Latitude dependence of magnetic field-line inclinations

It is shown that leading and following magnetic field lines are inclined toward each other by a few degrees at nearly all latitudes in both the north and south hemispheres. The amplitudes of these inclinations are lower by about a factor 3 for weak fields than for strong fields. There are significant differences between the hemispheres and from one activity cycle to the next in the leading and following polarity field-line inclinations at latitudes poleward of the activity latitudes. In a narrow latitude zone just south of the solar equator the inclinations of both the leading and following fields reduce to zero (or perhaps slightly negative values). Although one would expect such a zone at the equator, where diffusion will mix field lines with opposite inclinations from the two hemispheres, it is not clear why this zone should be on one side of the equator only. The results discussed here were obtained with Mount Wilson magnetograph data (1967–1992), and are confirmed in many respects with National Solar Observatory/Kitt Peak (NSO/KP) data (1976–1986).Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation.     

Electron Pitch-Angle Diffusion by ECH Waves in Earth and Jupiter Magnetospheres: Contribution to Diffuse Auroral Precipitation

Pitch-angle diffusion coefficients of electrons have been calculated for resonant interaction with electrostatic electron-cyclotron harmonic (ECH) waves using quasi linear diffusion theory. Calculations have been performed for the planets Earth and Jupiter at three radial distances for each planet. Electron precipitation fluxes have also been calculated and compared with observed fluxes. At Earth, electrons of energy ≤200 eV may be put on strong diffusion at L = 10. At lower L values, observed ECH wave amplitudes are insufficient to put electrons on strong diffusion. At Jupiter, electrons can be put on strong diffusion at all L values. However, the energy of electrons which may be put on strong diffusion decreases from about 1 keV at L = 7 to ~100 eV at L = 17. It is concluded that ECH waves may be partly responsible for diffuse auroral precipitation of low energy electrons at Jupiter for lower L values. At Earth contribution of ECH waves to diffuse aurora is quite small.     

Instrumental method for reducing error in compression-derived measurements of rainfall interception for individual trees

Abstract

This technical note presents an instrumental method for the precise and timely installation of mechanical displacement sensors to investigate stem compression and relaxation associated with whole-tree rainwater loading and evaporation, respectively. We developed this procedure in response to the conclusions of Friesen et al. (2008 Friesen, J. 2008. Tree rainfall interception measured by stem compression. Water Resources Research, 44 doi:doi:10.1029/2008 WR007074. [Google Scholar]), which called for the development of a precision mounting method for strain sensors on inherently-irregular trunk cross-sections so that rainfall interception, storage and evaporation may be distinguished from other strain-related phenomena. To supply precise sensor installation locations, high-resolution trunk profiles are generated using the LaserBark^TM automated tree measurement system. These scans are utilized to approximate the location of neutral bending axes. A routine then instructs a mobile rangefinder along the cross-section to optically indicate exact positioning for strain sensors over the bending axes. As imprecise sensor placement linearly increases error and diminishes signal-to-noise ratio, this automated installation routine is designed to remove significant distortions created by wind throw, off-centre loading within unevenly-distributed canopies, and human error that can lead to erroneous measurements of rainfall interception.

Citation Van Stan, J. T. II, Jarvis, M. T., Levia, D. F. Jr & Friesen, J. (2011) Instrumental method for reducing error in compressionderived measurements of rainfall interception for individual trees. Hydrol. Sci. J. 56(6), 1061–1066.     

坡地地形对竖向地震动反应谱特性的影响分析

为分析坡地地形对竖向地震动反应谱特性的影响规律,采用有限元数值分析方法,对黏弹性岩质坡地在白噪声输入下的响应进行计算。分析了坡地地形对场地竖向反应谱及谱比的影响,研究了随着坡高及坡角的增加,坡地斜坡段及平台段竖向反应谱及谱比的变化规律,给出了坡地斜坡段及平台段设计竖向地震动放大系数,有关的研究结论可为坡地上工程结构的抗震设计提供参考。     

Ionospheric Tomography Network of Egypt: A New Receiver Network in Support of the International Heliophysical Year

The International Heliophysical Year (IHY) 2007 is an international scientific program designed to coordinate observations of the heliosphere, the region of space from the solar surface through the solar wind and various planetary magnetospheres to the planetary upper atmospheres. A particular emphasis is given to the development of long-term international collaborations that will study the external drivers to the space environment and climate. The Ionospheric Tomography Network of Egypt (ITNE) is one such collaboration. It is a new chain of ionospheric tomography receivers that will be deployed to investigate the equatorial regions of the Earth’s ionosphere. The distribution of plasma density within 20° of the magnetic equator is highly sensitive to forcing from the solar wind through a process known as the equatorial fountain. ITNE will provide new observations of the density structures associated with the equatorial fountain.     

Accommodation of lithospheric shortening on Mercury from altimetric profiles of ridges and lobate scarps measured during MESSENGER flybys 1 and 2

The Mercury Laser Altimeter on the NASA MESSENGER mission has ranged to several ridges and lobate scarps during two equatorial flybys of the planet Mercury. The tectonic features sampled, like others documented by spacecraft imaging and Earth-based radar, are spatially isolated and have vertical relief in excess of 1 km. The profiles also indicate that the faulting associated with their formation penetrated to tens of kilometers depth into the lithosphere and accommodated substantial shortening. To gain insight into the mechanism(s) of strain accommodation across these structures, we perform analytical and numerical modeling of representative dynamic localization mechanisms. We find that ductile localization due to shear heating is not favored, given our current understanding of thermal gradients and shallow thermal structure of Mercury at the time of ridge and scarp formation, and is likely to be of secondary importance at best. Brittle localization, associated with loss of resistance during fault development or with velocity weakening during sliding on mature faults, is weakly localizing but permits slip to accumulate over geological time scales. The range of shallow thermal gradients that produce isolated faults rather than distributed fault sets under the assumption of modest fault weakening is consistent with previous models for Mercury’s early global thermal history. To be consistent with strain rates predicted from thermal history models and the amount of shortening required to account for the underlying large-offset faults, ridges and scarps on Mercury likely developed over geologically substantial time spans.     

Defining hydroclimatic regions using daily rainfall characteristics in the southern Appalachian Mountains

ABSTRACT

This paper addresses warm season hydroclimatic variability in the southern Appalachian region of the southeastern U.S., where precipitation can vary as much as 127?mm or more, with maximum seasonal totals exceeding 736?mm in extreme cases. Despite the occurrence of droughts, floods, and their socioecological impacts, hydroclimate variability is still poorly understood. This study characterizes the regional scale variations in the hydroclimate by examining the daily distribution of precipitation patterns in different topographic environments. Parameter-elevation relationships on independent slopes model (PRISM) gridded precipitation estimates are used to identify the location and frequency of different types of rainfall events. Several types of clustering algorithms are used as a regionalization approach to define areas where the precipitation regime exhibits similarities in its frequency of occurrence. The results are compared with internal validation statistics and a visualization is used to assess how well the resulting hydroclimatic regions align with different topographic environments. This study reveals the intricate spatial footprint of dry and wet regimes and demonstrates how clustering applications can be used with gridded climate data to determine where extremes are most likely to develop across mountain catchments.     

Direct evaluation of effectiveness of prefabricated vertical drains in liquefiable sand

A dynamic full scale testing program was performed to quantitatively assess the effectiveness of prefabricated vertical drains as a liquefaction countermeasure. The testing program involved a new in situ liquefaction testing technique, which uses a large hydraulic vibrator to generate waves propagating through an embedded instrumentation area to measure the coupled soil-pore water response. The effectiveness of prefabricated vertical drains is assessed experimentally by comparing the pore pressure generation, pore pressure dissipation, and settlement from two reconstituted soil specimens; one without a drain in place and the other with a single drain installed. Because the prefabricated drain was installed during the specimen preparation process, no accompanying densification during installation occurred. Therefore, the effect of drainage alone was evaluated. The testing results show that the drainage provided by prefabricated drains can significantly reduce pore pressure generation, accelerate post-shaking pore pressure dissipation, and limit associated settlement. The outcome also shows that the new developed in situ liquefaction testing technique can be an alternative to quantitatively evaluate the effects of various liquefaction remediation techniques.     

Chowdhury and Stedinger's approximate confidence intervals for design floods for a single site

A basic problem in hydrology is computing confidence levels for the value of the T-year flood when it is obtained from a Log Pearson III distribution in terms of estimated mean, estimated standard deviation, and estimated skew. In an important paper Chowdhury and Stedinger [1991] suggest a possible formula for approximate confidence levels, involving two functions previously used by Stedinger [1983] and a third function, λ, for which asymptotic estimates are given. This formula is tested [Chowdhury and Stedinger, 1991] by means of simulations, but these simulations assume a distribution for the sample skew which is not, for a single site, the distribution which the sample skew is forced to have by the basic hypothesis which underlies all of the analysis, namely that the maximum discharges have a Log Pearson III distribution. Here we test these approximate formulas for the case of data from a single site by means of simulations in which the sample skew has the distribution which arises when sampling from a Log Pearson III distribution. The formulas are found to be accurate for zero skew but increasingly inaccurate for larger common values of skew. Work in progress indicates that a better choice of λ can improve the accuracy of the formula.