Quasi-periodicities in Chinese precipitation time series

Summary Although climate change deeply affects China, climatic time series are expected to show quasi-periodic behavior. This hypothesis has been tested by means of Autocorrelation Spectral Analysis (ASA) to detect quasi-periodicities in precipitation time series of 132 climate stations spread over China for the period from 1951 to 2002. A Continuous Wavelet Transform (CWT) has also been applied in order to examine if these quasi-periods are stable in time. Finally, it has been tested whether precipitation series recorded at neighboring stations show similar spectral behavior and can thus be grouped. All in all, our hypothesis regarding quasi-periodicities has been verified. Most of the time series show significant quasi-periods. A 2–3 year quasi-periodicity is predominant in many different regions of China. The result of ASA is that precipitation series from neighboring stations often show similar quasi-periods and therefore a grouping seems to be justified. However, the outcome of CWT provides more detailed information. In north-eastern China several series show similar quasi-periods which are statistically significant at different times; here, a grouping would be incorrect. In addition, the results of CWT show a less uniform pattern of quasi-periods in the southern inland regions. Whereas ASA shows a relatively uniform pattern of 2–3 year quasi-periods, CWT detects 2–3, 4–5 and 6–7 year quasi-periods. Nevertheless, although the quasi-periods are detected as being unstable, time series from neighboring stations sometimes show analogous significant quasi-periods within the same time frame and can thus be grouped. This can be seen in the northern part of central China, near the border to North Korea and along the coast of the South China Sea. Authors’ addresses: Heike Hartmann, Lorenz King, Department of Geography, Justus Liebig University, Senckenbergstra?e 1, 35390 Giessen, Germany; Stefan Becker, Department of Geography & Urban Planning, University of Wisconsin-Oshkosh, Oshkosh, WI 54901, U.S.A.     

Stellar disruption by a supermassive black hole: is the light curve really proportional to t−5/3?

In this paper, we revisit the arguments for the basis of the time evolution of the flares expected to arise when a star is disrupted by a supermassive black hole. We present a simple analytic model relating the light curve to the internal density structure of the star. We thus show that the standard light curve proportional to   t ^−5/3  only holds at late times. Close to the peak luminosity the light curve is shallower, deviating more strongly from   t ^−5/3  for more centrally concentrated (e.g. solar type) stars. We test our model numerically by simulating the tidal disruption of several stellar models, described by simple polytropic spheres with index γ. The simulations agree with the analytical model given two considerations. First, the stars are somewhat inflated on reaching pericentre because of the effective reduction of gravity in the tidal field of the black hole. This is well described by a homologous expansion by a factor which becomes smaller as the polytropic index becomes larger. Secondly, for large polytropic indices wings appear in the tails of the energy distribution, indicating that some material is pushed further away from parabolic orbits by shocks in the tidal tails. In all our simulations, the   t ^−5/3  light curve is achieved only at late stages. In particular, we predict that for solar-type stars, this happens only after the luminosity has dropped by at least 2 mag from the peak. We discuss our results in the light of recent observations of flares in otherwise quiescent galaxies and note the dependence of these results on further parameters, such as the star/hole mass ratio and the stellar orbit.     

Strategies for finite element modelling of three dimensional hydrodynamic systems

The simulation of a system composed entirely of three dimensional elements is computationally very expensive and little practical analysis has been undertaken. In an effort to reduce cost the author in a previous paper presented a simplified three dimensional model that used the hydrostatic pressure approximation to eliminate the vertical momentum equation and a transformation of the basic equations to directly solve for the free surface profile. This paper will examine approaches to the reduction of simulation costs within the framework of the original approach and modifications to the basic formulation to improve the performance of the model when the flow bath is over system with variable bed elevations. Examples will be presented to demonstrate the effectiveness of these modifications.     

CHONDRULE VOLUME PERCENTS: STATISTICAL BEHAVIOR AND VISUAL-ESTIMATION GUIDES PRODUCED BY NUMERICAL SIMULATION

Estimates of the volume percents of chondrules in petrographic thin sections are notoriously unreliable, ranging widely among different observers for the same meteorite or even for the same thin section. The set of visual-estimation guides presented herein should help narrow the uncertainties in such estimates and lead to a more consistent picture of chondrule abundances than is now apparent from the literature. In generating this set of guides other quantitative measures were also retained and examined. First, the expected error in the volume abundance of chondrules, due solely to sampling of homogeneous rocks by random thin sections, decreases as the inverse of the volume abundance of the chondrules. Second, our experiments of “softly” settled chondrules could not exceed chondrule abundances of 60 vol %. If chondrule-bearing rocks are found to exceed this value, the physical environment where they accreted must have had a greater gravity field than is available on asteroid-size bodies.     

Evaluation of throughflow interceptors for controlling secondary soil and water salinity in dryland agricultural areas of southwestern Australia : II. Hydrological study

Short-term hydrological measurements at one site show that throughflow provided the dominant input of water but not of soluble salts to the salt-affected land. Interceptors will therefore reduce saltland waterlogging caused by inputs of throughflow from valley sides. Leakages through and beneath the monitored interceptors are problems which are partly attributable to incorrect design and construction, and partly to unfavourable soil properties.The salinity of deeper groundwaters was also too low to account for the quantities of soluble salts being exported from the site. This finding suggests that a proportion of the salts accumulated in situ and have only recently been mobilized within the site by increased inputs of fresh throughflow and relatively fresh groundwaters from the catchment of the salt-affected area.Control of deeper groundwater movements as well as throughflow is probably necessary in most locations, but the precise combinations in different situations, and the most appropriate techniques for controlling these water movements, require further research. Increased groundwater discharges are attributed to reduced transpiration by the replacement of deep-rooted, indigenous vegetation with shallow-rooted, seasonally growing exotic crops and pastures, rather than to increased groundwater recharge. The ideal method of controlling both water systems is likely to involve farm management strategies on saltland catchments, employing commercially useful vegetation which simulates the hydrological role of the native species, in conjunction with improvement of soil properties.     

THE INMAN,McPHERSON COUNTY,KANSAS METEORITE

Inman (find, 1966) is a single, relatively unweathered stone of 7.25 kg that contains fresh metal and only few weathering products away from fractures. It has a pronounced chondritic texture, with 38 vol % of the meteorite being made up of chondrules of virtually all textural types. The recalculated bulk analysis, particularly the ratios of Fe_total/SiO₂ (0.46), Fe°/Fe_total (0.35), and Fe°/Ni° (6.67) and the contents of Fe_total (19.45%) and metallic nickel-iron (7.94%), indicate that Inman is an L-group chondrite. The pronounced chondritic texture; the compositional variabilities of olivine, pyroxene, chromite, and ilmenite; the presence of a fine-grained, nearly opaque matrix, glass and twinned monoclinic low-Ca pyroxene indicate that the chondrite belongs to petrologic type 3.