Lab 3 - Munson

Lab 3: Atmospheric Pressure and Winds Instructions Watch the lectures on atmospheric pressure, winds and Coriolis Effect, and atmospheric circulation, and watch the video on atmospheric pressure. After you have reviewed the lectures, notes, and the video, use this document to work through your lab. Once you have finished answering all questions in this lab, submit your answers online in the link titled “Lab 3 – Atmospheric Pressure and Winds”. After the due date when your lab is graded, you will be able to review your lab and answers. When you first submit your lab, your score may appear low. Keep in mind that your lab instructor will need to grade your lab, especially the written responses. The computer can automatically grade and score multiple choice, matching, and true/false questions. Any written or essay responses will need to be graded by your instructor. Once your lab instructor grades those questions, your lab grade will be updated to the correct grade. Goals o Understand the concept of atmospheric pressure and how it plays a role in weather. o Interpret graphs to measure how atmospheric pressure changes with height above the Earth’s surface. o Identify high and low pressure centers on a weather map. o Understand and analyze the relationship of pressure to winds. o Interpret wind direction and speed using a weather map. Key Terms / Concepts Barometric Pressure Millibar Standard Sea-level Pressure Isobar Coriolis Effect Cyclone Anticyclone Pressure Gradient Force Once you have completed questions 1 through 40 below, fill in your answers in the assessment link online in module 4 folder titled “Lab 3 – Atmospheric Pressure and Winds”.

Instructions The purpose of this lab is to introduce you to the concept of atmospheric pressure and to become familiar with the relationship of pressure to winds. This lab will focus on constructing and interpreting graphs to measure how atmospheric pressure changes with height above the Earth’s surface. Each question below is worth .5 each. Some questions require you to use proper units. You will not be given proper credit if you choose to not use proper units for the questions below. Atmospheric Pressure and Altitude The Earth’s atmosphere is a compressible fluid comprised mainly of gases that are pulled to the surface by gravity. The weight of the atmosphere produces a force on the Earth’s surface called pressure , and the standard unit to measure atmospheric pressure is the millibar (mb). The average atmospheric pressure is 1013.2 mb, which is equivalent to 14.7lb/sq. inch. This is referred to as standard sea-level pressure and it varies for a particular time or place on Earth. Also, pressure determines wind speed and direction and affects whether or not we are going to have precipitation. The density of gas molecules in the atmosphere is greatest at the Earth’s surface (sea level) and thins as you travel higher in the atmosphere (Figure 1). At 5.6 kilometers (km) (equivalent to 3.47 miles) above the Earth’s surface, approximately one-half of the total mass of the atmosphere will be below you. At that height, fifty percent of the atmosphere will be above you. If you move another 5.6 km to 11.2 km (equivalent to 6.9 miles) above the earth’s surface, approximately one-fourth of the atmosphere will be above you, and three-quarters will be below you. The atmospheric mass decreases at a rate of 50 percent every 5.6 km you increase in height. In general, as you increase in elevation, there is less atmospheric mass and a decrease in atmospheric pressure.

Figure 1 Imagine yourself standing at several elevations (refer to column 1 ) when you fill in your answers in Table 1 below. Determine the atmospheric mass above and below for each elevation above sea-level in Table 4.1. The first two lines (responses in purple) have been completed for you. So, when you look at the percent atmospheric mass above in column 2 at being 100, this means as you stand at 0.0 km (surface of the Earth), 100 percent of the atmospheric mass is above you and 0% is below you (refer to column 2 ). To get values in column 3 , you will use the equation (100 – mass above). The atmospheric pressure on the surface is 1013.2 mb ( column 4 ). When you are standing at 5.6 km in elevation, you already know that half the atmospheric mass is above you and half is below you. So, to get the column 2 (percent atmospheric mass above), you divide by half, so 100 divided by 2 equals 50. You will divide by two all the way up in column 2 . So, when you stand at 5.6 km above the earth’s surface, 50 % of the atmosphere is above you. How much is below you now? If 50% is above you, 50% is below (this totals to 100%). The formula for the third column is 100 – mass above (100 - 50 = 50). So, at 5.6 km, 50% of the atmospheric mass is below you. What about atmospheric pressure? You would divide each value up by two in column 4 . So, 1013.2 mb divided by 2 equals 506.6 mb. Fill in the table below. You will notice that the blank cells have numbers encased in parentheses. The numbers will correspond to the lab assessment (and questions below) when you are ready to submit your answers online. Use proper units in (% or mb) for the questions below. Your responses should go to one decimal point, if needed. (refer to column 4 answers below). You can round your answers if, for example, you have an answer of 15.65, you can round to 15.7. If you have 15.43, you can submit your answer as 15.4. Note: You will have decimal points for columns 2 and 3 and 4 as you work through the table. Column 1 Column 2 Column 3 Column 4 Height (km) Percent Atmospheric Mass Above Percent Atmospheric Mass Below Atmospheric Pressure (mb) 33.6 1.6 98.4 15.8 28.0 3.1 96.9 31.7 22.4 6.3 93.8 63.3 16.8 12.5 87.5 126.7

11.2 25 75 253.3 5.6 50% 50% 506.6 mb 0.0 100% 0% 1013.3 mb Table 1. Atmospheric Mass and Pressure Use your answers here to fill in the assessment online. (1) What is the atmospheric mass above you at 11.2 km? ______________ (.5 point) (2) What is the atmospheric mass below you at 11.2 km? ______________ (.5 point) (3) What is the atmospheric pressure at 11.2 km? ______________ (.5 point) (4) What is the atmospheric mass above you at 16.8 km? ______________ (.5 point) (5) What is the atmospheric mass below you at 16.8 km? ______________ (.5 point) (6) What is the atmospheric pressure at 16.8 km? ______________ (.5 point) (7) What is the atmospheric mass above you at 22.4 km? ______________ (.5 point) (8) What is the atmospheric mass below you at 22.4 km? ______________ (.5 point) (9) What is the atmospheric pressure at 22.4 km? ______________ (.5 point) (10) What is the atmospheric mass above you at 28.0 km? ______________ (.5 point) (11) What is the atmospheric mass below you at 28.0 km? ______________ (.5 point) (12) What is the atmospheric pressure at 28.0 km? ______________ (.5 point) (13) What is the atmospheric mass above you at 33.6 km? ______________ (.5 point) (14) What is the atmospheric mass below you at 33.6 km? ______________ (.5 point) (15) What is the atmospheric pressure at 33.6 km? ______________ (.5 point) 16. Write a brief paragraph to describe the trend in atmospheric mass and pressure as you increase in altitude from the Earth’s surface. (.5 point) As you increase in altitude from the Earth’s surface, the atmospheric pressure and mass decreases. Pressure and Winds Differences in pressure from one place to another (at the same elevation) result in a pressure gradient . Put another way, the pressure gradient is the rate of change of atmospheric pressure between two points at the same elevation, and are the driving force of winds on Earth. A strong pressure gradient occurs when there is a large difference in pressure over a short distance. The winds will be strong. A weak pressure gradient results in weaker winds. The lines on a map that connect points of equal barometric pressure are called isobars. Remember, the isobar lines never cross one