what does baroclinic mean?

[JonathanBelles]

(topic)

[wxmann_91]

"The term "baroclinic" refers to the mechanism by which vorticity is generated. Vorticity is the curl of the velocity field. in general, the evolution of vorticity can be broken into contributions from advection (as vortex tubes move with the flow), stretching and twisting (as vortex tubes are pulled or twisted by the flow) and baroclinic vorticity generation, which occurs whenever there is a density gradient along surfaces of constant pressure. Baroclinic flows can be contrasted with barotropic flows in which density and pressure surfaces coincide and there is no baroclinic generation of vorticity."

http://en.wikipedia.org/wiki/Baroclinic_instability


"BAROCLINICITY- A cold air advection/warm air advection couplet that increases atmospheric instability. On analysis and forecast charts it is the isotherms crossing the height contours. "

http://www.theweatherprediction.com/jargon/


Simply stated, when you hear the term "baroclinic system", it means it's a midlatitude cyclone that derives its energy from temperature changes in the atmosphere and resultant instability from that change.

This is going to dynamic meteorology, which I'm not really good at, but I hope it helps a little.

[JonathanBelles]

thanx

[Derek Ortt]

baroclinic itself means that the fluid does not have a constant density (The Holton text book uses the definition of not a constant temperature... which is equivalent using the Ideal Gas Law); thus, there is a thermal wind associated with it (thermal wind is fancy for good old fashioned wind shear)

[DrCloud]

Ah, er, um ... In its most basic "baroclinic" means not constant with height/pressure (it's used in this sense to contrast with "barotropic", which is constant with height/pressure).

"Baroclinicity" refers to height variations that tend toward barclinic instability (as in "Yes, Bill, there's a lot of baroclinicity over western Canada today..."); and the process of baroclinic instability, what leads to mid-latitude storms (instabilities on the Jet Stream), requires that there be variations with height/pressure. One way to look at this is that you can't simulate baroclinic instability with a one-layer model; you need a two-layer model at least.

So, these other answers are right; but they started in the middle instead of at the beginning. HPH

[Wthrman13]

One can look at baroclinic instability (the type of instability that many large-scale atmospheric flows develop from) as the atmosphere redistributing itself on a large scale in such a way that it lowers its center of mass. Essentially if the north-south temperature gradient is large enough, a small wave or disturbance that is superimposed upon this gradient will be able to extract energy from the N-S temperature gradient in such a way that it redistributes the mass of the large-scale atmosphere. That is, the growing wave will cause warm air to rise (and move northward), and cold air to sink (and move southward). In doing so, the center of mass of the large-scale atmosphere is lowered, and the associated reduction in potential energy is converted to the kinetic energy of the wave. In order for this to happen and to get a growing disturbance, the wavelength of the disturbance has to be within a certain range of values (it can't be too small or too large), and the large-scale north-south gradient in temperature has to be large enough. If the wave isn't the right size, or the temperature gradient is too weak, baroclinic instability won't form. In practice, there are so many disturbances in the atmosphere in regions of strong north-south temperature gradients that one of them is bound to develop provided the gradient is strong enough. This is pretty much all that is going on when you see a developing extratropical cyclone. What the cyclone is telling you is something along the lines of "Hey! The horizontal temperature gradient in this region is getting too large, I need to even things out a bit!".

Obviously this is a greatly simplified sketch of baroclinic instability, but it's fundamentally nothing more than one of the atmosphere's myriad ways of redistributing imbalances in energy.