Geomagnetically induced currents over Iznik associated with geomagnetic storms

Abstract

Geomagnetic storms are major disturbances that occur in the Earth's magnetotail when there is significant amount of mass and momentum transferred into the magnetosphere from the solar wind as a result of magnetic reconnection. They are erratic in nature in that their occurrences cannot be predicted yet reliably. Thus, the studies in order to understand the geomagnetic storm characteristics is crucial in order to understand their behavior. Geomagnetically Induced Currents (GICs) are one of their direct results that one can observe through instruments and measure. GICs are electrical currents flowing from the magnetosphere to the ground along magnetic field lines through the ionosphere. They cause electrical power outages on the ground and cause economic damage. The purpose of this study is to investigate the GICs statistically in detail using the geomagnetic field observations recorded in Iznik magnetic observatory since 2005. Geomagnetic storms are global phenomena and their effects are seen over the globe in various ways starting from the high latitudes towards low latitudes. This study explores the geomagnetic storm effects on the ground magnetic field disturbances which are associated with the GICs. It is the first study in its kind exploring the geomagnetic storm effects over Türkiye located at mid-latitudes. Since the geomagnetic phenomena is global itself, the results obtained here have importance in order to understand their character as well as their effects, especially over the midlatitudes, to better deal with its adverse effects, such as electrical power problems that the companies have to cope with. The GICs are directly related to the changes in the geomagnetic field over time, in other words, the time derivative of the geomagnetic field (dH/dt). Any change in the configuration of the magnetic field is associated with an electrical current through the Faraday Law of Maxwell equations. Taking this as an advantage, it is possible to address the GICs by studying the variations in the ground magnetic fields since the magnetic fields are much easier to measure than measuring the electric fields at a region on the ground as the electric currents on the ground may be caused by various phenomena, artificial and/or natural, and thus require more sophisticated methods to record. This study explores the disturbances in the Iznik ground magnetic field statistically that occur in response to the geomagnetic storms from 2015 to 2023. First, the geomagnetic storm events were determined using the magnetic index Dst and the 68 magnetic storm event were determined. These events were made sure that they either correspond to a sudden commencement (SC) or sudden impulse in the solar wind. Following this, geomagnetic storm phases were determined for each storm event as well as the accompanying solar wind plasma and its magnetic field called as Inteplanetary Magnetic Field (IMF B) was obtained. Since the ultimate deriver of all variations both in the magnetosphere, in the ionosphere and on the ground is the solar wind plasma, the connection to the solar wind was also studied. The characteristics of the GICs, such as the strength, occurrence rate etc. and their dependence on the geomagnetic storm phases, solar wind plasma and IMF were determined. Solar win and IMF data used in this study were obtained from CDAWeb services at GSFC/NASA. It is shown that GICs over Iznik occur more frequently and stronger during the main phase of the geomagnetic storms as associated with the SC resulting from the solar wind compression of the magnetosphere. The magnitudes of GICs varies between 4 to 6 nT/min but GICs reaching to 83 nT/min are also observed. One of the unexpected results of this study is that GICs are found to occur as more frequently during the recovery phase as they occur during the main phase of the storm. While more GICs occur during the initial phase, the occurrence rates of GICs during the main and recovery phases are very close to each other. The analysis solar dependence of GICs were searched using solar wind dynamic pressure, speed, and density, and total IMF and southward component of the magnetic field (negative IMF BZ). Among these the highest correlation was found with the solar wind dynamic pressure. Between speed and density, it was shown that density is more influential compared to the speed as the correlations with speed is found to be much lower. The next solar wind parameter which affects GICs is found to be southward IMF BZ. Southward IMF BZ is responsible for the occurrence of geomagnetic storm and especially the strength of the main phase of the storm. Timely and accurate predictions of space weather phenomena are crucial in order to both understand the physical processes that lead to the space phenomena as well as for the purpose of taking precautions to reduce the economic damage and harm. Following the statistical analysis, the simulations were carried out for the selected three GIC events that involve SC by using Space Weather Modeling Framework (SWMF) and Calculate Magnetic Perturbations on the Ground from magnetosphere and ionosphere electrodynamics (CalcDeltaB) models from NASA's Community Coordinated Modelling Center (CCMC). The model that gives the magnetic field perturbations on the ground is the CalcDeltaB model and thus allows one to compare with the observations. Overall, it was found that the CalcDeltaB model overestimates the magnetic field variations on the ground and thus the GICs based on the relative errors. The level of the peak variations from the model was found to match with those observed, however, the time of the peaks were not correctly predicted. In general, when one compared the magnitude of the variations from the model, it can be seen that the model caught the general trend and magnitudes. However, because of the disagreements on the time of the variations result in high relative error calculations. The model agreed better when the ground disturbances were smaller. The model also provides the contributions from different magnetospheric currents on the occurrence of GICs. Detail examination on the results from the model for different current systems show that the most influential current system is the magnetopause currents (MPC), followed by field aligned currents (FAC), and these are followed by the ionospheric currents. The least effective current system is seen to be ionospheric currents which are ionospheric Hall currents (IHC) and ionospheric Pedersen currents (IPC). Between the two, it was found that IHC contributes more on the ground GICs and gives contribution as high as FACs do. All these differences between the observed and modelled GICs indicate where the model needs to be improved. In addition, it allows us to understand the physical causes of the ground disturbances during the magnetic storms resulting in GICs. This thesis has six chapters. The first chapter, Chapter 1, presents the terminology and gives some background on the space environment that is related GICs and literature survey on the subject. Second chapter (Chapter 2) gives data and methodology while third chapter (Chapter 3) presents the results from the analysis of the ground magnetic field data. The fourth chapter (Chapter 4) presents the correlations with magnetic storm phases, the fifth chapter (Chapter 5) model comparisons and the last chapter, Chapter 6 summarizes and concludes the study.