فصلنامه فیزیک زمین و فضا
سال چهل و دوم شماره 4 (زمستان 1395)

Land seismic data acquisition in most practical cases suffers from obstacles in fields which deviates geometry of the real acquired data from what was designed. These obstacles will cause gaps, narrow azimuth and offset limitation in the data. These shortcomings, not only prevents regular trace distribution in bins, but also distorts the subsurface image by reducing illumination of the target formation. However, some methods available can compensate the gaps in data due to field obstacles mainly by trace interpolation techniques. The common reflection surface (CRS) method that was previously introduced for seismic imaging in complex geological structures also could be used for trace interpolation to fill the gaps and to increase the fold of the data. In this study, we combined two different methods of trace interpolation and distribution in bins for solving the problem of gaps and low illumination of the target formation in a 3D seismic acquisition study area in the southwest of Iran. After processing old 2D lines available from the same area, the CRS parameters were obtained for proper definition of the acquisition design. Then by combining the CRS trace interpolation scheme and trace distribution, possible gaps in the data was resolved and regular trace distribution in all bins and azimuths were achieved. Result showed increasing redundancy in bins, which will prevent occurring gaps in data in case of inevitable field obstacles. Result shows that this strategy could be used to construct lost traces and prevent further problem in seismic imaging.

Tropical cyclone Haiyan (TCH) that formed over the West Pacific Ocean during 3-11 November 2013 has been investigated using three datasets of Japan Meteorology Agency, ECMWF and NCEP. Strength of TCH has been studied using two synoptic parameters of 10-m wind velocity and mean sea level pressure (MSLP). then, three dynamic parameters including vertical wind shear (VWSH) vector, helicity and potential vorticity (PV) together with the thermodynamic parameter of convective available potential energy (CAPE) have been calculated and analyzed during TCH life cycle. VWSH vector was analyzed in three classes of weak, moderate and strong shear, having northeasterly direction for most of TCH lifetime. Moreover, the helicity parameter was intensified to the tornadic instability (at about 6 hours later than the time of maximum 10-m wind speed), and its anomaly was located in the downshear quadrants for most of TCH life span. In addition, no significant PV anomaly was detected near TCH, but a subtropical PV anomaly was extended to the Philippines Islands before TCH eye reached this region. Also, CAPE parameter was intensified to strong instability class at about 48 hours earlier than the time of maximum 10-m wind speed and its anomaly was equally displaced in both up- and downshear quadrants. Finally, it can be concluded that 30-hourly lag between the time of CAPE maximum value and VWSH for which TCH was intensified to category 5.

In this paper a simple qualitative model of growth of a mixed layer adjacent to a uniform layer with a stably stratified layer is presented. The entrainment of a stably stratified layer into a turbulent mixed layer in a confined region was studied in laboratory for different Richardson numbers. The results for entrainment near a density stratified layer show that the entrainment rate is a weaker function of Ri than the case with a step density profile. It is also shown that the internal waves in the stratified region, with typical buoyancy period of about 10 s may interact with turbulence near the interface and create a non-uniform entrainment rate as an oscillatory behavior with a typical time scale of 150 s. The process is qualitatively consistent with processes associated with internal waves interaction with turbulence and create a momentarily buoyancy flux with different signs. Results of lidar observations of atmospheric boundary layer also show that the oscillation of aerosol layer is probably due to non-uniform entertainment in the interface between the mixed layer and free atmosphere. Although there seems to be a qualitative similarity between entrainment behavior at the top of the atmospheric mixed layer and laboratory experiments «mixing box», but the two are quite different as lab experiments are in an enclosure without mean flow, while the top of the mixed layer is a free solid boundary flow which may be associated with mean flow shear.

Groundwater vulnerability assessment is an effective informative method to provide basis for determining source of pollution. Vulnerability maps are employed as an important solution in order to handle entrance of pollution into the aquifers. A common way to develop groundwater vulnerability map is DRASTIC index. Meanwhile, application of the method is not easy for any aquifer due to choosing appropriate constant values of weights and ranks. Clustering technique would be an influential method for regionalization of groundwater flow zone to facilitate vulnerability assessment of groundwater aquifers. In this study, a new approach using k-means clustering is applied to make vulnerability maps. Four features of depth to groundwater, hydraulic conductivity, recharge value and vadose zone are considered at the same time as features of clustering. Five regions are recognized out of the Hashtgerd plain. Each zone corresponds to a different level of vulnerability. The results show that clustering provides a more realistic vulnerability map so that, Pearson’s correlation coefficients between nitrate concentrations and clustering vulnerability is 72%.

This paper describes the observation and analysis of vertical electron density before major earthquake above the Sumatra-Malaysia region during Indian Ocean major earthquake in 2004 in Aceh, Sumatra. The electron density profile in E-layer of ionosphere a few days before earthquake and a few hours after earthquake have been observed using the data from the CHAMP satellite. The data obtained from the CHAMP satellite based on GPS radio occultation technique, starting from 21st Dec, 2004 until 27th Dec, 2004, between 90 - 120 km altitude ranges. It is shown that significant anomaly can be detected as early as 3 days before the major earthquake above the preparation zone of earthquake epicentre through significant disturbances of the electron concentration in the ionosphere. In addition, the electron density in the ionosphere above the earthquake epicentre is observed to be very high during 8 hours before earthquake occurred. After a day of the earthquake occurrence, it is observed that the electron density decreases and the ionospheric region become more stable.

This study, by adopting an environmental approach to atmospheric circulation, estimates drought periods over a 20-year period (1992-2011) in 21 synoptic stations in Kerman, Yazd and Isfahan provinces, which share a long-term statistical period, using Standardized Precipitation Index (SPI). The data pertinent to 18 teleconnection patterns were derived and compared with climatic data of provinces under study and the relationship between major droughts in the region and these patterns was evaluated in accordance with correlation methods and multivariate regression model. According to the results, a total of 37.42% of annual SPI variation in Isfahan province, 51.09 % of SPI variation in Kerman province and 42.17% of SPI variation in Yazd province can be explained by these teleconnection patterns. Finally, the multivariate Scandinavian pattern (SCA) in Isfahan, East Atlantic (EA) pattern in Kerman and Tropical Southern Atlantic (TSA) pattern in Yazd were found to be the most effective patterns in explaining annual SPI changes in central Iran.

Polar mesospheric summer/winter echoes (PMSE/PMWE) are usually very strong radar echoes produced by ionospheric electron density fluctuations at half the radar wavelength. This paper studies the formation of electron density fluctuations in the PMSE/PMWE source region. Using a computational model, the current paper investigates the coupling of the neutral air turbulence with mesospheric dusty plasma as a generation source of fluctuations in plasma and dust densities as well as electric field. The impact of spectrum of irregularity wavelengths in neutral air turbulence including the presence of charged dust particles is investigated and extension of diffusion timescale for electron density fluctuations in smaller wavelength is studied. A comparison of the numerical results with VHF radar observations and in-situ rocket measurement of plasma density perturbations in the mesopause region is presented. The effect of dust density and dust-neutral collision frequencies on the coupling between neutral turbulence and the dust layer in PMSE source region is studied. The computational results are compared with the past theoretical predictions of impact of heavy charged dust on the wavenumber spectrum of electron irregularities. Formation of fluctuations in plasma and electric field in PMWE is then considered. The required plasma and dust parameters for neutral turbulence coupling in winter mesosphere are also determined.

One of the most important advantages of particle simulation as compared to fluid simulation is the capacity for working with and tracing particles. In particle simulations, the test particle method is usually used to get some idea of the behavior of plasma or other substances. In this method, first, a small number of particles are injected into the frame of static electromagnetic fields. Then, movement of particles is investigated using the pattern of the electromagnetic fields. This method is useful; however, as it is needed to work with non self-consistent fields, it lacks precision. In this work, we adapted the particle simulations method, adding the flexibility of working with self-consistent fields that come directly from the simulation. Here we have tried to investigate particle entry from the solar wind with northward Interplanetary Magnetic Field (IMF) to the magnetospheric cusp. Here we tried to trace several particles to the high altitude cusp in a self-consistent manner. To benchmark the self-consistent tracing, we compared our results and the results of test particle method with the observational data from CLUSTER satellite.