An increase in Pc1 wave activity prior to magnetic sudden impulses

Abstract

Abstract. The enhancement of Pcl wave activity after magnetic sudden impulses (Sis) is well established by ground-based and satellite measurements. This phenomenon is explained by compressions of the magnetosphere under the action of interplanetary shocks. In this paper we use long-term ground-based observations of Pcl to study the variation of the Pcl wave activity before Sis. We conclude that there is a tendency for an increase of the rate of Pcl occurrence as the time gets closer to the SI. We interpret this effect as an impact of the interplanetary foreshocks on the Earth's magnetosphere. IntroductionIt is known that a magnetic sudden impulse ( In this work we analyze long-term ground-based observations of Pcl magnetic pulsations to study the probability of the Pcl occurrence within the 1.5-hour time interval preceding the SI. We conclude that an increase in Pcl activity prior to Sis takes place. This new observation is discussed in terms of the We see that the distribution of n (k) is nonuniform with the maximum value n(1) -38 for the first interval 0-5 min. 25,185

Space weather effects on radio propagation: study of the CEDAR, GEM and ISTP storm events

“…3, 5, 8, 9, 17, and 18). While for night-time n-storms (numbers 1, 4, 6, 7, 10, and 13) the median value is τ o =2.4 h. This result is explained physically by the presence of energetic particle precipitation in the cusp and auroral zone in the day-time before a storm (Gulielmi et al, 2001), which ionizes the ionospheric F2-layer for a longer time, τ o =3.5 h, than at night, τ o =2.4 h, when precipitation occurs from the night-side of the plasma ring (auroral peak). The time of the path outage, t des (the interval of propagation failure), for the St. Petersburg-Heiss Island path (Table 1) depends on the LT or on the location of the path relative to the auroral absorption area.…”

“…These effects of ionization, heating, and absorption may be considered as ionospheric forerunners of SI. Gulielmi et al (2001) provide significant evidence of enhanced riometer absorption occurring up to 3 h before an SI using data from Sodankyla. At this time Sodankyla was considered to be equatorward of the cusp.…”

“…The location of the origin region of Pc1 is associated with the location of the plasmapause (Pudovkin et al, 1976). According to papers of Gulielmi et al (2001) and Kangas et al (2001), Pc1 can begin not only after SI, but also before it. The mechanism is that before the shock waves propagating in non-collision solar wind plasma, there are so-called pre-shock areas.…”

Impact of interplanetary shock on the ULF wave activity: A case study of the storm sudden commencement on September 22, 1999

“…Generation of the post-SSC Pc 1 is connected with magnetospheric compression due to its interaction with an interplanetary shock wave (Olson and Lee, 1983;Anderson and Hamilton, 1993;Kangas et al, 1998). Preshock Pc 1's are generated due to the magnetospheric interaction with upstream turbulence of an interplanetary shock wave (Kangas et al, 1998;Guglielmi et al, 2000). It is not clear yet, whether this process is limited only by the magnetospheric compression or involves some other mechanisms.…”

“…A number of authors (Troitskaya, 1961;Tepley and Wentworth, 1962;Heacock and Hessler, 1965;Troitskaya and Guglielmi, 1967;Saito and Matsushita, 1967;Kokubun and Oguti, 1968;Olson and Lee, 1983;Kangas et al, 1986Kangas et al, , 1998Anderson and Hamilton, 1993) have studied Pc 1 pulsations excited by storm sudden commencements (SSC). Less common are Pc 1 emissions observed several hours before SSC (Troitskaya, 1964;Kangas et al, 1998;Guglielmi et al, 2000). Generation of the post-SSC Pc 1 is connected with magnetospheric compression due to its interaction with an interplanetary shock wave (Olson and Lee, 1983;Anderson and Hamilton, 1993;Kangas et al, 1998).…”