Statistical investigation of magnetosphere-ionosphere-ground interaction over mid-latitudes during geomagnetic storms

Abstract

The phrase "space weather" is used to describe the conditions in space, more specifically in the solar system. Space weather is concentrated on the Sun since it is the solar system's primary energy source. The Sun's highly dynamic structure results in energy bursts that can take on a variety of shapes, including sudden energy bursts known as solar flares, bursts of plasma and magnetic field known as coronal mass ejections, and in some cases, an increase in the speed and density of the solar wind due to open magnetic field lines. Severe space weather events are what these phenomena are named since they create extreme changes in the space environment. By producing disruptions in the geomagnetic field and other aspects of the Earth's environment, extreme space weather causes the neutral conditions to shift in a negative way. Extreme space weather has an impact on satellite operations, ionospheric conductivity-based communication, and underground electrical cables. In this study, it is aimed to understand the effects of space weather on ground and ionospheric levels over mid-latitudes. There are various types of research in the literature about these effects, yet there are three points that separate this study from the other works in the literature. The first point is that this study is done for mid-latitudes rather than the more commonly researched over high and even low latitudes. The second point is that both the measurements for ground level and the ionospheric levels are done in Türkiye, so it is a study specifically done for Türkiye. The third point is that effects on both ground and ionosphere are studied together for the same cases which is unusual among the studies in the literature. The ground-level part of this study focuses on a phenomenon known as geomagnetically induced current (GIC). The geomagnetic field's rapid changes create an electric field that penetrates the ground itself. The power grid systems and underground pipes are affected by the electric current flowing at ground level. Although high latitude regions are the major danger area for GIC since they experience the most severe consequences there due to magnetic poles, GIC may occur everywhere, and the goal of this study is to look at GICs in the mid-latitude region. The ionosphere, which is the conducting layer of the atmosphere, is crucial to radio wave transmission in the atmosphere and, long-distance communication across the globe and with satellites in space. Particularly with the advancements in satellite technology, understanding the variations in the ionospheric electron density becomes critically important in many of the applications of these technologies, ranging from the military and navigational systems to the cellphones which are one of extremely essential parts of our daily lives. Thus, in this study, it is aimed to understand the variations in the ionospheric electron density during the geomagnetically disturbed days. In this study, three data sets have been used over Marmara Region, Türkiye (GG: ~ 40°N, GM: ~38°N). The first data set is geomagnetic field measurements obtained from Kandilli Geomagnetic Observatory located at Iznik (40°N, 29°E). This is the only geomagnetic observatory in Türkiye and is a member of INTERMAGNET. The 1-min resolution data is available on INTERMAGNET. 1-sec resolution data is obtained from the observatory for this study. 36 geomagnetically disturbed days between 2013 and 2015 have been chosen and those data have been used. The second data set is geomagnetic and geoelectric field measurements which obtained from the LEMI-414 magnetotelluric station located at Bozcaada (39°N, 26°E). The magnetotelluric station was operational between 2013 and 2014. Thus, 10 out of the previously mentioned 36 days were available to analyze. Both the geomagnetic and geoelectric field measurements are 1-sec resolution. The last data set is F-layer electron density measurements which obtained from the Dynasonde located at ITU Campus, Istanbul (41°N, 28°E). The data for the same 36 geomagnetically disturbed days have been used which are all 4-min resolution. Additionally, Disturbance Storm Time (Dst) index, and solar wind data from ACE and WIND spacecrafts have been used. The study consists of two main parts which are case studies and statistical studies. For the case studies, 3 geomagnetically disturbed days have been selected based on Dst from consecutive years, 17 March 2013 which is also known as the 2013 St. Patrick storm, 27 February 2014, and 9 September 2015. Case studies are done thoroughly via time series. The phases of the geomagnetic storms are determined as initial, main, and recovery phases. The variations in different parameters are analyzed. Dst and AE indices are used to determine the strength of the storms. The time derivative of the horizontal geomagnetic field which is considered as a reliable indicator for GIC is the main parameter for the ground-level effect. In the ionospheric part, the main parameter is the F-layer critical electron density difference between the active and quiet day periods. In the ionosphere, geomagnetic storms can have both negative and positive effects on the electron density which means the electron density might increase or decrease during the storm. Thus, while selecting the storms for case studies, this has been considered and both of these examples are shown. In order to be able to see the relationship with the solar plasma, satellite data is used, and the parameters selected are ion density, speed, total and southward interplanetary magnetic field (IMF Bt and Bz), and dynamic pressure. All of these parameters are compared with time series. The only case with electric field measurement is 27 February 2014, and for this case, also the northward and eastward electric field components are analyzed. The statistical part of the study consists of histogram analysis and linear relationships between physically meaningful pairs. It is aimed to understand the general behavior of the geomagnetic field and the ionosphere during geomagnetic storms with histograms. The averages and the possibilities are found for certain thresholds. Linear relationships between the 72 pairs have been determined by using scatter plots and calculating Pearson correlation coefficients. The reliability of the Pearson correlation coefficients is tested with Student's t-test at a 0.05 significance level. The aim of this analysis is to find out the possible dependency between the parameters, and determine what to expect based on the known variations for geomagnetic storms in various strengths. In overall, it is aimed to estimate to what extent the geomagnetic field and ionospheric electron density are affected by solar activity at mid-latitudes, and form a milestone to understand which physical processes are effective at our latitudes. Determining what kind of variations are seen in different phases of a storm gives information about the mechanisms driving the seen effect on the ground or in the ionosphere. As similar, determining which geomagnetic index or solar wind parameter also gives information about the affecting mechanism behind the change. It is believed that this study will give insights for future studies which will be done on the space weather effects over Türkiye.