A new method to estimate annual solar wind parameters and contributions of different solar wind structures to geomagnetic activity

Holappa, Lauri; Мурсула, К.; Asikainen, Timo

doi:10.1002/2014ja020599

Cited by 29 publications

(27 citation statements)

References 22 publications

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“…Previous studies have shown that solar wind speed is an important driver of long‐term (e.g., monthly and yearly) geomagnetic activity at low latitudes and midlatitude (Akasofu, ; Crooker, Feynman, & Gosling, ; Richardson, Cane, & Cliver, ; Richardson, Cliver, & Cane, ) and, especially, at high latitudes (Finch et al, ; Holappa, Mursula, & Asikainen, ; Holappa, Mursula, Asikainen, & Richardson, ; Lukianova, Mursula, & Kozlovsky, ; Mursula, Holappa, & Lukianova, ; Mursula, Lukianova, & Holappa, ) and of substorm activity (Tanskanen et al, ). Here we study to what extent the solar wind speed controls the seasonal variation of high‐latitude geomagnetic activity.…”

Section: Seasonal Variation Of Solar Wind Speed In 1995–2014mentioning

confidence: 99%

“…We would also like to note that even though the long‐term averages (e.g., monthly means) of high‐latitude indices, like the IL index, are mainly driven by high‐speed streams, they are also somewhat affected by transients like coronal mass ejections (see, e.g., Holappa, Mursula, & Asikainen, , Holappa, Mursula, Asikainen, & Richardson, ). However, the seasonal variation of high‐latitude indices based on the monthly values is predominantly determined by high‐speed streams.…”

Section: Seasonal Variation Of Solar Wind Speed In 1995–2014mentioning

confidence: 99%

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Seasonal Variation of High‐Latitude Geomagnetic Activity in Individual Years

2017

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We study the seasonal variation of high‐latitude geomagnetic activity in individual years in 1966–2014 (solar cycles 20–24) by identifying the most active and the second most active season based on westward electrojet indices AL (1966–2014) and IL (1995–2014). The annual maximum is found at either equinox in two thirds and at either solstice in one third of the years examined. The traditional two‐equinox maximum pattern is found in roughly one fourth of the years. We found that the seasonal variation of high‐latitude geomagnetic activity closely follows the solar wind speed. While the mechanisms leading to the two‐equinox maxima pattern are in operation, the long‐term change of solar wind speed tends to mask the effect of these mechanisms for individual years. Large cycle‐to‐cycle variation is found in the seasonal pattern: equinox maxima are more common during cycles 21 and 22 than in cycles 23 or 24. Exceptionally long winter dominance in high‐latitude activity and solar wind speed is seen in the declining phase of cycle 23, after the appearance of the long‐lasting low‐latitude coronal hole.

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Section: Seasonal Variation Of Solar Wind Speed In 1995–2014mentioning

confidence: 99%

Section: Seasonal Variation Of Solar Wind Speed In 1995–2014mentioning

confidence: 99%

Seasonal Variation of High‐Latitude Geomagnetic Activity in Individual Years

2017

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“…The main solar wind drivers of geomagnetic activity are interplanetary coronal mass ejections (ICME) and high‐speed streams (HSS) together with corotating interaction regions (CIR) (Richardson & Cane, ; Sawyer & Haurwitz, ; Tanskanen et al, ; Zhang et al, ). However, the relationship of HSSs and ICMEs to geomagnetic activity at different latitudes, as well as their occurrence over the solar cycle, varies considerably (Holappa et al, ; Holappa, Mursula, & Asikainen, ).…”

Section: Introductionmentioning

confidence: 99%

Solar Cycle Occurrence of Alfvénic Fluctuations and Related Geo‐Efficiency

et al. 2017

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We examine solar wind intervals with Alfvénic fluctuations (ALFs) in 1995–2011. The annual number, the total annual duration, and the average length of ALFs vary over the solar cycle, having a maximum in 2003 and a minimum in 2009. ALFs are most frequent in the declining phase of solar cycle, when the number of high‐speed streams at the Earth's vicinity is increased. There is a rapid transition after the maximum of solar cycle 23 from ALFs being mainly embedded in slow solar wind (<400 km/s) until 2002 to ALFs being dominantly in fast solar wind (>600 km/s) since 2003. Cross helicity increased by 30% from 2002 to 2003 and maximized typically 4–6 h before solar wind speed maximum. Cross helicity remained elevated for several days for highly Alfvénic non‐ICME streams, but only for a few hours for ICMEs. The number of substorms increased by about 40% from 2002 to 2003, and the annual number of substorms closely follows the annual cross helicity. This further emphasizes the role of Alfvénic fluctuations in modulating substorm activity. The predictability of substorm frequency and size would be greatly improved by monitoring solar wind Alfvénic fluctuations in addition to the mean values of the important solar wind parameters.

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“…They also found that the average geomagnetic activity during the passage of CMEs is stronger than during the passage of HSSs. Holappa et al [] recently developed a method to extract CME and HSS contributions to geomagnetic activity using independent component analysis. They confirmed that the CME‐ and HSS‐related geomagnetic activity peak in the solar maxima and declining phase, respectively, and also found that the amplitude of these two components over several solar cycles is similar.…”

Section: Introductionmentioning

confidence: 99%

Solar wind drivers of energetic electron precipitation

Asikainen

Ruopsa

2016

JGR Space Physics

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Disturbances of near‐Earth space are predominantly driven by coronal mass ejections (CMEs) mostly originating from sunspots and high‐speed solar wind streams (HSSs) emanating from coronal holes. Here we study the relative importance of CMEs and HSSs as well as slow solar wind in producing energetic electron precipitation. We use the recently corrected energetic electron measurements from the Medium Energy Proton Electron Detector instrument on board low‐altitude NOAA/Polar Orbiting Environmental Satellites from 1979 to 2013. Using solar wind observations categorized into three different flow types, we study the contributions of these flows to annual electron precipitation and their efficiencies in producing precipitation. We find that HSS contribution nearly always dominates over the other flows and peaks strongly in the declining solar cycle phase. CME contribution mostly follows the sunspot cycle but is enhanced also in the declining phase. The efficiency of both HSS and CME peaks in the declining phase. We also study the dependence of electron precipitation on solar wind southward magnetic field component, speed, and density and find that the solar wind speed is the dominant factor affecting the precipitation. Since HSSs enhance the average solar wind speed in the declining phase, they also enhance the efficiency of CMEs during these times and thus have a double effect in enhancing energetic electron precipitation.

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A new method to estimate annual solar wind parameters and contributions of different solar wind structures to geomagnetic activity

Cited by 29 publications

References 22 publications

Seasonal Variation of High‐Latitude Geomagnetic Activity in Individual Years

Seasonal Variation of High‐Latitude Geomagnetic Activity in Individual Years

Solar Cycle Occurrence of Alfvénic Fluctuations and Related Geo‐Efficiency

Solar wind drivers of energetic electron precipitation

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