排序方式: 共有11条查询结果,搜索用时 31 毫秒
1.
Ryan S. King William V. Deluca Dennis F. Whigham Peter P. Marra 《Estuaries and Coasts》2007,30(3):469-481
The invasion of North American tidal marshes byPhragmites australis, or common reed, is a large-scale ecological problem that has been primarily studied at small spatial scales. Previous local-scale
studies have provided evidence that the expansion ofPhragmites is facilitated by disturbance and increased nitrogen (N) associated with agricultural and urban-suburban (developed) land
uses along wetland-upland borders. We tested the generality of previous findings across a larger spatial scale and wider range
of environmental conditions in Chesapeake Bay, the largest estuarine ecosystem in the USA. We sampled 90 tidal wetlands nested
within 30 distinct subestuarine watersheds and examined the relationship between land use andPhragmites abundance and foliar N, an indicator of nitrogen availability. We estimated land use adjacent to wetland borders and within
subestuary watersheds and explored the importance of spatial proximity by weighting land use by its distance from the wetland
border or subestuary shoreline, respectively. Regression tree and changepoint analyses revealed thatPhragmites abundance sharply increased in almost every wetland where development adjacent to borders exceeded 15%. Where development
was <15% but natural land cover at the near the subestuary shoreline was low (<∼35%),Phragmites was abundant, suggesting that wetlands in highly modified watersheds also were susceptible to invasion, regardless of land
use adjacent to wetlands.Phragmites foliar N was markedly elevated in watersheds with >14–22% shoreline development, the same level of development that corresponded
to high levels of invasion. Our results suggest that development near wetlands is at least partially responsible for patterns
of invasion across Chesapeake Bay. Larger-scale phenomena, such as nitrogen pollution at the watershed-subestuary scale, also
may be facilitating invasion. Urbanization near coastlines appears to play an important role in the invasion success ofPhragmites in coastal wetlands of Chesapeake Bay and probably much of eastern North America. 相似文献
2.
TRACE observations from 15 April 2001 of transverse oscillations in coronal loops of a post-flare loop arcade are investigated. They are considered to be standing fast kink oscillations. Oscillation signatures such as displacement amplitude, period, phase and damping time are deduced from 9 loops as a function of distance along the loop length. Multiple oscillation modes are found with different amplitude profile along the loop length, suggesting the presence of a second harmonic. The damping times are consistent with the hypothesis of phase mixing and resonant absorption, although there is a clear bias towards longer damping times compared with previous studies. The coronal magnetic field strength and coronal shear viscosity in the loop arcade are derived. 相似文献
3.
C. H. Mandrini P. Demoulin B. Schmieder E. E. Deluca E. Pariat W. Uddin 《Solar physics》2006,238(2):293-312
A major two-ribbon X17 flare occurred on 28 October 2003, starting at 11:01 UT in active region NOAA 10486. This flare was
accompanied by the eruption of a filament and by one of the fastest halo coronal mass ejections registered during the October–November
2003 strong activity period. We focus on the analysis of magnetic field (SOHO/MDI), chromospheric (NainiTal observatory and
TRACE), and coronal (TRACE) data obtained before and during the 28 October event. By combining our data analysis with a model
of the coronal magnetic field, we concentrate on the study of two events starting before the main flare. One of these events,
evident in TRACE images around one hour prior to the main flare, involves a localized magnetic reconnection process associated
with the presence of a coronal magnetic null point. This event extends as long as the major flare and we conclude that it
is independent from it. A second event, visible in Hα and TRACE images, simultaneous with the previous one, involves a large-scale
quadrupolar reconnection process that contributes to decrease the magnetic field tension in the overlaying field configuration;
this allows the filament to erupt in a way similar to that proposed by the breakout model, but with magnetic reconnection
occurring at Quasi-Separatrix Layers (QSLs) rather than at a magnetic null point.
Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users. 相似文献
4.
X-ray bright points are small dynamic loop structures that are observed all over the solar corona. The high spatial and temporal
resolution of the TRACE instrument allows bright points to be studied in much greater detail than previously possible. This
paper focuses on a specific bright point which occurred for about 20 hours on 13–14 June 1998 and examines its dynamic structure
in detail. This example suggests that the mechanisms that cause bright points to form and evolve are more complex than previously
thought. In this case, reconnection probably plays a major part during the formation and brightening of the loop structure.
However, later on the foot points rotate injecting twist into the bright point which may cause an instability to occur with
dynamic results.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1017907406350 相似文献
5.
Brigitte Schmieder Nicole Mein Yuanyong Deng Cristiana Dumitrache Jean-Marie Malherbe Joachim Staiger E. E. Deluca 《Solar physics》2004,223(1):119-141
This paper is focused on the formation of two filaments in a complex center of decaying active regions (AR 8329 and AR 8326), located in the northern hemisphere. The observations were obtained in Hα by the Multi-channel Subtractive Double Pass spectrograph (MSDP mounted on the German telescope VTT in Tenerife) and EUV lines with TRACE (Transition Region And Corona Explorer). High Doppler shifts are found to be related to the ends of filament segments where canceling magnetic fields are also located (as seen on magnetograms from Big Bear Solar Observatory). At these locations, velocities along the line of sight, derived by using a cloud model method reach −20 km s−1, the segments of filaments merge and frequently a time-related sub-flare is observed by TRACE. The chirality of the filament segments has been determined by different methods: the segments of dextral chirality join together and form a long dextral filament, and a single filament of sinistral chirality forms end to end with the dextral filament but does not merge with it. Assuming a model of twisted flux tube for filament material, we suggest that the dextral filament has negative helicity and a relationship between its formation and the close by sunspot with the same sign of helicity. 相似文献
6.
Fitting and goodness-of-fit test of non-truncated and truncated power-law distributions 总被引:1,自引:0,他引:1
Recently, Clauset, Shalizi, and Newman have proposed a systematic method to find over which range (if any) a certain distribution behaves as a power law. However, their method has been found to fail, in the sense that true (simulated) power-law tails are not recognized as such in some instances, and then the power-law hypothesis is rejected. Moreover, the method does not work well when extended to power-law distributions with an upper truncation. We explain in detail a similar but alternative procedure, valid for truncated as well as for non-truncated power-law distributions, based in maximum likelihood estimation, the Kolmogorov-Smirnov goodness-of-fit test, and Monte Carlo simulations. An overview of the main concepts as well as a recipe for their practical implementation is provided. The performance of our method is put to test on several empirical data which were previously analyzed with less systematic approaches. We find the functioning of the method very satisfactory. 相似文献
7.
All of the Hinode telemetry data are to be reformatted and archived in the DARTS system at ISAS and mirrored to data centers around the word.
The archived data are distributed to users through the Internet. This paper gives an overview of the files in the archive,
including the file formats. All formats are portable and have heritage from the previous missions. From the reformatted files,
index information is created for faster data search. Users can perform queries based on information contained in the index.
This allows for searches to return observations that conform to particular observing conditions. 相似文献
8.
The transition region and coronal explorer 总被引:5,自引:0,他引:5
Handy B.N. Acton L.W. Kankelborg C.C. Wolfson C.J. Akin D.J. Bruner M.E. Caravalho R. Catura R.C. Chevalier R. Duncan D.W. Edwards C.G. Feinstein C.N. Freeland S.L. Friedlaender F.M. Hoffmann C.H. Hurlburt N.E. Jurcevich B.K. Katz N.L. Kelly G.A. Lemen J.R. Levay M. Lindgren R.W. Mathur D.P. Meyer S.B. Morrison S.J. Morrison M.D. Nightingale R.W. Pope T.P. Rehse R.A. Schrijver C.J. Shine R.A. Shing L. Strong K.T. Tarbell T.D. Title A.M. Torgerson D.D. Golub L. Bookbinder J.A. Caldwell D. Cheimets P.N. Davis W.N. Deluca E.E. McMullen R.A. Warren H.P. Amato D. Fisher R. Maldonado H. Parkinson C. 《Solar physics》1999,187(2):229-260
The Transition Region and Coronal Explorer (TRACE) satellite, launched 2 April 1998, is a NASA Small Explorer (SMEX) that
images the solar photosphere, transition region and corona with unprecedented spatial resolution and temporal continuity.
To provide continuous coverage of solar phenomena, TRACE is located in a sun-synchronous polar orbit. The ∼700 Mbytes of data
which are collected daily are made available for unrestricted use within a few days of observation. The instrument features
a 30-cm Cassegrain telescope with a field of view of 8.5×.5 arc min and a spatial resolution of 1 arc sec (0.5 arc sec pixels).
TRACE contains multilayer optics and a lumogen-coated CCD detector to record three EUV wavelengths and several UV wavelengths.
It observes plasmas at selected temperatures from 6000 K to 10 MK with a typical temporal resolution of less than 1 min. 相似文献
9.
Brigitte Schmieder Nicole Mein Yuanyong Deng Cristiana Dumitrache Jean-Marie Malherbe Joachim Staiger E. E. Deluca 《Solar physics》2004,223(1-2):119-141
This paper is focused on the formation of two filaments in a complex center of decaying active regions (AR 8329 and AR 8326), located in the northern hemisphere. The observations were obtained in Hα by the Multi-channel Subtractive Double Pass spectrograph (MSDP mounted on the German telescope VTT in Tenerife) and EUV lines with TRACE (Transition Region And Corona Explorer). High Doppler shifts are found to be related to the ends of filament segments where canceling magnetic fields are also located (as seen on magnetograms from Big Bear Solar Observatory). At these locations, velocities along the line of sight, derived by using a cloud model method reach −20 km s−1, the segments of filaments merge and frequently a time-related sub-flare is observed by TRACE. The chirality of the filament segments has been determined by different methods: the segments of dextral chirality join together and form a long dextral filament, and a single filament of sinistral chirality forms end to end with the dextral filament but does not merge with it. Assuming a model of twisted flux tube for filament material, we suggest that the dextral filament has negative helicity and a relationship between its formation and the close by sunspot with the same sign of helicity. 相似文献
10.
TRACE observations from 15 April 2001 of transverse oscillations in coronal loops of a post-flare loop arcade are investigated. They are considered to be standing fast kink oscillations. Oscillation signatures such as displacement amplitude, period, phase and damping time are deduced from 9 loops as a function of distance along the loop length. Multiple oscillation modes are found with different amplitude profile along the loop length, suggesting the presence of a second harmonic. The damping times are consistent with the hypothesis of phase mixing and resonant absorption, although there is a clear bias towards longer damping times compared with previous studies. The coronal magnetic field strength and coronal shear viscosity in the loop arcade are derived. 相似文献