# How many atmosphere layers?

The atmosphere layers surrounding the earth might remind you of the layers of an onion. Remember this?...

…“Ogres are like Onions – Layers!”

~Shrek

Does this green guy and Earth's blanket, the atmosphere, resemble the vegetable in this sense? You bet. So do the layered interiors of our Earth, Moon and Sun.

Each of the atmosphere layers lies above all parts of the world in the same order.

Each on takes on the shape of an oblate spheroid, like the planet itself. Each will be deeper over some regions than others. But they are all concentric.

So what if you were to go far enough straight up from any point on the surface?

You would ascend through the troposphere, stratosphere, mesosphere and thermosphere in that order. No matter where you start.

## Why do we care about the upper atmosphere layers?

Certainly if you're a pilot. Or a meteorologist. You would take serious interest in what's happening in the sky above. This undertaking forms the central part of aviation weather services.

See how I am doing it.

The atmosphere is a three-dimensional field. One that requires complicated computer models and atmospheric diagrams to understand.

Why does upper air flow modelling and research go on continuously? That's because elevated airflow affects what happens down here.

Now we’re sailing…
Does something interest you the way the atmosphere does for me? Ever thought you could make a profit from it?

## Atmosphere pictures

Once again, we have the troposphere, stratosphere, mesosphere and thermosphere above us. See the distances above the earth in kilometers on the left side of this diagram.

The air flows in a nearly frictionless path in the higher atmosphere layers. We make simpler and more accurate predictions at higher elevations because of these near ideal conditions called geostrophic flow. The standard atmospheric pressure levels are given in millibars in this chart below. A millibar is about one thousandth of the air pressure at the planet's surface.

## Air Pressure Science:

1000 millibars (mb) = 100 kiloPascals (kPa) = 14.50 pounds per square inch (psi) and 29.53 inches of mercury. This works out to about 99% of the average air pressure at sea level.

Pressure drops off with elevation. The inverse altitude - atmospheric pressure relation can be seen in the requisite levels which have these approximate heights above sea level (ASL):

1000 mb ~ 360 feet (110 m)

850 mb ~ 5000 feet (1500 m)

700 mb ~ 10,000 feet (3000 m)

500 mb ~ 18,000 feet (5400 m)

250 mb ~ 34,000 feet (10,200 m)

One thing, though. The precise heights of these atmosphere layers vary with location, current weather systems and seasons.

From these heights, we easily derive one of our most important quantities - LAYER THICKNESS. We get this by simply subtracting to find the difference in heights, in feet or meters, between two pressure levels.

## Why is thickness important?

Is is proportional to the average temperature for that layer. Actually meteorologists use virtual temperature which is corrected for humidity.

You can refer to a conversion table where temperature and thickness are compared. Then weather forecasters draw a map with lines of equal thickness and use them in a manner similar to how they would interpret isotherms, lines of equal temperature.

Storms like to form in areas where these lines crowd together, called baroclinic zones. What happens is changes in temperature, stability, wind shear and precipitation become more predictable.

The lowest part of the atmosphere, the troposphere, reaches up to about 36,000 feet or 11,000 metres in tropical regions. The pressure here drops off to a little over 20% of the surface pressure.

Meteorologists care most about this layer. The physical boundary at the top of the troposphere, called the tropopause, separates the troposphere and stratosphere atmosphere layers. Like a skin, it defines the vertical transition between two regions with very different temperature and flow characteristics.

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