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21.
P. C. H. Martens G. D. R. Attrill A. R. Davey A. Engell S. Farid P. C. Grigis J. Kasper K. Korreck S. H. Saar A. Savcheva Y. Su P. Testa M. Wills-Davey P. N. Bernasconi N.-E. Raouafi V. A. Delouille J. F. Hochedez J. W. Cirtain C. E. DeForest R. A. Angryk I. De Moortel T. Wiegelmann M. K. Georgoulis R. T. J. McAteer R. P. Timmons 《Solar physics》2012,275(1-2):79-113
In Fall 2008 NASA selected a large international consortium to produce a comprehensive automated feature-recognition system for the Solar Dynamics Observatory (SDO). The SDO data that we consider are all of the Atmospheric Imaging Assembly (AIA) images plus surface magnetic-field images from the Helioseismic and Magnetic Imager (HMI). We produce robust, very efficient, professionally coded software modules that can keep up with the SDO data stream and detect, trace, and analyze numerous phenomena, including flares, sigmoids, filaments, coronal dimmings, polarity inversion lines, sunspots, X-ray bright points, active regions, coronal holes, EIT waves, coronal mass ejections (CMEs), coronal oscillations, and jets. We also track the emergence and evolution of magnetic elements down to the smallest detectable features and will provide at least four full-disk, nonlinear, force-free magnetic field extrapolations per day. The detection of CMEs and filaments is accomplished with Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph (LASCO) and ground-based Hα data, respectively. A?completely new software element is a trainable feature-detection module based on a generalized image-classification algorithm. Such a trainable module can be used to find features that have not yet been discovered (as, for example, sigmoids were in the pre-Yohkoh era). Our codes will produce entries in the Heliophysics Events Knowledgebase (HEK) as well as produce complete catalogs for results that are too numerous for inclusion in the HEK, such as the X-ray bright-point metadata. This will permit users to locate data on individual events as well as carry out statistical studies on large numbers of events, using the interface provided by the Virtual Solar Observatory. The operations concept for our computer vision system is that the data will be analyzed in near real time as soon as they arrive at the SDO Joint Science Operations Center and have undergone basic processing. This will allow the system to produce timely space-weather alerts and to guide the selection and production of quicklook images and movies, in addition to its prime mission of enabling solar science. We briefly describe the complex and unique data-processing pipeline, consisting of the hardware and control software required to handle the SDO data stream and accommodate the computer-vision modules, which has been set up at the Lockheed-Martin Space Astrophysics Laboratory (LMSAL), with an identical copy at the Smithsonian Astrophysical Observatory (SAO). 相似文献
22.
Jellyfish populations in the southeastern Atlantic off the coast of Namibia have increased subsequent to the decline of small pelagic fisheries at the end of the 1960s, although the environment there has also become warmer and the waters off Walvis Bay have become richer in zooplankton in recent years. Laboratory experiments were conducted with the scyphozoan jellyfish Chrysaora fulgida to investigate the effects of food density (0, 30, 70, 100 or 150 Artemia nauplii 200 ml?1), feeding frequency (once daily or once every third day) and water temperature (12, 16 or 20 °C) on the asexual reproduction, growth and development of polyps. The results of a generalised linear mixed-effects model reveal that all variables impacted asexual reproduction, with greater polyp production attained at higher food concentrations, increased feeding frequencies and increased temperatures. The most common mode of asexual reproduction was by lateral budding. These laboratory results suggest that polyps of C. fulgida may have proliferated off Namibia in recent times, which would contribute to increased numbers of jellyfish there. 相似文献
23.
Estuaries are regarded as valuable nursery habitats for many commercially important marine fishes, potentially providing a thermal resource, refuge from predators and a source of abundant prey. To assess the extent of estuarine use by juvenile (0+) common sole (Solea solea), whiting (Merlangius merlangus) and European seabass (Dicentrarchus labrax) we: (1) developed techniques to distinguish between estuarine and coastally-caught juveniles using otolith chemistry; and (2) examined the accuracy with which multi-elemental signatures could re-classify juveniles to their region of collection.High-resolution solution-based inductively coupled plasma mass spectrometry (HB-SB-ICPMS) was used to quantify 32 elements within the juvenile otoliths; 14 elements occurred above detection limits for all samples. Some elemental distributions demonstrated clear differences between estuarine and coastally-caught fish. Multivariate analysis of the otolith chemistry data resulted in 95–100% re-classification accuracy to the region of collection. Estuarine and coastal signatures were most clearly defined for sole which, compared to bass and whiting, have low mobility and are less likely to move from estuarine to coastal habitats between larval settlement and later migration to adult stocks. Sole were the only species to reveal an energetic benefit associated with an estuarine juvenile phase. The physiological ability of bass to access upper estuarine regions was consistent with some elemental data, while the high mobility and restricted range of whiting resulted in less distinct otolith chemistries. 相似文献
24.
Temperature (i.e. habitat at any given temperature) is an ecological resource for which organisms compete to maximise growth and other fitness measures, but the temperature (thermal habitat)-resource concept has not been widely applied to the study of estuarine fish. Temperature–abundance relationships for 16 fish and four invertebrate species from the Thames estuary were analysed to test hypotheses regarding temperature resource partitioning. Significant temperature–abundance models were apparent, explaining >65% of the variability in 13 fish species and 50% of variability in three invertebrate species. Fish demonstrated differential responses to temperature across the range. Invertebrates generally preferred warmer conditions than fish. Calculated thermal niche breadths indicated species preferenda spread across the recorded temperature range and some separation along the thermal niche axis within the same functional guild or taxonomic group. Calculated overlap coefficients and resource separation ratios provided some evidence for resource separation and demonstrated that species closely aligned on other niche axes (e.g. physical habitat use, feeding type) were most likely to be separated in terms of their use of thermal habitat resources, suggesting where other niche axes variables are not separating species, division of the temperature resources may be preventing competition between fish species. Few fish species demonstrated significant overlap with potential invertebrate prey, suggesting facultative use of the estuary to exploit optimal thermal habitat rather than food supply. The temporal migration pattern of fish in estuaries is therefore interpreted as a response to resource separation along the temperature axis which limits potential competition between functionally or taxonomically similar species. Thermal resource partitioning in estuaries has temporal rather than spatial dimensions and provides an example of the niche compression/expansion hypothesis. 相似文献
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26.
Ship-based acoustic Doppler current profiler (S-ADCP) technology, used in survey mode, has enabled near- synoptic views of the in situ 3-D current field in the KwaZulu-Natal (KZN) Bight to be elucidated for the first time. Data acquired by the research vessels RS Africana and RS Algoa in June 2005, September 2007, March 2009 and July 2010 are presented. Each S-ADCP dataset showed similar circulation characteristics whereby the continental slope and outer shelf of the KZN Bight were strongly influenced by the south-westward flowing Agulhas Current. This was particularly evident in the extreme north between Cape St Lucia and Richards Bay where the shelf is narrowest and velocities exceeded 200 cm s?1. The widening of the bight to the south moves the Agulhas Current further from the coast, resulting in a diminishing velocity gradient on the outer shelf which terminates around the midshelf axis. The southern region of the bight was mostly influenced by the Durban cyclonic eddy (Durban Eddy), and in June 2005 and September 2007, by a cyclonic ‘swirl’ that occupied the entire southern half of the KZN Bight, the latter identified by a combination of S-ADCP-, satellite-derived SST- and ocean colour data. Satellite data showed low-chlorophyll offshore water to move into this swirl and northwards along the inner- and midshelf, reaching the Thukela River. Inner-shelf circulation north of the Thukela River was weak (<20 cm s?1) and highly variable. Satellite-tracked surface drogues deployed in the Durban Eddy found their way into the northward coastal current in the KZN Bight, with velocities exceeding 90 cm s?1 at times. The drogues also highlighted the strong influence of wind, especially in the northern bight between Durnford Point and Cape St Lucia, with residence times on the shelf exceeding 14 days, suggesting this region to be of biological importance particularly for recruitment. 相似文献
27.
G. D. R. Attrill L. K. Harra L. van Driel-Gesztelyi M. J. Wills-Davey 《Solar physics》2010,264(1):119-147
We study two CME events on 13 and 14 December 2006 that were associated with large-scale dimmings. We study the eruptions
from pre-event on 11 December through the recovery on 15 December, using a combination of Hinode/EIS, SOHO/EIT, SOHO/MDI, and MLSO Hα data. The GOES X-class flares obscured the core dimmings, but secondary dimmings developed
remote from the active region (AR) in both events. The secondary dimmings are found to be formed by a removal of bright coronal
material from loops in the plage region to the East of the AR. Using Hinode/EIS data, we find that the outflows associated with the coronal-dimming regions are highly structured. The concentrated outflows
are located at the footpoints of coronal loops (which exist before, and are re-established after, the eruptions), and these
are correlated with regions of positive magnetic elements. Comparative study of the Hinode/EIS and SOHO/EIT data shows that the reduction in outflow velocity is consistent with the recovery in intensity of the studied
regions. We find that concentrated downflows develop during the recovery phase of the dimmings and are also correlated with
the same positive magnetic elements that were previously related to outflows. 相似文献
28.
C. H. Mandrini M. S. Nakwacki G. Attrill L. van Driel-Gesztelyi P. Démoulin S. Dasso H. Elliott 《Solar physics》2007,244(1-2):25-43
Coronal dimmings are often present on both sides of erupting magnetic configurations. It has been suggested that dimmings
mark the location of the footpoints of ejected flux ropes and, thus, their magnetic flux can be used as a proxy for the flux
involved in the ejection. If so, this quantity can be compared to the flux in the associated interplanetary magnetic cloud
to find clues about the origin of the ejected flux rope. In the context of this physical interpretation, we analyze the event,
flare, and coronal mass ejection (CME) that occurred in active region 10486 on 28 October 2003. The CME on this day is associated
with large-scale dimmings, located on either side of the main flaring region. We combine SOHO/Extreme Ultraviolet Imaging
Telescope data and Michelson Doppler Imager magnetic maps to identify and measure the flux in the dimming regions. We model
the associated cloud and compute its magnetic flux using in situ observations from the Magnetometer Instrument and the Solar Wind Electron Proton Alpha Monitor aboard the Advance Composition Explorer. We find that the magnetic fluxes of the dimmings and magnetic cloud are incompatible, in contrast to what has been found
in previous studies. We conclude that, in certain cases, especially in large-scale events and eruptions that occur in regions
that are not isolated from other flux concentrations, the interpretation of dimmings requires a deeper analysis of the global
magnetic configuration, since at least a fraction of the dimmed regions is formed by reconnection between the erupting field
and the surrounding magnetic structures. 相似文献
29.
L. M. Green B. Kliem T. Török L. van Driel-Gesztelyi G. D. R. Attrill 《Solar physics》2007,246(2):365-391
To determine the relationship between transient coronal (soft X-ray or EUV) sigmoids and erupting flux ropes, we analyse four
events in which a transient sigmoid could be associated with a filament whose apex rotates upon eruption and two further events
in which the two phenomena were spatially but not temporally coincident. We find the helicity sign of the erupting field and
the direction of filament rotation to be consistent with the conversion of twist into writhe under the ideal MHD constraint
of helicity conservation, thus supporting our assumption of flux rope topology for the rising filament. For positive (negative)
helicity the filament apex rotates clockwise (counterclockwise), consistent with the flux rope taking on a reverse (forward)
S shape, which is opposite to that observed for the sigmoid. This result is incompatible with two models for sigmoid formation:
one identifying sigmoids with upward arching kink-unstable flux ropes and one identifying sigmoids with a current layer between
two oppositely sheared arcades. We find instead that the observations agree well with the model by Titov and Démoulin (Astron. Astrophys.
351, 707, 1999), which identifies transient sigmoids with steepened current layers below rising flux ropes. 相似文献
30.
Rocas, the only atoll in the South Atlantic, is located 266 km off the northeast Brazilian coast. Spatial patterns in community structure of meiofauna, particularly nematodes, and macrofauna were examined along a transect through the sediment path from windward to leeward of the Rocas Atoll sand flat. Differences in benthic community structure between four zones of the sand flat were found to be significant and related to the major local processes of carbonate-grain transport and sedimentation. Both meiobenthic and macrobenthic assemblages were significantly more diverse and abundant within the sediment inflow zone (the initial part of the detrital path of Rocas sand flat) than in the other zones, where a clear impoverishment of benthic invertebrates occurred. This first study of the benthos of an intertidal sand flat over a reef island in the Atlantic showed that the meiofauna is numerically dominated by the nematodes Metoncholainussp. 1 (Oncholaimidae) and Epsilonema sp. 1 (Epsilonematidade), whilst the macrofauna is largely dominated by oligochaetes and large Oncholaimidae nematodes. Analysis of the species composition, trophic structure and abundance of both the meiobenthos and the macrobenthos revealed an impoverished community subjected to an intense water-movement disturbance. 相似文献