MACS for Global measurement of the Solar wind velocity and the Thermal electron temperature during the Total solar eclipse on 11 August 1999     

Reginald  Nelson L.  Davila  Joseph M. 《Solar physics》2000,195(1):111-122

MACS for Multi-Aperture Coronal Spectrometer is a fiber-optic-based spectrograph designed and used to perform global measurement of the solar wind velocity and the thermal electron temperature of the solar corona during the total solar eclipse on 11 August 1999. The motivation for the construction of MACS was provided by the theory formulated by Cram (1976) for the formation of the K-coronal spectrum and a method for determining the radial profile of the thermal electron temperature of the solar corona. Based on this theory a subsequent application was carried out by Ichimoto et al. (1996) using a slit-based spectroscopic study during the total solar eclipse on 3 November 1994. We have modified Cram's theory to incorporate the role of the solar wind velocity in the formation of the K-corona and have identified wind and temperature sensitive intensity ratios. Instead of a slit-based spectrograph MACS consists of twenty fiber optic tips placed at the focal plane of the telescope and positioned to see different radii and latitudes of the solar corona. Another fiber is placed at the center of the frame and uses the lunar shadow for a measure of the background signal. The other ends of the fibers are vertically aligned and placed at the primary focus of the collimating lens of the spectrograph thus providing simultaneous spectra from all of the fibers. In this first paper (Paper I) we describe our instrument and the obtained coronal spectra. The final and complete results will be presented in Paper II (Reginald and Davila, 2000).  相似文献   

Landslides control the spatial and temporal variation of channel width in southern Taiwan: Implications for landscape evolution and cascading hazards in steep,tectonically active landscapes          下载免费PDF全文

Brian J. Yanites  Nate A. Mitchell  Joshua C. Bregy  Grace A. Carlson  Kirstyn Cataldo  Margaret Holahan  Graham H. Johnston  Amelia Nelson  Jeffery Valenza  Matthew Wanker 《地球表面变化过程与地形》2018,43(9):1782-1797

Intense precipitation or seismic events can generate clustered mass movement processes across a landscape. These rare events have significant impacts on the landscape, however, the rarity of such events leads to uncertainty in how they impact the entire geomorphic system over a range of timescales. Taiwan is steep, tectonically active, and prone to landslide and debris flows, especially when exposed to heavy rainfall events. Typhoon Morakot made landfall in Taiwan in August of 2009, causing widespread landslides in southern Taiwan. The south to north trend in valley relief in southern Taiwan leads to spatial variability in landslide susceptibility providing an opportunity to infer the long‐term impact of such landslide events on channel morphology. We use pre‐ and post‐typhoon imagery to quantify the propagating impact of this event on channel width as the debris is routed through the landscape. The results show the importance of cascading hazards from landslides on landscape evolution based on patterns of channel width (both pre‐ and post‐typhoon) and hillslope gradients in 20 basins along strike in southern Taiwan. Prior to Typhoon Morakot, the river channels in the central part of the study area were about 3–10 times wider than the channels in the south. Following the typhoon, aggradation and widening was also a maximum in these central to northern basins where hillslope gradients and channel steepness is high, accentuating the pre‐typhoon pattern. The results further show that the narrowest channels are located where channel steepness is the lowest, an observation inconsistent with a detachment‐limited model for river evolution. We infer this pattern is indicative of a strong role of sediment supply, and associated landslide events, on long‐term channel evolution. These findings have implications across a range of spatial and temporal scales including understanding the cascade of hazards in steep landscapes and geomorphic interpretation of channel morphology. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

A general Lagrangian tracking methodology for riverine flow and transport     

Jonathan Nelson  Yasuyuki Shimizu  Tomoko Kyuka  Scott Charlton 《地球表面变化过程与地形》2023,48(1):87-103

This article presents a new public domain tool for generalized Lagrangian particle tracking in rivers. The approach can be applied with a variety of two- and three-dimensional flow solvers. Particle advection by the flow is incorporated using flow fields from the chosen solver assuming particles follow the Reynolds-averaged flow, although some other simple passive and active particle behaviors are also treated. Turbulence effects are treated using a random walk algorithm with spatial step lengths randomly chosen from Gaussian distributions characterized by the diffusivity from the flow solver. Our work extends this concept to a general framework that is solver and coordinate system independent to allow easy comparisons between differing flow treatments. To better treat problems where detailed information is required in specific regions, the approach includes novel cloning and colligation algorithms which enhance local resolution at modest computational expense. We also provide tools for computing local concentrations and total exposure over a user-specified time interval. Several examples of predictions are provided to illustrate applications of the technique, including examination of the role of curvature-driven secondary flows, storage in lateral separation eddies, treatment of larval drift, treatment of fuel spill dispersion, river-floodplain connections, and sedimentation in floodplain ponds by tie channel connections. We also demonstrate that the model can reproduce analytically derived concentration profiles for simple diffusivities. These examples show that the Lagrangian particle tracking approach and the extensions proposed here are broadly applicable and viable for treating difficult river problems with multiple temporal and spatial scales. The examples also illustrate the utility of the cloning/colligation extensions and show how these can decrease the computational effort required on problems where high local resolution is required. Enhancement of the tools and even broader applicability can be achieved through the inclusion of multiple particle populations and particle–particle interactions.  相似文献   

The Golden meteorite fall: Fireball trajectory,orbit, and meteorite characterization     

P. G. Brown  P. J. A. McCausland  A. R. Hildebrand  L. T. J. Hanton  L. M. Eckart  H. Busemann  D. Krietsch  C. Maden  K. Welten  M. W. Caffee  M. Laubenstein  D. Vida  F. Ciceri  E. Silber  C. D. K. Herd  P. Hill  H. Devillepoix  Eleanor K. Sansom  Martin Cupák  Seamus Anderson  R. L. Flemming  A. J. Nelson  M. Mazur  D. E. Moser  W. J. Cooke  D. Hladiuk  Barbara Malečić  Maja Telišman Prtenjak  R. Nowell  The Golden Meteorite Consortium 《Meteoritics & planetary science》2023,58(12):1773-1807

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