OKpowdah Posted November 16, 2012 Share Posted November 16, 2012 Question for anyone with ideas. Given a model forecast field of frontogenesis, what is an easy, accurate, and useful way of determining *in the model* the instantaneous pivot point of a defined band of frontogenesis? Link to comment Share on other sites More sharing options...
OKpowdah Posted November 16, 2012 Author Share Posted November 16, 2012 I'm thinking of a product that would literally plot a point at the instantaneous location of pivoting Link to comment Share on other sites More sharing options...
heavy_wx Posted November 16, 2012 Share Posted November 16, 2012 Maybe you could calculate the change in frontogenesis with time and then find the location of minimum change in frontogenesis that is located within a band of frontogenesis. You could probably select a minimum threshold value for frontogenesis and then search through all the locations that are above that threshold, with the pivot point being where the time rate of change of frontogenesis is the smallest. I think some kind of ncl script to do this would be the best bet. Link to comment Share on other sites More sharing options...
OKpowdah Posted November 16, 2012 Author Share Posted November 16, 2012 Maybe you could calculate the change in frontogenesis with time and then find the location of minimum change in frontogenesis that is located within a band of frontogenesis. You could probably select a minimum threshold value for frontogenesis and then search through all the locations that are above that threshold, with the pivot point being where the time rate of change of frontogenesis is the smallest. I think some kind of ncl script to do this would be the best bet. The issue with that is then dealing with the Lagrangian rate of the change of frontogenesis ... where it is strengthening and weakening within the band itself What I'd like to do, I think, is treat a line of frontogenesis like a material curve, and analyze how it advects and deforms ... figuring out how to do that in the model is the tricky part .. I think... Link to comment Share on other sites More sharing options...
dendrite Posted November 16, 2012 Share Posted November 16, 2012 Maybe you could calculate the change in frontogenesis with time and then find the location of minimum change in frontogenesis that is located within a band of frontogenesis. You could probably select a minimum threshold value for frontogenesis and then search through all the locations that are above that threshold, with the pivot point being where the time rate of change of frontogenesis is the smallest. I think some kind of ncl script to do this would be the best bet. Frontogenesis can technically be increasing or deceasing in a stationary band though. Link to comment Share on other sites More sharing options...
forkyfork Posted November 16, 2012 Share Posted November 16, 2012 just draw it Link to comment Share on other sites More sharing options...
dendrite Posted November 16, 2012 Share Posted November 16, 2012 The issue with that is then dealing with the Lagrangian rate of the change of frontogenesis ... where it is strengthening and weakening within the band itself What I'd like to do, I think, is treat a line of frontogenesis like a material curve, and analyze how it advects and deforms ... figuring out how to do that in the model is the tricky part .. I think... Most of our bands seem to be influenced mostly by the confluence and shear terms of the equation. Have you tried playing around with plotting deformation or axes of dilatation with frontogenesis? Link to comment Share on other sites More sharing options...
ORH_wxman Posted November 16, 2012 Share Posted November 16, 2012 Usually the area where max deformation takes place at H5 is where the pivot point is. You can eyeball it frequently on where you see the greatest divergence in the height lines. That's a pretty rudimentary way to do it, but it works. Especially in rapidly deepening systems. In more marginal cases it is not so obvious. Link to comment Share on other sites More sharing options...
ORH_wxman Posted November 16, 2012 Share Posted November 16, 2012 Looking at EPV maps gives an indication as well. Frequently in deepening systems, the minimum in EPV will be where the max deformation and frontogenesis lines up and that is where the banding will setup for several hours. Link to comment Share on other sites More sharing options...
OKpowdah Posted November 16, 2012 Author Share Posted November 16, 2012 I understand how these relationships work qualitatively. I'm trying to think of the best way to determine physically in the model where the pivot point is and plot it over time. Link to comment Share on other sites More sharing options...
ORH_wxman Posted November 16, 2012 Share Posted November 16, 2012 I understand how these relationships work qualitatively. I'm trying to think of the best way to determine physically in the model where the pivot point is and plot it over time. Plot 5h wind vectors. That is probably the best crude way without overlaying a bunch of parameters. Its not easy...that's why bands aren't predicted in an exact spot very well. Link to comment Share on other sites More sharing options...
OKpowdah Posted November 17, 2012 Author Share Posted November 17, 2012 Most of our bands seem to be influenced mostly by the confluence and shear terms of the equation. Have you tried playing around with plotting deformation or axes of dilatation with frontogenesis? yeah, and that's why I feel pretty comfortable at least treating the frontogenesis band as a material line. From there the easiest thing to do might just be analyze for a storm-relative minimum wind velocity along the band. I've also thought about fooling around with calculating the moment of inertia within the band and investigating what if any relationship exists Link to comment Share on other sites More sharing options...
OKpowdah Posted November 17, 2012 Author Share Posted November 17, 2012 Plot 5h wind vectors. That is probably the best crude way without overlaying a bunch of parameters. Its not easy...that's why bands aren't predicted in an exact spot very well. The big challenge is quantifying this in a model. I can look at products that you describe and analyze for myself, but I'm trying to figure out the best way for a model to plot this ... in the end I envision an ensemble of pivot points plotted over time, maybe a density / probability field Link to comment Share on other sites More sharing options...
CoastalWx Posted November 17, 2012 Share Posted November 17, 2012 Looking at EPV maps gives an indication as well. Frequently in deepening systems, the minimum in EPV will be where the max deformation and frontogenesis lines up and that is where the banding will setup for several hours. Are there any good maps out there for that? Most of the time I look at theta-e or potential temp on BUFKIT and you can assume from that. Link to comment Share on other sites More sharing options...
Amped Posted November 17, 2012 Share Posted November 17, 2012 The bands also don't seem to have an exact pivot point. The motion is quite complex. Hires Sim reflectivity animation on the ewall site should tell you a lot in the short range. So will the animated HRRR. Link to comment Share on other sites More sharing options...
OceanStWx Posted November 17, 2012 Share Posted November 17, 2012 Are there any good maps out there for that? Most of the time I look at theta-e or potential temp on BUFKIT and you can assume from that. I would love a nice map online somewhere too, always kills me when I'm away from AWIPS and can't use my EPV procedures. Otherwise I'm stuck trying to visualize it in my heard through separation or folding of isentropes. Link to comment Share on other sites More sharing options...
heavy_wx Posted November 17, 2012 Share Posted November 17, 2012 The issue with that is then dealing with the Lagrangian rate of the change of frontogenesis ... where it is strengthening and weakening within the band itself What I'd like to do, I think, is treat a line of frontogenesis like a material curve, and analyze how it advects and deforms ... figuring out how to do that in the model is the tricky part .. I think... You could use a coordinate system along the long and short axes of the band of frontogenesis to determine the Lagrangian (moving grid) rate of change of frontogenesis for different locations within the band. These locations could be put into a matrix with the row and column indicating the position relative to the center of the band, where the short and long axes would intersect. At the next time step, you could subtract the Lagrangian change in frontogenesis at each point relative to the band axes from the Eulerian (static grid) change in frontogenesis to get basically the advection of frontogeneis. The minimum in the absolute value of advection of frontogenesis would be the location of the pivot point. Link to comment Share on other sites More sharing options...
heavy_wx Posted November 17, 2012 Share Posted November 17, 2012 I would love a nice map online somewhere too, always kills me when I'm away from AWIPS and can't use my EPV procedures. Otherwise I'm stuck trying to visualize it in my heard through separation or folding of isentropes. http://www.hpc.ncep.noaa.gov/mdd/mddoutput/ This site has some pretty good diagnostics including EPV. Link to comment Share on other sites More sharing options...
Ginx snewx Posted November 17, 2012 Share Posted November 17, 2012 I would love a nice map online somewhere too, always kills me when I'm away from AWIPS and can't use my EPV procedures. Otherwise I'm stuck trying to visualize it in my heard through separation or folding of isentropes. I do not know if this is what you are looking for but EPV is displayed under winter weather fields here http://www.spc.noaa.gov/exper/mesoanalysis/new/mobile.php Link to comment Share on other sites More sharing options...
OceanStWx Posted November 17, 2012 Share Posted November 17, 2012 I do not know if this is what you are looking for but EPV is displayed under winter weather fields here http://www.spc.noaa..../new/mobile.php I've used that before for nowcasting purposes, unfortunately there is no forecast with the mesoanalysis page. http://www.hpc.ncep..../mdd/mddoutput/ This site has some pretty good diagnostics including EPV. I had no clue they got that detailed with model output there. Now if only they did cross sections... Link to comment Share on other sites More sharing options...
Ginx snewx Posted November 17, 2012 Share Posted November 17, 2012 I like the Site Osu posted, there is another similar one I have bookmarked on my work PC. As far as Sam's quest, the Hart banding site might be useful. Link to comment Share on other sites More sharing options...
CoastalWx Posted November 17, 2012 Share Posted November 17, 2012 I totally forgot about that HPC page. Link to comment Share on other sites More sharing options...
ORH_wxman Posted November 17, 2012 Share Posted November 17, 2012 I wish the graphics on the HPC site were better, I've used that one before...but the graphics are kind of crude. Its nice to be able to zoom in with EPV. Link to comment Share on other sites More sharing options...
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