A discontinuity in which the magnetic field has no component normal to the discontinuity surface is called a tangential discontinuity. The kinetic theory of the internal structure of interplanetary tangential discontinuities has recently reached a level of maturity (DeKeyser and Roth , 1997) that allows meaningful comparison between theoretical predictions and in-situ observations without constraining all of the model parameters. In order to remove some of the theoretical ambiguities, very high time resolution plasma and magnetic field observations are necessary. The Plasma-Mag instrumentation will provide such a data set, significantly contributing to kinetic theory modeling efforts.
The high-time resolution plasma and magnetic field instruments onboard Triana will open a window into the inner structures of weak- and slow-interplanetary shocks, which should lead to a better understanding of their formation and dissipation mechanisms. Interplanetary shocks have been studied for a very long time. Even the internal structure of MHD shocks is comparatively well understood primarily from Earth bow-shock observations. However, very little is known about the structural variations due to the various types of MHD shock. The Earth's bow shock will provide Triana an excellent opportunity to study fast reverse strong MHD shocks. Interplanetary shocks may be too difficult to study from Triana, because their much greater speed past the spacecraft leaves too little time for reliable measurements.