tokens: of TD. In addition, the vector displacement ( of the two spacecraft is (−270.40, −47.21, −30.48) R E . It can be seen that the dot product of the TD normal (−0.098, 0.961, 0.258) and the vector displacement is negative. This means that Wind should have observed the “TD” earlier than ACE . In fact, the ACE spacecraft has observed this “TD” earlier than Wind . Thus, this DD should not be a TD. If we consider the DD to be an IS, the calculated DD propagation speed is 349.1 km s −1 in the rest frame, and the corresponding estimated time difference is 73.6 minutes, which is also different with the observed time difference (93.7 minutes). Even so, we consider that the DD should be an IS rather than a TD. As for the time deviation of the IS model, it may be caused by the following two factors. One is that the shock front may be not flat; the estimated time difference is not accurate. The other may be that not all the parts of the leading boundary of the reconnection exhaust meet the requirements of an IS, and the IS may be formed only somewhere within the boundary, with Wind and ACE crossing different parts of the leading boundary. Figure 3. Magnetic fields measured by Wind and ACE in the GSE coordinate system, where the dotted lines are for ACE , and the ACE time sequences were shifted by 94.1 minutes. 4. SUMMARY Previously, ISs were considered to be unphysical because they do not satisfy the so-called evolutionary conditions based on the theory of hyperbolic systems of conservation laws (Jeffrey Taniuti 1964 ; Kantrowitz Petschek 1966 ). Over the past more than four decades, there have been a large number of numerical investigations for ISs. In spite of evolutionary conditions, ISs are commonly observed to be stable shocks in numerical simulations (e.g., Wu 1987 ; Wu Hada 1991 ; Takahashi et al. 2013 , 2014 ), and two interplanetary ISs have been observed and reported (Chao et al. 1993 ; Feng Wang 2008 ). However, both ISs were identified through fitting the R-H relations based on one spacecraft observation. Our previous study (Feng et al. 2007 ) suggested that the analysis using a single spacecraft observation based only on the R-H relations could misinterpret a TD as an IS. In this study, we reported an IS associated with a magnetic reconnection exhaust, which was detected by the Wind and ACE spacecraft at 1 au on 2000 August 9. We investigated this shock by fitting the R-H relations and referring to the ACE observations. We fitted this discontinuity using the procedure of Lin et al. ( 2006 ) and found that the observed magnetic field and plasma data satisfy the R-H relations well. The normal Alfvén-Mach number is greater than unity in the preshock state and less than unity in the postshock state; the fast-mode Mach number in upstream and downstream regions are less than unity, and both slow-mode Mach numbers are greater than unity. The components of the preshock and postshock magnetic fields in the shock front have opposite signs. Namely,
ner_tags: O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Mission O O O O O O O B-Mission O O O O B-Mission O O O O O O O B-Mission O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Mission O B-Mission O O O O O O O O O O O O O B-Mission O B-Mission O O O O O O O O O O O B-Mission O O O B-Mission O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation O O O O O O O O O B-Model I-Model O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O B-Model I-Model O O O O O O O O O O O O O O O O O O O O O O O O O B-Mission O B-Mission O O O O O O O O O O O O O O O B-Model I-Model O O O O B-Mission O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O B-Model I-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O