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Gravity waves depend on the stability of the fluid (in this case, the atmosphere). If the fluid is unstable, the displaced air will accelerate away from its original location. It's the difference between a wave (stable) and a parcel (unstable). In meteorology, we usually discuss stability in terms of parcels because, although imperfect, the assumptions of parcel theory are close enough to be useful in explaining a lot of processes in the atmosphere.

For those who are genuinely interested, here are a couple of links that explain gravity waves:
http://www.theweatherprediction.com/habyhints/64/
http://www.physics.uwo.ca/~whocking/p103/grav_wav.html

Both links, of course, use parcels to help explain gravity waves. The second link is more detailed and introduces the related concept of the Brunt-Vaisala frequency (the period of a gravity wave oscillation; it is infinite or NaN for neutral stability and not purely real for unstable conditions), which is useful in meteorology.

Would you like to contribute to the discussion, or are you just here to troll me, as your most recent post implies?

There is no such thing as "too cold to snow"

http://www.theweatherpredictio...

http://www.forteantimes.com/st...

There is no such thing as "too cold to snow"

http://www.theweatherpredictio...

http://www.forteantimes.com/st...

You're obviously missing the point. You cite the highest thunderstorms, completely neglecting that not all thunderstorms are "highest".

http://theweatherprediction.com/habyhints2/536/

I take it then, that those thunderstorms that I have observed from above, while parked on a mountain highway, were just freaks of nature?

Obviously, something as powerful as a hurricane will affect the atmosphere all the way up to the ozone layer. Localized storms, on the other hand, are often only a few thousand feet high. 70,000 feet is an exceptional storm, and even 40,000 feet is a pretty large, and powerful storm.

Fine - try looking at it a different way. Let's say that Europa has an atmospheric density of 100 units. If someone were to say that Rhea's was one time thinner, what would the density of Rhea's atmosphere be?

Someone wouldn't say "one time thinner".... But let's say someone said Rhea's atmosphere was twice as thin, two times thinner, half as thick, whatever you prefer, as Europa's then the density of Rhea's atmosphere would be 50 units.

Go read this explanation of the difference in density between air and water, it will probably make this whole atmosphere thing make more sense.

Actually the bit about snow was misleading. The article was about sea ice thickness. Sea ice is caused by cold air flowing from a pole toward the equator and cooling the ocean. More about that in a bit.

Back to the bit about "to cold to snow". Really cold air carries very little water vapour.
http://www.theweatherprediction.com/habyhints/222/

Now back to the article. The article described 1 year sea ice thickness. This is ice that forms on the sea over one winter and is essentially a measure of how cold the air was that winter. So first thought is that more ice implies a colder winter. Yes I agree with that. The question is what is the average global temperature. Global warming (called climate change by those who think explaining all the details will confuse people) does not mean it warms up everywhere.

Fact: Cold air does not come from the polar regions. Cold air comes from high in the atmosphere where air radiates heat to space. Warm air comes from contact with sun warmed ground and sea.
http://www.rcn27.dial.pipex.com/cloudsrus/wind.html

So the polar regions are cold because they get more cold air dropped on them from high in the atmosphere. What pushes the whole cycle is "heat". We like to think of hot and cold as relative to our norms. Real tempeature is degrees Kelvin. So the polar regions just have less heat than the equatorial regions.

Back to the circulation putting more heat into the system results in a global warming but also in an accelerated wind system. This will push more cold air down at the poles. Essentially making the poles colder and the polar winds colder. This will make the polar regions colder --- when they are not heated by the sun.

So from global warming we can actually expect colder winters at the poles. Overall they will be shorter due to the added heat. There are lots of balances and more complex things. Particularly the global air circulation is not 1 cycle equator to poles, but banded. But the general idea is there.

Weather is measured by single data points called "Weather Stations." NOAA with their "gridpoint forecast" may average statistics between these stations to give a custom forecast between the two. However, at this point, we've moved farther from the data statistics that help to give us accuracy. i.e. it's highly speculative--and likely doesn't account for geographical features and cannot account for the highly unpredictable nature of weather. Especially for "scattered showers" and such.

So...

If it is "70% of the times we noted these weather conditions, rain occured", then that 70% is a much higher percentage than the actual probability that it will rain on me. This is because (probably) most of those "70%" of times did not see rain falling on every square meter of the prediction area.

The meteorologists do not have instruments on every square meter of the prediction area. They've got instruments at one or more weather stations. And the 70% is for how many times the rain occurred at that station under similar conditions (temperature, pressure, humidity, etc.) In all ways, a weather reading is a single datapoint, and since these statistics are derived from a single datapoint, they are singular as well. However, as I mentioned above, these things can be averaged between stations.

I'm guessing your "area coverage method" is some kind of averaging of these weather stations calculated statistics.

I found this explanation as well:
http://www.theweatherprediction.com/habyhints/284/

The interesting parts:

When referring to POP it is most accurate to say, "There is a ___% POP that any particular measurement station in the viewing area will get precipitation". For example, when averaged over many 30% POP days, a particular station should have precipitation 30% of the time if the forecaster or computer model is accurate.

and

All to often, people assume a 20% chance of rain means 20% of forecast area will get rain on that one day. This is often not the case for any one day. Often no precipitation occurs at all in the forecast area on days with a 20% POP since one component of POP is the chance that any precipitation will develop.