اعضای هیات علمی نجوم - مرکز نجوم و اختر فیزیک مراغه

درباره

سوابق تحصیلی

	Field of Study	Location	Start/End Date
BSc in Physics	Solid State Physics	University of Urmia, Iran	September 2000, February 2005
MSc in Physics	Astronomy & Astrophysics	University of Kurdistan, Iran	September 2006, March 2009
PhD in Physics	Astronomy & Astrophysics	University of Kurdistan, Iran	September 2012, September 2017

سوابق تدریس

فیزیک خورشید
الکترودینامیک
کیهان شناسی
روشهای پیشرفته ی محاسبات عددی و شبیه سازی در فیزیک
فیزیک عمومی
فیزیک پایه

زمینه های پژوهشی

تصویر تاج خورشید در طول موج 171 آنگستروم
لرزه نگاری اتمسفر خورشید
میدان مغناطیسی در اتمسفر خورشید
امواج مغناطوهیدرودینامیک در تاج خورشید

خلاصه مقالات

Karami K., and Ebrahimi Z., Phase-Mixing and Dissipation of Standing Shear Alfven Waves, Publications of Astronomical Society of Australia (PASA), 2009, 26, 448.
Karami K., Amiri S., Bahari K., and Ebrahimi Z., Resonantly damped oscillations of elliptically shaped stratified emerging coronal loops, Ap&SS, 2013, 347, 29.
Ebrahimi Z., and Karami K., Resonant absorption of kink magnetohydrodynamic waves by a magnetic twist in coronal loops, MNRAS, 2016, 462, 1002.
Ebrahimi Z., Karami K., & Soler R., The Effect of a Twisted Magnetic Field on the Phase Mixing of the Kink Magnetohydrodynamic Waves in Coronal Loops, 2017, ApJ, 845, 86.
Ebrahimi Z., Bahari K., Resonant absorption of kink oscillations in coronal flux tubes with continuous magnetic twist, MNRAS, 2019, 490, 1644.
Ebrahimi Z., Soler R., & Karami K., Phase Mixing of Kink MHD Waves in the Solar Corona: Viscous Dissipation and Heating, ApJ, 2020, 893, 157.
Karami, K. and Ebrahimi, Z., Damping of Standing Shear Alfven waves by the Phase Mixing, 2009, Proc. 13’th Meeting on Research in Astronomy (Zanjan: IASBS), 243.
Ebrahimi Z., & Karami K., Resonant absorption of kink MHD waves by magnetic twist in coronal loops, 2015, Proc. 8’th National Meeting in Astronomy and Astrophysics (Tehran: Amir Kabir University), 79.
Ebrahimi Z., & Karami K., Resonant absorption of kink MHD waves by magnetic twist in coronal loops, 2016, Proc. 19’th Meeting on Research in Astronomy (Zanjan: IASBS), 15.
Ebrahimi Z., Karami K., & Soler R., The effect of twisted magnetic field on the phase mixing of the kink magnetohydrodynamic waves in coronal loops, 2017, Proc. 20’th Meeting on Research in Astronomy (Zanjan: IASBS), 59.
Ebrahimi Z., Bahari K., Resonant absorption of kink magnetohydrodynamic waves in solar coronal flux tubes with a continuous and twisted magnetic field, 2019, Proc. 22’th Meeting on Research in Astronomy (Zanjan: IASBS).
Bahari K., & Ebrahimi Z., The Nature of Kink MHD Waves in the Solar Corona: Magnetic Twist and Phase Mixing, 2020, MNRAS, (accepted 2020, July, 3) In Press.
Ebrahimi Z., Karami K., & Soler R., The effect of viscosity on the kink magnetohydrodynamic waves in coronal flux tubes, 2020, Oral Presentation, Proc. 13’th National Meeting in Astronomy and Astrophysics (University of Kurdistan, Sanandaj), 65-68.
Bahari K., & Ebrahimi Z., The Nature of Kink MHD Waves in the Solar Corona: Magnetic Twist and Phase Mixing, 2020, MNRAS, 497, 1135.

کتاب ها

راهنمایی و مشاوره پایان نامه

تشویق ها

عضویت در مجامع علمی و انجمن ها

عضو حرفه ای انجمن نجوم ایران (ASI)

مقالات ارائه شده

عنوان مقاله : اثر اختلاط فازي روي ميرايي بسته موج آلفن ايستاده برشي

نویسندگان : کیومرث کرمی، زانیار ابراهیمی

نام کنگره یا سمینار : سیزدهمین گردهمایی پژوهشی نجوم

تاریخ و محل برگزاری : 8 و 9 بهمن 1387 دانشگاه تحصیلات تکمیلی در علوم پایه زنجان

نحوه ارائه : پوستر

چکیده : اثر اختلاط فازي روي ميرايي يك بسته موج آلفن ايستاده برشي در محيطي با سرعت آلفن غير يكنواخت مورد بررسي قرار مي گيرد. با استفاده از روش عددي تفاضل متناهی، معادله موج آلفن براي اين بسته موج در حالت پايه، به صورت عددي حل مي شود. نتايج ما نشان مي دهد كه تطبيق با نتايج هيوارتز و پريست (1983) براي اعداد رينولدز و لوندكويست R ≈ S ≥ 10^8 صورت مي گيرد. برای مقادير كوچكتر از اين، اثر ناشي از پهن شدگي بسته موج بر اثر ميرايي موج، غالب مي شود.

دانلود

مقالات چاپ شده در مجلات

عنوان مقاله : Phase-Mixing and Dissipation of Standing Shear Alfvén Waves

نویسنده رابط : کیومرث کرمی

عنوان مجله و شماره مجله : Publications of the Astronomical Society of Australia, 26, 448–453

نویسندگان : کیومرث کرمی، زانیار ابراهیمی

سال انتشار : 2009

چکیده : We study the phase mixing and dissipation of a packet of standing shear Alfvén waves localized in a region with non-uniform Alfvén background velocity.We investigate the validity of the exponential damping law in time, exp(−A*t^3), presented by Heyvaerts & Priest (1983) for different ranges of Lundquist, S, and Reynolds, R, numbers. Our numerical results shows that it is valid for (R, S) ≥ 10^7.

عنوان مقاله : Resonant absorption of kink magnetohydrodynamic waves by a magnetic twist in coronal loops

نویسنده رابط : کیومرث کرمی

عنوان مجله و شماره مجله : MNRAS, 462, 1002-1011

نویسندگان : زانیار ابراهیمی، کیومرث کرمی

سال انتشار : 2016

چکیده : There is ample evidence of twisted magnetic structures in the solar corona. This motivates us to consider the magnetic twist as the cause of Alfv´en frequency continuum in coronal loops, which can support the resonant absorption as a rapid damping mechanism for the observed coronal kink magnetohydrodynamic (MHD) oscillations. We model a coronal loop with a straight cylindrical magnetic flux tube, which has constant but different densities in the interior and exterior regions. The magnetic field is assumed to be constant and aligned with the cylinder axis everywhere except for a thin layer near the boundary of the flux tube, which has an additional small magnetic field twist. Then, we investigate a number of possible instabilities that may arise in our model. In the thin tube thin boundary approximation, we derive the dispersion relation and solve it analytically to obtain the frequencies and damping rates of the fundamental (l = 1) and first/second overtone (l = 2, 3) kink (m = 1) MHD modes. We conclude that the resonant absorption by the magnetic twist can justify the rapid damping of kink MHD waves observed in coronal loops. Furthermore, the magnetic twist in the inhomogeneous layer can cause deviations from P1/P2 = 2 and P1/P3 = 3, which are comparable with the observations.

عنوان مقاله : The Effect of a Twisted Magnetic Field on the Phase Mixing of the Kink Magnetohydrodynamic Waves in Coronal Loops

نویسنده رابط : زانیار ابراهیمی

عنوان مجله و شماره مجله : ApJ, 845, 86

نویسندگان : زانیار ابراهیمی، کیومرث کرمی، روبرتو سولر

سال انتشار : 2017

چکیده : There is observational evidence for the existence of a twisted magnetic field in the solar corona. This inspires us to investigate the effect of a twisted magnetic field on the evolution of magnetohydrodynamic (MHD) kink waves in coronal loops. With this aim, we solve the incompressible linearized MHD equations in a magnetically twisted nonuniform coronal flux tube in the limit of long wavelengths. Our results show that a twisted magnetic field can enhance or diminish the rate of phase mixing of the Alfvén continuum modes and the decay rate of the global kink oscillation depending on the twist model and the sign of the longitudinal (k_z) and azimuthal (m) wavenumbers. Also, our results confirm that in the presence of a twisted magnetic field, when the sign of one of the two wavenumbers m and k_z is changed, the symmetry with respect to the propagation direction is broken. Even a small amount of twist can have an important impact on the process of energy cascading to small scales.

عنوان مقاله : Resonant absorption of kink oscillations in coronal flux tubes with continuous magnetic twist

نویسنده رابط : زانیار ابراهیمی

عنوان مجله و شماره مجله : MNRAS, 490, 1644-1651

نویسندگان : زانیار ابراهیمی، کرم بهاری

سال انتشار : 2019

چکیده : There are observational evidences for the existence of twisted magnetic field in the solar corona. Here, we have investigated resonant damping of the magnetohydrodynamic (MHD) kink waves in magnetic flux tubes. A realistic model of the tube with continuous magnetic twist and radially inhomogeneous density profile has been considered. We have obtained the dispersion relation of the kink wave using the solution to the linear MHD equations outside the density inhomogeneity and the appropriate connection formula to the solutions across the thin transitional boundary layer. The dependence of the oscillation frequency and damping rate of the waves on the twist parameter and longitudinal wavenumber has been investigated. For the flux tube parameters considered in this paper, we obtain rapid damping of the kink waves comparable to the observations. In order to justify this rapid damping, depending on the sign of the azimuthal kink mode number, m = +1 or −1, the background magnetic field must have left- or right-handed twisted profile, respectively. For the model considered here, the resonant absorption occurs only when the twist parameter is in a range specified by the density contrast.

عنوان مقاله : Phase Mixing of Kink MHD Waves in the Solar Corona: Viscous Dissipation and Heating

نویسنده رابط : زانیار ابراهیمی

عنوان مجله و شماره مجله : ApJ, 893, 157

نویسندگان : زانیار ابراهیمی، روبرتو سولر، کیومرث کرمی

سال انتشار : 2020

چکیده : Magnetohydrodynamic (MHD) kink waves have been observed frequently in solar coronal flux tubes, which makes them a great tool for seismology of the solar corona. Here, the effect of viscosity is studied on the evolution of kink waves. To this aim, we solve the initial value problem for the incompressible linearized viscous MHD equations in a radially inhomogeneous flux tube in the limit of long wavelengths. Using a modal expansion technique the spatio-temporal behavior of the perturbations is obtained. We confirm that for large Reynolds numbers representative of the coronal plasma the decrement in the amplitude of the kink oscillations is due to the resonant absorption mechanism that converts the global transverse oscillation to rotational motions in the inhomogeneous layer of the flux tube. We show that viscosity suppresses the rate of phase mixing of the perturbations in the inhomogeneous region of the flux tube and prevents the continuous building up of small scales in the system once a sufficiently small scale is reached. The viscous dissipation function is calculated to investigate plasma heating by viscosity in the inhomogeneous layer of the flux tube. For Reynolds numbers of the order of 10^6–10^8, the energy of the kink wave is transformed into heat in two to eight periods of the kink oscillation. For larger and more realistic Reynolds numbers, heating happens, predominantly, after the global kink oscillation is damped, and no significant heating occurs during the observable transverse motion of the flux tube.

عنوان مقاله : Resonantly damped oscillations of elliptically shaped stratified emerging coronal loops

نویسنده رابط : کیومرث کرمی

عنوان مجله و شماره مجله : Astrophysics and Space Science, 347, 29-39

نویسندگان : کیومرث کرمی، سیروان امیری، کرم بهاری، زانیار ابراهیمی

سال انتشار : 2013

چکیده : The effects of both elliptical shape and stage of emergence of the coronal loop on the resonant absorption of standing kink oscillations are studied. To do so, a typical coronal loop is modeled as a zero-beta longitudinally stratified cylindrical magnetic flux tube. We developed the connection formulae for the resonant absorption of standing transversal oscillations of a coronal loop with an elliptical shape, at various stages of its emergence. Using the connection formulae, the dispersion relation is derived and solved numerically to obtain the frequencies and damping rates of the fundamental and first-overtone kink modes. Our numerical results show that both the elliptical shape and stage of emergence of the loop alter the frequencies and damping rates of the tube as well as the ratio of frequencies of the fundamental and its first-overtone modes. However, the ratio of the oscillation frequency to the damping rate is not affected by the tube shape and stage of its emergence and also is independent of the density stratification parameter.

عنوان مقاله : The nature of kink MHD waves in the solar corona: magnetic twist and phase mixing

نویسنده رابط : کرم بهاری

عنوان مجله و شماره مجله : MNRAS, 497, 1135

نویسندگان : کرم بهاری، زانیار ابراهیمی

سال انتشار : 2020

چکیده : To study the nature of magnetohydrodynamic (MHD) kink waves, the temporal behaviour of an initial kink perturbation of a typical coronal flux tube has been investigated in this paper. The flux tube has a transitional layer that separates the core region of the tube from the surrounding environment. In the transitional layer, the background density and magnetic field varies continuously from the internal to the external values. The magnetic field is straight and aligned with the tube axis in the internal and external regions of the flux tube, but is assumed to be twisted in the transitional layer. Hence, in the transitional layer the background Alfv´en speed is inhomogeneous and perturbations become out of phase due to the process of phase mixing. Our result shows that as the energy of the wave transfers to the local Alfv´en waves in the inhomogeneous region, the magnetic tension force becomes the dominant restoring force of the wave. The numerical results show that the nature of the small-scale oscillations in the transitional layer is determined by the ratio of the azimuthal components of the restoring forces.

عنوان مقاله : Resonant absorption of kink MHD waves in inclined and asymmetric coronal loops

نویسنده رابط : کیومرث کرمی

عنوان مجله و شماره مجله : MNRAS, 502, 2172

نویسندگان : سیروان امیری کیومرث کرمی زانیار ابراهیمی

سال انتشار : 2021

چکیده : This paper separately evaluates the effects of inclination and asymmetry of solar coronal loops on the resonant absorption of kink magnetohydrodynamic oscillations. We modelled a typical coronal loop by a straight and axisymmetric cylindrical magnetic flux tube filled with cold plasma. We solved the dispersion relation numerically for different values of the longitudinal mass density stratification. We show that, in inclined and asymmetric loops, the frequencies and their corresponding damping rates of the fundamental and first-overtone modes of kink oscillations are smaller in comparison with semi-circular uninclined loops with the same lengths. The results also indicate that, the period ratio P1/P2, increases with increasing the inclination of the loop, but it decreases less than 2 per cent while imposing the asymmetry to each loop side, up to 9.66 per cent of the loop length. The ratio of each mode frequency to its corresponding damping rate remain unchanged approximately while the inclination or the asymmetry imposed. Hence, we conclude that these ratios are reliable for inferring the physical parameters of coronal loops and coronal medium, regardless of the loop shape or the state of its inclination. In addition, in contrast with the effect of asymmetry, which is not significant on the period ratio P1/P2, when an observed oscillating loop has a smaller apex height, the state of its inclination is an important factor that should be considered, especially when the period ratio P1/P2, is taken into consideration for coronal seismology.

مرکز نجوم و اختر فیزیک مراغه - زانیار ابراهیمی

تماس الکترونیکی

درباره

سوابق تحصیلی

سوابق تدریس

زمینه های پژوهشی

خلاصه مقالات

کتاب ها

راهنمایی و مشاوره پایان نامه

تشویق ها

عضویت در مجامع علمی و انجمن ها

مقالات ارائه شده

عنوان مقاله : اثر اختلاط فازي روي ميرايي بسته موج آلفن ايستاده برشي

مقالات چاپ شده در مجلات

عنوان مقاله : Phase-Mixing and Dissipation of Standing Shear Alfvén Waves

عنوان مقاله : Resonant absorption of kink magnetohydrodynamic waves by a magnetic twist in coronal loops

عنوان مقاله : The Effect of a Twisted Magnetic Field on the Phase Mixing of the Kink Magnetohydrodynamic Waves in Coronal Loops

عنوان مقاله : Resonant absorption of kink oscillations in coronal flux tubes with continuous magnetic twist

عنوان مقاله : Phase Mixing of Kink MHD Waves in the Solar Corona: Viscous Dissipation and Heating

عنوان مقاله : Resonantly damped oscillations of elliptically shaped stratified emerging coronal loops

عنوان مقاله : The nature of kink MHD waves in the solar corona: magnetic twist and phase mixing

عنوان مقاله : Resonant absorption of kink MHD waves in inclined and asymmetric coronal loops

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