Snow-Push Processes in Pronival (Protalus) Rampart Formation: Geomorphological Evidence from Smørbotn, Romsdalsalpane, Southern Norway     

Richard A. Shakesby  John A. Matthews  Mark S. Berrisford  & Lindsey J. McEwen 《Geografiska Annaler: Series A, Physical Geography》1999,81(1):31-45

It is demonstrated that pronival (protalus) ramparts can be formed by a snow-push mechanism and need not accumulate in the conventional manner as a result of supranival processes. Ridges in pronival positions up to 1.2 m high and of unequivocal snow-push origin are described from two sites in Smørbotn cirque, Romsdalsalpane, southern Norway. The seven lines of evidence are: (1) parallel abrasion tracks on large boulders embedded in the substrate; (2) displaced surface and embedded clasts with proximal furrows; (3) corrugated (flute-like) substrate surfaces; (4) the sickle-shaped plan-form of the ridges; (5) generally asymmetrical ridge cross-profiles (shallow, concave proximal; steep, convex distal); (6) strong preferred orientations and dips of surface-embedded clasts on ridge proximal slopes; and (7) a subnival/pronival ridge comprising loosely packed diamicton forming along the contact zone between the snowbed and substrate. This evidence indicates ridge formation by snow sliding involving bulldozing of the substrate. Factors considered important in favouring snow push producing distinct pronival ramparts at the sites include: a maritime periglacial climate with heavy winter snowfall and rapid snow-firn conversion producing snow densities of up to 900 kg m^–3; a deformable substrate with relatively small inputs of rockfall or avalanche debris; and a steep headwall susceptible to snow avalanching and hence enhanced snow supply. Consideration is given to the prospect that larger pronival ramparts can form incrementally by a snow-push mechanism.  相似文献   

Helioseismic imaging of sunspots at their antipodes     

Charles Lindsey  Douglas C. Braun 《Solar physics》1990,126(1):101-115

Recent work by Braun, Duvall, and LaBonte has shown that sunspots absorb helioseismic waves. We propose that sunspot absorption causes a seismic deficit that should be imaged at the antipode of the sunspot. If these images are observable, it should be possible to produce seismic maps of magnetic regions on the far side of the Sun. This possibility opens a broad range of synoptic and diagnostic applications. Diagnostic applications would include lifetimes of higher-frequency modes, and possibly rotation of the solar interior and detection of subsurface magnetic structure. We outline elements of the theory of seismic imaging and consider some applications. We propose the extention of acoustic holography to solar interior diagnostics in the context of antipodal imaging.Now at the Institute for Astronomy, University of Hawaii, Honolulu, HI 96822, U.S.A.  相似文献   

Structure and evolution of large groups of Massive Close Binary systems     

C. Doom  J. P. De Grève 《Astrophysics and Space Science》1982,87(1-2):357-375

Using the definition of four important events in the evolution of Massive Close Binary systems, we define five observable evolutionary phases in the life of a Massive Close Binary system: OB+OB, WR+OB, C+OB, C+WR, and WR+WR. We define and compute a number of observable phenomena for large groups of Massive Close Binaries. For one burst of star formation, we compute the number of systems in different evolutionary phases, and the total mass loss as functions of the time. For continuous star formation, we determine the fraction of WR binary stars, occurring in different phases of massive close binary evolution, and a number of average quantities (mass, mass ratio) of WR binary systems. The results are compared with observations of WR binaries in the Galaxy and in Open Clusters.This research is supported by the national Foundation of Collective Fundamental Research (FKFO) of Belgium under contract Nr. 2.9009.79.  相似文献   

Superstructures in ankerite and calcite     

H.-R. Wenk  Hu Meisheng  T. Lindsey  J. W. Morris Jr. 《Physics and Chemistry of Minerals》1991,17(6):527-539

Two rhombohedral carbonates, ferroan dolomite (ankerite) and magnesian calcite from lower Jurassic ammonites, have been studied by transmission electron microscopy. The samples show small domains with the morphology of platelets parallel to (11 \(\bar 2\) 0) which have exceptionally well ordered superstructures and characteristic c-reflections. Diffraction patterns and contrast analysis of atomic resolution images indicate that the domains observed in ankerite are rich in Ca [Ca_0.75(Mg, Fe)_0.25CO₃] and those in calcite rich in Mg, and there is strong evidence that cation ordering is the cause for the observed superstructures which are proposed mainly on diffraction evidence. Rhombohedral carbonates have a close similarity to NaCl, with CO₃-groups substituting for Cl. Cation ordering patterns can therefore be discussed in analogy to f.c.c. alloys. We make use of ordering waves to describe superstructures and to qualitatively interpret kinetic conditions for their formation.  相似文献   

A review of recent observations of dust in Hii regions     

Lindsey F. Smith 《Astrophysics and Space Science》1975,34(1):49-55

The upper limit for the absorption cross section σ _H ^ext , of dust in Hii regions in the wave-length range 912–504 Å derived by Mezgeret al. (1974), is compatible with that expected for large dust grains, and a gas-to-dust ratio equal to that in the general interstellar medium. The albedo of the small grains must be high for λ>504 Å. This restriction is lifted if the visual extinction cross section of the grains in Hii regions is less than that for grains in the general interstellar medium. New observations of the Orion Nebula indicate that the visual extinction cross section is within a factor 2 of the value in the general interstellar medium.  相似文献   

Infrared continuum observations of five-minute oscillations     

C. A. Lindsey 《Solar physics》1977,52(2):263-281

Infrared continuum observations of the Sun at wavelengths between 10 and 30 show a nonisothermal response of the upper photosphere to compression waves associated with the five-minute oscillations. Observations were made with four broad-band filters with effective transmission wavelengths between 10 and 26 and with a 10 aperture. Further observations at submillimeter wavelengths with a 2 aperture did not resolve oscillatory fluctuations of five-minute period.Comparisons with velocity field data of Howard (1976) suggest that the relaxation time of the photosphere exceeds (300/2) seconds at the height of formation of the 26 continuum (_5000Å 10^-2). The photosphere reponds to 3 mHz oscillatory motion with considerably less compression than expected for simple acoustic modes in an adiabatically responsive atmosphere, confirming the evanescent character of the five-minute oscillations.  相似文献   

The impact of climate change on U. K. river flows: A preliminary comparison of two generations of probabilistic climate projections     

Alison Lindsey Kay  Glenn Watts  Steven C. Wells  Stuart Allen 《水文研究》2020,34(4):1081-1088

The impacts of climate change on future river flows are a growing concern. Typically, impacts are simulated by driving hydrological models with climate model ensemble data. The U.K. Climate Projections 2009 (UKCP09) provided probabilistic projections, enabling a risk-based approach to decision-making under climate change. Recently, an update was released—UKCP18—so there is a need for information on how impacts may differ. The probabilistic projections from UKCP18 and UKCP09 are here applied using the change factor method with catchment-based hydrological modelling for 10 catchments across England. Projections of changes in median, mean, high, and low flows are made for the 2050s, using the A1B emissions scenario from UKCP09 and UKCP18 as well as the RCP4.5 and RCP8.5 emissions scenarios from UCKP18. The results show that, in all catchments for all flow measures, the central estimate of change under UKCP18 is similar to that from UKCP09 (A1B emissions). However, the probabilistic uncertainty ranges from UKCP18 are, in all cases, greater than from UKCP09, despite UKCP18 having a smaller ensemble size than UKCP09. Although there are differences between the central estimates of change using UKCP18 RCP4.5, RCP8.5 and A1B emissions, there is considerable overlap in the uncertainty ranges. The results suggest that existing assessments of hydrological impacts remain relevant, though it will be necessary to evaluate sensitive decisions using the latest projections. The analysis will aid development of advice to users of current guidance based on UKCP09 and help make decisions about the prioritization of further hydrological impacts work using UKCP18, which should also apply other products from UKCP18 like the 12-km regional data.  相似文献   

Seismic Emission from A M9.5-Class Solar Flare     

A.-C. Donea  D. Besliu-Ionescu  P. S. Cally  C. Lindsey  V. V. Zharkova 《Solar physics》2006,239(1-2):113-135

Following the discovery of a few significant seismic sources at 6.0 mHz from the large solar flares of October 28 and 29, 2003, we have extended SOHO/MDI helioseismic observations to moderate M-class flares. We report the detection of seismic waves emitted from the β γ δ active region NOAA 9608 on September 9, 2001. A quite impulsive solar flare of type M9.5 occurred from 20:40 to 20:48 UT. We used helioseismic holography to image seismic emission from this flare into the solar interior and computed time series of egression power maps in 2.0 mHz bands centered at 3.0 and 6.0 mHz. The 6.0 mHz images show an acoustic source associated with the flare some 30 Mm across in the East – West direction and 15 Mm in the North – South direction nestled in the southern penumbra of the main sunspot of AR 9608. This coincides closely with three white-light flare kernels that appear in the sunspot penumbra. The close spatial correspondence between white-light and acoustic emission adds considerable weight to the hypothesis that the acoustic emission is driven by heating of the lower photosphere. This is further supported by a rough hydromechanical model of an acoustic transient driven by sudden heating of the low photosphere. Where direct heating of the low photosphere by protons or high-energy electrons is unrealistic, the strong association between the acoustic source and co-spatial continuum emission can be regarded as evidence supporting the back-warming hypothesis, in which the low photosphere is heated by radiation from the overlying chromosphere. This is to say that a seismic source coincident with strong, sudden radiative emission in the visible continuum spectrum indicates a photosphere sufficiently heated so as to contribute significantly to the continuum emission observed.  相似文献   

Parameterisation of incoming longwave radiation over glacier surfaces in the semiarid Andes of Chile     

Shelley MacDonell  Lindsey Nicholson  Christophe Kinnard 《Theoretical and Applied Climatology》2013,111(3-4):513-528

A good understanding of radiation fluxes is important for calculating energy, and hence, mass exchange at glacier surfaces. This study evaluates incoming longwave radiation measured at two nearby glacier stations in the high Andes of the Norte Chico region of Chile. These data are the first published records of atmospheric longwave radiation measurements in this region. Nine previously published optimised parameterisations for clear sky emissivity all produced results with a root mean square error (RMSE) ~20 W?m^?2 and bias within ±5 W m^?2, which is inline with findings from other regions. Six optimised parameterisations for incoming longwave in all sky conditions were trialled for application to this site, five of which performed comparably well with RMSE on daytime data <18 W?m^?2 and bias within ±6 W?m^?2 when applied to the optimisation site and RMSE <20 W?m^?2 and bias within ±10 W m^?2 when applied to the validation site. The parameterisation proposed by Mölg et al. (J Glaciol 55:292-302, 2009) was selected for use in this region. Incorporating the proposed elevation modification into the equation reduced the bias in the modelled incoming longwave radiation for the validation site. It was found that applying the parameterisation optimised in the original work at Kilimanjaro produced good results at both the primary and validation site in this study, suggesting that this formulation may be robust for different high mountain regions.  相似文献   

Constraining and enabling factors to using long-term climate information in decision-making     

Lindsey Jones  Clara Champalle  Sabrina Chesterman  Laura Cramer  Todd A. Crane 《Climate Policy》2013,13(5):551-572

We carry out a structured review of the peer-reviewed literature to assess the factors that constrain and enable the uptake of long-term climate information in a wide range of sectoral investment and planning decisions. Common applications of long-term climate information are shown to relate to urban planning and infrastructure, as well as flood and coastal management. Analysis of the identified literature highlights five categories of constraints: disconnection between users and producers of climate information, limitations of climate information, financial and technical constraints, political economy and institutional constraints and finally psycho-social constraints. Five categories of enablers to the uptake of long-term climate information in decision-making are also identified: collaboration and bridge work, increased accessibility of climate information, improvement in the underlying science, institutional reform and windows of opportunity for building trust.

Policy relevance

Our review suggests that stand-alone interventions aimed at promoting the uptake of climate information into decision-making are unlikely to succeed without genuine and sustained relationships between producers and users. We also highlight that not every decision requires consideration of long-term climate information for successful outcomes to be achieved. This is particularly the case in the context of developing countries, where the immediacy of development challenges means that decision makers often prioritize short-term interventions. Care should therefore be taken to ensure that information is targeted towards investments and planning decisions that are relevant to longer-term timescales.  相似文献