On the integration of intensity measurements of the solar center and limb near 300 nanometers

Two methods of integrating limb-darkening data to calculate the spectral irradiance are compared. Near 300 nm Moe and Milone's (1978) quadratic approximation to the limb darkening yields an integral 3% larger on average than the two linear segments of Kohl et al. (1980) when the same data are inserted in both formulas. As one would expect, the difference between the two calculations is directly proportional to Moe and Milone's quadratic coefficient. When Moe and Milone's data are inserted in the formula of Kohl et al., the calculated irradiance is 4% higher than when the data of Kohl et al. are used in the same formula. Possible reasons for this difference are suggested.     

Benthonic foraminifera as indicators of the paleoposition of the Subarctic Convergence in the Norwegian-Greenland Sea

A method is presented for correlating benthonic foraminiferal communities in Late Quaternary marine sediments on continental shelves and in coastal areas with the planktonic foraminiferal stratigraphy of the North Atlantic and Norwegian Sea deep-sea sediments.     

Landslide inventory in a rugged forested watershed: a comparison between air-photo and field survey data

Landslide inventories are routinely compiled by means of aerial photo interpretation (API). When examining photo pairs, the forest canopy (notably in old-growth forest) hides a population of “not visible” landslides. In the present study, we attempt to estimate how important is the contribution of landslides not detectable from aerial photographs to the global mass of sediment production from mass failures on forested terrain of the Capilano basin, coastal British Columbia. API was coupled with intensive fieldwork for identification and measurement of all landslides. A 30-year framework was adopted. We show that “not visible” landslides can represent up to 85% of the total number of failures and account for 30% of the volume of debris mobilised. Such percentages display high sub-basin variability with rates of sediment production varying by one order of magnitude between two sub-basins of the study area. This is explained qualitatively by GIS-based analysis of slope frequency distributions, drainage density, and spatial distribution of surficial materials. Such observations find further support in the definitions of transport-limited and supply-limited basins. As a practical consideration to land managers, we envisage that supplementary fieldwork for landslide identification is mandatory in transport-limited systems only. Fieldwork has demonstrated that gully-related failures have a greater importance than one could expect from API.     

Advances in Holocene mountain geomorphology inspired by sediment budget methodology

The sediment budget, which links sediment sources to sediment sinks with hydroclimatic and weathering processes mediating the response, is applied to the analysis of sediments in three alpine lakes in British Columbia. We provide two ways of using the sediment budget as an integrating device in the interpretation of mountain geomorphology. These approaches differ in their resolution and ability to budget the major components of the fine-sediment cascade in glaciated environments. Taken together, they provide an integrated index of landscape change over the Holocene. The first example compares the hydroclimatic controls of lake sedimentation for the last 600 years (A.D. 1370–1998) preserved in varved sediments from two of the lake basins. This hydroclimatological approach incorporates contemporary monitoring, air photo analysis, and detailed stratigraphy of sedimentation events within a single varve to infer the timing, sources, and preferred pathways of fine-grained sediments reaching the lake basins. The results indicate that glaciers, hillslope, and channel instability within the major subbasins are the principal sediment sources to the lake basins. Transitory sediment storage of glacially derived sediments within the channels is believed to modulate the episodic and more frequent delivery of sediments from adjacent hillslope and fluvial storage sites and direct routing of glacial rock flour during years of prolonged glacial melt. The second example, relying on the phosphorus geochemistry of sediments in an alpine lake basin, considers the evolution of phosphorus forms (from mineral to occluded and organic fractions) as a function of the soil development, inherent slope instability, and repeated cycles of glaciation and neoglaciation over the Holocene. This geochemical approach demonstrates that both neoglaciation and full glaciation have essentially zeroed the system in such a way that a high proportion of mineral phosphorus remains in the present lake sediments and the bioavailability of phosphorus (a key to ecosystem development) is low. Both examples illustrate the importance of variable sediment sources; the seasonality, frequency, and magnitude of sediment transfers; and the profound influence of ice cover over contemporary, neoglacial and Pleistocene time scales. They also signal the value of including both clastic and dissolved components in the sediment budget.     

Geological events during the early formation of a passive margin

The concept of plate tectonics implies that the normal sea floor spreading stage is preceded by a sequence of events associated with the break-up of continental crust. Thus, evidence of the early development of “non-failed” rifts is to be found at passive continental margins. Of special interest is the question of the extent of the continental crust and the structural and compositional changes associated with the change in crustal type. In addressing these topics, we have focused attention on the Norwegian margin between the Jan Mayen and Senja fracture zones (66°–70°N) in an attempt to understand its history of rifting and early sea floor spreading. p ]The southern part of this rifted margin is characterized by a wide shelf and the marginal Vøring Plateau interrupts a gentle slope at a level of about 1500 m. However, the margin becomes progressively narrower towards the north and a typical narrow shelf and steep slope emerge off the Lofo—tenVesterålen Islands (Fig. 1). In a reconstructed pre-opening configuration (Talwani and Eldholm, 1977) the narrowest part of the juxtaposed EastGreenland margin is found in the south and a wide shelf and slope corresponds to the Lofoten-Vesterålen margin.The most prominent structural element is a buried basement high underneath the Vøring Plateau. The high is bounded landward by the Vøring Plateau Escarpment, a major structural boundary which defines typical changes in the geophysical parameters. These are: (1) a sudden increase of depth to acoustic basement; (2) changes in the velocity-depth function; (3) a gravity gradient; and (4) a magnetic edge anomaly separating sea-floor spreading type anomalies from a quiet zone on the landward side (Talwani and Eldholm, 1972). These observations were interpreted in terms of a sharp ocea—ncontinent crustal transition along the escarpment with sea-floor spreading commencing between anomaly 24 and 25 time (56–58 m.y. B.P.). Alternatively, the concept of ancient oceanic crust landward of this escarpment and the possible existence of continental crust under the outer basement high have been argued and we refer to Eldholm et al. (1979) for a detailed discussion.     

A generalized theory for line formation in a homogeneous magnetic field

The formation of spectral lines in a homogeneous magnetic field has been studied. A new method for solving the transfer equations for polarized light has been found. Using this method, the Stokes parameters may be derived without any special assumptions regarding the model atmosphere. With the line formed by pure absorption, the expressions for the Stokes parameters may easily be adapted to numerical calculations. In order to illustrate the method, the line profile for the Zeeman triplet 5250 has been calculated using a photospheric model atmosphere.     

Models for different sunspot umbrae

An empirical approach to interpret the time evolution of the high spatial resolution Ca ii K line is presented. We specify the physical parameters, such as electron temperature, hydrogen density, and velocity (microturbulent and systematic) as functions of height. The electron density is obtained from scaled non-LTE solutions for hydrogen ionization. The population indices, and thus the Ca ii source functions, for a 5-level Ca ii atom are computed by using the generalized Newton-Raphson method. K line profiles are then synthesized for different evolutionary stages and are compared with the observed ones. The explanation of the ‘peculiar’ type profile is also attempted.     

Avalanche Run-Out on Counter-Slopes

Counter-slopes in avalanche paths influence avalanche flow in similarways as defence structures. Measurements and calculations of run-outon such slopes will improve our understanding of retaining damdesign. We have studied three different, well described avalancheevents; for each case we have calculated the run-out distance usingthe Noren, Irgens and Schieldrops continuum model (NIS), adjustingthe parameters to fit the simulated avalancheto the observed one. Using the same parameters, the run-out onidentical terrain, but without counter-slope, is computed. Comparisonbetween the energy dissipation in these different cases tells us whichtopography most efficiently retards an avalanche. With a smoothly curved valley bottom, the energy dissipation at agiven point on the opposite slope is less than on a flatrun-out. The explanation to this is that, when gravity retards anavalanche, a smaller portion of the energy loss is due to dissipationfrom viscous (velocity dependent) friction. When the avalanche travelsover a retaining dam, with much smaller curvature radii, a significantportion of the energy is dissipated. The consequence of this is that defence structures are not sodependent on the counter-slope inclination as on the curvature radiusin the transition to up-gradient. Further, introduction of acounter-slope in an avalanche path may conserve energy rather thancausing dissipation – if the inclination is not altered abruptlyenough. If the counter-slope is smooth, and not large enough tocompletely stop the avalanche, it will not reduce destructive energyon the downstream side. In fact, the destructive energy may bepartially conserved until the run-out.