Geomagnetic negative sudden impulses: Interplanetary causes and polarization distribution

Abstract

[1] We made a study of the characteristics of geomagnetic negative sudden impulses (SI À s) identified in the midlatitude geomagnetic SYM indices and the causative structures in the solar wind using data from the Wind and ACE spacecraft. A total of 28 SI À s with an amplitude larger than 20 nT in the H component SYM index were found over the period 1995 through 1999, with 50% of them occurring in conjunction with a positive sudden impulse, SI + (i.e., SI pair). In the SI pairs the amplitude of SI À was almost always larger than that of the preceding SI + . We attempted for the first time a classification of structures in the solar wind associated with SI À s. It is found that reverse shocks are not responsible for SI À s. Instead, SI À s are associated with varied structures such as tangential discontinuities at high-low speed stream interfaces, front boundaries of interplanetary magnetic clouds, and trailing edges of heliospheric plasma sheets. There is no preferential association of SI À s in our sample with any particular type of solar wind structure. We investigated statistically the polarization characteristics of SI À s at high latitude. The sense of the polarization in the auroral zone tended to be clockwise in the afternoon and counterclockwise in the morning. The rotational sense reversed in the polar cap. The latitudinal reversal occurred in the range from 65°to 80°. Thus the polarization distribution of SI À is not opposite to but is consistent with that of SI + . We suggest that the contribution from the longitudinal movement of a twin vortex ionospheric current system is dominant to produce the polarization of SC and SI À .

Fast acceleration of “killer” electrons and energetic ions by interplanetary shock stimulated ULF waves in the inner magnetosphere

“…Oscillations of magnetic field lines can be sustained in the magnetospheric plasma. Lower frequency waves contain more wave power and the power levels vary roughly inversely with the wave frequency [56]. A schematic overview of the relationship between various waves and energetic electrons is shown in Figure 4.…”

“…the front edge of the Heliosphere Plasma Sheet (HPS) [55]. Takeuchi et al [56] have undertaken a statistical investigation of interplanetary/solar wind sources of the solar wind dynamic negative impulses. They have found that the negative impulses are usually associated with solar wind discontinuity embedded within CIR, as well as the front edge of the interplanetary magnetic clouds and the trailing edge of HPS.…”

The driving mechanisms of particle precipitation during the moderate geomagnetic storm of 7 January 2005

“…As it provides one minute resolution, this index can be used to investigate the effects of P dyn pulses (e.g. Takeuchi et al, 2002). The quick look values for the upper and lower auroral electrojet indices (AU and AL, respectively) are given in the bottom two panels of Fig.…”

“…The signature of expansion is a negative sudden impulse (SI − ) in the horizontal component of the geomagnetic field measured at mid to low latitudes (e.g. Takeuchi et al, 2002).…”

The interaction of ultra-low-frequency pc3-5 waves with charged particles in Earth’s magnetosphere

“…Positive impulses at the front edge of the Heliosphere Plasma Sheet (HPS) may also act as a source of ULF waves (Winterhalter et al 1994). Statistical analysis of IP shocks and solar wind sources of negative impulses (Takeuchi et al 2002) suggest they are mostly caused by the solar wind discontinuity embedded inside CIRs, the front edge of interplanetary magnetic clouds, and the trailing edge of the HPS. Small-scale plasma bubbles located within CIRs also produce negative and positive pressure impulses at the front and trailing edge of the bubbles, respectively.…”