GEOL 1447 Name: _______________________ Meteorology Date: _______________________
Lab 3 Temperature Structure of the Lower Atmosphere
Main Lab Assignment
Adapted from Introduction to Meteorology Lab Manual by Professor Bart Geerts, University of Wyoming
I. Introduction
The vertical profile of atmospheric temperature, dewpoint (a measure of the moisture content of the air), and wind
speed and direction can be measured using an RS-80 radiosonde carried by a helium-filled rubber balloon. The
radiosonde measures pressure, temperature, and humidity directly. The temperature and humidity are measured
with two small devices on the “silver tongue” of the instrument. The pressure is measured with an aneroid
barometer located inside the instrument. Winds are calculated by receiving long wavelength radio transmissions
from several stations located around the Earth. As the instrument is in flight these data are reported back to the
ground station using radio telemetry, broadcasting at approximately 403 MHz. The data are received every 30 s
during flight, corresponding to a measurement approximately every 150 m, by a MicroCora receiving station, which
calculates the balloon altitude from the temperature and pressure data using an equation called the hydrostatic
equation.
Instruments of this type are flown twice a day at some 60 locations around the United States and at 600 locations
worldwide. The flights are all made at the same time 0000 and 1200 Z, corresponding to 1700 and 0500 MST
(Mountain Standard Time) or 1800 and 0600 MDT (Mountain Daylight Time). The soundings in Wyoming are made
at Riverton. The data from all of these soundings are collected within a matter of hours at a central location. In the
United States this is the National Centers for Environmental Prediction in Camp Springs, Maryland. These data are
then used to provide information for mathematical descriptions of the atmosphere that computationally simulate
atmospheric behavior and give forecasts of the weather.
II. Objectives This Lab’s goals are: 1. To explore how values of the pressure (p), temperature (T), and other parameters that characterize the state of the atmosphere vary with height. 2. To understand how to import data in EXCEL, and how to generate scatterplot charts. 3. To understand the temperature ‘lapse rate’ and determine how it varies with height. 4. To use observational data to identify the boundary between the two lowest layers of the atmosphere. III. Data Collection and Display You will obtain recent radiosonde data at Key West, Florida, import the data into EXCEL, and plot the temperature, dewpoint, winds, and pressure as a function of altitude. Then you will identify the troposphere, the tropopause, and the lower stratosphere. You will then be able to calculate the temperature lapse rate (the rate at which temperature changes as a function of altitude) for the troposphere and the stratosphere. Your instructor will help you with the four steps involved in plotting the data:
A. Collect the data. a. Go to http://weather.uwyo.edu/. b. Click on Upper air observations, then on Soundings. c. Pick yesterday’s 12 UTC sounding at DFW (labeled FWD on the map) using the following parameters.
i. Region should be North America ii. Type of Plot should be Text: List
iii. Year should be the current year iv. Month should be the current month v. From should be the previous day/12Z. For example, if the current day is the 15th, you would
select 14/12Z. vi. To should be the same as From
vii. Do not change the station number d. Click on the FWD station to bring up the data
i. A window will pop up with the data. Hold down “Ctrl+A” to select everything on the page. Copy the data using “Ctrl+C”
ii. Open Microsoft Word and paste the data into the window using “Ctrl+V”. iii. Delete the text above and below the measurements. This includes the dashed lines before and
after the column headings. iv. Save this document as a plain text (.txt) document under an easy to find location with the name
“data” B. Import the data into Excel.
a. Open EXCEL and select “Blank Workbook” i. Under the “Data” option in the menu area, select “Get Data” → From File → From Text/CSV
ii. Locate your data that you saved earlier and double click it to open it iii. On the screen that pops up, click “Load” at the bottom of the window iv. The data will import as a single column
b. Select Column “A” and then click on “Text to Columns” in the Data Tools area in the ribbon. i. Select “Delimited” in the window that pops up and then click “Next”
ii. Check the box that says “Space” on the next window and then click “Next” iii. Click “Finish”
c. Now, you should have all the sounding variables in separate columns. Let’s identify what they are.
PRES (hPa) Air Pressure
HGHT (m) Height Above Sea Level
TEMP (°C) Air Temperature in Celsius
DWPT (°C) Dewpoint temperature, or dewpoint for short. Also in Celsius. It is the temperature at which the air becomes saturated
RELH (%) Relative humidity, a relative measure of water vapor content in the air. It is expressed as a percentage of the maximum (saturation) amount of water vapor in the air.
MIXR (g/kg) The water vapor mixing ratio, the amount of water vapor (in grams) present in each kilogram of dry air.
DRCT (deg) The wind direction: Northerly (or from the North) is zero. An easterly wind is about 90, southerly is about 180, and westerly is about 270. A northeasterly wind has a DRCT of about 45 deg, etc.
SKNT (knots) Wind speed
The three remaining columns (THTA, THTE, THTV) are not relevant to this lab.
C. Plot temperature and dewpoint vs. height (scatterplot).
a. In EXCEL, go to insert, then Scatter, then Scatter with Smooth Lines and Markers. b. Then right click on the graphics window and click on Select data, and click on Add.
http://weather.uwyo.edu/
c. Click on the small icon to the right of x values. This allows you to select the column in the spreadsheet pertaining to your x-axis.
d. Then choose temperature for your x-axis (highlight all values in the TEMP column), and height for the y- axis (highlight all values in the HGHT column) using the same procedure in selecting HGHT values as you did TEMP.
e. Give this series a name (‘temperature’) and add a second series. f. This time plot dewpoint (DWPT) on the x-axis, and again height (HGHT) on the y-axis. g. Next you can label the x- and y- axis and you can take various steps to improve the layout of the chart. h. Then right click on the chart and click on Move chart, then click on New sheet. You can give the two lines
different colors, but that is not needed. They can both be black. If you desire, you can change the background color from grey to white to save some printer ink!
D. Print your temperature /dewpoint profile (ask the instructor with the choice and location of the printer if there
are troubles), AND your saved sounding text file currently on the desktop. YOU MUST INCLUDE THESE PRINTOUTS IN THIS ASSIGNMENT. MAKE SURE TO INCLUDE YOUR NAME ON THE TABLES AND GRAPHS
IV. Analysis of the Plotted Data
1. Label the troposphere and stratosphere on your temperature profile graph, using brackets to denote the entire layer. Also, label the one height that best corresponds to the tropopause. 2. How did you identify the tropopause from your graph of temperature versus altitude? 3. Could you have identified the tropopause based on a graph of pressure versus altitude alone? Why or why not? 4. Calculate the rate of cooling with increasing height (the ‘lapse rate’ or LR, expressed in °C per km), for the segments of the sounding listed below. Use the following formula for the rate of cooling with altitude (Z):
= −1000 × ( − )
−
Where: T = temperature (TEMP) Z = height (HGHT) For instance, let’s calculate the LR from the surface to 4 km: Here ‘upper’ refers to 4 km (or as close as possible to it) and ‘lower’ to the first row listed near the surface. Within EXCEL you can calculate the LR. Just pick and empty box below the data, and type in: =-1000*(click-click)/(click-click)
where each ‘click’ refers to a mouse-click on the box in the EXCEL sheet that contains the number you are looking for, starting with TEMP @ 4 km. Ask your instructor if you get stuck. As always, add the UNITS to your numerical answer. Now use your data to make the same calculations
a. LR (surface to 4 km):
b. LR (surface to tropopause):
c. LR (tropopause to the top of the sounding):
d. How do the lapse rates calculated above in questions 4b and 4c compare with what is mentioned in your textbook or notes? Does your temperature profile correspond to the lower part of the profile shown in your textbook?
e. A positive lapse rate implies that the air temperature decreases with height. How could you determine the sign of the lapse rate by just looking at your temperature profile (without doing any calculations)?
f. Look at the temperature and dewpoint profiles on your print-out. Does the dewpoint at any height exceed the air temperature for the same height? Discuss what would happen if the dewpoint was larger than the temperature.
5. Repeat EXCEL step D in the Data Collection and Display section: now generate a new XY (scatter) plot, but plot pressure (PRES) on the x-axis, and height (HGHT) on the y-axis. Again label the x- and y-axes of the plot appropriately, and draw a smooth line connecting the dots. Print this sheet and INCLUDE THE PRINTOUT in this assignment. Calculate the rate of decrease of pressure with height (dp/dz, expressed in hPa per km), using a similar formula as used for problem 4, but replacing the temperature values with pressure values:
=
−1000 × ( − )
−
a.
⁄ (1 km to 2 km, or the closest HGHT values to these):
b.
⁄ (9 km to 10 km, or the closest HGHT values to these):
c. Does the sign of the rate of decrease of pressure change with height?
d. How does the magnitude of the rate of change of pressure change with height?
e. Would you call the decrease of pressure with height in the 12 UTC Key West sounding a smooth linear decay, a smooth exponential decay, or an irregular decay (like the dewpoint for instance, see your dewpoint profile).
f. How do your answers to the questions 5a-5f above fit within the context of the discussion of the rate of pressure change with height in the textbook?
6. Repeat EXCEL step D above: now generate a new XY (scatter) plot, but plot mixing ratio (MIXR) on the x-axis, and height (HGHT) on the y-axis. Again label the x- and y-axes of the plot appropriately, and draw a smooth line connecting the dots. Print this sheet, and INCLUDE THE PRINTOUT in this assignment.
a. How does the water vapor mixing ratio vary with height above the surface up to the tropopause and above?
b. How much more water vapor is there near the surface, compared to layers in the upper troposphere? Hint: look at the column ‘MIXR’ in the EXCEL spreadsheet and find the highest value of MIXR, at or near the surface, as well as the lowest value near the tropopause. highest value: lowest value: ratio (lowest / highest):
c. Clearly the upper troposphere is an extremely dry environment: there is hardly any water vapor. Now if the air were to rise from near the surface to the upper troposphere, and if it were to cool following the temperature profile that you plotted, its dewpoint would have to decrease accordingly. What happens to all the water vapor that has to condense?
d. Look at the column of relative humidity values (RELH). Does the relative humidity decrease as rapidly with height as the mixing ratio? Describe how the relative humidity varies: does the change in relative humidity mirror changes in mixing ratio, or do you still find high values of relative humidity at some levels in the middle and/or upper troposphere?
7. Describe how the wind speed (SKNT) generally varies with height from the surface up to the top of the sounding.
In what region of the atmosphere does the sounding indicate the highest wind speeds?
8. Generally describe the changes in wind direction (DRCT) above the surface, referring to wind direction by the conventional points of the compass (e.g., a north-west wind is from the northwest, the angle is about 315 degrees).
Extra Credit: Numerical weather prediction relies on the frequent measurement of temperatures, winds, and humidities in the middle and upper troposphere. Higher accuracy can be achieved by releasing radiosonde balloons more frequently, and from more locations. What do you think the principal drawback is of relying solely on this strategy?
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