Secular trends in daily geomagnetic variations

Sellek, R.

doi:10.1016/0021-9169(80)90052-5

Cited by 16 publications

(25 citation statements)

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“…He also showed that the Sq amplitude is almost linearly proportional to the annual mean number of sunspots. Furthermore, Sellek (1980) found significant secular variation in the Sq amplitude due to the secular changes in the Earth's magnetic field. The present study shows that the long-period component of the monthly mean Sq amplitude varies with correspondence to a 10-to 12-year solar activity cycle as seen in the monthly mean solar F10.7 index shown in Figures 2 and 4.…”

Section: Elements To Determine the Sq Amplitudementioning

confidence: 91%

“…Extremely low Sq amplitude during the minimum of solar cycle 23/24 Sellek (1980) reported that the annual mean Sq amplitude observed at three equatorial to low-latitude stations (Huancayo, Hermanus, and San Juan) varies with strong dependence on an 11-year solar activity cycle, and in that study, the sunspot numbers were used as a good indicator of solar activity. He also showed that the Sq amplitude is almost linearly proportional to the annual mean number of sunspots.…”

Section: Elements To Determine the Sq Amplitudementioning

confidence: 94%

“…Many investigations of the long-term variation in the Sq amplitude have been performed using long-term geomagnetic field data and several related parameters such as sunspot numbers and the solar F10.7 flux since [Sellek 1980;Schlapp et al 1990;Macmillan and Droujinina 2007;Torta et al 2009;Elias et al 2010]. According to such research, it has been found that the Sq amplitude observed in middle-and low-latitude regions changes with dependence on seasons and solar activity in addition to the activities of solar and lunar tides in the ionosphere.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2014

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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.

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Section: Elements To Determine the Sq Amplitudementioning

confidence: 91%

Section: Elements To Determine the Sq Amplitudementioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

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

et al. 2014

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“…Sellek (1980) and Schlapp et al (1990) examined the residual Sq amplitude after subtracting the linear fit of the sunspot number to the Sq amplitude. 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.…”

Section: Long-term Variationmentioning

confidence: 99%

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

2016

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A record of the geomagnetic field on the ground sometimes shows smooth daily variations on the order of a few tens of nano teslas. These daily variations, commonly known as Sq, are caused by electric currents of several μA/m 2 flowing on the sunlit side of the Eregion ionosphere at about 90-150 km heights. We review advances in our understanding of the geomagnetic daily variation and its source ionospheric currents during the past 75 years. Observations and existing theories are first outlined as background knowledge for the nonspecialist. Data analysis methods, such as spherical harmonic analysis, are then described in detail. Various aspects of the geomagnetic daily variation are discussed and interpreted using these results. Finally, remaining issues are highlighted to provide possible directions for future work.

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“…[5] The paper by Sellek [1980] was one of the first works dealing with Sq trends. He found significant secular changes in Sq for Huancayo (12.0°S,284.7°E),Hermanus (34.4°S,19.2°E),and San Juan (18.1°N,293.8°E) that appear to result from changes in the Earth's main magnetic field, and in the case of Huancayo, the trend is also related to movements of the equatorial electrojet.…”

Section: Introductionmentioning

confidence: 99%

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

2010

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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.

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Secular trends in daily geomagnetic variations

Cited by 16 publications

References 1 publication

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

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

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

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

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