Lab 4 FA20 - Should be all As PDF

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ATMS 120: Fall 2020

Name and NetID:__________________ Lab #4: Tropical Cyclones 60 points. Remember to turn in a picture of your iCard along with your submission. Part #1 Hurricane Basics 8 points (2 points each) Imagine it is August 29, 2021, and the 12th named tropical cyclone just formed in the Caribbean and is forecast to move toward Florida. Answer the following questions. 1. 2.

3. 4.

If this tropical cyclone were to achieve a maximum sustained wind speed of 101 mph, where would it rank on the Saffir-Simpson Scale? Category 2 Would you consider the 2021 hurricane season to be above average, average, or below average in terms of hurricane activity? Above Average What would its name be? Larry Examine the map below, which has two arrows that show two possible tracks for the eye of this hurricane. Which hurricane track (#1 or #2) would produce the worst possible situation for Tampa, FL, in terms of storm surge and wind damage? Please explain why in one or two sentences. (Tampa’s distance from both tracks is exactly the same.) Track of hurricane eye #1

© 2020 Dept. of Atmospheric Sciences, University of Illinois-Urbana Champaign

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Part #2 Pressure vs. Wind 6 points (2 points each) The Figure below represents the observed relationship between the air pressure measured at the center of circulation and the maximum sustained winds for all tropical cyclones in the Atlantic Ocean from 1979-2015. Answer the following questions. (NOTE: the winds speeds are given in knots, not mph and 1 hPa = 1 mb.) 1.

Hurricane Dorian (2018) was a Category 5 hurricane on the Saffir-Simpson scale and hit Bahamas with maximum sustained winds of 185 mph. Use the graph below to estimate Dorian’s minimum pressure at landfall. 900mb

2.

Hurricane Humberto’s pressure bottomed out at 950 mb. According to the chart, what was Humberto’s wind speed (in knots) when its pressure fell to 950 mb? What rank on the Saffir-Simpson scale did Humberto achieve when its pressure was at 950 mb? 110 knots. Category 3

3.

The color shading on this graph represents the number of tropical cyclones at each wind and pressure interval that were used to create this plot. Based on the shading on this graph, are strong hurricanes or weak hurricanes more common? Weak hurricanes are more common

© 2020 Dept. of Atmospheric Sciences, University of Illinois-Urbana Champaign

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Part #3 Evacuating Houston 10 points Hurricane Harvey formed in the open Atlantic Ocean, but was a weak tropical cyclone until it entered the Bay of Campeche. Once in this bay, it rapidly intensified to a Category 4 hurricane and moved toward Texas, eventually flooding much of Houston. Houston was not placed under mandatory evacuation for several reasons. One of those reasons was logistical – evacuating 7 million people is a logistical nightmare. Let’s see how long it would take to evacuate the Houston metro area if everything ran smoothly (i.e., people were prepared and there were no accidents blocking roads, etc.). Using the information below, calculate how long (in days) it would take to evacuate all 7 million people from the Houston metro area. (Show all your work!) Assumptions: Assume all the people evacuate by car and that each car carries an average of 2.3 people Assume that all cars evacuate using major roadways (Interstates, expressways, highways) and that there are a total of 48 outbound lanes leaving the Houston metro area The rate of cars exiting the metro area is 1 car per 3.9 seconds per lane. In days 2.86 days

© 2020 Dept. of Atmospheric Sciences, University of Illinois-Urbana Champaign

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Part #4 Hurricane Maria’s eyewall speed 10 points After Hurricane Maria hit Dominica, it moved into the Caribbean and began tracking toward Puerto Rico. At the time this satellite image was created, a weather station on St. Kitts and Nevis measured a wind speed of 25 mph. This weather station was 70 miles from the center of Maria’s eye. The diameter of Maria’s eye was measured at 23 miles. Use this information to solve for the wind speed at this time in Maria’s eye wall. Use this wind speed to find the Hurricane Maria’s rank on the Saffir-Simpson scale when this image was taken. There is an excellent example of how to solve this on Fig. 24.22 on page 505 (Show all your work!).

© 2020 Dept. of Atmospheric Sciences, University of Illinois-Urbana Champaign

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25x70= 1750 m^2/hr 1750/11.5= 152.17 mi/hr Hurricane Maria belongs in Category 4 with the wind speed 152.17 mi/hr

Part #5 Coriolis Effect 10 points (8 for calculations 2 for the question) We learned that the reason hurricanes rotate is due to a balance of two forces – the Coriolis force and the pressure gradient force. Rather than performing calculating the Coriolis force on a hurricane, let’s see how much the rotation of the earth impacts the flight path of a game-winning Hail Mary touchdown pass for the Illini at Memorial Stadium. The equation below represents the east-west deflection due to the Coriolis force for objects that are moving south to north. Assume that the football was thrown a distance of 50 m in the air. Show all of your work!

© 2020 Dept. of Atmospheric Sciences, University of Illinois-Urbana Champaign

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2

∆ x=Ω v 0 t sin θ

2π 86164 s

Ω = angular velocity of the Earth = = 7.292*10-5 1/sec v0 = south-to-north velocity of the football = 25 m/s t = total time of travel for the ball = 2.0 seconds φ = latitude (keep in degrees) = 40°N Δx = east-west deflection (meters)

.004687m

If a football pass is thrown off target such that it is intercepted by the opposing team, is the Coriolis force to blame for this? Briefly discuss (2 points). No because Coriolis force only affects big changes in speed/direction and since the change in x is so small it is not to blame.

Part #6: Graphing Hurricane Irma’s Winds and Pressure 16 points, 10 for the graph and 2 per question Hurricane Irma was a powerful Category 5 hurricane as it hit the island of Barbuda. Hurricane strength is categorized using the Saffir-Simpson Scale, which ranks hurricanes based upon sustained wind speed. We have learned that wind is a result of a change in air pressure (i.e., the pressure gradient). Let’s use this idea to analyze data taken from Hurricane Irma. Download the spreadsheet of Irma data from Moodle.

© 2020 Dept. of Atmospheric Sciences, University of Illinois-Urbana Champaign

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Column A: Date and Time of the observation Column B: Wind Direction Column C: Sustained Wind Speed (m/s) Column D: Wind Gust Speed (m/s) Column E: Wind Gust Speed (mph) Column F: Pressure (mb) There are no data in columns B, C, and D after 5AM on Sept 6, 2017, because the anemometer was destroyed by the hurricane’s winds. However, the barometer, which was measuring the atmospheric pressure, continued to work. Please complete the following tasks: 1. Calculate the wind gust speed in mph (miles per hour) in column E using the data in Column D. 1 mph = 0.447 m/s 2. Create a graph of the wind gust speed and pressure as a function of the date and time. Please graph the entire data set even though there are no wind speed data after 5AM on Sept 6. Set the primary y-axis values to wind gust speed and the secondary y-axis to pressure (your own graph should look just like the Figure below). Please turn in a screenshot of your graph including the answer to the questions below.

Questions: 1. What relationship do you see between the pressure line and the wind speed line on your graph? (Hint: Remember that pressure gradients, not low pressure itself creates strong winds.)

© 2020 Dept. of Atmospheric Sciences, University of Illinois-Urbana Champaign

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Steeper slope for pressure line corresponded to higher wind speed. Inverse relationship between pressure and wind speed. 2.

The anemometer broke in the eyewall of the hurricane when the wind speeds reached 155 mph. After the eyewall passed over the weather station, the pressure dropped to its lowest value of 919.6 mb. At that point, there was no pressure gradient. What do you think happened to the wind speed at this point? Briefly explain why. (Hint: Remember that pressure gradients, not low pressure itself creates strong winds.) The wind speed dropped because in the eye of the hurricane it has no pressure gradient which means calm winds as low-pressure gradient means low wind speed.

3.

Please draw on your graph (or else sketch below) what you think the rest of the wind speed line would have looked like if the anemometer would not have failed and continued to operate until 23:54 Sept 6, 2017.

© 2020 Dept. of Atmospheric Sciences, University of Illinois-Urbana Champaign

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