|Smaller Scales: Five Physical Processes|
The interplanetary medium is a restless, changing medium that is very dynamic. We can draw an analogy with a river:
The large scales are bounded by banks; there may be islands about which the river flows, forming a bow wave; and there are even fast and slow streams within the river, due to deep or shallow channels. We can liken shocks to the passage of bores, which are surge waves caused by a narrowing of the river and consequent increase in the water level from minimum to maximum. In a bore the flow reverses direction, and changes from smooth to choppy and turbulent.
As we look at the river on smaller and smaller scales, we see vortices and waves, sometimes steep and cresting, sometimes like ripples. Twigs and leaves can be carried in a highly stochastic fashion, twisted and turned by the small-scale waves and turbulence on the river surface. As with the river, the small-scale character of the solar wind is ever changing and often highly complex.
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