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1.
Although the elemental composition in all parts of the solar photosphere appears to be the same this is clearly not the case
with the solar upper atmosphere (SUA). Spectroscopic studies show that in the corona elemental composition along solar equatorial
regions is usually different from polar regions; composition in quiet Sun regions is often different from coronal hole and
active region compositions and the transition region composition is frequently different from the coronal composition along
the same line of sight. In the following two issues are discussed. The first involves abundance ratios between the high-FIP
O and Ne and the low-FIP Mg and Fe that are important for meaningful comparisons between photospheric and SUA compositions
and the second involves a review of composition and time variability of SUA plasmas at heights of 1.0≤h≤1.5R
⊙. 相似文献
2.
D.R. Japaridze M.Sh. Gigolashvili V.J. Kukhianidze 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2007,40(12):1912-1916
The differential rotation of the patterns of the large-scale solar magnetic field during solar activity cycles 20 and 21 is investigated. Compact magnetic elements with the polarity of the general solar magnetic field have larger speed of rotation than the elements with the opposite polarity. The surface of the Sun was divided by 10°-zones. In all of them the average rotation rate of the magnetic elements with negative polarity is little higher than that of the magnetic elements with positive polarity, except for 50°-zone of the south hemisphere and at the 10° latitude of the north hemisphere.
The rates of differential rotation for large-scale magnetic elements with negative and positive polarities have similar behavior for both cycles of the solar activity.
The rotation rate varies at polarity reversal of the circumpolar magnetic fields. For the cycle No 20 in 1969–1970 the threefold reversal took place in the northern hemisphere and variations of rotation rate can be noticed for magnetic elements both with positive and negative polarity for each 10°-zone in the same hemisphere. 相似文献
3.
4.
Paul Withers T.J. Stubbs E. Mazarico 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(12):4099-4109
The existence of a “dense” lunar ionosphere has been controversial for decades. Positive ions produced from the lunar surface and exosphere are inferred to have densities that are – m?3 near the surface and smaller at higher altitudes, yet electron densities derived from radio occultation measurements occasionally exceed these values by orders of magnitude. For example, about 4% of the single-spacecraft radio occultation measurements from Kaguya/SELENE were consistent with peak electron densities of m?3. Space plasmas should be neutral on macroscopic scales, so this represents a substantial discrepancy. Aditional observations of electron densities in the lunar ionosphere are critical to resolving this longstanding paradox. Here we theoretically assess whether radio occultation observations using two-way coherent S-band radio signals from the Lunar Reconnaissance Orbiter (LRO) spacecraft could provide useful measurements of electron densities in the lunar ionosphere. We predict the uncertainty in a single LRO radio occultation measurement of electron density to be m?3, comparable to occasional observations by Kaguya/SELENE of a dense lunar ionosphere. Thus an individual profile from LRO is unlikely to reliably detect the lunar ionosphere; however, averages of multiple (10) LRO profiles acquired under similar geophysical and viewing conditions should be able to make reliable detections. An observing rate of six ingress occultations per day (2000 per year) could be achieved with minimal impact on current LRO operations. This rate compares favorably with the 378 observations reported from the single-spacecraft experiment on Kaguya/SELENE between November 2007 and June 2009. The large number of observations possible for LRO would be sufficient to permit wide-ranging investigations of spatial and temporal variations in the poorly understood lunar ionosphere. These findings strengthen efforts to conduct such observations with LRO. 相似文献
5.
R. J. Murphy 《Space Science Reviews》2007,130(1-4):127-138
Interactions of ions accelerated in solar flares produce gamma-ray lines and continuum and neutrons. These emissions contain
a rich set of observables that provides information about both the accelerated ions and the environment where the ions are
transported and interact. Ion interactions with the various nuclei present in the ambient medium produce gamma-ray lines at
unique energies. How abundance information is extracted from the measurements is discussed and results from analyses of a
number of solar flares are presented. The analyses indicate that the composition of the ambient gas where the ions interact
(typically at chromospheric densities) is different from that of the photosphere and more like the composition of the corona,
exhibiting low-FIP elemental enhancements that may vary from flare to flare. Evidence for increased Ne/O and the photospheric
3He abundance is also discussed. 相似文献
6.
Keith T. Strong 《Space Science Reviews》1994,70(1-2):133-142
We review recent observations by the Yohkoh-SXT in collaboration with other spacecraft and ground-based observatories of coronal loops and prominences. These new results point to problems that SoHO will be able to address. With a unique combination of rapid-cadence digital imaging (32 s full-disk and 2 s partial-frame images), high spatial resolution (2.5 arcsec pixels), high sensitivity (EM 1042 cm–3), a low-scatter mirror, and large dynamic range, SXT can observe a vast range of targets on the Sun. Over the first 21 months of Yohkoh operations, SXT has taken over one million images of the corona and so is building up an invaluable long-term database on the large-scale corona and loop geometry. The most striking thing about the SXT images is the range of loop sizes and shapes. The active regions are a bright tangle of magnetic field lines, surrounded by a network of large-scale quiet-Sun loops stretching over distances in excess of 105 km. The cross-section of most loops seems to be constant. Loops displaying significant increase in the ratio of the footpoint to loop-top diameter () are the exception, not the rule, implying the presence of widespread currents in the corona.All magnetic structures show changes. Time scales range from seconds to months. The question of how these structures are formed, become filled with hot plasma, and are maintained is still open. While we see the propagation of brightenings along the length of active-region loops and in X-ray jets with velocities of several hundred km/s, much higher velocities are seen in the quiet Sun. In XBP flares, for example, velocities of over 1000 km/s are common. Active-region loops seem to be in constant motion, moving slowly outward, carrying plasma with them. During flares, loops often produce localized brightenings at the base and later at the apex of the loop. Quiescent filaments and prominences have been observed regularly. Their coronal manifestation seems to be an extended arcade of loops overlying the filament. Reliable alignment of the ground-based data with the X-ray images make it possible to make a detailed intercomparison of the hot and cold plasma structures over extended periods. Hence we are able to follow the long-term evolution of these structures and see how they become destabilized and erupt. 相似文献
7.
T. S. Bastian 《Space Science Reviews》1994,68(1-4):261-274
Radio and X-ray observations of stellar flares provide the most direct probes of energy relaase particle acceleration, and energy transport on stars other than the Sun. In this review, the observational basis for our understanding of the flare phenomenon on other stars is briefly described and outstanding interpretive and theoretical issues are discussed. I shall confine my attention to objects which are solar-like, to the extent that they possess deep convective envelopes and display activity which is presumed to be magnetic in origin. These include pre-main sequence objects, classical flare stars, and close binaries. Future directions are briefly discussed. 相似文献
8.
F.B. Rizzato A.C.-L. Chian M.V. Alves R. Erichsen S.R. Lopes G.I. de Oliveira R. Pakter E.L. Rempel 《Space Science Reviews》2003,107(1-2):507-514
Langmuir waves and turbulence resulting from an electron beam-plasma instability play a fundamental role in the generation
of solar radio bursts. We report recent theoretical advances in nonlinear dynamics of Langmuir waves. First, starting from
the generalized Zakharov equations, we study the parametric excitation of solar radio bursts at the fundamental plasma frequency
driven by a pair of oppositely propagating Langmuir waves with different wave amplitudes. Next, we briefly discuss the emergence
of chaos in the Zakharov equations. We point out that chaos can lead to turbulence in the source regions of solar radio emissions.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
9.
C. De Jager 《Space Science Reviews》2005,120(3-4):197-241
10.
北京天文台在2.84GHz频率上观测到的带短时标精细结构的微波爆发与日本YOHKOH卫星上HXT在1991年10月-1992年12月观测到的硬X射线爆发(HXB)事件作了比较,发现在20个微波精细结构爆发事件只有12个与YOHKOH卫星记录的HXB有对应关系.本文对1992年6月7日典型事件中2.84GHz与HXB共同存在的百秒量级的准周期振荡作了分析及源区参数的计算,并作了简要的讨论. 相似文献