## 1 Introduction  
### Literature Overview  
Every cell of a biological system, embedded within the Sun and Earth's magnetic fields is continuously affected by the fluctuations of these magnetic fields that span over a wide range of frequencies [1]. Numerous studies exploring the connection between magnetic activity and biological systems of various living organisms were performed in recent years. For instance, the authors of [2] presented a biocompass model that may assist in fully uncovering the molecular mechanism of animal magnetoreception. Moreover, an evidence for the link between the natural extremely low frequency (ELF) fields and those found in many living organisms, was presented in [3]. In [4], the impact of weak geomagnetic disturbances on rat's biological systems was investigated and it was concluded that such disturbances affect cardiac and autonomic nervous system (ANS) functions. Similar effects emerge as human physiological systems get exposed to various changes in geomagnetic dynamics. Geomagnetic field line resonances as well as Schumann resonances (SR), occurring in the space between surface of the Earth and the ionosphere, produce a range of resonant frequencies that directly overlap with those of the human brain, ANS and cardiovascular system. Rhythms produced by the brain and heart are affected by the changes in geomagnetic conditions more strongly than the other physiological systems studied so far [5; 6; 7; 8; 9; 10; 11; 12]. Authors of [13] have shown that exposure to SR field induces a stress response process that results in the reduction of creatine kinase release of cardiac cell cultures. It was demonstrated in [14] via the artificial simulation of geomagnetic storm that such geomagnetic activity can cause a significant cardiovascular response. Moreover, results presented in [15] suggest that there is a connection between short-term geomagnetic disturbances and the number of deaths from cardiovascular diseases and myocardial infarction. The study conducted in [16] has shown that magnetic field changes can affect and enhance HRV indices involved in anti-aging or longevity. The study exploring a possible link between sunspots and pandemics related to the hypothesized possibility that microscopic biological entities can penetrate the interplanetary magnetic field barrier and reach the stratosphere during solar minimum was presented in [17]. Numerous research illustrates the influence of geomagnetic and solar activity on various physiological rhythms as well as the possible synchronization between the two [18; 19; 20; 21; 22]. Moreover, recent studies that involved continuous monitoring of heart rate variability (HRV) over longer time periods have revealed a surprising degree of synchronization between ANS activity and the changes in the amplitude of resonant frequencies produced by geomagnetic field-line resonances, Alfven waves (AW) and the SR [23]. These studies also found that the participants exhibited a hitherto unknown slow wave rhythm of approximately 2.5 days in their HRV which was highly synchronized among the study participants and the time-varying magnetic field data [11; 23]. Another relevant study examined changes in HRV in response to changes in geomagnetic, solar and cosmic ray activity over a five-month period. This study confirmed that daily ANS activity responds to changes in geomagnetic and solar activity during periods of normal undisturbed activity and it is initiated at different times after the changes in the various environmental factors and persist over varying time periods [24]. HRV characterizes the change in the time intervals between adjacent pairs of heartbeats and is an important measure reflecting ANS dynamics [25]. Patterns observed in HRV reveal the functional status of codependent regulatory systems that operate over different time scales to adapt to environmental and psychological challenges [26].