Characteristics of Pi 2 magnetic pulsations observed at the CPMN stations: A review of the STEP results

Abstract

From analyses of magnetic data from the Circum-pan Pacific Magnetometer Network (CPMN) stations, we can find the following wave characteristics of Pi 2 magnetic pulsations. (1) Pi 2 pulsations observed on the ground are an ensemble of various hydromagnetic modes excited at high, middle, low, and equatorial latitudes. Each mode exhibits its own propagation (timing) and spatial illumination. (2) There are apparent longitudinal propagation and latitudinal time delays of the maximum Pi 2 magnetic energy among the CPMN stations within 100 sec. (3) When a single low-latitude station is located in the sectors of 00-24 hr LT, 20-03 hr local time (LT), and 23-01 hr LT, respectively, 62%, 79%, and 100% of auroral breakups identified by the Polar satellite have associated Pi 2s. 66% of the low-latitude Pi 2s occur within 1 min of the auroral breakups, and 85% within 2 min. Pi 2s are still a good indicator of substorm onsets, but they should be used with care.

AKR modulation and global Pi2 oscillation

“…It suggests that the SCW did not sufficiently develop to exhibit typical magnetic bay signature during the present event. Contrary to such small magnitude of the bay variations, the amplitude of Pi2 for each station was comparative or larger than that of the normal amplitude reported by Yumoto et al [2001] for each latitudinal and local time region. The above observational facts bring up a question: How was the D component oscillation generated by such small magnitude SCW?…”

“…Olson [1999] summarized that the Pi2 signal is associated with the following two fundamental processes occurred at substorm expansion onsets: (1) response of the high-latitude ionosphere to sudden generation of field-aligned currents in association with the disruption of cross-tail current in the plasma sheet and (2) impulse response of the inner magnetosphere to the compressional waves that are generated at substorm onset. Yumoto et al [2001] summarized that the Pi2 pulsations observed on the ground consist of five hydromagnetic wave components excited by the above two processes. Olson [1999] and Yumoto et al [2001] stated that a compressional pulse (fast mode wave) causes field line resonances and surface waves at the plasmapause as well as cavity waves in the inner magnetosphere.…”

“…Yumoto et al [2001] summarized that the Pi2 pulsations observed on the ground consist of five hydromagnetic wave components excited by the above two processes. Olson [1999] and Yumoto et al [2001] stated that a compressional pulse (fast mode wave) causes field line resonances and surface waves at the plasmapause as well as cavity waves in the inner magnetosphere. Low-latitude Pi2 are recognized as a cavity oscillation [e.g., Yumoto, 1990;Takahashi et al, 2003] and are directly driven process by earthward propagating compressional pulses from the magnetotail [e.g., Kepko et al, 2001;Uozumi et al, 2009].…”

“…[4] As summarized by Olson [1999] and Yumoto et al [2001], Pi2 has different occurrence mechanisms for different Pi2 components. Thus many of past studies investigated each Pi2 component.…”

“…[3] Olson [1999] and Yumoto et al [2001] reviewed most of past Pi2 studies and constructed phenomenological overview of the Pi2 waves. Olson [1999] summarized that the Pi2 signal is associated with the following two fundamental processes occurred at substorm expansion onsets: (1) response of the high-latitude ionosphere to sudden generation of field-aligned currents in association with the disruption of cross-tail current in the plasma sheet and (2) impulse response of the inner magnetosphere to the compressional waves that are generated at substorm onset.…”