AKR modulation and global Pi2 oscillation

Abstract

[1] In this report we present a temporal relationship between ground Pi2 and auroral kilometric radiation (AKR). We analyzed six isolated substorm events, which were observed by the MAGDAS/CPMN ground magnetometer network and the plasma wave instrument onboard the Polar satellite. We found that the time derivative of the heightintegrated AKR power and the ground Pi2 D component had the same periodicity and that the two were synchronized with each other. When the D component fluctuated with the same (opposite) polarity as the magnetic bay variation, the AKR power tended to increase (decrease) during the corresponding interval. An isolated substorm event (AE ∼ 40 nT), which occurred around 10:19 UT on 24 January1997, was selected for a detailed study. The behavior of the Pi2 event can be interpreted by the substorm current wedge (SCW) and Pi2 propagation models. It is confirmed that the midlatitude and high-latitude D component oscillations can be treated as a proxy of the SCW oscillations, whereas the H component oscillations exhibited some phase shifts by the propagation delay of the Pi2 waves. That is, the temporal relation between the time derivative of the AKR power and the ground Pi2 suggests that the height-integrated AKR power was modulated coherently with the SCW oscillations.

Formation of a 3‐D Oscillatory Current System Associated With Global High‐Correlation Pi 2 Event: A Case Study

“…In global high-correlation Pi 2 events, the high-to middle-latitude Pi 2 in the H (geomagnetically northward) and D (geomagnetically eastward) components contain waveforms that are highly correlated with low-latitude H Pi 2. Uozumi et al (2011) found that not only the high-latitude Pi 2 but also middle-and low-latitude Pi 2, which are highly correlated with lowlatitude H Pi 2, can be treated in the framework of global high-correlation Pi 2. Uozumi et al (2011) found that not only the high-latitude Pi 2 but also middle-and low-latitude Pi 2, which are highly correlated with lowlatitude H Pi 2, can be treated in the framework of global high-correlation Pi 2.…”

“…Uozumi et al (2009) found that the H component of a high-latitude Pi 2 exhibits systematic group delays (|T| <~100 s) from the low-latitude Pi 2 in H. On the other hand, the delay time of the high-latitude Pi 2 in the D component to the low-latitude Pi 2 from the H component was not significant (|T|<~10 s) in the entire nighttime sector, and the high-latitude D component Pi 2s switched their polarity around 1 hr MLT dawnward of the auroral breakup center that was identified by global auroral image of the Polar satellite. Uozumi et al (2009Uozumi et al ( , 2011Uozumi et al ( , 2016 proposed a generation and propagation mechanism of global high-correlation Pi 2 event based on ground observations. Uozumi et al (2009Uozumi et al ( , 2011Uozumi et al ( , 2016 proposed a generation and propagation mechanism of global high-correlation Pi 2 event based on ground observations.…”

“…U09 applied the oscillating FAC model proposed by Lester et al (1983) to interpret the characteristics of the high-latitude Pi 2 in the D component. The present study is based on the oscillating FAC model developed by the successive studies of Uozumi et al (2009Uozumi et al ( , 2011Uozumi et al ( , 2016. What causes the mismatch between the SCW locations estimated by the McPherron and Lester methodology?…”

“…U16 pointed out that there remained open questions in Lester's model to be answered; that is, (1) the centers of the SCWs predicted based on the Lester's model were not always collocated with those predicted by the SCW model proposed by McPherron et al (1973). Uozumi et al (2009Uozumi et al ( , 2011Uozumi et al ( , 2016 proposed three possible wave elements that exist in global high-correlation Pi 2 events as follows: (1) fast-mode waves (δB FW ) that propagate from the Pi 2 source region in the nightside magnetosphere and observed mainly in low-latitude Pi 2 in the H component, (2) SCW oscillations (δB SCW ) observed mainly in the low-to high-latitude Pi 2 in the D component, and (3) directly driven Alfvénic waves (δB DA ) generated by δB FW through the mode-conversion process and observed as the main oscillation in the middle-to high-latitude Pi 2 in the H component with some group delays (see Uozumi et al, 2016, for more details). (2) Ideally, the ellipticity of a Pi 2 hodogram should be linear if the middle-latitude Pi 2 pulsation is directly associated with the substorm current system.…”

Auroral kilometric radiation from a nonstationary thin plasma cavity

“…During a width expansion, the intensity of the outgoing waves decreases. It is interesting to note that a similar correlation between the AKR power and low frequency oscillations of the magnetic field has been observed (Uozumi et al, 2011). For more detailed comparison with experimental data, it is also necessary to take into account the magnetic field and plasma inhomogeneities in the region of the AKR generation.…”