Earth's atmosphere (Meteorology)

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Earth's atmosphere (and its mechanics) can often be described in meteorology with very particular and specific terms. While meteorologists do use the more commonly understood standard terms for the earths atmospheric layers, these definitions are insufficient to describe most weather systems, as most weather tends to occur in the lower layers of the earth's atmosphere (most often the troposphere). Due to this deficiency, meteorologists have given further precision to their observations by dividing this small and highly relevant section of the atmosphere into upper, middle, and lower levels. Each level has its own individual characteristics and properties, and is semi-independent of the others - while events and phenomena on a particular level can interact with features in the adjacent levels it is also possible for the atmosphere to flow in different directions at the same time (known as wind shear).

The motion of wind, atmospheric/meterorological phenomena and events is also described in specific terms, most usually being "zonal" and "meridional" flow. While the earths atmosphere flows in general direction of west to east at the lower tropospheric layer, anomalies frequently arise, and so these terms are used to describe the difference between a flow that follows the general trend and a flow which is diverted from that trend.

On a synoptic scale (which can be thought of as the size/area and timespan of individual significant atmospheric events such as depressions or anticyclones rather than a global scale), observations of the motions, trends, and themes of yet smaller sections of the earths atmosphere are also often described in specialist terms.

1 Atmospheric levels
2 Atmospheric flow
3 Synoptic scale observations and concepts
4 See also
5 References
6 External links

[edit] Atmospheric levels

There are three "levels" often used by meteorologists to describe the height and vertical range of an atmospheric event or phenomenon. Each level is roughly defined, and so there can only be approximate definitions of each.

[edit] Low level

The lower level of the atmosphere is that which is at the surface (around sea level and upwards towards 6,000 to 8,000 feet above sea level. ^[1]

[edit] Mid level

The mid level lies between the lower and upper levels, corresponding to around roughly 6,000 - 25,000 feet.^[2]

[edit] Upper level

This is the highest of the three levels. The term applies to the portion of the atmosphere that is above the lower troposphere, generally 850 hPa and above.^[3]

[edit] Atmospheric flow

The flow of the atmosphere generally moves in a west to east direction. This however can often become interrupted, creating a more north to south or south to north flow. These scenarios are often described in meteorology by as zonal or meridional. These terms, however, tend to be used in reference to localised areas of atmosphere (at a synoptic scale)). A fuller explanation of the flow of atmosphere around the Earth as a whole can be found in the three-cell model.

[edit] Zonal Flow

A zonal flow regime is the meteorological term meaning that the general flow pattern is west to east along the earth's latitude lines, with weak shortwaves embedded in the flow.^[4] The use of the word "zone" refers to the flow being allong the Earths lattitudinal "zones". This pattern can buckle and thus become a meridional flow.

[edit] Meridional flow

Meridional Flow pattern of October 23, 2003. Note the amplified troughs and ridges in this 500 hPa height pattern.

When the zonal flow buckles, the atmosphere can flow in a more longitudinal (or meridional) direction, and thus the tem "meridional flow" arises. Meridional flow patterns feature strong, amplified troughs and ridges, with more north-south flow in the general pattern than west-to-east flow. ^[5]

[edit] Three-cell model

Main article: Atmospheric circulation

The three cells model attempts to describe the actual flow of the earths atmosphere as a whole. It is comprised of the tropical (Hadley cell), mid latititude (Ferrel cell), and polar (polar cell) regions of the earth, dealing with energy flow and global circulation. Its fundamental principle is that of balance - the energy that the earth absorbs from the sun each year is equal to that which it loses back into space, but this however is not a balance precicely maintained in each latitude due to the varying strength of the sun in each "cell" resulting from the tilt of the earths axis in relation to its orbit. It demonstrates that a pattern emerges to mirror that of the ocean - the tropics do not continue to get warmer because the atmosphere transports warm air poleward and cold air equatorward, the purpose of which appears to be that of heat and moisture distribution around the planet.^[6]

[edit] Synoptic scale observations and concepts

[edit] Forcing

Forcing is a term used by meteorologists to describe the situation where a change or an event in one part of the atmosphere causes a strengthening change in another part of the atmosphere. It is usually used to describe connections between upper, middle or lower levels (such as upper-level divergence causing lower level convergence in cyclone formation), but can sometimes also be used to describe such connections over distance rather than height alone. In some respects, tele-connections could be considered a type of forcing.