Long-term variation in the upper atmosphere as seen in the geomagnetic solar quiet daily variation

Abstract

Characteristics of long-term variation in the amplitude of solar quiet (Sq) geomagnetic field daily variation have been investigated using 1-h geomagnetic field data obtained from 69 geomagnetic observation stations within the period of 1947 to 2013. The Sq amplitude observed at these geomagnetic stations showed a clear dependence on the 10-to 12-year solar activity cycle and tended to be enhanced during each solar maximum phase. The Sq amplitude was the smallest around the minimum of solar cycle 23/24 in 2008 to 2009. The relationship between the solar F10.7 index and Sq amplitude was approximately linear but about 53% of geomagnetic stations showed a weak nonlinear relation to the solar F10.7 index. In order to remove the effect of solar activity seen in the long-term variation of the Sq amplitude, we calculated a linear or second-order fitting curve between the solar F10.7 index and Sq amplitude during 1947 to 2013 and examined the residual Sq amplitude, which is defined as the deviation from the fitting curve. As a result, the majority of trends in the residual Sq amplitude that passed through a trend test showed negative values over a wide region. This tendency was relatively strong in Europe, India, the eastern part of Canada, and New Zealand. The relationship between the magnetic field intensity at 100-km altitude and residual Sq amplitude showed an anti-correlation for about 71% of the geomagnetic stations. Furthermore, the residual Sq amplitude at the equatorial station (Addis Ababa) was anti-correlated with the absolute value of the magnetic field inclination. This implies movement of the equatorial electrojet due to the secular variation of the ambient magnetic field.

Change in turbopause altitude at 52 and 70° N

“…At first, there would appear to be a fundamental difference between the findings derived from [O] at a midlatitude station and those for ε from a high-latitude station, and indeed the paradox could be explained by either the respective methods and/or geographic locations. Usefully, in this context, Shinbori et al (2014) and Kozubek et al (2015) investigate such geographical diversity. However if one examines the period from 2002 onwards (corresponding to the high-latitude data set, but only about one-quarter of that from the mid-latitude station), a decrease in [O] corresponds with an increase in h turb .…”

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

“…In contrast to these results, Jarvis (2005) found a longterm decrease in the diurnal and semidiurnal spectral power at Lerwick (61.1°N, 358.8°E), Niemegk (52.1°N, 12.7°E), and Tucson (32.2°N, 249.3°E) after removal of solar activity and geomagnetic activity effects. Shinbori et al (2014) also found negative trends in the residual Sq amplitude (∼ 10 −4 nT per day) at many stations worldwide. Both Jarvis (2005) and Shinbori et al (2014) used the H -component geomagnetic field, the same as Elias et al (2010) and de Haro Barbas et al (2013).…”

“…Shinbori et al (2014) also found negative trends in the residual Sq amplitude (∼ 10 −4 nT per day) at many stations worldwide. Both Jarvis (2005) and Shinbori et al (2014) used the H -component geomagnetic field, the same as Elias et al (2010) and de Haro Barbas et al (2013). The discrepancies in the long-term trend reported by different authors are probably due to different approaches used in parameterizing solar activity effects.…”

Identification of the different magnetic field contributions during a geomagnetic storm in magnetospheric and ground observations

“…The pattern of the two current vortices in the sunlit hemisphere consists of currents circulating about foci at +30 and −30 • magnetic latitude. Viewed from the Sun, circulation is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere (Richmond et al, 1976;Takeda, 2002;Hawary et al, 2012;Yamazi and Yumoto, 2004;Shinbori et al, 2014). Applying the EMD procedure we found a set of 13 modes and 11 modes for the H and D component, respectively (see Fig.…”