Relativistic jets in Galactic superluminals and extragalactic active galactic nuclei may be surrounded by a wind near the central engine. Theoretical analysis and numerical simulation reveal considerable stabilization of relativistic jet flow by a wind to helical and higher order asymmetric modes of jet distortion. When velocities are measured in the source (inlet) frame, reduction in the absolute velocity difference between jet and wind, △v = v_(jet) - v_(wnd), provides stabilization in addition to stabilization provided by a high jet Lorentz factor, but a high Lorentz factor wind is not needed to stabilize a high Lorentz factor jet. However, the fundamental pinch mode is not similarly affected, and knots with spacing a few times the jet radius are anticipated to develop in such flows. Thus, we identify a mechanism that can suppress large-scale asymmetric structures while allowing axisymmetric structures to develop. Relativistic jets surrounded by outflowing winds will be more stable than if surrounded by a stationary or backflowing external medium. Knotty structures along a straight jet like that in 3C 175 could be triggered by pinching of an initially low Mach number jet surrounded by a suitable wind. As the jet enters the radio lobe, suppression of any surrounding outflow or backflow associated with the high-pressure lobe triggers exponential growth of helical twisting.
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