Interpreting Weather Satellite Data Introduction



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Tracking Hurricanes from Space

Interpreting Weather Satellite Data


Introduction
In the past, meteorologists based their weather predictions on information gathered by a worldwide network of observers on land and at sea. Even with reports from hundreds of stations every few hours, it was hard to see the large scale patterns that make weather prediction possible.
Today, satellites allow meteorologists to see the weather over the entire planet. In this activity, you will examine a series of satellite images of North America. You will study weather patterns and follow several major storms including one that battered the coast of Louisiana and other gulf states in 2005, causing loss of life and billions of dollars in damage.
You will work with your investigative team to examine the behavior and characteristics of tropical cyclones in order to predict the path and probable behavior of future severe storms.

A look at Katia
Ensure a working copy of ImageJ is installed on your computer, the computer is Internet enabled, and you have a copy of the Resources folder available. The Resources folder contains all the data files for this lesson.
Launch ImageJ.

On the ImageJ menu bar, click File > Import > Animated GIF, navigate to the Resources folder for this lesson, highlight Katia_Stack_HUIR.gif and click Open.
You should be looking at a stack of images. There are three ways to view the images.

    • You can press the > key to advance one frame or the < key to reverse one frame.

    • You can click the arrow buttons at each end of the horizontal scroll bar found at the bottom of the image window: right arrow advances one frame, left arrow reverses one frame.

    • You can drag the slider in the scroll bar and move it right (forward) or left (reverse).


ImageJ can also animate the stack and allows you to adjust the animation speed (frame rate or number of frames per second). Click Image > Stacks > Tools > Animation Options; set Speed to 3 fps; click OK. If the animation does not start automatically, press the back slash key \ to start or stop the animation at any time. Alternatively, you can start the animation by clicking the Play button in the lower left corner of the image window.

Continue to adjust the speed and animate the stack until you can easily observe changing patterns in the image sequence.
You may notice something strange about these images. Except for the changing clouds, nothing moves. As the earth rotates, some satellites orbit the planet at a speed of more than 11,000 kilometers (almost 6900 mi) per hour at an altitude of almost 38,000 km (more than 22,000 mi). To an observer on the ground, the satellite would appear to remain stationary over the same surface location. The effect in the image is that North America appears to be standing still. This satellite is in a geosynchronous orbit.



  1. From this information, briefly explain in your own words how a geosynchronous orbit works.



Looking for patterns
Watch the cloud patterns form, move, and disappear. Look for evidence of where and when the clouds first appear.
The information bar at the bottom of each frame shows the image is infrared, has a resolution of 8 km (about 5 mi) – that is, each pixel represents 8 km on the ground – and the date and time when the image was captured. The times are shown in 24-hour format, so anything over 12 hours is between noon and midnight. For example, the image with 9 1 2011 1915Z in the information bar was captured on September 1, 2011 at 1915Z. The Z (“Zulu” in the phonetic alphabet) means UTC or Universal Time Coordinate. UTC is the name of the time zone at the Prime Meridian (0 longitude). On a 12-hour clock, 1915Z would be 7:15 pm UTC.
Stop the stack animation and go to the first frame.
To convert between UTC and your local time, add or subtract an hour for every time zone difference between your location and the Prime Meridian. For example, to convert from UTC to Pacific Time (PST), subtract 8 hours from UTC. During Daylight Savings, subtract 7 hours to convert from UTC to PDT.



  1. At what local time was the first satellite image in this stack captured?




  1. At what local time was the last satellite image in this stack captured?



Animate the stack again and look at the areas where there are no clouds, both over land and over the oceans.



  1. How do the land areas change in brightness over time?




  1. How do the oceans change in brightness over time?




  1. In general, do the clouds appear darker or lighter than Earth’s surface?

Remember, the IR in the lower left corner of the image indicates this is an infrared image. The infrared camera capturing this image does not see visible colors the way your eyes do. It senses infrared radiation interpreted as temperature. In an infrared image, the whiter the gray tone, the colder the temperature; darker means warmer.





  1. From your personal experience, are clouds usually cooler or warmer than Earth’s surface?




  1. Complete the following sentence by filling in the blanks with either darker or lighter: “In these images, cold appears _____ and warm areas appear _____.”




  1. With this rule in mind, how can you tell which images were captured when the sun was shining on North America?




  1. Do the oceans change brightness as much as land areas do? Why do you think this happens?




  1. Complete this sentence by filling in the blanks with either quickly or slowly: “Land heats up and cools down _____ and water heats up and cools down _____.”




  1. Look at the spiraling cloud pattern on the right side of the image window. What is the relative temperature of the ocean near this spiral? (HINT: Compare relative temperature of the ocean to those of land and clouds by considering the graytone brightness in the image.)




  1. In general, do you see more clouds over the land or over the oceans? Why do you think this is true?

Look carefully at the cloud patterns changing throughout the animation.





  1. In general, in which direction do the cloud patterns move in each zone – east to west, or west to east?



Storms on the horizon



  1. Check out the swirling cloud patterns that look like suds going down the drain—what do you think they are?




  1. In which direction do these features rotate—clockwise or counterclockwise?



Click File > Open; navigate to the Resources folder, highlight Dry_Line.gif; click Open.
In this image, as Katia becomes a Category 1 hurricane with sustained winds of 121 km (75 mi) per hour, Tropical Storm Lee covers much of Louisiana, Mississippi, and Alabama with a sustained wind speed of 80 km (50 mi) per hour. Notice the band of clouds that forms along a diagonal line from the Oklahoma panhandle to the Great Lakes. This is called a Dry Line – a nonfrontal boundary between a hot, dry air mass from the southwest and a warm, moist air mass from the southeast. Clouds form in this region when dry air cools as it flows down the eastern side of the Rocky Mountains. It flows under and lifts the warm moist air from the Gulf of Mexico. As the warm air rises, it expands and cools until water vapor condenses and clouds form.
Most things in the natural world have a tendency to move from an area where there is more of it (such as high air pressure) to an area where there is less of it (such as low air pressure). Broadcast weather reports often refer to high and low pressure areas in the atmosphere. High pressure systems contain cool, dry, denser, sinking air, and low pressure systems contain warm, moist, less dense, rising air.



  1. Look again at areas in the images that do not have clouds. Complete the following sentence using the words low and high: “Large, clear areas are associated with ____ pressure systems and cloudy areas are associated with _____ pressure systems.”




  1. Which type of pressure system seemed to cover the southeastern states during the first 24 hours of the movie? How can you tell?



Close Dry_Line.gif.
Click File > Open, navigate to Emilia.png, click Open.
This is a GOES West image of the North Pacific Ocean from July 12, 2012 at 1800Z. Notice the three storm systems. NOAA Environmental Visualization Laboratory labeled the systems when the image was prepared for posting. Notice Tropical Storm Fabio has formed in the East Pacific. This is the sixth named storm of the 2012 Eastern Pacific Hurricane Season. Hurricane Emilia is entering an area of cooler sea surface temperatures and will begin to weaken. The remnants of Hurricane Daniel can be seen to the west of Hawaii.
During a hurricane season, the Pacific hurricanes are named in alphabetical order, and alternate between men’s and women’s names. For instance, the first hurricane of the season might be Annie, the second Barney, the third Carolyn, the fourth Douglas, and so on. Atlantic hurricanes are named the same way.



  1. Using this pattern, Katia is the _____ Atlantic hurricane of the season. (Which number?)




  1. What would be an appropriate name for the next hurricane of the season after Katia?



Close Emilia.png.
Click File > Import > Animated GIF; navigate to Katrina_Eye_Stack.gif; click Open.



  1. What kind of pressure system is this storm—high or low?

Look at the small dark hole that forms at the center of Katrina. This is the eye of the hurricane. The eye is where cold air is being pulled down into the heart of the hurricane to feed the powerful winds of the eye wall—the ring of clouds surrounding the eye. Since there is cold sinking air in the eye, the air is clear there. The dark color seen in the eye is the ocean’s surface.


Animate the stack. Adjust the animation speed as desired. Observe the complete stack animation several times.



  1. Describe what happens to Katrina—both the eye and the clouds—when it passes over land. Why do you think this occurs?




  1. What happens to the eye just before landfall—the point when it reaches the shore? Does the storm appear to get stronger or weaker?



Close Katrina_Eye_Stack.gif.


  • If needed, refer to a world globe, atlas, or one of the following online maps that shows ocean currents to help answer the following question: http://www.onr.navy.mil/focus/ocean/motion/currents1.htm and/or

http://www.maps.com/map.aspx?pid=15756



  1. Explain which current(s) is affecting Katia’s behavior and why.



How fast is Katia going?
There will be several steps to determining the average speed with which Hurricane Katia moves over the ocean.
Katia_Stack_HUIR.gif should still be open. First, you will choose any two frames of the animated stack, as far apart in time as possible, that clearly show Katia’s eye. Using the table on your answer sheet, record the slice number, date, and time of each of those two images. The slice number is the first number in the image information bar in the image window. In the example below, the slice number is 37 of 72.

Open Katia_Data.txt. (File > Open > Katia_Data.txt)
You may need to move between several image windows that are all open at the same time on your screen. Remember, only the active window will respond to ImageJ commands. In ImageJ there are two ways to activate a window:
Click once on an image window to make it the active window.

OR…

On the ImageJ menu bar, click Window and select the name of the image window you wish to make active.
To measure the distance in kilometers (or miles) there must be a distance reference for setting the measurement scale in ImageJ. You can use the distance scale on the tracking chart if at least two positions of Hurricane Katia are accurately marked on the chart. To mark the chart, you will need to know the latitude and longitude of the storm’s center on at least two different occasions. The images in the Katia stack are not calibrated to latitude and longitude, but they are stamped by NOAA with date and time. NOAA’s National Hurricane Center issues hourly advisories before and during each severe storm. The advisories are archived and available online for historical reference. Some of the advisory data for Hurricane Katia have been summarized in the table in Katia_Data.txt image window.
Look up the latitude and longitude of the center of the storm (eye) for each of the two images for which you recorded slice number, date and time in the table on your answer sheet. Record theses latitudes and longitudes in the same table.
Close Katia_Data.txt.
Open Track_Chart.tif.
You will use ImageJ to mark the Katia locations you selected on the tracking chart with “Katia,” date and time on your hurricane tracking chart.
Click Edit > Options > Colors. Using the drop down arrows, set Foreground color to black, Background color to white, Selection color to red. Click OK.





Double-click the Paintbrush Tool button. In the Paintbrush Tool dialogue, change Brush Width to 3 pixels. Click OK.
Click the Paintbrush Tool button again once. Place the cursor on the tracking chart at the desired latitude and longitude and left-click once. If the dot is in the wrong position, press Ctrl-z or click Edit > Undo. Reposition the cursor and try again. When the dot is in the correct spot, move the cursor to the second location and click once.
If both dots are in the correct positions, click the Scroll Tool button to deactivate the Paintbrush.
If the hurricane changes direction, feel free to add more location points on your tracking chart. Now, you will label each mark with the hurricane’s name (Katia), the date (ddMMMyy format), and the UTC time in 24 hour format.




Double-click the Text Tool button. In the Fonts dialogue, use the drop down arrow to change the font size to 8. Close the Font dialogue window.

Click the Text Tool button again once. On the tracking chart image, click and drag down and left to form a text insertion box. Release the mouse button, then click and hold in the text insertion box to drag it to a location next to the first dot you marked on your chart image and release.
Type the hurricane name (Katia) and press Enter (or Return). Type the date in ddMMMyy format (such as 09AUG10 for August 9, 2010); press Enter (or Return). Type the UTC time in 24 hour format (such as 0315Z for 3:15 AM). To set the text box, click once on a chart area outside the text box.
Repeat the last two steps to label the second point on your chart.
Click the Scroll Tool button to deactivate the Text Tool.
Find the distance scale in the upper right corner of your tracking chart. Zoom-in, if desired. You will use ImageJ, the distance scale, and the two points you just labeled to determine the distance between your hurricane location marks.
Click Line Selection Tool button . Click and hold on left end of distance scale, drag to 500 km mark on distance scale (the first mark to the right, not the right end) and release.
Click Analyze > Set scale; set Known distance to 500; set Unit of length to kilometer; click OK.

Click Analyze > Set measurement; uncheck everything in the Set Measurement dialogue; click OK.

Click Analyze > Clear results.
Click Line Selection Tool button. Click and hold on the center of the first hurricane location mark on your tracking chart, drag to the center of the second mark, and release.
Click Analyze > Measure. Read the results in the Results window. Remember, the number in the Length column is distance measured in kilometers.

When finished measuring, click the Scroll Tool button.



  1. How far in kilometers did Katia’s eye move between these two images?




  1. How many hours passed between these images?




  1. Calculate Katia’s average speed in kilometers per hour.



Close the Results window. Click No to saving the measurement.
The winds in a hurricane can reach nearly 200 miles per hour, while the hurricane as a whole moves over the ground at the speed you calculated. Katia was a typical hurricane of mid size and strength. Katrina was very strong and very large. Hurricanes can have different paths and different speeds. The amount of damage to populated areas is sometimes greater with smaller but slower moving hurricanes that expose the area to high winds and rain for longer periods of time.



  1. Describe something in your experience that travels at about the same speed as a hurricane.




  1. In what ways are satellites valuable in weather forecasting?



  • Close Track_Chart.tif. Close Katia_Stack_HUIR.gif. Exit ImageJ.


With guidance from your teacher, select and complete two or more of the Your Turn activities listed below.

Your Turn




  • Plot the path and speed of Hurricane Katrina on the same hurricane tracking chart using ImageJ. Compare the tracks of Katia and Katrina and study the images to see if you can tell what forces control a hurricane’s path. Add sufficient marks to the tracking chart to accurately describe the path of each storm system as imaged in their respective stacks. Based on your team’s additional research, extend the path to predict the future direction of the storm, its likely intensity, and potential areas of damage.




  • Carefully observe the ocean in the Katia animated stack and look for evidence of ocean currents and their direction of rotation.




  • Measure the diameter of Katia’s eye when it was a Category 3 hurricane and measure the average diameter of the entire Category 3 cyclone. (HINT: Using ImageJ, measure in number of pixels and multiply by 8 km/pixel.) Using the formula for the area of a circle, (1) calculate the area of the eye and (2) calculate the area of the storm. What percentage of the storm is the eye? Is the size of the eye (taken as a percentage of the storm’s area) the same for all hurricanes: Follow the same procedure for Hurricane Katrina. Compare the two hurricanes in terms of the eye size as a percentage of the storm size.




  • Research the ImageJ documentation to decide on a procedure for using ImageJ’s thresholding and measurement tools to determine the area of the eye and the area of the entire cyclone directly. Briefly describe the procedure your team agreed upon and then follow it. How do the results compare with your own calculations (last bullet above)? What do the results suggest about the relationship between the size of the eye and the strength of the storm?




  • List and explain at least five significant things you have learned about tropical cyclones from this activity. Working with your research team, prepare an oral report of your findings supported with graphic examples.

Tracking Hurricanes from Space



Interpreting Weather Satellite Imagery Answer Sheet


  1. From this information, briefly explain in your own words how a geosynchronous orbit works.



  1. At what local time was the first satellite picture in this stack captured?




  1. At what local time was the last satellite picture in this stack captured?




  1. How do the land areas change in brightness over time?




  1. How do the oceans change in brightness over time?



  1. In general, do the clouds appear darker or lighter than Earth’s surface?




  1. From your personal experience, are clouds usually cooler or warmer than Earth’s surface?




  1. In these images, cold appears ____________ and warm areas appear ____________.




  1. With this rule in mind, how can you tell which images were captured when the sun was shining on North America?




  1. Do the oceans change brightness as much as land areas do? Why do you think this happens?



  1. Land heats up and cools down _____ and water heats up and cools down _______.




  1. Look at the spiraling cloud pattern on the right side of the image window. What is the relative temperature of the ocean near this spiral? (HINT: Compare relative temperature of the ocean to those of land and clouds by considering the graytone brightness in the image.)



  1. In general, do you see more clouds over the land or over the oceans? Why do you think this is true?



  1. In general, in which direction do the cloud patterns move in each zone – east to west, or west to east?




  1. Check out the swirling cloud patterns that look like suds going down the drain—what do you think they are?



  1. In which direction do these features rotate—clockwise or counterclockwise?




  1. Large, clear areas are associated with__________pressure systems and cloudy

areas are associated with__________pressure systems.




  1. Which type of pressure system seemed to cover the southeastern states during the first 24 hours of the movie? How can you tell?



  1. Using this pattern, Katia is the__________Atlantic hurricane of the season.




  1. What would be an appropriate name for the next hurricane of the season after Katia?




  1. What kind of pressure system is this storm—high or low?




  1. Describe what happens to Katrina—both the eye and the clouds—when it passes over land. Why do you think this occurs?



  1. What happens to the eye just before landfall—the point when it reaches the shore? Does the storm appear to get stronger or weaker?



  1. Explain which current(s) is affecting Katia’s behavior and why.


Hurricane Katia Data

Slice No.

Date

UTC

Lat (N)

Lon (W)


































  1. How far in kilometers did Katia’s eye move between these two images?




  1. How many hours passed between these images?




  1. Calculate Katia’s average speed in kilometers per hour.



  1. Describe something in your experience that travels at about the same speed as a hurricane.



  1. In what ways are satellites valuable in weather forecasting?



More Lessons from the Sky, 2011, Satellite Educators Association Tracking Hurricanes from Space


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