Slow shock interactions in the heliosphere using an adaptive grid MHD model

Abstract

Abstract.A one-dimensional (1-D), time-dependent, adaptive-grid MHD model with solar wind structure has been used in the past to study the interaction of shocks. In the present study, we wish to study some fundamental processes that may be associated with slow shock genesis and their possible interactions with other discontinuities. This adaptivegrid model, suitable for appropriate spatial and temporal numerical simulations, is used for this purpose because its finer grid sizes in the vicinity of the steep gradients at shocks make it possible to delineate the physical parameters on both sides of the shocks. We found that a perturbation with deceleration of solar wind will generate an ensemble consisting of a forward slow shock, a fast forward wave and a reverse slow shock. On the other hand, a perturbation with an increase in acceleration of solar wind will generate both a slow shock and a fast shock. These two perturbations, although not unique, may be representative of momentum and pressure changes at the solar surface.During the transition of a fast shock overtaking a slow shock from behind, the slow shock might disappear temporarily. Also, during the process of the merging of two slow shocks, a slow shock-like structure is formed first; later, the slow shock-like structure evolves into an intermediate shock-like structure. This intermediate shock-like structure then evolves into an intermediate wave and a slow shock-like structure. Finally, the slow shock-like structure evolves into a slow shock, but the intermediate wave disappears by interacting with the non-uniform solar wind. This complex behavior demonstrates the non-unique nature of the formation of slow shocks, intermediate shocks and their derivative structures.We emphasize the main aim of this work to be both: (a) non-unique input physical parameters to explain the paucity of observed slow shocks, as well as (b) the impossibility of backward tracing to the history of input boundary conditions in view of the present inability to describe unambiguous inputs at the Sun.

Magnetohydrodynamic waves within the medium separated by the plane shock wave or rotational discontinuity

“…Though the free path of solar wind particles is of the order of 1 AU, which, strictly speaking, means that the solar wind is a collisionless plasma, the MHD approximation is often used in studying the processes in the solar wind. For example, Wu et al (2005) have used this approximation in the analysis of the evolution of slow shock waves and their interactions with other discontinuities in the heliosphere. The MHD approximation was utilised in most of the above-mentioned works by exploring the interaction of perturbations with MHD shock waves.…”

The evolution of shocks near the surface of Sun during the epoch of Halloween 2003

“…They found that a FSS can be destroyed by a forward fast shock (FFS) that overtakes it from behind and the strength of a FSS is decreased by following an FFS. During the transition of a fast shock's overtaking a slow shock from behind, the slow shock might disappear temporarily (Wu et al, 2005a). The study of Wu et al (2005a) also shows that during the process of the merging of two slow shocks, a slow shock-like structure is formed first; later, the slow shock-like structure evolves into an intermediate shock-like structure.…”

“…During the transition of a fast shock's overtaking a slow shock from behind, the slow shock might disappear temporarily (Wu et al, 2005a). The study of Wu et al (2005a) also shows that during the process of the merging of two slow shocks, a slow shock-like structure is formed first; later, the slow shock-like structure evolves into an intermediate shock-like structure. This intermediate shock-like structure then evolves into an intermediate wave (IW) and a slow shock-like structure.…”

“…In this paper, we use the same one-dimension, time-dependent, adaptive-grid, MHD model with a representative solar wind structure which was used by the previous workers (Wu et al, 1996a(Wu et al, ,b, 2004a(Wu et al, , 2005a to study the evolution and interaction of both slow and fast shocks from the surface of Sun through the heliosphere.…”

Numerical study of successive CMEs during November 4–5, 1998

“…The interaction of a shock with a magnetic cloud, the interaction of two shocks, and the interaction of two clouds have also been numerically modeled in the last 10 years [14][15][16][17][18][19][20][21][22][23] . Different physical phenomena occur during the propagation of a second, faster CME overtaking a first, slower CME.…”