Date: Wed, 25 Oct 2000 09:30:09 -0500 From: "Peter Banacos" X-Accept-Language: en MIME-Version: 1.0 To: John Molinari CC: David Schultz , map@atmos.albany.edu, map_disco@nssl.noaa.gov, ddowell@ou.edu, hblue@ou.edu, wicker@nssl.noaa.gov, doswell@nssl.noaa.gov Subject: Re: [Map_disco] Re: map discussion items: The Kicker and the Kickee Content-Transfer-Encoding: 7bit Dave, I resort to the argument I made in weather briefing yesterday. The first-order effect in "forcing" a cut-off low to move may be as simple as inducing flow over (i.e. in the vicinity of) the cut-off. I think Dr. Molinari refers to this below. What is true of a cut-off? It's essentially a vort max but the parallelism between the isovorts and the horizontal wind implies vorticity advection is near zero, and no significant height changes occur (through QG reasoning). Additionally, the basic current is light or small in comparison to the flow associated with the perturbation. The cut-off can transition to an "open wave" simply by strengthening the basic flow over it (this does not require the cut-off to weaken!). The approach of the upstream trough likely induces stronger flow (generally swly or wswly) over the cut-off from a significant distance, and the kickee transitions from a cut-off to an open wave where horizontal advection of vorticity resumes. The system then moves through QG height-tendency arguments. From your diagnostics Dave, it appears most of the vorticity advection associated with the kicker remains well upstream of the kickee. However, the cut-off possesses ample vorticity, and it only needs to become embedded in a stronger basic current for horizontal vorticity advection to be realized. We need a way to divide the wind field into components associated with the cut-off and the "mean" flow to test this. Pete John Molinari wrote: > Dave, > > Excellent questions on Henry's rule. I have often wondered about > the process by which one trough "kicks out" another. My view (which is > relatively uninformed--I think about the tropics!) is that the PV arguments > may be the easiest to understand, i.e., there are no simpler diagnostics > than a (QG) PV inversion. If the upstream trough gets close enough to > advect the other, i.e., to induce winds over the other, that would be the > reasoning that is easiest to understand. PV is really the ultimate > synoptician's tool. But that explanation is almost a kinematic one, and > the "real" dynamical reason may involve complex wave-wave > interactions. That may be territory that theoreticians have not yet worked > out, involving multiple scales of motion interacting. It seems that even > the most common synoptic behaviors are not easy to account for by existing > theory. That has certainly been my experience in the subtropics. > Keep asking the good questions! > > Cheers, > John > _______________________________________________