Contribution of wind, conductivity, and geomagnetic main field to the variation in the geomagnetic <i>Sq</i> field

Takeda, Masahiko

doi:10.1002/jgra.50386

Cited by 27 publications

(40 citation statements)

References 19 publications

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“…We take a rather simplified view of Takeda [] in order to understand our observational results. Takeda [] used a very simple expression for the magnitude ( A ) of the Y component geomagnetic daily variation on the basis of Fukushima 's [] model:

A = \frac{3}{4} μ_{0} normalΣU B_{z}

where μ 0 is the permeability of the vacuum (=4π×10 7 ), Σ is the effective ionospheric conductivity (S), U is zonal neutral wind speed (m s −1 ), and B z is the vertical geomagnetic field strength (nT). The constant 3/4 arises from the fact that the geomagnetic daily variation is produced not only by ionospheric currents but also by currents induced in the conductive Earth, which accounts for approximately 25% of the total effect.…”

Section: Discussionmentioning

confidence: 99%

“…In light that the midlatitude ionospheric current system is subject to the Cowling effect [ Takeda , ], the effective ionospheric conductivity is given as follows:

normalΣ = {normalΣ}_{P} + \frac{{normalΣ}_{H}^{2}}{{normalΣ}_{P}}

where Σ P and Σ H are height‐integrated Pedersen and Hall conductivities, respectively. Takeda [] computed Σ P and Σ H using the International Reference Ionosphere model [ Bilitza , ; Bilitza et al , ]. He pointed out that the solar cycle variation in A is almost solely due to changes in Σ.…”

Section: Discussionmentioning

confidence: 99%

“…It is found that both lunar and solar variations correlate slightly better with

\sqrt{F_{10.7}}

than F 10.7 . According to Takeda [], Pedersen and Hall conductivities at a given height are proportional to the electron number density N e . The electron number density tends to scale with

\sqrt{F_{10.7}}

in the dynamo region where the ionospheric plasma is largely in photochemical equilibrium.…”

Section: Discussionmentioning

confidence: 99%

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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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A = \frac{3}{4} μ_{0} normalΣU B_{z}

Section: Discussionmentioning

confidence: 99%

“…In light that the midlatitude ionospheric current system is subject to the Cowling effect [ Takeda , ], the effective ionospheric conductivity is given as follows:

normalΣ = {normalΣ}_{P} + \frac{{normalΣ}_{H}^{2}}{{normalΣ}_{P}}

Section: Discussionmentioning

confidence: 99%

“…It is found that both lunar and solar variations correlate slightly better with

\sqrt{F_{10.7}}

than F 10.7 . According to Takeda [], Pedersen and Hall conductivities at a given height are proportional to the electron number density N e . The electron number density tends to scale with

\sqrt{F_{10.7}}

in the dynamo region where the ionospheric plasma is largely in photochemical equilibrium.…”

Section: Discussionmentioning

confidence: 99%

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Geomagnetic lunar and solar daily variations during the last 100 years

Yamazaki

Kosch

2014

JGR Space Physics

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“…Recently, using long-term ionospheric conductivity and geomagnetic field data obtained at low-latitude stations, Takeda (2013) showed that solar activity effects cannot be clearly seen in the thermospheric neutral winds, which are derived from the Sq amplitude calculated from the Y component of the geomagnetic field. He pointed out that a major contribution of the solar activity effects on the Sq amplitude is not through the neutral wind velocity but instead through the height-integrated ionospheric conductivity.…”

Section: Elements To Determine the Sq Amplitudementioning

confidence: 99%

“…It is well known that the magnitude of the Sq variation has good correlation with solar activity indices such as sunspot numbers and the solar F10.7 index [e.g., Sellek 1980;Schlapp et al 1990;Macmillan and Droujinina 2007;Torta et al 2009;Elias et al 2010;Takeda 2013]. Sellek (1980) showed that the annual mean Sq amplitude obtained at San Juan at a low latitude is linearly proportional to the annual mean sunspot numbers using observation data during 1929 to 1965.…”

Section: Nonlinear Response Of the Sq Amplitude To The Solar F107 Indexmentioning

confidence: 99%

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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Day‐to‐day variability of midlatitude ionospheric currents due to magnetospheric and lower atmospheric forcing

2016

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As known from previous studies on the solar quiet (Sq) variation of the geomagnetic field, the strength and pattern of ionospheric dynamo currents change significantly from day to day. The present study investigates the relative importance of two sources that contribute to the day‐to‐day variability of the ionospheric currents at middle and low latitudes. One is high‐latitude electric fields that are caused by magnetospheric convection, and the other is atmospheric waves from the lower atmosphere. Global ionospheric current systems, commonly known as Sq current systems, are simulated using the National Center for Atmospheric Research thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model. Simulations are run for 1–30 April 2010 with a constant solar energy input but with various combinations of high‐latitude forcing and lower atmospheric forcing. The model well reproduces geomagnetic perturbations on the ground, when both forcings are taken into account. The contribution of high‐latitude forcing to the total Sq current intensity (Jtotal) is generally smaller than the contribution of wave forcing from below 30 km, except during active periods (Kp≥4), when Jtotal is enhanced due to the leakage of high‐latitude electric fields to lower latitudes. It is found that the penetration electric field drives ionospheric currents at middle and low latitudes not only on the dayside but also on the nightside, which has an appreciable effect on the Dst index. It is also found that quiet time day‐to‐day variability in Jtotal is dominated by symmetric‐mode migrating diurnal and semidiurnal tidal winds at 45–60° latitude at ∼110 km.

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Contribution of wind, conductivity, and geomagnetic main field to the variation in the geomagnetic Sq field

Cited by 27 publications

References 19 publications

Geomagnetic lunar and solar daily variations during the last 100 years

Geomagnetic lunar and solar daily variations during the last 100 years

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

Day‐to‐day variability of midlatitude ionospheric currents due to magnetospheric and lower atmospheric forcing

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