Characteristics of energy transfer of Pi 2 magnetic pulsations: Latitudinal dependence

Abstract

Abstract. To investigate the generation and propagation mechanisms of Pi 2 magnetic pulsations, we have analyzed magnetic field data t?om the 210 ø magnetic meridian (MM) stations. We used 50 Pi 2 events that were simultaneously observed at seven stations along the 210 ø MM during January 1995, and tbcused our analysis on associated magnetic energy, ((/X/--D2+(AD)2)/kt 0. The times when the amplitude of the magnetic energy attained the maximum (T,,,,x) were compared among these stations. We tbund that T,,,,,. has a latitudinal dependence. especially at highel' latitudes. which has not been previously reported. At Kotel'nyy (L=8.50) on the poleward side of the auroral region. T,,,,.,. occurred an average of 21 seconds earlier than T,,,,,. at Guam (L=I.01). and often as much as one minute earlier. The existence of latitudinal variation has implications tbr interpretation of issues related to timing of substorm onset; it is necessaD to consider the global t•atures of Pi 2 events in the study of auroral and magnetospheric substorms. We present ncx• 11ndings on the latitudinal dependence o1' Pi 2 energy translbr. especially at highel' latitudes and near the plasmapause. These findings can affect the interpretation of some results concerning substorm onset-timing issues. Statistical AnalysisThe magnetic pressure, or magnetic energy density, is defined as B-/2t, to. The magnetic energy carned by MHD waves is expressed by ((A/Dr+ (AD)2+ (ALD2)//a0 . That is, the variation of the magnetic energy is proportional to the squared amplitude of magnetic field variation. For Pi 2 events used in this paper, the contribution to the magnetic energy fi'om the Z component is small and negligible, and when the Z component has constant and significant contribution to the magnetic energy, the induction effect caused by ground conditions is considered. rather than the external source. Thus.•xe use ((_XH) 2 + (,_XD)2)//a0 as the estimate of variation in We note that the ZYK data had a timing error during Jan. -Mar. 1995. According to Kikuchi and Araki [1979]. the variation in the electric field accompanying a DP-2-type sudden commencement (sc) is transmitted instantaneously fi'om high latitude to the equator by Earth-ionosphere waveguide mode. Thus. by using three sc events that occurred in the interval, we have adjusted the timing of the ZYK data 1619

AKR modulation and global Pi2 oscillation

“…This value is consistent with DT corr = −2 and 0 s for EWA and KAT. Numerical estimation by Uozumi et al [2000] showed that DTOF between equatorial and low-latitude stations was small values (few seconds for L < ∼2). According to the study by Yumoto [1990] cavitylike oscillation was observed at almost the same L value station SKD (L = 2.11) as KAT (L = 2.14).…”

Tailward propagation of Pi2 waves in the Earth's magnetotail lobe

“…The automated procedure from the 210 meridian magnetometer chain (see e.g. Uozumi et al, 2000) found Pi2 onset at ∼13:37 UT. In Fig.…”

“…In this way the escaping waves will have the same characteristics as those of the resonant field line. Uozumi et al (2000Uozumi et al ( , 2004 studied the latitudinal propagation of Pi2s. Statistically, they find that the average time delay of the maximum of the Pi2 wave power between CHD and MSR is a few seconds, with CHD leading.…”

Pi 2 waves simultaneously observed by Cluster and CPMN ground-based magnetometers near the plasmapause

“…8) correspond to the cavity-mode oscillation of the plasmasphere in response to the above-presented hitting process, or to the propagation process itself of the Pi 2 signal within the plasmasphere, leaves room for argument, since we have no other satellites within the plasmasphere; ground observation only is not necessarily sufficient to separate out field-aligned travel time from radial travel time of Pi 2. For example, Uozumi et al (2000) statistically showed that Pi 2 signals propagating within the plasmasphere were observed earlier at smaller L on the ground (see their Fig. 3), unlike the one shown in this paper, and successfully explained it by their model cited above.…”

“…If we try to understand the observed phase pattern in terms of the Pi 2 propagation effect, we have to take into account the propagation time from Cluster to the ground along the magnetic field line. To calculate it, we use the procedure of Uozumi et al (2000Uozumi et al ( , 2007: we assume a cold plasma consisting of hydrogen ions and electrons, use the Tsyganenko 96 model for the magnetic field, use the model of Carpenter and Anderson (1992) for the equatorial plasma density, and use the power-law model for the field-aligned distribution of the plasma density n, i.e. n(r) = n eq (r/r eq ) −p , where r is the geocentric distance of any point on a field line, r eq is r on the equatorial plane, n eq is n there, and p is set to 3 (4) inside (outside) the plasmapause (Takahashi and Anderson, 1992).…”