Long-term behavior of annual and semi-annual S q variations

Yamazaki, Yosuke; Yumoto, K.

doi:10.5047/eps.2011.01.014

Cited by 13 publications

(9 citation statements)

References 27 publications

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“…These results show that the geomagnetic activity (described by Ap) is strongly linked to the solar cycle phase (solar activity is described by F10.7) and in this study, we were unable to exclude variations in foF2 related to geomagnetic activity. Analyzing geomagnetic data observed at Kakioka (Japan) and Gnangara (Australia) over almost five solar cycles, Yamazaki and Yumoto (2012) recently found that solar activity controls not only the stationary component of the geomagnetic solar quiet daily variation field (S q ) but also the annual and semi-annual components. They report that all three components have a positive linear correlation with sunspot numbers.…”

Section: Resultsmentioning

confidence: 99%

A long-term trend in the F2-layer critical frequency as observed at Alma-Ata ionosonde station

Vodyannikov

Yakovets

Litvinov

2014

Earth, Planets and Space

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In this study, we combine monthly median values for the F2-layer critical frequency (foF2), measured at Alma-Ata ionosonde station [43.25°N, 76.92°E] between 1000 and 1400 (local time), with historical data on the monthly mean values for solar radio flux at 10.7 cm (F10.7) and the geomagnetic activity index (Ap) (available at http://www.swpc. noaa.gov/), over the period from 1957 to 2012. These data are used to derive long-term trends in the upper ionosphere and to discuss their importance in the context of coupling between solar and geomagnetic activity in the ionosphere at middle latitudes.

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Section: Resultsmentioning

confidence: 99%

A long-term trend in the F2-layer critical frequency as observed at Alma-Ata ionosonde station

Vodyannikov

Yakovets

Litvinov

2014

Earth, Planets and Space

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“…The midlatitude S q current intensity during solar maximum is approximately twice as high as that during solar minimum [ Takeda , ]. The amplitude and phase of seasonal S q variations are also modulated by solar activity [ Yamazaki and Yumoto , ; Çelik et al , ]. The solar activity dependence of S q variations is mainly due to enhanced ionospheric conductivities during high solar activity periods, which lead to increased ionospheric currents [ Takeda et al , ].…”

Section: Introductionmentioning

confidence: 99%

Geomagnetic lunar and solar daily variations during the last 100 years

Yamazaki

Kosch

2014

JGR Space Physics

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This paper describes long-term changes in the geomagnetic lunar (L) and solar (S) daily variations. We analyze the eastward component of the geomagnetic field observed at eight midlatitude stations during 1903-2012. The amplitude and phase for the semidiurnal component of the L and S variations are examined. Both L and S amplitudes correlate with the solar activity index F 10.7 , revealing a prominent 11 year solar cycle. In both cases, the correlation is slightly better with √ F 10.7 than F 10.7 . The sensitivity of the L variation to solar activity is comparable with that of the S variation. The solar cycle effect is also found in the phase of the S variation but not apparent in the phase of the L variation. The ratio in the amplitude of the L to S variation shows a long-term decrease (approximately 10% per century), which may be due to a reduction in lunar tidal waves from the lower atmosphere to the upper atmosphere in association with climate change.

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“…These trends were attributed to solar extreme ultraviolet (EUV) radiation changes (Adler et al 1997;Yamazaki and Yumoto 2012), geomagnetic activity variations (Mikhailov and Marin 2001;Danilov 2002;Mikhailov 2001Mikhailov , 2006, the increase in greenhouse gas concentration (Bremer 1992(Bremer , 1998Upadhyay and Mahajan 1998;Ulich and Turunen 1997;Jarvis et al 1998), and/or secular variations of the Earth's main magnetic field (Foppiano et al 1999;Elias and Adler 2006;Elias 2009;Yue et al 2008;Richmond 2008, 2013;Cnossen et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Filtering ionosphere parameters to detect trends linked to anthropogenic effects

Elı́as

2014

Earth Planet Space

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The great concern about the global warming observed in the troposphere has generated a large interest in the study of long-term trends in the ionosphere since the early 1990s, which has now become a significant topic in global change investigations. Some research works link ionosphere trends to anthropogenic sources such as the increase in greenhouse gas concentration, and others to natural causes such as solar and geomagnetic activity long-term changes, and secular variations in the Earth's main magnetic field. In all the cases, in order to analyze ionospheric trends, solar activity effect must be filtered out first since around 90% of ionosphere parameter variance is due to solar variations. The filtering process can generate 'spurious' trends in the filtered data series which may lead to erroneous conclusions. foF2 data series which include solar cycle 23 are analyzed in the present work in order to detect the effect of different filtering procedures on the determination of long-term trends. In particular, solar cycle 23 seems to have had an extreme ultraviolet (EUV) emission greater than that deduced from traditional solar EUV proxies during the maximum epoch and lower during the minimum epoch. When solar activity is filtered assessing the residuals of a linear regression between foF2 and Rz, or between foF2 and F10.7, this fact may bias trend values especially because it is at the end of the time series. The length of the period considered for trend assessment, the saturation and hysteresis effect of some ionosphere parameters, and the solar EUV proxy used are also considered in this study in order to quantify a possible spurious trend that may result as a by-product of a filtering process. Since trends expected as a consequence of anthropogenic effects are relatively small, these spurious effects may surely mask, or enhance, trends expected from anthropogenic origins.

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Long-term behavior of annual and semi-annual S q variations

Cited by 13 publications

References 27 publications

A long-term trend in the F2-layer critical frequency as observed at Alma-Ata ionosonde station

A long-term trend in the F2-layer critical frequency as observed at Alma-Ata ionosonde station

Geomagnetic lunar and solar daily variations during the last 100 years

Filtering ionosphere parameters to detect trends linked to anthropogenic effects

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