The tropopause is important to us who fly below, in, or above it because so much happens below, in, or above it. Our aircraft performance changes as temperature changes and that tends to happen as we climb until we get to the tropopause. Many cloud types will stop at the tropopause. Weather fronts can be capped off by the tropopause. The jet stream is impacted by the tropopause and extreme shear levels can occur where the tropopause suddenly breaks with latitude. It is something we need to pay attention to!
Everything here is from the references shown below, with a few comments in an alternate color.
Figure: Tropopause height, from Meteorology Training, pg. 1-5
Generally speaking, the tropopause begins when the temperature lapse rate of the troposphere ends . . .
Figure: Troposphere Decrease in Temperature with Height, from AFH 11-203, figure 1-4
[AFH 11-203, ¶2.1] Most of the atmosphere’s moisture is concentrated in the troposphere, and is rarely found in significant amounts above the tropopause.
[AFH 11-203, ¶3.6] Temperature normally decreases with increasing altitude throughout the troposphere. This decrease of temperature with altitude is called the lapse rate, expressed in degrees per thousand feet. The standard lapse rate in the troposphere is 2 degrees C (3.6 degrees F) per 1,000 feet. This value serves as the basis for calibrating aircraft instruments and preparing performance charts. [ . . . ] Variation in the lapse rate may change with altitude. At a given time and place, the vertical temperature might decrease at a rate of 3°C per 1,000 ft from the ground to an altitude of 5,000 ft, at a rate of 1°C per 1,000 ft between 5,000 and 7,000 ft, and at 2°C per 1,000 ft above 7,000 ft until the tropopause is reached. Rarely does the temperature decrease at an orderly rate. In fact, temperature inversions are common in the troposphere, where temperature increases with height.
[Meteorology, pg. 1-4]
Figure: Tropopause breaks, from Meteorology Training, pg. 1-6
Figure: Three-cell model of the earth's circulation, from AFH 11-203, figure 5.1
[AFH 11-203, ¶5.3] Using the three-cell model [ . . . ] we see that the various circulations due to unequal heating combine to create the jet streams that are centered at 30°N/S and 60°N/S on average but constantly meander north and south. Winds generally increase with height through the troposphere due to the presence of a north-south temperature gradient in the mid-latitudes and the conservation of angular momentum, reaching a maximum near the tropopause. This wind maximum is called the jet stream. A jet stream, or "jet", is a meandering region of concentrated, higher wind speeds that circles the Earth. In the wintertime, there are often two or three predominant jet streams: the polar-front jet (PFJ) stream, the subtropical and the arctic jet streams. The main and best known jet stream is the polar-front jet stream which frequently enhances major weather system development in the mid-latitudes. Within the jet stream are concentrated pockets of the strongest winds, often called jet stream maxima or simply a "jet max". The strongest vertical motions associated with jet streams occur under jet maxima, and these motions are a major factor in the development of low pressure systems.
Because the height of the troposphere can change suddenly, as shown earlier, a jet stream is often located at these breaks in the temperature lapse rate.
Figure: Location of Polar/Subtropical Jet Streams in Relation to Tropopause, from AFH 11-203, figure 9.15
[AFH 11-203, ¶9.10] The tropopause is often a region of turbulence because of the marked variations in vertical motions which occur in, at, or below it. The tropopause is often devoid of clouds, so that turbulence encountered there will frequently be classified as clear air turbulence. Earlier we discussed the tropopause is higher at the equator than at the poles. However, there are generally two breaks in the tropopause--one between the arctic and polar air masses, and one between the polar and tropical air masses (Figure 9.15). It is where these breaks in the tropopause appear that a very important flight factor can be found--the jet stream.
[AFH 11-203, ¶9.13.3] If jet stream turbulence is encountered in a crosswind, it is not so important to change course or flight level. However, if it is desired to traverse the CAT area more quickly, either climb or descend after watching the temperature gauge for a minute or two. If the temperature is rising--climb; if it is falling--descend. This maneuver will prevent following the sloping tropopause or frontal surface and thereby staying in the turbulent area. If the temperature remains the same, you can either climb or descend.
[AFH 11-203, ¶13.5]
Figure: Significant Weather Chart, from Meteorology Training, pg. 24-5
[Meteorology, pg. 1-4]
You can get a "Mid Level SigWx (FL 100-450)" chart from www.aviationweather.gov. For example:
Figure: Significant Weather Chart, from www.aviationweather.gov
Weather for Aircrews, Air Force Handbook (AFH) 11-203, Volume 1, 1 March 1997, Department of the Air Force
Meteorology, JAA ATPL Training, Jeppesen Sanderson Inc., 2004
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