Understanding the surface hydrology of the Lake Eyre Basin: Part 1—Rainfall

This is the first of two papers that describe the surface hydrology of the Lake Eyre Basin (LEB) (1,140,000 km²) in central Australia and compares some key characteristics with those observed from arid regions globally. This paper concentrates on annual rainfall, whereas the second paper is devoted to streamflow. The first part describes the LEB's climate (arid to semi-arid), which is dominated by a subtropical high pressure ridge stretching latitudinally across central Australia. Then follow major analyses that include the characteristics of rainfall, wet and dry spell lengths and cumulative surpluses and deficiencies, rainfall trends and intra- and inter-decadal fluctuations, and the relationship between rainfall and El Niño-Southern Oscillation (ENSO). The paper concludes with six conclusions, the key ones being: the variability of the annual rainfall (based on the coefficient of variation) in the LEB is approximately 60% greater than that found for stations located in arid regions in the rest of the world; there is a bias towards longer lengths of dry years than observed in the rest of Australia; and, there is a significant lag correlation between rainfall and ENSO, particularly in the east and in the latter part of a year.     

Scaling of response spectrum and duration for aftershocks

Aftershocks have the potential to cause collapse of a structure that has been already damaged by the preceding main shock. Seismic safety of a structure should therefore be ascertained through a damage analysis using the anticipated main shock and few larger-aftershock motions. Simulation of aftershock motions needs characterization of the seismic hazard due to aftershocks, and therefore it will be useful to develop a conditional scaling model that can predict the response spectrum of an anticipated aftershock motion consistent with the design spectrum of the main shock motion anticipated at the same station. In this study an attempt is made to develop a conditional scaling model for the pseudo spectral velocity spectrum via linear regression analysis on the aftershock and main shock recordings for the 1999 Chi–Chi earthquake. It is shown that it may be possible to obtain a simpler and approximate version of the conditional model from an unconditional model. Damage-causing potential of a ground motion also depends on its strong motion duration (SMD) and therefore a conditional scaling model is developed for SMD of the aftershock motion in several narrow frequency-bands. The model is developed for the larger-aftershock motions and it is shown that a reasonable replacement of such a model may be obtainable directly from an unconditional model. Finally, a simple weighted averaging scheme is proposed to obtain the composite SMD from the SMDs for different frequency bands by using the pseudo spectral acceleration spectrum of the motion.     

The In-Flight Performance of the SOHO/CDS Grazing Incidence Spectrometer

We present the characteristics, operations history, performance, and calibration of the Grazing Incidence Spectrometer (GIS) of the Coronal Diagnostic Spectrometer onboard SOHO. The GIS sensitivity has been monitored in a direct manner by examining the quiet Sun count rates during 1996 – 2006, nearly a whole solar cycle of observations. Overall, the instrument, with its grazing-incidence optics and microchannel plates, has performed exceptionally well. For most spectral regions, changes in the instrument sensitivity have been very small over a 10-year period. The trends in sensitivities support the use of the radiometric calibration of Del Zanna et al. (Astron. Astrophys. 379, 708, 2001) throughout the mission. The verification of the detector performance over such a long period allows us to point out the spectral lines that can reliably be used for scientific analysis.     

A photometric study of the polar ring galaxy UGC 5600

We analyze our BVR _c photometry for UGC 5600, a candidate polar ring galaxy, obtained with the 6-m telescope. We have confirmed the existence of an inner polar ring and show that the outer ring-shaped structure represents spiral arms; i.e., UGC 5600 belongs to the rare class of gas-rich spiral galaxies with inner polar rings.     

Magnesium-iron compositional variance in hornblende pyroxene granulites

Hornblende-orthopyroxene-calcic pyroxene-plagioclase (andesine-labradorite) — magnetite-ilmenite±quartz assemblages are evidently the most common granulite facies representatives of basic rocks throughout the world, and they must represent a variance of more than one. Ramberg (1948) invoked an additional degree of freedom arising out of unequal fractionation of Mg and Fe in the ferromagnesian silicates in such rocks. This is examined in detail on the basis of chemical data on twentytwo hornblende-orthopyroxenecalcic pyroxene triads, half of them from the type charnockite area near Madras.Theoretical consideration of a magnesium-iron distribution model shows that in quartz-bearing hornblende pyroxene granulites, the Mg/Mg+Fe ratios of hornblende, orthopyroxene and calcic pyroxene are uniquely determined by temperature at constant pressure. But these assemblages contain quartz rarely and Mg-Fe distribution among the three can be best described by three exchange equilibria where, at constant temperature, there is a fixed relation between the Mg/Mg+Fe ratios of the minerals. Among these, the exchange equilibria between hornblende-orthopyroxene and hornblende-calcic pyroxene appear to be interdependent; however, they are known to be significantly modified by varying tetrahedral aluminium contents of hornblendes. Comparison of molecular Mg/(Mg+Fe) ratios of hornblendes and parent rocks strongly points to an absence of Mg-Fe compositional variance in the total system, a petrologically important corollary being that the hornblendes in these rocks are highly unlikely to be secondary after pyroxenes. The general variance of the assemblages is also discussed.     

Limit equilibrium method (LEM) of slope stability and calculation of comprehensive factor of safety with double strength-reduction technique

When the slope is in critical limit equilibrium(LE) state, the strength parameters have different contribution to each other on maintaining slope stability. That is to say that the strength parameters are not simultaneously reduced. Hence, the LE stress method is established to analyze the slope stability by employing the double strengthreduction(DSR) technique in this work. For calculation model of slope stability under the DSR technique, the general nonlinear Mohr–Coulomb(M–C) criterion is used to describe the shear failure of slope. Meanwhile, the average and polar diameter methods via the DSR technique are both adopted to calculate the comprehensive factor of safety(FOS) of slope. To extend the application of the polar diameter method, the original method is improved in the proposed method. After comparison and analysis on some slope examples, the proposed method's feasibility is verified. Thereafter, the stability charts of slope suitable for engineering application are drawn. Moreover, the studies show that:(1) the average method yields similar results as that of the polardiameter method;(2) compared with the traditional uniform strength-reduction(USR) technique, the slope stability obtained using the DSR techniquetends to be more unsafe; and(3) for a slope in the critical LE state, the strength parameter φ, i.e., internal friction angle, has greater contribution on the slope stability than the strength parameters c, i.e., cohesion.     

STEREO SECCHI and S/WAVES Observations of Spacecraft Debris Caused by Micron-Size Interplanetary Dust Impacts

Early in the STEREO mission observers noted that the white-light instruments of the SECCHI suite were detecting significantly more spacecraft-related “debris” than any previously flown coronagraphic instruments. Comparison of SECCHI “debris storms” with S/WAVES indicates that almost all are coincident with the most intense transient emissions observed by the radio and plasma waves instrument. We believe the debris is endogenous (i.e., from the spacecraft thermal blanketing), and the storms appear to be caused by impacts of large interplanetary dust grains that are detected by S/WAVES. Here we report the observations, compare them to interplanetary dust distributions, and document a reminder for future spacebased coronagraphic instrument builders.