WRAL WeatherCenter Blog

I am curious about the relationship of the jet stream and high and low pressure systems. Does the ripple of the jet create the pressure systems like eddys in flowing water? Or do the pressure systems cause the jet to bend around them?

Posted May 2, 2007

MIKE MOSS SAYS:     Britt,     One of the great challenges of weather forecasting is that it's not so much "or" as "and." The jet stream and areas of relatively low and high pressure both at the same altitude and down near the surface of the earth are all part of the same 3-dimensional blanket of air surrounding the planet, and are not separate, independent entities in the way that we sometimes tend to simplify them. This introduces something of a "chicken and egg" dilemma referred to in fluid dynamics (and other areas of physics where it is an issue) called "nonlinearilty." In this case, the jet stream is both modulated by the pressure and temperature fields that surround it, and also influences the movement and intensity of those pressure fields and the distribution of temperatures that help to strengthen or weaken them. Throw in the effects of flow across mountain chains, oceans and other topographic features, and the very important heating, cooling and radiative tranfer effects of the various transitions of water between gaseous, liquid and solid forms (including clouds and precipitation) and you have a very complex set of problems to solve in making a weather forecast, whether qualitatively through human analysis and prognostication, or numerical prediction using finite-differencing or spectral versions of the equations of motion and numerous other mathematical representations (some theoretical or "first principles" in nature, and others empirically based) of the physics involved.

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