Trends in the solar quiet geomagnetic field variation linked to the Earth's magnetic field secular variation and increasing concentrations of greenhouse gases

Abstract

Long‐term trends in solar quiet geomagnetic field variation (Sq) are studied in connection to the Earth's magnetic field secular variations and increasing greenhouse gas concentrations. Sq is mainly caused by ionospheric current systems that flow in the E region and depends, among other variables, on the ionospheric conductivities. These conductivities in turn depend on the Earth's main magnetic field (B) and the electron concentration in the E region, for which foE is a measure of its peak value. Since B shows secular variation, induced long‐term changes in Sq might be expected. Another possible mechanism that would be able to induce Sq trends is the increasing concentrations of greenhouse gases that produce a cooling effect in the upper atmosphere and, according to model predictions and experimental results, an increasing trend in foE. To detect if both mechanisms mentioned are able to induce trends in Sq, the Sq variation of the horizontal intensity (H) of three magnetic observatories (Apia, Fredericksburg, and Hermanus), for which B is decreasing, is analyzed for the period 1960–2001. We find significant increasing trends (6.6%, 5.4%, and 9.9%, respectively) which may be partially accounted for by B secular variations in the respective sites. The Sq trend expected from the theoretically predicted foE increase is low (∼0.5%), although positive, as is the observed trend.

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

“…They found significant trends (on the order of 10 −4 nT per day) in the residual data at some stations, but the trends were not always consistent among the stations. Elias et al (2010), using a similar technique, showed significant trends in the residual Sq amplitude at Apia (13.8°N, 171.8°W), Fredericksburg (38.2°N, 77.3°W), and Hermanus (34.4°S, 19.2°E) during 1960Hermanus (34.4°S, 19.2°E) during -2001. The trends in the residual Sq amplitudes were found to be all positive: 2.2 × 10 −4 nT/day, 1.3 × 10 −4 nT/day, and 2.1 × 10 −4 nT/day, respectively.…”

“…The trends in the residual Sq amplitudes were found to be all positive: 2.2 × 10 −4 nT/day, 1.3 × 10 −4 nT/day, and 2.1 × 10 −4 nT/day, respectively. Elias et al (2010) showed that these positive trends can be explained in part as the effect of long-term changes in the ionospheric conductivities. 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.…”

“…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

“…Observational evidence has confirmed many of these predictions, at least in a qualitative sense: the global mean neutral density at fixed heights of 250-400 km has been decreasing (Keating et al 2000;Emmert et al 2004;Emmert & Picone 2011), the ion temperature, which is closely coupled to the neutral temperature, has been decreasing at several stations (Donaldson et al 2010;Zhang et al 2011;Zhang & Holt 2013), and at many stations decreasing trends in the heights of the maximum electron density of the ionospheric E and F 2 layers have been found (Bremer 1992(Bremer , 2008Ulich & Turunen 1997;Jarvis et al 1998;Bremer et al 2012). It has also been suggested that the changes in the ionosphere arising from increased greenhouse gases could be responsible, at least partly, for observed longterm changes in the daily amplitude of magnetic perturbations associated with the solar quiet (Sq) current system flowing in the low-to mid-latitude dayside ionosphere (Torta et al 2009;Elias et al 2010). …”

Geomagnetic field and climate variability. 1. Spatial-temporal distribution of geomagnetic field and climatic parameters during XX century

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