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1.
S. P. Plunkett G. E. Brueckner K. P. Dere R. A. Howard M. J. Koomen C. M. Korendyke D. J. Michels J. D. Moses N. E. Moulton S. E. Paswaters O. C. St. Cyr D. G. Socker D. Wang G. M. Simnett D. K. Bedford D. A. Biesecker C. J. Eyles S. J. Tappin R. Schwenn P. L. Lamy A. Llebaria 《Solar physics》1997,175(2):699-718
We report observations by the Large Angle Spectrometric Coronagraph (LASCO) on the SOHO spacecraft of three coronal green-line
transients that could be clearly associated with coronal mass ejections (CMEs) detected in Thomson-scattered white light.
Two of these events, with speeds >25 km s-1, may be classified as ‘whip-like’ transients. They are associated with the core of the white-light CMEs, identified with
erupting prominence material, rather than with the leading edge of the CMEs. The third green-line transient has a markedly
different appearance and is more gradual than the other two, with a projected outward speed <10 km s-1. This event corresponds to the leading edge of a ‘streamer blowout’ type of CME. A dark void is left behind in the emission-line
corona following each of the fast eruptions. Both fast emission-line transients start off as a loop structure rising up from
close to the solar surface. We suggest that the driving mechanism for these events may be the emergence of new bipolar magnetic
regions on the surface of the Sun, which destabilize the ambient corona and cause an eruption. The possible relationship of
these events to recent X-ray observations of CMEs is briefly discussed.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004981125702 相似文献
2.
Korendyke C.M. Vourlidas A. Cook J.W. Dere K.P. Howard R.A. Morrill J.S. Moses J.D. Moulton N.E. Socker D.G. 《Solar physics》2001,200(1-2):63-73
The Very-high-resolution Advanced ULtraviolet Telescope (VAULT) experiment was successfully launched on 7 May 1999 on a Black Brant sounding rocket vehicle from White Sands Missile Range. The instrument consists of a 30 cm UV diffraction limited telescope followed by a two-grating, zero-dispersion spectroheliograph tuned to isolate the solar L emission line. During the flight, the instrument successfully obtained a series of images of the upper chromosphere with a limiting resolution of 0.33 arc sec. The resulting observations are the highest-resolution images of the solar atmosphere obtained from space to date. The flight demonstrated that sub-arc second ultraviolet images of the solar atmosphere are achievable with a high-quality, moderate-aperture space telescope and associated optics. Herein, we describe the payload and its in-flight performance. 相似文献
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4.
Gowri Srinivasan Elizabeth Keating John David Moulton Zora V. Dash Bruce A. Robinson 《Computational Geosciences》2012,16(3):551-563
A convolution-based particle tracking (CBPT) method was recently developed for calculating solute concentrations (Robinson
et al., Comput Geosci 14(4): 779–792, 2010). This method is highly efficient but limited to steady-state flow conditions. Here, we present an extension of this method
to transient flow conditions. This extension requires a single-particle tracking process model run, with a pulse of particles
introduced at a sequence of times for each source location. The number and interval of particle releases depends upon the
transients in the flow. Numerical convolution of particle paths obtained at each release time and location with a time-varying
source term is performed to yield the shape of the plume. Many factors controlling transport such as variation in source terms,
radioactive decay, and in some cases linear processes such as sorption and diffusion into dead-end pores can be simulated
in the convolution step for Monte Carlo-based analysis of transport uncertainty. We demonstrate the efficiency of the transient
CBPT method, by showing that it requires fewer particles than traditional random walk particle tracking methods to achieve
the same levels of accuracy, especially as the source term increases in duration or is uncertain. Since flow calculations
under transient conditions are often very expensive, this is a computationally efficient yet accurate method. 相似文献
5.
K. P. Dere G. E. Brueckner R. A. Howard M. J. Koomen C. M. Korendyke R. W. Kreplin D. J. Michels J. D. Moses N. E. Moulton D. G. Socker O. C. St. Cyr J. P. Delaboudinière G. E. Artzner J. Brunaud A. H. Gabriel J. F. Hochedez F. Millier X. Y. Song J. P. Chauvineau J. P. Marioge J. M. Defise C. Jamar P. Rochus R. C. Catura J. R. Lemen J. B. Gurman W. Neupert F. Clette P. Cugnon E. L. Van Dessel P. L. Lamy A. Llebaria R. Schwenn G. M. Simnett 《Solar physics》1997,175(2):601-612
We present the first observations of the initiation of a coronal mass ejection (CME) seen on the disk of the Sun. Observations
with the EIT experiment on SOHO show that the CME began in a small volume and was initially associated with slow motions of
prominence material and a small brightening at one end of the prominence. Shortly afterward, the prominence was accelerated
to about 100 km s-1 and was preceded by a bright loop-like structure, which surrounded an emission void, that traveled out into the corona at
a velocity of 200–400 km s-1. These three components, the prominence, the dark void, and the bright loops are typical of CMEs when seen at distance in
the corona and here are shown to be present at the earliest stages of the CME. The event was later observed to traverse the
LASCO coronagraphs fields of view from 1.1 to 30 R⊙. Of particular interest is the fact that this large-scale event, spanning
as much as 70 deg in latitude, originated in a volume with dimensions of roughly 35" (2.5 x 104 km). Further, a disturbance that propagated across the disk and a chain of activity near the limb may also be associated
with this event as well as a considerable degree of activity near the west limb. 相似文献
6.
Surfzone bathymetry often is resolved poorly in time because watercraft surveys cannot be performed when waves are large, and remote sensing techniques have limited vertical accuracy. However, accurate high-frequency bathymetric information at fixed locations can be obtained from altimeters that sample nearly continuously, even during storms. A method is developed to generate temporally and spatially dense maps of evolving surfzone bathymetry by updating infrequent spatially dense watercraft surveys with the bathymetric change measured by a spatially sparse array of nearly continuously sampling altimeters. The update method is applied to observations of the evolution of shore-perpendicular rip current channels (dredged in Duck, NC, 2012) and shore-parallel sandbars (observed in Duck, NC, 1994). The updated maps are compared with maps made by temporally interpolating the watercraft surveys, and with maps made by spatially interpolating the altimeter measurements at any given time. Updated maps of the surfzone rip channels and sandbars are more accurate than maps obtained by using either only watercraft surveys or only the altimeter measurements. Hourly altimeter-updated bathymetric estimates of five rip channels show rapid migration and infill events not resolved by watercraft surveys alone. For a 2-month observational record of sandbars, altimeter-updated maps every 6 h between nearly daily surveys improve the time resolution of rapid bar-migration events. 相似文献
7.
Martim A.B. Moulton Patrick A. Hesp Graziela Miot da Silva Camille Bouchez Muriel Lavy Guilherme B. Fernandez 《地球表面变化过程与地形》2019,44(2):459-470
Studies have shown that the impact of climate change, human and animal actions on coastal vegetation can turn stabilized dunes into active mobile dunes and vice versa. Yet, the driving factors that trigger vegetation changes in coastal dunes are still not fully understood. In the transgressive dunefields of the Younghusband Peninsula (south-east coast of South Australia) historical aerial photographs show an increase in vegetation cover over the last ~70 years. This study attempts to identify the causes of the changes in vegetation cover (1949 to 2017) observed in a typical section of the coastal dune systems of the Peninsula. Vegetation cover was first estimated for various years using the available historical aerial photography (long-term changes – 1949 to 2017) and recent satellite imagery (short-term annual changes – 2010 to 2017) for the area, and then results were discussed against the observed changes in climatic variables and rabbit density, factors that could have played a role in this transformation. Results of long-term changes show that the vegetation cover has increased significantly from 1949 to 2017, from less than 7% vegetation cover to almost 40%, increasing dune stabilization and forming parabolic dune systems. Periods with the largest growth in vegetation cover (1952-1956 and 2009-2013) coincide with a significant decline in rabbit numbers. Rabbit density was found to be the primary factor linked to the rapid vegetation growth and stabilization of the dunefield, for both decadal long-term (last 68 years) and annual short-term changes (last 8 years). Other factors such as changes in rainfall, aeolian sediment transport, land use practices, and the introduction of invasive plants have apparently played a limited to negligible role in this stabilization process. © 2018 John Wiley & Sons, Ltd. 相似文献
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R. Schwenn B. Inhester S. P. Plunkett A. Epple B. Podlipnik D. K. Bedford C. J. Eyles G. M. Simnett S. J. Tappin M. V. Bout P. L. Lamy A. Llebaria G. E. Brueckner K. P. Dere R. A. Howard M. J. Koomen C. M. Korendyke D. J. Michels J. D. Moses N. E. Moulton S. E. Paswaters D. G. Socker O. C. St. Cyr D. Wang 《Solar physics》1997,175(2):667-684
The newly developed C1 coronagraph as part of the Large-Angle Spectroscopic Coronagraph (LASCO) on board the SOHO spacecraft
has been operating since January 29, 1996. We present observations obtained in the first three months of operation. The green-line
emission corona can be made visible throughout the instrument's full field of view, i.e., from 1.1 R⊙ out to 3.2 R⊙ (measured
from Sun center). Quantitative evaluations based on calibrations cannot yet be performed, but some basic signatures show up
even now: (1) There are often bright and apparently closed loop systems centered at latitudes of 30° to 45° in both hemispheres.
Their helmet-like extensions are bent towards the equatorial plane. Farther out, they merge into one large equatorial ‘streamer
sheet’ clearly discernible out to 32 R⊙. (2) At mid latitudes a more diffuse pattern is usually visible, well separated from
the high-latitude loops and with very pronounced variability. (3) All high-latitude structures remain stable on time scales
of several days, and no signature of transient disruption of high-latitude streamers was observed in these early data. (4)
Within the first 4 months of observation, only one single ‘fast’ feature was observed moving outward at a speed of 70 km s-1 close to the equator. Faster events may have escaped attention because of data gaps. (5) The centers of high-latitude loops
are usually found at the positions of magnetic neutral lines in photospheric magnetograms. The large-scale streamer structure
follows the magnetic pattern fairly precisely. Based on our observations we conclude that the shape and stability of the heliospheric
current sheet at solar activity minimum are probably due to high-latitude streamers rather than to the near-equatorial activity
belt.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004948913883 相似文献
10.
Ahmad Jan Ethan T. Coon Scott L. Painter Rao Garimella J. David Moulton 《Computational Geosciences》2018,22(1):163-177
Integrated surface/subsurface models for simulating the thermal hydrology of permafrost-affected regions in a warming climate have recently become available, but computational demands of those new process-rich simu- lation tools have thus far limited their applications to one-dimensional or small two-dimensional simulations. We present a mixed-dimensional model structure for efficiently simulating surface/subsurface thermal hydrology in low-relief permafrost regions at watershed scales. The approach replaces a full three-dimensional system with a two-dimensional overland thermal hydrology system and a family of one-dimensional vertical columns, where each column represents a fully coupled surface/subsurface thermal hydrology system without lateral flow. The system is then operator split, sequentially updating the overland flow system without sources and the one-dimensional columns without lateral flows. We show that the app- roach is highly scalable, supports subcycling of different processes, and compares well with the corresponding fully three-dimensional representation at significantly less computational cost. Those advances enable recently developed representations of freezing soil physics to be coupled with thermal overland flow and surface energy balance at scales of 100s of meters. Although developed and demonstrated for permafrost thermal hydrology, the mixed-dimensional model structure is applicable to integrated surface/subsurface thermal hydrology in general. 相似文献