Publication Date:
2023-06-15
Description:
Generally, a corotating high-speed stream is formed when a high-speed stream (HSS) overtakes the slow wind, originating a corotating interaction region (CIR) upstream and a rarefaction region (RR) downstream. Mainly within CIRs and HSSs, the interplanetary magnetic field (IMF) presents wide fluctuations that can lead to the enhancement of geomagnetic activity. We propose a statistical investigation of the effects of Alfvénic and compressive fluctuations in corotating streams at 1 AU on the low-frequency geomagnetic activity, as observed at high latitudes geomagnetic observatories in both hemispheres. We select several corotating streams, together with the corresponding geomagnetic field data recorded at ground observatories. To better highlight the power variations of the geomagnetic field during the selected events, we previously compute, for each observatory, a long-term background over quiet periods of geomagnetic activity (low Kp index) to re-scale the power. We apply a rotation to the IMF and solar wind (SW) velocity components at 1AU into the Mean-Field Aligned reference frame, to identify two main directions: one aligned to the ambient magnetic field and one orthogonal to it. The power of both magnetic and velocity fields along the two main directions, together with two quadratic invariants commonly used to describe MHD turbulence, such as normalized cross-helicity and the normalized residual energy, allow discrimination between compressive and Alfvénic fluctuations. We compare the re-scaled geomagnetic field power to SW parameters, in particular, the power of IMF and SW velocity along the two directions and the two quadratic invariants.
Language:
English
Type:
info:eu-repo/semantics/conferenceObject
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