排序方式： 共有28条查询结果，搜索用时 15 毫秒
21.
B. Lavraud H. Rème M. W. Dunlop J. -M. Bosqued I. Dandouras J. -A. Sauvaud A. Keiling T. D. Phan R. Lundin P. J. Cargill C. P. Escoubet C. W. Carlson J. P. McFadden G. K. Parks E. Moebius L. M. Kistler E. Amata M. -B. Bavassano-Cattaneo A. Korth B. Klecker A. Balogh 《Surveys in Geophysics》2005,26(1-3):135-175
This paper gives an overview of Cluster observations in the high-altitude cusp region of the magnetosphere. The low and mid-altitude cusps have been extensively studied previously with a number of low-altitude satellites, but only little is known about the distant part of the magnetospheric cusps. During the spring-time, the trajectory of the Cluster fleet is well placed for dayside, high-altitude magnetosphere investigations due to its highly eccentric polar orbit. Wide coverage of the region has resulted and, depending on the magnetic dipole tilt and the solar wind conditions, the spacecraft are susceptible to encounter: the plasma mantle, the high-altitude cusp, the dayside magnetosphere (i.e. dayside plasma sheet) and the distant exterior cusp diamagnetic cavity. The spacecraft either exit into the magnetosheath through the dayside magnetopause or through the exterior cusp–magnetosheath interface. This paper is based on Cluster observations made during three high-altitude passes. These were chosen because they occurred during different solar wind conditions and different inter-spacecraft separations. In addition, the dynamic nature of the cusp allowed all the aforementioned regions to be sampled with different order, duration and characteristics. The analysis deals with observations of: (1) both spatial and temporal structures at high-altitudes in the cusp and plasma mantle, (2) signatures of possible steady reconnection, flux transfer events (FTE) and plasma transfer events (PTE), (3) intermittent cold (<100 eV) plasma acceleration associated with both plasma penetration and boundary motions, (4) energetic ions (5–40 keV) in the exterior cusp diamagnetic cavity and (5) the global structure of the exterior cusp and its direct interface with the magnetosheath. The analysis is primarily focused on ion and magnetic field measurements. By use of these recent multi-spacecraft Cluster observations we illustrate the current topics under debate pertaining to the solar wind–magnetosphere interaction, for which this region is known to be of major importance. 相似文献
22.
23.
24.
25.
Peter J. Cargill 《Solar physics》1993,147(2):263-268
Implications of the conjecture that the solar corona is heated by small-scale events (nanoflares) are examined. It is shown that even if these nanoflares are small-scale (heating areas much smaller than 1 arc sec2) and impulsive, the corona may still be rather homogeneous. In particular, the filling factor (defined as the ratio of the coronal volume radiating in X-rays and EUV to the total volume) can easily be of order unity. Future experimental determination of the filling factor could prove useful in estimating the volume of coronal material that is heated during nanoflares.Work performed at Beam Physics Branch, Plasma Physics Division, Naval Research Laboratory, Washington, D.C., U.S.A.Mailing Address: Code 6790, NRL, Washington, D.C. 20375, U.S.A. 相似文献
26.
Resource estimation from historical data: Mercury, a test case 总被引：4，自引：0，他引：4
A simple technique based on historical records of tonnage and grade of ore produced provides a means for calculating how much of a mineral product will be available in the future at various average grades. Estimates made on this basis are independent of geologic considerations or changing economic and political factors, although they are based on mining history, which was largely determined by these factors. The relatively minor element, mercury, was used for the test case reported here, but the method has been found applicable to forecasts of resources for other mineral products. Mercury resources available in ore in which the average grade is as low as 0.1% are estimated to be 53 ×10
6
kg (1.5 ×10
6
flasks) for the United States and 1551 ×10
6
kg (45 ×10
6
flasks) for the world; this amount is more than adequate to meet predicted demand to the year 2000. The expectable price of mercury in 1978 dollars at this 0.1% grade is projected to be $58.75 per kg ($2,025 per flask), but at a 10% annual inflation rate, it would be more than $12,000 per flask. To satisfy just the projected U.S. demand for mercury by 2000, the price is calculated to be $48.96 per kg ($1,688 per flask) in 1978 dollars at an average annual grade of 0.12%. 相似文献
27.
S. Krucker M. Battaglia P. J. Cargill L. Fletcher H. S. Hudson A. L. MacKinnon S. Masuda L. Sui M. Tomczak A. L. Veronig L. Vlahos S. M. White 《Astronomy and Astrophysics Review》2008,16(3-4):155-208
This review surveys hard X-ray emissions of non-thermal electrons in the solar corona. These electrons originate in flares and flare-related processes. Hard X-ray emission is the most direct diagnostic of electron presence in the corona, and such observations provide quantitative determinations of the total energy in the non-thermal electrons. The most intense flare emissions are generally observed from the chromosphere at footpoints of magnetic loops. Over the years, however, many observations of hard X-ray and even γ-ray emission directly from the corona have also been reported. These coronal sources are of particular interest as they occur closest to where the electron acceleration is thought to occur. Prior to the actual direct imaging observations, disk occultation was usually required to study coronal sources, resulting in limited physical information. Now RHESSI has given us a systematic view of coronal sources that combines high spatial and spectral resolution with broad energy coverage and high sensitivity. Despite the low density and hence low bremsstrahlung efficiency of the corona, we now detect coronal hard X-ray emissions from sources in all phases of solar flares. Because the physical conditions in such sources may differ substantially from those of the usual “footpoint” emission regions, we take the opportunity to revisit the physics of hard X-radiation and relevant theories of particle acceleration. 相似文献
28.
Solar and Heliospheric Causes of Geomagnetic Perturbations during the Growth Phase of Solar Cycle 23
Bothmer V. Veselovsky I. S. Dmitriev A. V. Zhukov A. N. Cargill P. Romashets E. P. Yakovchouk O. S. 《Solar System Research》2002,36(6):499-506
A database is compiled for the study of solar and heliospheric causes of geomagnetic perturbations with the daily average index A
> 20 that were observed in the period 1997–2000. The number of such events (more than 200) progressively increased and fluctuated as the current solar cycle developed. It is established that geomagnetic storms are generated by dynamical processes and structures near the center of the solar disk in a zone of several tens of degrees, and these processes are responsible for the appearance in the Earth's region, within several tens of hours, of quasistationary and transient solar wind streams with a sufficiently strong southward component of the heliospheric magnetic field. These streams lasted more than a few hours. The following structures can serve as morphological indicators for the prediction of the appearance of such streams: (1) active and disappearing filaments derived from synoptic -maps of the Sun, (2) solar flares, (3) coronal holes and evolving active regions, and (4) the heliospheric current sheet. The geometry of coronal mass ejections needs further observational study. 相似文献