Lapse_Rates_Lab.docx

Lapse Rates Lab -Graphs on the last two pages- Temperature is very important in Meteorology. For example, one of the most important parts of the forecast is the temperature of air at the surface of the Earth, just because people want to know. Meteorologists find that the air temperature aloft is also necessary if they are to assess the stability of the atmosphere. If it is too cold aloft or too hot at the surface, the atmosphere is unstable . Hot, light air in bottom layers with cold, dense air above leads to vertical air motions. Thus, we need to know the lapse rate . In this lab we will evaluate the lapse rate, given a series of temperatures at different altitudes. This is called a sounding and it is usually done by releasing a radiosonde balloon, although we will not do that. The radiosonde is equipped with a thermometer and a radio, among other weather devices, and it transmits the temperatures at many different levels. Since the weather is international in scope, countries have treaties and agreements to share weather data such as soundings. One of the conventions of the agreements is that temperatures aloft are measured using the Celsius scale. The United States is virtually alone in our continued use of Fahrenheit degrees, but American meteorologists do follow the Celsius convention for upper air temperatures. To convert from Fahrenheit to Celsius, use the following formula: Temperature in °C = (Temperature in °F - 32)÷1.8 To convert from Celsius to Fahrenheit temperatures, use the following formula: Temperature in °F = 1.8 x (Temperature in °C) + 32 In addition, there is another scale, used for scientific calculation, called the Kelvin scale. To convert between Celsius and Kelvin temperatures, simply add or subtract 273°: Temperature in °K = Temperature in °C + 273 Temperature in °C = Temperature in °K - 273 Temperature Conversion Assignment Perform the following conversions. Write your answers here. On a separate page, show (neatly!) all work in doing your calculations (Show at least one decimal): a. 50°C = _______°F f. 5°F = ______°C k. 17°C = ______°K b. 6000°C = _______°F g. 1472°F = _____°C l. -73°C = _______K c. -150°C = _______°F h. 85°F = ______°C m. 300°K = _____°C d. 26°C = _______°F i. -120°F = _____°C n. 283°K = ______°F e. 37.78°C =_______°F j. 132°F = ______°C o. 6000°K =______°F

Lapse Rate Assignment + Graphing Practice The lapse rate is the change of temperature as you go aloft in the atmosphere: Lapse Rate = Temperature at level 1 - Temperature at level 2 altitude at level 1 - altitude at level 2 Lapse rates are expressed either in °F/1000 feet or °C/km . There is no final division to divide the temperature by the altitude, so - 10°F/1000 feet is the final way to express a lapse rate for example. In the troposphere the temperature usually decreases with increasing altitude. This will make a negative lapse rate (note the name ‘negative just means as you go up in the air the temperature is expected to decrease for every X feet you go up). For example, suppose the temperature at 1000 feet is 60°F and the temperature at 5000 feet is 20°F. Using the formula above, the lapse rate would be: Note the order of operations here! (60°F - 20°F)/(1000-5000 feet) = 40°F/-4000 feet = -10°/1000 feet What happens in the above equation is a total measure of 40°F change for a total of 4000ft. Note the ‘-4000ft’ part, that means over a distance of 4000ft. To make this lapse rate make sense we have to divide the equation one last time to make sure the denominator (the feet part) is at 1000ft, that way we can see the true lapse rate over 1000ft. 40 and -4000 would be divided by -4, this would get us -10°F and 1000ft for a lapse rate of -10°/1000 feet. Note this lapse rate would explain the temp drop on average per 1000ft between 1000ft and 5000ft in the example. This lapse rate is negative. That is the normal situation in the troposphere. When the temperature increases with height, the lapse rate will be positive . This is the opposite of the usual case in the troposphere and is called an inversion. So there are two types of lapse rates, a normal or negative rate (like - 5°F/1000 feet ) and an inversion ( 4°F/1000 feet ), note the 4 is a statement that its positive number and temperature is increasing with altitude, but those may be only for a selective bit of the atmosphere. Basically a normal lapse rate would be something like - 5°F/1000 feet and inversion lapse rate would be 4°F/1000 feet . To calculate lapse rates one needs a series of temperatures at various atmospheric levels. Assume that a summer morning radiosonde has given us the following sounding: Station A Temperature (°F): 70 54 52 58 47 37 26 18 18 15 0 Level (feet): 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 1. Plot this sounding on the graph paper supplied with this lab. Put altitude on the Y (side) axis, increasing toward the top of the page. Put temperature on the X (bottom) axis, increasing toward the right. Suggestion: Use 1 box for each °F and 10 boxes for each 1000 feet. Label each axis. Plot the points and connect them with straight, ruled lines. Note here, you will need to plot on an image- so using a drawing tool is helpful or you can copy the image and edit it in another image editing software tool (MS Paint, Paintbrush for Mac, etc.) 2. Calculate the lapse rates for the following layers: 0 feet to 1000 feet, 0 feet to 3000 feet, 2000 feet to 3000 feet, 3000 feet to 10,000 feet. Show your work . Show the answers to this and all other questions at the end of this file. Remember to express each lapse rate in units of °F/1000 feet, NOT °F/3000 feet or °F/7,000 feet.

3. Of the four lapse rates you calculated in question 2, which (from x thousand feet to y thousand feet) are “normal”? (Remember, a “normal” lapse rate is negative) Label the normal lapse rates found for question 2 with the word “normal.” 4. Of the four lapse rates you calculated in question 2, which are inversions ? Label the inversion lapse rates found for question 2 with the word “Inversion.” 5. What is the average lapse rate from 0 feet to 10,000 feet? Use the top and bottom levels only Remember to express the lapse rate in °F/1000 feet, NOT °F/10000 feet. Is this overall lapse rate normal or is it an inversion? Next, the following sounding is in the more conventional Celsius units: Station B Temperature (°C): 20 17 13 10 7 3 0 -4 -8 -11 -15 Level (km): 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0 5. Plot this sounding on graph paper. Label all axes and title the graph . Plot the points and connect them with straight, ruled lines. Use a different color if possible. If you only have one color, make the Station B sounding a dashed line. Include a key to the lines. Note the graph paper attached to the end of the lab. Or you can hand draw your own graph. 6. What is the lapse rate from 0 km to 3 km? Use the correct unit for your answer, °C/km ( NOT ° C/3 km). Normal or inversion? 7. The more negative a lapse rate is, the more unstable it is because cold air above warm air tends to overturn. Compare the lapse rates of each 1000 foot (or 0.3 km) layer to determine which is more unstable. So compare 0 - 1000 feet versus 0 - 0.3 km, 1000 - 2000 feet versus 0.3 - 0.6 km, 2000 - 3000 feet versus 0.6 - 0.9 km, etc. Notice that even those the average lapse rates for the complete soundings were about the same, individual layers could be very different.  Which is the most stable layer on either sounding (which selection of the layers levels has warm air over colder air)?  Which is the most unstable layer (which layer has colder air above warmer air)?

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