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Bioelectromagnetism

ap index is a measure of the general level of geomagnetic activity over the globe for a given day. A

mean, 3-hourly “equivalent amplitude” of magnetic activity based on K index data from 11 Northern

and 2 Southern Hemisphere magnetic observatories between the geomagnetic latitudes of 46° and 63°

(Lockwood et al., 2019). ap values are given in units of 2 nT.

Ap index is a daily index determined from eight ap index values. Tat is, the Ap index is defned as

the earliest occurring maximum 24-hour value obtained by computing an eight-point running average

of successive 3-hour ap index values during a magnetic storm event and is uniquely associated with the

storm event. Ap values are given in units of 2 nT.

Even in the absence of magnetic storms, the GMF could be changed on various time scales longer

than decades as described above. Most of the shorter-scale temporal changes of the GMF are estimated

to be due to the efects of the ionosphere and magnetosphere outside the Earth. A British clockmaker,

inventor, and geophysicist, George Graham in 1722 (Graham, 1724a,b) discovered that the diurnal cycle

of GMF is a regular change in the daily cycle. Te diurnal cycle can be clearly seen on days when the

GMF perturbation by the solar wind is small, so it is termed a “geomagnetic quiet day.”

Te cause of diurnal changes on geomagnetic quiet days is the ionosphere at an altitude of 100 km

or more from the Earth’s surface. Te ionosphere is warmed by radiant heat from the Sun during the

daytime, cooled at nighttime, and the wind is generated inside the ionosphere. Ten, the ionized gas is

also carried with the wind. Tis interaction between the motion of the ionized gas and the GMF induces

a large-scale “eddy current” that is counterclockwise in the Northern Hemisphere and clockwise in

the Southern Hemisphere during the daytime when viewed from outside the Earth. Tis eddy current

always appears on the side of the Earth-facing the Sun. Te GMF emanating from the Earth’ surface

passes under this eddy current and thereby changes every day. Tis is the generation mechanism of the

diurnal cycle of the GMF.

Gmitrov and Gmitrova (2004) investigated how changes in the GMF afect cardiovascular regulation

under laboratory conditions. Barorefex sensitivity estimated from BP and HR responses to intravenous

injection of phenylephrine and nitroprusside, showed signifcant negative correlations between increas­

ing the geomagnetic disturbance and barorefex sensitivity, heart rate variability (HRV), and arterial

BP (Gmitrov and Gmitrova, 2004). Tese fndings support the theory that geomagnetic disturbances

afect neurocardiovascular regulatory centers (Gmitrov and Gmitrova, 2004). Gmitrov (2005) further

reported that the geomagnetic disturbance worsens microcirculation impairing arterial barorefex vas­

cular regulatory mechanism. Te reduced barorefex sensitivity may increase mortality afer myocardial

infarction (Garcia et al., 2014). Gmitrov (2005) recommends on days with intense geomagnetic activity,

and especially during geomagnetic storms, to intensify the therapy of ischemic cerebral and heart dis­

ease to improve microcirculation in brain tissue and in the myocardium to decrease the risk of cerebral

strokes and myocardial infarctions.

Human studies have shown that changes in time-varying MFs above 80 nT over a 3-hour period

signifcantly reduce melatonin levels in the body (Weydahl et al., 2001). In addition, a greater reduction

of excretion in a melatonin metabolite 6-OHMS was observed when increased geomagnetic activity

was combined with an elevated 60 Hz MF or reduced ambient light exposures (Burch et al., 1999, 2008).

As for a plausible mechanism of the decrease of melatonin by time-varying MFs, a possible change in

the spatial structure of the photoreceptor pigment rhodopsin due to the EF (eddy current) induced

by the time-varying MF has been proposed and MFs might also change either the electric activity of

the pinealocytes or their ability to produce melatonin or both (Selmaoui and Touitou, 1995; Touitou

et al., 2010). Tese reduced levels of melatonin, along with other individual factors, may be involved

in the development of myocardial ischemia due to the GMF changes (Raygan et al., 2019). Rapid or

sudden fuctuations in geomagnetic and solar activity, as well as magnetic storms, appear to be able to

act as stressors to alter regulatory processes such as melatonin/serotonin balance (Bergiannaki et al.,

1996; Rapoport et al., 1997; Burch et al., 1999), BP, respiratory, reproductive, immune, neurological, and

cardiac processes (Ghione et al., 1998; Chernouss, 2001; Cherry, 2002). Geomagnetic disturbances are

associated with signifcant increases in depression, psychiatric disorders, psychiatric hospitalizations,