Solar wind observations associated with a slow forward shock wave at 0.31 AU

Abstract

A slow forward shock-type discontinuity observed by Helios 1 on day 147, 1980, at 0.31 AU is analyzed in detail, employing high-resolution (40.5 s) plasma and magnetic field measurements. It is shown within the bounds of uncertainties in the various parameters (1) that this event is not an MHD discontinuity, as the total pressure balance is violated and as the entropy increases across this structure even after inclusion of the alpha particles, (2) that the Hada-Kennel relations, i.e., Ti/Te < 1 and/3 < 1, are satisfied upstream of this event even after inclusion of the alpha particles, indicating that steepening of MHD slow waves dominates Landau damping, (3) that the Rankine-Hugoniot relations are fulfilled to an absolute difference of <10 -5 by employing any possible combination of an upstream with a downstream time-averaged data set, (4) that the MHD evolutionary conditions are satisfied for any solution to the jump conditions, and (5) that the shock speed, the amplitudes, and the relative amplitudes associated with this event are absolutely comparable to those derived earlier for fast mode shock waves within 1 A U. It is shown that this event is an almost quasi-perpendicular slow forward MHD shock wave. INTRODUCTIONFirst observational evidence on the possibility that slow mode MHD shock waves might actually be present in the interplanetary medium was given by Chao and Olbert [ 1970], who presumably identified two slow forward shocks, and by Burlaga and Chao [1971], who "most probably" found one reverse and one forward slow shock. More recently, Feldman et al. [1984] and Smith et al. [1984] provided partial evidence that the lobe-plasma sheet boundary in the central part of the distant geomagnetic tail is often a slow mode shock. Up to now, these examples of interplanetary slow shocks could be regarded as the more serious candidates in the sense (1) that all the plasma and magnetic field parameters necessary for their identification have been taken into account, and (2) that it has been shown that the observations do, within their bounds of uncertainties, fulfill both the Rankine-Hugoniot relations and the "evolutionary conditions" [e.g., Chao, 1970] for MHD shock waves.Two further yet rather essential tests in association with slow shocks, which actually have to be carried out before the optimization of the space probe data to the shock model, have, however, not been realized by these authors. First is to explicitly show that their events are not MHD discontinuities. A more comprehensive study of several slow mode shock-type discontinuities observed by the Helios space probes within 1 AU has unfortunately revealed that by including the alpha particles many of these events are MHD discontinuities rather than shock waves [e.g., Hsieh and . Second is to prove that by following the relations derived by Hada and Kennel [1985] the plasmadynamical conditions of the upstream medium do actually allow for a steepening rather than for a damping of MHD slow waves.

Shock parameter calculations at weak interplanetary shock waves

“…In fact the a tion that entropy increases at shocks measured in t has featured as a test in the identification of possib shocks. For instance Richter et al (1985) used a sim pression to expression 1 for precisely this use. Previo this Chao (1973) used a two component plasma exp with the added simplifying condition of quasi-neutr an investigation of non-linear wave steepening in th wind.…”

“…Previo this Chao (1973) used a two component plasma exp with the added simplifying condition of quasi-neutr an investigation of non-linear wave steepening in th wind. Smith and Burton method (Smith and Burton, 1988). Equation (1) (below) is used to check for entropy increases across the shock waves.…”

Theory and observation of double discontinuities

“…A small number of slow shocks have been observed in interplanetary space (Chao and Olbert, 1970;Burlaga and Chao, 1971;Richter et al, 1985;Whang et al, 1996) and in the magnetotail (Feldman et al, , 1985(Feldman et al, , 1987Smith et al, 1984;Seon et al, 1995;Saito et al, 1995Saito et al, , 1996.…”

Magnetic Energy Storage and Release

“…First of all , observational evidences have been found for the existence of slow shocks in interplanetary space (CHAO and OLBERT, 1970;BURLAGA and CHAD, 1971;RICHTER et al , 1985aRICHTER et al , , 1985bHUNDHAUSEN et al, 1987;RICHTER, 1988), and this has stimulated great enthusiasm for the investigation of slow shocks. Based on observations of coronal mass ejections (CMEs), HUNDHAUSEN et al (1987) suggested that slow shocks of concaveupward shapes may form for most CME events.…”