مجله ژئوفیزیک ایران
سال هشتم شماره 1 (پیاپی 20، بهار 1393)

Reflection seismic data is often contaminated by a variety of coherent and incoherent noises. Ground-roll is a type of surface wave. It is a form of coherent linear noise، which propagates at the surface of the earth، at low velocity and low frequency. This kind of noise will often obscure the seismic reflection data. Various methods have been introduced by many authors to attenuate the ground-roll in reflection seismic data. Most of these methods are based on a transform. Deighan and Watts (1997) tried to eliminate the ground-roll by using the wavelet transform. A number of researchers used Karhunen-Loeve transform to suppress the ground-roll noise from seismic data (Liu، 1999; Montagne and Vasconcelos، 2006). Porsani et al. (2009) presented the singular value decomposition (SVD) filtering method for attenuation of the ground-roll. In this method، the seismic data must first be NMO corrected. Naghizadeh and Sacchi (2011) eliminated the ground-roll noise by scale and direction guided curvelet transform. One of the most important and common methods to attenuate coherent linear noise such as ground-roll in a prestack gather is based on the radial trace transform. It is a simple coordinate transform of offset-time (X-T) into the radial-time (R-T) coordinate. This transform was introduced and developed in the Stanford Exploration Project by Clearbout (1975)، Ottolini (1979، 1982) and Taner (1980). They used the radial trace transform for migration of seismic data and multiple attenuation. Clearbout (1983) and Henley (1999، 2000 and 2003) attenuated the coherent linear noise by the radial trace transform. We can separate the coherent linear noise from reflection seismic data when the transform coordinate paths are appropriately aligned with the coherent noise direction in the X-T domain. Applying the radial trace transform on a seismic shot gather causes coherent linear noise which is distributed across many traces in the X-T domain maps into relatively few radial traces and reduces their frequency. The most straightforward technique to reduce coherent noise in the R-T domain is to apply a high-pass (low-cut) filter to the radial traces. In practice، interpolation is an important stage in the radial transform and can leave a damaging impact on performance. Therefore، application of the transform will result in missing data. However، advanced interpolation methods can reduce the omitted data problem. In this study، we used a different method based on radial trace filtering، named local radial trace mean filtering that does not require a forward/inverse radial trace transform. Consecquently، it does not require interpolation algorithms. To investigate the efficiency of the proposed method، we test the local radial trace mean filtering on both synthetic and real seismic data. We also compare the obtained results by those from the f-k filtering for seismic data ground-roll suppression. To investigate further، we apply the method on synthetic seismic contaminated by random noise and find that the method is not sensitive to the presence of random noise. Also، in cases where the receiver intervals are not the same، unlike the f-k filtering، local radial trace mean filtering is very effective. Therefore، we can say that the local radial trace mean filtering method is a suitable tool for coherent linear noise attenuation، especially the ground-roll.

A fluid, which is stable under the action of buoyancy, can oscillate under the influence of buoyancy and Coriolis forces. The resulting ageostrophic oscillations with a frequency between Coriolis and buoyancy frequencies are called inertia–gravity waves, abbreviated as IGWs, hereafter. Typically, the phase speeds of IGWs are 15 to 35 ms-1, their vertical wavelengths are 500 m to 15 km and their horizontal wavelengths are 50 to 1000 km.This study is concerned with uncertainties in two common methods to study IGWs: the hodograph method and the method that uses the horizontal divergence field to estimate the wave characteristics. To this end, a noticeable IGW event that occurred during 7 to February 2012 over Iran was investigated. This event was accompanied by the passage of a synoptic system and a noticeable amount of precipitation. Moreover, this IGW event was simulated with the Weather Research and Forecasting (WRF) mesoscale model using the NCEP FNL (final analyses) data for 72 hours, from 12UTC 6 February until 12UTC 9 February. The setup of the model included a horizontal resolution of 25km, 35 levels in the vertical direction with a model top of 10 hPa (~30 km) and a time step of 150 s. The wave properties such as wave frequency and period, intrinsic phase speed, group velocity and horizontal and vertical wavelengths obtained based on the horizontal divergence field as the main determining quantity were investigated. This is possible, because the procedure avoids an explicit treatment of the background field, which has a zero divergence, and is applicable to waves of an arbitrary wavelength. Observational data were obtained from radio soundings launched from four upper-air stations on the above dates. Previous studies have shown that the presence of IGWs leads to perturbations in temperature and wind fields. Therefore, IGWs structures can be identified by the fluctuations which are obtained after subtracting the background flow. The preliminary analysis of the observational data gives a typical vertical wavelength of 0.5-6 km. Subtraction is performed either by fitting a polynomial of sixth degree or applying a high-pass filter to suppress perturbations with scales larger than 6 km. Vertical wind and temperature profiles obtained from the observational data as well as a numerical simulation were plotted and compared against each other at the same time and the same location. The results showed that the simulated data were smoother and more homogeneous than the observed data, because the IGW amplitude was damped by the explicit and implicit diffusion of the numerical model. Nevertheless, with a medium resolution, the wave characteristics estimated from the horizontal divergence field were satisfactory. An estimation of the wave properties showed that a high-frequency wave with ω/ f > 5 was emitted in this case. The quantity ω/ f was an estimate for the wave frequency scaled by the inertial frequency. For the observed data, hodographs were plotted for that part of stratospheric and tropospheric wind profiles with maximum wave activity. This method had an acceptable performance in the assessment of the qualitative features of the wave. However, a great uncertainty appeared in the quantitative characteristics of the observed IGWs. Uncertainties are greater when a polynomial fitting was used in separating perturbation from the mean field, as it sometimes created overshoots. On the other hand, filters often damped the wave amplitudes. In addition to the sensitivity of the background removal, some of the information was out of reach because of the superposition of either multiple waves or a wave packet with its reflection as shown by Zhang et al. (2004). Intrinsic frequencies determined by this method were typically close to the Coriolis frequency. This study, like other previous studies (Plogounven et al., 2003; Zhang et al., 2004; Guest et al., 2000; Lue and Kuo, 2012) suggests that the nature of the hodograph method is only able to detect the low-frequency part of the IGW spectra. Considering the limitations and uncertainties of the hodograph method, it should be used in conjunction with other methods such as those based on the horizontal divergence field, Stokes parameters and radar observations.

Depth detection of magnetic bodies is the most important goal in magnetic data interpretation, and there are so many different methods for this purpose. After Nabighian (1972) proposed the analytic signal and used it for magnetic data interpretation, so many authors and researchers have used the definition of analytic signal in magnetic data interpretation (Roest et all,1992; Hsu et all, 1996, 1998; Thurston and Smith, 1997; Smith et all, 1998; Thurston et all, 2002; Salem et all, 2005, 2008; Keating, 2010). The analytic signal is a complex relation, which its real and imaginary parts are horizontal and vertical derivatives of the magnetic field, respectively. Therefore, the analytic signal can be introduced by amplitude and phase. Both amplitude and phase can be used in magnetic data interpretation. The maximum amplitude of an analytic signal can be used for edge detection (the maximum amplitude of an analytic signal is located on the body), and also for depth estimation. The depth estimation methods based on the amplitude of the analytic signal use the maximum amplitude of different orders of the analytic signal. The local wavenumber is based on the gradient of phase and recently it has been used in magnetic data interpretations, such as edge and depth detection of magnetic sources. Like the amplitude of the analytic signal, high orders of the local wavenumber are calculated and used in magnetic data interpretation. The local wavenumber is used for depth detection in two ways: 1) Depth estimation based on the maximum value of local wavenumber: The maximum value of the local wavenumber is located on the magnetic bodies and with a priori knowledge about the model of magnetic bodies (for example: contact, thin dike, horizontal cylinder, …), magnetic source depth can be estimated. In this way, the depth detection’s equation only use the second order derivative of magnetic field. Therefore, it is more suitable for interpretation of noisy data. However, in early stages of exploration, usually there is not any knowledge about the model of sources. Also, the depth can be estimated without any prior knowledge about the model, but it uses the third order derivative of the magnetic field. 2) The estimation of depth and horizontal location of source using the enhanced local wavenumber. In this method, a linear equation was obtained that estimates the depth and the horizontal location of the magnetic bodies without any prior knowledge about the model. A window is passed over the data and this linear relation is solved by the least square method. These methods only use the second order derivative of the magnetic field. These methods are applicable on profile and gridded data. In this study, the local wavenumber-based methods are introduced and their advantages and disadvantages are discussed by applying to synthetic data. For these methods, we have developed code in MATLAB software. These methods are also applied to a magnetic anomaly in Ciriz in Kerman Province, Iran.

In projects of reserves estimation, we would like to reduce the estimation variance and related uncertainty. This reduction usually requires extensive and costly drilling. Multivariate geostatistical methods could be noted as an inexpensive and budget saving method to reduce the estimation variance. Often, there exists much secondary data that must be considered in a geostatistical reservoir modeling. All secondary data being used as a secondary variable must be highly correlated with the primary one. This work introduces the collocated cokriging and kriging with an external drift to incorporate sulphide factor as secondary information to estimate the copper content in a porphyry system. The study area was one of the desirable areas of copper, located in Kerman Province. Sulphide factor as highly correlated and fully covered data was selected to improve the estimation of copper in this region. In collocated cokriging, the number of the secondary information used for estimation is reduced to the estimation location. However, the datum colocated with primary data implementations of collocated cokriging is often limited to a single secondary variable. Improved models would be constructed if multiple variables were accounted for simultaneously. Contrary to cokriging, kriging with an external drift does not make explicit the structural link between the target variable and the auxiliary variable, for the latter is considered to be deterministic. After determining the mean of the estimation variance, experimental results showed that both methodologies incorporating secondary information led to better results than ordinary kriging that did not incorporate any sulphide factor data. The ordinary kriging method uses only cupper assay information‚ while in collocated cokriging and kriging with an external drift, both cupper assay and sulphide factor information are used as an auxiliary variable. The validation sample was used to compare the performance of the methods. Collocated cokriging and kriging methods with an external drift based on mean absolute error (MAE), root mean square error (RMSE) and the correlation coefficient of real and estimated values (R) illustrate better results.

Balouchestan Provinces. The epicenter (59.2E, 28.35 N) has been reported 52 kilometers away from the city of Mohammad Abad Rigan. Although there was no fault pointed on the geological maps in terms of the location of this earthquake, the aftershocks were recorded in two temporary seismological networks using 10 stations altogether from December 24, 2010 to January 24, 2011. In addition, the data recorded in the IIEES broadband seismic network was added to the mentioned data during the process. The goal of operating temporary seismic networks was aftershocks analysis in this area. Investigation and study of aftershocks behavior has done based on three component waveforms. This study contains three main parts. The first part is operation network, data gathering and preprocessing. In the second part, we try to locate and relocate aftershocks based on new database. The third part is fault pale solutions of aftershocks based on p-wave polarity technique. Locating over 500 aftershocks in the network, we recognized a fault with the length of 30 km, southwestnortheast strike and 32 NE trends. The most of aftershocks are located in a depth range of 2-15km; while a few earthquakes have greater depth to 23km. Investigation of the rate of aftershocks showed that the number of them decreased as time increased during three weeks. After that, the rate of aftershocks was increased for two weeks and finally another large earthquake happened in the area with magnitude of 6.3. Therefore, decomposing and distinguishing of aftershocks of first mainshock from foreshocks of the second mainshock is a great change here. In this study, we assume all events as aftershocks of first mainshock. Determining 28 focal mechanisms pertinent to the aftershocks as well as perpendicular sections on the aftershocks, we recognized the strike slip right - lateral fault, with a tensional component, dip 90 degree which met the surface. It i s worth noting that according to the geological evidence and comparison with the results obtained; this region has a complex structure. Also, it comprised some right - lateral parallel strike slip faults bringing about wrinkles in the given area. Our results are in good agreement with the geological and morphotectonic evidence. The mechanism and trend of the Mohammad Abad fault can be interpreted with the previous GPS measurements in eastern part of Iran.

Geophysicists and engineers require both accurate and high-resolution seismic surveys. A detailed analysis of the interrelationships between seismic velocity, seismic attenuation, porosity, and permeability makes reliable predictions about the petrophysical propertiesof hydrocarbon reservoirs. Surface reflections, VSP and cross-hole seismic methods have been used to determine velocities and lithological discontinuities within a reservoir. Seismic velocities of the sedimentary rocks have been used as indicators of their petrophysical properties. Vp/Vs ratio is as a lithology indicator (Domenico, 1984). Vp/Vs can be used to discriminate between limestones and dolomites. Also, Vp/Vs has been used successfully for direct hydrocarbon detection, especially with AVO techniques. In general, the velocity ratio depends on the matrix of material, state of saturation, degree of consolidation, differential pressure, porosity and pore geometry. The effect of a fluid on Vp/Vs is significant, but not as much as that of lithology. Tight gas sandstones typically have a Vp/Vs value lower than 1.7, while shales usually have a Vp/Vs value higher than 1.7. The presence of gas-saturation in sandstones will even lower the Vp/Vs further (when the Vp/Vs ratio is close to 1.6) and overpressure can make Vp/Vs ratio even less (<1.5). These results can be used to interpret the seismic data in tight gas sandstones. Pickett (1963) demonstrated Vp/Vs as a lithology indicator. Castagna et al. (1985) introduced some empirical relations that relate Vp to Vs. Vp/Vs is sensitive to gas in most clastic reservoirs and Vp/Vs often shows a reduction due to the presence of gas (Kithas, 1976; McCormack et al., 1985). Castagna et al. (1993) published other empirical relations that relate Vp to Vs. Elastic properties of rocks are also most important in determination of rock types. The elastic properties of rocks can be determined from the velocities of the longitudinal, transverse waves, and density. The Lamé parameter (λ) is a measure of a rock brittleness, which is a function of Young's modulus. This parameter plays an important role in the discrimination of gas sands from carbonates or shale in sedimentary rocks. Therefore, well logs are used to determine the elastic properties of rocks. A classical sonic log employs the acquisition and analysis of the data with a simple monopole source. In general, the compressional wave velocity is easily determinable in all rock types with a full-waveform sonic tool. A logging device which has been used to analyze the formations around the borehole is called Dipole Shear Sonic Imager (DSI). A dipole source generates the flexural modes, which determine the shear velocity. Since compressional waves travel faster than any other waves, travel times are easily determined from the first arrival for each receiver. For hard formations, where the shear wave velocity is greater than the fluid velocity of the P-wave, shear waves are present in the recorded wave trains. When the shear velocity is less than fluid velocity of P-wave, the shear mode does not exist for the monopole. The shear velocity can be determined either by inverting a Stoneley wave velocity, or by conducting a flexural mode survey. Inverting the Stoneley wave velocity for detection of shear velocity is a good technique in soft rocks. In this investigation logs from two wells in the South Pars Gas Field are analyzed. From the analysis of DSI, Vp-Vs relations are developed. However, the relations between elastic properties of rocks and petrophysical properties are found for calculation of elastic properties. For Kangan (K1 and K2) and Dalan (K3 and K4) formations, the relationships between Vp and Vs in two boreholes are determined. P-wave versus S-wave velocity crossplots for all layers show a good relationship. An estimation of S-wave velocity based on Vp was used for regions for which we did not have cores and log data. Relations between Vp and Vs for other parts of this field were found based on S-wave velocity as well. Finally, the bulk modulus, Young's modulus, shear modulus and λ are calculated based on the well log data.

Based on the climate divisions, Iran is mostly located in the arid and semi-arid regions. Changes in amount of precipitation have a great effect on water resources, agriculture and the economy of regions. Atmospheric circulation pattern has a determinative role in the temporal and spatial distribution of precipitation and some other meteorological parameters. Thus, abnormalities of these patterns compared to the long-term mean in dry and wet spells is one way that can determine the effective atmosphere patterns in changes in precipitation during these spells. A number of studies have described the relationship between the pressure patterns and the precipitation anomalies over monthly and seasonal time scales. Kutiel et al. (2001) found that the relationship between regional sea-level pressure (SLP) patterns and the dry or wet monthly precipitation conditions over Turkey was significant in winter and non-existent in summer. Pressure patterns associated with dry conditions usually show positive SLP departures, and vice versa. There is a strong relationship between the pressure patterns associated with wet conditions. Similar atmospheric variations and relationships have been found for precipitation over the eastern Mediterranean Basin and Greece, especially during winter (Maheras et al. 1999). They investigated the influence of the large-scale winter mid-tropospheric circulation on the Greece's precipitation. They concluded that the spatial distribution of winter precipitation over Greece was related to the eastern North Atlantic-European midtropospheric circulation fields. A considerable part of precipitation in the northern coasts of Iran falls in autumn season. Investigating the relation between the mean monthly anomalies of pressure patterns and the extreme low precipitation conditions in autumn in the northern coastline of Iran (Mazandaran, Gilan and Golestan provinces) is the main purpose of this study. Rainfall data comprised monthly totals for the period from 1977 to 2011, in seven stations across the northern coasts of Iran. It consisted of monthly precipitation totals (mm) for October to December in a 35-year period from the meteorological synoptic stations. Also, the grid point data (Sea level pressure and 500hPa) were extracted from the National Center for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis dataset. A grid data with 2.5°×2.5° resolution was selected for the area between 0°E -90°E and 15-80°N for three months (October-December) over a 30-year period (1981-2010). Therefore, using monthly precipitation data of seven synoptic stations during 35 years(from 1977 to 2011) for October, November and December, dry and wet spells weredetermined based on precipitation departures from the standard deviation so that, if adifference between the long-term mean precipitation and the standard deviation ofprecipitation in that month was less (or more) than the occurred precipitation, it wasselected as dry (or wet) spell. Then monthly and seasonal pressure patterns and theiranomalies were studied for those months of autumn that had minimum or maximum ofprecipitation during the 35 years.Also, seasonal and monthly mean sea level pressure and 500-geaopotential heightanomalies for the two regions defined in the text were extracted during the period 1981-2010. Then, by normalizing the values of pressure, 500-geaopotential height and rainfallduring the months of October, November, December, and the season of autumn of thesequantities and relationships between them were studied.The results of study are as follow:1- In low (high) precipitation periods, the geopotential height is dominated by a ridge(trough) and positive (negative) anomaly in north of Iran.2- Another reason for low precipitation in north of Iran is the development and establishment of a low pressure in this region that is usually accompanied at the same time with development of a high pressure in Siberia. In high precipitation, the situation is reversed. 3- Attenuation (development) of the zonal component of the wind in Caspian Sea has an effective role in increasing (decreasing) the precipitation of this area. 4- Pressure patterns over the two regions have an important role in producing dry and wet spells in the northern coasts of Iran 5- Developing and strengthening of a high-pressure system over Europe and low-pressure systems in the Northeastern region of the Caspian Sea (Area 1) are associated with wet conditions along the southern coast of the Caspian Sea and vice versa. Considering the precipitation mechanism in the northern coast of Iran is of great complexity and that the numerical weather prediction models are not accurate enough to predict rainfall in this region, especially in the medium and long term forecasts, the anticipated large-scale quantities such as pressure are expected to enhance the ability to predict rainfall in the northern coast of Iran.

The objective of this study is the 3D modeling inversion of gravity anomalies in order to obtain a density model in different depth sections. We used a new method based on stochastic methods. Among the stochastic methods that can be applied for solving inverse optimization problems in geophysics are meta-heuristic algorithms which are based on artificial intelligence. The ant colony algorithm is categorized in this group of algorithms. It works on the basis of probability and trial and error and follows ant's behavior in finding the shortest distance between the nest and the food. This behavior of ants is closely similar to the inverse problems in geophysics which try to find the best solution for the unknowns in observation model. Therefore, this idea is applied for solving linear inverse problems. A MATLAB-based inversion code for the presented method was prepared. To examine the performance of this method, three different artificial models were assayed. The structure of these models was considered as a combination of 3- dimentional cubes so as to model every unknown geometrical structure. In the first example, our purpose was to investigate interferential anomalies resulting from two simple models with different density contrasts located in different depths. In the second example, to show the ability of the algorithm in an inversion using small anomalies, a model of an irregular geometry was assessed in different depths. Finally, in the third example, an interferential anomaly resulting from two models of complicated geometry, namely T and L and of different density contrasts was assessed. This method was applied for artificial models with and without noise. The results show that for an inversion by the use of the ant colony algorithm, there is no need to separate the interferential anomaly and it is possible to use it for a combination of density contrasts. Also, this algorithm is able to inverse anomalies of an order of 103MGAL. These anomalies belong to very small causative bodies such as: cavities and small orebodies. These anomalies are the main object of enviromental or engineering geophysics. The algorithm is semi-authomatic and search the best results without comprehensive pre-conditions. The method is well designed to consider the multiple anomalies in complex conditions. This character enables us to use it for interpretation of complex anomalies caused by geological sources where most of the semi-authomatic methods are useless. On the other hand, the inversion algorithm can be applied for different density contrasts. Relative positive or negative anomalies could be obtained by applying this method. This means that all different anomalies regarding their density contrasts can be detected and modelled through this method. Therefore we are not forced to isolate the object anomalies for inversion and this makes its application fast and easy for the whole surface of the Bougure residual anomalies. This character is very rarely obtainable in the published inversion algorithms. This character is particularly helpful when we would like to invert the precise data in the case of engineering geophysics. Another advantage of this method is its velocity due to its usage of probability and trial and error theory. This advantage is very important when we are facing with a large set of data and parameters to invert. The high number of parameters is a major problem in linear inversion methods, but can be treated by this method very properly.

Seismic records are generally affected by various types of noise, such as ground rolls, multiples, random noise, reflection and reflected refraction from near surface structures.Random noise resulting from random oscillation during data acquisition is one of the most important and harmful noises that exist in seismic data over all times and frequencies. Much effort has been made to attenuate this type of noise from seismic data. The predictive filter is commonly used for random noise attenuation from seismic data. This filter can be used in various domains such as the f-x domain (Haris and White, 1997) and the discrete Cosine domain (Lu and Liu, 2007). Bekara and van der Ban (2009) attenuated the coherent and random noises using a combination of empirical mode decomposition (EMD) and Fourier transform. EMD decomposes a time series into a finite set of signals called intrinsic mode functions (IMFs). They represent different oscillations embedded in the data. They are built to satisfy two conditions: (1) The number of extrema and the number of zero crossings must be equal or differ at most by one, and (2) at any point the mean value ofthe local maxima envelope and the local minima envelope must be zero. Bekara and van der Ban (2009) transformed seismic section from the t-x domain to an f-x domain by Fourier transform. Then, they applied EMD to a constant-frequency slice in the f-x domain and removed the first IMF. In the FX-EMD method, the denoised seismic section can be obtained by reversing the EMD and Fourier transform, respectively. The time–frequency transform of a signal shows a variation in the frequency contents of a signal with time. Ideally, the time-frequency representation only provides information about the frequency moments without mutual information about the adjacent instants. Stockwell (1996) introduced the S-transform which is a combination of shorttime Fourier (STFT) and wavelet transforms. It uses a variable window length and the Fourier kernel. However, the S-transform suffers from a poor energy concentration in the time-frequency domain. It has a poor time resolution at lower frequencies and a poor frequency resolution at higher frequencies. Sahu et al. (2009) proposed a modified Gaussian window which scales with the frequency in an efficient way to obtain a better energy concentration of the S-transform. Han-peng et al. (2011) used the time-frequency transform instead of Fourier transform (TFX-EMD) for considering the nonstationary property of the seismic data. They obtained the denoised seismic section by applying the EMD to a constant-frequency slice and removing the first IMF in t-f-x domain. Due to the presence of random noise in the other IMFs, removing the first IMF is not always an appropriate approach. One of the best algorithms in EMD-based noise attenuation is the interval thresholding of the IMFs. The main idea of this algorithm is to determine an aproperiate threshold value and to apply it to the considered IMFs. In this study, we modified the TFX-EMD algorithm by changing the EMD denoising strategy. We used the interval thresholding of IMFs instead of removing the first IMF in the t-f-x domain. We evaluated the efficiency of our method on both synthetic and real seismic sections and compared the obtained results with those of the FX-EMD and traditional TFX-EMD methods. The comparison shows that the new EMD denosing strategy in the t-f-x domain can effectively suppress random noise and has a better performance than the other two approaches. Also, in our method, unlike the FX-EMD and traditional TFX-EMD, the steep events are preserved.

The prevailing synoptic pattern and the characteristics of the regional atmospheric circulation were studied in order to understand the predominant mechanism which governs the dry and wet spells over the southern coast of the Caspian Sea (SCCS). Monthly precipitation data from 20 weather stations located in the SCCS were analyzed for a 30-year period (1974-2003). Over this period, 10 widespread dry and 10 widespread wet months were identified for the Caspian region by investigating the spatial and temporal distributions of precipitation. Gridded precipitation data for the Middle East, provided by Asian Precipitation-Highly Resolved Observational Data Integration Towards Evaluation of the Water Resources (APHRODITE) on 0.5×0.5 degree grid along with the NCEP/NCAR reanalysis dataset on a 2.5×2.5 degree global grid were employed to determine the characteristics of the atmospheric circulation and to identify the predominant synoptic patterns during the dry and wet spells. The results indicated that the existence of a very strong ridge in the middle troposphere along with the formation of a strong anticyclone in the lower atmosphere over the northern-side of the Black Sea can be considered as the main features of the wet spells over the SCCS. The findings also indicated that the wind direction at the lower atmosphere over the Caspian Sea can be used as an appropriate criterion to separate the wet and dry spells over the SCCS so that the northerly prevailing wind during the wet spells is replaced with the southerly prevailing wind during the dry spells. Additionally, the occurrence of the dry and wet spells in the region is associated with the formation of a sea-saw pattern in vertical velocity values over the Caspian Sea. During the wet spells, formation of the descending prevailing motions over the north half of the Sea simultaneously leads to predomination of the ascending prevailing motions over the southern part. Meanwhile, during the dry spells, a reverse pattern resulting from the ascending and descending motions dominates over the Caspian region. The findings also show that it is reasonable to use the sea-level pressure changes in the Black Sea region as an appropriate index (predictor) to interpret the spatial and temporal variations of precipitation over the SCCS. In this way, during the wet spells, an increase in the sea level pressure over the Black Sea and its consequent positive feedbacks including an anticyclonic circulation over the Black Sea, northerly wind strengthening over the Caspian Sea, and air ascending over the southern part of the Caspian Sea will eventually cause an increase in precipitation over the SCCS. A reverse condition will be found in the dry spells. The investigation of the cyclones and anticyclones frequency and track during dry and wet spells indicates that the northern corridor of the Black Sea plays a very significant role in occurrence of the dry and wet spells over the SCCS. It is found that during the wet spells, the activity of the anticyclones in the northern corridor of the Black Sea is considerably increased. On the other hand, during the dry spells, a decrease in the activity of anticyclones in the north corridor is associated with a significant increase in the activity of cyclones in the region. In addition, an increase in the activity of anticyclones over the Middle East region and the Siberian high-pressure activity over the eastern-side of the Caspian Sea are taken into account as the main features of the dry spells.