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1.
Brynildsen N. Brekke P. Fredvik T. Haugan S. V. H. Kjeldseth-Moe O. Maltby P. Harrison R. A. Pike C. D. Rimmele T. Thompson W. T. Wilhelm K. 《Solar physics》1998,179(2):279-312
We have studied the dynamics in the sunspot transition region between the chromosphere and the corona and investigated the extension of the flow field into the corona. Based on EUV spectra of a medium size sunspot and its surroundings, NOAA 7981, observed with CDS and SUMER on SOHO, we derive line-of-sight velocities and study the line profiles for a series of emission lines.The flow field in the low corona is found to differ markedly from that in the transition region. In the transition region the relative line-of-sight velocity shows an upflow in the umbra and relatively large areas with downflow that cover part of the penumbra. The spatial extent of these areas with upflow and downflow increases with increasing temperature in the transition region, but the whole flow field changes character as the temperature increases from the upper transition region to the low corona. Based on a calibration of the SUMER wavelength scale we find that the entire sunspot transition zone appears to be moving downwards towards the chromosphere. The relation between this finding and the general tendency for transition-region lines to show a net red shift is discussed.Several of the transition-region spectral line profiles are observed to show two line components with Gaussian shape and line-of-sight velocities that differ markedly. Several of the line profiles that are composed of two spectral line components occur close to the dividing line between up- and downflow. A discussion of this observation is presented. In small regions with spatial extent of a few arc sec we detect enhanced continuum emission underlying explosive events. The similarities between explosive events with continuum emission and the moustaches observed in H close to sunspots are so striking that we are tempted to introduce the notation transition-region moustaches. 相似文献
2.
Peter G. Brewer Edward Peltzer Izuo Aya Peter Haugan Richard Bellerby Kenji Yamane Ryuji Kojima Peter Walz Yasuharu Nakajima 《Journal of Oceanography》2004,60(4):751-758
We have carried out a small-scale (∼20 l) CO2 sequestration experiment off northern California (684 m depth, ∼5°C, background ocean pH ∼7.7) designed as an initial investigation
of the effects of physical forcing of the fluid, and the problem of sensing the formation of a low pH plume. The buoyant CO2 was contained in a square frame 1.2 m high, exposing 0.21 m2 to ocean flow. Two pH electrodes attached to the frame recorded the signal; a second frame placed 1.9 m south of the CO2 pool was also equipped with two recording pH electrodes. An additional pH electrode was held in the ROV robotic arm to probe
the fluid interface. Local water velocities of up to 40 cm sec−1 were encountered, creating significant eddies within the CO2 box, and forcing wavelets at the fluid interface. This resulted in rapid CO2 dissolution, with all CO2 being depleted in a little more than 2 days. The pH record from the sensor closest (∼10 cm) to the CO2 showed many spikes of low pH water, the extreme value being ∼5.9. The sensor 1 m immediately below this showed no detectable
response. The electrodes placed 1.9 m distant from the source also recorded very small perturbations. The results provide
important clues for the design of future experiments for CO2 disposal and biogeochemical impact studies. These include the need for dealing with the slow CO2 hydration kinetics, better understanding of the fluid dynamics of the CO2-water interface, and non-point source release designs to provide more constant, controlled local CO2 enrichments within the experimental area.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
The narrow slope-confined warm core of the West Spitsbergen Current (WSC) is a major pathway for warm and saline Atlantic Water to enter the Arctic Ocean. Long-term mean northward cooling and freshening rates in the warm core of the WSC are calculated with error ranges, and heat loss estimates are derived. The observed combination of cooling and freshening is not consistent with a hypothesis of pure isopycnal offshore mixing, but rather suggests influence from diapycnal mixing connected, for example, to exchange with shelf waters. 相似文献
4.
Brynildsen N. Brekke P. Fredvik T. Haugan S. V. H. Kjeldseth-Moe O. Maltby P. Harrison R. A. Wilhelm K. 《Solar physics》1998,181(1):23-50
We present high spatial and spectral resolution observations of one active and one quiet-Sun region, obtained with CDS and SUMER on SOHO. The connections between the line profile parameters are studied and a systematic wavelength shift towards the red with increasing peak line intensity (line broadening) is detected. The large scatter in the data calls for another approach. We apply conditional probability analysis to a series of EUV emission lines and find significant correlations between line profile parameters. For a given interval in wavelength shift we find that: (1) line profiles with large intensities (line widths) and red shifts above the average constitute an increasing fraction of the profiles as the relative wavelength shift increases, (2) line profiles with large intensities (line widths) and blue shifts compared to the average, on the other hand, constitute a decreasing fraction of the profiles as the relative wavelength shift increases. These results extend the findings of an earlier quiet-Sun study from one to several emission lines and expand the validity to include the active region. Interestingly, the active region observations show correlations between peak line intensity and wavelength shift in the coronal lines.The tendency for red-shifted profiles to be more intense than blue-shifted profiles will shift line profiles derived by integrating along the slit towards the red. From the present observations we are not able to determine the fraction of the net red shift that emerges from this correlation. We suggest that the same mechanism is responsible both for the correlation between the line profile parameters and for the differential red shift between the transition region and chromospheric emission lines. 相似文献
5.
The focussing of gravitational radiation by the interior and exterior gravitational field of a Newtonian gravitational lens
is considered. A graphical method for determining the caustic structure of a Newtonian gravitational lens is presented and
the caustic structure of a solar type gravitational lens is discussed. Estimates of the amplitude magnification in the caustic
region indicate that waves with frequencies less than a critical cutoff frequency ω
c
are not amplified significantly. For a lens of massM this cutoff frequency is ω
c
≈(10-1πM)-1; for the Sun ω
c
≈104s-1.
Work supported in part by National Science Foundation Grant PHY78-05368. 相似文献
6.
N. Brynildsen P. Brekke T. Fredvik S. V. H. Haugan O. Kjeldseth-Moe P. Maltby R. A. Harrison C. D. Pike T. Rimmele W. T. Thompson K. Wilhelm 《Solar physics》1998,179(1):43-74
EUV spectra of a medium-size sunspot and its surroundings, NOAA 7981, were obtained on 2 August 1996 with the Coronal Diagnostic Spectrometer (CDS) and the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) on the Solar and Heliospheric Observatory (SOHO). The spectral lines formed in the transition region and corona show considerable structure and large deviations from a uniform spatial distribution over the active region. Enhanced EUV emissions in transition region lines are concentrated in small regions outside the umbra of the sunspot throughout most of the observing sequence. Only during a short, active period do we find an enhanced line emission that reaches into the umbra. Preliminary values for the umbral intensity are given.Marked changes are detected between the spatial distribution of line emission in the transition region and the low corona. The difference is not limited to cool and hot non-flaring loops not being cospatial, but includes differences both regarding the time variability and the orientation and size of the emission features. Whereas both rapid ( 4 and 2 min) and slow ( 10 and 12 h) temporal variations are found in the chromosphere (Hei 584 Ú) and transition region (Ov 629 Ú), the response in the low corona (Mgix 368 Ú) is slow ( 5 h). Furthermore, marked differences between the spatial distributions in the Mgviii 315 Ú, Mgix 368 Ú lines formed in the low corona and the coronal Fexiv 334 Ú, Fexvi 360 Ú lines are detected. 相似文献
7.
Brynildsen N. Maltby P. Brekke P. Haugan S.V.H. Kjeldseth-Moe O. 《Solar physics》1999,186(1-2):141-191
We present results from a study of the spatial distributions of line emission and relative line-of-sight velocity in the atmosphere above 17 sunspot regions, from the chromosphere, through the transition region and into the corona, based on simultaneous observations of ten EUV emission lines with the Coronal Diagnostic Spectrometer – CDS on SOHO. We find that the spatial distributions are nonuniform over the sunspot region and introduce the notation 'sunspot loop' to describe an enhanced transition region emission feature that looks like a magnetic loop, extending from inside the sunspot to the surrounding regions. We find little evidence for the siphon flow. Attention is given to the time variations since we observe both a rapid variation with a characteristic time of a few to several minutes and a slow variation with a time constant of several hours to 1 day. The most prominent features in the transition region intensity maps are the sunspot plumes. We introduce an updated criterion for the presence of plumes and find that 15 out of 17 sunspots contain a plume in the temperature range logT5.2–5.6. The relative line-of-sight velocity in sunspot plumes is high and directed into the Sun in the transition region. Almost all the sunspot regions contain one or a few prominent, strongly redshifted velocity channels, several of the channels extend from the sunspot plume to considerable distances from the sunspot. The flow appears to be maintained by plasmas at transition region temperatures, moving from regions located at a greater height outside the sunspots and towards the sunspot. The spatial correlation is high to moderate between emission lines formed in the transition region lines, but low between the transition region lines and the coronal lines. From detailed comparisons of intensity and velocity maps we find transition region emission features without any sign of coronal emission in the vicinity. A possible explanation is that the emission originates in magnetic flux tubes that are too cold to emit coronal emission. The comparisons suggest that gas at transition region temperature occur in loops different from loops with coronal temperature. However, we cannot exclude the presence of transition region temperatures close to the footpoints of flux tubes emitting at coronal temperatures. Regions with enhanced transition region line emission tend to be redshifted, but the correlation between line emission and relative line-of-sight velocity is weak. We extend our conditional probability studies and confirm that there is a tendency for line profiles with large intensities and red shifts (blue shifts) above the average to constitute an increasing (decreasing) fraction of the profiles as the wavelength shift increases. 相似文献
8.
Line shifts for some emission lines on the SOHO/CDS NIS detector appear to be strongly correlated with local intensity gradients along the slit in a way that seems impossible to explain with a physical solar model. Line widths also show a correlation with local intensity gradients. The most plausible instrumental explanation seems to be an elliptical, tilted point-spread function inducing the line shifts. A toy model demonstrating the essentials of the observed behaviour is presented. The effective point-spread function of the instrument appears to modify the line shape into something other than a Gaussian, leaving highly structured residuals after line fitting, including 'ghost' images in some pixel planes. The cause of these effects is yet unknown, but they should warrant experiments on the engineering model to reproduce the observed effects, shedding light on the nature of the aberrations. 相似文献
9.
Homogeneous, nonrotating flow over a backward-facing rounded step is simulated using the 2D vertical version of two general
circulation models, a z-coordinate model—the Massachusetts Institute of Technology general circulation model (MITgcm)—and a σ-coordinate model—the Bergen Ocean Model (BOM). The backward-facing step is a well-known testcase since it is geometrically
simple but still embodies important flow characteristics such as separation point, reattachment length, and recirculation
of the flow. The study compares the core of the two models and uses constant eddy viscosities and diffusivities. The Reynolds
numbers ranges from 2·102 to 2·106. The results correspond with previously published results having a relatively stationary separation point and a fluctuating
reattachment length due to downslope propagating eddies released from the reattachment zone for Reynolds numbers higher than
or equal to 2 · 104. For Reynolds number within the laminar regime, the flow is stationary. The discrepancies between the models increase by
enhancing Reynolds numbers. The σ-coordinate model experiences a reduction in eddy sizes with increasing resolution and Reynolds numbers in correspondence
with published experiments, while the size of the eddies are independent of the Reynolds number using the MITgcm. Due to mixing
generated by the staircase topography, the z-coordinate model gives a better convergence of the separation point and reattachment length compared with the BOM; however,
this conclusion might change with the inclusion of a relevant turbulence scheme. 相似文献
10.
Brekke P. Kjeldseth-Moe O. Brynildsen N. Maltby P. Haugan S. V. H. Harrison R. A. Thompson W. T. Pike C. D. 《Solar physics》1997,170(1):163-177
EUV spectra obtained with the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO) show significant flows of plasma in active region loops, both at coronal and transition region temperatures. Wavelength shifts in the coronal lines Mgix 368 Å and Mgx 624 Å corresponding to upflows in the plasma reaching velocities of 50 km s-1 have been observed in an active region. Smaller velocities are detected in the coronal lines Fexvi 360 Å and Sixii 520 Å. Flows reaching 100 km s-1 are observed in spectral lines formed at transition region temperatures, i.e., Ov 629 Å and Oiii 599 Å, demonstrating that both the transition region and the corona are clearly dynamic in nature. Some high velocity events show even higher velocities with line profiles corresponding to a velocity dispersion of 300–400 km s-1. Even in the quiet Sun there are velocity fluctuations of 20 km s-1 in transition region lines. Velocities of the magnitude presented in this paper have never previously been observed in coronal lines except in explosive events and flares. Thus, the preliminary results from the CDS spectrometer promise to put constraints on existing models of the flows and energy balance in the solar atmosphere. The present results are compared to previous attempts to observe flows in the corona. 相似文献