CWS 5B

3D"{short

ATMOSPHERIC PRESSURE IN THE VERTICAL

Radiosonde data can be employed in a variety= of ways to provide meteorologists with powerful analytical tools. Data at vari= ous atmospheric levels above a station can be plotted in the radiosonde profile on the Stüve diagram that we exami= ned in Investigation 2B. Here we consider atmospheric temperature and pressure con= ditions above two stations about 1500 km apart. Radiosonde observations at 0000Z 7 October 2009 (091007/0000) from Atlanta (FFC= ), Georgia, and Minneapolis (MPX), Minnesota, depic= ting the tropospheric conditions over those stations are plotted on Stüve diagrams shown in Image 1 and Image 2, respectively. According to the Image 3 surface map for the same time, Atlanta was reporting a temperature of 70 °F while Minneapolis was 44 °F. As seen on t= he surface map, a strong cold front was passing eastward and was between the t= wo cities. Additional details of surface weather conditions in these regions c= an be found in the Wednesday, 7 October 2009, Daily Weather Summary.

1= . Trace with heavy pencil lines or a highlighter the temperature profiles (plotted curves to the right on the Stüve diagrams)= for each station. Comparing the two temperature curves, the atmosphere (up to a= bout 250 mb) was cooler above [(Minneapolis)(A= tlanta)]. (Note: This can be seen by laying one Stüve printout over the other and holding up to the light.)

2= . The following table lists a portion of the text data from the two radiosonde observations (complete data for the most r= ecent soundings are available from the course website section, Upper Air, "Upper Air Data - Text"). Pressure levels given are the so-called "mandatory" levels reported in each station's sounding plus the surface. The surface pressures differed somewhat (partially due to their altitude differences) and are listed as the first (lowest) entries. The data are presented with the highest pressures at the bottom as is found in the o= pen atmosphere.

Pressure (mb= )	Atlanta (FFC)		Minneapolis (MPX)
Temp (°C)	Altitude (m)		Temp (°C)	Altitude (m)
100	–74= .1	16470		–54= .7	16190
200	–56= .5	12310		–45= .3	11680
300	–35= .5	9620		–46= .5	8970
400	–20= .1	7540		–34= .1	7030
500	–7.= 7	5850		–22= .5	5430
700	9.0	3149		–9.= 3	2887
850	15.6	1523		–0.= 9	1359
925	19.0	798		3.2	678
970 (sfc)	---	---		6.8	287
986 (sfc)	22.6	245		---	---

3= . Compare the altitudes of the following pressure levels on the two soundings. The following pressures which were at lower altitudes over Atlanta (FFC) than over Minneapolis (MPX):
[(925 mb)(= 700 mb)(500 mb)(300 mb)(100 mb)(none of these)].

4= . Constant-pressure "surfaces" are those that can be imagined as surfaces in the atmo= sphere on which the air pressure is everywhere the same, for example, the 500-mb surface. Comparing the pressure surfaces from 925 mb to 100 mb, the top of the plotted soundings, indicates that those constant-pressure surfaces slope from the generally wa= rmer air over Atlanta [(downward)(upward)] to= the cooler air over Minneapolis.

It may be noted that the coldest temperature = of the soundings was found over Atlan= ta. It is characteristic that lower latitude stations have colder temperatures = at the boundary of the troposphere and stratosphere (trop= opause) than higher latitude stations.

5= . In general, as one moves toward Earth's poles, one would expect the altitudes = of a particular constant-pressure surface to become [(higher)(lower)].

6= . This altitude change of a given pressure surface as one moves poleward is in response to [(higher)(= lower)] average temperatures in the underlying air columns.

7= . Assume you were to fly from Minneapolis to Atlanta maintaini= ng a 30,000-foot (9144 m) altitude as indicated by your pressure altimeter. Usin= g a pressure altimeter, you are actually flying along a constant-pressure surface. (To visualize this flight, you can compare the altitudes of the 30= 0-mb levels of the two stations, a pressure that is found near 30,000 feet.) As = you approach Atlanta, your aircraft would actually be at a [(higher)(lower)] altitude than that indicat= ed by your altimeter.

8= . If you were to fly from Minneapolis to Atlanta while mai= ntaining an actual altitude of 30,000 feet, the air pressure outside your pla= ne would [(gradually increase)(= remain the same)(gradually decrease)].

9= . The tropopause, the level where the temperature bec= omes nearly constant (isothermal) or begins to increase with height (inversion), marks the top of the troposphere and can be seen in both Stüve diagrams. The tropopause over Atlanta was reported at 115 mb while that over Minneapolis was a= t 320 mb. The depth of the troposphere (surface to tropopause) is termed "thickness" and is re= lated to the average temperature of the air column. The troposphere was "thicker" over [(Minneapolis)(A= tlanta)] where the average temperature in the troposphere was generally greater.

Changes in tropospheric conditions above a s= tation with passing weather systems can also be tracked with = Stüve diagrams. This is one example of the influence of a strong passing cold fro= nt on tropospheric temperatures. You might also co= mpare quite different stations such as Hilo, Hawaii and Anchorage, Alaska, from the course website or a similar pair of warm/cold locations via the Plymouth State University page.

If directed by your instructor, place the answers to Investigation 5B and Current Weather Studies 5B on the B Answer Form linked from the AMS Weather Studies website.

©Copyright 2009, American Meteorological Society