In this paper, we analyze the time delay between the occurrence of the minima in the geomagnetic Dst, SYM-H indices and the horizontal magnetic component (H) measured in the Teoloyucan Magnetic Observatory (TEO) of Mexico. This difference was calculated in Universal Time for 15 geomagnetic storms (Dst≤-100nT) occurred during the descending phase of solar cycle 23. We found that, when the TEO was at the dayside, dawn and dusk, the time difference was negative, indicating that the minimum appeared first in the Dst, SYM-H reported by Kyoto, and afterwards in the H reported by TEO. On the other hand, when the TEO was close to midnight the difference was positive, indicating that the minimum occurred first at TEO and afterwards in Dst. We noticed that 14 out of 15 geomagnetic storms followed this behavior, except the most intense one of the sample. For the rest of the storms, it seems that the cause of the delay is not the intensity of the magnetic field at minimum but the intensity of the current systems present during the storm occurrences.
The incidence of geomagnetic storms may be associated with changes in circulatory physiology. The way in which the natural variations of the geomagnetic field due to solar activity affects the blood pressure are poorly understood and require further study in controlled experimental designs in animal models. In the present study, we tested whether the systolic arterial pressure (AP) in adult rats is affected by simulated magnetic fields resembling the natural changes of a geomagnetic storm. We exposed adult rats to a linear magnetic profile that simulates the average changes associated to some well-known geomagnetic storm phases: the sudden commencement and principal phase. Magnetic stimulus was provided by a coil inductor and regulated by a microcontroller. The experiments were conducted in the electromagnetically isolated environment of a semi-anechoic chamber. After exposure, AP was determined with a non-invasive method through the pulse on the rat's tail. Animals were used as their own control. Our results indicate that there was no statistically significant effect in AP when the artificial profile was applied, neither in the sudden commencement nor in the principal phases. However, during the experimental period, a natural geomagnetic storm occurred, and we did observe statistically significant AP increase during the sudden commencement phase. Furthermore, when this storm phase was artificially replicated with a non-linear profile, we noticed a 7 to 9 % increase of the rats' AP in relation to a reference value. We suggested that the changes in the geomagnetic field associated with a geomagnetic storm in its first day could produce a measurable and reproducible physiological response in AP.
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