Teleconnections between oceanic–atmospheric indices and drought over Iran using quantile regressions

ABSTRACT

In this research, the Bayesian quantile regression model is applied to investigate the teleconnections between large oceanic–atmospheric indices and drought standardized precipitation index (SPI) in Iran. The 12-month SPI time series from 138 synoptic stations for 1952–2014 were selected as the drought index. Three oceanic–atmospheric indices, the North Atlantic Oscillation (NAO), the Southern Oscillation Index (SOI) and the Multivariate El Niño/Southern Oscillation Index (MEI), were selected as covariates. The results show that NAO has the weakest impact on drought in different quantiles and different regions in Iran. La Niña conditions amplified droughts through all SPI quantiles in western, Caspian Sea coastal regions and southern regions. The positive phase of MEI significantly modulates low SPI quantiles (i.e. drought conditions) throughout the Zagros region, Caspian Sea coastal regions and southern regions. The study shows that the effect of large oceanic–atmospheric indices have heterogeneous impacts on extreme dry and wet conditions.     

A note on the noise amplitudes in some strong motion accelerographs

The amplitudes of digitization and processing noise in strong motion digital and analog accelerographs are discussed and compared with those for hand and automatic digitization. By finding the period bands for which the signal-to-noise ratio in recorded accelerograms is greater than one, the values for the pass-band cutoff periods for data processing are presented. The Empirical scalings for amplitudes in terms of: (1) earthquake magnitude and epicentral distance and, (2) Modified Mercalli Intensity at the recording site have been employed.     

Weathering and soils formation on different parent materials in Golestan Province,Northern Iran

Geochemical, mineralogical, and micromorphological characteristics of soils and their relevant parent rocks including loess, ignimbrite, sandstone and limestone were investigated to identify the soil-parent material uniformity and the weathering degree of soils in Golestan Province, northern Iran. Highly developed Calcixerolls and moderately developed Haploxerepts were formed on loess and limestone, respectively. In contrast, the soils formed on ignimbrite and sandstone were non-developed Entisols. Illite was the dominant clay mineral found in ignimbrite and sandstone in both the A horizon and parent material. In loess derived soils however, smectite was dominant especially in the Bt horizon compared to its parent material indicating partly to its pedogenic formation. In limestone, illite and vermiculite were dominant both in the A and C horizons. Ti/Zr ratio proved that the studied soils were closely related to their underlying parent materials geochemically. Chemical index of alteration (CIA), micromorphological index of soil development (MISECA), smectite/illite+chlorite ratio and magnetic susceptibility were applied to investigate the degree of soil development. Results showed that the most and the least developed soils were those formed on loess deposits and limestone, respectively. Application of the different geochemical and pedogenetic approaches was proved to be useful in identifying the relevance of soils to their underlying parent materials and also their degree of development.     

Capacity of quartz fibers with high filtration efficiency for capturing soot aerosol particles

Two proposed quartz fibrous filters with dissimilar solid volume fractions and thicknesses are investigated for their efficiency in removing soot aerosol particles from air. Soot particles are sourced from a candle burning in a chamber, and the tests involve 1.5 h of continuous loading of particles at three different flow rates: 4.5, 8.15 and 9.55 l/min. The fractional efficiency, morphology and pressure drop of both clean and loaded filters are studied using a scanning mobility particle sizer, scanning electron microscope and differential pressure gauge. Both filters have relatively similar levels of efficiency 93% for particle size (100–400 nm) at the lowest flow rate. At higher flow rates, the re-entrainment process effects the filtration efficiency of both filters. At the higher flow rate of 8.15 l/min, the filter with a higher solid volume fraction and thickness shows a higher pressure drop and an efficiency level of 95%. Increasing the flow rate to 9.55 l/min helps to pass the particles with diameters larger than 100 nm through two filters. This phenomenon decreases the fractional efficiency of both filters during the loading time.     

Numerical modeling of sediment scouring phenomenon around the offshore wind turbine pile in marine environment

In recent years, with daily progress in technology, application of wind turbines for energy generation has become common all around the world. Installation of these turbines at sea encountered a great deal of challenge. One of the most important challenges is scouring around the piles of these turbines due to sea waves and current interaction. Many studies have been conducted in this respect; however, the results are insufficient, and the phenomenon remains poorly understood in tripod wind turbines. In this work, an attempt is made by combining the waves and currents, and changing the substructure of the turbine and the type of the bed materials, to extend the investigation of this phenomenon. The current research is focused on presenting the trend of changes in the amount of scouring. By changing the conditions (including variation in the wave height, variation of the current velocity, variation of the pile diameter, and variation in the size of bed particles), one can arrive at an appropriate estimate and prediction of the shape and the depth of the scour pit.     

Evaluation and modeling scouring and sedimentation around downstream of large dams

Flip buckets are often used at the end of chute spillways to dissipate energy and direct flow to submergence plunge pool and especially in large dams. Flip buckets with central deviation also are a specific and new design of these buckets that have a transverse slope and are mixed in plan with a curvature. In this paper, the experimental and numerical simulation study of sediment scouring in such flip bucket has been targeted. Extensive experimental data are obtained from physical model studies conducted at Water Research Institute, Iran. The flow field with various flood discharges in a range of Froude numbers (Fr?=?\(V/\sqrt {gh}\): 3.5–7.5) in Flow3D model was compared to experimental results obtained from a similar model. Analyzing the simulated models in the Flow3D model and comparing the results with the experimental model, the hydraulic parameters of the pressure, velocity and depth of flow are determined. Considering the accuracy of the numerical model in simulating bed scouring, this model can be used for similar cases in large dams. The results of the simulation model compare well with the experimental results in parameters of the maximum scour depth, profile scouring and the ridge height which accumulates around downstream of the scour hole. This investigation improves the understanding of bed topography effects of downstream dams in high-velocity jet impact based on experimental observations and simulation analysis.     

Diagenetic and Depositional Impacts on the Reservoir Quality of the Upper Jurassic Arab Formation in the Balal Oilfield,Offshore Iran

The Kimmeridgian‐Tithonian aged Arab Formation, as the main reservoir of the Jurassic succession in the Balal oilfield, located in the offshore region of the Iranian sector of the Persian Gulf, is investigated in this study. The formation is composed of dolomites and limestones with anhydrite interbeds. Based on detailed petrographic studies, six microfacies are recognized, which are classified in four sub‐environments including supratidal, intertidal, lagoonal and the high energy shoal of a homoclinal carbonate ramp. The main diagenetic features of the studied succession include dolomitization, anhydritization, cementation, micritization, fracturing and compaction. Based on stable isotope data, dolomitization of the upper Arab carbonates is related to sabkha settings (i.e. evaporative type). In terms of sequence stratigraphy, three shallowing‐upward sequences are recognized, based on core and wireline log data from four wells of the studied field. Considering depositional and diagenetic effects on the reservoir quality, the studied facies are classified into eight reservoir rock types (RRT) with distinct reservoir qualities. Dolomitization has played a major role in reservoir quality enhancement, whereas anhydritization, carbonate cementation, and compaction have damaged the pore throat network. Distribution of the recognized RRTs in time and space are discussed within the context of a sequence stratigraphic framework.     

Application of Electrical Resistivity Imaging for Engineering Site Investigation. A Case Study on Prospective Hospital Site,Varamin, Iran

The article addresses the application of electrical resistivity imaging for engineering site investigation in Pishva Hospital, Varamin, Iran. Some aqueduct shafts exist in the study area backfilled by loose materials. The goals of this study are to detect probable aqueduct tunnels and their depth, investigate filling quality in the shafts as well as connection(s) between them. Therefore, three profiles were surveyed by dipoledipole electrode array. Also, to investigate the potentially anomalous areas more accurately, five additional resistivity profiles were measured by a Combined Resistivity Sounding-Profiling array (CRSP). According to the results of 2-D inversion modelling, a main aqueduct tunnel was detected beneath the central part of the site. Finally, the resistivity pattern of the detected aqueduct system passing the investigated area was provided using the obtained results.