We present high-resolution observations of the large active region BBSO No. 1167 (Boulder No. 5060) which cast new light on the structure of sunspot regions. We obtained excellent data, highlighted by videomagnetograms (VMG) obtained with our 65-cm telescope, which give unprecedented spatial resolution, about 0.5' for much of two 11-hr periods. This permitted us to see details of the field evolution and flows in the AR. The H filtergrams and D3 filtergrams permit study of these magnetic changes compared to spots and chromospheric structure.The region was a huge but simple active region (CMP July 2, 1988) in which we observed rapid flux emergence for several days. Because the new flux generally matched the old, there were few large flares. However, there were 14 flares on June 28 and 29, mostly in two sites. The first site was a spot which already existed when the active region appeared on the east limb. This site showed little change of magnetic structure during our observing period. The second site is an area disturbed by new flux emergence, which included a spot which formed and disappeared in two days, and a rapidly moving p spot. Flares ocurring at one site almost always produced footpoints at the other. The delay between flash phases of the same flare at the two sites ranges from 40 to 160 s.The magnetograms show complex fine structure, with some closely interwined regions of opposite polarity. In a region of new flux emergence, positive (leading polarity) flux flows along elongated channels immersed in the negative flux. Moving magnetic features occur around all of the spots.We point out other interesting aspects of this large region: (1) While there is extensive penumbra around the main umbrae, there is also significant penumbra apparently unrelated to any spot. These unusual penumbrae are either due to flux returning to the surface, flux left behind by the moving umbra, or associated with pores that appear and disappear. (2) We observed umbrae to move faster than the accompanying penumbrae, and concluded that penumbrae are not a simple extension of the umbra. (3) We found that combining spots of the same polarity do not completely merge, but are always separated by a thin light bridge. This means that the emerging flux loops are discrete entities. 相似文献
We analysed the hard X-ray and microwave flux spectra of the solar flare (BATSE No. 1791) on 2 November 1991, which started at 16:11:03 UT and ended at 16:56:10 UT. This flare is particularly interesting because of its deep cyclic intensity modulation. Data are available simultaneously from the 16-channel BATSE/LAD hard X-ray and 45-frequency OVRO microwave database. We quantitatively compare the time variations in profiles of the hard X-ray spectral photon index, the 50 keV X-ray flux, and microwave spectral indices (at both high and low frequency ends). As expected, the X-ray photon spectral index decreases as the hard X-ray flux increases. This pattern appears in all the sub-peaks. This is consistent with previous observations that hard X-ray emission hardens at the emission peak. However, the behaviour of the high-frequency microwave index is unexpected. We observe an anti-correlation between the high-frequency microwave index and the hard X-ray photon index during the course of the flare. Finally, we study the arrival time of microwave flux peaks as a function of frequency and find that the microwave peak at a higher frequency comes earlier than that at a lower frequency. A maximum delay of 72 s is found among the main peaks at different frequencies. Shorter delays are found for the other five sub-peaks. 相似文献
The zircon SHRIMP dating of the Zhangtiantang granite gave an age of 159±7 Ma., which shows that the granite was produced
at the early Late Jurassic. The Ar-Ar plateau ages of biotite and K-feldspar from the Zhangtiantang pluton are 153.2±1.1 Ma
and 135.8±1.2 Ma, respectively. The Ar-Ar anti-isochrone ages of biotite and K-feldspar are 152.5±1.7Ma and 135.4±2.7Ma, respectively.
The ages represent the isotopic closure ages of minerals in the pluton. The Zhangtiantang granites are regarded as peraluminous
crust-derived type granites to possess the typical geochemical characteristics of calc-alkaline rocks on continental margin,
with enriched Si, K, Al (average value of A/CNK as 1.18), HREE, Rb, U, and Th, heavily depleted V, Cr, Co, Ni, Ti, Nb-Ta,
Zr, Sr, P, and Ba, strongly negative Eu and common corundum normative (average value of C as 1.84). The εNd(t) values of the Zhangtiantang granite are −5.84 to −7.79, and t2DM values are 1.69 to 1.83 Ga, which indicates partial melting of continental-crust metamorphic sedimentary rocks during the
Middle Proterozoic.
The cooling history of the Zhangtiantang granitic pluton indicates that the cooling velocity of pluton was faster (about 67°C/Ma)
from zircon (158 Ma) to biotite (152 Ma), and was slower (about12°C/Ma) from biotite (152.5 Ma) to K-feldspar (135.8 Ma).
It can be deduced that the temporal gap (about 10 Ma) between the granite formmation and W-Sn mineralization in South China
may be related to ordinary magma-hydrothermal processes by the variational cooling curve of the pluton. The Zhangtiantang
pluton was formed in a compressive setting, with differentiation evolution and mineralization occurring in a relative relaxation
setting. 相似文献
An active region loop system was observed in a decaying active region for three hours by TRACE and BBSO in a joint campaign on September 27, 1998. Continuous mass motion was seen in Hα offband filtergrams throughout the three hours, and some UV loops were exhibited transient brightenings. We find that: (1) cool material was flowing along the loops at a speed of at least 20 km s?1. Further, in Hα red and blue wings, we see mass motion along different loops in opposite directions. This is the first report of a counter-streaming pattern of mass motion in an Hα loop system. (2) Transient brightenings of different UV loops at different times were observed at C?iv 1550 Å. These brightened UV loops were located in the same region and at the same altitudes as the Hα loops. The observations show a clear correlation between the transient brightenings of UV loops and mass motion in Hα loops. (3) Both footpoints of the loop system were located in regions of mixed magnetic polarities. Frequent micro-flares at one footpoint of the loops with small-scale brightenings spreading along the loop leg were observed before the brightening and rising of one C?iv loop. Similar to the case of a filament, the continuous mass motion along the loops seems important for maintaining the cool Hα loop system at coronal height. There may be an indication that the mass motion in cool Hα loops and the correlated transient brightening of the active region loops were due to the small-scale chromospheric magnetic reconnection at the footpoint regions of the loop system.
“Elementary bursts” refer to fine time structures on scales of tens of milli-second to a few seconds in flare radiations.
In this paper, we investigate temporal and spatial properties of elementary bursts by exploiting high-cadence Hα (100 ms)
and hard X-ray (125 – 500 ms) observations of an impulsive flare on March 16, 2000. We find that the time scale of 2 – 3 s
is likely an upper limit of the elementary bursts in this event, at which hard X-ray emissions observed by different instruments
correlate, low energy (≤30 keV) hard X-rays and Hα flux correlate, and Hα emissions at conjugate flare kernels correlate.
From our methods, and also largely limited by instrument resolutions, there is a weak indication of existence of sub-second
structures. With the high-resolution Hα data, we also attempt to explore the spatial structure of “elementary bursts” by determining
the average spatial displacement of Hα peak emission between successive “elementary bursts” defined from hard X-ray light
curves. We find that, at the time scale of 3 s, the smallest spatial scale, as limited by the imaging resolution, is about
0.4″. We discuss these results with respect to mechanisms of fragmented magnetic energy release. 相似文献
We studied the size, correlation lifetime and horizontal velocity amplitude of supergranules in regions with different magnetic activity. We found that the supergranule velocity cells have similar scale, correlation lifetime and horizontal velocity amplitude in the unipolar enhanced magnetic network regions and in the mixed-polarity quiet Sun. However, the correlation lifetime of magnetic structure is much longer in the enhanced network. We investigated the velocity pattern of moving magnetic features (MMF) surrounding a decaying sunspot. The velocity of MMFs is consistent with the outflow surrounding the sunspot as measured by Dopplergrams. The velocity cell surrounding the sunspot has a much larger velocity amplitude and a longer lifetime than regular supergranule cells. We found that ephemeral regions (ER) have a slight tendency to emerge at or near boundaries of supergranules. Almost all the magnetic flux disappears at the supergranule boundaries. In most cases, two poles of cancelling features with opposite magnetic polarities approach along the boundaries of supergranules. 相似文献
Applying spatial and temporal averaging techniques to several long sequences of Dopplergrams obtained at the solar disk center and near the limb, we confirmed the persistent supergranule velocity pattern. After excluding the 5-min oscillation and supergranule velocity fields from the disk center Doppler data, we find that the velocity structure shows a typical scale of 7 Mm, consistent with the scale of mesogranules found by November, Toomre, and Gebbie (1981) and November et al. (1982). However, this velocity pattern does not show properties of the cellular convection. It is not coherent for more than one hour, the period during which the raw Doppler images are averaged to remove the 5-min oscillation. Furthermore, we did not find convection patterns in the scale of mesogranules from the Doppler data obtained near the solar limb. We propose that the mesogranule velocity structure found by November et al. might be the uncorrected part of the 5-min oscillation and granule velocity. 相似文献