Monitoring of Mesoscale Precipitation Systems in the Alps and the Northern Alpine Foreland by Radar and Rain Gauges     

M. Hagen  H.-H. Schiesser  M. Dorninger 《Meteorology and Atmospheric Physics》2000,72(2-4):87-100

Summary.  Mesoscale convective precipitation systems in the Alpine region are studied by analyzing radar and rain gauge data. The data from weather radars in Austria, France, Germany, and Switzerland are combined into a composite. Availability of radar data restricts the study mainly to the northern part of the Alpine region. Mesoscale convective systems (MCS) occur often in this region and are comparable to large systems observed in the USA. Seven precipitation events lasting one to six days from the years 1992–1996 are examined in detail. They all moved west to east and showed no diurnal preference in formation or dissipation. They reach sizes of 2 − 6 · 10⁴ km². MCS with leading-line trailing-stratiform structure tended to be larger and more intense. A 25-year set of rain gauge data indicates that a giant MCS (covering more than 4 · 10⁴ km² with more than 30 mm/day) occurs every 6 years in the northern Alpine region. MCS occur more frequently in the southern Alpine region. Received February 25, 1999/Revised June 29, 1999  相似文献   

The hydrodynamic foundation for salmon lice dispersion modeling along the Norwegian coast     

Asplin  Lars  Albretsen  Jon  Johnsen  Ingrid Askeland  Sandvik  Anne Dagrun 《Ocean Dynamics》2020,70(8):1151-1167

Ocean Dynamics - Norway has complicated dynamics in the coastal ocean and in the fjords. In this area is also the largest salmon aquaculture industry in the world. The salmon industry is valuable...  相似文献   

Badass gully morphodynamics and sediment generation in Waipaoa Catchment,New Zealand     

Ian C. Fuller  Florian Strohmaier  Samuel T. McColl  Jon Tunnicliffe  Michael Marden 《地球表面变化过程与地形》2020,45(15):3917-3930

Large (>0.1 km²) gully–mass movement complexes (badass gullies) are significant contributors to the sediment cascade in New Zealand's steepland East Coast Region catchments. The scale of change taking place in these gully systems allows significant evolution in morphology and sediment dynamics to be tracked at annual to decadal timescales. Here we document changes in two adjacent badass gullies in Waipaoa catchment (Tarndale and Mangatu) to infer sediment generation processes and connectivity using a morphological budgeting approach. A baseline dataset for this study is provided by a LiDAR-derived digital elevation model (DEM) in 2005. We produced new DEMs and orthophoto mosaics using photogrammetry in 2017, 2018, and 2019 to quantify gully morphodynamics and associated volumes of sediment erosion and deposition in both systems as they co-evolved. Results indicate ongoing rapid development of both gully complexes. Severe erosion took place at the gully heads with lowering and migration (up to 25 m vertically and laterally) of the topographic divide separating the two gullies between 2005 and 2019. Over the same period, net lowering of each gully system was ~250 mm year⁻¹. Key sediment-generating processes included surface erosion, deep-seated landslides, and debris flows. Longer term, the overall contribution of sediment from both badass gullies to the Waipaoa catchment has been declining. In the mid-20th century, both gullies yielded in excess of 300 kt year⁻¹. From 2005 to 2019, 80 kt year⁻¹ was yielded from Tarndale and 110 kt year⁻¹ from Mangatu. Our most recent surveys demonstrated considerable variability in sediment yield, ranging from 76 kt year⁻¹ (2017–2018) to 291 kt year⁻¹ (2018–2019). The annual variability observed reflects the complex morphodynamics of discrete hillslopes and tributary fans in these badass gully systems and underlines the importance of integrating decadal and annual surveys when assessing system trajectory. © 2020 John Wiley & Sons, Ltd.  相似文献   

Sr isotope systematics during melt generation by intrusion of basalt into continental crust   总被引：1，自引：1，他引：0  

Kurt M. Knesel  Jon P. Davidson 《Contributions to Mineralogy and Petrology》1999,136(3):285-295

We have studied the Sr isotopic composition of partial melts of biotite granite generated experimentally and by intrusion of basalt into the Sierra Nevada Batholith. The experiments employed large, 3-cm cubes of granite to duplicate natural grain-boundary textures and were performed in air over the temperature interval 1000–1250 °C, to simulate basalt-induced wall rock and xenolith melting in the shallow crust. In both the experimental and natural analogs, fusion of plagioclase + alkali-feldspar ± quartz and biotite + plagioclase ± quartz results in the formation of colorless and brown melt (quenched to glass) respectively. Accordant with this melting behavior, brown glasses are enriched in radiogenic Sr and MgO, FeO, CaO, and TiO₂ relative to colorless glasses. These results support recent studies indicating that the isotopic compositions of crustal melts can reflect the relative contributions of mineral phases entering the melt, rather than the isotopic composition of the bulk source rock. In addition, we show that at shallow-crustal conditions preferential breakdown of biotite leads to initial high-⁸⁷Sr/⁸⁶Sr, low-Sr concentration melts. However, as the degree of melting increases, melts become less radiogenic yet are more enriched in elemental Sr due to loss of biotite from the restite and increased consumption of feldspars. Our results therefore suggest, if partial melts of granitic crust segregate rapidly during episodic magmatic underplating, successive melt batches can evolve from high-⁸⁷Sr/⁸⁶Sr to low-⁸⁷Sr/⁸⁶Sr liquids as melting progresses. Received: 25 August 1998 / Accepted: 10 March 1999  相似文献   

Variability and predictability of Antarctic krill swarm structure   总被引：6，自引：0，他引：6  

Geraint A. Tarling  Thor Klevjer  Sophie Fielding  Jon Watkins  Angus Atkinson  Eugene Murphy  Rebecca Korb  Mick Whitehouse  Russell Leaper 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(11):1994-2012

Swarming is a fundamental part of the life of Euphausia superba, yet we still know very little about what drives the considerable variability in swarm shape, size and biomass. We examined swarms across the Scotia Sea in January and February 2003 using a Simrad EK60 (38 and 120 kHz) echosounder, concurrent with net sampling. The acoustic data were analysed through applying a swarm-identification algorithm and then filtering out all non-krill targets. The area, length, height, depth, packing-concentration and inter-swarm distance of 4525 swarms was derived by this method. Hierarchical clustering revealed 2 principal swarm types, which differed in both their dimensions and packing-concentrations. Type 1 swarms were generally small (<50 m long) and were not very tightly packed (<10 ind. m⁻³), whereas type 2 swarms were an order of magnitude larger and had packing concentrations up to 10 times greater. Further sub-divisions of these types identified small and standard swarms within the type 1 group and large and superswarms within the type 2 group. A minor group (swarm type 3) was also found, containing swarms that were isolated (>100 km away from the next swarm). The distribution of swarm types over the survey grid was examined with respect to a number of potential explanatory variables describing both the environment and the internal-state of krill (namely maturity, body length, body condition). Most variables were spatially averaged over scales of 100 km and so mainly had a mesoscale perspective. The exception was the level of light (photosynthetically active radiation (PAR)) for which measurements were specific to each swarm. A binary logistic model was constructed from four variables found to have significant explanatory power (P<0.05): surface fluorescence, PAR, krill maturity and krill body length. Larger (type 2) swarms were more commonly found during nighttime or when it was overcast during the day, when surface fluorescence was low, and when the krill were small and immature. A strong pattern of diel vertical migration was not observed although the larger and denser swarms tended to occur more often at night than during the day. The vast majority of krill were contained within a minor fraction of the total number of swarms. These krill-rich swarms were more common in areas dominated by small and immature krill. We propose that, at the mesoscale level, the structure of swarms switches from being predominantly large and tightly packed to smaller and more diffuse as krill grow and mature. This pattern is further modulated according to feeding conditions and then level of light.  相似文献   

Petrogenesis of Miller Range 07273, a new type of anomalous melt breccia: Implications for impact effects on the H chondrite asteroid          下载免费PDF全文

Alex M. Ruzicka  Melinda Hutson  Jon M. Friedrich  Mark L. Rivers  Michael K. Weisberg  Denton S. Ebel  Karen Ziegler  Douglas Rumble III  Alyssa A. Dolan 《Meteoritics & planetary science》2017,52(9):1963-1990

Miller Range 07273 is a chondritic melt breccia that contains clasts of equilibrated ordinary chondrite set in a fine‐grained (<5 μm), largely crystalline, igneous matrix. Data indicate that MIL was derived from the H chondrite parent asteroid, although it has an oxygen isotope composition that approaches but falls outside of the established H group. MIL also is distinctive in having low porosity, cone‐like shapes for coarse metal grains, unusual internal textures and compositions for coarse metal, a matrix composed chiefly of clinoenstatite and omphacitic pigeonite, and troilite veining most common in coarse olivine and orthopyroxene. These features can be explained by a model involving impact into a porous target that produced brief but intense heating at high pressure, a sudden pressure drop, and a slower drop in temperature. Olivine and orthopyroxene in chondrule clasts were the least melted and the most deformed, whereas matrix and troilite melted completely and crystallized to nearly strain‐free minerals. Coarse metal was largely but incompletely liquefied, and matrix silicates formed by the breakdown during melting of albitic feldspar and some olivine to form pyroxene at high pressure (>3 GPa, possibly to ~15–19 GPa) and temperature (>1350 °C, possibly to ≥2000 °C). The higher pressures and temperatures would have involved back‐reaction of high‐pressure polymorphs to pyroxene and olivine upon cooling. Silicates outside of melt matrix have compositions that were relatively unchanged owing to brief heating duration.  相似文献   

An alternative method for interpreting jet erosion test (JET) data: part 1. Theory          下载免费PDF全文

Calvin W. Rose  Jon M. Olley  Arman Haddadchi  Andrew P. Brooks  Joe McMahon 《地球表面变化过程与地形》2018,43(3):735-742

The jet erosion test (JET) is a widely applied method for deriving the erodibility of cohesive soils and sediments. There are suggestions in the literature that further examination of the method widely used to interpret the results of these erosion tests is warranted. This paper presents an alternative approach for such interpretation based on the principle of energy conservation. This new approach recognizes that evaluation of erodibility using the jet tester should involve the mass of soil eroded, so determination of this eroded mass (or else scour volume and bulk density) is required. The theory partitions jet kinetic energy flux into that involved in eroding soil, the remainder being dissipated in a variety of mechanisms. The energy required to erode soil is defined as the product of the eroded mass and a resistance parameter which is the energy required to entrain unit mass of soil, denoted J (in J/kg), whose magnitude is sought. An effective component rate of jet energy consumption is defined which depends on depth of scour penetration by the jet, but not on soil type, or the uniformity of the soil type being investigated. Application of the theory depends on experimentally determining the spatial form of jet energy consumption displayed in erosion of a uniform body of soil, an approach of general application. The theory then allows determination of the soil resistance parameter J as a function of depth of scour penetration into any soil profile, thus evaluating such profile variation in erodibility as may exist. This parameter J has been used with the same meaning in soil and gully erosion studies for the last 25 years. Application of this approach will appear in a companion publication as part 2. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

An alternative method for interpreting JET erosion test (JET) data: Part 2. Application          下载免费PDF全文

Arman Haddadchi  Calvin W. Rose  Jon M. Olley  Andrew P. Brooks  Joe McMahon  Timothy Pietsch 《地球表面变化过程与地形》2018,43(3):743-754

This paper reports the results of jet tester experiments on soil samples of uniform properties which allow quantitative application of the new theory proposed in part 1 of these publications. This theory explores the possibly that a more adequate indicator of soil erodibility may be obtained by using the mass (and so volume) of soil eroded by the jet and the depth of scour penetration, rather than by using penetration depth alone, as assumed in the commonly‐used data interpretation method. It is shown that scour geometry can be well described using a generalized form of the Gaussian function, defined by its standard deviation and maximum depth. Using a published expression for jet kinetic energy flux, the new theory divides this flux into that used to erode soil, and the remainder which is dissipated in a variety of ways. Jet experiments on a specially‐prepared uniform soil sample are reported which provide the key to determining the spatial variability in the profile resistance to erosion offered by field soils. This resistance is expressed in the work required to erode unit mass of soil, denoted as J (in J/kg). The paper also gives results obtained on the profile variation in J for jet tests carried out at riverine sites on the upper Brisbane River, Queensland, Australia. As expected in most natural soil profiles, the results show an increase in J with depth in the profile. The soil resistance (J) is compared to the traditional interpretation of soil erodibility, (k_d). The graphical comparison of these two indicators illustrates the inverse type of relationship between them which is expected from their respective definitions, but this relationship is associated with significant scatter. Possible reasons for this scatter are given, together with comments on jet tester experience in a wide variety of soil types. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Late quaternary speleogenesis and landscape evolution in the northern Apennine evaporite areas          下载免费PDF全文

Andrea Columbu  Veronica Chiarini  Jo De Waele  Russell Drysdale  Jon Woodhead  John Hellstrom  Paolo Forti 《地球表面变化过程与地形》2017,42(10):1447-1459

Gypsum beds host the majority of the caves in the north‐eastern flank of the Apennines, in the Emilia Romagna region (Italy). More than six hundred of these caves have been surveyed, including the longest known epigenic gypsum cave systems in the world (Spipola‐Acquafredda, ~11 km). Although this area has been intensively studied from a geological point of view, the age of the caves has never been investigated in detail. The rapid dissolution of gypsum and uplift history of the area have led to the long‐held view that speleogenesis commenced only during the last 130 000 years. Epigenic caves only form when the surface drainage system efficiently conveys water into the underground. In the study area, this was achieved after the dismantling of most of the impervious sediments covering the gypsum and the development of protovalleys and sinkholes. The time necessary for these processes can by constrained by understanding when caves were first formed. The minimum age of karst voids can be indirectly estimated by dating the infilling sediments. U–Th dating of carbonate speleothems growing in gypsum caves has been applied to 20 samples from 14 different caves from the Spipola‐Acquafredda, Monte Tondo‐Re Tiberio, Stella‐Rio Basino, Monte Mauro, and Castelnuovo systems. The results show that: (i) caves have been forming since at least ~600 kyr ago; (ii) the peak of speleogenesis was reached during relatively cold climate stages, when rivers formed terraces at the surface and aggradation caused paragenesis in the stable cave levels; (iii) ~200 000 years were necessary for the dismantling of most of the sediments covering the karstifiable gypsum and the development of a surface mature drainage network. Besides providing a significant contribution to the understanding of evaporite karst evolution in the Apennines, this study refines our knowledge on the timescale of geomorphological processes in a region affected by rapid uplifting. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Reconciling Storegga tsunami sedimentation patterns with modelled wave heights: A discussion from the Shetland Isles field laboratory     

Alastair G. Dawson  Sue Dawson  Stein Bondevik  Pedro J. M. Costa  Jon Hill  Iain Stewart 《Sedimentology》2020,67(3):1344-1353

  相似文献