Soundings
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Introduction
Where there are clouds, the air must be saturated or very close to saturated. In this activity we will compare the moisture content of the atmosphere as observed by soundings with the surface observations of clouds.
Objectives
Be able to indicate the levels that may have clouds by inspecting soundings
References
Earlier lab activities on relative humidity, dew-point depression, and soundings.
Instruction
We learned earlier that
 | the air is saturated when the RH is 100% |
| the RH is near 100% when the DPD (dew-point depression) is close to 0 |
| in the text form of a sounding, the DPD is either given or can be calculated quickly by mentally subtracting Td from T |
| in the GIF form of a sounding, the DPD can be estimated by observing how close together the T and Td are |
The rule of thumb we'll use to inspect soundings for clouds is the following:
| CLOUD RULE OF THUMB: Layers that may have clouds are those in which two or more adjacent levels have a DPD < 3°C. |
With this rule in mind, link to the following pages and notice that the Meteograms indicate the cloud conditions and approximate levels and that the soundings seem consistent with the rule above.
| Cloud Free Sounding |
| Clouds |
| Clouds and Precipitation |
When we inspect soundings, we should remember that they were obtained by sending up a radiosonde that took about 30 minutes to travel through the troposphere in which clouds normally occur. Also, the radiosonde was moving horizontally with the winds as well as vertically. Hence, the air it sampled may not be representative of what was viewed from the surface at 00Z or 12Z.
| If the weather conditions were clear or completely cloudy over a large region surrounding the rawinsonde launch site at the time of the launch, then the sounding was probably representative of the conditions observed from the surface at the launch site. |
| If the weather and cloud conditions were changing rapidly or were highly variable at the time of the launch, then we would expect that there might be more disagreement between the sounding and surface observations. |
Web Examples
Let's compare some current surface and upper-air observations using Meteograms and Soundings. We'll use clickable maps so that we can easily refer to the same location for both. (You may wish to use the table below to organize your work)
First, inspect a Surface Map and locate regions that have the following conditions
| region that is clear or cloud free |
| region experiencing continual precipitation |
| region with clouds but no precipitation |
Then look at some Meteograms in each of the regions you have identified for a location that (1) was reporting the condition at either 00Z or 12Z and that (2) is a sounding location.
| location that is clear or cloud free |
| location experiencing continual precipitation |
| location with clouds but no precipitation |
Now, inspect the soundings (see the links below) at the locations you have identified and compare the surface observations of clouds and precipitation with the soundings. How closely is our CLOUD RULE OF THUMB satisfied?
Below are several different sources for soundings. The first source is the University of Wyoming, which we have used before. The second source is COMET (click this link to learn more about COMET). From the University of Wyoming you have to look at the text and GIF forms separately. At COMET only the GIF form is available.
Soundings from the University of Wyoming (select Text:List or GIF:Stuve, sounding time, and station identifier)
Soundings from COMET: Stuve form available but not text.
Soundings from the College of DuPage: Notice that the text form lists the dew-point depression and both the text and Stuve forms list the tropopause level.
| Region | Station IDs | Notes | |
Cloud Free |
|||
Continual Precipitation |
|||
Clouds & No Precipitation |
Practice Questions
1. Match the three soundings below to the following sets of surface observations:
_______ clear
_______ precipitation
_______ clouds but no precipitation
| A |  |
| B |  |
| C |  |
2. Use our cloud rule of thumb to estimate the bottom and top of those layers that may have clouds in the following sounding.
Date:1200Z 28 JAN 99
Station: GYX
WMO ident: 74389
Latitude: 43.89
Longitude: -70.25
--------------------------------------------------
LEV PRES HGHT TEMP DEWP RH DD WETB DIR SPD
mb m C C % C C deg knt
--------------------------------------------------
SFC 1005 125 -11.7 -18.7 56 7.0 -13.0 30 12
1 1000 163 -11.9 -19.9 51 8.0 -13.3 30 12
2 947 577 -14.9 -19.8 66 4.9 -15.7 13 12
3 925 755 -14.1 -18.4 70 4.3 -14.9 10 12
4 916 829 -13.7 -17.3 74 3.6 -14.5 3 11
5 898 982 -9.9 -10.8 93 0.9 -10.2 344 10
6 850 1405 -11.3 -12.3 92 1.0 -11.6 285 9
7 700 2894 -11.5 -12.6 92 1.1 -11.8 290 30
8 656 3391 -12.1 -13.4 90 1.3 -12.5 290 38
9 500 5420 -24.3 -26.2 84 1.9 -24.6 290 57
10 442 6305 -31.5 -35.5 68 4.0 -31.9 295 74
11 427 6549 -32.1 -40.1 45 8.0 -32.9 295 87
13 356 7824 -35.3 -57.3 9 22.0 -36.4 291 135
14 341 8122 -37.5 -53.5 17 16.0 -38.4 292 140
15 323 8492 -40.7 -46.7 52 6.0 -41.1 294 145
16 300 8990 -44.5 -51.5 46 7.0 -44.8 295 150
Answers
1. C clear
A precipitation
B clouds but no precipitation
2. Using our rule of thumb, we would estimate the cloud base at 982 meters and the top at 5420 meters. The layer consisting of adjacent levels with DPD < 3°C is indicated in bold, red text below.
Date:1200Z 28 JAN 99
Station: GYX
WMO ident: 74389
Latitude: 43.89
Longitude: -70.25
--------------------------------------------------
LEV PRES HGHT TEMP DEWP RH DD WETB DIR SPD
mb m C C % C C deg knt
--------------------------------------------------
SFC 1005 125 -11.7 -18.7 56 7.0 -13.0 30 12
1 1000 163 -11.9 -19.9 51 8.0 -13.3 30 12
2 947 577 -14.9 -19.8 66 4.9 -15.7 13 12
3 925 755 -14.1 -18.4 70 4.3 -14.9 10 12
4 916 829 -13.7 -17.3 74 3.6 -14.5 3 11
5 898 982 -9.9 -10.8 93 0.9 -10.2 344 10
6 850 1405 -11.3 -12.3 92 1.0 -11.6 285 9
7 700 2894 -11.5 -12.6 92 1.1 -11.8 290 30
8 656 3391 -12.1 -13.4 90 1.3 -12.5 290 38
9 500 5420 -24.3 -26.2 84 1.9 -24.6 290 57
10 442 6305 -31.5 -35.5 68 4.0 -31.9 295 74
11 427 6549 -32.1 -40.1 45 8.0 -32.9 295 87
13 356 7824 -35.3 -57.3 9 22.0 -36.4 291 135
14 341 8122 -37.5 -53.5 17 16.0 -38.4 292 140
15 323 8492 -40.7 -46.7 52 6.0 -41.1 294 145
16 300 8990 -44.5 -51.5 46 7.0 -44.8 295 150
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Revised 06/16/04