Abstract
Abstract. Interplanetary transients with particular signatures different from the normal solar wind have been observed behind interplanetary shocks and also without shocks. In this paper we have selected four well-known transient interplanetary signatures, namely: magnetic clouds, helium enhancements and bidirectional electron and ion fluxes, found in the solar wind behind shocks, and undertaken a correlative study between them and the corresponding solar observations. We found that although commonly different signatures appear in a single interplanetary transient event, they are not necessarily simultaneous, that is, they may belong to different plasma regions within the ejecta, which suggests that they may be generated by complex processes involving the ejection of plasma from different solar regions. We also found that more than 90% of these signatures correspond to cases when an Hα flare and/or the eruption of a filament occurred near solar central meridian between 1 and 4 days before the observation of the disturbance at 1 AU, the highest association being with flares taking place between 2 and 3 days before. The majority of the Hα flares were also accompanied by soft X-ray events. We also studied the longitudinal distribution of the associated solar events and found that between 80% and 90% of the interplanetary ejecta were associated with solar events within a longitudinal band of ±30° from the solar central meridian. An east-west asymmetry in the associated solar events seems to exist for some of the signatures. We also look for coronal holes adjacent to the site of the explosive event and find that they were present almost in every case.Key words. Interplanetary physics · Interplanetary shocks · Solar wind plasma · Solar physics · Flares and mass ejections
Highlights
The origin of large-scale transient phenomena in the solar wind was initially attributed toares at the Sun [see for instance Hundhausen (1972) and the review by Gosling (1993)], but later associations with prominence eruptions were found (e.g. Joselyn and MacIntosh, 1981)
After the discovery of coronal mass ejections (CMEs) (e.g. Tousey, 1973; Gosling et al, 1974) a combined study of the Helios spacecraft solar wind measurements and the observations of the Solwind coronagraph on board the P78-1 satellite showed that IP shocks were virtually always associated with CMEs (Sheeley et al, 1985), the majority of CMEs are not associated with IP shocks
A statistical study carried out by Harrison (1994) of the CMEs observed by the Solar Maximum Mission (SMM) satellite in 1986 and 1987 showed that only 14% of them were associated with an X-rayare within a temporal window of 2 h centred on the ®rst moment of observation of the CME and within 50° from the limb
Summary
The origin of large-scale transient phenomena in the solar wind was initially attributed toares at the Sun [see for instance Hundhausen (1972) and the review by Gosling (1993)], but later associations with prominence eruptions were found (e.g. Joselyn and MacIntosh, 1981). In the IPS study period we looked for the events where a plasma cloud (a region of enhanced density) and/or magnetic cloud was present behind a transient shock according to satellite observations, and found such clouds only in 40% of the cases (Bravo and Lanzagorta, 1994). This has been explained by arguing that the angular extension of the shock is much wider than that of the associated piston (Borrini et al, 1982a; Richardson and Cane, 1993). In this paper we took a set of 108 IP events taken from the literature where dierent transient signatures (magnetic clouds, helium enrichments and bidirectional electrons and ions) were observed in the solar wind behind shocks in the ecliptic plane at $1 AU to study the dierent combinations of signatures in each IP transient event, and look for their possible association with near-surface solar eruptive events
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