H2Otown_WX Posted November 28, 2011 Share Posted November 28, 2011 So I'm doing this assignment in which I have to diagnose areas of significant warm and cold air advection on 500 and 700 mb charts. I'm confusing myself because I had thought the strongest advection occurred when isoheights were perpendicular to isotherms but apparently it's the other way around? Or is there strong advection in both cases? In other words, as long as there is perpendicularity in some form, is the advection maximized? ThermalAdvection1.bmp Thermal Advection2.bmp Link to comment Share on other sites More sharing options...
H2Otown_WX Posted November 28, 2011 Author Share Posted November 28, 2011 Sorry for the crappy MS paint diagrams but this is about as good as I can do: Link to comment Share on other sites More sharing options...
heavy_wx Posted November 28, 2011 Share Posted November 28, 2011 Yes, advection is maximized when the height contours are perpendicular to the isotherms, assuming that the wind is geostrophic. This can be explained mathematically because thermal advection is related to the dot product of the temperature gradient and the wind vector and a dot product of two vectors is maximized when the vectors are 90 degrees apart. Link to comment Share on other sites More sharing options...
H2Otown_WX Posted November 28, 2011 Author Share Posted November 28, 2011 Yes, advection is maximized when the height contours are perpendicular to the isotherms, assuming that the wind is geostrophic. This can be explained mathematically because thermal advection is related to the dot product of the temperature gradient and the wind vector and a dot product of two vectors is maximized when the vectors are 90 degrees apart. Right, learned that in Vector Calculus recently..but you are saying both of those scenarios I painted would yield strong advection, not just the first one? Link to comment Share on other sites More sharing options...
heavy_wx Posted November 28, 2011 Share Posted November 28, 2011 Right, learned that in Vector Calculus recently..but you are saying both of those scenarios I painted would yield strong advection, not just the first one? Well it depends on the spacing of the isotherms and the height contours. The tighter the spacing, the greater the magnitude of the wind and temperature gradient will be. From the drawings you have, it looks like the isotherms are spaced further apart on the second image then the first image. The height contours look to have about the same spacing in both cases. So there would be greater thermal advection in the first case because the temperature gradient is greater and the wind magnitudes are the same. Link to comment Share on other sites More sharing options...
H2Otown_WX Posted November 28, 2011 Author Share Posted November 28, 2011 Well it depends on the spacing of the isotherms and the height contours. The tighter the spacing, the greater the magnitude of the wind and temperature gradient will be. From the drawings you have, it looks like the isotherms are spaced further apart on the second image then the first image. The height contours look to have about the same spacing in both cases. So there would be greater thermal advection in the first case because the temperature gradient is greater and the wind magnitudes are the same. Okay, that makes sense. I was just sort of rough-sketching those as examples of isotherms perpendicular to isoheights and vice versa. Would it be fair to say, for all intents and purposes, assuming geostrophic wind, that the first case would likely not yield the temperature change that the second case would despite the aforementioned stronger gradient because a zonal flow would be less likely to produce air mass changes than a meridional flow? Link to comment Share on other sites More sharing options...
heavy_wx Posted November 28, 2011 Share Posted November 28, 2011 If the isotherms and height contours are equally spaced and perpendicular to each other, the temperature change will be the same regardless of whether the flow is zonal or meridional. So if the temperature gradient in the first case is stronger and with the same wind speed as in the second case, the first case would have stronger warm air advection and therefore a greater temperature change. Link to comment Share on other sites More sharing options...
H2Otown_WX Posted November 28, 2011 Author Share Posted November 28, 2011 If the isotherms and height contours are equally spaced and perpendicular to each other, the temperature change will be the same regardless of whether the flow is zonal or meridional. So if the temperature gradient in the first case is stronger and with the same wind speed as in the second case, the first case would have stronger warm air advection and therefore a greater temperature change. Assuming the first case is WAA..okay, thanks a lot OSUwx. Link to comment Share on other sites More sharing options...
heavy_wx Posted November 28, 2011 Share Posted November 28, 2011 Assuming the first case is WAA..okay, thanks a lot OSUwx. No problem. Link to comment Share on other sites More sharing options...
LocoAko Posted November 28, 2011 Share Posted November 28, 2011 Assuming the first case is WAA..okay, thanks a lot OSUwx. It would have to be, since in almost all cases your geostrophic wind would blow with higher heights to its right. So in your image, the winds would be blowing from right to left and from +6C air to +2C air. That being said, the winds in both your cases are blowing from warmer air toward colder air so the only thing that would affect the magnitude of your WAA is the spacing of the isotherms or the spacing of the isohyets (which would cause a stronger geostrophic wind). Link to comment Share on other sites More sharing options...
isohume Posted November 28, 2011 Share Posted November 28, 2011 Thermal advection is okay to look at on plan view charts, but to get a better feel for the magnitude and relation to sfc heating/cooling or changes in instability, etc...you should look at layers of thermal advection. One way to do this is by looking for where the winds back or veer with height. According to the thermal wind equation...veering winds equate to waa and backing to caa in a layer. This is easy to analyze on Bufkit cross sections or profiles. Of course, the velocity and degree of turning will account for the overall magnitude of themal advection occurring. Bufkit profile showing a 1-hr snaphot of caa btw H9-H85 Bufkit Sigma winds showing waa/caa pattern through time in the same layer. Link to comment Share on other sites More sharing options...
L.B. LaForce Posted December 14, 2011 Share Posted December 14, 2011 What exactly are the sigma winds? Is there a difference in using those over just looking at the time profiles, and looking to see if the winds veer or back? Link to comment Share on other sites More sharing options...
Rainman Posted December 14, 2011 Share Posted December 14, 2011 What exactly are the sigma winds? Is there a difference in using those over just looking at the time profiles, and looking to see if the winds veer or back? The models use a variety of coordinate systems. Sigma is a terrain-following coordinate. I found this reference that might help: http://atmo.tamu.edu...01/vertres.html If you look at the 850mb winds, for example, you're looking at a pressure surface that dips and rises. The same can be said for other coordinate systems, such as isentropic or sigma coordinates. Sigma just rises and falls with the terrain. Isentropic coordinates depend on potential temperature. You are probably fine just looking at whatever you use to see if the winds veer or back. I think his point was just that it's just better to look at a deep layer to diagnose temperature advection rather than just one level. The reason for this is described by the QG Height Tendency equation and is beyond the scope of this course :-D Link to comment Share on other sites More sharing options...
isohume Posted December 14, 2011 Share Posted December 14, 2011 What exactly are the sigma winds? Is there a difference in using those over just looking at the time profiles, and looking to see if the winds veer or back? The Sigma winds are the actual vertical coordinate system of the particular model used. It's a convenient way for Bufkit to show time series winds w/o having to calculate and display interpolated winds at say 50 mb intervals or so. You can look at profile winds or the VWP too to determine the thermal advection in a layer. To me tho, it's more clear using Sigma winds as I can see the change in separation of the various Sigma levels quickly and distinctly. Edit: sorry Rainman, I didn't see your post, which I totally agree with. Looks like we both responded at the same time. Link to comment Share on other sites More sharing options...
L.B. LaForce Posted December 14, 2011 Share Posted December 14, 2011 Ahh ok, figured it had something to do with sigma coordinate systems. Also, QG theory is next semesters dynamics Link to comment Share on other sites More sharing options...
H2Otown_WX Posted December 15, 2011 Author Share Posted December 15, 2011 Thermal advection is okay to look at on plan view charts, but to get a better feel for the magnitude and relation to sfc heating/cooling or changes in instability, etc...you should look at layers of thermal advection. One way to do this is by looking for where the winds back or veer with height. According to the thermal wind equation...veering winds equate to waa and backing to caa in a layer. This is easy to analyze on Bufkit cross sections or profiles. Of course, the velocity and degree of turning will account for the overall magnitude of themal advection occurring. Bufkit profile showing a 1-hr snaphot of caa btw H9-H85 Bufkit Sigma winds showing waa/caa pattern through time in the same layer. Thanks for the tip isohume. I'm just starting to familiarize myself with BUFKIT and I was wondering what sigma winds were used for so that should help. I'm sure another quick way of determining changes in stability would be to look at the temperature profile at some pressure level/ height and see how it changes frame by frame. I know NAM BUFKIT has hour by hour so I think that would work. Maybe not as well for the GFS which I think has only 3-hr increments. Link to comment Share on other sites More sharing options...
isohume Posted December 15, 2011 Share Posted December 15, 2011 Thanks for the tip isohume. I'm just starting to familiarize myself with BUFKIT and I was wondering what sigma winds were used for so that should help. I'm sure another quick way of determining changes in stability would be to look at the temperature profile at some pressure level/ height and see how it changes frame by frame. I know NAM BUFKIT has hour by hour so I think that would work. Maybe not as well for the GFS which I think has only 3-hr increments. That's right...the GFS has a 3-hr resolution, the NAM 1-hr. I'm not sure if you have the latest Bufkit or not, but the latest version allows you to load dprog/dt model output. You can now compare the past several model runs for trends and continuity. Also...the ensemble SREF is now available. This has made the already great Bufkit a much more powerful prognostic tool, imo. Link to comment Share on other sites More sharing options...
H2Otown_WX Posted December 15, 2011 Author Share Posted December 15, 2011 That's right...the GFS has a 3-hr resolution, the NAM 1-hr. I'm not sure if you have the latest Bufkit or not, but the latest version allows you to load dprog/dt model output. You can now compare the past several model runs for trends and continuity. Also...the ensemble SREF is now available. This has made the already great Bufkit a much more powerful prognostic tool, imo. I do have the latest version. BUFKIT can do a lot it seems..I don't understand some of the terms yet but as I progress I feel like it is going to be really helpful with forecasting. It's a mystery to me why our program hardly references it. Link to comment Share on other sites More sharing options...
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