Relationship between the IMF azimuthal angle and solar wind velocity

The relationship between the IMF azimuthal angle and plasma velocity has been studied independently for three types of solar wind streams (recurrent and transient high-speed streams and low-speed background wind) based on the interplanetary medium parameters measured in the near-Earth orbits in 1964–1996. The relationships between the IMF azimuthal angle cotangent and plasma velocity are close to linear but strongly differ from one another and from the theoretical relationship for all types of streams. These differences area caused by the magnetic field disturbance on the time scales smaller than a day, and the effect of this disturbance has been studied quantitatively. The effective periods of rotation of the IMF sources on the Sun, depending on the solar cycle phase, have been obtained from the relations between the IMF azimuthal angle cotangent and plasma velocity. During the most part of the solar cycle, the periods of rotation of the IMF sources are close to the period of rotation of the solar equator but abruptly increase to the values typical of the solar circumpolar zones in the years of solar minimums.     

Geomagnetic Reversals and Dynamo Bursts in a Simple Geodynamo Model

The question of what exactly happens with the geodynamo process during the reversal of a geomagnetic field is studied in a simple geodynamo model. The geodynamo action is described by the so called dynamo number characterizing the joint action of the main drivers of the geomagnetic field, i.e., the differential rotation and mirror–asymmetric convection. In mirror-asymmetric convection, for instance, in the northern hemisphere, there are more right vortices than left vortices, whereas in the southern hemisphere, there are more left vortices than right vortices. The effect of the magnetic field on the flow is described by the suppression of the mirror asymmetry: due to this suppression, e.g., in the northern hemisphere, the excess of right vortices over left vortices decreases. It is also assumed that due to this suppression, the mirror asymmetry can change its sign; i.e., the number of left vortices in the northern hemisphere can become larger than the number of right vortices. Correspondingly, the dynamo number can also change its sign. It is shown that the short-term changes of the sign of the dynamo number are responsible for the very short time span accommodating the reversal, when compared to the interval between the reversals.     

Basin effects on ground motion: the case of a high-resolution experiment in Cephalonia (Greece)

In this study data and results of a high-resolution experiment in Cephalonia (Greece) regarding empirical basin effects are presented. A total of 59 velocimeters and 17 accelerometers were deployed in the basin of Argostoli Cephalonia (Greece), for a period of 7 months (September 2011–April 2012). Due to high seismicity of the western Greece and surrounding area this array recorded thousands of local, regional and global events. Data used in this work come from a selection of 162 regional and local earthquakes, 3 km ≤ R ≤ 600 km, with magnitude range, 1.0 ≤ M ≤ 5.2. Based on high signal-to-noise ratio recordings and two selected reference stations, variation of several intensity measures (PGA, PGV, Arias Intensity, Cumulative Absolute Velocity), significant duration, HVSR and SSR of ground motion recordings on soil sites within the basin is carefully examined for a range of frequencies of engineering interest. Comparison of results with a detailed 2D geologic model shows a good consistency both in amplification and frequency domain. Influence of “reference” site on ground motion variation of soil sites is also discussed in light of our results. Finally, it is suggested that 2D or/and 3D theoretical modeling should be performed given the availability of geological and geophysical parameters to define a realistic model of the basin. Results of this study can undoubtedly serve in model validation and improvement of ground motion simulation tools.     

Higher-mode force response in multi-story strongback-braced frames

Strongback-braced frames employ an essentially elastic steel truss, or strongback, that distributes demands more uniformly to delay or prevent story mechanisms. Because inertial forces are no longer limited by the formation of a story mechanism, strongback-braced frames can exhibit large elastic force demands, particularly in the higher modes. This paper characterizes the higher-mode force response of strongback-braced frames. Four-story archetypes were designed using nonlinear dynamic analyses to incorporate higher-mode force demands into the design process. The response of the archetypes was compared with that of reference buckling-restrained braced frames that were allowed to form story mechanisms. The force demands in the strongback were then described using equivalent-static forces to represent the inertial forces induced by the higher modes. Force demands in the strongback arise from a yielding first-mode ‘pivoting’ and elastic higher-mode ‘bending’ response. These higher-mode force demands are elastic, ill-constrained by the strength of the yield mechanism, and depend significantly on the choice of ground motion record used for the analysis. In remaining elastic in the higher modes, the strongback distributes demands more uniformly and mitigates the formation of story mechanisms. Consequently, design and analysis methods for strongback-braced frames need to include estimates for these near-elastic higher-mode force demands.     

Strong slope-aspect control of regolith thickness by bedrock foliation

The porous near-surface layer of the Earth's crust – the critical zone – constitutes a vital reservoir of water for ecosystems, provides baseflow to streams, guides recharge to deep aquifers, filters contaminants from groundwater, and regulates the long-term evolution of landscapes. Recent work suggests that the controls on regolith thickness include climate, tectonics, lithology, and vegetation. However, the relative paucity of observations of regolith structure and properties at landscape scales means that theoretical models of critical zone structure are incompletely tested. Here we present seismic refraction and electrical resistivity surveys that thoroughly characterize subsurface structure in a small catchment in the Santa Catalina Mountains, Arizona, USA, where slope-aspect effects on regolith structure are expected based on differences in vegetation. Our results show a stark contrast in physical properties and inferred regolith thickness on opposing slopes, but in the opposite sense of that expected from environmental models and observed vegetation patterns. Although vegetation (as expressed by normalized difference vegetation index [NDVI]) is denser on the north-facing slope, regolith on the south-facing slope is four times thicker (as indicated by lower seismic velocities and resistivities). This contrast cannot be explained by variations in topographic stress or conventional hillslope morphology models. Instead, regolith thickness appears to be controlled by metamorphic foliation: regolith is thicker where foliation dips into the topography, and thinner where foliation is nearly parallel to the surface. We hypothesize that, in this catchment, hydraulic conductivity and infiltration capacity control weathering: infiltration is hindered and regolith is thin where foliation is parallel to the surface topography, whereas water infiltrates deeper and regolith is thicker where foliation intersects topography at a substantial angle. These results suggest that bedrock foliation, and perhaps by extension sedimentary layering, can control regolith thickness and must be accounted for in models of critical zone development. © 2020 John Wiley & Sons, Ltd.     

Dinoflagellate cyst assemblages in recent sediments of Visakhapatnam harbour,east coast of India: Influence of environmental characteristics

The distribution and abundance of dinoflagellate cysts in recent sediments from Visakhapatnam harbour, east coast of India was investigated and compared with sediment characteristics and physico-chemical variables of the overlying water column. The cyst abundance varied from 11 to 1218 cysts g^–1 dry sediment. Changes in the cyst assemblages from phototrophic to heterotrophic forms were observed from inner to outer harbour stations, and related to changes in environmental characteristics. Enhanced cyst production of potentially harmful dinoflagellate Protoceratium reticulatum was recorded in the inner harbour stations with higher nutrient concentrations. Protoperidinium cysts were the most diversified group, and were dominant in the outer harbour stations having improved water conditions and circulation. This study points out the potential use of dinoflagellate cyst populations in providing information on environmental conditions.     

EFFECT OF SNOW FENCE HEIGHT ON WIND SPEED

Abstract

Accumulations of snow behind fences may increase the water yield in windswept areas. The efficiency of snow collection depends on the reduction in wind speed in the lee of the fence. Wind speeds have been measured to windward and to leeward of vertical slat fences from 6 to 16 ft. high. The down-wind measurements were made at distances of 2.5H, 5H and 10H from the fence where H is the height of the fence. Speed measurements at various levels were integrated up to the height of the fence and the percentage reduction in wind speed was calculated. Expressions are given for the velocity reduction factor at distances down-wind of fences having a bottom gap, and for the cross-sectional area of a fully developed drift.     

Statutes and Bye-laws of the International Association of Hydrological Sciences

Abstract

A baseflow recession constant, which can be derived from a simple exponential equation, is used to characterize the behaviour of low flows. Its derivation and quantification is important to the water industry. The use of a computer statistical package that speeds up its derivation has been tried and found to be more effective than the present tedious manual and subjective techniques. It is therefore advocated in this paper.     

Climate change and the oceans – What does the future hold?

The ocean has been shielding the earth from the worst effects of rapid climate change by absorbing excess carbon dioxide from the atmosphere. This absorption of CO₂ is driving the ocean along the pH gradient towards more acidic conditions. At the same time ocean warming is having pronounced impacts on the composition, structure and functions of marine ecosystems. Warming, freshening (in some areas) and associated stratification are driving a trend in ocean deoxygenation, which is being enhanced in parts of the coastal zone by upwelling of hypoxic deep water. The combined impact of warming, acidification and deoxygenation are already having a dramatic effect on the flora and fauna of the oceans with significant changes in distribution of populations, and decline of sensitive species. In many cases, the impacts of warming, acidification and deoxygenation are increased by the effects of other human impacts, such as pollution, eutrophication and overfishing.