Coupling of macroscopic and small scale phenomena

Collisionless microscopic phenomena such as anomalous resistivity, particle acceleration and heat conduction have been successfully treated by particle simulations. Such simulations are usually restricted to volume elements and time scales that are small compared to global scales or even the space and time steps in macroscopic codes. Despite the recent code advances and increases in computing power, it remains necessary to determine the effect of macroscopic dynamics on small scale phenomena and vice versa. The sensitivity of microscopic simulation results to macroscopic boundary conditions is demonstrated. Macroscopic codes, on the other hand, are examined for their dependence on microscopic details. The consequences for the design and analysis of simulation experiments in space physics are discussed. Combining macroscopic and microscopic aspects in a single simulation, despite the usual disparity of scales, will remain a challenging problem.