Interplanetary shock waves generated by solar flares

Abstract

Recent observational and theoretical studies of interplanetary shock waves associated with solar flares are reviewed. An attempt is made to outline the framework for the genesis, life and demise of these shocks. Thus, suggestions are made regarding their birth within the flare generation process, MHD wave propagation through the chromosphere and inner corona, and maturity to fully-developed coronal shock waves. Their subsequent propagation into the ambient interplanetary medium and disturbing effects within the solar wind are discussed within the context of theoretical and phenomenological models. The latter -based essentially on observations -are useful for a limited interpretation of shock geometric and kinematic characteristics. The former -upon which ultimate physical understanding depends -are used for clarification and classification of the shocks and their consequences within the solar wind. Classification of limiting cases of blast-produced shocks (as in an explosion) or longer lasting ejecta (or 'piston'-driven shocks) will hopefully be combined with the study of the flare process itself.The theoretical approach, in spite of its contribution to clarification of various concepts, contains some fundamental limitations and requires further study. Numerical simulations, for example, depend upon a non-unique set of multi-parameter initial conditions at or near the Sun. Additionally, the subtle but important influence of magnetic fields upon energy transport processes within the solar wind has not been considered in the numerical simulation approach. Similarity solutions are limited to geometrical symmetries and have not exploited their potential beyond the special cases of the blast and the constant-velocity, piston-driven shock waves. These continuum fluid studies will probably require augmentation or even replacement by plasma kinetic theory in special situations when observations indicate the presence of anomalous transport processes. Presently, for example, efforts are directed toward identification of detailed shock structures (as in the case of Earth's bow shock) and of the disturbed solar wind (such as the piston).Further progress is expected with extensive in situ and remote monitoring of the solar wind over a wide range of heliographic radii, longitudes and latitudes.

Arrival times of Flare/Halo CME associated shocks at the Earth: comparison of the predictions of three numerical models with these observations

“…it was assumed that the leading edge of the white light CME was coincident with the shock surface). In this case, the lower speed V s which was not used was assumed to represent the lower, slower, coronal speed of the selfsimilarly expanding quasi-hemispherical shock (Dryer, 1974).…”

“…The initial explosion (flare) drives a shock at what is assumed to be a constant speed (V s ) for a specified length of time τ estimated using X-ray duration measurements. Details are given by Dryer (1974); Dryer and Smart (1984); Smart et al ( , 1986; Smart and Shea (1985); Lewis and Dryer (1987) and Smith, Dryer and Armstrong (1993). The shock, thereafter, decelerates to a blast wave as it expands outwards (with V s ∼ R −1/2 , where R is the heliocentric radius).…”

Propagation of a spheromak: 1. Some comparisons of cylindrical and spherical magnetic clouds

“…We give, in Table 1, the steady state solar wind parameters used in these studies. When a magnetic cloud is introduced with a speed higher than the ambient, then its body (within r < r•) has this speed and the velocity falls smoothly down to the ambient speed within its envelope (r, < r < r by Dryer [1974]). Basically, this standoff distance is a function of the geometrical divergence.…”

Regarding the detectability and measurement of coronal mass ejections

“…It later emerged that these ''fast transient events'' had been observed on the ground for decades (DeMastus et al 1973). They were quickly associated with interplanetary shocks that had been measured by in-situ spacecraft since the early Space Age , and identified by many as blast waves from solar flares (e.g., Dryer 1974). While the latter has now been debunked (see the paper by Gosling (1993) and the many papers surrounding the famous ''solar flare myth'' debate), the former is generally accepted to be a correct association.…”