Rate of Change of Large-Scale Solar-Wind Structure

Owens, M. J.; Chakraborty, Nachiketa; Turner, Harriet; Lang, Matthew; Riley, Pete; Lockwood, Mike; Barnard, Luke; Chi, Yutian

doi:10.1007/s11207-022-02006-4

Cited by 5 publications

(3 citation statements)

References 80 publications

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“…As solar wind structure is expected to be primarily a function of solar cycle phase (e.g. Owens, 2020), we also construct a solar activity index (SAI, Owens et al, 2022), aimed at characterising the progression of the solar cycle independent of the variation in sunspot cycle amplitude:…”

Section: Near-earth Solar Wind Datamentioning

confidence: 99%

Annual Variations in the Near-Earth Solar Wind

Owens

Lockwood

Barnard

et al. 2023

Preprint

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Earth’s orbit and rotation introduces systematic annual variations in geomagnetic activity, most notably via the changing orientation of the dayside magnetospheric magnetic field with respect to the heliospheric magnetic field (HMF). However, aside from these geometric effects, it is generally assumed that the solar wind is randomly sampled throughout the year. But systematic changes in the intrinsic solar wind conditions in near-Earth space could arise due to the variation in Earth heliocentric distance and heliographic latitude over the year. In this study we use 24 years of Advanced Composition Explorer (ACE) data to investigate the annual variations in the scalar properties of the solar wind, namely the solar wind proton density, the radial solar wind speed and the HMF intensity. All parameters do show some degree of systematic annual variation, with amplitudes of around 10 to 20%. For HMF intensity, the variation is in phase with the Earth’s heliocentric distance variation, and scaling observations for distance largely removes the variation. For proton density and solar wind speed, however, scaling for distance does not affect the variation and the annual phase is inconsistent with Earth’s heliocentric distance variation. Instead we attribute the annual variations to Earth’s heliographic latitude variation and systematic sampling of higher speed solar wind at higher latitude. These variations are most strongly ordered at solar minimum. Conversely, combining scalar solar wind parameters to produce dynamic pressure and potential power input to the magnetosphere estimates results in solar maximum exhibiting a greater annual variation, with an amplitude of around 40%. This suggests Earth’s position in the heliosphere makes a significant contribution to space weather, in addition to the well studied geometric effects.

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Section: Near-earth Solar Wind Datamentioning

confidence: 99%

Annual Variations in the Near-Earth Solar Wind

Owens

Lockwood

Barnard

et al. 2023

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

“…As the solar wind structure is expected to be primarily a function of the solar cycle phase (e.g. Owens, 2020), we also construct a solar activity index (SAI, Owens et al, 2022), aimed at characterising the progression of the solar cycle independent of the variation in sunspot cycle amplitude:…”

Section: Near-earth Solar Wind Datamentioning

confidence: 99%

Annual Variations in the Near-Earth Solar Wind

Owens,

Lockwood,

Barnard

et al. 2023

Sol Phys

Self Cite

View full text Add to dashboard Cite

Earth’s orbit and rotation produces systematic variations in geomagnetic activity, most notably via the changing orientation of the dayside magnetospheric magnetic field with respect to the heliospheric magnetic field (HMF). Aside from these geometric effects, it is generally assumed that the solar wind in near-Earth is uniformly sampled. But systematic changes in the intrinsic solar wind conditions in near-Earth space could arise due to the annual variations in Earth heliocentric distance and heliographic latitude. In this study, we use 24 years of Advanced Composition Explorer data to investigate the annual variations in the scalar properties of the solar wind, namely the solar wind proton density, the radial solar wind speed and the HMF intensity. All parameters do show some degree of systematic annual variation, with amplitudes of around 10 to 20%. For HMF intensity, the variation is in phase with the Earth’s heliocentric distance variation, and scaling observations for distance largely explains the observed variation. For proton density and solar wind speed, however, the phase of the annual variation is inconsistent with Earth’s heliocentric distance. Instead, we attribute the variations in speed and density to Earth’s heliographic latitude variation and systematic sampling of higher speed solar wind at higher latitudes. Indeed, these annual variations are most strongly ordered at solar minimum. Conversely, combining scalar solar wind parameters to produce estimates of dynamic pressure and potential power input to the magnetosphere results in solar maximum exhibiting a greater annual variation, with an amplitude of around 40%. This suggests Earth’s position in the heliosphere makes a significant contribution to annual variations in space weather, in addition to the already well-studied geometric effects.

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“…In global heliospheric solar wind simulations, it was also found that the solar wind variability is strongly correlated with the solar cycle, with the corona and heliosphere being more variable at the solar maximum. However, limiting the analysis of the simulations to the solar equatorial region strongly reduces the difference between solar maximums and minimums (Owens et al 2022).…”

Section: Introductionmentioning

confidence: 99%

Relation between Latitude-dependent Sunspot Data and Near-Earth Solar Wind Speed

Jiao,

Liu,

Zhang

et al. 2023

ApJ

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Solar wind is important for the space environment between the Sun and the Earth and varies with the sunspot cycle, which is influenced by solar internal dynamics. We study the impact of latitude-dependent sunspot data on solar wind speed using the Granger causality test method and a machine-learning prediction approach. The results show that the low-latitude sunspot number has a larger effect on the solar wind speed. The time delay between the annual average solar wind speed and sunspot number decreases as the latitude range decreases. A machine-learning model is developed for the prediction of solar wind speed considering latitude and time effects. It is found that the model performs differently with latitude-dependent sunspot data. It is revealed that the timescale of the solar wind speed is more strongly influenced by low-latitude sunspots and that sunspot data have a greater impact on the 30 day average solar wind speed than on a daily basis. With the addition of sunspot data below 7.°2 latitude, the prediction of the daily and 30 day averages is improved by 0.23% and 12%, respectively. The best correlation coefficient is 0.787 for the daily solar wind prediction model.

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Rate of Change of Large-Scale Solar-Wind Structure

Cited by 5 publications

References 80 publications

Annual Variations in the Near-Earth Solar Wind

Annual Variations in the Near-Earth Solar Wind

Annual Variations in the Near-Earth Solar Wind

Relation between Latitude-dependent Sunspot Data and Near-Earth Solar Wind Speed

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