METR 201: Physical Processes in the Atmosphere Thought Questions on Radiosonde Soundings Dr. Dave Dempsey Dept. of Geosciences SFSU, Spring 2013

For the questions below, refer to the four vertical profile plots of temperature, dew-point temperature, and wind speed and direction ("soundings") provided as handouts. The observations on these plots were recorded by a radiosonde launched from Oakland International Airport (KOAK) at 00Z and 12Z February 7, 2011 and 00Z and 12Z February 15, 2011:

You might also find the vertical profile of long-term, global average temperature in the atmosphere useful:

1. There are two line plots on each graph, showing temperature and dew-point temperature. Which one is which, and how can you tell?

2. What was the temperature (in °C) recorded at the earth's surface on each sounding? What was the surface pressure (in millibars [mb])? How do you think this would this compare to the sea-level pressure at KOAK? (The elevation of KOAK is 3 meters above sea level.)

3. An important property of the atmospheric temperature profile is the rate at which the temperature decreases with increasing altitude, expressed as the decrease in temperature per unit of vertical distance. This is called the atmospheric lapse rate (or environmental lapse rate). How can you tell by looking at the temperature plot on a radiosonde sounding where the atmospheric lapse rate is relatively large (that is, temperature decreases rapidly with increasing altitude), where it decreases slowly with altitude, where it doesn't change at all with increasing altitude, and where it increases with increasing altitude?

4. The troposphere is the lowest layer in the atmosphere. Like other atmospheric layers, it is defined in terms of how the temperature typically varies with increasing altitude within it.
• Within the troposphere, the temperature typically decreases relatively rapidly with increasing altitude (sometimes with small exceptions here and there).
• Much of what we consider "weather" (notably storms, clouds, precipitation) occurs in the troposphere.
• The troposphere contains about 80% of the mass of the entire atmosphere (on the average).
• It's long-term global average altitude is about 11 kilometers (km) or about 7 miles (about 36,000 ft.). It's altitude varies a little from day to day and seasonally, and it varies from around 8 km (in polar regions) to around 16 km (at tropical latitudes).
• Jet aircraft typically cruise at this sort of altitude.

The tropopause is the boundary between the troposphere below and the stratosphere above. At the tropopause, the temperature generally stops decreasing rapidly with increasing altitude and either starts decreasing much more slowly, hardly changes at all with increasing altitude, or actually increases with altitude. At what level (in terms of altitude in meters and in kilometers, and in terms of pressure in millibars) is the tropopause located on each sounding? How can you tell where it is visually, in terms of the shape of the temperature plot? Where is the troposphere on each sounding?

5. A temperature inversion is a layer in which the temperature increases with increasing altitude. On each sounding, are there any temperature inversions in the troposphere? If so, where? How can you tell, based on the shape of the temperature plot?

6. For clouds to form, air must first become saturated with water vapor, which occurs when the temperature falls to equal the dew-point temperature, or (less common) the dew-point temperature rises to equal the temperature, or (also less common) some of each. If there were any clouds present at the times of these radiosonde soundings, at what level(s) would they most likely have been? Why?

7. Describe how the wind speed varies with increasing altitude on each sounding. At what level is the wind the fastest? How fast is it there?

8. Describe how the wind direction varies with increasing altitude. Is the wind observed at the surface representative of the wind at higher altitudes?

9. Dew-point temperature tells us something about the amount of water vapor in the air. Based on these soundings, where does the air tend to have the most water vapor in it, generally speaking?

10. For each 00Z and 12Z pair of soundings, where in the troposphere did the largest temperature change occur? How large was it?

Home |*| ANNOUNCEMENTS |*| Syllabus |*| Assignments, Quizzes, Handouts, etc.