Calculation of atmospheric electric fields penetrating from the ionosphere

The spatial distributions of electric fields and currents in the Earth’s atmosphere are calculated. Electric potential distributions typical of substorms and quiet geomagnetic conditions are specified in the ionosphere. The Earth is treated as a perfect conductor. The atmosphere is considered as a spherical layer with a given height dependence of electrical conductivity. With the chosen conductivity model and an ionospheric potential of 300 kV with respect to the Earth, the electric field near the ground is vertical and reaches 110 Vm⁻¹. With the 60-kV potential difference in the polar cap of the ionosphere, the electric field disturbances with a vertical component of up to 13 V m⁻¹ can occur in the atmosphere. These disturbances are maximal near the ground. If the horizontal scales of field nonuniformity are over 100 km, the vertical component of the electric field near the ground can be calculated with the one-dimensional model. The field and current distributions in the upper atmosphere can be obtained only from the three-dimensional model. The numerical method for solving electrical conductivity problems makes it possible to take into account conductivity inhomogeneities and the ground relief.     

Reaction of the critical frequency of the <Emphasis Type="Italic">F</Emphasis>2 layer to a sharp depletion in atmospheric pressure

Changes in the critical frequencies of the F2 layer at several midlatitude stations of ionospheric vertical sounding during a sharp depletion in atmospheric pressure under quiet solar and geomagnetic conditions are analyzed. It is shown that in such periods, the observed foF2 values differ from the mean values by approximately 10–15% and the deviations from the mean could be both negative (in the daytime hours) and positive (at night). Such variations in foF2 could be referred to the known class of ionospheric disturbances observed under a quiet geomagnetic situation, that is, to the so-called “Q-disturbances.” Analysis of wavelet spectra of foF2 variations shows the presence in the F region of oscillations of various periods (from 0.5 to 10 days). The decrease in the amplitude of daily variations during pressure depletion is found. Presumably, the observed effect is caused by the dynamic impact of waves formed in the lower atmosphere on the ionospheric F2 layer.     

Modeling of RC columns strengthened with RC jackets

Constructing concrete jackets is a common technique when strengthening reinforced concrete (RC) columns, particularly in seismic regions. However, there are many uncertainties concerning the behavior of the composite specimen, particularly at the interface between the old and new concrete. In this paper, monotonic finite element (FE) analyses are performed to examine the behavior of strengthened columns under monotonic and cyclic loading. Through investigating two independent series of experimental results, it is demonstrated that monotonic FE analysis with appropriate assumptions can simulate both monotonic and cyclic loading conditions to a reasonable degree of accuracy. According to the results of this study, it is found that a simulation of the interface between the old and the new concrete is vital and cannot be ignored by simply considering a perfect bond at the interface. In the case of strengthened RC columns subjected to cyclic loading, strength degradation at the interface has to be included and can be effectively modeled by reducing the coefficients of friction and adhesion by using a proposed formula. Finally, the effect of jacket concrete shrinkage is simulated that leads to a reduced maximum load and stiffness of strengthened columns. Copyright © 2011 John Wiley & Sons, Ltd.     

Large debris avalanches and associated eruptions in the Holocene eruptive history of Shiveluch Volcano, Kamchatka, Russia

 Shiveluch Volcano, located in the Central Kamchatka Depression, has experienced multiple flank failures during its lifetime, most recently in 1964. The overlapping deposits of at least 13 large Holocene debris avalanches cover an area of approximately 200 km² of the southern sector of the volcano. Deposits of two debris avalanches associated with flank extrusive domes are, in addition, located on its western slope. The maximum travel distance of individual Holocene avalanches exceeds 20 km, and their volumes reach ∼3 km³. The deposits of most avalanches typically have a hummocky surface, are poorly sorted and graded, and contain angular heterogeneous rock fragments of various sizes surrounded by coarse to fine matrix. The deposits differ in color, indicating different sources on the edifice. Tephrochronological and radiocarbon dating of the avalanches shows that the first large Holocene avalanches were emplaced approximately 4530–4350 BC. From ∼2490 BC at least 13 avalanches occurred after intervals of 30–900 years. Six large avalanches were emplaced between 120 and 970 AD, with recurrence intervals of 30–340 years. All the debris avalanches were followed by eruptions that produced various types of pyroclastic deposits. Features of some surge deposits suggest that they might have originated as a result of directed blasts triggered by rockslides. Most avalanche deposits are composed of fresh andesitic rocks of extrusive domes, so the avalanches might have resulted from the high magma supply rate and the repetitive formation of the domes. No trace of the 1854 summit failure mentioned in historical records has been found beyond 8 km from the crater; perhaps witnesses exaggerated or misinterpreted the events. Received: 18 August 1997 / Accepted: 19 December 1997     

Bifurcation of volcanic plumes in a crosswind

Bent-over buoyant jets distorted by a crosscurrent develop a vortex pair structure and can bifurcate to produce two distinct lobes which diverge from one another downwind. The region downwind of the source between the lobes has relatively low proportions of discharged fluid. Factors invoked by previous workers to cause or enhance bifurcation include buoyancy, release of latent heat at the plume edge by evaporating water droplets, geometry and orientation of the source, and the encounter with a density interface on the rising path of the plume. We suggest that the pressure distribution around the vortex pair of a rising plume may initially trigger bifurcation. We also report new experimental observations confirming that bifurcation becomes stronger for stronger bent-over plumes, identifying that bifurcation can also occur for straight-edged plumes but gradually disappears for stronger plumes which form a gravity current at their final level and spread for a significant distance against the current. Observations from satellites and the ground are reviewed and confirm that volcanic plumes can show bifurcation and a large range of bifurcation angles. Many of the bifurcating plumes spread out at the tropopause level and suggest the tropopause may act on the plumes as a density interface enhancing bifurcation. Even for quite moderate bifurcation angles, the two plume lobes become rapidly separated downwind by distances of tens of kilometers. Such bifurcating plumes drifting apart can only result in bilobate tephra fall deposits. The tephra fall deposit from the 16 km elevation, SE spreading, bifurcating volcanic plume erupted on 15 May 1981 from Mt Pagan was sampled by previous workers and clearly displayed bilobate characteristics. Examples of bilobate tephra fall deposits are reviewed and their origin briefly discussed. Bilobate deposits are common and may result from many causes. Plume bifurcation should be considered one of the possible mechanisms which can account for come examples of bilobate tephra fall deposits.     

Correcting lateral boundary biases in regional climate modelling: the effect of the relaxation zone

Climate Dynamics - Regional climate models (RCM) are an important tool for simulating atmospheric information at finer resolutions often of greater relevance to local scale climate change impact...     

Empirical Orthogonal Function (EOF) analysis of monsoon rainfall and satellite-observed outgoing long-wave radiation for Indian monsoon: a comparative study

Summary The present study involves the use of Empirical Orthogonal Function (EOF) analysis/Principal Component Analysis (PCA) to compare the dominant rainfall patterns from normal rainfall records over India, coupled with the major modes of the Outgoing Long-wave Radiation (OLR) data for the period (1979–1988) during the monsoon period (June–September). To understand the intraseasonal and interannual variability of the monsoon rainfall, daily and seasonal anomalies have been obtained by using the (EOF) analysis. Importantly, pattern characteristics of seasonal monsoon rainfall covering 68 stations in India are highlighted.The purpose is to ascertain the nature of rainfall distribution over the Indian continent. Based on this, the percentage of variance for both the rainfall and OLR data is examined. OLR has a higher spatial coherence than rainfall. The first principal component of rainfall data shows high positive values, which are concentrated over northeast as well as southeast, whereas for the OLR, the area of large positive values is concentrated over northwest and lower value over south India apart from the Indian ocean. The first five principal components explain 92.20% of the total variance for the rainfall and 99.50% of the total variance for the outgoing long-wave radiation. The relationship between monsoon rainfall and Southern Oscillations has also been examined and for the Southern Oscillations, it is 0.69 for the monsoon season. The El-Niño events mostly occurred during Southern Oscillations, i.e. Walker circulation. It has been found that the average number of low pressure system/low pressure system days play an important role during active (flood) or inactive (drought) monsoon year, but low pressure system days play more important role in comparison to low pressure systems and their ratio are (16:51) and (13:25) respectively. Significantly, the analysis identifies the spatial and temporal pattern characteristics of possible physical significance.     

Effect of Natural and Anthropogenic Factors on Soils,Soil Water,and Subsoil Water in Kola Peninsula

The concentrations of mobile compounds of S, Cu, and Ni are determined in podzol soils in the Murmansk region taken at different distances from Severonikel Copper–Nickel Plant and their variations are analyzed. The concentrations are found to have an effect on the distribution of these elements in lysimetric and subsoil waters.     

Observations of the upper frequency cutoffs of the auroral kilometric radiation

Intense auroral kilometric radiation (AKR) is being frequently observed with POLRAD from the Auroral Probe (Interball-2). Observations of the abrupt upper frequency cutoffs (UFCs) in the spectra of AKR are reported. The UFCs can be observed at a frequency range from 300 to 700 kHz, corresponding to AKR generation altitudes from approximately 4800 to 2100 km, and are distributed in magnetic local time (MLT) hours similarly to the AKR events, with a maximum at 1 h MLT. The observed frequency extent of the UFCs is 12 kHz, and is often determined by the instrumental resolution (4 kHz). It is suggested that the UFC may be associated with an abrupt switching on of the generation mechanism, when the electron density becomes sufficiently low inside a plasma depletion at an altitude where the ratio of f_pe/f_ce crosses some threshold value. The steepness of the UFCs can imply a non-linear process of generation. The estimated distance of the e-folding field aligned wave amplification is between 3 and 8 km. The UFCs are sometimes, though very seldom (10%), accompanied by narrow band (less than 4 kHz) ridges of radiation observed at the cutoff frequency. They are smoothly drifting in frequncy for several minutes. The power density of radiation in the ridge can be up to 2 orders of magnitude stronger than in the accompanying wide band emission of AKR. The ridge at UFC can imply either energy concentration at the source bottom, or focusing, if specific conditions for the escape of the radiation are assumed.     

Intercomparison of210Pb measurements at GEOSECS station 500 in the northeast Pacific

During reoccupation of the GEOSECS-I test station in May, 1979, more than eighty 30-liter Niskin samples were collected in profile, many as replicates, for²¹⁰Pb intercomparison measurements by the WHOI, SIO and Yale groups. In addition to the inter-laboratory comparisons, the SIO group also carried out extensive experiments to test the effect of sample scavenging method. Pb equilibration time (storage effect), and filtration process on the measured²¹⁰Pb results.The intercomparison measurements indicate that there is a general agreement between the various sets of data. The sample set which allows a direct comparison at the same depth was available in most cases only between two of the three groups. The direct paired comparison shows that (1) the WHOI data are systematically 3% lower than the SIO data; (2) there are no systematic differences observed between the SIO and Yale data although the scatter is rather large; (3) the Yale data are systematically higher than the WHOI data by about 8%.The SIO experiments show that (1) the two scavenging methods employed (Fe(OH)₃ and Co-APDC co-precipitation) yield identical²¹⁰Pb results; (2) variation of Pb carrier equilibration time or of storage time has no discernible effect; (3) the filtration apparatus and procedure employed at this station do not result in²¹⁰Pb loss or contamination.The²¹⁰Pb profile structure and absolute concentration measured earlier at the same location (GOGO-II test station and GEOSECS station 347) agree with those of station 500 within 10%. The present profile shows a minimum²¹⁰Pb concentration around 500 m depth, marking the penetration depth of the flux of excess²¹⁰Pb from the atmosphere. There is a mild mid-depth maximum around 2500–3000 m. The²¹⁰Pb/²²⁶Ra activity ratio decreases monotonically from about 1 at the²¹⁰Pb minimum to about 0.5 near the bottom. The particulate²¹⁰Pb profile shows a systematic increase from the subsurface water to the bottom water by a factor of 5. This feature has been observed in many GEOSECS particulate²¹⁰Pb profiles.