The extratropical transition of the Cyclone Chapala and its impact on the Mid latitude weather systems: ridge development over the Jet Stream
Mahmoud
Safar
Institute of Geophysics, University of Tehran
author
Sarmad
Ghader
Institute of Geophysics, University of Tehran
author
Farhang
Ahmadi-Givi
Institute of Geophysics, University of Tehran
author
Alireza
Mohebalhojeh
Institute of Geophysics, University of Tehran
author
Majid
Mazraeh-Farahani
Institute of Geophysics, University of Tehran
author
text
article
2018
per
The cyclone Chapala was the second strongest tropical cyclone among the cyclones that has been formed and recorded over the Arabian Sea. On October 28, 2015, the cyclone Chapala developed over western India from the monsoon trough. After reaching its peak intensity on October 30, 2015, it started to move toward the Yemeni island of Socotra. Then, on November 2, 2015, the cyclone entered the Gulf of Aden and became the strongest cyclone ever developed in that water area. The cyclone Chapala was finally decayed on November 4, 2015. The present work is devoted to the study of the extratropical transition of the cyclone Chapala and its impact on the development of mid-latitude disturbances and, in particular, the jet stream over the western part of Iran. In fact, the main objective of the current work is to find out whether there is any link between the extreme rainfall over western Iran and the cyclone Chapala via the extratropical transition of the cyclone and its impact on the development of mid-latitude weather systems including the jet stream. To this end, the Weather Research and Forecasting (WRF) model is used to simulate the cyclone Chapala during its lifetime from the development stage to the decay stage. The advanced research WRF model is a fully compressible, non-hydrostatic mesoscale numerical weather prediction model. This model has been developed at National Center for Atmospheric Research (NCAR). For the ARW dynamical core, an Arakawa-C horizontal grid is used, and for temporal integration of governing equations, a Runge–Kutta scheme with a smaller time step for fast waves (such as sound waves) is used. The WRF model simulations are performed for the period 1 to 11 November 2015. To perform the WRF model simulations, the NCEP FNL (Final) Operational Global Analysis data, which are available operationally every six hours, are used to prepare the initial and lateral boundary conditions. In this study, the ARW dynamical core of the WRF model is used. The WRF model is configured with one nest and 45 km horizontal grid resolution in a Lambert projection. The computational domain of the WRF model covers Iran, the Persian Gulf, the Oman Sea and the Arabian Sea. In addition, the following physical parametrizations are used: the WSM3 scheme for the microphysics, the RRTM scheme for the longwave radiation, the Dudhia scheme for the shortwave radiation, the MM5 method for the surface layer, the Noah method for the land surface, the YSU scheme for the planetary boundary layer, and the Kain–Fritsch scheme for the cumulus convection. Further, to simulate the air parcel trajectories, the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) is used. The HYSPLIT model can be used for numerical simulation of air parcel trajectories as well as the complex transport, dispersion, chemical transformation, and deposition simulations. Here, the HYSPLIT is coupled with the WRF model to carry out forward and backward simulations of air parcel trajectories over Iran during the period of the activity of the cyclone Chapala. The diagnostics like potential vorticity, as computed and presented based on the WRF numerical model results and the air parcel trajectory simulations by the HYSPLIT model, point to a clear transfer of mass and energy from the tropical lower troposphere to the upper troposphere in midlatitudes during the extratropical transition of the cyclone Chapala. The marked effect of the cyclone on the weather systems leading to the extreme precipitation in the southwest of Iran is confirmed.
Iranian Journal of Geophysics
Iranian Geophysical Society
2008-0336
11
v.
4
no.
2018
1
18
https://www.ijgeophysics.ir/article_49799_4af5159fcb2b1028e2bf9da0c9d2aeb8.pdf
Rupture details of 18 June 2007 Kahak and 27 September 2010 North of Kazeroon earthquakes imaged by back-projection of teleseismic P-wave
mahsa
chenari
Institute of Geophysics, University of Tehran
author
zaher hosein
shomali
Institute of Geophysics, University of Tehran
author
text
article
2018
per
For large earthquakes, rupture characteristics including rupture velocity and fault extension are important parameters that reflect the fault properties and complexities. One of the most important tasks for earthquake monitoring agencies is to determine a finite source rupture model as quickly as possible so that a map of regions with the strongest shaking can be provided to guide emergency response and rescue. In many cases, the epicenter is not the most severely damaged region. One of the recently used methods to image the source and rupture details is back-projection (reverse time migration), which has some advantages comparing to traditional methods such as finite-fault source inversion; since it is much faster (the computation is relatively easier than inversion) and it can be applied to different frequency bands, even high frequencies, and the only a priori information required is a radial velocity model and a hypocentral estimate. In this method, seismic arrays at teleseismic distances are used. Since the back-projection technique is sensitive to the array geometry, array response function (ARF) is used to choose the array with the least artifact. In order to compute the ARF, the process is the same except the fact that the synthetic seismograms are used instead of real seismograms. To investigate the rupture propagation and energy release of two earthquakes, 2007/06/18 Mw 5.9, Kahak, and 2010/09/27 Mw 5.5, north of Kazeroon, a back-projection of teleseismic P-wave with X4 (China) and YP (northeast China) seismic network arrays, vertical component data high-pass filtered at 1.0 Hz are used. It is assumed that the first part of the seismograms is due to the failure at hypocentre and later parts come from rupture front. To determine the rupture propagation that is necessary to know which point in source area has caused the radiation of energy, a grid of points in source area is set. This grid covers most of the aftershocks region. The back-projection analysis used in this study does not have very good depth resolution, so that grid is 2-Dimensional and the depth of grid is constant; hence, the waveforms are stacked at every time window for all grid points and the back-projection method determines which grid points are the source of seismic radiation in each time window of the teleseismic P waves. In this method, seismograms are stacked for grid point to obtain a direct image of the source. Stacking procedures sums the energy that is radiated from the grid point constructively and cancels out other energy patterns present in the seismograms. Resulting maps show the squared amplitudes of the stacks, which are proportional to the radiated high frequency seismic energy. According to the results, for Kahak earthquake, the rupture is in order of 1.9±0.006 km-1 and the rupture front propagates southwest to northeast about 8±1 seconds. For north of Kazeroon earthquake, the rupture velocity is 1.6±0.003 km and the total time of propagation is 15±1 seconds. The back-projection method is usually used to determine slip distribution of large earthquakes using a very dense array. However in this study we show that the back-projection method can even be extended to study moderate size earthquakes.
Iranian Journal of Geophysics
Iranian Geophysical Society
2008-0336
11
v.
4
no.
2018
19
39
https://www.ijgeophysics.ir/article_49968_52cf23429d3ceafb71ec1bfdafac2f91.pdf
Assessment of CMIP5 climate models with observed precipitation in Iran
jafar
Masoompour Samakosh
climatology, Departeman of Geography, Razi University
author
morteza
miri
PhD. Department of Climatology, University of Tehran
author
fatemeh
purkamar
MSc, Faculty of Geography, Razi University
author
text
article
2018
per
The changes in precipitation that depend on future climatic changes highly affect environmental processes and the use of ecosystem services, especially water sources. Because providing necessary material for human beings is mostly dependent on water sources, the reliable prediction of precipitation and water sources, affected by climate change, is of considerable importance. Nowadays, there are centers and various models worldwide that simulate the state of future climate of the earth by different scenarios, e.g., the scenario of release physical and computational structure. Simulations of world climate models have been archived by CMIP project, which are regarded as one of the most important sources to study the climate condition of the 21st century. The simulations from models of general atmospheric circulation, which is a part of CMIP5, are as the basis for the conclusions of international committee related to future climatic changes. The data can be used to assess future climatic changes in local or regional scales, whether directly or after presenting downscale. Although the predictions of general circulation models are reliable enough, ignoring some important features of each region, especially developing countries and the ones with high environmental diversity like Iran, make the data of these models need accurate assessment in various spatial and temporal scales. Therefore, the present study aims to assess the accuracy of precipitation data from eight models (BCC-CSM1.1, CCSM4, CESM1-BGC, CESM1-CAM5, CMCC-CM, EC-EARTH, MIROC5and MIR- CGCM3) of general atmosphere circulation according to high spatial accuracy for Iran applying statistical tests. Statistic indices like R, R^2, RMSE, BIAS, EF, NARMSE, SLOPE, and IA were applied to choose the most appropriate model, out of eight, up close to real data of the country.The findings reveal that Although the models used to calculate rainfall has not high reliability, but also it is too weak to estimate the stations’ extreme events. Besides, in a similar study, Hidalgo and Alfaro (2014) believe that most of the CMIP5 models have low ability to estimate the precipitation of central regions of the USA. Regionally, output accuracy for north-eastern and western regions is more than other parts of the country. Besides, the accuracy for coastal regions of Iran (Oman and Caspian) is very low and practically useless, which is due to the special geographical condition and the contrast of land and water in these regions. In fact, the assessment of future precipitation output of these models under scenario 4.5 and 8.5 presents the same findings; the correctness of predictions in northern half (except for Caspian beaches) is more than the southern half. Scenario 4.5 shows better results in northeast and west while scenario 8.5 shows better results in southern beaches, especially southeast of the country. The findings from the process of precipitation from CCSM4 model, under scenarios 4.5 and 8.5, show that the process of future precipitation changes will not be significant for any region and the slope is from weak to average.
Iranian Journal of Geophysics
Iranian Geophysical Society
2008-0336
11
v.
4
no.
2018
40
53
https://www.ijgeophysics.ir/article_53232_e34b6623a5d356b154f7bfd827680a56.pdf
Regional and optimal estimation of total electron content using pseudorange observations
Saleh
mafi
Department of Surveying and Geomatics Engineering, Faculty of Engineering, University of Tehran
author
taha
Sadeghi chorsi
Department of Surveying and Geomatics Engineering, Faculty of Engineering, University of Tehran
author
Saeed
Farzaneh
Faculty of engineering school of surveying engineering, University of Tehran
author
text
article
2018
per
Total Electron Content (TEC) is one of the most important factors in monitoring the variable structure of ionosphere. Global Positioning System (GPS) is a useful and affordable instrument in TEC prediction through ground receivers. In this research, Vertical Total Electron Content (VTEC) is calculated in a GPS station using code observations and an approach is introduced for precise, and local modeling of this quantity. For doing this, a geometry-free combination of P1 and P2 observables is made and TEC for every satellite in an epoch is obtained using this combination and Differential Code Biases (DCB) of satellite and receiver. The calculated parameter shows total electron content in the direction of signal propagation in ionosphere layer. Besides, a mapping function is used for transforming TEC to VTEC. For doing this transformation, there are various mapping functions the common examples of which are geometric mapping function and empirical mapping function. In order to increase the precision and reduce systematic errors of calculations, the geometric mapping function is used. After calculation of VTEC for every satellite, it is necessary to obtain the amount of VTEC in zenith direction of the station. For doing this, a weighted function is used that inversely relates to the elevation angle of the satellite. The proposed weighted function provides an optimum and precise formula for calculation of VTEC in zenith direction of the station. In order to investigate the accuracy of calculations, all of the results are compared with the VTEC grids of International GNSS Service (IGS), and finally, the conclusions for every specific method are shown like weighted average, normal average and nearest vertex. In other words, IGS ionospheric products are considered as accurate and precise VTEC and the results are compared with these VTECs. As everybody knows, IGS VTECs are produced in a grid and thus, for calculation of VTEC in a specific point, mathematical approaches like weighted average of VTECs in surrounded vertexes of the point should be used. Conclusions illustrate the calculation of VTEC using proposed approach has a good adaption with the weighted average of VTECs around the Ankara grid station. The other results are also illustrated in diagrams. In addition, the periodic behavior of ionosphere at different times are also modeled, and the method is improved for optimum estimation of VTEC at various times. The only thing that is important is the local nature of this method, which is useful in one cell of IGS ionospheric network only.
Iranian Journal of Geophysics
Iranian Geophysical Society
2008-0336
11
v.
4
no.
2018
54
66
https://www.ijgeophysics.ir/article_53685_4537a5e3894a6798c2702073f02ab0be.pdf
Modeling of amplitude and phase variations of converted waves versus offset and VP/VS ratio
Hossein
Jodeiri Akbari Fam
Faculty of Mining Engineering, Sahand University of Technology
author
Navid
Shad Manaman
Faculty of Mining Engineering, Sahand University of Technology
author
text
article
2018
per
Shear wave information plays a valuable role in the interpretation of seismic data and reservoir characterization studies. Due to the high cost and technical difficulties in data recording of full elastic seismic data (3D-9C), using converted waves can be helpful to extract valuable S-wave information. Analysis of the amplitude and phase variations of converted waves with offset would be useful in better identification of converted reflections in the seismic sections and uncertainty reduction in the processing and interpretation of these data. In this regard, by using Zoeppritz equations, the energy distribution of different seismic modes (P-P, S-S, P-Sv, and Sv-P) on the interface of the layers with different acoustic impedances at various incidence angles has been studied. Then, by using forward modeling and ray tracing methods, it should be obtained that how converted waves propagate in isotropic and anisotropic media. Besides, the effect of the Vp/Vs variations in the travel time and amplitude of the converted modes are inspected. For data recorded by receivers oriented in the same direction as the seismic source (both vertical or both horizontal), the polarity of converted waves is the same in the positive and negative offsets. However, if the direction of receivers is perpendicular to the seismic source, the converted waves will have opposite polarities on different sides of the source. Moreover, for primary P-Sv reflections, the largest P-to-S conversion occurs beyond the critical angle that is related to large source-receiver offsets. In contrast, S-to-P conversion significantly appears before the critical angle. However, it should be noted that for the same takeoff angle, the Sv-P and P-Sv waves will be recorded in the same offset, because the P-Sv incidence angle equals the Sv-P reflection angle and vice versa. For example, the synthetic models show that in seismic layers with Vp/Vs = and horizontal reflector, maximum P-Sv conversion occurs at an incidence angle of about 64° and reflection angle of about 31°, while maximum Sv-P conversion occurs around 31° angle of incidence and around 64° angle of reflection. This means that from the viewpoint of source-receiver distance, depending on the intended depth, mid and far offsets data are necessary for good recording of the conversion mode reflections. Moreover, according to Snell law and Zoeppritz equations, in the case of converting Sv to P, the transmitting converted P-wave would have a small amplitude. Hence, in Sv-P studies, only the converted waves with purely Sv incoming and purely P reflection are considered.
Iranian Journal of Geophysics
Iranian Geophysical Society
2008-0336
11
v.
4
no.
2018
67
92
https://www.ijgeophysics.ir/article_53942_1294510cdfbc4cd2f82c269ccbaf1c17.pdf
Focal mechanism of Mountain front fault (MFF) at a longitude of 46 to 48.5 Degree
Sotodeh
Mohammadnia
International Institute of Earthquake Engineering and Seismology (IIEES)
author
Mohammadreza
Abbassi
International Institute of Earthquake Engineering and Seismology
author
Gholam
Javan-Doloei
International Institute of Earthquake Engineering and Seismology
author
Mohsen
Azqandi
International Institute of Earthquake Engineering and Seismology (IIEES)
author
text
article
2018
per
One of the most seismically active parts of Iran is Zagros area. The basement-involved active fold-thrust belt of the Zagros in southwest Iran is underlain by numerous seismogenic blind basements thrust covered by the folded Phanerozoic sedimentary rocks. The present morphology of the Zagros active fold-thrust belt is the result of its structural evolution and depositional history: a platform phase during the Paleozoic; rifting in the Permian Triassic; passive continental margin (with sea-floor spreading to the northeast) in the Jurassic-Early Cretaceous; subduction to the northeast and ophiolite-radiolarite emplacement in the Late Cretaceous; and collision-shortening during the Neogene.Besides, there are a lot of different faults in Zagros, for example, the Main Zagros Reverse Fault (MZRF), the Main Recent Fault (MRF), the High Zagros thrust belt, the High Zagros Fault (HZF), and Mountain Front Fault (MFF). This study is focused on the last-mentioned one. The MFF flexure is introduced for the first time by Falcon (1961) and then is presented as the mountain front fault by Berberian and Tchalenko (1976)], which delimits the Zagros simple fold belt and the Eocene-Oligocene Asmari limestone outcrops to the south and southwest. The Mountain front fault (MFF), is a segmented master blind thrust fault with important structural topographic, geomorphic and seismotectonic characteristics. Therefore, the study and recognition of seismic parts of Iran are important. The aim of this study is to determine the focal mechanisms of Mountain Front Fault (MFF) at a latitude of 46 to 48.5 degree in Zagros. Due to the salt layers, large earthquakes rarely reach the surface. In such cases, the seismic method is an appropriate tool to understand the faulting mechanisms. By means of focal mechanisms, it is possible to gain information about the fault geometry and its related mechanism. The data used in this study are from International Institute of Earthquake Engineering, and Seismology (IIEES) and Institute of Geophysics of the University of Tehran (IGUT). Because of some wrong relocation, during this study relocated them to reach a well-relocated data base and better results. Getting the focal mechanism of an earthquake can occur in various ways. In this study, first, the waveform modeling by Isola software was used to find the focal mechanisms. To determine the accuracy of focal mechanism solutions obtained by waveform modeling, the polarity method was used to solve focal mechanisms. Besides, some of these earthquakes have also been reported by CMT. After determining focal mechanism solutions with the stated method, they were compared with CMT, and all the focal mechanism were mapped in the area so that the trend of this part of MFF can be recognized better. Because there are many earthquakes in this area, a reliable decision can be made. By looking at the maps, it is easily understandable that the trend in this part is obviously EW. Finally, the prevailing trend that obtained in the study area is found. Most of these earthquakes are trending EW. The study of 31 focal mechanisms in the area has permitted to constrain the faulting mechanism of MFF.
Iranian Journal of Geophysics
Iranian Geophysical Society
2008-0336
11
v.
4
no.
2018
93
106
https://www.ijgeophysics.ir/article_55997_62f8cea9ce4d4d7ec238680c8cf19db5.pdf
Expansion of roughness length parameterization in the ocean surface layer based on measured data
Ahmad
Zadeghabadi
Department of Marine and Atmospheric Science (non-Biologic), ّFaculty of Marine Science and Technology, University of Hormozgan
author
Hossein
Malakooti
Department of Marine and Atmospheric Science (non-Biologic), Faculty of marine science and technology, University of Hormozgan
author
Ali
Mohammadi
Space Physics Department, Institute of Geophysics, University of Tehran
author
text
article
2018
per
Charnock scheme is known as the most widely used method to calculate the flux exchange in the ocean surface layer. Due to the simplicity of the application and run with minimum meteorological data, it is one of the most popular schemes in the surface layer. Edson et al. (2013) introduced the method of variable coefficients for the Charnock relationship and used data collected from four oceanic field experiments for this purpose. They have introduced a linear regression equation among neutral wind speeds at 10 m (U10N) in range of 7 to 18 m/s with coefficients of Charnock relation. This proposed linear equation is considered by the investigators in the recent versions of 3.8 and 3.9 of the WRF model and is evaluated in some cases. This scheme is considered as the default for the calculation of surface fluxes. The applicability of this method only for U10N between 7 and 18 m/s is known as a disadvantage of this scheme. In this study, the aforementioned problem (U10N limitation) was considered, and neutral wind velocity at 10 m was fitted measured data of Edson in a range of 5 to 30 m/s by a second-order function. However, the average error in second-order fitness has slightly increased, but considering speeds of 18 to 30 m/s can cover a slight decrease in fitness accuracy. For U10N higher than 30 m/s, according to a large number of studies in the field of reducing or fixed drag coefficients at speeds above 30 m/s, the assumption of reducing the Charnock coefficient was studied for U10N more than 30 m/s. The Charnock coefficient was assumed at U10N higher than 30 m/s would decrease linearly with increasing wind speed and eventually reach zero at 90 m/s. Due to the lack of physical interpretation for zeroing the Charnock coefficient at 90 m/s, the maximum U10N of 80 m/s is considered, which is equal to 0.005 for the value of the Charnock coefficient. Modification of the Edson et al. (2013) scheme in this paper has led to a reduction in the growth rate of the drag coefficient. The main results of the present research are that even with zeroing the Charnock coefficient at 90 m/s and taking into account the maximum U10N at 80 m/s in the Edson et al. scheme, the reduction in drag coefficient at U10N more than 30 m/s cannot be created. Therefore, if future measurements suggest additional flux production at U10N higher than 30 m/s for the Edson et al. scheme, stronger strikes are needed to reduce roughness length, and the decreasing trend does not occur in the drag coefficient even with zeroing the Charnock coefficient. Therefore, it is seen that adding ocean spray effects to well-known schemas such as Charnock has many problems. In this study, although the main defects of the Edson et al. scheme (Quasi-exponential growth of the drag coefficient with increasing wind speed) have been resolved, more field measurements will be required for the scheme verification proposed in this paper.
Iranian Journal of Geophysics
Iranian Geophysical Society
2008-0336
11
v.
4
no.
2018
107
122
https://www.ijgeophysics.ir/article_54202_b584820f6538f8566429dbd52f965408.pdf
Back projection resistivity fast imaging technique for 2D electrical resistivity data
Ata
Eshaghzadeh
Institute of Geophysics, University of Tehran
author
Alireza
Hajian
Department of physics, Najafabad Branch, Islamic Azad University
author
text
article
2018
per
Electrical resistivity techniques are well-established and applicable to a wide range of geophysical problems. 2D resistivity measurements can give information about both the lateral and vertical variations of the subsurface resistivity and can be used in a qualitative fashion for the identification of the structure and depth of masses. The resistivity inverse problem involves constructing an estimate of a subsurface resistivity distribution, which is consistent with the experimental data. This is a fully non-linear problem and its treatment involves iterative full matrix inversion algorithms, which can give good quality results. The back-projection resistivity technique (BPRT) can be applied to a set of apparent resistivity measures to quickly obtain an approximate image of the resistivity distribution of the investigated volume. This technique is based on the consideration that a resistivity perturbation in a point element (voxel) of a bounded region produces a change in voltage thus an apparent resistivity anomaly at the surface of the region, according to a sensitivity coefficient. The value of the coefficient is dependent on the position of the voxel considered in respect of both the current and the voltage dipoles, in agreement with the sensitivity theorem of Geselowitz. This consideration suggests that it is possible to correlate all the measured resistivity values, weighted by the appropriate sensitivity coefficients to each voxel of the investigated volume and to estimate the resistivity value of each cell of the model using a weighted summation of the apparent resistivity measurements. The BPRT considering a two-step approach. Initially, a damped least squares solution is obtained after a full matrix inversion of the linearized geoelectrical problem. Furthermore, on the basis of the results, a subsequent filtering algorithm is applied to the Jacobian matrix, aiming at reducing smoothness, and the linearized damped least square inversion is repeated to get the final result. This fast imaging technique aims at increasing the resistivity contrasts, and practically, since it does not require a parameter set optimization, it can be used to easily obtain fast and preliminary results. The procedure proposed in this work consists of four steps: (1) Evaluation of sensitivity matrix B, (2) Inversion of matrix B using a damped LSQR solution, (3) Recalculation of a filtered Jacobian matrix B‘ obtained by means of a correlation filter, (4) Inversion of the filtered sensitivity matrix. The proposed technique is tested on resistivity synthetic data from the Schlumberger, Wenner, Dipole-dipole and Pole-pole arrays, the objective of which is to find the optimal parameter set. The synthetic tests carried out with 2D data suggested that a good compromise for 2D inversions is to choose 𝜆 for the Schlumberger, Wenner, Dipole-dipole and Pole-pole arrays, 0.1, 20, 1 and 0.5, respectively. Furthermore, all the synthetic tests carried out with 2D data suggested that a good compromise for 2D inversions is to choose 𝜒 ≈ 5. The approximate images using the BPRT inverse modeling for all synthetic data, with and without random noise, is compared with the least square inversion by RES2DINV software. Finally, a field case is discussed, and the comparison between the back-projection and inversion is shown.
Iranian Journal of Geophysics
Iranian Geophysical Society
2008-0336
11
v.
4
no.
2018
123
145
https://www.ijgeophysics.ir/article_54471_2e8f6758d40bc27d2c6eb13675ebbe38.pdf
The evaluation of snow model in NOAH-MP coupled with WRF model during the periods of heavy snow over the northern and western regions of Iran
Mehraneh
Khodamorad Pour
Faculty of Agriculture Bu-Ali Sina University
author
Parviz
Irannejad
Institute of Geophysics, University of Tehran
author
Samira
Akhavan
Faculty of Agriculture Bu-Ali Sina University
author
Khaled
Babei
Water Organization
author
text
article
2018
per
Land surface schemes have considerable significance in the regional climate models. Due to their role in both surface’s energy and water budget, snow processes are among the most important components of the surface schemes. Snow cover fraction, because of extreme temporal and spatial changes and various features, including high albedo coefficient and very low conductivity, plays an important role in the snow models. This research evaluates snow parameterization in the Advanced Weather Research and Forecasting model (WRF) coupled with the NOAH-MP as a land surface scheme, improved NOAH scheme, through the advanced canopy, snow, and runoff modeling. The snow cover fraction of this scheme is estimated through the hyperbolic tangent relationship between snow height, snow density, and snow melt factor. The snowmelt factor in this model is pre-determined as one since its calibration is difficult due to the lack of access to the observational data at weather stations, using satellite images, and lack of images at most of the snowfall time periods because of the cloud coverage in most parts. For this reason, in this research, the snow cover fraction is evaluated with the default snowmelt coefficient of the model. The WRF-NOAHMP model runs in two separate zones, the northern (Ardebil, Gilan, and Mazandaran provinces) and the western (Kurdistan and Hamedan provinces) regions of Iran, through one-way nesting method with the spatial resolution of 15 kilometers and 5 kilometers for mother and inner domains and during the several periods of heavy snow in the winter of 2013 and 2014. The daily Modis images of the Terra Satellite were used to evaluate the snow cover fraction. Based on the digital elevation model and land use maps, the study area is categorized into five areas, including forests, rangelands, low lands, and mountainous regions with high and low slopes. The WRF-NOAHMP model is successful in predicting the snow cover fraction in most areas, except mountainous areas with high slopes and rangeland areas; however, the model’s best performance is for low lands due to the highest efficiency coefficient (0.64), the smallest Bias error (-2.4), and Mean Absolute Error (9.4). Moreover, the skill level of the model’s performance (using the area under ROC curve) is good in predicting snowfall in most areas, except for the rangeland area. The WRF-NOAHMP is unsuccessful in estimating the snow depth in forests and mountainous areas with high slopes due to the negative efficiency coefficient, while it has the highest efficiency in estimating snow depth in low lands and mountainous areas with a low slope. Evaluation of the simulated minimum temperature by the model indicates the model’s success in estimating the minimum temperature in all studied areas because of the positive efficiency coefficients. The results of this study show the success of the WRF-NOAHMP in the prediction of the minimum temperature in different regions, while it still has a great deal of uncertainty in the parameterization of the snow cover fraction and the snow depth in mountainous areas with complex topography and areas with surface heterogeneity as well as the parameterization of the snow canopy.
Iranian Journal of Geophysics
Iranian Geophysical Society
2008-0336
11
v.
4
no.
2018
146
163
https://www.ijgeophysics.ir/article_54789_047976cfd884f87546c826cd5626f10d.pdf