Oxygen and bulk element abundances in Luna 20 fines

Abundances of O, Si, Al and Mn have been determined in Luna 20 fines sample 22001,9 by instrumental neutron activation analysis. The abundances of O, Si and Al are among the highest we have observed in lunar samples and reflect a highlands origin for much of this regolith sample. The Luna 20 abundances reported here most closely resemble those we have determined in four samples of two Apollo 16 fines, rock 14310, and a clast from breccia 15459. The Luna 20 $\text{O}\text{Si}$ ratio of 1.96 ± 0.05 is similar to that in most other lunar samples, but the $\text{Al}\text{Si}$ ratio of 0.532 ± 0.024 is exceeded only by our data on the Apollo 16 fines. This $\text{Al}\text{Si}$ ratio is in agreement with the value of 0.55 ± 0.06 determined by the remote X-ray fluorescence experiment for the highlands between Mare Crisium and Mare Smythii which lie near the Luna 20 site (Adleret al., 1972).     

Results of deep seismic soundings along international profile VII in Czechoslovakia and poland

Summary The paper deals with the results of DSS measurements along international profile VII, carried out by Czechoslovak and Polish geophysicists in 1970 – 71. The profile situation is shown in Fig. 1. By 1971 part of the profile in the region of the Bohemian Massif between points 1 and 3 and in Poland between points 5 and 7 had been surveyed (Fig. 2). The seismograms were used to construct the travel-time curves of the fundamental types of waves P^K, P^M, P_n (Fig. 4). The mean velocities were computed from the travel-time curves of the reflected waves (P^M and P^K) and the refracted waves (P_g). Isolines of the mean velocities could be constructed for the region of the Bohemian Massif (Fig. 6). The velocity data found were used for the depth interpretation of the travel-time curves of the principal types of waves and to construct a seismic section (Fig. 8). In the region of the Pre-Sudeten block the thickness of the crust was found to be 34–37 km, and in the Sudeten it increased to 40 km. Towards the south the thickness of the crust gradually reduces to 30 km in the system of the Luice faults. In the Bohemian Cretaceous the thickness of the crust is about 30 km. Further to the south, in the region of the Moldanubicum, the thickness of the Earth's crust increases rapidly, and at the southern border of the Central Bohemian pluton it reaches values of about 42 km.     

Subsurface electric fields of a grounded cable of finite length for both frequency and time domain

Summary The subsurface electric fields of a current-carrying cable are examined for both steady-state and transient situations. Closed form expressions are obtained for two of the electric field components, and a numerical integration is used to obtain the third component. Waveforms for a stepfunction current excitation are displayed. The results have possible application to pulsed downlink communication in mine rescue operations.     

Mascali,Mount Etna Region Sicily: An Example of Fascist Planning During the 1928 Eruption and Its Continuing Legacy

The 1928 eruption of Etna, Sicily, although the largest such event this century, has not been studied in detail. In this paper the nature of the eruption, the destruction it caused – including the complete devastation of the town of Mascali (pre-eruption population 2,000) – and emergency responses of the authorities to it are reviewed in the context of fascist politics and planning priorities. It is contended that, although at one level the response to the 1928 eruption was successful, at another fascism merely continued and enhanced a reactive, propitiatory approach to hazard mitigation. We argue that this legacy was not successfully overcome until the middle of the nineteen eighties. Finally contemporary Italian moves towards a more proactive approach to disaster planning, both generally and in the context of Etna, are discussed.     

Constructing the Coronal Magnetic Field By Correlating Parameterized Magnetic Field Lines With Observed Coronal Plasma Structures

A method is presented for constructing the coronal magnetic field from photospheric magnetograms and observed coronal loops. A set of magnetic field lines generated from magnetogram data is parameterized and then deformed by varying the parameterized values. The coronal flux tubes associated with this field are adjusted until the correlation between the field lines and the observed coronal loops is maximized. A mathematical formulation is described which ensures that (i) the normal component of the photospheric field remains unchanged, (ii) the field is given in the entire corona over an active region, (iii) the field remains divergence-free, and (iv) electric currents are introduced into the field. It is demonstrated that a parameterization of a potential field, comprising a radial stretching of the field, can provide a match for a simple bipolar active region, AR 7999, which crossed the central meridian on 1996 November 26. The result is a non-force-free magnetic field with the Lorentz force being of the order of 10^–5.5 g cm s^–2 resulting from an electric current density of 0.079 A m^–2. Calculations show that the plasma beta becomes larger than unity at a relatively low height of 0.25 r supporting the non-force-free conclusion. The presence of such strong non-radial currents requires large transverse pressure gradients to maintain a magnetostatic atmosphere, required by the relatively persistent nature of the coronal structures observed in AR 7999. This scheme is an important tool in generating a magnetic field solution consistent with the coronal flux tube observations and the observed photospheric magnetic field.     

On the origin of solar metric type II bursts

The vast majority of solar flares are not associated with metric Type II radio bursts. For example, for the period February 1980–July 1982, corresponding to the first two and one-half years of the Solar Maximum Mission, 95% of the 2500 flares with peak >25 keV count rates >100 c s^–1lacked associated Type II emission. Even the 360 largest flares, i.e., those having >25 keV peak count rates >1000 c s^–1, had a Type II association rate of only 24%. The lack of a close correlation between flare size and Type II occurrence implies the need for a 'special condition' that distinguishes flares that are accompanied by metric Type II radio bursts from those of comparable size that are not. The leading candidates for this special condition are: (1) an unusually low Alfvén speed in the flaring region; and (2) fast material motion. We present evidence based on SMM and GOES X-ray data and Solwind coronagraph data that argues against the first of these hypotheses and supports the second. Type II bursts linked to flares within 30° of the solar limb are well associated (64%; 49/76) with fast (>400 km s^–1) coronal mass ejections (CMEs); for Type II flares within 15° of the limb, the association rate is 79% (30/38). An examination of the characteristics of 'non-CME' flares associated with Type IIs does not support the flare-initiated blast wave picture that has been proposed for these events and suggests instead that CMEs may have escaped detection. While the degree of Type II–CME association increases with flare size, there are notable cases of small Type II flares whose outstanding attribute is a fast CME. Thus we argue that metric Type II bursts (as well as the Moreton waves and kilometric Type II bursts that may accompany them) have their root cause in fast coronal mass ejections.     

Determining short-term changes in the hydraulic properties of a sandy-loam soil by a three-run infiltration experiment

ABSTRACT

Soil structure-dependent parameters can vary rapidly as a consequence of perturbing events such as intense rainfall. Investigating their short-term changes is therefore essential to understand the general behaviour of a porous medium. The aim of this study is to gain insight into the effects of wetting, perturbation and recovery processes through different sequences of Beerkan infiltration experiments performed on a sandy-loam soil. Two different three-run infiltration experiments (LHL and LLL) were carried out by pouring water at low (L, non-perturbing) and high (H, perturbing) heights above the soil surface and at short time intervals (hours, days). The results demonstrate that the proposed method allows one to capture short-term variations in soil structure-dependent parameters. The developed methodology is expected to simplify the parameterization of hydrological models with temporally variable soil hydraulic properties.     

An experiment on reservoir representation schemes to improve hydrologic prediction: coupling the national water model with the HEC-ResSim

ABSTRACT

This study experiments with reservoir representation schemes to improve the ability to model active water management in the National Water Model (NWM). For this purpose, we developed an integrated water management model, NWM-ResSim, by coupling the NWM with HEC-ResSim, and two reservoir representation schemes are tested: simulation of reservoir operations and retrieval of scheduled operations. The experiments focus on a pilot reservoir domain in the Russian River basin – Lake Mendocino, California – and its contributing watershed. The evaluation results suggest that the NWM-ResSim improves the simulation performance of reservoir outflow from this managed reservoir over the NWM default level pool routing scheme. The degree of this improvement depends on the suitability of the operation guidance; the reservoir operations simulation scheme could have acceptable errors for the purposes of water resources management, but not for flood operations. Results of the retrieval scheme of scheduled operations demonstrated better performance for sub-daily flood operations.     

Magnetism and thermal evolution of the terrestrial planets

Of the terrestrial planets, Earth and probably Mercury possess substantial intrinsic magnetic fields generated by core dynamos, while Venus and Mars apparently lack such fields. Thermal histories are calculated for these planets and are found to admit several possible present states, including those which suggest simple explanations for the observations; whule the cores of Earth and Mercury are continuing to freeze, the cores of Venus and Mars may still be completely liquid. The models assume whole mantle convection, which is parameterized by a simple Nusselt-Rayleigh number relation and dictates the rate at which heat escapes from the core. It is found that completely fluid cores, devoid of intrinsic heat sources, are not likely to sustain thermal convection for the age of the solar system but cool to a subadiabatic, conductive state that can not maintain a dynamo. Planets which nucleate an inner core continue to sustain a dynamo because of the gravitational energy release and chemically driven convection that accompany inner core growth. The absence of a significant inner core can arise in Venus because of its slightly higher temperature and lower central pressure relative to Earth, while a Martian core avoids the onset of freezing if the abundance of sulfur in the core is ?15% by mass. All of the models presented assume that (I) core dynamos are driven by thermal and/or chemical convection; (ii) radiogenic heat production is confined to the mantle; (iii) mantle and core cool from initially hot states which are at the solidus and superliquidus, respectively; and (iv) any inner core excludes the light alloying material (sulfur or oxygen) which then mixes uniformly upward through the outer core. The models include realistic pressure and composition-dependent freezing curves for the core, and material parameters are chosen so that the correct present-day values of heat outflow, upper mantle temperature and viscosity, and inner core radius are obtained for the earth. It is found that Venus and Mars may have once had dynamos maintained by thermal convection alone. Earth may have had a completely fluid core and a dynamo maintained by thermal convection for the first 2 to 3 by, but an inner core nucleates and the dynamo energetics are subsequently dominated by gravitational energy release. Complete freezing of the Mercurian core is prohibited if it contains even a small amount of sulfur, and a dynamo can be maintained by chemical convection in a thin, fluid shell.