The development of the substorm in auroral radio absorption

Observations with a meridional chain of riometers in the auroral zone show that the onset of an auroral absorption substorm is usually preceded by weak activity. This activity sometimes takes the form of a weak bay-like event, moving slowly equatorward. Its velocity (typically 200–500 m/sec) is consistent with the inward convection of energetic plasma in the magnetosphere— that is, with E × B drift in an electric field of about 1.3 mV/m. The bay intensifies as it moves, indicating energization of the plasma during convection.     

Paleoecological evidence for abrupt cold reversals during peak Holocene warmth on Baffin Island, Arctic Canada

A continuous record of insect (Chironomidae) remains preserved in lake sediments is used to infer temperature changes at a small lake in Arctic Canada through the Holocene. Early Holocene summers at the study site were characterized by more thermophilous assemblages and warmer inferred temperatures than today, presumably in response to the positive anomaly in Northern Hemisphere summer insolation. Peak early Holocene warmth was interrupted by two cold reversals between 9.5 and 8 cal ka BP, during which multiple cold-stenothermous chironomid taxa appeared in the lake. The earlier reversal appears to correlate with widespread climate anomalies around 9.2 cal ka BP; the age of the younger reversal is equivocal but it may correlate with the 8.2 cal ka BP cold event documented elsewhere. Widespread, abrupt climate shifts in the early Holocene illustrate the susceptibility of the climate system to perturbations, even during periods of enhanced warmth in the Northern Hemisphere.     

Holocene temperature history of northern Iceland inferred from subfossil midges

The Holocene temperature history of Iceland is not well known, despite Iceland's climatically strategic location at the intersection of major surface currents in the high-latitude North Atlantic. Existing terrestrial records reveal spatially heterogeneous changes in Iceland's glacier extent, vegetation cover, and climate over the Holocene, but these records are temporally discontinuous and mostly qualitative. This paper presents the first quantitative estimates of temperatures throughout the entire Holocene on Iceland. Mean July temperatures are inferred based upon subfossil midge (Chironomidae) assemblages from three coastal lakes in northern Iceland. Midge data from each of the three lakes indicate broadly similar temperature trends, and suggest that the North Icelandic coast experienced relatively cool early Holocene summers and gradual warming throughout the Holocene until after 3 ka. This contrasts with many sites on Iceland and around the high-latitude Northern Hemisphere that experienced an early to mid-Holocene “thermal maximum” in response to enhanced summer insolation forcing. Our results suggest a heightened temperature gradient across Iceland in the early Holocene, with suppressed terrestrial temperatures along the northern coastal fringe, possibly as a result of sea surface conditions on the North Iceland shelf.     

Anisotropic diffusion of solar cosmic rays

A simple model is described for solar cosmic ray events which appears to be in reasonable accord with observations. The model is based partly on some earlier models, together with the assumption that the diffusion of particles is strongly anisotropic due to the presence of the interplanetary magnetic field. Some remarks concerning the limitations of the diffusion equation are included, and it is pointed out that the propagation of solar cosmic rays might be best described in terms of an analogy to electrical transmission lines rather than to the conduction of heat as is usually done.     

断裂引起的应变量计算方法

本文介绍了断裂引起的应变量计算方法。断裂作用可导致连续应变和非连续应变。连续应变与断裂位移,断裂长度比值及断裂面上有效应力成正相关关系。影响非连续应变的因素有：断裂几何形态、断裂的旋转性、断裂规模。已经提出三种断裂旋转机制：刚性旋转,垂直剪切和斜向剪切。对于这三种机制,我们分别建立了断裂非连续应变的计算公式。这些公式与断裂的旋转角度和位移大小相关。刚性旋转时,断块内部没有任何塑性变形,因此地层的长度没有变化。它引起的非连续应变最小。垂直剪切作用使断块内地层变形,但水平方向的地层长度不变。推算的公式表明,对于相同的原始数据,它引起的非连续应变比刚性旋转机制引起的非连续应变大。斜向剪切也使断块内地层变形,但水平方向的长度也不变。在同等条件下,它引起的非连续应变比垂直剪切机制引起的非连续应变大。     

Cosmic Rays and Clusters of Galaxies

The presence of a significant population of relic relativistic electrons - created at an early epoch of the Universe - has been invoked to explain the diffuse EUV emission excess observed in a number of galaxy clusters. While the postulated inverse Compton scattering of the 3° K background radiation by cosmic ray electrons might indeed be utilized as an important diagnostic tool for the physical nature of the intracluster cosmic rays, it is shown here that continuous generation plus reacceleration would be necessary if the conditions on the observed energy spectral distribution and energy supply rate are to be met in the case of clusters with large radio halos. This revised version was published online in July 2006 with corrections to the Cover Date.     

Climate of the Little Ice Age and the past 2000 years in northeast Iceland inferred from chironomids and other lake sediment proxies

A sedimentary record from lake Stora Viearvatn in northeast Iceland records environmental changes over the past 2000 years. Downcore data include chironomid (Diptera: Chironomidae) assemblage data and total organic carbon, nitrogen, and biogenic silica content. Sample scores from detrended correspondence analysis (DCA) of chironomid assemblage data are well correlated with measured temperatures at Stykkishólmur over the 170 year instrumental record, indicating that chironomid assemblages at Stora Viearvatn have responded sensitively to past temperature changes. DCA scores appear to be useful for quantitatively inferring past temperatures at this site. In contrast, a quantitative chironomid-temperature transfer function developed for northwestern Iceland does a relatively poor job of reconstructing temperature shifts, possibly due to the lake’s large size and depth relative to the calibration sites or to the limited resolution of the subfossil taxonomy. The pre-instrumental climate history inferred from chironomids and other paleolimnological proxies is supported by prior inferences from historical documents, glacier reconstructions, and paleoceanographic studies. Much of the first millennium AD was relatively warm, with temperatures comparable to warm decades of the twentieth century. Temperatures during parts of the tenth and eleventh centuries AD may have been comparably warm. Biogenic silica concentrations declined, carbon:nitrogen ratios increased, and some chironomid taxa disappeared from the lake between the thirteenth and nineteenth centuries, recording the decline of temperatures into the Little Ice Age, increasing soil erosion, and declining lake productivity. All the proxy reconstructions indicate that the most severe Little Ice Age conditions occurred during the eighteenth and nineteenth centuries, a period historically associated with maximum sea-ice and glacier extent around Iceland.