to grow during the same epoch. Subsequently, there occurred a sudden surge of the electrojet intensity, while the growth of the ring-current levelled off. Later variations of both the AE and Dst indices were very complex. After the surge, the AE index continued to decline and became as low as ~250 nT during the maximum epoch of this major storm (when the Dst decrease attained the maximum values). This trend can also be seen in many other major storms, but is often masked by changes of ε. One possible cause for such features for ε ? 1019erg/s?1 is that the neutral wind is generated by the motion in the lower ionosphere, reducing the electrojet intensity and enhancing the ring-current particle-injection rate. 相似文献
274.
A. K. Kolesov 《Astrophysics》1985,22(3):339-346
275.
The recent twelve-state R-matrix calculations of electron excitation rates in Ciii by Berrington are used to derive level populations applicable to the solar transition region. Line ratios R = I(2p
2 3
P
e
- 2s2p
3
P
°)/I(2s2p
1
P
° - 2s
2 1
S
e
) and R
2=I(2p
2 1
S
e
- 2s2p
1
P
°)/I(2p
2 3
P
e
- 2s2p
3
P
°) deduced from these data in conjunction with the relevent transition probabilities are found to be in much better agreement with the observed quiet Sun values than those determined from the level population calculations of Keenan et al. 相似文献
276.
The Strand Fiord Formation is a volcanic unit of early Late Cretaceous age which outcrops on west-central and northwestern Axel Heiberg Island in the Canadian Arctic Archipelago. The formation is part of the thick Sverdrup Basin succession and immediately precedes the final basin foundering event. The Strand Fiord volcanics are encased in marine strata and thin southward from a maximum thickness of 789+ m on northwestern Axel Heiberg to a zero edge near the southern shore of the island. Tholeiitic icelandite flows are the main constituent of the formation with volcaniclastic conglomerates, sandstones, mudrocks and rare coal seams also being present. The lava flows range in thickness from 6 to 60 m and subaerial flows predominate. Both pahoehoe and aa lava types are common and the volcanic pile accumulated mostly by the quiet effusion of lavas. The volcaniclastic lithologies become more common near the southern and eastern edges of the formation and represent lahars and beach to shallow marine reworked deposits. The Strand Fiord volcanics are interpreted to represent the cratonward extension of the Alpha Ridge, a volcanic ridge that was active during the formation of the Amerasian Basin. 相似文献
277.
The accuracy of the AE index as a measure of the joule heat production rate is examined for a typical substorm event on 18 March 1978 by estimating the global joule heat production rate, as a function of time, using data obtained from the IMS six meridian chains. In spite of the fact that the AE index had had an initial slow growth which was followed by a rapid growth, the joule heat production rate attained a high level during the slow growth and thus their variations were considerably different from those of the AE index. Therefore, although the AE index is statistically linearly related to the global joule heat production rate, one should be cautious in assuming that details of time variations of the AE index during individual events represent those of the joule heat production rate. 相似文献
278.
279.
We investigate the evolution of rotation period and spindown age of a pulsar whose surface magnetic field undergoes a phase
of growth. Application of these results to the Crab pulsar strongly indicates that its parameters cannot be accounted for
by the field growth theories. 相似文献
280.
N. S. Chauhan 《Astrophysics and Space Science》1985,112(1):185-192
The treatment followed by Coxet al. (1973) for the estimation of the effects of thermal imbalance on the pulsational stability of stars is applied to Roche and point source (Chandrika Prashad) model. The calculations suggest that the eigenvalues obtained for the above model are correct to 0(t
ff/ts). The expressions for stability coefficients and corresponding eigenfunctions for the stars in thermal imbalance for the above models have also been derived. 相似文献