Multiple ground‐based and satellite observations of global Pi 2 magnetic pulsations

Abstract

Four Pi 2 magnetic pulsations, observed on the ground at L = 1.2–6.9 in the interval from 2300 UT on May 22 to 0300 UT on May 23, 1985, provide new evidence of a global nature of Pi 2 pulsations in the inner (L ≲ 7) region of the magnetosphere bounded by the plasma sheet during quiet geomagnetic conditions. In the present study, magnetic data have been collected from stations distributed widely both in local time and in latitude, including conjugate stations, and from the AMPTE/CCE spacecraft located in the magnetotail. On the basis of high time resolution magnetic field data, the following characteristics of Pi 2 have been established: horizontal components, H and D, of the Pi 2 oscillate nearly antiphase and in‐phase, respectively, between the high‐ and low‐altitude stations in the midnight southern hemisphere. Both the H and D components of the Pi 2 have nearly in‐phase relationships between the nightside and the dayside stations at low latitude. The Pi 2 amplitude is larger at the high‐latitude station and decreases toward lower latitudes. The dominant periods of the Pi 2 are nearly identical at all stations. Although a direct coincidence between spacecraft‐observed and ground‐based global Pi 2 events does not exist for these events, the Pi 2 events are believed to be a forced field line oscillation of global scale, coupled with the magnetospheric cavity resonance wave in the inner magnetosphere during the substorm expansive phase.

Initial Results from the 210.DEG. Magnetic Meridian Project-Review.

“…However, it is still an open question whether the Yumoto et al (1989) scenario is consistent with these observational results. In order to answer the question, in the near future we will further analyze the 210° MM chain data, including data from around the plasmapause and simultaneously obtained by the ISTP (AKEBONO, GEOTAIL) satellites.…”

“…Many workers have studied Pi 2 magnetic pulsations observed on the ground and in space; however, the generation and propagation mechanisms of these pulsations are still open to question. Yumoto et al (1989) proposed a possible scenario for the excitation and propagation mechanisms of substorm-associated global Pi 2 pulsations. Atthe onset of substorm expansion, hydromagnetic impulse disturbances are launched, perhaps in association with tail reconnection (or current disruption) in the nearEarth plasma sheet.…”

“…In order to check the Yumoto et al (1989) scenario, we analyzed data from stations along the 210° MM. Figure 10 hemisphere and at Biak, Weipa, Birdsville, and Adelaide in the southern hemisphere from 1206 to 1226 UT on October 19, 1992.…”

Near-equatorial Pi2 and Pc3 waves observed by CHAMP and on SAMBA/MAGDAS stations

“…At high latitudes, Pi2 pulsations are typically observed around the local midnight and are associated with the substorm onset. Although auroral substorm disturbance is confined to a relatively narrow range of longitudes around local midnight, low-latitude Pi2s occur over an extremely large range of longitudes (Yumoto et al, 1990;Li et al, 1998). These results have suggested a global cavity mode as a mechanism of low-latitude Pi2 pulsations (Yeoman and Orr, 1989).…”

High spatial and temporal resolution observations of an impulse-driven field line resonance in radar backscatter artificially generated with the Tromsø heater

“…For example, Sutcli e and Yumoto (1989;, Yeoman and Orr (1989), Yumoto (1990), Yumoto et al (1990), Lin et al (1991), Yeoman et al (1991) have all proposed that low-and midlatitude Pi2 pulsations are driven by compressional cavity resonances.…”