| 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 adaptive-grid
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. |