| Autor: |
Laitinen, J., Holappa, L., Vanhamäki, H. |
| Předmět: |
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| Zdroj: |
Geophysical Research Letters; 9/16/2024, Vol. 51 Issue 17, p1-10, 10p |
| Abstrakt: |
Recent studies have suggested that the interplanetary magnetic field (IMF) By ${B}_{y}$ component modulates particle precipitation during solstices, or periods of high dipole tilt Ψ ${\Psi }$. So far this explicit IMF By ${B}_{y}$‐effect has only been shown in statistical studies. Here we analyzed a sequence of high‐speed stream (HSS) driven events of auroral (<30 ${< } 30$ keV) and medium energy (>30 ${ >} 30$ keV and >100 ${ >} 100$ keV) particle precipitation. We show that when HSSs are comparable in terms of IMF and solar wind parameters, they can lead to systematically stronger particle precipitation in individual events when the signs of By ${B}_{y}$ and Ψ ${\Psi }$ are opposite. We also perform a superposed epoch analysis of 485 HSSs giving further evidence that the By ${B}_{y}$‐effect is especially significant during HSSs. This is likely due to the persistent IMF By ${B}_{y}$ polarity during HSSs. We show evidence that the By ${B}_{y}$ dependence in particle precipitation is caused by a similar By ${B}_{y}$ dependence in substorm occurrence. Plain Language Summary: Intervals of fast solar wind occur the most during the declining phase of the 11‐year solar cycle. Such events are associated with a highly varying north‐south component of the magnetic field of the solar wind, which is known to increase geomagnetic activity. On the contrary to the north‐south directed magnetic field, the east‐west directed field remains very stable during events of fast solar wind. Recent studies have shown that the eastward (westward) magnetic field of the solar wind increases geomagnetic activity in the northern hemispheric winter (summer). We show observations of this effect in geomagnetic activity and particle precipitation from December 2007 to January 2008, when the Earth was hit by two recurring intervals of fast solar wind. We also show statistical results of this effect from intervals of fast solar wind in winter and summer seasons. Key Points: The interplanetary magnetic field (IMF) By ${B}_{y}$ component modulates electron precipitation during high dipole tilt (solstices)The explicit IMF By ${B}_{y}$ dependence of electron precipitation is demonstrated to be strong during high‐speed streamsElectron precipitation is 60%–70% stronger for By ${B}_{y}$ > 0 in northern winter and for By ${B}_{y}$ < 0 in northern summer [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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