Why pressure coordinate is preferred than distance to see vertical structure of the atmosphere?

Question

Usually vertical structure of the atmosphere is expressed in pressure scale, in meteorology, than expressing the altitude in distance (kilo meter) measured from the surface of the earth.
My question is why we use pressure scale than distance?

Answer 1

There are many reasons that meteorologists use pressure coordinates (as described above) but it all boils down to making the equations easier. Meteorologists use equations to model the atmosphere. Using pressure coordinates eliminates the density term...an important factor in meteorology but one that can't be measured directly. Pressure coordinates remove density from the equations making them easier to work with and able to use real observations rather than derived ones, which increase error.
And, by making the equations easier, it makes conceptual models easier to use. On the job meteorologists usually don't sit down and calculate the vorticity advection (spin) but they know what it means when they see it on a 500mb map.

Answer 2

Any meteorologist could answer this better than me, but I'll give you a semi-educated explanation.

I'm assuming that what you're referencing is weather graphics that present the data for various pressures, e.g. 850mb, 700mb, 500mb, etc., rather than altitudes, or heights. Such as this:

http://www.spc.noaa.gov/obswx/maps/500_070114_12.gif

That is the 500mb graphic for this morning over the USA.

Meteorologists are better able to analyze the current conditions and prepare forecasts by looking at the characteristics of the atmosphere using pressures as a constant rather than heights. It is more of an apples-to-apples comparison (location to location) vs. apples-to-oranges, which would be the case if they used heights.

Some of the parameters that are important to compare, location to location, are temperatures, dewpoints, wind speed, and wind direction. When there are differences in these parameters at two different locations at the same pressure, it has meaning. However, if you compare them for two different locations, but at the same height, say....5000 meters, the data is relatively meaningless because there are two different pressures, and the different pressures influence those parameters.

For example, if you have air that is 5 degrees C over Denver at 700mb (not today, but it's just a hypothetical!), then you have a reading of 9C over Amarillo at 700mb, that is pertinent data.

However, if you looked at a graphic that revealed that it was 5C over Denver at 10,000 feet (above sea level), and 9C over Amarillo at 10K feet, it would be relatively useless information.

Why? Because the pressures would certainly be different, if only a little, and the different pressures would affect the temperature (because of lapse). It would be an apples-to-oranges comparison. There would be two factors affecting the data rather than one: Location and pressure, rather than just location.

Answer 3

The surface chart is a constant height chart - mean sea level - and it has isobars - lines of constant pressure.

Upper air charts are constant pressure charts and they have contour lines showing the height of the pressure surface. It would be just as easy to draw a constant height chart as a constant pressure chart and there would be no loss or gain of information.

The reason constant pressure charts are used is that altimeters in aeroplanes are a type of barometer. They give the height of the plane from changes in air pressure. Aeroplanes fly at constant pressure levels not constant heights above sea level. If the planes are at constant pressures then it is sensible for the charts to be at constant pressures. The forecast winds and temperatures will be for the level where the plane is flying.