Department of Physics
Permanent URI for this collectionhttps://repository.mu.edu.et/handle/123456789/106
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Item EFFECT OF THE ENSO PHASES ON RAINFALL VARIABILITY OVER THE NORTHERN HIGHLANDS OF ETHIOPIA(Mekelle University, 2025-06-21) SETEGN WALELIGNThis study investigates the effects of the El Niño-Southern Oscillation (ENSO) phases on rainfall variability over the Northern Highlands of Ethiopia, focusing on four key stations—Debre Birhan, Kombolcha, Woldia, and Lalibela—from 2011 to 2020. Utilizing descriptive statistics, Mann-Kendall trend tests, Sen’s slope estimator, and correlation analyses, the research evaluates seasonal (Belg, Kiremt, and Bega) and monthly rainfall patterns in relation to ENSO events. The results reveal significant regional variability in rainfall responses to ENSO phases. During El Niño years, Belg rainfall decreases notably in Woldia (-31.3%) but increases in Lalibela (+40.4%), while Kiremt rainfall declines in Debre Birhan (-8.1%). Conversely, La Niña years enhance Belg rainfall across all stations, with Woldia experiencing a 32.7% increase. Time series analysis indicates upward rainfall trends in Debre Birhan (+8.6 mm/year) and Lalibela (+10.5 mm/year), linked to intensified Kiremt rains, whereas Woldia faces declining Belg rainfall (-14.2 mm/year), threatening earlyseason agriculture. The study underscores ENSO’s critical role in modulating rainfall variability, with implications for agriculture and water resource management. Positive trends in Lalibela and Debre Birhan suggest opportunities for improved crop yields, while Woldia’s rainfall decline highlights vulnerabilities requiring adaptive strategies such as drought-resistant crops. These findings advocate for localized climate adaptation policies to mitigate ENSO-induced risks and leverage favorable rainfall patterns in Ethiopia’s highlands.Item RADIO-LOUD CME-CME POTENTIAL INTERACTIONS IN SOLAR CYCLE 24 IN THE YEARS 2009-2018(Mekelle University, 2024-12-28) Mebrahtu Gebremedhin TekaRadio loud (RL) CMEs are those associated with solar type II radio bursts. These CMEs might interact with each other on their way from the solar surface to the interplanetary medium. As a result ,these CMEs leave a radio signature on the dynamic spectrum and bright white enhancement on the white-light images. In this research ,we have found a total set of 32 possible interacting CMEs and 16 associated DH type II bursts are registered on the NASA SOHO/LASCO CDAW catalogue for the period spanning from 2009 to 2018. However , only the DH component of the radio bursts were considered. This possibility of interaction was estimated by a thorough investigation of the origins of the CMEs and the simultaneity of enhancement on the CMEs difference images on the LASCO field of view and the intensification of the burst on the dynamic spectrum of the Wind/WAVES. A primary CME is mainly emitter of the DH burst and the preceding interacts with it. By tracking the whitelight images of these CMEs ,the height-time diagrams are obtained. Our results show that most of the primary CMEs are halo and averagely much faster (1482.3 kms-1) than the preceding CMEs (841.6 kms-1). More over ,drift rate of DH type IIs ,time duration of pre and pri-CMEs and interaction height are found to be 1.82 MHzs-1 , ∼34.6 min and ∼5.3 Ro ,respectively. The pre-CMEs are found to be less energetic than the primary CMEs. Most of the interacting CMEs were originating from the western regions of the Sun. Studying the properties of interacting RL CMEs and their kinematics are important to be able to make predications before a CME arrival and make proper arrangements both on the ground and in space.Item COMPARISON OF RADIO-QUIET AND RADIO-LOUD FAST-WIDE CORONAL MASS EJECTIONS IN SOLAR CYCLE 24(Mekelle University, 2025-06-21) Haylay Gebrehiwet AssefaCMEs are complex phenomena associated with solar activity. RQ CMEs lack type II radio bursts in the metric and DH wave lengths,whereas,RL CMEs are associated with metric or DH type II bursts.This thesis focuses on comparing the properties of radio-quiet (RQ) and radio-loud (RL) FW Coronal Mass Ejections (CMEs) during Solar Cycle 24 (2008-2019 ),Using data from multi-instrument and multi-spacecraft sources such as Solar Heliospheric Observatory (SOHO), Solar Terrestrial Relations Observatory (STEREO), and Wind spacecraft. The study begins with a 115 Fast Wide (FW) CMEs, characterized by speeds (V ≥900 km/s) and angular width (W ≥ 600 ), observed during Solar Cycle 24. By utilizing data from LASCO/SOHO, SECCHI/STEREO, and wind/WAVES instruments, we identified 58 RQ CMEs and 57 RL CMEs.The RL CMEs had an average speed of (1415 km/s) compared to (1145 km/s) RQ CMEs.Moreover, RL CMEs also have more acceleration (+34 m/s2) than RQ( +19 m/s2) CMEs. The average width of the RL (3310),CMEs is much larger than the average width of RQ (2000) CMEs. We also found that 38% of RQ CMEs and 28% of RL CMEs come from the NW quadrant, while 19% of RQ CMEs and 30% of RL CMEs come from the NE quadrant.The fraction of full halo CMEs(82.5% ) was largest for the RL CMEs,but smaller for RQ(21%) CMEs. RL CMEs are associated with stronger flares (80% X and M class), whereas RQ CMEs are linked to weaker flares (65% C class and 32.5% M class). RL CMEs are more energetic than RQ CMEs.Item Silicon Doped Intermediate Band Solar Cell as a Solution for Upgrading the Efficiency of Solar Cell(Mekelle University, 2025-06-21) Tefera Ayalew AsfawThe development of intermediate band solar cell is aimed in enhancing photocurrent and preserve the output voltage due to the surge of sensitivity to solar spectrum. Sensitivity to solar spectrum increased due to two-step absorption that allows to absorption of photons having energy less than band gap energy. In this work device fabrication process and analysis of the recorded data for the doping five layer of InAs QDs in GaAs p-i-n solar cell structures is presented by aiming to enhance light absorption capability, to improve charge carrier transport and a highly efficient solar cell by growing the thin film using molecular beam epitaxy (MBE). Intermediate band solar cells (IBSCs) increase solar power conversation efficiency exceeding Shockley-Queisser, which is the maximum efficiency attainable by conventional single-junction solar cells. This can happen utilizing an intermediate band (IB) within the bandgap of the semiconductor material, allowing for the absorption of two sub-bandgap photons (with energies less than the bandgap) to excite an electron to the conduction band. And this cause for an increase of current density, and provide non-reduced output voltage, consequently efficiency of the solar cell increase. Intermediate band within the band gap of a semiconductor with Si- doping, the current density JSC decreases from 31.84 mAcm-2 for the doping level 1011cm-2 and significant increase with optimized Si-doping for the doping level 5x1011 cm-2 to 32.75 mAcm-2. Si dopants can substitute both Ga and As sites forming point defect and this attributed for the change of values of JSC and VOC, This change because of photons with energies lower than the conventional bandgap can still generate charge carriers. In general, intermediate band improve charge carriers transport by providing a path way and generating more charge carriers; doping quantum dots, or introducing impurities, can significantly improve solar energy conversion efficiency. Doping of SC modify the electronic properties of quantum dots, enhance charge separation, suppress recombination losses, and improve charge transport, ultimately leading to higher power output.Item UNDERSTANDING GEOMAGNETIC STORM IN RELATION TO THE SUNSPOT NUMBER DURING SOLAR CYCLE 24 AND 25(Mekelle University, 1994-12-28) Tesfaye AyalewGeomagnetic storms, caused by disturbances in Earth’s magnetosphere due to solar activity, are significant drivers of space weather and have profound effects on technological systems and infrastructure. This study investigates the relationship between geomagnetic storms and sunspot numbers, a primary indicator of solar activity, during solar cycles 24 and 25. Solar cycle 24, marked by historically low sunspot numbers and subdued solar activity, contrasts with solar cycle 25, which is projected to exhibit increased solar intensity. The research employs a multi-faceted approach, analyzing data from solar wind parameters, interplanetary magnetic fields, and geomagnetic indices such as Dst and Kp. Through statistical analysis and correlation studies, it examines the influence of sunspot number variations on the frequency, intensity, and duration of geomagnetic storms. Additionally, the study explores the distinct characteristics of geomagnetic activity during these two solar cycles, identifying key patterns and trends. By establishing a clearer understanding of the connection between sunspot numbers and geomagnetic storms, this research contributes to the development of more accurate predictive models for space weather events. These findings hold significant implications for improving preparedness and mitigation strategies to safeguard satellite operations, communication systems, and power grid stability against space weather impacts.Item UNDERSTANDING THE CHARACTERISTICS OF IONOSPHERIC DISTURBANCES DUE TO GEOMAGNETIC STORM OF MOTHERS DAY 2024(Mekelle University, 2025-01-21) Seid EshetuWe studied ionospheric responses due to geomagnetic storms of mothers day 2024,on global scale to find the sources that triggered the ionospheric variations. In particular, we analyze the total electron content(TEC), averaged electric field (Ey) , solar wind velocity Vsw, Plasma Density (ρ),Plasma temperature (T),interplanetary magnetic field along z-axis (IMF- Bz), geomagnetic disturbance storm time index (Dst), and solar flux F10.7 index. A geomagnetic storm is a major disturbance of Earth’s magnetosphere that occurs when there exists an exchange of energy from the solar wind into the space environment surrounding Earth. The largest storms that result from these conditions are associated with coronal mass ejections (CMEs). The effects of all these all have an outcome of Magetospheric compression. That is , the sudden increase in solar wind speed and southward IMF Bz compressed the ionosphere, reducing the standoff distance of the magneto-pause. Magnetic reconnection allowed solar wind energy transfer efficiently into the magnetosphere, driving geomagnetic currents and accelerating charged particles. The sharp drop in Dst reflects a strengthened ring current, which forms as energetic particles circulate around earth. Enhanced electric currents flowing through the ionosphere caused joule heating, leading to the thermal expansion of the upper atmosphere. This can alter ionospheric density and composition, affecting satellite drag and radio wave propagation. Secondly, at mid latitudes, ionospheric storm Enhanced Densities (SEDs) are likely to have formed due to electric field -driven plasma transport from lower to higher latitudes. Thirdly, Southward IMF conditions and enhanced electric fields can generate ionospheric irregularities, such as plasma bubbles, which degrade GNSS navigation signals and radio communications. Lastly but not the least, increased particle precipitation due to magnetospheric disturbances enhanced auroral emissions in polar auroral regions, indicating energy deposition from the magnetosphere into the ionosphere.Item COMPARATIVE STEADY OF EARTH’S MAGNETIC FIELD VARIABILITY, SQ-CURRENTS AND EQUATORIAL ELECTROJET OVER INDIAN, AFRICAN AND AMERICAN SECTORS(Mekelle University, 2024-12-28) Bogale FentayeThe earth’s magnetic field during day and night is not the same due to different factors. The sun’s radiation is one of the parameters to influence the variability of the earth’s magnetic field in different sectors. The variation of magnetic field in turn produces huge variation in ionospheric currets such as the Sq- current, Equatorial Electrojet (EEJ), counter electrojets (CEJ). Equatorial electrojet (EEJ) is enhanced current flowing from west to east during day time at dip equator between ±30 latitude at an altitude of about 107 Km. This high concentration of electric current flowing from west to east in a narrow belt flanking the dip equator on the sunward hemisphere has been termed the equatorial electro jet. Our objective is to study , variation of the earth’s magnetic field strength, Sq- current, EEJ and CEJ for African sector and American sector and the Indian sector. The magnetic field strength in the Indian sector is relatively stronger as the geomagnetic equator passes close to southern India, influencing EEJ intensity and variability. While in the African sector, the geomagnetic field is weaker compared to the Indian sector, resulting in higher ionospheric conductivity and often stronger EEJ current, When we come to the American sector the Geomagnetic field is relatively weakest but features a more significant magnetic declination (the angle between geographic and geomagnetic north), particularly in the south America. The declination impacts the electrodynamics, introducing additional east-west variability.Item RUNAWAY CANDIDATE STARS OF THE LARGE MAGELLANIC CLOUD FROM GAIA EDR3 PROPER MOTION(Mekelle University, 2025-06-21) Abrha Mesfin GebrehaweriaWe investigated the relative proper motions and their corresponding tangential velocities with respect to the field stars and the LMC. A 15 arcminiutes radius area was set around the target stars to identify the field stars of the LMC. A step wise Parallax, CMD, and PM selections were applied to minimize foreground contaminations. Astrometric excess noise information was used to filter the field stars from star like objects such as unresolved binaries. Radial distances and magellanic coordinates were calculated to confirm if our target stars were members of the LMC and whether they escape from the LMC. The relative proper motions of the target stars with respect to their field is found in the range of (0.204 ± 0.662)- (19.3 ± 0.64) masyr-1 with their corresponding relative tangential velocities of (48.5 ±157)- (4569.8±151.3) kms-1. Hence, eight of them are high velocity runaways and the two stars are not runaways. We also calculated the relative proper motions and tangential velocities of our target stars with respect to the LMC and we found proper motions with in the range (0.64 ± 0.13) - (19.77± 0.14) masyr-1 with their corresponding tangential velocities in the range of (150.5±30.30 ) -( (4687.3± 33.68) kms-1. We proposed the ejection scenarios of the target stars and finally concluded that eight of our target stars are runaways of the LMC but two target stars are not runaway.