Flare-associated Disturbances Research Articles

Spatial structure of flare‐associated perturbations in the solar wind simulated by a two‐dimensional numerical MHD model

The dynamic behavior of flare‐associated disturbances has been investigated using a time‐dependent two‐dimensional MHD numerical model for a one‐fluid solar wind with adiabatic expansion. Simulations of the development and propagation of perturbations have been performed between 18 Rs and 226 Rs (where Rs= solar radius) in an angular sector of the equatorial plane of the sun 90° wide. Several test computations have been carried out with different initial pulse characteristics. These pulses are set arbitrarily at the inner boundary assuming that a shock wave is already formed. The parameters are the velocity of the shock front, the angular width of the perturbation, and its time duration at 18 Rs. It is shown that in every case the time delay between 18 Rs and 226 Rs depends on the total amount of energy released by the prototype flare (hence in the pulse). This dependence is stronger with the initial velocity than with the angular width. Also it appears that the shock wave propagates according to a power law of time: R=atb. After a relatively short time the expansion of the wave is dominated by the internal energy so that the longitudinal extent of the perturbation at 1 AU seems to be only a function of the time elapsed after the arrival of the front shock at this distance. The existence of a reverse shock which is formed after a few hours is shown to last a time long enough to reach 1 AU. Its longitudinal extension is limited to the area around the flare central meridian where the pressure gradient induced by the initial condition is strong enough.

Motion of the sources for type II and type IV radio bursts and flare-associated interplanetary disturbances

Shock waves are indirectly observed as the source of type 2 radio brusts, whereas magnetic bottles are identified as the source of moving metric type 4 radio bursts. The difference between the expansion speeds of these waves bottles is examined during their generation and propagation near the flare regions. It is shown that, although generated in the explosive phase of flares, the behavior of the bottles is quite different from that of the waves and that the speed of the former is generally much lower. It is shown that the transit times of disturbances between the sun and the earth give information about the deceleration of shock waves to their local speeds observed near the earth's orbit. A brief discussion is given on the relationship among magnetic bottles, shock waves near the sun, and flare-associated disturbances in interplanetary space.

Expansion Pattern of Flare-associated Disturbances near the Earth's Orbit during October 23 to November 4, 1968

A series of solar flares accompanying type II and type IV radio bursts were observed while the active region McMath No. 9740 was on the solar disk during October 23 to November 4, 1968. Most of these flares were also associated with solar cosmic rays and SSC geomagnetic storms1. More than ten times of SSC storms were observed on the Earth during this period. Their source flares were identified by using solar and geomagnetic data (refs 2, 3 and K. S. and J. K. Chao, to be published). From these identified records, I estimate the transit times of flare-associated disturbances between the Sun and the Earth.

Simulation of driven flare-associated disturbances in the solar wind

The dynamics of nonspherical flare-associated disturbances are considered when the outflow of energetic material at 0.1 AU, which gives rise to the disturbance, is maintained for an arbitrary period of time. The propagation of such disturbances into the interplanetary medium is examined under conditions of different total disturbance energies, energy flux densities, and sizes of the disturbance region at 0.1 AU. The development of these disturbances is followed by using numerical solutions of time dependent two-dimensional hydrodynamic flow in spherical coordinates. Decreasing the total disturbance energy by reducing its duration produces an increase in transit time to 1 AU, ranging from ~37 hours for Eioi= 2.9 x 1032 ergs to 58 hours for Etot= 2.8 x 1030 ergs, all for disturbances contained initially in a cone of a half angle equal to 15 deg . Variation of energy flux density at O.1 AU shows that disturbances of constant total energy propagate to 1 AU more slowly as the flux density at 0.1 AU decreases. Disturbances that differ only in the area that contains the outflow at 0.1 AU reflect this condition in the shock front shapes at larger heliocentric distances, smaller initial areas resulting in shock fronts with a smallermore » radius of curvature at 1 AU.« less

Two-dimensional simulation of flare-associated disturbances in the solar wind

The propagation of flare-associated disturbances through the interplanetary medium is examined by using numerical solutions of time-dependent two-dimensional hydrodynamic flow in spherical coordinates. The study is limited to blast wave phenomena, and the dependence on initial disturbance energy and angular extent is examined. For constant energy disturbances initially occupying cones of half angle up to ∼15° at 0.1 AU, the angular dependence of the transmit time to 1 AU and of the shock shape at 1 AU is very small. For disturbance energies at 0.1 AU of a few times 1030 ergs, transit times to 1 AU are ∼65 hours. The calculated disturbance shapes at 1 AU and the transit times are found to be in good agreement with the observational data.