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It is generally accepted that CMEs result from eruptions of magnetic fluxropes, which are dubbed as magnetic clouds in interplanetary space. Thecomposition (including the ionic charge states and elemental abundances) isdetermined prior to and/or during CME eruptions in the solar atmosphere, anddoes not alter during magnetic cloud propagation to 1 AU and beyond. It hasbeen known that the composition is not uniform within a cross sectionperpendicular to magnetic cloud axis, and the distribution of ionic chargestates within a cross section provides us an important clue to investigate theformation and eruption processes of flux ropes due to the freeze-in effect. Theflux rope is a three dimensional magnetic structure intrinsically, and itremains unclear whether the composition is uniform along the flux rope axis asmost magnetic clouds are only detected by one spacecraft. In this paper wereport a magnetic cloud that was observed by ACE near 1 AU on 1998 March 4--6and Ulysses near 5.4 AU on March 24--28 sequentially. At these times, bothspacecraft were located around the ecliptic plane, and the latitudinal andlongitudinal separations between them were $\sim$2.2$^{\circ}$ and$\sim$5.5$^{\circ}$, respectively. It provides us an excellent opportunity toexplore the axial inhomogeneity of flux rope composition, as both spacecraftalmost intersected the cloud center at different sites along its axis. Ourstudy shows that the average values of ionic charge states exhibit significantdifference along the axis for carbon, and the differences are relatively slightbut still obvious for charge states of oxygen and iron, as well as theelemental abundances of iron and helium. Besides the means, the compositionprofiles within the cloud measured by both spacecraft also exhibit somediscrepancies. We conclude that the inhomogeneity of composition exists alongthe cloud axis.

The Inhomogeneity of Composition along the Magnetic Cloud Axis