مجله ژئوفیزیک ایران
سال چهاردهم شماره 2 (پیاپی 47، تابستان 1399)

Focal mechanism and surface slip data are used to investigate the relationship between kinematic studies conducted on young geological units, especially in trenches of paleoseismolical sites, Late Pleistocene and Holocene in age. It has shown that there is direct relationship between data obtained on surface and seismic data in depth. Kinematic measurements in three trenches for paleoseismological sites on North Tehran Thrust, Mosha fault and Firuzkuh fault are used to calculate the stress tensor. Stress tensors and their associated fault planes and focal mechanism data are compared. Fault planes obtained from calculated stress tensors whose fault planes lie parallel or close to the general trends of Mosha and Firuzkuh faults are in good agreement with focal mechanism. The third trench on North Tehran Thrust displayed insufficient data to obtain an appropriate stress tensor, however the average of strikes, dips and rakes allow to propose a paleofocal mechanism for an area of seismic quiescence. Based on fault plane inversion and focal mechanisms, overall, maximum (σ1~N045±5) and minimum (σ3) principal stresses are subhorizontal and the intermediate principle stress (σ2) is vertically oriented. This is consistent with a dominant strike-slip regime. The Mosha fault (trending N100E, dipping to North) is a left-lateral strike-slip fault with a minor extensional component and joins Firuzkuh fault (trending N60E, dipping to South) as strike-slip fault with a compressional component.

The recent studies suggest that the predictability of the surface weather, in medium and long-range time scales, is influenced by the dynamic coupling of the tropospheric and stratospheric circulations. Therefore, the main goal of the present study with the central focus on the southwest Asia is investigation of the details of coupling mechanisms. The NCEP/NCAR reanalysis data are used, including temperature, geopotential height and horizontal wind components at different pressure levels from 1968 to 2015. The region of study includes Iran and extends westward to the Mediterranean Sea. The iso-potential vorticity surface of 2 PVU (a PVU equals ) is taken to represent the dynamical tropopause and the potential temperature, geopotential height and pressure are interpolated at the 2 PVU surface.First, with a method similar to that of Thompson et al. (2002), the dates corresponding to the occurrence of stratospheric polar vortex were identified and classified into cases of strong and weak polar vortices. The anomalies of pressure, geopotential height and potential temperature were then computed with respect to the long-term mean for the cases of polar vortex. Analysis of the results shows that in the southwest Asia, associated with the cases of strong vortex increase in pressure and decrease in potential temperature and geopotential height are observed at the tropopause. Further, in cases of weak vortex, the southwest Asia is mainly in the surf zone and less influenced by the polar vortex compared to the cases of strong vortex which enclose a significant portion of the region. The fact that a larger part of the southwest Asia is located within the inner part of the strong vortices makes their impact on the tropopause more marked.In the second part of the study, the focus is on the most extreme cases of strong and weak events in the long-term period which occurred in February 1974 and November 2009, respectively. In addition to presenting the details of the life cycle of the two cases, the time-lagged correlation coefficients were computed between the tropopause quantities in the region and the geopotential height anomaly at 10hPa between 60°N and 90°N degrees, which is the index introduced by Thompson et al. (2002). The time series of the correlation coefficients averaged over Iran reveals a meaningful delay of about eight to ten days for the impact of the strong polar vortex felt on the tropopause in Iran. Given that this time delay is within the limit of medium-range prediction, further studies on the impact of polar vortex are needed to improve the predictability of the surface weather in the region.

The unfavorable consequences of the expansion of the metropolitans, including urban heat island and air pollution, have attracted the attention of urban managers to strategies for improving environmental conditions. In recent years, along with population growth and high energy consumption, as well as building materials replacing permeable surfaces and urban green spaces, deteriorate the urban heat island phenomenon and air quality in Tehran. Given the significant area of roof surfaces in urban areas, the application of new and environmentally friendly technologies such as the development of cool and green roofs, with heat island modification impact, can play a positive role in reducing cooling energy consumption and improving air quality. Therefore, to study the mutual interaction between meteorological parameters and changes in the urban structure and its possible side effects on air quality, numerical simulation of green roof and cool roof strategies based on the urbanized coupled meteorological-chemical model (WRF/Chem/SLUCM) during the period June 15 to 30, 2016, have been conducted in Tehran metropolitan area. Results show that the development of cool roofs with an averaged diurnal temperature decrease (-0.65°C) and a decrease in the heat flux (-57 W/m2) has a positive role in the reduction of Tehran heat island. Also, the relative reduction of atmospheric pollutant concentrations has also been achieved in numerical simulations. It shows that the decrease in the height of the boundary layer and turbulence process as a result of the decrease in near-surface temperature has not caused a significant change in the air quality in Tehran. The development of green roofs has led to a daily (nightly) decrease (increase) in the air temperature. The increase in temperature during the night was noticeable (up to +0.53°C), and it is a result of the high emissivity of vegetation, as well as a decrease in wind speed in the vicinity of green roof surfaces which slows down the natural ventilation over the city. Furthermore, an increase in the near-surface humidity also predicted in both strategies which improves the environmental comfort satisfaction in the summer hot and dry days. Comparison of these strategies performance shows that cool roof has a significantly sensible cooling effect than green roofs, and the process of reducing pollutants, especially at night, is more favorable in cool roofing strategy. Consequently, since the cooling efficiency of green roofs depends on soil moisture content, as well as comparing construction costs and no need for specific infrastructure, the development of cool roofs in Tehran metropolis is recommended.

The problem of datum transformation; determination of parameters for transferring curvilinear coordinate from one ellipsoid to another, is one of the main problems in geometrical geodesy. The problem draws the attentions of many researchers due to its role in the integration of all types of data in the geospatial database framework. Although the problem is one of the oldest geometrical problems by its nature, it is still challenging because of the newly introduced Earth gravitational models and precise global coordinate measurements using the global positioning systems. Different methods have been introduced by many famous geodesists like Molodensky (1962), Vanicek (1986) and others.In this paper, we developed a full mathematical model for determination of datum transformation parameters based on ellipsoidal approximation. It is theoretically and numerically compared with the previously developed model with spherical approximation. For small area, both models lead to the same accuracy while we expect to achieve higher with the ellipsoidal approximation in wider area.     Moreover, lack of ellipsoidal height in the old data sets is one of the main obstacles for the implementation of the classical transformation schemes. Herein, we introduced two methods for solving this problem. The Earth Gravitational Models (EGMs) which were wieldy available in the new century, thanks to the Earth gravity field’s dedicated missions, were employed to get an estimate of the geoidal heights of the data point with enough accuracy. Alternatively, the idea of the widely used polynomial approximating correcting surface was considered to model the geoid height at the area of computation. The numerical results showed that the second alternative was most helpful. Higher accuracy and better fitness in terms of statistical goodness of fit criteria were the outcomes of the implementation of the polynomial approximating correcting surface.     In order to show the performance of the ellipsoidal approximation as well as the idea of polynomial correcting surface, 150 points were selected in the Nigeria. The curvilinear coordinates of the data points were given both in the CLARCK-1880 (local old coordinates) and the World Geodetic System 1984 (WGS84) as the global new coordinates. The old coordinates of the data points were geodetic latitudes, geodetic longitudes and orthometric heights where the new coordinate set is fully geodetic components. A quadratic polynomial mathematical model was employed to approximate the geoid surface in the country. The achieved results showed its reasonable accuracy.

Accurate prediction of squall lines that accompany thunderstorms is a challenging task. A squall line was recorded in Dayyer port station over the southwest of Iran in Bushehr province, on 19 March 2017. In this study, the properties associated with the mentioned squall line including the time of formation, growth and destruction of the convective cells in terms of intensity and vertical growth, as well as the associated precipitation and other meteorological features are simulated using the WRF-ARW model with 3-dimensional variational (3DVAR) assimilation and control experiment (CTRL) for 18UTC 18 March 2017 with two domains of 27 and 9-km horizontal resolution. Radial winds and reflectivity of Bushehr Doppler Weather Radar (DWR) along with surface and upper-level observational synoptic data are used to simulate the above mentioned squall line event with the aim of updating initial and boundary conditions through 3DVAR assimilation in WRF model. In order to verify the simulated properties associated with the squall line event, the horizontal wind speed, mean sea-level pressure, surface temperature and surface relative humidity, as well as time series of reflectivity and vertical growth in the squall line location on Bushehr DWR were compared with the corresponding observational data. To assess the performance of accumulated precipitation forecasts, the fraction skill score (FSS) curves are plotted for different rainfall thresholds 0.5, 5, 10 and 15 mm/day. In general, the results showed that the radar data assimilation has a significant effect on the simulation of the characteristics accompanied with the squall line event such that without data assimilation, the WRF model is not capable of simulating the squall line thoroughly. The results of 3DVAR simulation are also much closer to the observational data in predicting the features along the squall line. The absolute value of the mean errors in simulations with assimilation for surface horizontal wind speed, surface temperature, mean sea level pressure, and surface relative humidity were decreased by 27%, 7%, 18%, and 10%, respectively, compared to those without assimilation. The formation time and growth of convective cells, their horizontal distributions, vertical structure, and their destruction time in 3DVAR simulation are closer to the verifying observational data. The 3DVAR simulation also achieved significant success in predicting 6-h accumulated precipitation with a threshold value of above 10 mm. Also, the value of error in 3DVAR simulation in 6-h accumulated precipitation at synoptic stations in Bushehr province was decreased by 33%, compared to those without assimilation.

In the present study, using the ERA-INTERIM reanalysis data for geopotential height, horizontal wind speed and relative vorticity at 300, 200, 150, 100 and 50 hPa levels, the wave activity and wave activity flux for cyclonic and anticyclonic Rossby wave breaking events that occurred over Europe during the winter time 1979-2018, were calculated and analyzed. Results showed that in anticyclonic (cyclonic) wave breaking events, a narrow (wide) trough with north-east/south-west (north-west/south-east) axis and associated potential vorticity with values around 5-8 (4-6) 1e6 PVU are extended from Europe to the west (east) of Mediterranean.  In the anticyclonic wave breaking events, the wave amplitude and their associated potential voriticity are higher compared to cyclonic events and also the associated jet streams form in higher latitudes over Europe and the Mediterranean. It appears that intensification of the trough and its extention to lower latitudes over the Mediterranean is associated with intensification of the ridge over northwest of Europe, while in cyclonic wave breaking events the insification of the trough over the east of Europe is associated with intensification of the ridge in lower latitudes over the west of the Mediterranean. The waves in anticyclonic wave breaking events move to lower latitudes over the Mediterranean, while in cyclonic wave beakings, the waves move to north of Europe. Therefore, the anticyclonic (cyclonic) wave breaking events are generally associated with equatorward (poleward) flux of wave activity, downstream of the trough in latitudes lower (higher) than 40N, which causes the intensification (weakening) of synoptic waves over the Mediterranean and west of Asia. Also, the value of equatorward wave activity is 1.5 times more than those of poleward fluxes. It was found that in anticyclonic wave breakings, the downward wave activity flux is around twice, when compared to cyclonic wave breaking events. Our results showed that during anticyclonic wave breaking, the equatorward of wave activity flux at 40N over west of Europe is larger than its value over the East Mediterranean and west of Asia, while during cyclonic wave breaking events the poleward flux of wave activity over west of Europe is negligible and it becomes equatorward over east of Europe and west of Asia. It seems that the reason is the existence of a ridge over Euroasia which results in the formation of a blocking over east of Europe and consequently causes the intensification of troughs in lower latitudes. As such, in addition to the lesser number of cyclonic wave breakings compared to those of anticyclonics, the cyclonic wave breaking events are relatively weaker than anticyclonic breakings over Europe.

Reliable wave estimation in complex body of waters from geographical point of view is a matter of high importance. Main straits in the world, such as the Strait of Hormuz are major referent for this issue. Marine activities such as coastal management and ship routing, navigation, maintenance, and installation of offshore infrastructure are all greatly dependent on reliable wave estimations. Predicting waves in a region requires a well-developed wave model that can account for the shallow water wave mechanisms like their generation, propagation, and dissipation. On the other hand, reliable input wind data is a pre-requisite for realistic wave estimation, while the winds over such environments are highly affected by the land features around the straits. The wind data accuracy is also dependent on horizontal resolution of the models to capture the meso-scale dominant phenomena in the interest region. This study aims to develop a wave model employing SWAN wave model, in order to improve wave estimations over the Strait of Hormuz, where is highly affected by geographical complexity. Initially, the simulation is carried out for more than one month from January to May for period of 40 days of 2011. The main parameters of the model were assigned based on a comprehensive sensitivity analysis study and the model performance was verified based on the available archive field data for two stations Jask and Larak in the eastern part and western part of Strait of Hormuz, respectively. The numerical modeling activities are conducted to adopt two sources of surface wind data. The first adopted dataset, ECMWF’s hourly ERA5 product, is based on the presence of meso-scale locally convective phenomena such as land-seas breeze which is dominant in a water body like the Persian Gulf. ERA5 reanalysis dataset, which is the best available wind source, misses these features (because of low resolution) and in turn, when it is used to force the wave models, may result in predicting less accurate wave fields. For improving wind data accuracy, the second dataset, i.e., the high resolution meso-scale atmospheric model WRF was adopted to generate a more realistic wind field. This model reflects the meso-scale phenomena and using it to force the wave model, reflects more accurate wave fields over study area. Different model resolutions are also tested and the result showed that reducing the horizontal resolution for wind field improves the result. The final model results show a significant improvement in wave estimations in the middle of the Strait of Hormuz for coupling wave model SWAN and using WRF wind data. For Larak station, the RMSE decreases 10 percent in comparison to ERA5 wave data and CC (Corolation Coefficient) get to about 0.75. For Jask staion in eastern part of Strait of Hurmoz, ERA5 wave data CC is about 0.9 which is the best performance.