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1.
The roll manoeuvre of SOHO on September 3, 1997 provided the opportunity to study the northern coronal hole with SUMER slits
in east-west orientation, so that polar plumes and inter-plume lanes could be observed simultaneously. A preliminary analysis
of the observations shows that lines emitted by ions with the lowest formation temperatures (with the exceptions of Ne7+ and Ar7+) have the largest ratios of plume to lane radiances at heights between 35 000 km and 70 000 km above the photosphere. All
lines have narrower widths inside plumes than outside. Electron densities have been deduced in plumes and lanes from Si VIII
and Mg VIII line radiance ratios. The Mg IX pair was used to determine the corresponding electron temperatures. Neon (with
a high first-ionization potential) is found to be less abundant relative to magnesium (with low FIP) in a plume compared to
an inter-plume lane, but the variation is smaller than previously determined Ne/Mg abundance ratios in a plume relative to
the photosphere.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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Spectra of the northern polar coronal hole measured with the SUMER spectrometer on SOHO on 25 October 1996 are analyzed. We
present spectra taken at locations on the solar disk where part of the spectrometer slit intersects a polar coronal hole region
and an area of brighter emission from outside of the coronal hole area. By comparing the line intensities between the parts
of the spectrum taken inside the "dark" area of the coronal holes and the brighter regions, we work out the signatures of
the specific coronal hole in the chromosphere, transition region and lower corona. We find that emissions of neutral atom
lines, of which there are many in the spectrum of SUMER, show no difference between the coronal hole and the bright boundary
areas, whereas all ionized species show strong intensity enhancements, including the continuum emissions of carbon and hydrogen.
These enhancements are larger than in normal quiet Sun areas.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
5.
Klaus Wilhelm 《Space Science Reviews》2012,172(1-4):57-68
Observations of emission lines in the vacuum-ultraviolet spectral range with calibrated instrumentation provide crucial information on the prevailing plasma temperatures in the solar atmosphere. Coronal-hole temperatures measured by the SUMER spectrometer on SOHO will be presented in this contribution. Electron temperatures can be estimated from the formation temperatures of the observed emission lines. Line-ratio and emission-measure analyses, however, offer higher accuracies. Typical electron temperatures at altitudes of H<200?Mm in coronal holes are below 1?MK in bright structures—the coronal plumes—with higher values in darker areas—the inter-plume regions. Line-width measurements yield effective ion temperatures, which are much higher than the electron temperatures. Observations of line profiles emitted from species with different masses allow a separation of the effective temperatures into ion temperatures and unresolved non-thermal motions along the line of sight. 相似文献
6.
The discovery of polygonal terrain on Mars underlain by ice heightens interest in the possibility that this water-bearing habitat may be, or may have been, a suitable habitat for extant life. The possibility is supported by the recurring detection of terrestrial microorganisms in subsurface ice environments, such as ice wedges found beneath tundra polygon features. A characterization of the microbial community of ice wedges from the high Arctic was performed to determine whether this ice environment can sustain actively respiring microorganisms and to assess the ecology of this extreme niche. We found that ice wedge samples contained a relatively abundant number of culturable cells compared to other ice habitats (~10(5) CFU·mL(-1)). Respiration assays in which radio-labeled acetate and in situ measurement of CO(2) flux were used suggested low levels of microbial activity, though more sensitive techniques are required to confirm these findings. Based on 16S rRNA gene pyrosequencing, bacterial and archaeal ice wedge communities appeared to reflect surrounding soil communities. Two Pseudomonas sp. were the most abundant taxa in the ice wedge bacterial library (~50%), while taxa related to ammonia-oxidizing Thaumarchaeota occupied 90% of the archaeal library. The tolerance of a variety of isolates to salinity and temperature revealed characteristics of a psychrotolerant, halotolerant community. Our findings support the hypothesis that ice wedges are capable of sustaining a diverse, plausibly active microbial community. As such, ice wedges, compared to other forms of less habitable ground ice, could serve as a reservoir for life on permanently cold, water-scarce, ice-rich extraterrestrial bodies and are therefore of interest to astrobiologists and ecologists alike. . 相似文献
7.
K. Stucki S.K. Solanki I. Rüedi J.O. Stenflo A. Brković U. Schühle K. Wilhelm M.C.E. Huber 《Space Science Reviews》1999,87(1-2):315-318
We analyze SUMER spectra of 14 lines belonging to 12 ions, obtained on both sides of the boundary of polar coronal holes as
well as at other locations along the limb. We compare line intensities, shifts and widths in coronal holes with values obtained
in the quiet Sun. We find that with increasing formation temperature, spectral lines show an increasingly stronger blueshift
in coronal holes relative to the quiet Sun at an equal heliospheric angle. The width of the lines is generally larger (by
a few km/s) inside the coronal hole. Intensity measurements show the presence of the coronal hole in Ne VIII lines as well
as in Fe XII, with evidence for a slightly enhanced emission in polar coronal holes for lines formed below 105 K.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
Two studies performed with SUMER (the Solar Ultraviolet Measurements of Emitted Radiation spectrometer on SOHO) in September
1996 are presented. Spatial scans, a long exposure time and a broad spectral window provide reliable line profiles for various
regions of the Sun (off-limb corona, coronal hole, quiet Sun, bright and dark regions on disk) and for different formation
temperatures (Si II, 14 000 K; C IV, 100 000 K; Ne VIII, 630 000 K). Line intensity, position and width distributions are
presented together with the line positions relative to the wavelength seen above the limb.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
9.
P. Lemaire K. Wilhelm U. Schühle W. Curdt A.I. Poland S.D. Jordan R.J. Thomas D.M. Hassler J.-C. Vial 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,20(12):2249-2258
The increase of our understanding of the processes acting in the solar corona and maintaining it is strongly dependent on the quality of the data that are obtained to check theories. The fine structure of the solar atmosphere seen from the photosphere and extending to the hottest parts of the corona requires data with high resolution in all parameter space (angular, spectral and temporal). To constrain the hypotheses that are proposed to describe the solar corona, it is necessary to establish an accurate energy budget taking into account the processes which are acting from the chromosphere to the corona. Some requirements can be established and compared with the data collected so far (or about to be collected) with the present SUMER (Solar Utraviolet Measurements of Emitted Radiations) instrumentation. 相似文献
10.
Klaus Wilhelm Eckart Marsch Bhola N. Dwivedi Uri Feldman 《Space Science Reviews》2007,133(1-4):103-179
In Part I of this review, the concepts of solar vacuum-ultraviolet (VUV) observations were outlined together with a discussion
of the space instrumentation used for the investigations. A section on spectroradiometry provided some quantitative results
on the solar VUV radiation without considering any details of the solar phenomena leading to the radiation. Here, in Part
II, we present solar VUV observations over the last decades and their interpretations in terms of the plasma processes and
the parameters of the solar atmosphere, with emphasis on the spatial and thermal structures of the chromosphere, transition
region and corona of the quiet Sun. In addition, observations of active regions, solar flares and prominences are included
as well as of small-scale events. Special sections are devoted to the elemental composition of the solar atmosphere and theoretical
considerations on the heating of the corona and the generation of the solar wind. 相似文献