On Normal Mode Aided Modelling: Application to Asian Monsoon     

Frank Schmidt 《Meteorology and Atmospheric Physics》2000,73(3-4):189-210

Summary A new concept of utilizing generalized normal mode initialization (NMI) for modelling is investigated. This NMI-balancing adapts real data to model solutions. For eigenmodes of typical (climatological) structure and a simple 1- or more-layer shallow water model, anomalous flow of special episodes or events can be identified with mode groups giving distinctive signals. If these signals are part of the model solution or of the complement of the data to the model solution and how this is changed by introducing additional physical mechanisms to the model, gives hints for improvement. In applying this to multi-scale interactions of Asian monsoon, in particular a seventeen-years background knowledge and the anomalous flow of years 1991, 1977, 1978 we have a challenging test frame. Particular topics are: (1) Mei Yu rains in China, the representation of particular aspects of them by certain mode groups, the degree of independence of the corresponding signals on other modes, and the role of dissipation; (2) detection of El Ni?o-Southern Oscillation (ENSO) in atmospheric (reanalysis) data minus the NMI-balanced model solution; (3) Madden-Julian Oscillations (MJO) and the introduction of diabatic processes, and finally (4) aspects of dynamic stability. From among the results which are new or we simply have become aware of we pull out that atmospheric processes generally can be represented by modes or mode groups neither straight forward nor uniquely. Introduction of some dissipation schemes to the model was not helpful but rather destroyed the realistic structure of atmospheric dynamics. A parameterization of diabatic processes passes signals present in the data but not in the NMI-balanced model solution through to such being part of the latter, in case of MJO but not yet in case of ENSO. Ocean dynamics proves to be indispensable. Nevertheless there are imprints of essential atmospheric processes hidden on certain (e.g., most unstable) modes and partially recovered by NMI-balancing. Received July 19, 1999 Revised December 29, 1999  相似文献   

Low‐mass visual binaries in the solar neighbourhood: The case of HD 141272     

T. Eisenbeiss  A. Seifahrt  M. Mugrauer  T. O. B. Schmidt  R. Neuhuser  T. Roell 《Astronomische Nachrichten》2007,328(6):521-526

We search for stellar and substellar companions of young nearby stars to investigate stellar multiplicity and formation of stellar and substellar companions. We detect common proper‐motion companions of stars via multi‐epoch imaging. Their companionship is finally confirmed with photometry and spectroscopy. Here we report the discovery of a new co‐moving (13 σ) stellar companion ∼17.8 arcsec (350AU in projected separation) north of the nearby star HD141272 (21 pc).With EMMI/NTT optical spectroscopy we determined the spectral type of the companion to be M3±0.5V. The derived spectral type as well as the near infrared photometry of the companion are both fully consistent with a M_⊙ dwarf located at the distance of HD141272 (21 pc). Furthermore the photometry data rules out the pre‐main sequence status, since the system is consistent with the ZAMS of the Pleiades. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Imaging H i in the lensing galaxy 2237+0305     

D. G. Barnes  R. L. Webster  R. W. Schmidt  A. Hughes 《Monthly notices of the Royal Astronomical Society》1999,309(3):641-650

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Material flow in sunspots     

W. Schmidt 《Astronomische Nachrichten》2003,324(4):374-375

Observations nowadays reveal more and more details about the small‐scale structure of the penumbra and umbra. Recent measurements of the motions in the penumbra indicate that (i) the Evershed flow is confined to a thin photospheric layer and (ii) the material rises from and sinks to subphotospheric layers within the penumbra. This flow pattern solves the question of the mass budget of the Evershed flow in a natural way. The nature of umbral dots and their role for the spot's energy budget remains unclear, since they are obviously unresolved even in the best existing measurements.  相似文献   

Sediment budgeting of short-term backfilling processes: The erosional collapse of a Carolingian canal construction     

Johannes Schmidt  Lukas Werther  Johannes Rabiger-Völlmer  Franz Herzig  Birgit Schneider  Ulrike Werban  Peter Dietrich  Stefanie Berg  Sven Linzen  Peter Ettel  Christoph Zielhofer 《地球表面变化过程与地形》2020,45(14):3449-3462

Sediment budgeting concepts serve as quantification tools to decipher the erosion and accumulation processes within a catchment and help to understand these relocation processes through time. While sediment budgets are widely used in geomorphological catchment-based studies, such quantification approaches are rarely applied in geoarchaeological studies. The case of Charlemagne's summit canal (also known as Fossa Carolina) and its erosional collapse provides an example for which we can use this geomorphological concept and understand the abandonment of the Carolingian construction site. The Fossa Carolina is one of the largest hydro-engineering projects in Medieval Europe. It is situated in Southern Franconia (48.9876°N, 10.9267°E; Bavaria, southern Germany) between the Altmühl and Swabian Rezat rivers. It should have bridged the Central European watershed and connected the Rhine–Main and Danube river systems. According to our dendrochronological analyses and historical sources, the excavation and construction of the Carolingian canal took place in AD 792 and 793. Contemporary written sources describe an intense backfill of excavated sediment in autumn AD 793. This short-term erosion event has been proposed as the principal reason for the collapse and abandonment of the hydro-engineering project. We use subsurface data (drillings, archaeological excavations, and direct-push sensing) and geospatial data (a LiDAR digital terrain model (DTM), a pre-modern DTM, and a 3D model of the Fossa Carolina] for the identification and sediment budgeting of the backfills. Dendrochronological findings and radiocarbon ages of macro remains within the backfills give clear evidence for the erosional collapse of the canal project during or directly after the construction period. Moreover, our quantification approach allows the detection of the major sedimentary collapse zone. The exceedance of the manpower tipping point may have caused the abandonment of the entire construction site. The spatial distribution of the dendrochronological results indicates a north–south direction of the early medieval construction progress. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

Imaging Hydrological Processes in Headwater Riparian Seeps with Time‐Lapse Electrical Resistivity          下载免费PDF全文

Mark R. Williams  Anthony R. Buda  Kamini Singha  Gordon J. Folmar  Herschel A. Elliott  John P. Schmidt 《Ground water》2017,55(1):136-148

Delineating hydrologic and pedogenic factors influencing groundwater flow in riparian zones is central in understanding pathways of water and nutrient transport. In this study, we combined two‐dimensional time‐lapse electrical resistivity imaging (ERI) (depth of investigation approximately 2 m) with hydrometric monitoring to examine hydrological processes in the riparian area of FD‐36, a small (0.4 km²) agricultural headwater basin in the Valley and Ridge region of east‐central Pennsylvania. We selected two contrasting study sites, including a seep with groundwater discharge and an adjacent area lacking such seepage. Both sites were underlain by a fragipan at 0.6 m. We then monitored changes in electrical resistivity, shallow groundwater, and nitrate‐N concentrations as a series of storms transitioned the landscape from dry to wet conditions. Time‐lapse ERI revealed different resistivity patterns between seep and non‐seep areas during the study period. Notably, the seep displayed strong resistivity reductions (～60%) along a vertically aligned region of the soil profile, which coincided with strong upward hydraulic gradients recorded in a grid of nested piezometers (0.2‐ and 0.6‐m depth). These patterns suggested a hydraulic connection between the seep and the nitrate‐rich shallow groundwater system below the fragipan, which enabled groundwater and associated nitrate‐N to discharge through the fragipan to the surface. In contrast, time‐lapse ERI indicated no such connections in the non‐seep area, with infiltrated rainwater presumably perched above the fragipan. Results highlight the value of pairing time‐lapse ERI with hydrometric and water quality monitoring to illuminate possible groundwater and nutrient flow pathways to seeps in headwater riparian areas.  相似文献   

Modeling the Impact of Stream Discharge Events on Riparian Solute Dynamics     

Muhammad Nasir Mahmood  Christian Schmidt  Jan H. Fleckenstein  Nico Trauth 《Ground water》2019,57(1):140-152

The biogeochemical composition of stream water and the surrounding riparian water is mainly defined by the exchange of water and solutes between the stream and the riparian zone. Short-term fluctuations in near stream hydraulic head gradients (e.g., during stream flow events) can significantly influence the extent and rate of exchange processes. In this study, we simulate exchanges between streams and their riparian zone driven by stream stage fluctuations during single stream discharge events of varying peak height and duration. Simulated results show that strong stream flow events can trigger solute mobilization in riparian soils and subsequent export to the stream. The timing and amount of solute export is linked to the shape of the discharge event. Higher peaks and increased durations significantly enhance solute export, however, peak height is found to be the dominant control for overall mass export. Mobilized solutes are transported to the stream in two stages (1) by return flow of stream water that was stored in the riparian zone during the event and (2) by vertical movement to the groundwater under gravity drainage from the unsaturated parts of the riparian zone, which lasts for significantly longer time (> 400 days) resulting in long tailing of bank outflows and solute mass outfluxes. We conclude that strong stream discharge events can mobilize and transport solutes from near stream riparian soils into the stream. The impact of short-term stream discharge variations on solute exchange may last for long times after the flow event.  相似文献   

The Geochemical Effects of Microbial Humic Substances Reduction     

John D. Coates  Romy Chakraborty  Susan M. O&#x;Connor  Claudia Schmidt  Jürgen Thieme 《洁净——土壤、空气、水》2001,28(7):420-427

As part of a study on microbial redox alteration of humic substances we investigated the potential effect of this metabolism on the fate of heavy metals and hydrocarbons as a result of conformational alteration of the humic molecular structure due to microbial reduction. Our studies indicate that the microbial reduction of humic acids (HA) results in significant morphological and geochemical alterations. X‐ray microscopy analysis indicate that the conformational structure of the humic colloids is altered as a result of the redox change. In the reduced state, the HA appeared as small dense particles, on reoxidation, large loose aggregates were formed. In addition, spectrofluorometric studies indicated that the binding capacity of the HA for naphthalene was decreased by 10% when the HA was reduced. Similarly, the reduced HA yielded higher surface tension values at all concentrations tested which is indicative of a more hydrophilic and less hydrophobic solute. On reoxidation, the surface tension values reverted back to values similar to those obtained for the untreated oxidized HA. These data indicate that the hydrophobicity of the HA is altered on biological reduction of the HA and that this alteration is reversible. In contrast the reduced HA demonstrated a 15% higher affinity for heavy metals such as divalent cobalt than the oxidized HA. In addition to increasing the binding capacity of HA for heavy metals, the reduction of the HA also decreased the bioavailability and toxicity of bound heavy metals such as chromium. When incubated in the presence of Cr(III) and HA, cells of Escherichia coli grew much more rapidly in the presence of the reduced HA suggesting that the higher metal binding capacity of the reduced humic substances resulted in a removal of the Cr(III) from solution and hence reduced its bioavailability and toxicity. These studies demonstrate that HA redox state and reduction of humic acids by microorganisms can have a significant effect on the molecular morphology and binding constants of HA for heavy metals and hydrocarbons and also directly affects the bioavailability of these compounds in the environment.  相似文献   

The GREGOR adaptive optics system     

Th. Berkefeld  D. Schmidt  D. Soltau  O. von der Lühe  F. Heidecke 《Astronomische Nachrichten》2012,333(9):863-871

The new 1.5‐m German solar telescope GREGOR at the Observatorio del Teide, Tenerife, is equipped with an integrated adaptive optics system. Although partly still in the commissioning phase, the system is already being used used for most science observations. It is designed to provide diffraction‐limited observations in the visible‐light regime for seeing better than 1.2″. We describe the AO system including the optical design, software, wavefront reconstruction, and performance (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Assessment of susceptibility to landslides through geographic information systems and the logistic regression model     

Riegel  Roberta Plangg  Alves  Darlan Daniel  Schmidt  Bruna Caroline  de Oliveira  Guilherme Garcia  Haetinger  Claus  Osório  Daniela Montanari Migliavacca  Rodrigues  Marco Antônio Siqueira  de Quevedo  Daniela Muller 《Natural Hazards》2020,103(1):497-511

Natural Hazards - The increase in the frequency of natural disasters in recent years and its consequent social, economic and environmental impacts make it possible to prioritize areas of risk as an...  相似文献