Take the 300mb chart for instance. I often will show charts like this:
|Fig 1 -- NAM 6 hour forecast of 300mb height (contours) and winds (colors) at 18Z, May 18, 2011.|
|Fig 2 -- Color-shaded version of figure 1 in IDV.|
But remember--these are heights above the ground. When we look at height contours of a particular pressure surface, we're actually looking at a topographical map of the elevation of that surface above the ground. As such, if we were to consider a three-dimensional map of the 300mb surface, it would look something like this:
|Fig 3 -- Same as figure 2, only tilted.|
|Fig 4 -- Side view of figures 2/3 looking north.|
Now, the 300mb surface doesn't actually vary as much as these figures imply. I've greatly exaggerated the vertical scale on these to show the features. If I decrease the exaggeration, the horizontal cross section in figure 4 quickly turns to this:
|Fig 5 -- Figure 4 at a much smaller vertical exaggeration.|
Also, the troposphere isn't nearly as thick as that outline box implies. The tropopause is usually at 10-15 km above the ground. Once again, compared to horizontal scales of thousands of kilometers, the troposphere is a very, very thin layer. It would be hard to even see it if we looked at a cross section over the US at actual scale. So, we exaggerate it vertically quite a bit to show these small contrasts.
Anyhow, I just wanted to use this kind of 3-d visualization to remind people that all these flat, horizontal maps we look at are representations of a three-dimensional atmosphere. The troughs and ridges on an upper-air map really are troughs and ridges in the height of that surface. It's a great topography that's constantly changing. And, even though these changes may seem small in scale, they make all the difference when it comes to our weather.