Long‐term changes in solar quiet (Sq) geomagnetic variations related to Earth's magnetic field secular variation

Abstract

The daily amplitude of the solar quiet (Sq) magnetic variation of the horizontal intensity, H, of observatories at low and midlatitudes is analyzed, in search of significant long‐term trends. These trends are expected based on secular variations of the Earth's magnetic field (B) and increasing concentrations of greenhouse gases which can affect Sq for instance through their effect on ionospheric conductivities and E‐region electron concentration. The hourly horizontal geomagnetic field component, H, measured at Apia, Fredericksburg, Hermanus, Bangui, and Trivandrum was analyzed for the period 1960–2000. The solar activity effect was filtered out from the daily Sq amplitude of H, and then linear trends were calculated and compared to trend values obtained from the Coupled Magnetosphere‐Ionosphere‐Thermosphere model. Linear trends were calculated separately for periods of different secular trends in the magnetic field intensity, B. We found significant trends in experimental data for Apia, Fredericksburg, Hermanus, and for the period 1960–1983 for Bangui. There is reasonable quantitative agreement between experimental and simulated trends, and a qualitative agreement with trends expected from the secular trend in B.

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

“…However, the observed long-term trends in the residual Sq amplitudes were greater than those expected from the conductivity changes; thus, other contributions such as CO 2 might also play a role. de Haro Barbas et al (2013) compared these trends with the results obtained from the CMIT model, confirming the role of the secular variation of the geomagnetic field in the long-term changes in Sq. 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). The discrepancies in the long-term trend reported by different authors are probably due to different approaches used in parameterizing solar activity effects.…”

The importance of geomagnetic field changes versus rising CO2levels for long-term change in the upper atmosphere

“…Recent comparisons of observed trends with the simulations carried out by Cnossen & Richmond (2013) indicate that magnetic field changes could be responsible for most of the trends in Sq amplitude at three out of five of the stations that were investigated (De Haro Barbas et al 2013), while they could only explain about 8% of the observed trend in ion temperature at Millstone Hill (Zhang & Holt 2013). It still remains unclear whether the increase in CO 2 concentration could be responsible for the remainder, although this seems unlikely based on the results shown here.…”

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

“…In the present study, such long-term variation of the Sq amplitude could not be detected near the South Atlantic anomaly region because of the small number of geomagnetic stations distributed in this region. De Haro Barbas et al (2013) also showed that small negative variation of the Sq amplitude can be seen in Europe, India, the eastern part of America, and the southern part of China. The value of the negative Sq trend was ranged from −0.1 to 0.0 nT/year.…”

“…They explained more than 50% of their trend values with the secular variation in the ambient magnetic field and less than 10% with the increase in greenhouse gases. Recently, De Haro Barbas et al (2013) performed a comparison between the observed and simulated trends in the Sq amplitude at six geomagnetic stations during 1960 to 2000 using Coupled MagnetosphereIonosphere-Thermosphere (CMIT) simulations. They found that the trends in the observed Sq amplitude are in good agreement with the trends expected from the secular variation in the Earth's main magnetic field.…”