Heliolatitude regularities of magnetically disturbed days with daily average geomagnetic index Dst<–100 nT

Abstract

This paper considers storm days for a period 1966–2015 when the daily average geomagnetic Dst index was <–100 nT. The distribution of the number of days with a high daily average Dst is shown to depend on Earth’s heliolatitude φ: the number of days increases with the absolute value of φ in both solar hemispheres. It is found, as expected, that the seasonal distribution of storm days with Dst<–100 nT has equinoctial maxima. Moreover, there is a noticeable increase in the number of such days in July and November. It is noted that at Earth’s heliolatitudes 4.1°–5.0° there is a sharp increase in the number of storm days. It is established that this increase occurs during storm events in July and November, which stand out against the seasonal distribution of highly disturbed days.