Book review

Offshore Soil Mechanics edited by Philip George and David Wood. Cambridge University Engineering Department and Lloyd's Register of Shipping, London, 1976. 468 pp. £7.50 + shipping.

Beach Processes and Sedimentation by Paul D. Komar. Prentice‐Hall, Inc. Englewood Cliffs, New Jersey, 1976. 429 pp., $26.95.     

Flows,flares, and formation of umbrae and light bridges in BBSO region No. 1167

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.     

The infrared spectrum of asteroid 433 Eros

The mineralogical composition of asteroid Eros has been determined from its infrared spectrum (0.9–2.7μm; 28cm^?1 resolution). Major minerals include metallic NiFe and pyroxene; no spectroscopic evidence for olivine or plagioclase feldspar was found. The IR spectrum of Eros is most consistent with a stony-iron composition.     

The formation of saturn's satellites and rings,as influenced by saturn's contraction history

We have used Pollack et al.'s 1976 calculations of the quasi-equilibrium contraction of Saturn to study the influence of the planet's early high luminosity on the formation of its satellites and rings. Assuming that the condensation of ices ceased at the same time within Jupiter's and Saturn's primordial nebulae, and using limits for the time of cessation derived for Jupiter's system by Pollack and Reynolds (1974) and Cameron and Pollack (1975), we arrive at the following tentative conclusions. Titan is the innermost satellite at whose position a methane-containing ice could condense, a result consistent with the presence of methane in this satellite's atmosphere. Water ice may have been able to condense at the position of all the satellites, a result consistent with the occurrence of low-density satellites close to Saturn. The systematic decrease in the mass of Saturn's regular satellites with decreasing distance from Saturn may have been caused partially by the larger time intervals for the closer satellites between the start of contraction and the first condensation of ices at their positions and between the start of contraction and the time at which Saturn's radius became less than a satellite's orbital radius. Ammonia ices, principally NH₄SH, were able to condense at the positions of all but the innermost satellites.Water ice may bave been able to condense in the region of the rings close to the end of the condensation period. We speculate that the rings are unique to Saturn because on the one hand, temperatures within Jupiter's Roche limit never became cool enough for ice particles to form before the end of the condensation period and on the other hand, ice particles formed only very early within Uranus' and Neptune's Roche limits, and were eliminated by gas drag effects that caused them to spiral into the planet before the gas of these planets' nebula was eliminated. Gas drag would also have eliminated any rocky particles initially present inside the Roche limit.We also derive an independent estimate of several million years for the time between the start of the quasi-equilibrium contraction of Saturn and the cessation of condensation. This estimate is based on the density and mass characteristics of Saturn's satellites. Using this value rather than the one found for Jupiter's satellites, we find that the above conclusions about the rings and the condensation of methane-and ammonia-containing ices remain valid.     

Weak solar fields and their connection to the solar cycle

We discuss the weak solar magnetic fields as studied with the BBSO videomagnetograph (VMG). By weak fields we mean those outside active and unipolar regions. These are found everywhere on the Sun, even where there never have been sunspots. These fields consist of the network and intranetwork (IN) elements. The former move slowly and live a day or more; the latter move rapidly (typically 300 m s^–1) and live only hours. To all levels of sensitivity the flux is concentrated in discrete elements, and the background field has not been detected. The smallest detectable elements at present are 10¹⁶ Mx. The IN elements emerge in bipolar form but appear to flow in a random pattern rather than to the network edges; however, any expanding network element is constrained by geometry to move toward the edges.Because of the great number and short lifetime of the IN elements the total flux emerging in that form exceeds that emerging in the ER by two orders of magnitude and the flux in sunspots, by a factor 10⁴. However, the flux separation is small and there is no contribution to the overall field. In contrast with our earlier results, merging of IN fields is more important than the ephemeral regions as a source of new network elements.The conjecture that all solar magnetic fields are intrinsically strong is discussed and evidence pro and con presented. For the IN fields the evidence suggests they cannot exceed 100 G. For the network fields there is evidence on either side.Reconnection and merging of magnetic fields takes place continually in the conditions studied.Because there is a steady state distribution, the amout of new elements created by merging or emergence must balance that destroyed by reconnection or fission and diffusion of the stronger elements.Solar Cycle Workshop Paper.     

DRIFT VOLUME IN THE SOUTHERN PENINSULA OF MICHIGAN—A PRODIGIOUS PLEISTOCENE ENDOWMENT

Michigan's Southern Peninsula is by far the largest drift repository in the Great Lakes Area. Thickness of the glacial sediments averages 85 m and volume, previously unknown, exceeds 9300 km³. The distribution, however, is very uneven, as is the underlying bedrock surface. These variations and known surface characteristics provide a basis for the first qualitative and quantitative identification of distinct drift realms. Even the smallest of the eight realms contains about 35% more drift than the better known Kettle Moraine tract of Wisconsin, which encompasses 50% more area. Comparative analysis within the peninsula shows that Pleistocene glaciation completely transformed the topography to the north, whereas the southern half has palimpsest relationships with subcropping formations. [Key words: drift, drift volume, Michigan, Great Lakes, Pleistocene.]     

柴达木盆地北缘古生代超高压带中花岗质岩浆作用

祁连南缘古生代超高压变质带 (榴辉岩年龄为 4 6 6～ 4 95 Ma)上一套中高级变质岩系 (达肯大坂片麻岩 )中存在三类花岗岩组合 : 类 :石英二长闪长岩 -花岗闪长岩 -二长花岗岩 , 类 :二长花岗岩 -二云母花岗岩-含白云母花岗岩 -正长花岗岩 , 类 :花岗闪长岩 -二长花岗岩 -黑云母花岗岩。 类岩石组合中的二长花岗岩锆石SHRIMP年龄为 4 73Ma, 类岩石组合中的正长花岗岩锆石 SHRIMP年龄为 4 4 6 Ma, 类岩石组合中的二长花岗岩锆石 SHRIMP年龄为 397Ma。从三类花岗岩组合的组成矿物来看 , 类和 类的矿物组合主要为斜长石、角闪石、石英、碱性长石、黑云母 , 类的矿物组合为钾长石、石英、白云母、黑云母、斜长石 ;从岩石地球化学特征上看 , 类和 类花岗岩为 型花岗岩 ,岩石的 Si O2 =6 1%～ 6 9% ,Na2 O/ K2 O>1,ANK<1,δEu=0 .7～ 1.0 ; 类花岗岩为 S型花岗岩 ,岩石的 Si O2 =70 %～ 76 % ,Na2 O/ K2 O<1,ANK>1,δEu=0 .1～ 0 .3;从构造环境上看 , 类花岗岩形成于岛弧环境或活动大陆边缘 , 类花岗岩形成于同碰撞 , 类花岗岩形成于碰撞后。结合区域地质特征 ,我们认为 ,早奥陶世 ,南祁连洋板块向北俯冲于祁连陆块之下 ,规模不大的南祁连洋很快闭合 ,但俯冲下去的大洋板块仍拖动柴达木陆块继续俯冲 ,俯冲