THE ATMOSPHERE IN THE VERTICAL

Objectives:

The atmosphere has depth as well as horizontal dimensions. For a more complete understanding of weather, knowledge of atmospheric conditions in the vertical is necessary. Air, a highly compressible fluid held to the planet by gravity and squeezed under its own weight, thins rapidly with increasing altitude. The atmosphere is heated primarily from below, is almost always in motion, and contains a substance (water) that continually cycles through it while undergoing changes in phase.

After completing this investigation, you should be able to:

• Describe the vertical temperature structure of the atmosphere in the troposphere (the “weather” layer) and in the lower stratosphere.
• Compare the temperature profile specified by the U.S. Standard Atmosphere with actual soundings of the lower atmosphere.

Introduction:

Figure 1 shows the average vertical temperature profile of essentially the entire atmosphere as a function of the altitude above Earth’s surface.

Figure 1. Variation of average temperature with altitude in the atmosphere.

Figure 2 is a Stüve diagram, one type of temperature/pressure graph of the lower portion of the atmosphere, used for plotting atmospheric conditions. Figure 2 focuses on the lowest 16 km of Figure 1.

Figure 2. Vertical atmospheric chart (Stüve diagram).

Plot the data points given below onto Figure 2 and connect adjacent points with solid straight lines. Note that altitude is plotted along the right vertical axis increasing from bottom to top, and temperature is plotted along the horizontal axis increasing from left to right.

Altitude (km)	Temperature (°C)
16	- 56.5
11	- 56.5
0	+ 15.0

1. You have drawn the temperature profile of the lower portion of the “U.S. Standard Atmosphere.” The Standard Atmosphere describes representative or average conditions of the atmosphere in the vertical. As seen in Figure 1, the temperature profile from the surface to 11 km depicts the lowest layer of the atmosphere, called the [(troposphere)(stratosphere)(mesosphere)(thermosphere)].

2. The lower portion of the [(troposphere)(stratosphere)(mesosphere)(thermosphere)] is evident immediately above 11 km in Figure 2 where temperatures remain steady with increasing altitude through several kilometers.

3. The troposphere is characterized generally by decreasing temperature with altitude, significant vertical motion, appreciable water vapor, and weather. According to the Standard Atmosphere data provided in item 1 above, the temperature within the troposphere decreases with altitude at the rate of about [(4.5)(5.1)(6.5)] C degrees per km.

4. Air pressure is plotted along the left vertical axis of the figure in millibars (mb) with pressure decreasing upward, as it does in the atmosphere. Air pressure, which is very close to 1000 mb at sea level in the Standard Atmosphere, decreases most rapidly with altitude in the lowest part of the atmosphere. The Figure 2 diagram shows that an air pressure of 500 mb (about half that at sea level) occurs at an altitude of about [(5.5)(8.3)(11.0)(16.0)] km above sea level.

5. Because air pressure is determined by the weight of the overlying air, half of the atmosphere by weight or mass is above the altitude at which the air pressure is 500 mb and half of it is below that altitude. In other words, half of the atmosphere by weight or mass is within about [(5.5)(8.3)(11.0)(16.0)] km of sea level.

6. Other pressure levels can be found similarly. For example, 10% of the atmosphere is located above the altitude where the pressure is [(100)(900)] mb.

7. In other words, it can be seen in Figure 2 that at the altitude of approximately [(5.5)(8.3)(11.0)(16.0)] km above sea level, 10% of the atmosphere by weight is above and 90% is below.

On Sunday evening, 15 September 2013, a relatively cool and dry (low humidity) air mass seen in Investigation 2A was advancing southeastward across the country’s midsection. The leading edge of this air mass was marked by cold fronts. The area to the south and east of the frontal systems was experiencing air much warmer than that following the frontal systems.

In addition to weather conditions at Earth’s surface, conditions in the atmosphere above the surface are also very important. Upper atmospheric data are collected by radiosondes at 00Z and 12Z each day from about 70 stations across the U.S. as part of a worldwide effort of sensing the three-dimensional atmosphere for purposes of weather analysis and forecasting.

The data in the following table were obtained by the rawinsonde (a radiosonde instrument tracked for wind information) observation from Buffalo, New York, at 00Z 16 SEP 2013. Using the respective pressure levels from the table, plot the corresponding temperatures over Buffalo on the Figure 2, Stüve diagram that you used to plot the Standard Atmosphere conditions in the introductory portion of this activity. The course website’s User’s Guide provides links for an additional copy of the Stüve diagram if necessary. [Note: Remember that the pressure scale decreases upward along the left side.] Connect the successive points with dashed straight line segments or an alternate color to distinguish the Buffalo profile from the Standard Atmosphere plot.

Pressure (mb)	Temperature (°C)	Altitude (m)
100	–60.9	16520
150	–59.1	14000
186	–59.1	12648
200	–56.1	12190
300	–35.7	9500
400	–20.3	7440
500	–9.7	5750
700	0.6	3091
850	6.6	1518
992 (surface)	17.8	215

8. On 16 September at 00Z, from the surface up to about the 200-mb pressure level, the atmosphere over Buffalo was [(warmer than)(about the same as)(colder than)] Standard Atmosphere conditions.

The tropopause is a defined boundary that separates the troposphere below from the stratosphere above. In the troposphere, temperatures generally decrease as the altitude increases. In the lower stratosphere, temperatures are typically constant (termed isothermal) or they increase with altitude (called a temperature inversion).

9. Based on the temperature pattern determined by the Buffalo data you plotted, the tropopause above Buffalo at 00Z on 16 September 2013 was located at a pressure level of [(300)(200)(186)(100)] mb.

10. The tropopause over Buffalo at this time occurred at an altitude near [(9.5)(12.5)(15.5)] km above sea level according to the altitude scale on the Stüve diagram. This can be confirmed from the table values.

11. This was at [(a lower)(the same)(a higher)] altitude compared to the altitude of the tropopause in the Standard Atmosphere. (Recall from the first part of this investigation, the Standard Atmosphere tropopause occurs at 11 km or 11,000 m.)

12. From the table of radiosonde data, at 00Z on 16 SEP 2013 over Buffalo, the pressure of 500 mb occurred at an altitude of [(5450)(5580)(5750)] m. Five hundred millibars is about one-half of the atmospheric pressure at sea level. Since air pressure is determined by the weight of the overlying air, this means one-half of the mass of Buffalo’s atmosphere was above this altitude and one-half below.

13. In the Standard Atmosphere a pressure of 500 mb occurs at an altitude of 5574 m (18,289 ft.). The altitude of the 500-mb level over Buffalo at the time of this sounding was [(higher than)(the same as)(lower than)] that of the Standard Atmosphere. This relatively warm atmospheric column reflected the warm air of the summer season that had mixed throughout the lower atmosphere.

14. Our Stüve diagram is scaled to allow plotting of atmospheric data up to a pressure of 100 mb (about 16 km). At a level where the atmospheric pressure is 100 mb, about [(10%)(25%)(50%)] of the atmosphere’s mass remains above.

The actual Buffalo 00Z 16 SEP 2013 rawinsonde sounding reported atmospheric conditions to 28 mb (at 24541 m) where the expanding balloon lifting the radiosonde finally burst. There was still about 3% of air by mass or weight above that!

Figure 3 is the plotted Stüve diagram for Buffalo (BUF) for 0000Z 16 SEP 2013 (labeled 130916/0000). Current Stüve diagrams are provided for selected cities from the course website (Upper Air, “Stüves for Selected Cities”). The Figure 3 Stüve is plotted using all the data from the Buffalo rawinsonde observation up to 100 mb. On the course website, under the Upper Air section, “Upper Air Data - Text” provides the tabular listing of all data from observations that correspond to the latest plotted soundings.

On the Figure 3 Stüve diagram, the heavy plotted black curve to the right connects temperatures while the heavy plotted curve to the left connects dewpoints. (Recall from Investigation 2A, dewpoint is a measure of atmospheric water vapor content.) Trace over the temperature line with a pen or marker to highlight it. Winds at various levels are plotted to the right of the graph area using the convention of the surface station model. For example, the fastest winds above Buffalo were at about 230 mb. They were generally from the west at about 80 knots (one pennant and three long feathers on wind shaft). Additional lines on the Stüve diagram will be discussed in a later investigation.

15. On the Figure 3 Stüve diagram, note the temperature patterns from about 715 mb up to 700 mb, from about 680 to 660 mb, and especially from about 620 to 610 mb. These layers are examples of [(isothermal conditions)(normally decreasing temperatures)(temperature inversions)]. Compare the temperature profile you have constructed on Figure 2 with the temperature sounding of Figure 3. Note the difference in detail, which shows the complexity of atmospheric conditions. Knowledge of the finer structure of the temperature profile is often very important in interpreting atmospheric processes and motions above the surface.

Figure 3. Stüve diagram for Buffalo, NY (BUF) rawinsonde observation at 0000Z 16 SEP 2013.

For other rawinsonde examples, look at the Stüve diagram for Hilo, Hawaii, Anchorage, Alaska or others from the Upper Air section on the course website. Relative to the Standard Atmosphere, Hawaii is typically warmer while Alaska is colder. Below the table of cities on the Upper Air Stüves webpage or text data webpage, a link provides access to upper air data and rawinsonde plots worldwide.

You might wish to plot the upper air data for your nearest site on a blank Stüve diagram (“Blank Stüve - T, p lines”) found under the Extras section on the course website. These plots can then be compared with the computer-analyzed version. View Stüve diagrams when weather systems pass your location. Atmospheric structure changes during frontal passages and major storms can be quite dramatic.