Fasil Tesema

University of Bergen | UiB · Department of Physics and Technology

Plain Language Summary The Earth's magnetosphere is a dynamic region shaped by the interplay between the solar wind and Earth's magnetic field. This interaction occurs at the boundary of the magnetosphere (magnetopause) through a process known as magnetic reconnection, giving rise to Flux Transfer Events (FTEs), which are magnetic structures that c...

Magnetosheath jets are plasma structures that are characterised by enhanced dynamic pressure and/or plasma velocity. In this study, we investigate the formation of magnetosheath jets in four two-dimensional simulation runs of the global magnetospheric hybrid-Vlasov model Vlasiator. We focus on jets whose origins were not clearly determined in a pre...

Flux transfer events (FTEs) are transient magnetic flux ropes at Earth’s dayside magnetopause formed due to magnetic reconnection. As they move across the magnetopause surface, they can generate disturbances in the ultra-low frequency (ULF) range, which then propagate into the magnetosphere. This study provides evidence of ULF waves in the Pc2 wave...

Magnetic reconnection is a crucially important process for energy conversion in plasma physics, the substorm cycle of Earth's magnetosphere and solar flares being prime examples. While 2D models have been widely applied to study reconnection, investigating reconnection in 3D is still in many aspects an open problem. Finding sites of magnetic reconn...

Plain Language Summary We perform state‐of‐the‐art simulations of the interaction of near‐Earth space environment with the incoming material ejected from the Sun. The response of Earth's magnetic field to such ejecta is known as a “geomagnetic storm.” Our simulation approach captures the motion of protons more accurately than commonly used fluid mo...

The precipitation of charged particles from the magnetosphere into the ionosphere is one of the crucial coupling mechanisms between these two regions of geospace and is associated with multiple space weather effects, such as global navigation satellite system signal disruption and geomagnetically induced currents at ground level. While precipitatin...

Magnetosheath jets are plasma structures that are characterised by enhanced dynamics pressure and/or plasma velocity. A jet generation mechanism that has been widely discussed in observational and numerical studies is steepened Ultra Low Frequency (ULF) waves interacting with the bow shock. However, other formation mechanisms have also been propose...

We present methods and algorithms that allow the Vlasiator code to run global, three-dimensional hybrid-Vlasov simulations of Earth's entire magnetosphere. The key ingredients that make Vlasov simulations at magnetospheric scales possible are the sparse velocity space implementation and spatial adaptive mesh refinement. We outline the algorithmic i...

The precipitation of charged particles from the magnetosphere into the ionosphere is one of the crucial coupling mechanisms between these two regions of geospace and is associated with multiple space weather effects, such as global navigation satellite system signal disruption and geomagnetically induced currents at ground level. While precipitatin...

Numerical simulation models that are used to investigate the near-Earth space plasma environment require sophisticated methods and algorithms as well as high computational power. Vlasiator 5.0 is a hybrid-Vlasov plasma simulation code that is able to perform 6D (3D in ordinary space and 3D in velocity space) simulations using adaptive mesh refineme...

Ultra-low frequency (ULF) waves in the Pc3 range, with periods between 10–45 s, are routinely observed in Earth’s dayside magnetosphere. They are thought to originate in the foreshock, which extends upstream of the quasi-parallel bow shock and is populated with shock-reflected particles. The foreshock is permeated with ULF waves generated by ion be...

Ultra-low frequency (ULF) waves are routinely observed in Earth’s dayside magnetosphere. Here we investigate the influence of externally-driven density variations in the near-Earth space in the ULF regime using global 2D simulations performed with the hybrid-Vlasov model Vlasiator. With the new time-varying boundary setup, we introduce a monochroma...

Numerical simulation models that are used to investigate the near-Earth space plasma environment require sophisticated methods and algorithms together with high computational power. Vlasiator is a hybrid-Vlasov plasma simulation code that, as of recent technological developments, has been able to perform 6D (3D in ordinary space and 3D in velocity...

Characteristics of pulsating aurora (PsA) at the equatorward part of the auroral oval have been well described in the literature by previous studies. We extend our knowledge on high-latitude PsA observations by analysing 68 PsA events from the optical observatory on Svalbard, at 75° magnetic latitude. We found that the pulsating emission structures...

Energetic particle precipitation associated with pulsating aurora (PsA) can reach down to lower mesospheric altitudes and deplete ozone. It is well documented that pulsating aurora is a common phenomenon during substorm recovery phases. This indicates that using magnetic indices to model the chemistry induced by PsA electrons could underestimate th...

Pulsating aurorae (PsAs) are low-intensity diffuse type aurora, which switches on and off with a quasi-periodic oscillation period from a few seconds to ∼ 10 seconds. They are predominantly observed after midnight magnetic local time, during the recovery phase of substorms, and at the equatorward boundary of the auroral oval. Pulsating aurorae are...

Energetic particle precipitation associated with pulsating aurora (PsA) can reach down to lower mesospheric altitude and deplete ozone. It is well documented that pulsating aurora is a common phenomenon during substorm recovery phases. This indicates that using magnetic indices to model the chemistry induced by PsA electrons could underestimate the...

A total of 10 radars from the Super Dual Auroral Radar Network (SuperDARN) in Antarctica were used to estimate the spatial area over which energetic electron precipitation (EEP) impacts the D-region ionosphere during pulsating aurora (PsA) events. We use an all-sky camera (ASC) located at Syowa Station to confirm the presence of optical PsAs, and t...

A set of 24 isolated, 46 compound, and 36 multi-night substorm events from the years 2008–2013 have been analysed in this study. Isolated substorm events are defined as single expansion–recovery phase pairs, compound substorms consist of multiple phase pairs, and multi-night substorm events refer to recurring substorm activity on consecutive nights...

A set of 24 isolated, 46 compound and 36 multi-night substorm events from the years 2008–2013 have been analysed in this study. Isolated substorm events are defined as single expansion-recovery phase pairs, compound substorms consist of multiple phase pairs, and multi-night substorm events refer to recurring substorm activity on consecutive nights....

Ten radars from the Super Dual Auroral Radar Network (SuperDARN) in Antarctica were used to estimate the spatial area over which energetic electron precipitation (EEP) impacts the D-region ionosphere during pulsating aurora (PsA) events. We use an all-sky camera located at Syowa Station to confirm the presence of optical PsA, and then use the Super...

Pulsating aurora (PsA) is a diffuse type of aurora with different structures switching on and off with a period of few seconds. It is often associated with energetic electron precipitation (>10 keV) resulted in the interaction between mag-netospheric electrons and electromagnetic waves in the magnetosphere. Recent studies categorize pulsating auror...

Pulsating auroras (PsAs) are low‐intensity diffuse aurora, which switch on and off with a quasiperiodic oscillation period from a few seconds to ∼10 s. They are predominantly observed after magnetic midnight, during the recovery phase of substorms and at the equatorward boundary of the auroral oval. PsAs are caused by precipitating energetic electr...

Two winters of nightglow intensity observations of the atomic oxygen 630-nm redline emission at Bahir Dar (11.60N,37.40E) were collected from measurements between November 2015 and March 2017 by the selection of 89 nights of quality data. The solar activity trend during the 2015-2017 period was decreasing with the solar flux activity varying within...

Monthly variations of averaged nighttime thermospheric winds have been investigated over Abuja, Nigeria (Geographic: 9.06°N, 7.5°E; Geomagnetic: 1.60°S). The reports are based on Fabry-Perot interferometer measurements of Doppler shifts and Doppler broadening of the 630.0 nm spectral emission. The results were obtained during a period of weak solar...

Fabry–Perot interferometer (FPI) measurements of thermospheric temperatures and winds show the detection and successful determination of the latitudinal distribution of the midnight temperature maximum (MTM) in the continental mid-eastern United States. These results were obtained through the operation of the five FPI observatories in the North Ame...

Theoretical simulations have shown that gravity wave (GW) seeded perturbations amplified by Rayleigh-Taylor Instability (RTI) results in ESF (equatorial spread F); however, there have been limited observational studies using simultaneous observations of GW and ionospheric parameters. In this paper, for the fist time, simultaneous atmospheric temper...

Measurements of equatorial thermospheric winds, temperatures, and 630 nm relative intensities were obtained using an imaging Fabry–Perot interferometer (FPI), which was recently deployed at Bahir Dar University in Ethiopia (11.6° N, 37.4° E, 3.7° N magnetic). The results obtained in this study cover 6 months (53 nights of useable data) between Nove...

Recently some works have been done to investigate the characteristics of wavelike oscillation from the ionospheric total electron content (TEC) fluctuations without considering components of fluctuation that can be embedded together. Decomposing wavelike oscillations from TEC fluctuations and investigating their characteristics is very important si...

The response of the ionosphere to intense magnetic storms has been studied using total electron content (TEC). TEC data recorded by a series of GPS receivers at a longitude 35°E covering a wide range of latitudes (32°S to 68°N, geographic) is analyzed to study spatio-temporal modifications of the vertical TEC (vTEC) during storms on 07 and 09 March...

Plasma density irregularities may result in fluctuations in both amplitude and phase of radio waves propagating through the ionosphere. This phenomenon can be observed by the characteristics of the radio signal coming from orbiting satellites. Typically GPS satellites are used in such purposes. When the trans-ionospheric radio signals from GPS sate...